438 - Effect of Stocking Rate During Gestation on Subsequent Performance of Growing Beef Cattle

Beef cows in the southeastern United States are likely maintained on pasture during mid-gestation, a critical period for fetal development of traits important to performance of the growing/finishing calf. Climate projections are for increased warming with highly variable precipitation in this region. Forage quantity and quality are affected by temperature and precipitation. Thus, in order to obtain a better understanding of downstream effects from cow nutrition during gestation on subsequent performance of growing cattle, we analyzed 579 records of crossbred steers and heifers born (fall and winter) to cows grazing typical forages in Overton, Texas. Cows were involved in a long-term stocking rate study and were assigned to either high (H; 4 cow/calf ha^-1) or low (L; 2 cow/calf ha^-1) treatment groups. Cow body condition scores (BCS; 1–9) were collected at breeding and weaning. Calves produced were pastured from weaning to approximately 1 to 1.5 years of age, then shipped to a commercial feedlot and subsequently slaughtered at a commercial facility. Calf data included birth weight, weaning weight (~240d), yearling weight, on-feed weight, final pre-harvest weight, hot carcass weight (all weights in kg), dressing percentage, marbling score, yield grade, backfat thickness (cm), ribeye area (cm²), and kidney-pelvic-heart fat (%). Differences (P < 0.05) between treatment groups were determined by a general linear model in SAS with stocking rate as the main effect. Mean separation was accomplished using Tukey’s test. Cow BCS (H; 4.27 ± 0.06 vs L; 5.64 ± 0.07, P < 0.0001), final pre-harvest weight (H; 594.80 ± 6.18 kg vs L; 619.85 ± 6.12 kg, < 0.005), hot carcass weight (H; 366.60 ± 3.89 kg vs L; 383.17 ± 3.74, P < 0.003), and ribeye area (H; 90.52 ± 0.90 cm² vs L; 93.74 ± 1.03 cm², P < 0.03) were all lower in H than L. Calf weaning weight followed a similar trend (H; 289.24 ± 2.58 kg vs L; 296.56 ± 3.08 kg, P < 0.07). Diminished nutritional provision to the fetus during mid-gestation was apparently manifest as epigenetic effects on offspring performance.