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1724
Serum anti-mullerian hormone as an indicator of fertility in Katahdin ewes
Individual ewes vary in reproductive performance parameters, such as age at first lambing, twinning rate, and ability to breed during off-season. Previous studies indicate that anti-mullerian hormone (AMH) in circulation reflects the total pool of follicles within the ovaries, and is positively correlated with fertility. In this study, retrospective analysis was used to determine if AMH could serve as an indicator of ewe fecundity. Serum samples were collected from 152 Katahdin ewes ranging from 0.5 to 7 yr of age, their pregnancy and lambing rate recorded, and estimated breeding values obtained from the National Sheep Improvement Program. Anti-mullerian hormone was analyzed using an equine and ovine AMH enzyme-linked immunosorbent assay (ELISA) kit. Continuous variables were analyzed by ANOVA and categorical data by chi-squared, using JMP® (SAS institute) software. Serum AMH ranged from 0.04 to 0.39 ng/mL, with mean of 0.17 ng/mL. Mean serum AMH was similar (P = 0.37) across all ewe age groups (< 1, 1 to 2, 2 to 3 and > 4 yr). The distribution of AMH concentrations was divided into quartiles (AMH Q1 through Q4, with the Q1 lowest and Q4 the highest). There was no relationship (fall; P = 0.65; summer; P = 0.11) between AMH quartile and mean number of lambs born (NLB) from fall and summer breeding. No correlation (P = 0.39) was found between individual estimated breeding value for NLB and serum AMH concentration. A significant correlation (P < 0.01; r = 0.411) existed between mean NLB per individual ewe during summer (0.79) and fall (1.44). Overall pregnancy rate was higher (P <0.01) for fall (79%) than summer (48%) breeding. It was noted that 25/68 (36.8%) of ewes < 2 yr of age fell into the lowest AMH quartile (Q1) as compared with 13/84 (15.5%) for older ewes. Similarity of AMH among different ewe age groups and a lower percentage of older ewes in AMH Q1 could reflect particular selection criteria.
Keywords: Anti-mullerian hormone, ewes, reproductive performance