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Summary
Nonpuberal estrus (NPE), occurring without luteal tissue development, is common in heifers nearing puberty. Heifers with a puberal first estrus were older and showed higher progesterone levels beforehand.
Area of Science:
- Reproductive endocrinology
- Animal science
- Veterinary medicine
Background:
- Puberty onset in heifers is crucial for reproductive success.
- Understanding estrous cycles and luteal function is key to managing breeding programs.
- Nonpuberal estrus (NPE) is characterized by estrous behavior without subsequent luteal tissue development.
Purpose of the Study:
- To determine the frequency of nonpuberal estrus (NPE) in Simmental X Hereford-Brahman heifers.
- To compare characteristics of heifers exhibiting NPE versus those with luteal development after first estrus.
- To investigate the relationship between initial body weight and puberal estrus.
Main Methods:
- 43 heifers were monitored weekly for estrus and blood sampled.
- Blood samples were analyzed for serum progesterone (P4) concentrations via radioimmunoassay.
- Daily sampling occurred around observed estrous behaviors to confirm luteal function.
Main Results:
- 62.8% of heifers exhibited NPE, while 37.2% had luteal development after first estrus.
- Heifers with a puberal first estrus were older (376 days) than those with NPE (334 days).
- Puberal estrus heifers showed higher pre-estrus serum P4 concentrations (2.5 ng/mL) compared to NPE heifers (1.2 ng/mL).
Conclusions:
- Nonpuberal estrus is a common phenomenon in heifers approaching puberty.
- Puberal first estrus is associated with older age and elevated pre-estrus progesterone levels.
- Initial body weight may influence the timing of puberal estrus, though not statistically significant in this study.