528 - Late-Breaking: Late Gestation Metabolizable Energy Intake Increases Colostrum Yield and Alters Colostrum Composition in Beef Cattle

The objective was to determine how late gestation metabolizable energy (ME) intake impacts beef cow colostrogenesis. Angus-Simmental primiparous (n = 47) and multiparous (n = 109) cattle were blocked by expected calving date and randomly assigned to receive diets that supplied 80% (LME; n = 53), 100% (CME; n = 52), or 120% (HME; n = 51) of the ME requirement. Treatments were balanced by initial BW and fed for 53 d prior to calving. Cow body weight was recorded d -53, -39, -25, -10, and -3 relative to calving and retrospectively conceptus-corrected. Calves were weighed and measured prior to suckling. Colostrum was hand-stripped from all cows for compositional analysis and a subset (n = 16/treatment) was fully milked using a milking machine. Data were analyzed (PROC GLIMMIX) as a randomized block design, including the fixed effects of treatment, parity, and treatment×parity and the random effects of block and cow(block). Day and its interactions were included for repeated measurements. Treatment did not affect (P ≥ 0.73) cow BW or conceptus-corrected BW. Calf chest circumference was lesser (treatment×parity: P = 0.023) for primiparous vs. multiparous calves if their dams consumed LME or CME, but not if their dams consumed HME. Feeding HME rather than LME increased (P = 0.006) colostrum yield. The LME diet increased (P = 0.004) colostrum IgG concentration over HME; however, HME colostrum yielded more (P = 0.005) total IgG. Crude protein and urea-N were elevated (P < 0.001) in LME colostrum, whereas HME colostrum contained more (P = 0.026) lactose. Low ME colostrum fat was greater (P = 0.013) than CME and beta-hydroxybutyrate was increased (P < 0.001) in LME vs. CME and HME colostrum. These data provide insight regarding nutrient partitioning during late gestation and demonstrate that beef cow colostrogenesis is responsive to prepartum ME intake.