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Urea, as a low-cost and widely available non-protein nitrogen, is an economical alternative to protein feeds in ruminant diets. However, the problem of urea utilization efficiency in ruminant production in China restricts the popularization and application of urea in actual production. This paper summarizes the main application methods of urea in ruminant production and the factors affecting the utilization of urea by ruminants, providing valuable references for further proposing strategies to improve the efficiency of urea utilization in ruminants and promoting the popularization and application of urea in ruminant production. [ABSTRACT FROM AUTHOR]

The increasing costs of traditional protein sources, such as soybean meal (SBM), have prompted interest in alternative feeds for ruminants. Non-protein nitrogen (NPN) sources, like urea, offer a cost-effective alternative by enabling rumen microorganisms to convert NPN into microbial protein, which is crucial for ruminant nutrition. However, the rapid hydrolysis of urea in the rumen can result in excessive ammonia (NH3) production and potential toxicity. Slow-release urea (SRU) has been developed to mitigate these issues by gradually releasing nitrogen, thereby improving nutrient utilization and reducing NH3 toxicity risks. This review explores SRU's development, types, mechanisms, and benefits, highlighting its potential to enhance ruminal fermentation, microbial protein synthesis, and overall feed efficiency. SRU formulations include polymer-coated urea, lipid-coated urea, calcium-urea, starea, and zeolite-impregnated urea, each designed to control nitrogen release and minimize adverse effects. Studies have demonstrated that SRU can improve microbial nitrogen efficiency and reduce nitrogen losses, although results regarding feed intake, digestibility, and milk yield are mixed. These discrepancies indicate that factors such as SRU type, diet formulation, and animal breed may influence outcomes. Continued research is essential to optimize SRU applications, aiming to enhance ruminant production, economic viability, and environmental stewardship. [ABSTRACT FROM AUTHOR]

Urinary nitrogen (UN) excretion and milk production traits of 35 groups of 15 grazing cows each were measured over two years. Urine volume and N concentration were measured with urine sensors and daily UN excretion was calculated for four consecutive days. Milk yield, composition and cow liveweight (LW) were used to estimate daily dry matter intakes (DMI) based on back-calculated animal energy requirements and feed metabolisable energy (ME). Different N fractions in the diet were estimated using laboratory data and protein digestion equations. Mean estimates of N intake and UN excretion were 460 and 227 g N/d, respectively. Urinary-N represented 52% of the N consumed, which aligns with indoor N balance studies. Urinary N excretion was weakly correlated (r = 0.29) with dietary N intake, but moderately correlated (r = 0.63–0.67) with diet N concentration, diet N:ME ratio, and diet effective rumen degradable protein (ERDP). The ERDP balance had moderate to strong correlations with N utilisation efficiency (r = −0.89) and the UN expressed relative to N intake (r = 0.59) and N in milk (r = 0.78). These relationships illustrate the potential of urine sensors and energy-based estimations of intake to assess the influence of dietary management strategies to mitigate UN excretion from grazing animals. [ABSTRACT FROM AUTHOR]

The increasing costs of traditional protein sources, such as soybean meal (SBM), have prompted interest in alternative feeds for ruminants. Non-protein nitrogen (NPN) sources, like urea, offer a cost-effective alternative by enabling rumen microorganisms to convert NPN into microbial protein, which is crucial for ruminant nutrition. However, the rapid hydrolysis of urea in the rumen can result in excessive ammonia (NH3) production and potential toxicity. Slow-release urea (SRU) has been developed to mitigate these issues by gradually releasing nitrogen, thereby improving nutrient utilization and reducing NH3 toxicity risks. This review explores SRU’s development, types, mechanisms, and benefits, highlighting its potential to enhance ruminal fermentation, microbial protein synthesis, and overall feed efficiency. SRU formulations include polymer-coated urea, lipid-coated urea, calcium-urea, starea, and zeolite-impregnated urea, each designed to control nitrogen release and minimize adverse effects. Studies have demonstrated that SRU can improve microbial nitrogen efficiency and reduce nitrogen losses, although results regarding feed intake, digestibility, and milk yield are mixed. These discrepancies indicate that factors such as SRU type, diet formulation, and animal breed may influence outcomes. Continued research is essential to optimize SRU applications, aiming to enhance ruminant production, economic viability, and environmental stewardship.

This study aimed to evaluate the production and milk composition of crossbreed F1 Holstein x Zebu (1/2 HxZ) cows grazing on Marandu grass (Urochloa brizantha cv. Marandu) or Tifton-85 (Cynodon spp.) supplemented with different protein concentrate. 36 H x Z cows (±514 kg of body weight) were used. The cows had ± 65 days in milk and were distributed in a randomized block design, in a 2 x 3 factorial arrangement, i.e., two types of grass (Marandu and Tifton-85 grass), three types of protein supplementation (2.0 kg of concentrate with low rumen degradable protein; 2.0 kg of concentrate with high rumen degradable protein; and no concentrate feed). Both grass produced similar amounts of forage mass, kg.h-1. The nutritional value for both grasses was also similar in all the variables analyzed, such as crude fat, crude protein, carbohydrates, non-fiber carbohydrates, neutral detergent fiber, and, acid detergent fiber. The milk yield was not affected by the different grasses used for grazing. Only the lactose content was higher in cows grazing on marandu grass than in Tifton-85 grass (P=0.032). The cows that did not receive concentrate had lower daily milk yield (P=0.010) and a lower percentage of lactose (P=0.011). In conclusion, both grasses can be used for grazing F1 ½ H x Z cows, and protein supplementation, regardless of its ruminal degradability, in this situation is necessary to increase milk production. [ABSTRACT FROM AUTHOR]

Tropical foliage is an alternative source for protein enrichment in the dairy ration. However, due to the expensive, laborious, and time-consuming data-gathering method, its degradability database for inclusion in ration formulation is still lacking. This study aims to estimate tropical foliage's in situ protein degradability (RDP) using chemical compositions, in vitro digestibilities, and near infrared reflectance spectroscopy (NIRS) methods. The study used one hundred ten tropical foliage samples and observed chemical composition, in vitro dry and organic matter digestibility, and in situ degradation characteristics variables. NIRS spectra were collected to calibrate and validate the in situ degradation characteristics. Correlations were made prior to regression analysis. The results showed that tropical foliage varied in ash (3.02%-18.3%), crude protein (CP) (11.6%-30.7%), crude fiber (CF) (10.2%-29.8%), neutral detergent fiber (NDF) (31.0%-58.2%), acid detergent fiber (ADF) (18.7%-44.1%), dry matter digestibility (DMD) (23.9%-73.2%), organic matter digestibility (OMD) (25.6%-73.9%), and in situ RDP (21.0%-75.4%). The foliage was highly degraded (RDP > 60%) except for Calliandra calothyrsus (59%). In situ RDP significantly correlated with ash, CP, CF, DMD, and OMD with coefficient correlations (r) of 0.43, 0.60, -0.33, 0.74, and 0.76, respectively. Estimation of RDP using chemical composition and in vitro digestibility followed the equation: RDP (%)= 0.69 + 2.122 CP (%) with R²= 0.41 (p<0.01) and RDP (%)= 0.162 ash + 1.270 CP -0.104 CF + 0.489 IVOMD, with R²= 0.68, p<0.01). Calibration of NIRS using in situ RDP resulted in a regression coefficient (R²) of 0.78. It is concluded that RDP tropical foliage can be estimated more accurately using NIRS compared to in vitro digestibility and chemical composition. [ABSTRACT FROM AUTHOR]

Synchronization of rumen degradable protein (RDP), non-fiber carbohydrate (NFC), and sulfur availability are needed for optimum microbial protein synthesis (MPS), rumen fermentation activity, and feed digestibility. Cassava and corn are rich in NFC content and have different carbohydrate characteristics. Most of the tropical feedstuff is deficient in sulfur, thus it needs to be supplemented in the ration. This study aimed to compare the effect of corn and cassava as NFC sources and sulfur supplementation on fermentability and digestibility using in vitro study. The experiment used a 2 × 3 factorial randomized block design with four different dairy cattle rumen liquor as replications (block). The first factor was NFC sources (corn and cassava), and the second factor was the level of sulfur supplementation (0%, 0.1%, 0.2%). Parameters observed include fermentability (rumen pH, NH3 concentration, total volatile fatty acids (VFA), molar proportion of VFA, MPS, rumen bacteria, and protozoa population) and in vitro digestibility (dry matter (IVDMD) and organic matter (IVOMD)). Data were tested using ANOVA followed by the Duncan test. The result showed an interaction between rumen pH (P<0.05). The NH3 concentration was low in cassava treatment, while total VFA did not have a significant effect. Corn treatment produced a higher iso-butyrate and isovalerate than cassava treatment (P<0.05). The rumen microbes, MPS, IVDMD, and IVDMD, did not differ among the treatments. Cassava could replace corn as an NFC source for tropical dairy ration along with providing RDP in balance ratio and sulfur supplementation. [ABSTRACT FROM AUTHOR]

In India, there is a shortage of both energy as well as proteinacious feed and fodders for livestock. Protein rich feeding ingredients are costlier which enhances the cost of feeding the animal. By maximizing the use of protein rich feed supplement within the digestive system of ruminants, we can either reduce the quantity of protein in the diet or can enhance the production of the animals. Protected nutrient technology is one such approach, involving feed management through passive rumen manipulation, by which the dietary nutrients (mostly fat and protein) are protected from rumen degradation, allowing these nutrients to bypass rumen and get digested and then absorbed from the lower digestive tract. The present study was done as an On Farm Testing (OFT) at farmer’s field to evaluate feeding of bypass protein feed supplement on milk production in graded Murrah buffaloes at Gwalior district of Madhya Pradesh. Twenty lactating buffaloes in their 2nd to 3rd lactation cycles were selected for the 50-day experiment period. Animals were divided into two equal groups namely Farmers practice control group (T1) and recommended practice group (T2). The control group animals (T1) received no supplementation in diet however recommended practice group (T2) animals received supplementation of 100 gms of bypass protein supplement per day in their diet for a period of 50 days. The average milk yield for 50 days period under OFT was recorded as 8.40 liters/buffalo/day and 7.70 liters/buffalo/day for supplemented group buffaloes and farmers practice group buffaloes respectively. The yield enhancement due to technological intervention was to the tune of 9.13 per cent over farmers practices. The data clearly reveal that net return from supplemented animals was higher to the tune of 8.19% over the farmers practice. [ABSTRACT FROM AUTHOR]

Simple Summary: This study was conducted to evaluate intake and performance of beef cattle provided different protein supplements on pasture. Protein sources were rumen degradable protein (RDP) and rumen undegradable protein (RUP) supplied as pressed blocks provided in two time periods. Protein supplement was provided before and during the breeding season. Intake, intake behavior, and weight gain were compared between cattle offered either protein type. Typically, due to the RDP available during the summer grazing season, supplementation is not conducted. However, due to the RDP content of forages, RUP may be beneficial for grazing animals to provide a more direct protein source for the animal. Therefore, this study analyzed how effectively RUP or RDP supplementation was for grazing animals and found that protein type did impact intake behavior of both heifers and cows. Angus and Red Angus-based yearling heifers (n = 40) and lactating cows (n = 51) were each used in a complete randomized design and stratified by weight and body condition score to one of two treatments: (1) pressed supplement block containing rumen undegradable protein (RUP) and (2) pressed supplement block containing rumen degradable protein (RDP). Heifer and cow supplement intake displayed (p < 0.01) a treatment × period interaction. The RUP heifers and RDP cows consumed more in Period 2 than Period 1, whereas RDP heifers and RUP cows consumed more in Period 1 than Period 2, respectively. Intake rate demonstrated (p < 0.01) a treatment effect for heifers, with RUP consuming supplement faster than the RDP treatment. Intake rate for cows demonstrated (p < 0.01) a treatment × period interaction with RUP cows in Period 1 having faster intakes than Period 2, and RDP cows having the inverse. Cow intake variation displayed (p < 0.01) a treatment × period interaction with RUP cows having more variation in Period 2, while RDP cows had less variation in intake in Period 2. In conclusion, RDP and RUP impacted intake behavior of cows and heifers but had minimal impacts on performance. [ABSTRACT FROM AUTHOR]

Two experiments were conducted to evaluate the effect of supplementation with two sources of non-protein nitrogen at different feeding times on the performance, ingestive behavior, and rumen metabolism of growing Nellore bulls during the dry season. Exp. 1: One hundred and twenty Nellore bulls, weighing 206 ± 39 kg of initial body weight (BW) and 12 months of age, were divided into 20 paddocks, and they were used in randomized block design in a 2 × 2 factorial arrangement to evaluate performance and ingestive behavior. Exp. 2: 12 rumen cannulated animals with 509 ± 59 BW, divided into 4 paddocks, were used in a triple Latin square 4 × 4 in a 2 × 2 factorial arrangement to evaluate metabolism. The factors were 2 non-protein nitrogen sources (urea or slow-release urea) and 2 feeding times (07:00 or 13:00 at 4 g/kg BW of supplement). There was no influence of non-protein sources, supplementation time, or their interaction on the grazing time or the trough time during daytime, nighttime, or total (P ≥ 0.16). There were no interactions or factor effects on ADG (P ≥ 0.45) or final body weight (P ≥ 0.39). There was an interaction between supplementation time and collection time (P < 0.01) on ruminal pH. Animals supplemented in the morning had greater total SCFA at 18 h after supplementation (P = 0.03). The supplementation time and the non-protein nitrogen sources did not alter the ingestive behavior or animal performance of young Nellore cattle. [ABSTRACT FROM AUTHOR]

Background and Aim: Dairy ration formulations should consider the synchronization of the rumen degradable protein (RDP) to rumen undegradable protein (RUP) ratio (RDPR) with non-fiber carbohydrate (NFC) to achieve optimum microbial protein synthesis (MPS), reduce feed costs, and reduce N excretion to the environment. This study aimed to investigate the effect of RDPR and NFC synchronization on in vitro digestibility, fermentability, and MPS. Materials and Methods: The experiment used a 3×3 factorial randomized block design with four replications. The first factor was RDPR (RDPR1=50:50; RDPR2=55:45; RDPR3=60:40) and the second factor was NFC levels (NFC1=30%, NFC2=35%, NFC3=40%). The experimental diets were evaluated using a two-stage in vitro method. The examined parameters included rumen pH, NH3 concentration, total volatile fatty acid (VFA) concentration, the molar proportion of VFAs, rumen microbes (protozoa and total bacteria population), and MPS. Data were analyzed using ANOVA, followed by the Duncan test. Results: The results show that neither RDPR nor NFC affected rumen pH, NH3, total VFA, and the rumen microbe population. The interaction between RDPR and NFC affected the molar proportion of acetate, iso-butyrate, and n-valerate. The combination of RDPR1 and NFC1 produced a lower molar proportion of acetate (49.73%) than the other treatment combinations (>54%). The acetate to propionate ratio was influenced by the NFC levels, in which NFC2 and NFC3 produced the highest ratio (p

Background and Aim: Feeding ruminants must notice the degradability of feed, especially protein. Microbial rumen requires ammonia from rumen degradable protein (RDP) beside that ruminant require bypass protein or rumen undegradable protein (RUP) and microbial crude protein. The aim of the study was to discover the best RDP:RUP ratio in beef cattle diets commonly used by Indonesian farmers using an in vitro methodology. Materials and Methods: Samples of Pennisetum purpureum, Leucaena leucocephala, Indigofera zollingeriana, cassava, maize, palm kernel cake, rice bran, and tofu waste were formulated into dietary treatments (dry matter [DM] basis). All experiments were carried out using a 3×3×2 factorial, randomized block design with three replications. Treatments consisted of three protein levels (12%, 14%, and 16%), two energy levels (65% and 70%), and three RDP:RUP ratio levels (55:45, 60:40, and 65:35). The experimental diets were incubated in vitro using buffered rumen fluid for 48 h at 39°C. After incubation, the supernatants were analyzed to determine pH, ammonia concentration, total volatile fatty acid (VFA), and microbial protein synthesis. The residues were analyzed to determine DM, organic matter, protein, and RUP digestibility. Results: Increased protein, energy, and RDP levels increased digestibility, ammonia concentrations, total VFAs, and microbial protein synthesis (p

Objective: This study aimed to investigate the effects of rations incorporating rumen degradable protein (RDP), non-fiber carbohydrate (NFC), and sulfur on nutrient utilization, milk production, milk quality, and the economic aspects of dairy goats., Methods: In the first study, five treatments were tested in a block-randomized design to examine in vitro fermentability and digestibility. Treatments included P0 (control diet), P1 (P0 + 7.5% cassava-NFC), P2 (P0 + 7.5% cassava-NFC and 5% soybean), P3 (P0 + 7.5% cassava-NFC and 5% autoclaved soybean), and P4 (P0 + 7.5% cassava-NFC, 5% autoclaved soybean, and 0.1% sulfur). In the second study, sixteen lactating Saanen-Ettawa crossbreed dairy goats (initial milk production = 0.97 ± 0.25 L/head/day, 30 DIM; body weight = 44.44 ± 7.20 kg) were assigned into four groups and fed treatment diets: R0 (basal diet), R1 (R0 + 12% autoclaved soybean), R2 (R0 + 12% autoclaved soybean and 9% cassava-NFC), and R3 (R0 + 12% autoclaved soybean, 9% cassava-NFC, and 0.11% sulfur). The diets were offered for 7 weeks with a two-week adaptation period. Parameters observed include milk production and quality, milk fatty acids, blood hematology and metabolites, and economic aspects. The study used a block randomized design with initial weight as a block., Results: The treatment diets in the first study had no effect on in vitro fermentability and digestibility. Treatments R2 and R3 resulted in higher milk production than R0 and R1. Milk quality remained consistent across treatments, while solid non-fat, lactose, and protein was higher in R2 and R3. Blood hematology was unaffected by the treatments. Nutrient efficiency and income over feed cost were enhanced by R2 and R3 treatments., Conclusion: Protected RDP using autoclaved soybean and cassava-NFC maintained in vitro digestibility, even though it did not improve in vitro fermentability. Precision dairy ration based on RDP, NFC, and sulfur positively impacts milk production, nutrient efficiency, and animal health in dairy goats.

The objectives of this study were to evaluate the effect of differences in protein type and delivery method on rumen dynamics and nutrient digestion. Cows were allotted to rumen degradable protein (RDP) or rumen undegradable protein (RUP) and self-fed (SF) salt-limited pressed blocks or hand-fed (HF) loose supplement, resulting in four dietary treatments. There was a delivery effect (p = 0.04) on neutral detergent fiber (NDF) intake, as the SF animals consumed more NDF than HF animals. The RDP-SF animals had greater NDF digestibility (p = 0.04) and water intake (p = 0.03) than the three other treatments. Supplement intake displayed a protein type effect (p = 0.03), as RDP-supplemented animals consumed more supplement on a g·kg body weight (BW)−1 d−1 basis than RUP animals. There was an effect of protein type (p = 0.02) and delivery method (p = 0.03) on fluid flow rate, with RUP and HF cows having greater liquid flow rates. Ruminal pH was lower (p < 0.01) in RDP-HF cows than RDP-SF cows at all hours, except 4-h post-feeding. RDP-SF animals had the greatest (p < 0.01) concentrations of ruminal ammonia. Valerate ruminal concentrations were greater (p = 0.04) in RDP supplemented animals compared to RUP supplemented animals. In conclusion, self-fed supplements containing RDP may enhance the use of low-quality forages and increase ruminal ammonia concentrations.

Slow-release urea (SRU) is a coated non-protein nitrogen (NPN) source for ruminant nutrition. This study applied a meta-analytic technique to quantify the effect of a commercial SRU (Optigen®, Alltech Inc., Nicholasville, KY, USA) on the performance of beef cattle. Data were extracted from 17 experiments and analysed using the random-effects model to estimate the effect size of SRU on dry matter intake (DMI), crude protein intake (CPI), live weight gain (LWG) and feed efficiency (FE) of growing and finishing beef cattle. There was no effect of feeding SRU on the overall DMI and CPI of beef cattle. Dietary inclusion of SRU improved the overall LWG (+92 g/d/head) and FE (+12 g LWG/kg DMI/head) of beef cattle. Notably, SRU supplementation in growing cattle exhibited a better improvement on LWG (130 vs. 60 g/d/head) and FE (18 vs. 8 g LWG/kg DMI/head) compared with finishing cattle. Moreover, SRU showed consistent improvements on the LWG and FE of beef cattle under several study factors. Simulation analysis indicated that positive effects of SRU on LWG and FE improved profitability through reduction in feed cost and reduced the emission intensity of beef production. These results indicate that SRU is a sustainable NPN solution in beef cattle production.

In tropical regions, protein supplementation is a common practice in dairy and beef farming. However, the effect of highly degradable protein in ruminal fermentation and microbial community composition has not yet been investigated in a systematic manner. In this work, we aimed to investigate the impact of casein supplementation on volatile fatty acids (VFA) production, specific activity of deamination (SAD), ammonia concentration and bacterial and archaeal community composition. The experimental design was a 4×4 Latin square balanced for residual effects, with four animals (average initial weight of 280±10 kg) and four experimental periods, each with duration of 29 days. The diet comprised Tifton 85 (Cynodon sp.) hay with an average CP content of 9.8%, on a dry matter basis. Animals received basal forage (control) or infusions of pure casein (230 g) administered direct into the rumen, abomasum or divided (50 : 50 ratio) in the rumen/abomasum. There was no differences (P>0.05) in ruminal pH and microbial protein concentration between supplemented v. non-supplemented animals. However, in steers receiving ruminal infusion of casein the SAD and ruminal ammonia concentration increased 33% and 76%, respectively, compared with the control. The total concentration of VFA increased (P0.05) in species richness and diversity of γ-proteobacteria, firmicutes and archaea between non-supplemented Nellore steers and steers receiving casein supplementation in the rumen. However, species richness and the Shannon–Wiener index were lower (P

Meeting metabolizable protein requirements of finishing cattle without overfeeding protein requires reliable estimates of site and extent of digestion. Current estimates of rumen degradable (RDP) and undegradable protein (RUP), as well as intestinal digestibility of RUP (dRUP) may be inadequate. Thus, the objectives of this experiment were to quantify RDP, RUP, and dRUP of common feedstuffs and evaluate nutrient composition as a predictor of RDP, RUP, and dRUP. Ruminally cannulated steers (n = 6) consuming a finishing diet were enrolled in replicated 3 × 3 Latin squares. Within each Latin square period, steers were assigned a feedstuff classification for in situ ruminal incubation. Single-source ingredients were classified as grain (steam-flaked and whole-shelled corn, wheat, and milo), protein (wet and dried corn distillers grains, Sweet Bran, cottonseed meal, canola meal, and soybean meal), and roughage (cotton burrs, alfalfa hay, wheat hay, sorghum × sudangrass hay, wheat silage, and corn stalks). Nutrient composition was determined for all feedstuffs using wet chemistry procedures. Feedstuffs were lyophilized, ground through a 2-mm screen, aliquoted into in situ bags, and ruminally incubated for 0, 4, 8, 12, 24, or 48 h. Samples were composited within incubation time point, analyzed for crude protein (CP), corrected for microbial contamination, and fit to non-linear models to estimate RDP and RUP using calculated passage rate. Subsamples of in situ digested feedstuffs underwent in vitro pepsin-pancreatin digestion and CP analysis to estimate dRUP. Statistical analyses were conducted using JMP Pro 16.0 and R (v4.1.0). On average, RUP estimates were 37.0% decreased (P < 0.05) for protein ingredients, yet grains and roughages were not different (P > 0.73) compared with NASEM (2016) empirical values, respectively. However, average dRUP was 11.9% and 33.1% reduced (P < 0.01) for protein ingredients and roughages, yet grain dRUP was not different (P = 0.16) compared with NASEM (2016) values, respectively. Neutral detergent fiber (NDF) and CP explained a substantial portion of the variation in RDP (P < 0.01, R2 = 0.94, RMSE = 2.26). Acid detergent fiber, NDF, and CP explained considerable variation in dRUP (P < 0.01, R2 = 0.91, RMSE = 5.43). Models were predictive when applied to independent data from the literature for estimates of RDP (R2 = 0.93; RMSE = 3.72) and dRUP (R2 = 0.83; RMSE = 6.06). There was slope (-0.09; P < 0.05) and mean bias (-1.30; P < 0.01) for RDP prediction validation but only mean bias (4.90; P < 0.01) in dRUP prediction validation models. Collectively, these data suggest that dRUP of protein ingredients and roughages are less than values reported by the NASEM (2016). Furthermore, CP and NDF may be useful for predicting RDP, RUP, and dRUP. [ABSTRACT FROM AUTHOR]

The present study was conducted to investigate the effect of alternative true-protein sources to soybean meal, with different ruminal degradability, using a sugarcane-based diet, on nutrient digestion, ruminal fermentation, efficiency of microbial protein synthesis and passage rate in prepubertal dairy heifers. Eight crossbred rumen- and duodenum-cannulated Holstein × Gyr dairy heifers (202.0±11.5 kg BW) were evaluated in a 4 × 4 Latin square experimental design with four treatments and four periods in two simultaneous replicates. Dietary treatments were: soybean meal; cottonseed meal; peanut meal; and sunflower meal. When associated with diets containing sugarcane, the different protein sources did not affect intake or digestibility of dry mater, crude protein, organic matter and neutral detergent fiber. The average ruminal pH, NH3-N and concentration of total volatile fatty acids were not different among the diets supplied. The concentration of butyric acid was different among the protein sources, wherein the animals fed the diet with sunflower meal presented lower values than those fed the other sources. Diets did not affect nitrogen balance, microbial nitrogen, microbial synthesisefficiency, estimated dry matter flow, or passage rate. Alternative protein sources can be used to reduce the costs without changing the animal metabolism.

Cattle production in Brazil is mainly based on the use of pasture as the main source of nutrients. Supplementation together with the correct pasture management has been one of the main tools to optimize animal production. In addition, understanding how the animal adjusts its ingestive behavior, determining the time spent grazing, rumination and idle time is a fundamental parameter for the development of nutritional management strategies. This research aimed to identify if canopy height and protein supplementation interfere in daytime behavior of Girolando breed in Marandu Palisadegrass pastures with intermittent defoliation. The experiment was conducted at Instituto de Zootecnia in Nova Odessa, São Paulo, Brazil. The method used was the visual observation and the activities of the animals were written every 10 minutes (grazing, rumination and idle time), from 6:30 a.m. to 6:30 p.m., thus comprising 12 continuous hours. The cattle were properly identified with colored ribbon around the neck. Treatments consisted in two supplements (100% and 140% of rumen degradable protein requirement), and pre-grazing and post-grazing canopy heights (25 cm and 15 cm respectively), according to a completely randomized design in 2x2 factorial arrangement with 3 replications, from April to May 2017. African Mahogany seedlings were planted in February/2016, in three rows or one row (5 m between trees) spaced 15 m apart (Marandu Palisadegrass 4,500 m2 paddocks) but were not considered in this work, since they were with 67 cm average height, without interference in pasture growth. Data were subjected to analysis of variance using PROC MIXED of SAS® (Statistical Analysis System, version 9.3) statistical package. The means of the treatments were estimated using "LSMEANS" and the comparison between them performed by Student t test (P

The objective of this study was to examine the effect of reducing rumen-degradable protein (RDP) and rumen-undegradable protein (RUP) proportions on feed intake, milk production, and N-use efficiency in primiparous and multiparous cows exposed to warm climates. Eighteen primiparous and 30 multiparous mid-lactation Holstein cows were used in a completely randomized design with a 2 × 2 factorial arrangement of treatments. Cows were randomly assigned to 1 of 4 dietary treatments formulated to contain 2 proportions of RDP (10 and 8%) and 2 proportions RUP (8 and 6%) of dry matter (DM) indicated as follows: (1) 10% RDP, 8% RUP; (2) 8% RDP, 8% RUP; (3) 10% RDP, 6% RUP; and (4) 8% RDP, 6% RUP. Protein sources were manipulated to obtain desired RDP and RUP proportions. Diets were isoenergetic and contained 50% forage and 50% concentrate (DM basis). Cows were individually fed the 10% RDP, 8% RUP diet 3 wk before treatment allocation. Cows were exposed to the prevailing Tennessee July and August temperature and humidity in a freestall barn with no supplemental cooling. Main effects and their interaction were tested using the Mixed procedure of SAS (least squares means ± standard error of the mean; SAS Institute Inc., Cary, NC). Observed values of nutrient intake and milk production were used to obtain NRC (2001) model predictions. Cows showed signs of heat stress throughout the study. Reducing from 10 to 8% RDP decreased dry matter intake (DMI; 0.9 kg/d) at 8% RUP, but increased DMI (2.6 kg/d) at 6% RUP in primiparous cows. Reducing from 10 to 8% RDP decreased milk yield (10%) at 8% RUP, but increased yield (14%) at 6% RUP. Treatments did not affect yield of energy-corrected milk. For multiparous cows, treatments did not affect DMI. Reducing from 10 to 8% RDP decreased yield of energy-corrected milk (3.4%) at 8% RUP, but increased yield (8.8%) at 6% RUP. Reducing from 10 to 8% RDP and 8 to 6% RUP both increased N-use efficiency for primiparous and multiparous cows. The NRC model underestimated metabolizable protein and RUP supply, and overestimated RUP requirements, resulting in predictive losses of milk yield 1.4 to 1.8 times greater than observed values. In summary, the reduction of RDP and RUP proportions did not affect DMI, whereas the RUP reduction at 10% RDP had a small negative effect on energy-corrected milk yield. However, reduction of RDP and RUP consistently improved N-use efficiency of heat-stressed multiparous cows. The reduction of RDP and RUP proportions reduced DMI and milk yield but did not affect energy-corrected milk yield in primiparous cows, indicating a limited supply of nutrients. [ABSTRACT FROM AUTHOR]

The effects of microbial contamination (MC) on CP degradability of concentrate feeds are still controversial. Therefore, the aim of this study was to use 15N to estimate the impact of MC on estimations of CP fractions (the soluble fraction of CP [a], the insoluble but potentially degradable fraction of CP [b], and the rate of digestion of fraction b [kd]) of concentrate feeds. Twelve types of feed were evaluated: 6 energy concentrates--wheat bran (Triticum aestivum L.), rice meal (Oryza sativa L.), ground corn (Zea mays L.), ground sorghum (Sorghum vulgare Pers.), ground corn cob (Zea mays L.), and soybean hulls [Glycine max (L.) Merr.]--and 6 protein concentrates--cottonseed meal (Gossypium hirsutum L.), soybean meal [Glycine max (L.) Merr.], ground bean (Phaseolus vulgaris L.), peanut meal (Arachis hypogaea L.), sunflower meal (Helianthus annuus L.), and corn gluten meal (Zea mays L.). The feeds were divided into 4 groups and were incubated in the rumen of 4 crossbred bulls. The samples were incubated for 0, 2, 4, 8, 16, 24, 48, and 72 h. To estimate the MC of the incubated residues, the ruminal bacteria were labeled with 15N via continuous intraruminal infusion of 15(NH4)2SO4. There was no difference (P = 0.738) between corrected and uncorrected parameters a, b, and kd for all feeds that were evaluated. All of the feed tests followed an exponential model of degradation, and the model fitted well to the data, except for corn gluten meal, probably because the maximum incubation time that was used (72 h) was not long enough to allow for an accurate estimation of the degradation profile. Therefore, correction of ruminal protein degradation to MC is irrelevant with regards to the concentrates that were studied. [ABSTRACT FROM AUTHOR]

Con el fin de evaluar el efecto de niveles crecientes de proteína degradable en rumen (PDR) sobre las concentraciones de amonio y piruvato en hígado, se utilizaron 15 vacas Holstein que cursaban los primeros cien días posparto. Estas se asignaron aleatoriamente a tres tratamientos experimentales que consistieron en el suministro de un suplemento alimenticio comercial al que se le adicionó urea de tal manera que se incrementará el consumo de PDR en aproximadamente 0 (T0), 10 (T1) y 15% (T2) respecto a los requerimientos. A estas vacas se les determinaron las concentraciones hepáticas de amonio (Ahep) y piruvato (Pihep). Se realizó un balance nutricional de energía neta de lactancia (ENL), proteína metabolizable (PM), PDR y proteína no degradable en rumen (PNDR) donde se encontraron diferencias significativas entre los tratamientos (PIn order to test the effect of growing levels of diet rumen degradable protein on hepatic concentrations of ammonia and piruvate, fifteen cows Holstein in their first one hundred post calving days were used. They were assigned at random to three different experimental treatments, which consisted on the supply of a commercial feeding supplement without any addition of urea as a source of NNP (T0); the second treatment (T1) consisted on the supply of the same supplement with an addition of urea, so that the supply of PDR was increased 10% approximately to the requirements;finally, in the third treatment, (T2) the cows were given the same supplement which was added with enough urea so that the supply of PDR was increased 15% approximately to the requirements. In these cows were determined hepatic concentrations of ammonia (Ahep) and pyruvate (Pyhep). The concentrations of Ahep were different among treatments, whereas the concentrations of Pihep were similar. Negative relations between Ahep and ENL, Ahep and PNDR, Ahep, and PM, were found it; while Pihep was positively related with Ahep. These results suggest the metabolizable protein use as energy source, increasing nitrogen excess and probably rest amino acids for biosynthetic process.

Feeding extra protein as an attempt to increase amino acid flux to the intestine may increase lactational performance of dairy cattle. The objective of this study was to compare lactating dairy cow diets containing 16% crude protein (CP), adequate in rumen degradable protein (RDP) and metabolizable protein (MP) according to NRC (2001), with diets containing 17.5% CP. Forty-two Holstein cows (27 primiparous and 15 multiparous, with 172 days in milk) were used in a 3 ´ 3 Latin Square design with 14 replicates. Control diet consisted of 16% CP, adequate in RDP and MP . Crude protein content of diets was increased to 17.5% by feeding extra soybean meal and cottonseed meal (SBCS17.5) to increase diet MP, or extra urea (U-17.5) to increase diet RDP. The experiment was carried out during 60 days with three periods. Animals were group-fed a total mixed ration and milked twice a day. Dry matter intake was higher for the U-17.5 diet (p < 0.15) than for the control diet. Milk (p < 0.01) and 3.5% fat corrected milk (FCM-3.5%) (p < 0.05) yields were increased by extra soybean and cottonseed meal (SBCS-17.5) but not by extra urea (U-17.5). Milk fat content and yield were not affected by treatments (p > 0.05). Milk protein content decreased (p < 0.01) by feeding extra urea (U-17.5). However, higher (p < 0.01) protein yields were observed for the SBCS-17.5 treatment. For cows milking around 29 kg d-1, increasing diet CP content to 17.5%, by feeding extra soybean and cottonseed meal, beyond recommendations for RDP and MP, increased yields of milk, yields of 3.5% fat corrected milk and yields of milk protein.O fornecimento de dietas com maior teor de proteína para aumentar o fluxo de aminoácidos para o intestino pode aumentar o desempenho lactacional. Compararam-se dietas para vacas em lactação contendo 16% de proteína bruta (PB), adequada em proteína degradável no rúmen (PDR) e proteína metabolizável (PM) (NRC, 2001) com dietas com maiores teores de PB (17,5%) . Quarenta e duas vacas (27 primíparas e 15 multíparas, com 172 dias em lactação) foram utilizadas em um delineamento do tipo Quadrado Latino 3 ´ 3, com 14 repetições. A dieta controle continha 16% de PB e era adequada em PDR e PM de acordo com o NRC (2001). O teor de PB das dietas foi aumentado para 17,5% através do aumento no fornecimento de farelo de soja e de algodão (SBCS-17,5) para aumentar a PM, ou uréia (U-17,5) para aumentar a PDR. O experimento teve duração de 60 dias com três subperíodos. Os animais foram alimentados em grupo com ração completa e ordenhados duas vezes ao dia. O consumo de matéria seca foi maior para a dieta U-17,5 (p < 0,15) do que para a dieta controle. A produção de leite (p < 0,01) e de leite corrigido para gordura 3,5% (LCG-3,5%) (p < 0,05) foram aumentadas com o maior fornecimento de farelo de soja e de algodão (SBCS-17,5) mas não pelo maior fornecimento de uréia (U-17,5). O teor e a produção de gordura do leite não foram afetados (p > 0,05) pelos tratamentos. O teor de proteína foi reduzido (p < 0,01) pelo maior fornecimento de uréia (U-17,5); enquanto maior produção de proteína do leite (p < 0,01) foi observada para o tratamento SBCS-17,5. Para vacas produzindo em torno de 29 kg d-1, aumentar o teor de PB para 17,5%, por meio do maior fornecimento de farelo de soja e de algodão, acima das recomendações do NRC (2001) para PDR e PM, resultou em aumentos na produção de leite, leite corrigido para gordura e de proteína do leite.

Polyphenol oxidase in red clover (RC) silage reduces lipolysis and consequently protects its constituent fatty acids (FA) against biohydrogenation by ruminal microorganisms. Fatty acid biohydrogenation could be further inhibited by reducing the nitrogen (N) supply to ruminal bacteria. To compare the effects of RC and alfalfa (AL) silage fed in diets differing in rumen-degradable protein supply on the transfer efficiency of polyunsaturated FA from diet to milk, and on the resulting FA profile of milk fat, 8 multiparous Holstein dairy cows (72 ± 17 days in milk) were used in a replicated 4 × 4 Latin square design (21-day periods including 14 days of adaptation). Four treatments were compared in a 2 × 2 factorial arrangement with AL or RC fed in diets formulated to provide 100% (RDP‐100) or 85% (RDP‐85) of calculated rumen-degradable protein requirements. Rumen-degradable protein concentrations were adjusted by varying the supplies of ground vs. steam-flaked corn grains, and untreated vs. heat-treated soybean meals. Feeding RC, as compared with AL diets, decreased ruminal ammonia-N concentration as well as urea-N in plasma and milk. Intakes of c 9 c 12 18:2 and c 9 c 12 c 15 18:3 were lower for cows fed RC, but their secretion in milk and their apparent transfer efficiency from diet were greater as compared to cows fed AL. As a result, feeding RC increased the concentrations of c 9 c 12 18:2 and c 9 c 12 c 15 18:3, but decreased the proportions of t 11 18:1, c 9 t 11 18:2, and t 11 c 15 18:2 in milk fat. These results are consistent with the lower effective ruminal disappearance of c 9 c 12 18:2 and c 9 c 12 c 15 18:3 in RC as determined by a 96 h in sacco incubation, and the lower abundance of ruminal bacteria capable of hydrolyzing dietary lipids and hydrogenating polyunsaturated FA ( Ruminococcus albus and Ruminococcus flavefaciens ) in the rumen content. The apparent transfer efficiency of c 9 c 12 18:2 from diet to milk was further increased by feeding RDP‐85 as compared with RDP‐100 diet. Feeding RC decreased concentrations of linear odd-chain FA (11:0, 13:0, 15:0, 17:0, and c 9 17:1) and increased proportions of branched-chain FA (iso13:0, iso14:0, iso15:0, iso16:0, iso17:0, anteiso15:0, and anteiso17:0) in milk fat as compared with AL. In conclusion, as compared with AL, cows fed RC produced milk with greater concentrations of major forage FA ( c 9 c 12 18:2 and c 9 c 12 c 15 18:3) and lower proportions of intermediates in ruminal biohydrogenation of these FA. Variations in milk fat concentrations of odd- and branched-chain FA, which are synthesized in the rumen by various microbial populations, may be reflecting the effects of forage source on ruminal fermentation. [ABSTRACT FROM AUTHOR]

O objetivo neste trabalho foi avaliar a digestibilidade aparente de rações com diferentes teores de proteína degradável no rúmen (PDR) e fonte de amido de baixa degradabilidade ruminal (milho moído) em ovinos. Utilizaram-se quatro ovinos castrados, sem raça definida (SRD), com peso vivo médio de 38,5 kg, em um delineamento experimental quadrado latino 4 x 4. As quatro rações experimentais utilizadas foram compostas de 75% de volumoso (feno de aveia) e 25% de concentrado à base de milho moído (MM), farelo de soja (FS), farelo de algodão (FA), farinha de peixe (FP), uréia e sal mineral, compostas com quatro teores de PDR (46, 50, 54 e 58% de PDR nas rações). Determinaram-se a digestibilidade aparente total dos nutrientes e o balanço de nitrogênio nos animais alimentados com as rações experimentais. Os consumos de MS, MO, PB, amido, FDN e FDA não diferiram entre as rações testadas. Da mesma forma, o nitrogênio ingerido (NI), o N excretado nas fezes e na urina, em g/dia, o balanço de nitrogênio (%NI) e os coeficientes de digestibilidade da MS, MO, PB, FDN e FDA não diferiram entre as rações experimentais, sendo estimados valores médios de 31,68; 6,34; 11,31 g/dia e 44,27% NI, respectivamente, e de 71,90; 73,00; 79,70; 61,10; e 52,00%, respectivamente. Independentemente dos teores de PDR em rações contendo milho como fonte de amido de baixa degradabilidade ruminal, não houve efeitos sobre a digestibilidade aparente dos nutrientes e o balanço de nitrogênio em ovinos.Four castrated sheep averaging 38.5 kg of body weight were randomly assigned to a 4 x 4 Latin square to evaluate the apparent digestibility of nutrients and nitrogen balance (NB) on diets containing different levels of rumen degradable protein (RDP): 46, 50, 54, and 58% and ground corn. The four experimental diets were composed by 75% of forage (oat hay) and 25% of concentrate containing ground corn (GC), soybean meal (SM), cottonseed meal (CM), fish meal (FM), urea, and mineral salt. No significant differences were observed on the intakes of DM, OM, CP, starch, NDF, and ADF by increasing the dietary RDP levels. Nitrogen intake (NI), urinary N excretion, fecal N excretion, and NB expressed as % NI averaged, respectively, 31.68 g/d, 6.34 g/d, 11.31 g/d, and 47.27% and did not differ across diets. Similarly, apparent total tract digestibilities of DM, OM CP, NDF, and ADF averaged, respectively, 71.90, 73.00, 79.70, 61.10, and 52.00% and did not differ when the RDP level was increased in the diet. It can be concluded that both digestibility of nutrients and NB were not affected by different dietary RDP levels under the conditions of this trial.

The aim of this study was to evaluate the effects of ruminal and abomasum protein supplementation in cattle consuming tropical forages on nutritional characteristics, fibrolytic enzymatic activity, in vitro degradation of insoluble fiber, and the ruminal microbial community profile. Two experiments were sequentially conducted and differed only in the forage quality that was offered: medium-quality forage (MQF, 78.4 g of crude protein, CP/kg of dry matter, DM) and high-quality forage (HQF, 98.6 g CP/kg DM). Four Nellore young bulls fitted with rumen and abomasum cannulas were utilized, and the following supplementation schemes were evaluated: control (only forage), daily supply of 230 g of additional CP (casein) into the rumen, daily supply of 230 g of additional CP into the abomasum, and supply of 115 g of additional CP into the rumen and 115 g of additional CP into the abomasum. Experiments were conducted using a 4 × 4 Latin square design where two sequential squares were used, one for MQF and other for HQF. The improvement in forage quality increased (P < 0.05) intake, fiber digestibility, and nitrogen retention. Supplementation, independently of site (rumen, abomasum or both), increased (P < 0.05) nitrogen balance in the rumen and in the animal’s body. Ruminal supplementation increased (P < 0.05) rumen ammonia nitrogen concentration and consequently in vitro degradation rate of neutral detergent fiber. Enzymatic activity was not affected (P > 0.05) by forage quality. However, in disagreement with data of degradation and digestibility, decreases in enzymatic activity were observed mainly for post-ruminal supplementation. The improvement of forage quality increased (P < 0.05) the richness and diversity associated with liquid fractions from ruminal fluid, although there was no effect on solid fractions. The improvement in forage quality and protein supplementation increases nitrogen accretion in the animal body. Well-defined associations cannot be established between production characteristics and enzymatic activities, and rumen microbial diversity in cattle fed tropical forages and receiving protein supplementation. [ABSTRACT FROM AUTHOR]

O objetivo deste trabalho foi avaliar o efeito de níveis de inclusão de nitrogênio não protéico, em suplementos fornecidos a tourinhos Hereford, com 17 meses e peso médio de 220 kg, alimentados com feno de tifton (Cynodon dactylon) ad libitum. Os tratamentos avaliados foram: feno + suplemento sem uréia; feno + suplemento com 0,28 g de uréia kg-1 PV0,75; feno + suplemento com 0,55 g de uréia kg-1 PV0,75; feno + suplemento com 0,83 g de uréia kg-1 PV0,75 e feno + suplemento com 1,11 g de uréia kg-1 PV0,75. O feno apresentou, na média, 3,86% de proteína bruta e 84,66% de fibra em detergente neutro. Não se constatou efeito da suplementação sobre a digestibilidade da matéria orgânica, matéria orgânica do feno, fibra em detergente neutro, celulose e hemicelulose; o consumo total desses itens respondeu quadraticamente à suplementação com níveis crescentes de nitrogênio não protéico. A suplementação não afetou a excreção fecal metabólica de matéria orgânica, o que sugere aumento na taxa de passagem (variação no consumo) e na taxa de digestão (digestibilidade constante). O consumo de matéria orgânica digestível apresentou comportamento quadrático com aumento dos níveis de uréia na dieta. Quando o nível de proteína degradável no rúmen foi equivalente a 8,1% da matéria orgânica digestível, a relação de consumo entre esses componentes foi otimizada.The objective of this work was to evaluate the effect of nonprotein nitrogen supplementation levels on the digestibility of low-quality hay (Cynodon dactylon), which was offered ad libitum to Hereford bulls aging 17 months and weighing 220 kg. The evaluated treatments were: hay + no urea supplement; hay + supplement with 0.28 g urea kg- 1 BW0.75; hay + supplement with 0.55 g urea kg-1 BW0.75; hay + supplement with 0.83 g urea kg- 1 BW0.75 and hay + supplement with 1.11 g urea kg- 1 BW0.75. Hay composition presented 3.86% of crude protein and 84.66% of neutral detergent fiber. Digestibility of organic matter, organic matter of forage, neutral detergent fiber, cellulose and hemicellulose were not affected by nonprotein nitrogen level; total intake of these components showed a quadratic response to nonprotein nitrogen supplementation. Organic matter metabolic fecal excretion was not affected by supplementation, suggesting a simultaneous increase in both passage (intake increase) and digestion rates (stable digestibility). The digestible organic matter intake showed a quadratic response with the increase of urea supplementation levels. The relationship between rumen degradable protein intake and digestible organic matter intake showed a maximization point, when rumen degradable protein intake was equivalent to 8.1% of digestible organic matter intake.

Avaliaram-se os consumos, as digestibilidades aparentes dos nutrientes e a produção e composição do leite de vacas no terço inicial da lactação recebendo dietas contendo níveis crescentes (20; 23; 26 e 29% da matéria natural - MN) de proteína bruta (PB) no concentrado. Foram utilizadas 12 vacas em lactação da raça Holandesa, puras e mestiças (Holandês x Zebu), distribuídas em três quadrados latinos (4x4). Foram utilizados quatro períodos de 15 dias cada, considerando-se uma semana de adaptação. A dieta consistiu de 60% de silagem de milho como volumoso e 40% de concentrado. Os consumos de matéria seca (MS), PB, fibra em detergente neutro (FDN) e nutrientes digestíveis totais (NDT) aumentaram linearmente, enquanto o consumo de carboidratos não-fibrosos (CNF) apresentou redução linear com os níveis de PB no concentrado. As digestibilidades da MS, matéria orgânica (MO), PB e FDN elevaram linearmente em função dos teores de PB. A produção de leite (PL) e PL corrigida para 3,5% de gordura, as quantidades de gordura e proteína e suas concentrações no leite não foram afetadas pelos níveis de PB no concentrado. No entanto, a PL corrigida para 3,5% de gordura de 29,08 kg/dia foi numericamente superior para o nível de 26% de PB na MN do concentrado. O concentrado contendo 26% de PB utilizado na proporção de 40%, que correspondeu a 15,5% na MS da dieta total, permitiu melhores respostas na produção de leite em vacas produzindo em média 28 kg/dia de leite no terço inicial da lactação e alimentadas com silagem de milho como volumoso.The intake, total apparent digestibility of nutrients and milk production and composition were evaluated in early lactation cows fed with increasing levels (20; 23; 26 and 29% natural matter - NM) of crude protein (CP) in concentrate. Twelve crossbred Holstein cows were assigned to three latin square (4x4), in four periods of 15 days each (one week of adaptation). The feeding consisted of 60% of cow silage and 40% of concentrate. The intakes of dry matter (DM), CP, neutral detergent fiber (NDF), and total digestible nutrients (TDN) intakes increased linearly and the nonfiber carbohydrates (NFC) intake showed linear reduction as CP levels in the concentrate increased. DM, organic matter (OM), CP and NDF digestibilities increased linearly with CP levels. Milk production (MP), corrected MP, fat and protein levels in milk were not influenced by CP levels in the concentrate. Nonetheless, corrected MP for 3.5% fat was 29.08 kg/day in 26% of CP in NM of the concentrate. CP level of 26%, in a proportion of 40% concentrate, correspondent to 15.5% DM in the feed, showed better results of milk production, average of 28 kg/day, in early lactation of cows fed with corn silage.

In tropical regions, protein supplementation is a common practice in dairy and beef farming. However, the effect of highly degradable protein in ruminal fermentation and microbial community composition has not yet been investigated in a systematic manner. In this work, we aimed to investigate the impact of casein supplementation on volatile fatty acids (VFA) production, specific activity of deamination (SAD), ammonia concentration and bacterial and archaeal community composition. The experimental design was a 4×4 Latin square balanced for residual effects, with four animals (average initial weight of 280±10 kg) and four experimental periods, each with duration of 29 days. The diet comprised Tifton 85 (Cynodon sp.) hay with an average CP content of 9.8%, on a dry matter basis. Animals received basal forage (control) or infusions of pure casein (230 g) administered direct into the rumen, abomasum or divided (50 : 50 ratio) in the rumen/abomasum. There was no differences (P>0.05) in ruminal pH and microbial protein concentration between supplemented v. non-supplemented animals. However, in steers receiving ruminal infusion of casein the SAD and ruminal ammonia concentration increased 33% and 76%, respectively, compared with the control. The total concentration of VFA increased (P<0.05) in steers receiving rumen infusion of casein. SAD and the microbial protein concentration did not vary significantly among treatments during the feeding cycle, but mean SAD values were greater in steers supplemented in the rumen and rumen/abomasum. Ruminal ammonia concentration was positively correlated with SAD in animals receiving ruminal infusion of casein. Polymerase chain reaction–denaturing gradient gel electrophoresis (PCR-DGGE) analysis revealed low similarity between treatments, animals and time of sample collection. Richness analysis and determination of the Shannon–Wiener index indicated no differences (P>0.05) in species richness and diversity of γ-proteobacteria, firmicutes and archaea between non-supplemented Nellore steers and steers receiving casein supplementation in the rumen. However, species richness and the Shannon–Wiener index were lower (P<0.05) for the phylum bacteroidetes in steers supplemented with casein in the rumen compared with non-supplemented animals. Venn diagrams indicated that the number of unique bands varied considerably among individual animals and was usually higher in number for non-supplemented steers compared with supplemented animals. These results add new knowledge about the effects of ruminal and postruminal protein supplementation on metabolic activities of rumen microbes and the composition of bacterial and archaeal communities in the rumen of steers. [ABSTRACT FROM PUBLISHER]

Increased dietary inclusion of rapidlyfermentable carbohydrates and a great proportion of corn-derived CP may result in increased rumen degradable protein (RDP) microbial requirements and reduced RDP supply, respectively. An experiment was conducted to evaluate the effect of processing and moisture content of corn grain in finishing diets concurrently balanced to meet increased RDP requirements on feedlot cattle performance. A semi-dent corn hybrid crop was harvested and stored as drywhole (DWC), dry-rolled (DRC), whole high-moisture (WHMC), or rolled high-moisture (RHMC) corn (89.3% DM and 32.4% moisture for dry and highmoisture corn, respectively). Four dietary treatments containing 78.8-79.0% corn grain were arranged by adding (DM basis) 0.15, 0.20, 0.0, or 0.0% of urea to DWC, DRC, WHMC, or RHMC-based diets, respectively, to meet RDP requirements, which were measured in previous experiments using the same corn hybrid as in the present experiment. Angus steers (n = 144; 356 ± 2.7 kg initial BW) were group-housed in 24 pens, fed once daily from d 1 to 86, and held off feed and water for 16 h to record initial and final BW. Data were analyzed as a randomized complete block (6) design. Rate of BW gain and HCW increased and DMI decreased (P ≤ 0.02) from dry and whole to moist and rolled corn-fed steers (Table 1). Consequently, steers fed the RHMC-based and 0%-urea diet were finished at heavier BW and were more efficient (P ≤ 0.02) converting feed into BW and carcass compared with steers fed any of the other diets. Feeding high-moisture compared with dry corn led to improved cattle performance and might reduce urea-derived costs. The convenience of using RHMC instead of WHMC may rely upon the balance between improved animal performance and increased feed costs associated with corn processing. [ABSTRACT FROM AUTHOR]

This is the first of three articles reviewing the interrelationships between nutrition and fertility. The three articles together will give a comprehensive and evidence-based approach for the general practitioner to investigate and advise their clients in this area. [ABSTRACT FROM AUTHOR]

A rumen simulation technique apparatus with eight 800 mL fermentation vessels was used to investigate the effects of rumen degradable protein (RDP) level and non-fibre carbohydrate (NFC) type on ruminal fermentation, microbial growth, and populations of ruminal cellulolytic bacteria. Treatments consisted of two NFC types (starch and inulin) supplemented with 0 g/d (low RDP) or 1.56 g/d (high RDP) sodium caseinate. No significant differences existed among dietary treatments in the apparent disappearance of dietary nutrients except for dietary N, which increased with increased dietary RDP (P<0.001). Compared with starch, inulin treatments reduced the molar proportion of acetate (P<0.001), the acetate:propionate ratio (P<0.001), and methane production (P=0.006), but increased the butyrate proportion (P<0.001). Increased dietary RDP led to increases in production of total volatile fatty acid (P=0.014) and methane (P=0.050), various measures of N (P⩽0.046), and 16s rDNA copy numbers of Ruminococcus flavefaciens (P⩽0.010). Non-fibre carbohydrate source did not affect daily microbial N flow regardless of dietary RDP, but ammonia N production was lower for inulin than for starch treatments under high RDP conditions (P<0.001). Compared with starch treatments, inulin depressed the copy numbers of Fibrobacter succinogenes in solid fraction (P=0.023) and R. flavefaciens in liquid (P=0.017) and solid fractions (P=0.007), but it increased the carboxymethylcellulase activity in solid fraction (P=0.045). Current results suggest that starch and inulin differ in ruminal volatile fatty acid fermentation but have similar effects on ruminal digestion and microbial synthesis in vitro, although inulin suppressed the growth of partial ruminal cellulolytic bacteria. [ABSTRACT FROM AUTHOR]

Thirty six multiparous Danish Holstein cows, 222 days from calving with a standard deviation (±) of 102 days, 627±7kg of body weight, and 32±3kg/d energy corrected milk were used to investigate the effect of forage particle size (FPS) and dietary urea supplementation on excretion of phosphorus (P) in feces and urine when cows were fed P below requirement. Dietary P content was 2.5gP/kg DM in all treatments. Treatments (CONTROL, SHORT and LOW-N) were all based on the same content of forage ingredients but varied in FPS and dietary urea content. In CONTROL and SHORT rumen degradable protein was optimized according to the Nordic protein evaluation system by supplementing dietary urea, whereas urea was excluded in LOW-N in order to obtain a supply of rumen degradable protein below requirements. It was hypothesized that dietary factors that reduce saliva secretion via reduced chewing activity will reduce the inevitable loss of endogenous P (IL) of P and that dietary factors that reduce the supply of rumen degradable protein in the form of dietary urea will result in a decrease in rumen microbial incorporation of P and in turn increase digestibility of P and hereby reduce IL of P. In SHORT FPS of grass hay was reduced to a theoretical particle size of 3mm, as compared to 40–60mm in CONTROL and LOW-N. Rations were fed for ad libitum intake for 16d and balance trials were conducted on d 15 and 16. Indigestible neutral detergent fiber was used as an internal marker to estimate fecal output and total tract digestibilities. The obtained negative P balances confirmed that dairy cows were fed below P requirement, indicating that treatment effects on fecal P excretion mainly originated from variations in IL. Fecal P excretion was not reduced with reduced forage particle size despite reduction in chewing time. Fecal excretion of P was not affected by reduced dietary urea supply below requirement despite a reduction in digestibility of OM. Therefore, the results of the present study do not support the concept that fecal loss of endogenous P is affected by FPS. Nor do the results support the concept that fecal loss of endogenous P is affected by supply of rumen degradable protein. [ABSTRACT FROM AUTHOR]

The objective of this study was to use 15N to label microbial cells to allow development of equations for estimating the microbial contamination in ruminai in situ incubation residues of forage produced under tropical conditions. A total of 24 tropical forages were ruminai incubated in 3 steers at 3 separate times. To determine microbial contamination of the incubated residues, ruminai bacteria were labeled with 15N by continuous intraruminal infusion 60 h before the first incubation and continued until the last day of incubation. Ruminai digesta was collected for the isolation of bacteria before the first infusion of 15N on adaptation period and after the infusion of 15N on collection period. To determine the microbial contamination of CP fractions, restricted models were compared with the full model using the model identity test. Avalué of the corrected fraction "A" was estimated from the corresponding noncorrected fraction by this equation: Corrected "A" fraction (ACPC) = 1.99286 + 0.98256 x A" fraction without correction (ACPWC). The corrected fraction "B" was estimated from the corresponding noncorrected fraction and from CP, NDF, neutral detergent insoluble protein (NDIP), and indigestible NDF (iNDF) using the equation corrected "B" fraction (BcpC) = -17.2181 - 0.0344 x fraction "B" without correction (BcpWC) + 0.65433 x CP + 1.03787 x NDF + 2.66010 x NDIP - 0.85979 x iNDF. The corrected degradation rate of "B" fraction (kd)was estimated using the equation corrected degradation rate of "B" fraction (kdCPC) = 0.04667 + 0.35139 x degradation rate of "B" fraction without correction (kdCPWC) + 0.0020 x CP - 0.00055839 x NDF - 0.00336 x NDIP + 0.00075089 x iNDF. This equation was obtained to estimate the contamination using CP of the feeds: %C = 79.21 x (1 - e-°0555t) x e-0.0874CP jt was concluded that A and B fractions and kd of CP could be highly biased by microbial CP contamination, and therefore these corrected values could be obtained mathematically, replacing the use of microbial markers. The percentage of contamination and the corrected apparent degradability of CP could be obtained from values of CP and time of incubation for each feed, which could reduce cost and labor involved when using 15N. [ABSTRACT FROM AUTHOR]

Abstract: The biochemical mechanisms that limit voluntary intake of one-seed juniper by browsing ruminants are not well understood. Twelve Rambouillet ewes (78±2.3kgBW) and 12 Boer-Spanish does (54±1.4kgBW) were used in a split-plot sequence design to investigate the effects of adding protein, quebracho tannins (QTs), and polyethylene glycol (PEG) on one-seed juniper intake and preference and on ruminal VFA and plasma AA concentrations. Animals received sudangrass hay and isoenergetic basal diets (4 does and 4 ewes/diet) with either rumen degradable (RDP) or rumen undegradable (RUP) protein (12.5% CP) or no additional protein (control, 5% CP) during four 15-d periods. The control, RDP, and RUP diets were considered the main plot, whereas the four supplement treatments were analyzed as the split-plot effects. Period 1 allowed for adaptation to basal diets and served as a baseline phase. In periods 2–4, animals were offered juniper leaves and twigs (period 2), juniper plus QT (10% of basal diet; period 3), and juniper plus QT plus PEG (50g/animal; period 4). Juniper intake by sheep and goats was not affected (P >0.88) by RDP or RUP when animals were first exposed to juniper, but marginally increased (P <0.10) in period 4 (QT+PEG) regardless of the basal diet. Prior exposure to juniper did not affect (P =0.61) the preference ratio for juniper, but goats had higher preference ratio for juniper (P <0.01) when receiving PEG (period 4). Concentrations of total VFA tended to increase in sheep (P =0.10) and goats (P =0.14) fed protein supplements and molar proportions shifted toward acetate for goats fed RDP and RUP (P =0.07) and to butyrate for sheep fed RDP (P =0.01). Initial juniper exposure (period 2) elevated concentrations of acetate, propionate, and butyrate (P <0.01), but the effect was extinguished in periods 3 and 4 with addition of QT (P <0.05). Supplementation with PEG transiently mitigated the depressor effect of QT on acetate, propionate, and butyrate concentration at 12h post juniper feeding (P <0.01). RDP in goats and to a greater extent RUP in sheep increased plasma concentrations of various AA, especially the branched chained Val, Ile, and Leu (P <0.05). Plasma concentrations of several AA, including Met, Cyst, Glu, Gly, Gln, Asn, Thr, Ser, and Phe, decreased with ingestion of juniper (period 2) and juniper plus QT (period 3). Concentrations of some AA that were depressed by ingestion of juniper and QT were partially restored with supplemental PEG (P <0.05). Protein, terpenes, tannins, and PEG interacted to influence rumen VFA and plasma AA, which were related to intake of juniper and basal diets. [Copyright &y& Elsevier]

Abstract: The present study was conducted in order to examine the effects of diets with different ruminal degradable protein sources on the performance of lactating goats fed pelleted total mixed rations (PTMR). Forty multiparous Jonica goats in early-lactation were divided into two equal groups and fed for 135 days the experimental diets. Two types of PTMR were formulated to be isonitrogenous and isocaloric while providing different rumen degradable levels of crude protein: (1) high-degradable protein diet (HD) containing soybean meal, sunflower meal and urea (46% N), and (2) low-degradable protein diet (LD) including only corn gluten meal. Apparent digestibility of the two PTMR was tested using Jonica bucks placed in individual pens and results indicated significant differences (P <0.05) for crude protein, crude fibre, neutral detergent fibre and acid detergent fibre nutrients’ utilization. In milk performance trial, no significant differences (P >0.05) were registered in dry matter intake and milk yield. Goats fed LD diet containing corn gluten meal showed the highest milk fat, protein and casein concentration, but not significant differences (P >0.05) were observed on other milk components and renneting properties. It was concluded that a decrease of rumen degradable protein (RDP) level in PTMR does not negatively influence nutrient utilization and milk production and composition of Jonica dairy goat. [Copyright &y& Elsevier]

The current study investigated the effect of concentration and efficiency of use of rumen degradable protein (RDP) on the nitrogen content of excreta and urea content of urine, as well as on ammonia emissions. Ammonia emission from excreta is mainly affected by the urea concentration in urine which, in turn, mainly results from protein degradation and the efficiency of use of protein in the rumen. The variable component in diets with equal crude protein content (13.2 ± 0.13 % ) was the type of protein, which was either highly rumen degradable barley (B) or slowly rumen degradable maize (M). The urine dry matter contained a significantly higher concentration of nitrogen (P = 0.0015) and urea (P = 0.0012) when the barley diet was fed. In conditions of similar ambient temperature (°C) and humidity (%) the average ammonia emission from excreta also increased (P = 0.0001). The results reveal that, from the viewpoint of reducing emissions, in addition to the crude protein content, the amount, efficiency of use and precise rationing of rumen degradable protein play an important role when diets containing low levels of crude protein are fed. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this study was to examine the effects of pelleted total mixed rations (PTMR) containing two crude protein (CP) levels and N sources with different ruminal degradability on milk yield and composition of lactating ewes. The experiment, which lasted 14 weeks, was conducted during the spring and summer of 2007 and used 80 multiparous Comisana ewes in mid-lactation, reared in permanent stabling. A 2×2 factorial design was used, with ewes receiving two levels of CP (low 15.5% CP and high 17.5% CP) and two type of N sources with different rumen degradable protein (low and high) for each dietary treatment: (1) high-degradable protein diet (17.5% CP) composed by soybean meal, sunflower meal and urea (HPHD), (2) low-degradable protein diet (17.5% CP) included only corn gluten meal (HPLD), (3) high-degradable protein diet (15.5% CP) composed by soybean meal, sunflower meal and urea (LPHD), and (4) low-degradable protein diet (15.5% CP) included only corn gluten meal (LPLD). In order to evaluate in vivo digestibility of PTMRs, four adult rams were placed in metabolic cages and their individual faeces and urine were collected. In the performance trial, ewe milk yield was recorded daily and Individual milk samples were analysed weekly for milk composition and to determine milk renneting parameters. The 17.5% CP diets led to better nutrient apparent digestibility coefficients and had positive effects on milk production than the 15.5% CP diets. Similar results were obtained for corn gluten meal diets, compared to diets containing soybean meal, sunflower meal and urea. Data showed that corn gluten meal diets have had a positive effects on milk fat (P <0.05), but not on milk protein, lactose and renneting parameters. All ewes gained weight during the experimental period, but the body weight change was not significant among treatments. Our findings indicate that an increase in rumen undegradable protein (RUP) content does not negatively affect nutrient digestibility of sheep rations and milk yield and composition. [Copyright &y& Elsevier]

The article focuses on a study which examined the effect of undegradable dietary protein and plane of nutrition on the performance of growing crossbred heifers. A total of sixteen cossbred heifers were selected for the study and divided into 4 groups. It was noted that the total dry matter intake, roughage DM intake, DM intake per body weight and DM intake per metabolic body size did not differ among the different groups.

Abstract: Effects of cutting frequencies on herbage biomass production and nutritive value of Morus alba and Calliandra calothyrsus were investigated. Forage regrowth was harvested at frequencies of 1, 2, 4 and 6 months which constituted the four treatments. Degradabilities, to establish nutritive values, were measured at 0, 3, 6, 12, 24, 48, 72, 96 and 120h of rumen incubation by a nylon bag technique using three rumen fistulated steers. Crude protein (CP) of M. alba declined linearly (P<0.05) from 234.4 to 169.3g/kg DM as it matured from 1 to 6 months, while in C. calothyrsus CP decreased (P<0.05) at a decreasing rate from 232.7 to 156.0g/kg DM with increasing maturity. Neutral detergent fibre (NDF) and acid detergent lignin increased (P<0.05) with increasing maturity. C. calothysus and M. alba leaf:stem ratio decreased from 3.3 to 0.4 and 2.9 to 0.7, respectively, with increasing maturity. While C. calothyrsus had the highest total herbage biomass yield of 45.9t/(hayr−1) at the 4 months cutting frequency, M. alba had yields of 18.6 and 18.4t/(hayr−1) at 2 and 6 months, respectively. Highest (P<0.05) effective CP degradability of 901.3g/kg CP occurred in M. alba at a cutting frequency of 1 month while in C. calothyrsus the highest (P<0.05) value was 492.8g/kg CP at 2 months. Consequently, in all treatments, rumen degradable CP (RDP) was consistently higher in M. alba (96.5–199.2g/kg CP) than in C. calothyrsus (52.5–105.2g/kg CP) but decreased (P<0.05) with increasing maturity. Digestible undegradable CP (DUP) was affected (P<0.05) by increasing maturity, but was lower in M. alba compared to C. calothyrsus. Although C. calothyrsus was superior to M. alba in annual herbage biomass production and DUP, it had lower RDP than M. alba and the nutritional value of both greatly depends on maturity and leaf:stem ratio. Cutting management options that involve harvesting C. calothyrsus and M. alba at maturities between 2 and 4 months, when leaf:stem ratio is greater than 1.0, is crucial in making a decision when to harvest fodder of high nutritional value. This suggests that smallholder farmers in Uganda can efficiently use M. alba and C. calothyrsus in rations to improve dairy cattle productivity, if harvested at maturities between 2 and 4 months. [Copyright &y& Elsevier]

Two trials were conducted to determine the effects of rumen degradable protein (RDP) level and source on the duodenal essential amino acid (AA) composition of Dohne Merino wethers. The animals had ad libitum access to wheat straw (32 g crude protein (CP)/kg DM; 742 g neutral detergent fibre (NDF)/kg DM) and water. In the first experimental treatments casein provided 0, 40, 80, 120 and 160 g supplemental RDP/d. In experiment two, urea-nitrogen replaced 0, 25, 50, 75 and 100% of the true protein in the isonitrogenous treatments. Expressing essential AA concentration as a percentage of duodenal protein indicated that increasing RDP levels tended to decrease arginine, but significantly increased tryptophan concentrations. Histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, valine and total essential AA concentrations were not affected by dietary RDP level. Increasing the urea-N content of RDP supplements significantly decreased isoleucine, leucine, lysine, phenylalanine, tryptophan, valine and total essential amino acid (TEAA) concentrations. Histidine and threonine proportions also tended to decrease with higher non-protein N levels. When the essential AA profile is expressed in relation to lysine, the concentrations of histidine, leucine, phenylalanine and threonine decreased significantly. Arginine and valine showed a decreasing trend and tryptophan increased significantly as RDP levels were raised. The largest differences appeared between 0 and 40 g RDP supplementation, while the AA patterns for the rest of the treatments remained relatively constant. Substituting urea for true RDP induced a variable response in arginine and isoleucine, but did not affect any of the other AA's. Increasing RDP intakes significantly increased the duodenal flow of every essential AA, except arginine, and showed a strong tendency to increase TEAA flow as well. Replacing true RDP with urea significantly reduced the flow of methionine and tryptophan and also tended to decrease lysine availability in the duodenum. Individual AA and TEAA flow to the duodenum were also numerically decreased by a minimum of 34% as urea-N was increased. It appears that the qualitative duodenal essential AA profile in sheep fed low quality forages is relatively insensitive to RDP level or source. The daily essential AA flow to the duodenum seems to be compromised by urea substitution for true RDP. [ABSTRACT FROM AUTHOR]

The main purpose of this study was to examine sources of variation in free amino acids (FAA) in the rumen and their relative contribution to the total duodenal amino acid supply. Six cannulated lactating dairy cows fed three concentrate mixtures differing in ruminally degradable intake protein (101, 114 and 134 g kg[sup -1] dry matter) at two levels of intake (19.3 vs 9.8 kg dry matter day[sup -1]) were used. The mean sums of the prefeeding concentrations of 15 FAA in ruminal liquid were 589 and 515 μM at a high and low feeding level, respectively. One hour postfeeding the corresponding values were 2212 and 1097 μM. Free amino acid profiles in ruminal liquid were significantly correlated to dietary amino acid (AA) profiles. The contribution to the total duodenal AA supply from the ruminal outflow of FAA was estimated for mean sums of FAA and for Lys, Met, Thr and His. Less than 2% of the total duodenal AA flow was contributed by passage of ruminal FAA. It is concluded that the supply of FAA to the small intestine is insignificant even in high-yielding cows with a high ruminal liquid passage rate. Intraruminal supplementation of mixtures of free Lys, Met and Thr (100, 200, 300 and 400 mmol of each) caused (P < B0.05) a transient increase in the sums of the net concentrations of the 12 other AA in ruminal liquid 1 h after dosage, with values of 205, 546, 641 and 945 μM, respectively. [ABSTRACT FROM AUTHOR]

Simple Summary: Ruminant animals have two specific protein requirements: the protein required by the animal, and the protein required by the microorganisms that exist within the rumen of the animal. These requirements are satisfied by rumen undegradable (RUP) and rumen degradable protein (RDP), respectively. Within the rumen, RDP is hydrolyzed, while RUP is digested and absorbed in the small intestine. As these proteins are digested differently, we studied their impact on the digestion process of low-quality forage. Overall, we found that a RDP supplement, when fed in a self-fed form, may enhance the digestion and use of low-quality forages. This may assist producers in selecting supplementation programs for their operation. The objectives of this study were to evaluate the effect of differences in protein type and delivery method on rumen dynamics and nutrient digestion. Cows were allotted to rumen degradable protein (RDP) or rumen undegradable protein (RUP) and self-fed (SF) salt-limited pressed blocks or hand-fed (HF) loose supplement, resulting in four dietary treatments. There was a delivery effect (p = 0.04) on neutral detergent fiber (NDF) intake, as the SF animals consumed more NDF than HF animals. The RDP-SF animals had greater NDF digestibility (p = 0.04) and water intake (p = 0.03) than the three other treatments. Supplement intake displayed a protein type effect (p = 0.03), as RDP-supplemented animals consumed more supplement on a g·kg body weight (BW)−1 d−1 basis than RUP animals. There was an effect of protein type (p = 0.02) and delivery method (p = 0.03) on fluid flow rate, with RUP and HF cows having greater liquid flow rates. Ruminal pH was lower (p < 0.01) in RDP-HF cows than RDP-SF cows at all hours, except 4-h post-feeding. RDP-SF animals had the greatest (p < 0.01) concentrations of ruminal ammonia. Valerate ruminal concentrations were greater (p = 0.04) in RDP supplemented animals compared to RUP supplemented animals. In conclusion, self-fed supplements containing RDP may enhance the use of low-quality forages and increase ruminal ammonia concentrations. [ABSTRACT FROM AUTHOR]

Two experiments were conducted to evaluate the effects of increasing urea in a corn silage cattle diet and ensiling time (ET) impact on rumen undegradable crude protein (RUP) content of corn silage. In Exp. 1, ten ruminally- and duodenally cannulated heifers (body weight 265 ± 16 kg) were utilized in a 4 × 4 Latin square design and treatments were urea included at 0, 0.5, 1, or 1.5% of dietary dry matter (DM). In Exp. 2, corn silage samples were collected during feedout at 32-d intervals from the time of ensiling (d 0) to 160 d post-ensiling followed by separation in water to forage and grain components. Forage and grain samples were ruminally incubated in two steers to calculate RUP content of corn silage. In Exp. 1, DM intake increased linearly from 5.7 to 6.8 kg/d as urea inclusion increased (P < 0.001). Apparent total tract digestibility of DM and organic matter increased linearly from 55.8% to 60.8%, and 60.1% to 64.9%, respectively (P < 0.001). Total tract digestibility of neutral and acid detergent fiber increased linearly with increasing urea inclusion (P ≤ 0.004). In Exp. 2, the RUP content of the corn grain component decreased from 43.7% of CP at day 0 to 15.8% and 10.0% of CP after 32 and 96 d of ensiling, respectively (quadratic, P < 0.01). The RUP content of the forage averaged 19.3% of CP across ET ranging from 21.5 to 17.8% of CP (P ≥ 0.28). Estimated from the individual components, the RUP content of whole corn silage decreased from 32% to 17.1% of CP after 160 d in storage, a portion of which is digestible. Urea supplementation improved digestibility of corn silage diets and RUP content of corn silage decreased with storage time, primarily driven by changes in the corn grain component. [ABSTRACT FROM AUTHOR]