102 High-forage vs. high-concentrate diets fed to pregnant beef heifers: Impacts on maternal feeding behavior and feed efficiency, blood metabolite and hormone profiles in the dam and calf, and postnatal growth of the male offspring

The objective of this study was to evaluate the impact of feeding gestating replacement heifers a high-concentrate (HC) diet or a high-forage (HF) diet from 15 days pre-breeding through calving on: feeding behavior and feed efficiency in the dam, blood metabolite and hormone profiles in the dam and calf, and postnatal growth of the male offspring. Angus crossbred heifers (n = 46; approximately 14 months of age; initial body weight [BW] 337 ± 37.7 kg) were ranked by BW and randomly assigned to one of two dietary treatments: high-forage (75% forage:25% concentrate; HF, n = 24) or high-concentrate (25% forage:75% concentrate; HC, n = 22). Fifteen days after treatment initiation, heifers were bred via artificial insemination with male-sexed semen, and treatments continued until parturition. Heifers were weighed every 14 days with treatment deliveries adjusted to target BW gains of 0.45 kg/day in the first two-thirds of gestation and 0.79 kg/day in the last third of gestation. Blood was collected at six-time points pre-breeding through calving, and feed data was measured using the Insentec Roughage Intake Control system. Blood serum and plasma were analyzed for metabolite and hormone concentrations. Data were analyzed using the MIXED procedure of SAS with individual animal as the experimental unit, using repeated measures where appropriate. Significance was considered at P ≤ 0.05. There was no difference in average daily gain (P = 0.50), but HC dams had greater (P < 0.01) gain:feed, dry matter intake (DMI) per visit and meal, eating rate, and time eating per visit to the feed trough compared to HF dams. In contrast, HF dams had greater (P < 0.01) DMI per day, time eating per meal and day, and a greater number of visits and meals than HC heifers. Concentrations of cortisol, insulin-like growth factor 1 (IGF-1), and glucose were greater (P < 0.01) for HC than HF dams; however, HF dams had a greater (P < 0.01) concentration of blood urea nitrogen (BUN). At birth, HF calves had greater (P ≤ 0.03) concentrations of IGF-1 and non-esterified fatty acids (NEFA) than HC calves, but no differences were observed (P ≥ 0.16) at weaning. Calving ease was greater (P = 0.03) in HF dams than HC dams; however, no differences (P ≥ 0.88) were observed in calf birth BW or postnatal weight gain. These findings demonstrate that feeding high-concentrate diets impacts feeding behavior, feed efficiency, and blood metabolite and hormones in beef heifers, and alters circulating blood metabolites and hormones in the offspring at birth. The results support utilization of limit-fed high-concentrate diets to pregnant heifers as indicated by economic or environmental signals; however, further postnatal evaluation is warranted to determine whether latent fetal programming effects are unmasked later in production.