FERTILITY Is Important To Us
Reproductive efficiency is the most important factor determining profitability of a commercial cow-calf operation. Therefore, reproduction is at the forefront of the GAR genetic selection program. The best “tool” for improving the genetics controlling reproduction in Angus cattle is the use of expected progeny differences (EPD) for heifer pregnancy rate (HP).
HP EPDs are calculated from breeding records indicating whether the daughters of a bull become pregnant during their first breeding season. The length of the breeding season, the number of matings and the use of natural service or AI are not factors used in determining the HP EPD. Instead, the HP EPD is simply an indicator of the likelihood of a bull's daughters becoming pregnant at some time in their first breeding season.
Figure 1 provides an example of the use of heifer pregnancy EPDs. Assume there are 100 daughters for each of the two bulls, managed and treated alike in the same breeding environment. When comparing the two bulls, one would expect an average of five more pregnant daughters out of 100 from Bull A compared with Bull B. Essentially Bull A’s daughters have a 5% greater chance of becoming pregnant than Bull B’s daughters.
Figure 1. Heifer Pregnancy EPD Example¹
¹ From AAA website: http://www.angus.org
It is estimated that the heritability of HP is 13%. That indicates that 13% of the variation in pregnancy success is due to genetics. In a preliminary study of the data used in the American Angus Association (AAA) Genetic Evaluation for HP, researchers noted that “Although its heritability is low, some improvement in fertility can be made by selecting on heifer pregnancy rate.” They also noted that the genetic correlation between heifer pregnancy rate and lifetime pregnancy rate was over 90%.
The AAA staff published the first Research Report on Heifer Pregnancy Evaluation in 2007. That evaluation was updated recently and now includes 28,597 heifer breeding records used to generate EPDs for 760 sires. While this may sound impressive, it points to a major problem in calculating meaningful HP EPDs – not enough records. The 28,597 heifer breeding records used to calculate HP EPDs may seem like a lot, but it is less than 1/200th of the number of records used to generate the EPDs for birth weight in the Spring 2011 national sire evaluation. We need more heifer breeding records!
Gardiner Angus Ranch has supported the effort to calculate accurate HP EPDs. Since 2004, we have submitted breeding records on 3,225 heifers. That represents 11.3% of all records in the current database.
Figure 2. Heifer Pregnancy EPDs - selected GAR bulls¹ ²
|GAR Sire||HP EPD|
|GAR Retail Product||+11%|
|GAR New Design 5050||+9%|
|GAR Grid Maker||+6%|
|GAR Yield Grade||+3%|
¹ A higher HP EPD is more favorable
² Breed average HP EPD is +8%
Other Angus breeders can submit heifer breeding data electronically by entering the American Angus Association login area and clicking on the “Submit Data” tab. “AHIR Yearling Heifer Breeding Data” should be selected from the list of submissions and the set of eligible heifers should be indicated. Once the list of heifers is generated, data for each heifer can be entered. Data submitted is processed and added to the database used to calculate EPDs for heifer pregnancy. Processing heifer pregnancy data is done at NO COST TO THE BREEDER. Additional data makes the HP EPDs more accurate.