ARS | Publication request: Reproductive Tract Differences in Repeat-Breeder Cows

Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: March 7, 2010
Publication Date: July 1, 2010
Citation: Cushman, R.A., Miles, J.R., Echternkamp, S.E. 2010. Reproductive Tract Differences in Repeat-Breeder Cows [abstract]. Journal of Animal Science. 88 (E-Supplement 2):220. (Abstract #168).

Technical Abstract: The objective of the study was to evaluate the reproductive tracts of repeat-breeder cows that failed to calve in two consecutive years compared to cows that calved regularly. The hypothesis was that repeat-breeder cows would have smaller reproductive tracts and fewer antral follicles. Beef cows ranging from 3 to 13 years of age were classified as repeat-breeder (n = 37) or control (n = 34) cows. Cows were examined twice daily for behavioral estrus and artificially inseminated 12 h after observed estrus. Three to 8 days after estrus cows were slaughtered, reproductive tracts were recovered and transported to the laboratory. All visible antral follicles were counted, ovaries were measured and weighed, and the diameter of the endometrium was measured in a subset of cows (n = 44) at the thickest point on the horn ipsilateral to the corpus luteum. The uterus was flushed and embryos were collected. Granulosa cells from small antral follicles (< 5 mm) were pooled and frozen for real-time RT-PCR analysis. Reproductive traits were analyzed using the GLM or GLIMMIX procedure of SAS with group as the independent variable and day and age as co-variates. Repeat-breeder cows had smaller ovaries (P =< 0.006) when corrected for day (P > 0.13) and age (P > 0.17) and fewer follicles (P = 0.02) when corrected for day (P = 0.0009) and age (P = 0.42). There was no difference in endometrial diameter (P = 0.46), or granulosa cell anti-Mullerian Hormone (P = 0.87) or Pentraxin 3 (P = 0.63) mRNA levels between repeat-breeder and control cows when corrected for day (P > 0.16) and age (P > 0.44), but embryo recovery rate tended to be greater in control cows (P = 0.06). Regression analysis identified a positive relationship of antral follicle count to endometrial diameter (P = 0.009) and ovarian size (P < 0.0001). Fewer ovarian antral follicles in repeat-breeder cows may contribute to reduced fertility. The positive relationship between antral follicle count and endometrial diameter suggests that the number of ovarian follicles may influence proliferation of the endometrium in the early luteal phase of the cow.