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Insufficient readily fermentable energy combined with extensive degradation of proteins in alfalfa (Medicago sativa L.) may result in poor forage N utilization by ruminants. Using the inherent genetic variability and differences between harvests, our objective was to compare the effect of contrasting concentrations of nonstructural carbohydrates (NSC) in alfalfa on rumen fermentation and microbial protein synthesis. Individual genotypes of the alfalfa cultivar AC Caribou grown near Québec City, Québec, Canada, were harvested at the vegetative and early flowering stages, dried at 55 degrees C, ground, and analyzed for soluble carbohydrates (fructose + sucrose + glucose + pinitol) and starch. Approximately 20 genotypes having, respectively, the highest and lowest NSC concentrations were pooled to constitute 2 contrasted 1-kg forage samples. Samples of high- (17.9% DM) and low- (7.4% DM) NSC alfalfa were respectively allocated to separate dual-flow fermenters in a completely randomized design with 3 replications. Rumen inoculum was obtained from 4 ruminally fistulated cows in early lactation that were fed a TMR with a 50:50 forage to concentrate ratio. A 10-d incubation period was used, with the first 6 d serving as an adaptation period followed by 4 d of sampling with solid and liquid dilution rates in the fermenters set at approximately 2.0 and 4.3%/h, respectively. High versus low NSC concentration in alfalfa significantly enhanced the apparent digestibility of OM (59.1% for high-NSC alfalfa vs. 54.4% for low-NSC alfalfa) and DM (60.0 vs. 54.3%) and the true digestibility of DM (74.1 vs. 64.7%). Increasing NSC concentration in alfalfa (high vs. low) significantly decreased ruminal pH (6.85 vs. 7.08) and NH(3)-N concentration (26.0 vs. 33.6 mg/dL) and increased total VFA concentration (94.9 vs. 83.0mM). Molar proportions of acetate, isobutyrate, and isovalerate significantly decreased, whereas molar proportions of propionate and butyrate significantly increased with high-NSC alfalfa, resulting in a more glucogenic fermentation. More importantly, microbial N flow (263 vs. 230 mg/d) and bacterial N efficiency (41.1 vs. 29.6% of available N), measured using (15)N as a microbial marker, both significantly increased with the high-NSC alfalfa. These results indicate that increasing the concentration of NSC in alfalfa promotes a glucogenic fermentation and enhances microbial N synthesis in the rumen., (Copyright 2010 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

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Microbial protein synthesis in the rumen would be optimized when dietary carbohydrates and proteins have synchronized rates and extent of degradation. The aim of this study was to evaluate the effect of varying ruminal degradation rate of energy and nitrogen sources on intake, nitrogen balance, microbial protein yield, and kinetics of nutrients in the rumen of growing kids. Eight Boer goats (38.2 ± 3.0 kg) were used. The treatments were arranged in a split-plot Latin square design with grain sources (barley or corn) forming the main plots (squares). Grain processing methods and levels of protein degradability formed the subplots in a 2 2 factorial arrangement for a total of 8 dietary treatments. The grain processing method was rolling for barley and cracking for corn. Levels of protein degradability were obtained by feeding untreated soybean meal (SBM) or heat-treated soybean meal (HSBM). Each experimental period lasted 21 d, consisting of a 10-d adaptation period, a 7-d digestibility determination period, and a 4-d rumen evacuation and sampling period. Kids fed with corn had higher purine derivatives (PD) excretion when coupled with SBM compared with HSBM and the opposite occurred with barley-fed kids (P = 0.01). Unprocessed grain offered with SBM led to higher PD excretion than with HSBM whereas protein degradability had no effect when processed grain was fed (P = 0.03). Results of the current experiment with high-concentrate diets showed that microbial N synthesis could be maximized in goat kids by combining slowly fermented grains (corn or unprocessed grains) with a highly degradable protein supplement (SBM). With barley, a more rapidly fermented grain, a greater microbial N synthesis was observed when supplementing a low-degradable protein (HSBM). [ABSTRACT FROM AUTHOR]

Forages cut in the afternoon (p.m.) generally yield a higher concentration of nonstructural carbohydrates (NSC) than those cut in the morning (a.m.). We aimed to compare the effects of p.m.-cut red clover baleage (p.m.-RC) versus a.m.-cut RC baleage (a.m.-RC) on milk yield, concentrations and yields of milk components, and apparent total-tract digestibility of nutrients in late-lactation Holstein cows. Twelve multiparous and 2 primiparous Holstein cows received a total mixed ration containing, on a dry matter (DM) basis, 65% p.m.-RC or a.m.-RC plus 35% concentrate in a cross-over design with 14 d for diet adaptation and 7 d for data and sample collection. One RC field was split in 2 with the first half cut in the afternoon (1600 h) and the second half in the following morning (0600 h). The p.m.-RC and a.m.-RC contained (% of DM): 12.6 versus 9.43% NSC in samples collected before the beginning of the experiment and 7.49 versus 7.79% NSC in samples collected during the sampling periods (i.e., d 14 to 21). The total mixed rations averaged 18.2 and 17.5% NSC for the p.m.-RC and a.m.-RC, respectively. Feeding p.m.-RC or a.m.-RC did not improve feed intake or milk yield and composition in late-lactation dairy cows. However, milk urea N and plasma urea N were both lowest in cows offered p.m.-RC. With the exception of the apparent total-tract digestibility of DM, which was highest in cows fed p.m.-RC, no other changes in nutrient digestibility were observed. Similarly, no treatment effect was observed for the urinary excretion of N and purine derivatives. Further research is needed to better understand NSC losses during storage and the associated effects on baleage quality and animal performance. [ABSTRACT FROM AUTHOR]

The effect of the length of the daylight period before cutting (0, 2, 4, 8, or 12 hours) on water soluble carbohydrates, starch, and total non-structural carbohydrates (TNC) concentrations was assessed on alfalfa (Medicago sativa cv AC Caribou) grown under controlled conditions. We also determined the impact of the length of the daylight period on rumen fermentation assessed by in vitro gas production. Forage samples (n=4) at each sampling time were dried at 55°C immediately after harvest, ground to pass a 1 mm screen, and incubated for up to 142 h in an anaerobic medium inoculated with rumen fluid. Regular measurements of gas were taken to assess the rate of fermentation using the following gas production model (Y = A {1- e [-b (t-T) -c (√ t - √ T)]}). At the end of the incubation period, samples of the liquid phase were analysed for ammonia-N and volatile fatty acids. Gas production model parameters and measured effluent parameters were analyzed as a completely randomized design with 5 duration of daylight and 4 replicates per treatment. Starch and TNC concentrations in alfalfa increased (mean starch = 4.2, 5.6, 5.6, 4.5 and 10.4% DM; mean TNC = 11.9, 13.7, 14.0, 12.9 and 18.5% DM; P < 0.001) with the length of the daylight period. Rumen fermentation also increased (P < 0.01) with the length of the daylight period before cutting as shown by parameters (half-life; mean = 10.09, 10.61, 10.56, 10.24, 11.32 h and maximum values; mean = 231.5, 236.3, 236.9, 230.7, 248.9 ml) describing cumulated gas production curves. Propionate concentrations in the liquid phase increased linearly (mean = 11.8, 11.6, 12.8, 13.6, 14.6 mmol/L; P = 0.01) with a longer daylight period. Increasing the daylight period up to 12 h before cutting favoured the accumulation of starch and TNC in alfalfa and had a positive effect on rumen fermentation. [ABSTRACT FROM AUTHOR]

Abstract: A study was conducted to determine effects of water soluble carbohydrate (WSC) concentration on ensiling characteristics, chemical composition and in vitro digestibility of forage millet and forage sorghum. Two cultivars (regular and high WSC content) of each forage were harvested at late vegetative stage and ensiled in mini-silos for 0, 2, 4, 8, 16 and 48d. Ensiled forages went through a rapid fermentation as indicated by a sharp decline in pH during the first 2d of ensiling. Between day 0 and 8 post-ensiling, pH was higher (P<0.05) for ensiled millet than ensiled sorghum forages and was lower for high WSC than regular cultivars. Lactic acid concentration was higher (P<0.05) in high WSC than in regular cultivars and was not affected by forage type. Chemical composition of the 45-d silages showed that forage millet silages contain more (P<0.05) neutral (aNDF) and acid detergent fiber than forage sorghum silages. Fiber fractions were not affected by WSC content except for lignin(sa), which was higher (P<0.05) for regular versus high WSC cultivars. Soluble and non-protein N were higher (P<0.05) in forage millet than forage sorghum silages and were higher for high WSC versus normal cultivars. In vitro gas production, degradation rate and volatile fatty acid production were not affected by forage type but were higher (P<0.05) for high WSC versus normal cultivars. In vitro dry matter and aNDF digestibilities were higher for forage sorghum versus forage millet silages, and were higher for high WSC versus normal cultivars. High WSC content improved ensiling characteristics of both forages, but the effect was more pronounced for forage sorghum than for forage millet. Based on chemical composition and in vitro data, we conclude that the feeding value of forage sorghum silage is superior to that of forage millet silage when harvested at the same stage of physiological development. [Copyright &y& Elsevier]

Shifting the cutting of grass from morning to afternoon has been shown to increase the concentration of nonstructural carbohydrates (NSC) in forages. We compared the effects of diets (66:34, forage:concentrate ratio) containing a mix (% of the diet dry matter) of baleages (46.5%) and silages (19.3%) harvested from timothy cut in the afternoon (p.m.-cut TIM diet) or morning (a.m.-cut TIM diet) on omasal flows of NSC and nitrogenous fractions, ruminal and total-tract digestibilities of nutrients, plasma concentration of AA, and milk yield and composition. Eight ruminally cannulated Holstein cows averaging (mean ± standard deviation) 31.4 ± 6.13 kg/d of milk, 136 ± 17.0 d in milk, and 611 ± 66.4 kg of body weight in the beginning of the experiment were used in a crossover design with 21-d periods (14 d for diet adaptation and 7 d for data and sample collection). Intake of total ethanol-soluble carbohydrates (TESC; +150 g/d), starch (+129 g/d), and total NSC (TESC plus starch = +278 g/d) was greater with feeding the p.m.- than the a.m.-cut TIM diet. Likewise, the apparent ruminal digestibilities of TESC (+149 g/d), starch (+167 g/d), and total NSC (+316 g/d) increased in the p.m.-cut TIM diet. Diets, however, had no effect on the omasal flows and apparent ruminal and total-tract digestibilities of dry matter and organic matter. Intake of N increased in cows fed the p.m.- versus the a.m.-cut TIM diet (562 and 528 g/d, respectively) despite no effect of diets on dry matter intake. Diets did not affect the omasal flows of total nonammonia N, total bacterial nonammonia N, nonammonia and nonbacterial N, and individual AA, and the efficiency of microbial protein synthesis in the rumen. Contrarily, supply of rumen-degradable protein increased (+9.2%) in cows fed the p.m.-cut TIM diet, with this response driven by the 6.4% increase in N intake. Plasma concentrations of essential and nonessential AA followed the omasal flow of AA and were not changed by diets. Feeding the p.m.- versus the a.m.-cut diet significantly increased yields of 4% fat-corrected milk and milk fat, and tended to increase energy-corrected milk, milk true protein, and milk lactose yields. Overall, feeding the p.m.-cut TIM diet to mid-lactation dairy cows did not improve microbial protein synthesis and omasal flow of AA, and these responses were in line with the lack of a treatment effect on dry matter intake. [ABSTRACT FROM AUTHOR]

Carbohydrates in forage crops can be divided into neutral detergent-insoluble fiber and neutral detergent- soluble carbohydrates (NDSC); the latter includes organic acids (OA), total ethanol:water-soluble carbohydrates (TESC), starch, and neutral detergent-soluble fiber (NDSF). The accurate and efficient estimation of NDSC in forage crops is essential for improving the performance of dairy cattle. In the present study, visible and near-infrared reflectance spectroscopy (NIRS) were applied to evaluate the feasibility of predicting OA, TESC, starch, NDSF, NDSC, and all related constituents used to calculate these 5 carbohydrate fractions in timothy and alfalfa. Forage samples (n = 1,008) of timothy and alfalfa were taken at the first and second harvests at 2 sites in 2007; samples were dried, ground, and then scanned (400 to 2,500 nm) using an NIRSystems 6500 monochromator. A calibration (n = 60) and a validation (n = 15) set of samples were selected for each species and then chemically analyzed. Concentrations of TESC and NDSC in timothy, as well as starch in alfalfa, were successfully predicted, but many other carbohydrate fractions were not predicted accurately when calibrations were performed using single-species sample sets. Both sets of samples were combined to form new calibration (n = 120) and validation (n = 30) sets of alfalfa and timothy samples. Calibration and validation statistics for the combined sets of alfalfa and timothy samples indicated that TESC, starch, and NDSC were predicted successfully, with coefficients of determination of prediction (Rp²) of 0.92, 0.89, and 0.93, and a ratio of prediction to deviation (RPD) of 3.3, 3.1, and 3.6, respectively. The NDSF prediction was classified as moderately successful (R² = 0.88, RPD = 2.8). The NIRS prediction of was unsuccessful (R². = 0.38, RPD = 1.3). All related constituents were predicted successfully (Rp² > 0.90, RPD > 3.0) by NIRS except ethanol-insoluble residual OM, with Rp², = 0.75 and RPD = 1.9. Our results confirm the feasibility of using NIRS to predict NDSC, its fractions, and other related constituents, except for OA and ethanol-insoluble residual OM, in timothy and alfalfa forage samples. [ABSTRACT FROM AUTHOR]

Alfalfa (Medicago sativa L.) cut at sundown (p.m.) has been shown to have a greater concentration of total nonstructural carbohydrates (TNC) than when cut at sunup (a.m.). Eight ruminally cannulated Holstein cows that were part of a larger lactation trial were used in a crossover design (24-d periods) to investigate the effects of alfalfa cutting time on digestibility and omasal flow of nutrients. Alfalfa was cut at sundown or sunup, field-wilted, and harvested as baleage (530 ± 15.0 g of dry matter/kg of fresh matter). The difference in TNC concentration between p.m. and a.m. alfalfa within each pair of bales fed daily during the 10 d of data and sample collection varied from -10 to 50 g/ kg of dry matter. Each pair of bales was fed for ad libitum intake to cows once daily with no concentrate. During the 3 d of omasal sampling, intake (+0.8 kg/d) and omasal flow of organic matter (OM; +0.42 kg/d) tended to be greater when cows were fed p.m. vs. a.m. alfalfa, but no differences were found for ruminal and postruminal digestion of this nutrient. Similarly, N apparently digested ruminally and postruminally did not differ when feeding p.m. vs. a.m. alfalfa. However, N truly digested in the rumen, as a proportion of N intake, was significantly greater in cows fed p.m. (79%) vs. a.m. alfalfa (74%), thus suggesting that longer wilting time of alfalfa cut at sundown increased forage proteolysis. Supply of rumen-degradable protein did not change (2,716 g/d) when averaged across treatments, whereas omasal flow of non-NH3 nonbacterial N was significantly decreased (-29 g/d) when feeding p.m. vs. a.m. alfalfa. Omasal flow of total bacterial non-NH3 N (NAN) increased (+21 g/d) significantly when cows were fed p.m. vs. a.m. alfalfa possibly because bacteria from cows fed p.m. alfalfa captured significantly more NH3 than those from cows fed a.m. alfalfa. Therefore, greater availability of fermentable energy as TNC appears to increase the capacity of microbes to uptake NH3-N and convert it to microbial protein. Enhanced OM intake can also explain the observed increase in bacterial protein synthesis with p.m. alfalfa. Efficiency of bacterial protein synthesis, expressed on a fermented OM basis or as grams of bacterial NAN per gram of rumen-degradable N, did not differ between p.m. and a.m. alfalfa. Conversely, bacterial efficiency, as grams of bacterial NAN per gram of N intake, was significantly increased when cows were fed p.m. baleage. No significant difference between forage treatments was found for the omasal flow of total AA from omasal true digesta, suggesting no benefit of daytime cutting management on the passage of total AA to the lower gastro-intestinal tract. Enhancing energy intake and TNC concentration of alfalfa by shifting forage cutting from sunup to sundown increased protein synthesis and NH3 uptake by ruminal bacteria indicating an improvement in N utilization. [ABSTRACT FROM AUTHOR]