Evaluation of prior grazing experience on reproductive performance in beef heifers

An important part of any production system is the reproductive performance associated with replacement heifers. In the majority of beef operations, heifers are moved to a drylot for a period of time to be weaned and then must again be moved to a forage grazing situation. Therefore, experiments were conducted to determine whether previous grazing experience affected performance and conception rates. In Exp. 1, beef heifers were moved to a forage grazing situation after a 44-d weaning period in the drylot [EXPER (experienced); n = 33] or were moved to a forage grazing situation 27 d before the start of the breeding season [NIV (naïve); n = 32]. In Exp. 2, beef heifers were moved to a forage grazing situation before the breeding season (EXPER; n = 207) or were moved to a forage grazing situation immediately following AI (NIV; n = 214). In Exp. 1, after being moved, NIV heifers lost 1.6 ± 0.08 kg/d for the first week they were turned to grass compared with EXPER heifers that gained 0.88 ± 0.08 kg/d (P < 0.0001). This resulted in a linear (P < 0.01) BW gain among EXPER heifers and a quadratic (P = 0.04) BW gain among NIV heifers. In Exp. 2, EXPER heifers had increased ADG (P < 0.01; 0.58 ± 0.03 kg/d) from AI to pregnancy diagnosis and more (P = 0.04) became pregnant to AI (59.4%) compared with NIV heifers (0.21 ± 0.03 kg/d and 49.1%). In summary, transitioning naive heifers to pasture resulted in BW loss during the first week after movement, and if this transition occurred immediately following AI, pregnancy success to AI was reduced.