Impact of Managing Cow-calf Pairs on Pasture or in a Dry Lot during a 10 day Synchronization Period on Reproductive Performance and Weight Change in Cows and their Calves

Abstract Text:   The objective of this project was to determine the effects of moving cow-calf pairs from summer pastures in early- to mid-July into dry lots for a 10 day estrus synchronization and breeding period on reproductive performance and weight change in cows and their calves. Cow-calf pairs (n = 427) were stratified by calf sex and days postpartum and randomly assigned to one of two treatments: 1) pairs were removed from summer pastures and managed in dry lots during a 10 day synchronization and breeding window (DL, n = 212), 2) pairs remained on summer pasture for the synchronization and breeding period, and were gathered for each of 3 separate handling events to facilitate AI (CON, n = 215). The DL group was provided ad libitum grass hay, while the CON group had ad libitum access to native range pastures with both groups having equal access to a vitamin/mineral supplement. All cows were exposed to 7-d CO-Synch + CIDR protocol with fixed-time AI (d 10) at 60-66 h after CIDR removal. Single day, unshrunk BW of cows and calves were recorded on day -10 and d 0 relative to breeding, with additional calf BW collected on d 35 and 88 and cow BW on d 95. Presence of a viable fetus was determined in cows on d 35 and 95 via transrectal ultrasonography. Both cows and calves in the DL group had reduced (P ≤ 0.04) weight gain during the 10 day synchronization window compared with the CON group. No differences (P ≥ 0.36) were observed between treatments for pregnancy rate at d 35 (49.5% and 52.3% for CON and DL, respectively) or d 95 (91.1% and 89.6% for CON and DL, respectively), or cow BW on d 95. However, calves in the DL treatments were 6.8 kg lighter (P ≤ 0.003) on d 35 and 8.5 kg lighter on d 88 (weaning) compared with calves in the CON group. Managing cow-calf pairs in the dry lot for a 10 day estrus synchronization and breeding period did not affect final pregnancy rates, but did have a negative impact on calf weaning weights.

Keywords: beef cattle, breeding management, calf performance