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ARS Home » Plains Area » Miles City, Montana » Livestock and Range Research Laboratory » Research » Publications at this Location » Publication #293819
Title: Effect of pubertal status and number of estrous cycles prior to the breeding season on pregnancy rate in beef heifers

Author
item VRASPIR, R - University Of Nebraska
item SUMMERS, A - University Of Nebraska
item Roberts, Andrew
item FUNSTON, R - University Of Nebraska

Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/15/2013
Publication Date: 6/21/2013
Citation: Vraspir, R.A., Summers, A.F., Roberts, A.J., Funston, R.N. 2013. Effect of pubertal status and number of estrous cycles prior to the breeding season on pregnancy rate in beef heifers. Western Section of Animal Science Proceedings. 64:116-120.

Interpretive Summary: Three experiments were conducted to evaluate whether pubertal status prior to breeding influences pregnancy rate in beef heifers. Records were collected at West Central Research and Extension Center, North Platte, NE from 2002 to 2011 (Exp. 1; n = 1,005) and Gudmundsen Sandhills Laboratory, Whitman, NE from 1997 to 2011 (Exp. 2; n = 1,253). Heifers in Exp. 1 and 2 were classified as either being pubertal or non-pubertal at the start of breeding. In Exp. 3, (n = 156) heifers were classified by number of estrous cycles (0, 1, 2, 3, or = 4) exhibited prior to breeding. In Exp. 1 and 2, pubertal heifers were heavier and older at start of breeding and had greater pregnancy rates (94 vs. 88 ± 2%; 90 vs. 82 ± 2% in Exp. 1 and 2, respectively) than non-pubertal heifers. Pubertal heifers also tended to have more pregnancies from AI (62 vs. 56 ± 4%), produced more calves within the first 21 d of calving, and weaned older, heavier calves than heifers that had not reached puberty. In Exp. 3, heifers pubertal prior to the breeding season had greater pregnancy rates (85 ± 8%) than non-pubertal heifers (68 ± 8%) and pregnancy rate tended to increase with increasing the number of estrous cycles (68, 81, 91, 93, and 82 ± 9% for 0, 1, 2, 3, or = 4 estrous cycles, respectively). Second season pregnancy rate was greater for heifers that were pubertal prior to first breeding than non-pubertal, and was greatest for heifers that had = 2 estrous cycles before first breeding season (80, 87, 100, 97, and 98 ± 8% second season pregnancy rate for 0, 1, 2, 3, or = 4 estrous cycles, respectively). Pregnancy rate was greater for heifers achieving puberty prior to breeding, which was influenced by age and BW. However, earlier onset of puberty did not significantly improve first pregnancy rates.

Technical Abstract: Three experiments were conducted to evaluate whether pubertal status prior to breeding influences pregnancy rate in beef heifers. Records were collected at West Central Research and Extension Center, North Platte, NE from 2002 to 2011 (Exp. 1; n = 1,005) and Gudmundsen Sandhills Laboratory, Whitman, NE from 1997 to 2011 (Exp. 2; n = 1,253). Heifers in Exp. 1 and 2 were classified as either being pubertal or non-pubertal at the start of breeding. In Exp. 3, (n = 156) heifers were classified by number of estrous cycles (0, 1, 2, 3, or = 4) exhibited prior to breeding. In Exp. 1 and 2, pubertal heifers were heavier (P = 0.04) and older (P < 0.07) at start of breeding and had greater (P < 0.01) overall pregnancy rate (94 vs. 88 ± 2%; 90 vs. 82 ± 2% in Exp. 1 and 2, respectively) than non-pubertal heifers. Pubertal heifers also tended (P = 0.08) to have greater AI pregnancy rate (62 vs. 56 ± 4%, Exp. 1), produced more calves within the first 21 d of calving (P < 0.01), and weaned older (P = 0.05), heavier (P < 0.01) calves than heifers that had not reached puberty (Exp. 2). In Exp. 3, heifers pubertal prior to the breeding season had greater (85 ± 8%, P = 0.05) pregnancy rates (68 ± 8%) than non-pubertal heifers and pregnancy rate tended (P = 0.15) to be influenced by the number of estrous cycles (68, 81, 91, 93, and 82 ± 9% for 0, 1, 2, 3, or = 4 estrous cycles, respectively). Second season pregnancy rate was greater for heifers reaching puberty prior to first breeding (97 vs. 80 ± 7%, P < 0.01) and was influenced (P = 0.03) by the number of estrous cycles, where heifers having = 2 estrous cycles had greater pregnancy rate (80, 87, 100, 97, and 98 ± 8% for 0, 1, 2, 3, or = 4 estrous cycles, respectively) than non-pubertal heifers. Pregnancy rate was greater for heifers achieving puberty prior to breeding, which was influenced by age and BW. However, earlier onset of puberty did not significantly improve first pregnancy rates.