76 Does supplemental protein and rumen-protected methionine improve performance and digestibility during late-gestation in beef cows?

Abstract

Abstract Methionine (MET) is likely the first limiting amino acid in low-protein forages fed to beef cattle during late-gestation. Therefore, the objective of this study was to determine if supplemental protein and rumen-protected MET improve cow performance and apparent tract digestibility (TTD) during late-gestation. This study used 147 late-gestation Angus crossbred cows and heifers in a 3x2 factorial arrangement for dietary treatments. The cattle were randomly assigned to one of six diets formulated to 90, 100 or 110% of metabolizable protein (MP) requirements (NRC, 2016), with (without) 9 g/d of rumen-protected MET (MetaSmart, Adisseo Inc.). These diets were fed for approximately 8 wks before calving. All data was analyzed as a randomized block design using SAS 9.4 PROC GLIMMIX procedure. Cows fed at 90% MP requirements lost body weight (BW), while cows fed at 100% and 110% MP requirements maintained and (or) gained BW over the trial (P = 0.02). Similarly, cows fed at 90% MP requirements lost more pregnancy corrected BW than cows fed at 100% and 110% MP requirements (P = 0.01). However, supplemental MET did not affect body weight gains (P > 0.07). Cows and heifers fed at 90% MP requirements had reduced TTD for crude protein compared to cattle fed to 110% MP requirements (P < 0.001), MET supplementation did not impact TTD (P > 0.20). Additionally, cattle fed at 90% MP requirements had increased serum cholesterol and reduced urea concentrations compared to cows fed to 100% and 110% MP requirements (P < 0.0001). MET supplementation increased serum concentrations for glucose, isoleucine, leucine, lysine, serine, threonine and valine (P < 0.02). Calf birth weights were not significantly impacted by dietary treatment (P > 0.31). Feeding cows above their MP requirements may improve late-gestation performance and CP digestibility. Supplemental MET may increase amino acid utilization but did not improve beef cow performance or digestibility parameters measured in late-gestation.