154 - Supplementation of Late Gestation Metabolizable Energy in Beef Cows Reduces Mobilization of Body Reserves Prepartum

Abstract: This study evaluated how late gestation metabolizable energy (ME) intake affects performance and metabolism in beef cattle. Primiparous (PP; n = 45) and multiparous (MP; n = 107) Angus-Simmental cows were blocked by calving date and randomly assigned to treatments providing 80 (LME; n = 52), 100 (CME; n = 51), or 120% (HME; n = 49) of ME requirements for 53 d prior to calving. Postpartum, cows were fed the same diet. Rib and rump fat depths were measured by ultrasonography on d -54, -40, -26, -13, 13, 27, and 55 relative to calving. Plasma and serum were collected on d -53, -39, -25, -10, -3, 7, 13, 27, and 55 relative to calving. Serum glucose, beta-hydroxybutyrate, non-esterified fatty acids (NEFA), and urea, and plasma insulin were measured. Data were analyzed using PROC GLIMMIX with the fixed effects of treatment, parity, and treatment×parity, and random effects of block and cow (block), accounting for repeated measures. Absolute loss of rib and rump fat prepartum was lesser (P ≤ 0.03) for HME. Primiparous heifers lost more (P < 0.01) rib fat prepartum. Prepartum serum urea and NEFA were elevated (P < 0.01) for LME, whereas glucose was elevated (P < 0.01) for HME compared to LME. Multiparous cows had greater (P ≤ 0.02) serum NEFA and plasma insulin prepartum, whereas PP heifers had elevated (P < 0.01) glucose. Treatment did not affect (P ≥ 0.56) the absolute loss of rib nor rump fat postpartum. Serum urea was greater (P < 0.01) in LME than HME postpartum. Multiparous cow serum urea and beta-hydroxybutyrate postpartum was elevated (P ≤ 0.01) postpartum, whereas PP cows had elevated (P < 0.01) plasma insulin. Supplementing excess ME during late gestation reduced mobilization of body reserves before calving but prepartum effects did not continue postpartum.