Postinsemination diet change on reproductive performance in beef heifers

Abstract

An important part of any production system is the reproductive performance associated with developing heifers. However, previous research has reported that grazing behavior is learned at weaning, and moving heifers from a drylot environment to a grazing environment immediately following insemination can negatively affect pregnancy success. Therefore, this project was conducted to determine whether this decrease in pregnancy success is associated with diet change alone and how diet change can affect circulating concentrations of progesterone and BUN. Angus crossbred heifers (n = 336) were developed on a forage diet from weaning to breeding. Seven days before the start of the breeding season all heifers were brought into a drylot and synchronized with the Select Synch + CIDR protocol. Immediately after AI, heifers were returned to forage (RNG), returned to forage and supplemented with 2.22 kg/d per animal of dried distillers grains with solubles (RNG-S), or moved into a drylot (DLT). Blood samples were collected on d −7; at AI; and 2, 14, and 42 d after AI. Circulating concentrations of progesterone and BUN were analyzed in all serum samples. There were no differences among treatments in AI or breeding season pregnancy success. Heifers in the RNG-S treatment had greater (P < 0.01) BUN concentrations at 2, 14, and 42 d after AI compared with DLT and RNG. The RNG-S heifers had greater concentrations of progesterone on d 14 after AI (P = 0.02) compared with DLT, and concentrations were greater on d 14 and 42 after AI (P < 0.02) for RNG heifers compared with DLT. In summary, when heifers were developed on a forage-based developing diet and moved to range, range with supplementation, or to a drylot, there was no detectable effect on pregnancy success; thus, a change in diet alone, as long as BCS is not negatively affected, immediately following AI was not sufficient to reduce pregnancy success.