Fertility in dairy cows is determined by the establishment of pregnancy, which involves a series of events such as uterus involution, estrous cycle re-establishment, ovulation, fertilization, and progesterone production. Genetic selection for fertility is based on reducing the time from calving to pregnancy, but the importance of individual components may vary depending on the reproductive management system used. A better understanding of the genetics of these components is needed for consistent performance across different systems.
- Dairy cow selection indices have changed markedly in the past 25 yr
- This situation is not unlike that found in the swine industry, where selection for litter size resulted in the creation of the “highly prolific sow” where 40% of litters have more live born than teats available for nursing (Kraeling and Webel, 2015)
- Genetic selection for fertility as practiced today is leading to the rapid improvement in reproductive performance of dairy cattle
- Refined phenotypes may lead to the creation, evaluation, and implementation of new traits that place selection pressure on estrous cyclicity, estrus expression, and absence of silent ovulation
- These new traits will need to be evaluated relative to existing traits to determine whether they provide additional value beyond direct selection for Days open (DO)
- Timed artificial insemination (AI) programs do not invalidate DO but it is necessary to understand the effect of timed AI (TAI) on the components of DO
Daily BCS measured on 2 individual cows, A and B, using an automated BCS camera (DeLaval, Tumba, Sweden). Two cows with identical beginning BCS are shown (scale 1 to 5; thin to obese). Cow A lost >0.5 points during the first 120 d, whereas cow B lost approximately 0.1 point. Selecting against excessive BCS loss early postpartum improves fertility (
M.C. Lucy (2019) reports that dairy cow selection indices have changed in the past 25 years, with a focus on improving fertility. Genetic selection for fertility has led to improvements in reproductive performance. The text discusses various factors that can affect fertility, including health, hormone levels, and immune function. Genetic selection for disease resistance and body condition score can improve fertility. The interval from calving to conception, known as “days open,” is an important fertility trait. Timed artificial insemination programs can control the timing of insemination but may introduce noise into fertility evaluations. Genetic selection based on data from timed artificial insemination cows can improve fertility. The text also discusses the advantages and disadvantages of genetic selection for fertility, as well as the challenges in measuring and phenotyping estrus. Further research is needed to understand the correlation between activity increases and mounting behavior during estrus. The text concludes by mentioning the challenges faced in the swine industry when selecting for litter size.
The authors suggest that this review discusses the components of dairy cow fertility, how fertility traits are addressed, the impact of management systems on genetic selection for fertility, potential new fertility traits for genetic selection, and future research directions.
Lucy, M. C. (2019). Symposium review: Selection for fertility in the modern dairy cow—Current status and future direction for genetic selection. Journal of Dairy Science, 102(4), 3706–3721.
