Effects of weaning programs on serum metabolites and hepatic IGF-1 mRNA of first-calf heifers or mature cows

Effects of early weaning calves on serum metabolites and hepatic insulin-like growth factor-1 messenger RNA (IGF-1 mRNA) of first-calf heifers or mature cows was investigated. Treatments were arranged in a 2 x 2 factorial and included 14 crossbred first-calf heifers and 14 crossbred mature cows assigned randomly to one of two treatment regimens: early-weaned (EW, calves weaned at an average age of 114 d) or normal-weaned (NW, calves weaned at an average age of 197 d). Blood samples were collected from dams on d 114, 141, 197 and 205 postpartum via coccygeal venipuncture. Heifers with calves EW experienced a greater increase (parity x weaning; P = 0.02) in BW over heifers with calves NW, but no change in BW due to weaning was observed for mature cows (P>0.71). Early weaning (vs. NW) increased (P<0.05) body condition (BC) and change in BC of heifers and cows. Effects of weaning regimen or parity were not observed for ADG. There were no parity x weaning or parity x weaning x d interactions (P>0.16) observed for serum IGF-1, serum non-esterified fatty acids (NEFA), or serum urea nitrogen (SUN). A parity x d interaction (P<0.05) for hepatic IGF-1 mRNA, serum IGF-1 and SUN, and a trend for parity x d for NEFA (P<.0.10) were observed, but no differences were detected between first-calf heifers and mature cows within sampling d. Early weaning tended to decrease (P = 0.06) SUN compared with NW status. These results suggest that EW can increase BW and BC in first-calf heifers, and decrease SUN in both first-calf heifers and mature cows. However, no other differences in performance or serum chemistry were detected between first-calf heifers and mature cows with either weaning regimen applied, in open rangeland conditions of the arid southwest United States during drought.