Evidence That Mammary Gland Infection/Injury During Pregnancy in Dairy Cows May Have a Negative Impact on Size of the Ovarian Reserve in Their Daughters.

Abstract

The effect of disease on maternal environment, which has a crucial role in embryo development and subsequent health of offspring, has not been examined extensively in cattle. Therefore, the purpose of this study was to determine if a persistent mammary gland infection such as mastitis and correspondingly a chronically high (> 200,000 units) somatic cell count (SCC) in milk of pregnant dairy cows has a potential negative impact on size of the ovarian reserve (total number of healthy follicles and oocytes in ovaries) and potentially fertility of their offspring. This study was conducted at Green Meadow Farms Inc. in Elsie, MI and used 192, 12-mo-old Holstein heifers. Each animal was injected with 2 injections of prostaglandin F2 alpha (PG) spaced 11 d apart. To assess relative size of the ovarian reserve in each heifer, a single blood sample was removed 4 d after the 2nd PG injection and assayed for concentration of anti-Müllerian hormone (AMH), and ovarian ultrasonography was used to determine number of follicles ≥ 3 mm in diameter and ovary size. Results confirm previous observations that AMH concentrations were highly variable among animals but positively correlated (P < 0.001) with both ovary size and number of antral follicles. To determine if a chronic mammary gland infection during pregnancy of dairy cows was associated with alterations in AMH concentrations and correspondingly size of the ovarian reserve in their offspring, we next tested whether number of SCC measurements > 200,000 for each heifer's dam was associated with alterations in the serum AMH concentration in each heifer. Number of SCC measurements > 200,000 per individual cow is an accurate index of recurrent udder infections, injury and/or inflammation. A total of 5 to 7 measurements of SCC were made for each dairy cow beginning 2 mo before pregnancy and continuing throughout pregnancy. Number of SCC measurements > 200,000 ranged from 0 to 5 per individual cows, thus cows were separated into groups based on their number of SCC measurements > 200,000. Cows with 4 or 5 SCC measurements > 200,000 were ~2 years older (P < 0.01, 6.1 vs 4.4 yrs old) and tended (P < 0.09) to produce less milk compared with cows that had 0 to 3 SCC measurements > 200,000. Results showed that the daughters of cows with 4 and 5 SCC measurements > 200,000 also had markedly lower (P < 0.02) AMH concentrations as young adults compared with daughters of the cows with 0 to 3 SCC measurements > 200,000. Although mechanisms are unclear, our results imply that a chronic mammary infection or injury during pregnancy of older cows (as predicted by a high number of SCC measurements > 200,000) is associated not only with low milk production, but also with diminished size of the ovarian reserve and perhaps reduced reproductive performance (fertility and reproductive lifespan) of their daughters. Research supported by USDA-NRI 2004-01697, 2007-01289 to JJI. (poster)