The effects of bull exposure and lasalocid on the development of replacement beef heifers
Autor: | D. R. Ward, R. P. Del Vecchio, W. P. Sutherland, W. P. McCaughey, J. A. Small |
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Rok vydání: | 2000 |
Předmět: | |
Zdroj: | Canadian Journal of Animal Science. 80:615-624 |
ISSN: | 1918-1825 0008-3984 |
Popis: | At weaning in the fall, crossbred heifers (n = 224), born in either the winter (January–February) or spring (March–April), were assigned on the basis of age, sire-breed and body weight to one of two similar winter housing facilities (with or without sterilized bulls), and to one of two forage-based (87%) diets (with or without lasalocid, 200 mg d−1) within each housing facility. Observations for estrus were made twice daily. Timed AI (66 h after PGF2α) was used to breed heifers for the first time at 14 mo of age. Plasma progesterone concentrations were used to confirm estrus/ovulation and to determine the PGF2α response rate. Bull exposure advanced puberty in winter-born heifers, but delayed puberty in spring-born heifers (P ≤ 0.029). Similarly, timed AI pregnancy for winter-born heifers was higher with than without bull exposure (58.9 vs. 32.5 ± 5.3%; P = 0.017) while the opposite occurred for the spring-born group (27.1 vs. 59.1 ± 4.7%; P |
Databáze: | OpenAIRE |
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