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Nonpuberal Estrus in Beef Heifers^{1, 2, 3, 4,}

Texas A&M University Agricultural Research and Extension Center, Overton 76834

Abstract

The frequency of occurrence of behavioral estrus without subsequent development of functional luteal tissue (termed nonpuberal estrus, NPE), was determined in 43 Simmental x Hereford-Brahman heifers. Blood samples were collected weekly from the start of the study to first behavioral estrus and then daily from d 1 (d 0 = estrus) through d 14 following first and subsequently observed estrous behaviors. All blood samples were analyzed for serum progesterone (P₄) concentrations by radioimmunoassay. More heifers (62.8%) exhibited NPE than had luteal development after their first behavioral estrus (37.2%). There was a tendency for fewer light-weight heifers (240 kg at the start of the experiment) to exhibit a puberal first estrus compared with the heavyweight (>240 kg at the start of the experiment) heifers (31.2% vs 68.8%, respectively; P=.12). Heifers that had a puberal first estrus were older (376 ± 12 d vs 334 ± 9 d, P<.05) compared with heifers that had NPE. Weight at first behavioral estrus was similar between heifers that had a puberal first estrus and those that had NPE (298 ± 8 kg and 289 ± 6 kg, respectively). More heifers that had a puberal first estrus also had an elevation in serum P₄ concentrations before that first estrus (64.3% vs 20.0%, P<.05), and the serum P₄ elevation was greater (2.5 ± .4 ng vs 1.2 ± .1 ng, P<.05) than heifers that had NPE. We have concluded from these results that NPE is a common occurrence in heifers approaching puberty. Further, observation of behavioral estrus should not be the sole criterion for puberty in heifers.

¹ Journal Paper TA 21113, Texas Agr. Exp. Sta.

² The authors express sincere thanks to fellow colleagues, T. C. Nelsen, R. E. Short, D. A. Phelps and R. B. Staigmiller at Miles City, MT, for their help with the analysis and presentation of this data.

³ The authors also thank D. A. Neuendorff for expert technical assistance.

⁴ This study was a contribution to Western Regional Project W-112, Reproductive Performance in Domestic Ruminants.

⁵ Address reprint requests to: Dept. of Vet. Physiol. Sci., Univ. of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 0W0.