Abstract
This study evaluated how corn supplementation and age of female affected body weight (BW), body condition score (BCS), artificial insemination (AI) pregnancy rate, and blood metabolites (nonesterified fatty acid [NEFA], β-hydroxybutyrate [BHBA], and blood urea nitrogen [BUN]) when grazing lush spring pasture. Angus and Angus × Simmental beef females (n = 361) were blocked by location, stratified by BW and BCS, and then were assigned to groups (n = 8 groups/treatment combination; 9-14 females/group). The study utilized a stratified, randomized complete block design with a 2 × 2 factorial arrangement of treatments. The four treatment combinations were: yearling heifers receiving no supplement (CON-H); yearling heifers receiving supplement of dry-rolled corn (SUPP-H; 1.81 kg as-fed/heifer/d) for 42 d; 2-yr-old lactating cow-calf pairs receiving no supplement (CON-C); and 2-yr-old lactating cow-calf pairs receiving supplement of dry-rolled corn (SUPP-C; 1.81 kg as-fed/cow/d) for 42 d. Supplementation began at AI (end of April) when cows began grazing tall fescue (Festuca arundinacea schreb)-red clover (Trifolium pratense) pastures. Pasture forage was collected weekly for analysis. Throughout the study, forage crude protein decreased (P < 0.01) over time, but acid detergent fiber (ADF), neutral detergent fiber, dry matter, forage height, and forage mass all increased (P < 0.01) over time. Females receiving SUPP tended (P = 0.10) to have greater BW and greater BW change over the supplementation period. Supplementation × age effects for BCS were detected (P = 0.04); SUPP-H had greater BCS than all other treatment combinations at d 42. Cow BHBA was greater (P < 0.01) compared with heifers. Female NEFA increased (P < 0.01) from d 12 to 42. Control females had greater (P = 0.02) serum NEFA concentrations compared with SUPP females. Control females had greater (P = 0.03) BUN concentrations compared with SUPP females. Cow BUN was greater (P < 0.01) than heifer BUN. Supplementation effects were not detected (P ≥ 0.25) for AI or overall pregnancy rate. In conclusion, there were no supplementation × age interactions excluding d 42 BCS. Supplementation regardless of female age tended to improve d 42 BW and BW change. Cow BHBA and BUN was greater compared with the heifers, whereas the supplemented females had decreased NEFA and BUN. Cows tended to have greater AI pregnancy rates than heifers, but supplementation did not affect AI or overall pregnancy rates.