Effects of Winter vs. Year-round Supplementation of Multiparous Bos Indicus-influenced Beef Cows on Offspring Postnatal Growth, Immunity, and Carcass Characteristics

Abstract

\n This 2-yr study evaluated the effects of winter vs. year-round supplementation of Bos indicus-influenced beef cows on offspring feedlot performance. Brangus cows (82–84 cows/yr) were stratified by BW and BCS (475 ± 67 kg; 4.85 ± 0.73) and randomly assigned to bahiagrass pastures (13–14 cows/pasture). Treatments were randomly assigned to pastures (2 pastures/treatment/yr) and consisted of winter supplementation with molasses (MOL-W), or year-round supplementation with molasses (MOL-Y) or cubes (CUB-Y). Supplements were isocaloric and isonitrogenous (75% TDN, 20% CP; DM basis). Total yearly supplement DM amount was 272 kg/cow for all treatments. At weaning (d 421), 33–35 steers/yr were vaccinated against bovine respiratory disease, transported for 720 miles to the feedlot, penned according to prepartum pasture distribution, and fed the same corn silage-based diet until harvest. Data were analyzed using SAS GLIMMIX procedure. Cow BCS at calving was greater (P < 0.01) for MOL-Y and CUB-Y vs. CON cows. Calving rate, calving date, calf birth weight, and calf preweaning BW did not differ (P ≥ 0.22) among treatments. Steer feedlot BW did not differ (P ≥ 0.36) at time of feedlot entry but was greater (P ≤ 0.05) for MOL-Y and MOL-W steers vs. CUB-Y steers at feedlot exit. Plasma haptoglobin concentrations at feedlot entry were greater (P = 0.05) for CUB-Y vs. CON steers, with MOL-Y steers being intermediate, whereas plasma cortisol concentrations at feedlot entry were greater (P ≤ 0.05) for CUB-Y vs. MOL-Y and MOL-W steers. Marbling score, yield grade, and carcass weight did not differ (P ≥ 0.14), but CON steers had greater fat thickness at the 12th rib than MOL-Y and CUB-Y steers. Hence, year-round supplementation (molasses or cubes) of beef cows increased cow BCS at calving but had minor effects on offspring post-weaning growth and immunity compared to winter supplementation of molasses.