Influence of Prepartum Dietary Protein Concentration on Beef Cow Performance and Calf Growth, Carcass Characteristics, and Plasma Glucose and Insulin Concentrations

Abstract Text: Objectives of this study were to investigate the effects of prepartum dietary protein concentration on cow performance, lactation, and reproduction, as well as calf growth, carcass characteristics, and plasma glucose and insulin concentrations. Spring-calving, multiparous cows (n = 49; BW = 657±70 kg) were blocked by BW and allotted to 2 dietary treatments: (1) 19% modified wet distillers grains plus solubles (MDGS), 54% oatlage, and 27% corn silage (REQ), or (2) 39% MDGS, 41% oatlage, and 20% corn silage (HP). Treatment diets were formulated to be isocaloric, and REQ and HP provided 100% and 128% of CP requirement, respectively. Cows were limit-fed from 90 d prepartum to calving. All cows were fed a common diet postpartum. Cow BW and BCS were recorded at 90 d prepartum and 24 h post-calving. Milk production was estimated by the weigh-suckle-weigh technique at 69±11 d of age. Calf BW was measured at birth and weaning (121±11 d of age). Calves (n = 42) were fed a common feedlot diet after weaning and individual DMI was recorded using GrowSafe. Plasma glucose and insulin concentrations were analyzed on a subset of calves (n = 12/treatment) 90, 120, 150, 180, 210, and 240 min post-feeding, 1 d prior to slaughter. All calves were slaughtered 221 d post-weaning at a target 12^th rib fat thickness (BF) of 1.4 cm, determined via ultrasound. Dietary treatment had no effect (P ≥ 0.31) on cow BW or BCS change from 90 d prepartum to calving. Prepartum treatment did not affect (P = 0.51) calf BW at birth. There was no effect (P ≥ 0.32) of prepartum treatment on cow milk production, conception rates, or calf weaning BW. Feedlot DMI, ADG, G:F, and final BW were not affected (P ≥ 0.32) by treatment. No differences (P ≥ 0.31) in HCW, marbling score, or LM area were detected. Calves from cows fed HP had greater BF (P < 0.01) and yield grades (P < 0.01), and tended to have more KPH (P = 0.08) than calves from cows fed REQ. Calves from cows fed HP had decreased (P < 0.01) plasma glucose and insulin concentrations but increased (P< 0.01) glucose to insulin ratios when compared to calves from cows fed REQ.  Although feeding cows 128% of CP requirement from 90 d prepartum to calving did not affect cow performance or calf growth, it increased calf carcass adiposity.

Keywords: beef cow, fetal programming, protein