The lactating dairy cow is not as fertile as she once was. And the likely culprit is not going to go away. But wait, there’s hope for ol’ Bessie. This story will outline the likely reasons for the decline of dairy cow fertility and discuss reproductive management methods to help alleviate this problem.
Infertility of the lactating dairy cow continues to be a critical problem limiting profitability and sustainability of dairy farms [1, 2]. Reproductive performance of lactating dairy cows is dependent upon service rate (or estrus detection rate), fertility of the service sire, and maternal fertility. Service rate can be controlled utilizing Ovsynch technology (Figure 1; [3, 4]). The majority of dairy producers in the U.S. regulate time to first and subsequent artificial inseminations (AI) with Ovsynch technology . High fertility sires can be chosen utilizing the USDA-AIPL summaries sire conception rates. Yet, maternal fertility, defined as the mother’s ability to ovulate a competent oocyte and provide an oviductal and uterine environment capable of fertilization and complete embryonic and fetal development, continues to be the key limiting factor for successful reproductive performance in lactating dairy cows.
Conception rates of lactating cows are approximately 30 percent compared to 60 percent for virgin dairy heifers [4, 6] when inseminated following a detected estrus. Increasing conception rates of lactating cows to that of heifers would allow producers to employ the most profitable calving interval strategies for cows with different milk production levels. Aspects of maternal fertility that are limiting to conception and embryonic/fetal development are becoming better understood. Modifications to Ovsynch also are being developed to enhance maternal fertility while continuing to control service rate.
Why is Fertility Compromised in Lactating Dairy Cows?
Circulating concentrations of steroid hormones significantly change following the transition from heifer to lactating cow. Serum concentrations of progesterone and estrogen are reduced by about 50 percent in cows compared with heifers, even though the corpus luteum (CL; the structure in the ovary that produces progesterone) and ovulatory follicle (the structure in the ovary that produces estrogen and ovulates the egg) are larger in cows.
Duration of estrus also is longer in heifers. This is likely due to greater amounts of estrogen in circulation compared with cows. The difference in progesterone appears to influence follicular growth by prolonging the age of the ovulatory follicle. Therefore, oocytes (eggs) from the ovulatory follicle of lactating dairy cows may have a lesser chance to be fertilized or develop into a competent embryo compared with oocytes of heifers which have greater concentrations of progesterone .