Optimizing the genetics of dairy cattle has long been a focus for researchers, producers and the dairy industry, driven by the dual goals of enhancing milk yield and improving overall herd fertility. As global demand for dairy products continues to rise, the pressure to produce high-yielding cows has been increasing. However, this pursuit often brings with it a significant challenge: the historical trade-off between high milk production and reproductive efficiency.
For proficient outputs, modern dairies using year-round calving require well-functioning reproductive programs that enable sufficient replacement rates, optimal milk yields and a consistent income all year long.
Infertility in lactating dairy cows represents a major challenge for dairy producers. Reduced reproductive performance has been associated with declines in economic returns due to reduced milk yield per cow per day, lower production of replacement heifers and increased culling.
Historically, high milk production has been associated with a decrease in the fertility of lactating dairy cows. This decrease in fertility could be due to genetic factors, as other characteristics (like milk production and conformation traits) were prioritized over fertility in the selection for dairy cattle.
Increased individual milk production has been achieved in part due to improvements in management as well as intensive genetic selection. This increase in milk production has also been shown to be associated with reduced reproductive performance, which has become a major concern for farmers and the dairy industry. However, the interpretation of observed associations between greater milk yield and poor reproductive performance may require critical evaluation, as it has been shown to be a complex relationship. Additionally, inappropriate management practices of high-producing dairy cows may significantly contribute to the inability of dairy cows to conceive and maintain pregnancy, regardless of milk yield.
This challenge poses a crucial question for the dairy industry: Can we breed cows that excel in both milk production and fertility? Advances in genetic research, coupled with the integration of precision dairy technologies, offer promising pathways to achieve this balance. By leveraging genomic selection, producers can now identify and propagate desirable traits more accurately than ever before. Furthermore, the inclusion of fertility-related traits in breeding programs is gaining traction, aiming to create a more sustainable and profitable dairy herd.
The objective of a study conducted at the University of Guelph – Ridgetown Campus was to assess the relationship between genomic daughter pregnancy rate (gDPR), genomic merit for milk production (gMilk) and pregnancy at first A.I. and pregnancy losses (PL). A cohort of 6,739 Holstein cows (1st lactation: n = 2,636; 2nd lactation: n = 2,057; 3rd lactation: n = 2,046) were enrolled in the study. These cows were subjected to a timed A.I. protocol to aim first service around 60 days in milk. Pregnancy diagnoses was conducted at days 32 and 60 post-A.I. using ultrasonography. Pregnancy loss was defined as a pregnant cow on day 32 that was nonpregnant on day 60. For the genetic evaluation, hair samples were collected from the tail switch and cows were genotyped using a SNP platform.
Cows were grouped into four categories based on their median for the genomic daughter pregnancy rate (gDPR) and genomic merit for milk production (gMilk): low gDPR and low gMilk (LgDPR_LgMilk), high gDPR and low gMilk (HgDPR_LgMilk), low gDPR and high gMilk (LgDPR_HgMilk), and high gDPR and high gMilk (HgDPR_HgMilk).
The results indicated a mild negative correlation between gDPR and gMilk. Pregnancy per A.I. was significantly influenced by the combination of gDPR and gMilk, with higher pregnancy rates observed in groups with high gDPR (Figure 1). Additionally, cows with higher gDPR exhibited lower pregnancy loss rates compared to the low gDPR groups. Interestingly, milk production at day 60 was highest in cows with high gMilk, regardless of their gDPR status (Figure 2).
These findings suggest that selecting for both high gDPR and high gMilk can potentially enhance both reproductive efficiency and milk production in dairy herds. The study provides compelling evidence that genetic markers such as gDPR can be instrumental in improving reproductive outcomes without compromising milk yield, paving the way for more balanced and sustainable breeding strategies in dairy cattle.
References omitted but are available upon request by sending an email to an editor.
