Repeat-Breeder Females in Beef Cattle: Influences and Causes1

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