Interaction of early metabolizable protein supplementation and virginiamycin on feedlot growth-performance and carcass characteristics of calf-fed Holstein steers

One hundred sixty-eight Holstein steer calves (133.4 ±7.9 kg) were used to evaluate the influence of virginiamycin (VM) supplementation on cattle growth performance and liver abscess incidence, and the effect of feeding 100% vs 87% of metabolizable protein (MP) requirements during the initial 112 d on growth performance, efficiency of energy utilization, and carcass characteristics. Steers were balanced by weight and assigned to 28 pens (6 steers/pen). During the initial 112-d feeding period, dietary treatments consisted of two levels of metabolizable protein (100 vs 87% of expected requirements during the initial 112 d feeding period; NASEM, 2000) supplemented with or without 22.5 mg/kg virginiamycin (Phibro Animal Health, Teaneck, NJ 07666) in a 2×2 factorial arrangement. There were no VM × MP supplementation interactions (P ≥ 0.14) on any of the parameters measured in both experiments. Calf-fed Holstein steers supplemented VM increased (P ≤ 0.03) overall ADG, G:F, observed/expected NE values for maintenance and gain, and final body weight (BW). Cattle fed VM also increased (P ≤ 0.04) carcass weight, dressing percent, and longissimus muscle area. However, there was no effect (P ≥ 0.22) of VM supplementation on any other carcass characteristics. Calf-fed Holstein steers fed 100% MP requirements during the initial 112 d feeding period had greater (P ≤ 0.02) ADG, G:F, observed/expected NE values for maintenance and gain, and live BW compared to steers fed 87% of the expected metabolizable protein requirements. However, there was no effect (P ≥ 0.17) of MP supply during the initial 112-d period on overall (342 d) growth performance measurements. The incidence of liver abscesses was low (averaging 7.7%) and not affected by dietary treatments. We conclude that independently of MP supplies, supplemental VM enhances overall growth performance and efficiency of energy utilization of calf-fed Holstein steers.

PSIII-23 Maternal metabolizable protein level and rumen-protected methionine impacts on beef steer progeny gene expression in muscle and liver

This experiment evaluated how maternal metabolizable protein level and rumen-protected methionine supplementation during late gestation impacts expression of genes associated with fetal programming in beef steer offspring. In a 3 x 2 factorial arrangement, 138 Angus crossbred cows were randomly assigned one of three metabolizable protein (MP) treatments (fed to meet 90, 100, or 110% of MP requirements), with(without) 9 g/d of rumen-protected methionine (MET; Smartamine®M, Adisseo Inc.). The isocaloric diets were fed for the last 8 weeks of gestation. Steer progeny (n = 51) were assigned to one of seven pens by weight and received a common corn-based grower diet (58% corn silage, 26% alfalfa haylage, 15% soybean meal) for 47 days, followed by a finisher diet (78% high moisture corn, 12% alfalfa haylage, 8% soybean meal) for 115 ±31.5 days until slaughter. At slaughter, samples of Sternomandibularis muscle and liver were collected and snap-frozen in liquid nitrogen for RNA isolation and analysis of gene expression for growth, myogenic, and adipogenic genes. Data were analyzed using PROC GLIMMIX in SAS, with maternal MP level and MET supplementation as fixed effects, and pen as a random effect. Exceeding maternal MP requirements increased expression of myogenic regulatory factor, myogenin (MYOG; 90% MP: 0.72, 100% MP: 0.94, and 110% MP: 1.00; SEM = 0.083, respectively; P = 0.02) in muscle from steer progeny at slaughter. Methionine supplementation decreased expression of pyruvate kinase (PKM; MET: 0.81, No MET: 1.16; SEM = 0.092; P = 0.02) in muscle, which is associated with lean tissue growth. Maternal nutritional treatment did not influence hepatic gene expression (P ≥ 0.06). These data suggest that maternal nutrition may impact progeny muscle development, while maintaining metabolic function of the liver.

Metabolizable Protein: 1. Predicting Equations to Estimate Microbial Crude Protein Synthesis in Small Ruminants

Microbial crude protein (MCP) produced in rumen could be estimated by a variety of protocols of experimental sampling and analysis. However, a model to estimate this value is necessary when protein requirements are calculated for small ruminants. This model could be useful to calculate rumen degradable protein (RDP) requirements from metabolizable protein (MP). Then, our objective was to investigate if there is a difference in MCP efficiency between sheep and goats, and to fit equations to predict ruminal MCP production from dietary energy intake. The database consisted of 19 studies with goats (n = 176) and sheep (n = 316), and the variables MCP synthesis (g/day), total digestible nutrients (TDN), and organic matter (OM) intakes (g/day), and OM digestibility (g/kg DM) were registered for both species. The database was used for two different purposes, where 70% of the values were sorted to fit equations, and 30% for validation. A meta-analytical procedure was carried out using the MIXED procedure of SAS, specie was considered as the fixed dummy effect, and the intercept and slope nested in the study were considered random effects. No effect of specie was observed for the estimation of MCP from TDN, digestible Organic Matter (dOM), or metabolizable energy (ME) intakes (P > 0.05), considering an equation with or without an intercept. Therefore, single models including both species at the same fitting were validated. The following equations MCP (g/day) = 12.7311 + 59.2956 × TDN intake (AIC = 3,004.6); MCP (g/day) = 15.7764 + 62.2612 × dOM intake (AIC = 2,755.1); and MCP (g/day) = 12.7311 + 15.3000 × ME intake (AIC = 3,007.3) presented lower values for the mean square error of prediction (MSEP) and its decomposition, and similar values for the concordance correlation coefficient (CCC) and for the residual mean square error (RMSE) when compared with equations fitted without an intercept. The intercept and slope pooled test was significant for equations without an intercept (P < 0.05), indicating that observed and predicted data differed. In contrast, predicted and observed data for complete equations were similar (P > 0.05).

Metabolizable Protein: 2. Requirements for Maintenance in Growing Saanen Goats

This study aimed to estimate the protein requirements for the maintenance of growing Saanen goats of different sexes from 5 to 45 kg of body weight (BW) using two methods and applying a meta-analysis. For this purpose, two datasets were used. One dataset was used to evaluate the effects of sex on the protein requirements for maintenance using the comparative slaughter technique. This dataset was composed of 185 individual records (80 intact males, 62 castrated males, and 43 females) from six studies. The other dataset was used to evaluate the effects of sex on the protein requirements for maintenance using the N balance method. This dataset was composed of 136 individual records (59 intact males, 43 castrated males, and 34 females) from six studies. All studies applied an experimental design that provided different levels of N intake and different levels of N retention, allowing the development of regression equations to predict the net protein requirement for maintenance (NPM) and the metabolizable protein (MP) requirements for maintenance (MPM) in Saanen goats. The efficiency of MP use for maintenance (kPM) was computed as NPM/MPM. The efficiency of MP use for gain (kPG) was calculated using the equation of daily protein retained against daily MP intake above maintenance. A meta-analysis was applied using the MIXED procedure of SAS, in which sex was considered a fixed effect, and blocks nested in the studies and goat sex were considered as random effects. The NPM did not differ between sexes, irrespective of the approach used. The daily NPM estimated was 1.23 g/kg0.75 BW when using the comparative slaughter technique, while it was 3.18 g/kg0.75 BW when using the N balance technique for growing Saanen goats. The MPM estimated was 3.8 g/kg0.75 BW, the kPM was 0.33, and the kPG was 0.52. We observed that the NPM when using the comparative slaughter technique in growing Saanen goats is lower than that recommended by the current small ruminant feeding systems; on the other hand, the MPM was similar to previous reports by the feeding systems. Sex did not affect the protein requirements for maintenance and the efficiencies of use of metabolizable protein.