U.S. dairy producers have had access to sire conception rate data as part of sire proofs since 2008. SCR is based on actual conception rates observed on cows in the first through fifth lactation, and first through seventh AI service. For Holsteins, sires need more than 100 services in the past year, and more than 300 services in the past four years, to generate an SCR proof. It has been a useful tool for helping producers rank the relative fertility of sires.
Similar information has not been available in the expected progeny differences published for beef sires. Instead, the beef industry has used an indirect measure of fertility, scrotal circumference, as a predictor of fertility. A larger SC indicates greater fertility.
The increased use of beef sires on dairy cattle has raised questions on the relative fertility of beef vs. dairy sires. Specifically, does using beef sires result in reduced fertility?
Fertility differences
A 2020 study by McWhorter et al. dove into this very topic. The breeding records of over 5,000 beef sires of more than 50 breeds were obtained. Angus was the predominant breed represented, with over 95% of the matings. Ninety-one percent of the Angus-sired breedings were to Holstein cows. There were too few services for other breed combinations to draw meaningful conclusions.
Data was divided out separately for cows vs. heifers. For lactating Holstein cows, data from 1,344 Angus sires were compared to 15,401 Holstein sires. In all, there were 233,379 inseminations for the Angus sires and 14,474,142 inseminations for the Holstein sires. The mean conception rates for Angus sires used on Holstein cows and Holstein sires on Holstein cows were similar at 33.77% and 34.29%, respectively. It’s important to note that the mean service number for Angus on Holsteins was 3.04, which was greater than the 2.13 average service number observed for Holstein on Holstein matings.
For Holstein heifers, data from 443 Angus sires was compared to 12,129 Holstein sires. There were 19,437 Angus inseminations and 2,261,250 Holstein inseminations. The mean conception rates for Angus on Holstein and Holstein on Holstein were 52.96% and 55.34%, respectively. Again, there was a difference in mean service number for Angus on Holstein and Holstein on Holstein matings: 2.83 and 1.92, respectively.
Ideally, an SCR for beef sires would also be calculated using the increasing amount of data from these matings. McWhorter et al. also looked at this and found a similar SCR between Angus and Holstein sires, but a lower reliability for Angus sires due to fewer matings.
Earlier this year, Weigel et al. (UW-Madison, unpublished) did a similar analysis of conventional, sexed semen and beef-on-dairy inseminations in herds predominately located in the Western part of the U.S. and found similar results. Average conception rates for inseminations of lactating dairy cows were 33.8% with conventional Holstein semen, 34% with sexed Holstein semen, 37.5% with conventional Jersey semen, 35.5% with sexed Jersey semen, and 35.4% with conventional beef (primarily Angus) semen. Again, there were differences in how the semen was used, with sexed semen used more frequently on younger cows and for first and second services, and with beef semen used more heavily for repeat services.
Study implications
What does this all mean? Comparisons in fertility should go beyond comparing raw averages. Factors such as lactation number, service number and level of production have an influence, in addition to the sire.
In most cases, when comparing the fertility of beef sires to Holstein sires within a herd, we’re also comparing different populations of females. Scenarios include breeding first service to sexed dairy semen, and later services to beef; breeding the highest genetic-merit cows to sexed dairy semen and lower-merit cows to beef; and breeding first-lactation cows to sexed dairy semen and older cows to beef. In all these examples, we are no longer comparing apples to apples. Simply comparing average conception rates in these scenarios can be deceiving.
For more information, please visit fyi.extension.wisc.edu/dairy, or view the recording from our Badger Dairy Insight webinar Improving Dairy Farm Efficiency Through Genetics below. All Badger Dairy Insight recordings can be found on the Farm Ready Research website.
