Repeat-Breeder Females in Beef Cattle: Influences and Causes1,2
作者： R. R. Maurer , S. E. Echternkamp
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摘要: Straightbred and crossbred heifers (165) cows (241) that were nonpregnant after exposure to fertile bulls for two consecutive breeding periods of 45 60 d (repeat breeders) contemporary (102) had produced a calf in the previous calving season (controls) placed with observed mating. Repeat-breeder control females slaughtered at 2 51 postmating. Data accumulated over 4 yr. From records, repeat breeders more (P<.05) difficulty than controls. Percentages anatomical aberrations or anovulation 10.9 3.6, 0 2.9, respectively, repeatbreeder females. Repeat fewer (P<.01) normal embryos higher nonreeovery rates an embryo oocyte Precentages normal, degenerate, unfertilized, nonrecoveries 42.3, 8.9, 8.0 40.8, 76.8, 9.1, 6.0 8.1 controls, respectively. 1-to 3-ram follicles controls (25.4 36.5, respectively). On 6 postmating, (P<.O1) serum progesterone concentrations repeat-breeders (2.7 vs 1.8 ng/ml, Chromosome found lymphocytes 19 133 (14.3%) repeat-breeders. Increased reproductive tract, increased anovulations, lower recovery rate embryo, 6, 1to 3~mm chromosomal abnormatilities are possible causes fertility repeat-breeder (
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