Anti-Müllerian Hormone (AMH): a biomarker for the ovarian reserve, ovarian function and fertility in dairy cows

This review summarizes studies we conducted to test the hypothesis that size of the ovarian reserve (number of healthy follicles and oocytes in ovaries) positively impacts ovarian function and fertility in cattle. Key results, primarily in Bos Taurus dairy cattle, show that antral follicle count (AFC) during follicular waves is highly variable between individuals, but very highly repeatable within individuals. Cycling heifers with low (≤ 15 follicles ≥ 3 mm, ~20% of a herd) vs a high AFC (≥ 25, ~20% of a herd) have a smaller ovarian reserve, higher FSH but lower AMH, androstenedione, estradiol and progesterone concentrations. Moreover, cattle with low AFC have a thinner endometrium, decreased response of granulosal, thecal or luteal cells to FSH or LH and a poorer response to superovulation compared to cattle with high AFC. Interestingly, cows with a very high AFC as heifers have reduced fertility, fewer lactations and shorter herd longevity; whereas cows with a low vs intermediate AFC have reduced fertility, fewer lactations and shorter herd longevity. AMH concentrations are static within individuals but highly positively correlated with AFC, but fertility is not correlated with circulating AMH concentration in heifers and dairy cows with low vs a higher AMH as heifers have reduced fertility and a shorter herd longevity. AMH concentrations in dairy heifers is a moderately heritable trait (36%), and negatively impacted by inadequate maternal nutrition during early pregnancy or high maternal somatic cell count. We conclude that genetic or environmental manipulations of AMH could enhance size of the ovarian reserve and ovarian function, thereby improving fertility, response to superovulation and longevity in dairy cows.