Title: Pregnancy Rates of Beef Heifers Bred Either on Puberal or Third Estrus
Abstract: The objective of this study was to determine if pregnancy rates (PR) differed between beef heifers bred to fertile bulls on either their puberal (E1, n = 89) or third (E3, n = 67) estrus. Heifers were obtained from two lactations (Manhattan, LI; and Miles City, L2), and the experiment was conducted at Miles City. Heifers were assigned randomly within location to either E1 or E3. Heifers were fed to gain .56 kg•head−1•d−1 and observed twice daily for estrus. After exhibiting first estrus (puberty) and breeding, each heifer in E1 was palpated rectally on d 6, 9 and 12 ± 1 d (estrus = d 0) for the presence of a corpus luteum, and a venous blood sample was collected for assay of progesterone by radioimmunoassay. Heifers in E3 were palpated and bled on the same schedule as heifers in E1 after first estrus and after being bred to a fertile bull at third estrus. Pregnancy rates were determined by rectal palpation at approximately 38 d post-breeding. Location of origin did not affect (P>.10) weight at puberty or weight at breeding; however, heifers from L1 were younger (P<.05) than heifers from L2 at puberty and breeding. Pregnancy rates were 57 and 78% for heifers in E1 and E3, respectively (P<.05). Weight at breeding did not influence (P>.10) pregnancy rates. The probability of heifers in E1 becoming pregnant increased (P<.05) with increasing age, while age was not a factor (P>.10) for heifers in E3. These results indicated that fertility of puberal estrus in beef heifers is lower than third estrus. Higher fertility of third estrus may be related to maturational changes associated with cycling activity.
Publication Year: 1987
Publication Date: 1987-09-01
Language: en
Type: article
Indexed In: ['crossref', 'pubmed']
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Cited By Count: 242
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