208 Nutrient Restriction During Late Gestation Alters Beef Heifer Colostrum Composition

Abstract

Abstract We hypothesized that late gestational nutrient restriction of beef heifers would decrease nutrient partitioning to the mammary gland, resulting in less colostrum nutrient availability for neonatal calves. Fall-calving Hereford-SimAngus heifers (single-sired; BW: 451 ± 28 [SD] kg; BCS: 5.4 ± 0.7) bred to a single sire were individually fed 100% (control; n = 12) or 70% (nutrient restricted; NR; n = 13) of NASEM net energy and metabolizable protein requirements for maintenance, pregnancy, and growth from d 160 of gestation to calving. Diets were based on chopped sorghum sudan hay (1.74 Mcal ME, 6.66% CP, 72.0% NDF; DM basis) supplemented to meet targeted nutritional planes. Calving was observed for all females, and total colostrum from one rear quarter was collected pre-suckling (50.5 ± 17 min [SD] postpartum). Colostrum nutrient composition was determined by colorimetric assays run on a UV-visible light microplate reader. Data were analyzed with treatment, calving date, and calf sex (when P < 0.25) as fixed effects. We have previously reported that single-quarter colostrum weight and volume were 40% less (P = 0.04) in NR compared with control heifers. Colostrum lactose concentration was not affected (P = 0.32) by treatment, but yield differences resulted in 46% less (P = 0.03) total single-quarter colostrum lactose in NR than control. Colostrum from NR heifers had 36% greater (P = 0.004) protein concentration than control, but greater colostrum yield of control heifers allowed for total protein to be unaffected (P = 0.57) by treatment. Nutrient restricted heifers had 23% less (P = 0.04) colostrum urea N concentration and 60% less (P = 0.01) total colostrum urea N than control. Late gestational nutrient restriction (P ≥ 0.59) did not affect colostrum triglyceride concentration or total. In summary, energy and protein restriction had disparate effects on nutrient partitioning to colostrum in primiparous beef females.