Genetic Selection for Reproduction: Current Reproductive Status of the National Herd; Application of Selection Indexes for Dairy Producers

Authors: Norman, H; Wright, Janice; Hubbard, Suzanne; Kuhn, Melvin; Miller, Robert

Submitted to: Dairy Cattle Reproduction Council Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/2/2007
Publication Date: 11/2/2007
Citation: Norman, H.D., Wright, J.R., Hubbard, S.M., Kuhn, M.T., Miller, R.H. 2007. Genetic Selection for Reproduction: Current Reproductive Status of the National Herd; Application of Selection Indexes for Dairy Producers. Dairy Cattle Reproduction Council Proceedings. Denver, CO, Nov. 2-3, pp. 69-78.

Interpretive Summary: Using service sires with higher conception rates returns a profit fairly quickly. We recommend using bull fertility as a secondary selection trait after production traits, profit traits, and profit indexes. Selection for improved cow fertility is possible and recommended, but most benefits are delayed for 2 years or more. Most breeders should select service sires for overall lifetime merit that includes daughter fertility rather than for daughter fertility alone. However, producers with herd fertility problems may choose to emphasize DPR extensively, which can be done with little loss in overall net merit. The extent that dairy producers should emphasize fertility depends on their management system. All producers would be wise to consider service-sire fertility and DPR when choosing herd sires. By using a few bulls that average 3.0% for PTA DPR (equivalent to a decrease of 12 days open), much of the genetic decline in fertility from using high producing bulls for 40 years could be recovered in one generation.

Technical Abstract: Using service sires with higher conception rates returns a profit fairly quickly. However, the heritability of bull fertility after AI organizations remove bulls with inferior fertility based on sperm morphology is essentially 0. Thus, little genetic improvement in male fertility is expected over time. Pecsok et al. (1994) reported that a premium of $2 could be paid for semen per 1% improvement in fertility. Thus, a unit of semen from a bull with an ERCR of +2 would be worth $8 more than a unit from a bull with an ERCR of '2. Clay and McDaniel (2001) recommended using bull fertility as a secondary selection trait after production traits, profit traits, and profit indexes. Selection for improved cow fertility is possible and recommended, but most benefits are delayed for 2 years or more. Most breeders should select service sires for overall lifetime merit that includes daughter fertility rather than for daughter fertility alone. However, producers with herd fertility problems may choose to emphasize DPR extensively, which can be done with little loss in overall net merit. The benefits of enhanced reproductive efficiency are the same whether they are achieved through superior bull or cow fertility. Those benefits include lower semen cost, improved ability to optimize lactation and lifetime yields, reduced culling due to delayed or failed conception, and more herd replacements. The extent that dairy producers should emphasize fertility depends on their management system. All producers would be wise to consider service-sire fertility and DPR when choosing herd sires. However, those traits are especially important for grazing herds with seasonal calving. By using a few bulls that average 3.0% for PTA DPR (equivalent to a decrease of 12 days open), much of the genetic decline in fertility from using high producing bulls for 40 years could be recovered in one generation. Genetic evaluations for DPR can make a difference to dairy producers that need to improve herd fertility. Selection for improved reproduction is possible and can be extremely effective. However, the general recommendation still is to select for overall merit based on a genetic-economic index appropriate for the current milk market.