Search

Objective The objective was to compare the effects of 4 implant management strategies involving long-duration implants on growth performance and dietary NE use of calf-fed Holstein steers. Materials and Methods A total of 192 calves were used in a 335-d experiment. Treatments were as follows: S1S1 = Synovex ONE (200 mg of trenbolone acetate and 28 mg of estradiol benzoate; Zoetis Animal Health, New York, NY) on arrival and Synovex ONE on d 168; S1SP = Synovex ONE on arrival and Synovex Plus (200 mg of trenbolone acetate and 28 mg of estradiol benzoate; Zoetis Animal Health) on d 224; SCE = Synovex C (100 mg of progesterone and 28 mg of estradiol benzoate; Zoetis Animal Health) on arrival and Encore (43.9 mg of estradiol; Elanco Animal Health, Greenfield, IN) on d 112; and SCS1 = Synovex C on arrival and Synovex ONE on d 112. Results and Discussion Steers implanted with Synovex ONE on arrival had greater (P Implications and Applications Implant strategies that incorporate long-acting implants to avoid terminal implantation when animals have greater days on feed did not improve calf-fed Holstein steer growth performance. Indeed, using a noncoated hormonal implant during the late finishing phase (implantation at 224 d on feed) increased overall peNEg, representing greater efficiency on cattle growth performance.

Objectives The objective of this research was to evaluate the influence of rumen-protected methionine and lysine on growth performance of calf-fed Holstein steers during the initial 84-d feedlot phase and relate responses to measures of AA supply to the small intestine. Material and Methods Seventy-two Holstein steer calves (128 ± 9 kg) were blocked by weight and assigned to 12 pens (6 steers per pen). Steers were fed a diet based on steam-flaked corn formulated to provide 105% of theoretical MP requirements plus 0, 0.4, and 0.8% Smartamine ML (Adisseo, Alpharetta, GA; 55% l -lysine-HCl and 15% dl -methionine coated with a pH-sensitive polymer). Six Holstein steers (143 ± 13 kg) with cannulas in rumen and proximal duodenum were used in a crossover design to evaluate characteristics of digestion and AA supply to the intestine of the basal diet plus 0 versus 0.8% Smartamine ML. Results and Discussion Methionine and lysine supplementation did not affect DMI (P = 0.27) but enhanced ADG, gain efficiency (linear effect, P = 0.03), and estimated dietary NE (linear effect, P = 0.04). Amino acid supplementation increased (P Implications and Applications Supplementation with rumen-protected methionine and lysine may enhance gain efficiency and dietary energetics of growing Holstein calves during the early growing phase. The magnitude of the response is likely dependent on the otherwise general adequacy of nonspecific MP.

The substitution of sorghum stover with sugarcane top silage [0 (T1), 5 (T2) and 10% (T3) DM] in high concentrate diets for feedlot hair lambs was evaluated in two experiments. In experiment one, ruminal dry matter degradability (RDMD) was evaluated in three ruminally cannulated 6-month-old Pelibuey sheep in a 3 × 3 Latin square design. The RDMD was determined by the nylon bag technique at incubation times of 4, 8, 12, 24, 48 and 72 h. There was no effect of diet (P > 0.05) for the rapidly degraded (a) or degradable fraction (b) of dry matter. The maximum degradability (a + b) was greater for T3 than T1 (P 0.05). Effective degradability at 6% h−1 of ruminal turnover (k) was lower for T2 (P 0.05) for T1 than for T3. Growth performance of feedlot hair lambs was evaluated in a second experiment using the same diets as in experiment one. Twenty-seven 5-month-old intact crossbred male hair lambs (19.04 ± 1.56 kg) were assigned at random to 9 pens (3 lambs per pen). The feeding trial lasted for 63 days. Feed intake decreased (P 0.05) on feed efficiency (gain/feed intake). It is concluded that ensiled sugarcane tops is a practical alternative to substitute for sorghum stover in diets for growing finishing feedlot lambs. Partial replacement of sorghum stover with ensiled sugar tops does not negatively affect daily weight gain.

Plascencia, A., Alvarez, E.G., Montanto, M., Salinas-Chavira, J. and Zinn, R.A. 2009. Effects of dietary calcium levels on growth-performance and digestive function in cattle fed a high-fat finishing diet. J. Appl. Anim. Res., 36: 179–184. A growth performance and digestion trial was conducted to evaluate the influence of dietary calcium level on the feeding value of a high-fat (11%) finishing diet. Treatments consisted of three levels of dietary Ca: 0.50, 0.70 and 0.90% (DM basis). Ca source was limestone and yellow grease was included as supplemental fat. There were no treatment effects (P>0.20) on DMI. Increasing dietary Ca level enhanced ADG (P 0.10) on total tract digestion of OM, ...

One hundred twelve Holstein steers (115 ± 5 kg) were used in a 167-d performance trial. Two forage sources [rice straw vs sudangrass (SG) hay] and two levels of fibrolytic enzyme supplementation (0 vs 0.17% Yeasture®, Cenzone Tech, Inc., San Marcos, CA) were evaluated in a 2 x 2 factorial arrangement. Experimental diets (steam-flaked, corn-based) contained 15% (DM basis) forage. Forages were ground to pass through a 2.5-cm screen prior to incorporation into completely mixed diets. Fibrolytic enzyme supplementation did not affect (P> 0.20) cattle performance. Forage source did not affect (P>0.20) ADG; however, DMI tended (P=0.14) to be slightly (2%) greater for the diets containing rice straw. Dietary NEm and NEg were greater (3 and 5%, respectively; P

Two trials were conducted to evaluate four common methods of corn processing for cattle simultaneously. Experimental diets contained 75.3% corn grain. Corn processing treatments were 1) steam-flaked corn ( SFC ; density = 0.31 kg/L), 2)dry-rolled corn ( DRC ; density = 0.58 kg/L), 3) ground corn ( GC ), and 4) whole corn ( WC ). Treatment effects on feedlot performance were evaluated in a 112-d finishing trial involving 120 crossbred yearling steers (311 kg). Cattle fed WC had less (7%; P m and NEg were similar (P=0.46) for dry corn treatments, but increased (11.5 and 14.7%, respectively; P FS ; %) and apparent total tract starch digestion: Total tract starch digestion (%) = 102.4 − 0.72FS (n = 16; r 2 = − 0.97; P

Two trials were conducted to evaluate the addition of a forage-fat blend (FFB) as a substitute for grain in finishing diets for feedlot cattle. Treatments consisted of a steam-flaked wheat-based finishing diet containing 15, 29, or 45% FFB. The FFB contained 80% chopped alfalfa hay and 20% yellow grease and was formulated to have NEm and NEg values similar to that of wheat. In Trial 1, 126 crossbred steers (225 ± 5.4 kg) were used to evaluate treatment effects on growth performance and dietary NE. In Trial 2, three Holstein steers (448 ± 21 kg) with cannulas in the rumen and proximal duodenum were used to evaluate treatment effects on characteristics of digestion. Increasing the FFB did not affect (P>0.10) ADG, but decreased gain efficiency (linear effect, P 0.10) ruminal digestion of starch, N, or microbial N (MN) efficiency, but decreased (linear effect, P 0.10) postruminal digestion of OM, starch, and N, but decreased postruminal digestion of fatty acids (linear effect, P 0.10) percentage of total tract starch, N, and ADF digestion, but decreased the percentage of total tract digestion of OM (linear effect, P 15%, dietary NE and, hence, BW gain efficiency may decrease. The magnitude of the effect of FFB inclusion rate on energy recovery is a predictable function of the relationship between fatty acid intake and intestinal fatty acid digestion.

Two levels of supplemental vitamin A (VA; 2,200 and 11,000 IU/kg as retinyl palmitate) were compared across three supplemental vitamin E (VE) treatments (none, 100 mg/kg all rac α-tocopheryl acetate [TA-100], and 100 mg/kg RRR α-tocopherol [TO-100]). Trial 1 involved 90 crossbred calves (199 kg). There were no interactions (P>0.10) between VA and VE on health and performance. Increasing VA depressed gain (20%, P 0.10) by VA. There were no effects (P>0.10) of VE on health and performance. Trial 2 involved 108 Holstein steers. There was an interaction (P

Ninety medium-framed crossbred steers (245 kg) were used in a 205-d feeding trial to evaluate the influence of 4, 8, and 12% supplemental fat (tallow soap stock) on feedlot growth performance. Increasing level of fat supplementation depressed ADG ( P P P P m was 1.00 with 4% supplemental fat and declined ( P m of tallow soap stock declined in a near rectilinear fashion from 5.65 Mcal/kg at the 4% level of supplementation to 2.85 Mcal/kg at the 12% level of supplementation. Six Holstein steers (296 kg) with T cannulas in the rumen and proximal duodenum were used to evaluate treatment effects on digestive function. Ruminal digestion of OM ( P P P .10) postruminal digestion of OM, ADF, starch, and N. Postruminal digestion of lipid decreased ( P P

Four Holstein steers (382 kg) with cannulas in the rumen and proximal duodenum were used in a 4 × 4 Latin square experiment. Treatments consisted of 90% concentrate (steam-flaked cornbased) diet supplemented with either 5.5% soybean meal (SBM) or .8, 1.2, or 1.6% urea (dry matter basis). All diets contained 4% tallow. There were no treatment effects (P>.10) on ruminal pH and ammonia concentrations. Ruminal digestion of organic matter, acid detergent fiber, and starch tended to increase with supplemental urea level. There was a quadratic component (P .10) across treatments. Nonammonia nitrogen entering the small intestine/nitrogen intake decreased linearly (P .10) on daily weight gain, dry matter intake, and diet net energy. Observed:expected net energy increased (P

J. Anim. Sci. Vol. 88, E-Suppl. 2/J. Dairy Sci. Vol. 93, E-Suppl. 1/Poult. Sci. Vol. 89, E-Suppl. 1 49 Practical relationships between morbidity and growth performance. V. R. Bremer1, G. E. Erickson*1, T. J. Klopfenstein1, D. R. Smith1, K. J. Hanford1, R. E. Peterson2, L. O. Burciaga-Robles2, D. B. Faulkner3, and C. R. Krehbiel4, 1University of Nebraska, Lincoln, 2Feedlot Health Management Services, Okotoks, Alberta, Canada, 3University of Illinois, Urbana, 4Oklahoma State University, Stillwater.

Two isonitrogenous diets (12.5% CP) containing 20 (20% NPN) or 40% (40% NPN) of the N as nonprotein N were evaluated with 0 or 10 mg laidlomycin propionate (LP)/kg in a 2 x 2 factorial arrangement. Changes in dietary NPN:N ratio were developed by partial substitution of urea N for fish meal N. In Trial 1, four Holstein steers (349 kg) with cannulas in the rumen and proximal duodenum were used to evaluate treatment effects on digestive function. Total tract OM digestion was slightly greater (1.2%, P.10) for diets containing 20% of N as NPN, due to greater (3.4%, P.05) postruminal OM digestion. Supplemental LP decreased passage of microbial N to the small intestine (7.4%, P.10) and ruminal degradation of dietary CP (DIP, 8.1%, P.10). Decreasing the NPN:N ratio decreased microbial N flow to the small intestine (7.5%, P.10) and DIP (15%, P.01) and increased (6%; P.05) the flow of indispensable amino acids to the small intestine. Supplemental LP increased (P.10) ruminal pH. There were no treatment effects (P.10) on ruminal molar proportions of acetate or propionate. In Trial 2, 120 Holstein steers (122 kg) were used to evaluate treatment effects on growth performance. Decreasing the NPN:N ratio increased ADG (P.01) by 36, 40, and 16%, respectively, for the initial three 56-d periods of the trial. Overall, ADG was 17% greater (P.01) for cattle consuming diets containing 20 vs 40% NPN. Decreasing the NPN:N ratio increased (P.01) gain efficiency by 17 and 14%, respectively, for the initial two 56-d periods. Overall, gain efficiency was 6% greater (P.01) for diets containing 20% NPN. Dietary NPN:N ratio did not influence (P.10) the NE value of diets. Supplemental LP did not affect DMI (P.10) but increased ADG (6%, P.01) and gain efficiency (5%, P.05) and decreased (11%, P.05) the maintenance energy requirements. Protein nutrition limited growth performance of calves receiving the 20% NPN diets during the initial 112 d of the trial. With the 40% NPN diets, protein nutrition limited growth performance throughout most of the trial (d 1 to d 224). We conclude that LP will enhance daily weight gain and gain efficiency of calf-fed Holstein steers. Conventional urea-based diets will not diminish response to LP, although they may not meet the metabolizable amino acid requirements of calf-fed Holsteins during the first three-quarters of the feeding period.

Four Holstein steers (212 kg) with cannulas in the rumen and proximal duodenum were used in a 4 x 4 Latin square experiment to study the influence of degree of ruminal biohydrogenation (BH) on the feeding value of supplemental fat. Treatments consisted of an 88% concentrate finishing diet supplemented with 1) 2% yellow grease (control); 2) 4% formaldehyde-protected fat (Rumentek), 2% yellow grease (LBH); 3) 2% Rumentek, 4% yellow grease (MBH); or 4) 6% yellow grease (HBH). Ruminal BH of HBH, MBH, and LBH diets was 74, 68, and 54%, respectively. High-fat supplementation decreased (7%, P.05) intestinal digestibility of 18:0 but increased intestinal digestibility of 18:1 (3%, P.10), 18:2 (14%, P.01), and 18:3 (23%, P.05). Increases in intestinal digestibility of 18:0 (quadratic effect, P.05), 18:1 (linear effect, P.01), 18:2 (linear effect, P.01), 18:3 (linear effect, P.05), and total fatty acids (linear effect, P.05) were inversely related to BH. For every 1% increase in the proportion of 18:1 fat entering the small intestine, the digestibility of 18:0 increased 1%. High-fat supplementation depressed ruminal digestion of OM (11%, P.05), NDF (16%, P.05), starch (6%, P.05), and feed N (12%, P.01). Formaldehyde-protein protection of fat diminished its depressing effects on ruminal digestion of NDF (quadratic effect, P.10) and enhanced ruminal escape of feed N (linear effect, P.10). Postruminal digestion of OM was greater (4.6%, P.10) for high-fat diets. High-fat diets decreased (P.05) total tract digestion of OM (1.9%), NDF (7.4%), and starch (.5%). Postruminal and total tract digestibility of OM, NDF, N, and starch was not affected (P.10) by BH. In a 125-d finishing trial, 100 yearling steers (362 kg) were used to evaluate treatment effects on growth performance. High-fat diets did not affect (P.10) ADG but increased (P.10) feed efficiency (9%, P.10), dietary NEm (7.6%, P.05), and dressing percentage (9%, P.05). The magnitude of the increase in dressing percentage was inversely related (linear effect, P.10) to BH. We conclude that decreasing ruminal BH will increase postruminal digestibility of fat, and hence the NE value of dietary fat. The synergistic effect of increasing the proportion of 18:1 on intestinal digestion of fat enables higher levels of fat supplementation. Protecting fat from BH minimizes the detrimental effects of supplemental fat on fiber digestion.

Crossbred yearling steers (n = 125; 372 kg) were used in a 109-d finishing trial. Steers were fed an 88% concentrate diet containing 65% corn (DM basis) as 1) dry rolled corn (DRC); 2) tempered rolled corn (TRC), 43 mg surfactant (SarTemp)/kg corn; 3) TRC, 172 mg surfactant/kg corn; 4) TRC, 430 mg surfactant/kg corn; and 5) steam-flaked corn (SFC). Corn moisture was greater (3.5%, P.01) for TRC than for DRC but less (10%, P.05) than for SFC. Starch enzymatic reactivity was less for TRC than for either DRC (18%, P.05) or SFC (42%, P.01). Tempering increased the integrity of rolled corn and reduced the amount of particles less than 2 mm in diameter by 54% (P.01). Steam flaking corn increased (P.01) proportion (78%) of the grain having a particle size distribution of greater than 8 mm, as compared with TRC (25%) and DRC (3%). Compared with DRC, tempering enhanced (P.10) ADG (9%), feed efficiency (5%), and dietary NE (3%). Daily weight gain was similar (P.10) for TRC and SFC. Feed efficiency (P.10) and dietary NE (P.01) were greater (6%) for SFC than for TRC. There were no differences (P.10) between DRC and TRC in ruminal and total tract digestion of OM, N, and starch, and in ruminal microbial efficiency. Ruminal digestion of OM decreased (linear effect, P.05) and ruminal microbial efficiency increased (linear effect, P.05) with increasing surfactant concentration. Ruminal digestion of OM and starch, and flow of nonammonia N to the small intestine were greater (31, 56, and 14%, respectively, P.01) for SFC than for TRC. Postruminal and total tract digestion of OM, N, and starch, and dietary DE were greater (P.01) for SFC than for TRC. We concluded that tempering corn will enhance animal performance. Increasing the concentration of surfactant used in tempering may enhance ruminal microbial efficiency and lean tissue growth.

We used 216 Holstein steers (151 kg) in a 262-d trial to evaluate the influence of dietary magnesium level (.19, .25, and .32%) and laidlomycin propionate (LP; 0 vs 11 ppm, air-dry basis) on growth performance and NE value of the diet. During the initial 112 d of the trial, LP increased (P.01) ADG (6.3%) and feed efficiency (4.2%). From d 112 until slaughter, LP increased (P.05) ADG (9.7%) and feed efficiency (4.5%). Across the 262-d feeding period, LP supplementation enhanced (P.01) ADG (8.9%) and feed efficiency (6.3%). There was an interaction (P.05) between dietary Mg and LP on NE value of the diet. The enhancement in NE value of the diets owing to LP with .19, .25, and .32% dietary Mg were .5, 3.0, and 5.9%, respectively. Six Holstein steers (302 kg) were used in a 6 x 6 Latin square experiment to evaluate treatment effects on characteristics of ruminal and total tract digestion. There were no treatment interactions (P.10) on site and extent of digestion of OM, starch, and N. Supplemental Mg increased (quadratic effect, P.10) ruminal OM digestion. Neither LP nor dietary Mg level affected (P.10) ruminal digestion of starch and feed N. Supplemental LP decreased (15%, P.05) ruminal microbial efficiency. Total tract digestion of OM and N increased (linear effect, P.01) with increasing dietary Mg level. There were interactions between LP and dietary Mg level on ruminal soluble-Mg concentration (linear effect, P.01) and Mg absorption (quadratic effect, P.05). Apparent total tract Mg digestion increased owing to LP (P.01) and dietary Mg level (linear effect, P.01). There were no treatment effects (P.10) on ruminal pH. Dietary Mg level did not influence (P.10) ruminal VFA concentrations or molar proportions. Supplemental LP increased (14%; P.10) total ruminal VFA concentration but did not affect (P.10) VFA molar proportions. We conclude that LP will increase daily weight gain and feed efficiency of calf-fed Holstein steers and that this response may be enhanced by increasing dietary Mg level.

We used 80 medium-framed yearling crossbred heifers (357 kg) in a 110-d trial to evaluate the influence of dietary protein level (11 vs 14%) on the feeding value of dry-rolled (DRC) and steam-flaked corn (SFC). All diets contained 1% urea; cottonseed meal (CSM) was the source of supplemental undegradable intake protein (UIP). Steam flaking corn reduced DMI (9%, P.10) and increased (P.01) feed efficiency (14%), dietary NEm (13%), and NEg (15%). Steam flaking increased the NEm by 17% and NEg by 19%. Supplemental CSM decreased (P.10) feed efficiency (7%) and dietary NEm (4%) and NEg (6%). There were no treatment effects (P.10) on carcass characteristics. Steam flaking corn increased (P.05) fecal pH and reduced (P.01) fecal starch. Supplemental CSM increased (P.01) fecal pH and reduced (P.01) fecal starch. Four Holstein steers (413 kg) were used in a 4 x 4 Latin square experiment to evaluate treatment effects on digestive function. Steam flaking corn increased (P.05) flow of nonammonia N (11%, P.05) and microbial N (15%, P.01) to the duodenum. Supplemental CSM increased the flow of microbial N (6%, P.01), feed N (21%, P.10), and nonammonia N (12%, P.05) to the duodenum. The UIP value of CSM was 28% for the DRC diet and 52% for the SFC diet. Steam flaking corn increased (P.01) ruminal starch digestion (26%) and total tract digestibility of OM (17%), N (15%), starch (19%), and GE (17%). Steam flaking increased the DE value of corn by 21%. Supplemental CSM did not influence (P.10) postruminal or total tract starch digestion. Supplemental CSM decreased (7%, P.10) the DE value of the diet. We conclude that increasing the postruminal protein supply of a corn-based finishing diet beyond that provided by urea supplementation, alone, will not enhance starch digestion or the energy value of the diet.

One hundred twenty crossbred steers (294 kg, initially) were used in a 141-d finishing trial. Four concentrations (8, 16, 24, and 32% of diet DM) of cottonseed meal (CSM, prepressed solvent-extracted) replaced steam-flaked corn in a corn-based finishing diet. Increasing level of CSM decreased ADG (linear component, P.10), feed efficiency (linear component, P.01), and dietary NE (linear component, P.01). Observed dietary NE was 99% of expected at 8 and 16% CSM but 95% of expected at higher levels of inclusion (linear component, P.05). Level of CSM did not influence (P.10) dressing percentage, longissimus area, fat thickness, or retail yield. Eight Holstein steers (285 kg) were used in a replicated 4 x 4 Latin square design to evaluate treatment effects on characteristics of digestion. Ruminal digestibility of OM decreased (linear component, P.05) as CSM increased, although ruminal digestibility of starch and feed N were not affected (P.10). Ruminal escape protein from CSM was 58%. Total tract starch digestion was not altered (P.10), but total tract digestibility of OM and GE decreased (linear component, P.05) and digestion of N increased (linear component, P.01) as CSM replaced steam-flaked corn. The ratio of observed to expected DE value of the diets was similar across CSM levels, averaging .99. Thus, comparative DE value of CSM was not affected by level of inclusion, averaging 3.32 Mcal/kg. We conclude that the NEm and NEg values of CSM are 1.88 and 1.24 Mcal/kg, respectively, and in close agreement with tabular values. However, CSM should not exceed 16% of DMI, because higher levels may depress cattle performance and replacement value of CSM.

A feeding trial involving 160 crossbred steers (357 kg) and a metabolism trial involving eight Holstein steers (189 kg) cannulated in the rumen and proximal duodenum were conducted to evaluate the interaction of dietary Mg level (.18 vs .32%, DM basis) and supplemental fat (0% supplemental fat vs 4% tallow [T], yellow grease [YG], or griddle grease [GG]) on growth performance and NE value of the diet. Dietary Mg level did not influence (P.10) growth performance. Daily weight gain was lower (11%, P.05) for steers fed GG than for those fed YG. Supplemental fat decreased (5%, P.10) DMI and increased (P.05) gain efficiency (7%). There was a fat x Mg level interaction (P.01) for dietary NE. The increase in dietary NEg with T and YG supplementation was similar (8.6 vs 8.0%) for diets containing .18 and .32% Mg. In contrast, the increase in dietary NEg with GG supplementation was 8.9% with .18% dietary Mg, but the NEg value of the diet did not increase when GG was added to diets with .32% dietary Mg. Dressing percentage was lower (1.5%, P.1) and retail yield was greater (2.2%, P.05) for steers fed GG- than for steers fed YG-supplemented diets. Increasing dietary Mg level increased kidney, pelvic, and heart fat (5.5%, P.05). There was a fat x Mg level interaction (P.1) for marbling score. With diets containing no supplemental fat, increasing dietary Mg decreased (15.2%) the marbling score, and with diets containing supplemental fat, increasing dietary Mg increased (7.2%) the marbling score. Fat supplementation decreased (P.01) ruminal and total tract digestion of OM (10 and 3.5%, respectively) and NDF (37 and 17%, respectively). Supplemental fat did not affect (P.10) Ca digestion but decreased (41.7%, P.01) apparent Mg digestion. Increasing dietary Mg level increased (77.7%, P.05) apparent Mg digestion. There were no treatment effects (P.10) on postruminal fatty acid digestion. Fat supplementation decreased (17.3%, P.01) the acetate:propionate molar ratio. Total ruminal protozoal counts were increased (12.7%, P.05) by increasing dietary Mg level and decreased (12.9%, P.05) by fat supplementation. We conclude that supplemental fats may depress Mg absorption. Increasing dietary magnesium levels beyond current recommendations may increase marbling scores in cattle fed fat-supplemented diets but may not affect growth performance or dietary NE. The NE value of fat is a predictable function of level of fat intake.

Two trials were conducted to evaluate the influence of malic acid supplementation on ruminal fermentation. In Trial 1, six Holstein steers (300 kg) with ruminal cannulas were used in a crossover design experiment to study the influence of malic acid (MA) on ruminal metabolism during glucose-induced lactic acidosis. Treatments consisted of a 77% steam-flaked barley-based finishing diet supplemented to provide 0 or 80 g/d of MA. After a 13-d dietary adjustment period, 1 kg of glucose was infused into the rumen 1 h after the morning feeding. Ruminal pH was closely associated (R2 = .70) with ruminal DL-lactate concentration. Malic acid supplementation increased (P.01) ruminal pH 3 h after the glucose infusion. However, there were no treatment effects (P.10) on ruminal VFA molar proportions or ruminal and plasma DL-lactate concentrations. In Trial 2, four Holstein steers (150 kg) with cannulas in the rumen and proximal duodenum were used in a crossover design experiment to evaluate the influence of MA supplementation on characteristics of digestion. Treatments consisted of an 81% steam-flaked barley-based finishing diet supplemented to provide 0 or 80 g/d of MA. There were no treatment effects (P.10) on ruminal and total tract digestion of OM, ADF, starch, and feed N or on ruminal microbial efficiency. Malic acid supplementation increased (P.05) ruminal pH 2 h after feeding. As with Trial 1, there were no treatment effects (P.10) on ruminal VFA and DL-lactate concentrations. We conclude that supplementation of high-grain finishing diets with MA may be beneficial in promoting a higher ruminal pH during periods of peak acid production without detrimental effects on ruminal microbial efficiency or starch, fiber, and protein digestion. There were no detectable beneficial effects of MA supplementation on ruminal and plasma lactic acid concentrations in cattle fed high-grain diets.

Ruminally degradable intake protein (DIP) and metabolizable indispensable amino acid (MIAA) requirements of feedlot steers were evaluated. Dietary treatments consisted of isocaloric 80% concentrate steam-flaked corn-based diets containing either .8% urea, 1.5% fish meal (FM), 3.0% FM, 4.5% FM, or 4.5% soybean meal (SBM). Treatment effects on characteristics of ruminal and total tract digestion were evaluated using four Holstein steers (249 kg) with cannulas in the rumen and proximal duodenum. Ruminal digestibility of OM (RDOM; P.05) and feed N (P.01) and microbial N flow (MNF; P.01) to the small intestine were greater with urea as the supplemental N source. The level of DIP was closely associated (R2 = .89) with MNF. Postruminal digestibility of OM was greater (P.05) for FM than for urea-supplemented diets, compensating for lower RDOM. There were no treatment effects (P.10) on DOM. As the level of FM was increased, MIAA increased linearly (P.01). Intestinal MIAA were similar (P.10) for urea- and SBM-supplemented diets. Treatment effects on 56-d growth performance were evaluated using 100 medium-framed crossbred steers (231 kg). Daily weight gain (linear effect; P.01), DM intake (linear effect; P.10), feed efficiency (linear effect; P.05), and diet NE (linear effect; P.05) increased with level of FM supplementation. Daily weight gain (P.10) and DM intake (P.05) were greater for urea- than for SBM-supplemented diets. Using bovine tissue as the reference protein, the biological value (based on chemical score) of the intestinal chyme protein averaged 73%; methionine was first-limiting. There was a close association (R2 = .99) between methionine supply to the small intestine and observed/expected dietary NE. The metabolizable methionine requirement (MMETR, g/d) of medium-framed feedlot steers can be reliably predicted from measures of BW and ADG (MMETR = 1.565 + .0234ADG[268 - (29.4 x .0557BW(.75)ADG(1.097))/ADG] + .0896BW(.75)). There was a very close association (R2 = .89) between DIP and MNF (MNF = 13.7DIP - .66DIP(2) + 25.9). At maximal observed synthesis, DIP accounted for 76% of the MNF. A minimum of 100 g DIP/kg of total tract digestible OM was required to maximize RDOM and MNF.

Using ammonium sulfate, three levels of dietary S (.15, .20, and .25%, DM basis) were evaluated in a finishing trial with 108 yearling crossbred heifers (384 kg). The basal diet contained (DM basis) 4% alfalfa hay, 6% sudangrass hay, 74% steam-flaked corn, 4% yellow grease, 6% cane molasses, and 6% protein-mineral supplement. Increasing dietary S decreased ADG (quadratic effect, P.10), DMI (linear effect, P.10), feed efficiency (quadratic effect, P.10), diet NE (quadratic effect, P.10), and longissimus muscle area (linear effect, P.05). Six Holstein steers (218 kg) with cannulas in the rumen and proximal duodenum were used to evaluate treatment effects on characteristics of digestion. Treatment effects on ruminal and total tract digestion of OM and N were small (P.10). However, ruminal digestion of ADF and starch was slightly lower (quadratic effect, P.10), and postruminal digestion of ADF and starch was correspondingly greater (quadratic effect, P.05) with supplemental S. Dietary S level did not influence (P.10) ruminal synthesis of microbial N. Increasing dietary S did not influence (P.10) ruminal pH or lactic acid. Increasing S decreased molar proportions of acetate (quadratic effect, P.10) and increased molar proportions of propionate (linear effect, P.10). We conclude that S in excess of .20% of dietary DM may have detrimental effects on growth performance and dietary NE. Excessive dietary S may also compromise carcass merit by decreasing longissimus muscle area.

Published regression equations relating digestibility of starch to fecal starch concentration have slopes that differ by over 5-fold. Hence, nutritionists have questioned their legitimacy. Total-tract starch digestibility and concentration of starch in feces are interlocked mathematically by 2 factors—starch content of the diet and digestibility of diet DM. Digestibility data compiled from the published literature including 201 diets fed to lactating dairy cows and 191 diets fed to feedlot cattle were employed to re-examine the relationships of digestibility to fecal concentrations of starch and NDF. Regression analyses and plots clearly illustrated imprecision of this relationship when diet starch content and digestibility of diet DM were ignored. Furthermore, because fecal starch and diet digestibility are related inversely, mathematics implies that starch digestibility is related curvilinearly to fecal starch concentration. Effects of site of starch digestion on extent of digestion and energetic efficiency also were examined. Direct digestibility measurements for nutrients and energy can preclude errors involved with in vitro availability assays, prove more economical than laboratory procedures to predict nutrient digestibility, and provide more applicable data concerning energy availability when compared with summing tabular means for feedstuffs from publications or from computerized diet formulation programs. When combined with DMI, direct digestibility measurements should markedly improve precision for quantifying amounts of nutrients and energy available for maintenance and performance by productive ruminants in dairies or feedlots. As with all analytical procedures, accurate digestibility measurement requires representative sampling and proper analysis of diets and feces.

Lopez, J.R., Montano Gomez, M.F., Jorquera, A.P., Chavira, J.S. and Zinn, R.A. 2007. Dietary phosphorus requirement of Holstein steers during early growing period. J. Appl. Anim. Res., 31: 113–115. Ninety-six Holstein steer calves (120.7±5.3 kg) were used to evaluate the influence of dietary phosphorus level (0.27, 0.31, 0.35 and 0.39%, DMB) on growth-performance during the initial 105 d on feed. Dicalcium phosphate was the source of supplemental phosphorus. All diets were formulated to contain 0.85% calcium (DMB). Dietary phosphorus level did not affect (P>.10) DMI or body size measurements. However, increasing dietary phosphorus level increased ADG (linear component, P