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Title: Association between age and ovarian morphology in crossbred beef cows

item Cushman, Robert - Bob

Submitted to: Midwestern Section of the American Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: 11/8/2007
Publication Date: 9/20/2008
Citation: Cushman, R.A. 2008. Association between age and ovarian morphology in crossbred beef cows [abstract]. Journal of Animal Science. 86 (E-Supplement 3):106-107 (Abstract #231).

Interpretive Summary:

Technical Abstract: Depletion of the ovarian reserve is associated with reproductive senescence in mammalian females. In women, the number of antral follicles detectable by ultrasound varies greatly, but decreases with age, resulting in decreased fertility. Similarly, the number of follicles present in the bovine ovary varies greatly among cows at all ages, and a large ovarian reserve positively influences calving interval and ovulatory response to exogenous gonadotropins. The present study tested the hypothesis that antral follicle counts (AFC) decrease as beef cows age. Pairs of ovaries were collected from crossbred beef cows (n = 176; 0 to 9 years of age) at necropsy, all visible antral follicles were counted, and the ovaries were weighed. Antral follicle counts and total ovarian weight (TOW), defined as the sum of the weight in grams of the two ovaries, were regressed on age. There was a quadratic effect of age on AFC such that AFC increased until 5 years of age and decreased thereafter (AFC = 16.7 + 11.5(year) - 1.28(year x year); P < 0.001, r-square = 0.20). In contrast, total ovarian weight continued to increase linearly through 9 years of age (TOW = 2.37 + 2.4(year); P < 0.001, r-square = 0.63). There was a positive relationship between follicle count and ovarian weight (P < 0.001; r-square = 0.26). Within an animal, ovarian phenotypes were highly correlated, resulting in a strong positive relationship between the number of follicles in the left ovary and the number of follicles in the right ovary (P < 0.001, r-square = 0.89). The weight of the left ovary was also highly correlated with the weight of the right ovary (P < 0.001, r-square = 0.78). Therefore in beef cows, antral follicles begin to decline at 5 years of age. The continued increase in ovarian weight through 9 years of age suggests either that ovarian mass continues to increase with age or that cows with larger ovaries remain in the production herd longer, possibly due to a larger ovarian cortical mass and a greater number of follicles at a young age.