Monensin supplementation during la e gestation of beef cows alters maternal plasma concentrations of insulin-like growth factors 1 and 2 and enhances offspring preweaning growth

This study evaluated the effects of maternal prepartum supplementation of dried distillers grains (DDG), with or without monensin addition, on maternal performance and physiology and offspring preweaning growth. On day 0 (approximately 197 +/- 4 d prepartum), 150 multiparous, Brangus crossbred beef cows were ranked by their initial body weight (BW; 524 +/- 51 kg) and body condition score (BCS; 5.0 +/- 0.63), and then randomly assigned into one of 15 bahiagrass (Paspalum notatum) pastures (10 cows and 8.1 ha/pasture). Maternal treatments were randomly assigned to pastures (5 pastures/treatment) and consisted of no prepartum supplementation of DDG (NOSUP) or supplementation of DDG at 1 kg/cow/d (dry matter basis; DM) added with 0 mg (SUP) or 200 mg/d of monensin (SUPMO) from days 0 to 77. Effects of maternal treatment and maternal treatment x day of the study were not detected (P >= 0.63) for any forage data. Cow BCS on day 35 and near calving (day 77) did not differ (P >= 0.19) between SUP and SUPMO cows but both groups had greater (P <= 0.001) BCS compared with NOSUP cows. Cow BCS at the start of the breeding season (day 142) and on day 168 were the greatest (P < 0.0001) for SUPMO cows, least for NOSUP cows, and intermediate (P >= 0.02) for SUP cows. Maternal plasma concentrations of glucose did not differ (P <= 0.25) among treatments. Plasma concentrations of insulin-like growth factor 1 (IGF-1) on day 77 were the least for NOSUP cows (P <= 0.0.5) and did not differ (P= 0.66) between SUP and SUPMO cows, whereas plasma concentrations of IGF-2 on days 35 and 77 were greatest (P <= 0.0.5) for SUPMO cows and did not differ (P >= 0.60) be- tween NOSUP and SUP cows. Birth BW of first offspring did not differ (P >= 0.77) between SUP and SUPMO calves but NOSUP calves were lighter at birth (P <= 0.05) compared with SUP and SUPMO calves. Percentage of cows pregnant with a second offspring did not differ (P= 0.72) between SUP and SUPMO cows and were the least for NOSUP cows (P <= 0.05). First offspring BW at weaning (day 325) was greatest (P <= 0.05) for SUPMO calves, least for NOSUP calves, and intermediate for SUP calves. Therefore, adding monensin into prepartum DDG supplements for Bos indicus-influenced beef cows did not increase cow prepartum BCS but led to greatest offspring preweaning growth, likely by modulating maternal plasma concentrations of IGF-1 and IGF-2 during gestation. Lay summary Supplementing protein and energy during third trimester of gestation provides an opportunity to impact fetal development and increase offspring growth performance from birth to weaning. Including feed additives, such as ionophores, into protein and energy supplements during late gestation of beef cows has been poorly explored, particularly for Bos indicus-influenced beef cattle. In the current study, cows were assigned to receive no precalving supplementation, precalving supplementation of protein and energy, or precalving supplementation of protein and energy added with ionophore (monensin) for 77 d during late gestation. After calving, all cows and their calves were managed similarly. Overall, cows that received precalving supplementation (with or without monensin) had greater body condition score at calving and pregnancy percentage and weaned heavier calves compared with cows that did not receive precalving supplementation. Adding monensin to maternal supplements did not improve maternal performance compared with maternal supplementation without monensin but increased preweaning growth of their offspring.