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U.S. Department of Agriculture3,4,, Clay Center, NE 68933
Abstract
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.
1 The authors are grateful to Dr. R. Fries for examining metaphase preparations; to Betty Petitjean and Suzanne Annis for technical assistance; to Gary Peterson, Becky Gerlach, Gale Johnson, Margie McAlhany, Jennie Stora, Dave Janssen, Roy Lansford and Roger Stokes for the care and breeding of the cattle; and to Linda Parnell for stenographic work. Cooperation of the Nebraska Agr. Exp. Sta., Univ. of Nebraska, Lincoln, is acknowledged.
2 Presented in part at the 14th Meeting of the Mid-western Section of ASAS June 9 and 10, 1981, Lincoln, Nebraska, and at the 10th Inter. Congr. Anim. Reprod. Artif. Insem., June 10 to 14, 1984, Urbana, IL.
3 Mention of a trade name, proprietary product or specific equipment does not constitute a guarantee or warranty by the USDA and does not imply its approval to the exclusion of other products that may also be suitable.
4 Agricultural Research Service, Roman L. Hruska U.S. Meat Animal Research Center.
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