Developmental and reproductive characteristics of beef heifers classified by pubertal status at time of first breeding

Authors: Roberts, Andrew; GOMES DA SILVA, ALINE - Universidade Federal De Mato Grosso; SUMMERS, ADAM - New Mexico State University; Geary, Thomas; FUNSTON, RICK - University Of Nebraska

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/2017
Publication Date: 12/8/2017
Publication URL: http://handle.nal.usda.gov/10113/6471077
Citation: Roberts, A.J., Gomes Da Silva, A., Summers, A.F., Geary, T.W., Funston, R.N. 2017. Developmental and reproductive characteristics of beef heifers classified by pubertal status at time of first breeding. Journal of Animal Science. 95(12):5629-5636. doi:10.2527/jas2017.1873.

Interpretive Summary: Current industry guideline for replacement heifer development is to implement feeding strategies to maximize proportion of heifers attaining puberty by start of breeding to result in high pregnancy rates. However, feeding to maximize proportion pubertal by start of breeding diminishes selection against later maturing animals which may also be less desirable for other production traits. Data from over 3600 heifers collected for 10 or more years at the West Central Research and Extension Center, North Platte, NE, Gudmundsen Sandhills Laboratory, Whitman, NE, and USDA, ARS, Fort Keogh Livestock and Range Research Laboratory, Miles City, MT, were retrospectively analyzed to evaluate growth and reproductive performance of beef heifers classified by pubertal status prior to first breeding. Heifers that failed to achieve puberty by start of breeding were born later, grew slower based on weight and carcass characteristics, were less efficient in feed to gain, had lower pregnancy rates and produced lighter calves than heifers that were pubertal by start of breeding. Based on these results, implementing feeding strategies to increase proportion of heifers that achieve puberty prior to first breeding could result in propagation of undesirable characteristics.

Technical Abstract: Data collected for 10 or more years at the West Central Research and Extension Center, North Platte, NE (n = 1,104); Gudmundsen Sandhills Laboratory, Whitman, NE (n = 1,333); and USDA, ARS, Fort Keogh Livestock and Range Research Laboratory, Miles City, MT (n = 1,176) were retrospectively analyzed to evaluate growth and reproductive performance of beef heifers classified by pubertal status prior to first breeding. Concentrations of progesterone in serum from 2 blood samples collected 9 to 11 d apart prior to start of the breeding season were used to classify heifers as pubertal (progesterone = 1.0 ng/mL in 1 or both samples) or non-pubertal (progesterone < 1.0 ng/mL in both samples). Average date of birth was earlier (P < 0.06) and proportion born in the first 21 d of the calving season was 10 to 20 percentage points greater for heifers that were pubertal at start of breeding compared with heifers not pubertal by start of breeding. Heifers that were pubertal by start of breeding were 7 to 10 kg heavier (P < 0.01) and 1 cm taller (P < 0.01) at weaning than heifers not pubertal by start of breeding. Differences in body weight persisted through start of breeding to pregnancy diagnosis. Heifers that achieved puberty by start of breeding had greater (P < 0.05) feed intake and G:F during post-weaning development, and had greater (P < 0.01) loin muscle are and fat thickness over the loin at approximately 1 yr of age when compared with heifers not pubertal by start of breeding. Heifers that achieved puberty before start of breeding had greater (P < 0.01) gain from birth to weaning, but slower (P < 0.1) rates of gain from start of breeding through time of pregnancy diagnosis. Pregnancy rate was greater (P < 0.01) for heifers that were pubertal at start of breeding. In heifers that became pregnant, those that were pubertal before start of breeding calved earlier (P < 0.01) with a greater (P < 0.01) percentage calving in first 21 d of calving than heifers not pubertal at start of breeding. Calves from heifers that achieved puberty before start of breeding were heavier at weaning (P < 0.01) than calves from heifers that had not achieved puberty by start of breeding. In summary, heifers that failed to achieve puberty by start of breeding were less desirable for several traits evaluated. Based on these results, implementing feeding strategies to increase proportion of heifers that achieve puberty prior to first breeding could result in propagation of undesirable characteristics.