394 Exploring the relationships between cow-calf management systems as affected by protein/methionine nutrition during gestation on the performance of cow-calf pairs prior to weaning

Abstract

Abstract A three-way factorial arrangement was used to assess impacts of protein/methionine nutrition during gestation and two lactational management systems on performance of cow-calf pairs pre-weaning. 140 crossbred beef cows were managed in drylot and randomly assigned to one of six nutritional treatments during the third trimester of gestation. Cows were fed to meet 110% (HP), 100% (MP), or 90% (LP) of metabolizable protein requirements for late-gestation (NRC, 2016), with(without) rumen-protected methionine (RPM) for 8 weeks prior to parturition. Post-partum, cow-calf pairs were managed in drylot (DL) and fed ad libitum, a ration formulated to meet lactational nutrient requirements, or rotationally grazed on pasture (PAS). Cow body weights (BW) and body condition scores (BCS) and calf BW were recorded at regular intervals. All data were analyzed using PROC GLIMMIX (SAS v9.4). HP cows were heaviest at calving (P = 0.02), but calf birthweight was unaffected by gestational nutrition (P > 0.19). Gestational nutrition did not impact cow conception rate (CR), or calf BW and ADG (P > 0.17). Lactational management system (PAS, DL) did not affect cow BCS or CR (P > 0.13), but impacted cow and calf BW and ADG. PAS calves were heavier, had greater ADG, and heavier weaning BW than DL calves (P < 0.02). This came at the expense of BW loss throughout lactation and lower ADG for PAS cows, versus BW gains and greater ADG for DL cows (P < 0.0001). An interaction between protein level and RPM supplementation was present for cow BW at calving and weaning, and BW change throughout lactation (P < 0.04), with tendencies for interactions for cow ADG and BCS (P < 0.09). Overall, prepartum protein/methionine supplementation did not affect calf performance prior to weaning, but may have affected cow performance during lactation. Rotationally grazing cow-calf pairs on pasture improved pre-weaning calf gains, but reduced cow gains throughout lactation.