Reproductive Challenges of High Producing Dairy Cows

Within a dairy herd, total milk production is determined by the proportion of cows producing milk at any given time and the level of milk production of the individual cows within the herd. Improving reproductive efficiency helps to maintain the maximal number of cows producing milk at optimal levels. Reproductive efficiency in dairy cattle currently is suboptimal primarily due to four factors: 1) poor detection and expression of estrus behavior, 2) a high incidence of anovular cows near the end of the voluntary waiting period, 3) poor conception rates of lactating cows, and 4) a high incidence of pregnancy loss for cows that conceive. Over the past decade, the development of hormonal protocols that synchronize follicular development, luteal regression, and ovulation thereby allowing for timed AI without the need to rely on visual estrus detection has helped to overcome factor 1 and to some extent factor 2 above, and development of systematic resynchronization systems for cows failing to conceive to an AI service is underway. Regarding factor 3, the body of scientific literature supports the notion that fertility of lactating dairy cows has decreased over the past 50 years. Factor 3 is closely related to factor 4 because fertility assessed at any point during pregnancy is a function of both conception rate and pregnancy loss. Development of strategies that reduce the rate of embryonic loss after AI will therefore result in an increase in conception rate. A final factor that negatively affects reproduction in dairy cattle is twinning, and the observation that twinning has increased in dairy cattle over time suggests a concurrent change in one or more of these causative factors during this same period. Management strategies need to be developed to avoid or mitigate the negative effects of twinning in dairy herds, especially if twinning rates continue to increase. Future development of reproductive management strategies during the next decade must be focused on both the applied and basic aspects of understanding and overcoming the limitations imposed by these factors.