Bull Selection for the Modern Holstein: Balancing Production, Fertility, and Health Traits

Why a total-merit index comes first

Every bull sale catalogue can make a case for a different trait. Type, milk, components, feet, calving ease, feed efficiency: there is always a leader on something. The reason breeders use a total-merit index is that it forces the trade-offs into dollars. Lifetime Net Merit, published by the Council on Dairy Cattle Breeding, ranks dairy animals on their combined genetic merit for nearly 40 economically important traits and estimates the lifetime profit difference an animal is expected to pass on. USDA geneticists introduced it in 1994, and it has been revised repeatedly as the industry's priorities changed.

The revision history is worth knowing because it shows how the definition of a "good" bull has moved. CDCB's published history lists udder, feet and legs and body weight composites added in 2000, Daughter Pregnancy Rate in 2003, calving traits in 2006, Heifer and Cow Conception Rate in 2014, Cow Livability in 2017, disease resistance through a health sub-index in 2018, and Residual Feed Intake, Heifer Livability and Early First Calving in 2021. The April 2025 update shifted emphasis toward butterfat, cow livability and heifer livability, and away from protein and productive life, with more negative emphasis on the body weight composite and more weight on feed efficiency. A bull ranked a decade ago on a different formula may look different now.

Why not just chase one trait

A recent review in the Journal of Animal Science on potential negative effects of genomic selection explains the risk. Traits that are in the index, explicitly or implicitly, move in the desired direction. Traits that are neglected change according to their genetic correlations with the traits being selected. Historically, intense selection for production improved yield while fitness traits deteriorated, and adding those fitness traits to the index helped offset the decline. Under genomic selection the genetic trends are faster, which magnifies correlated responses in neglected traits. The practical lesson is simple: whatever you leave out of your selection, you do not control.

A working framework

Step 1: Set a floor and a ranking

Use total merit (Net Merit or your A.I. company's equivalent) to rank bulls, then set minimum standards for the traits you cannot afford to lose. Many herds set floors on fertility, livability and udder health, and then rank within that group on total merit.

Step 2: Check fertility directly

Holstein Association USA's guidance on haplotypes stresses selecting primarily on fertility traits such as Daughter Pregnancy Rate, Heifer Conception Rate, Cow Conception Rate and the Fertility Index. Fertility is expensive to fix with management alone. Our article on pregnancy rate explains why it matters so much for herd economics.

Step 3: Check health and longevity

Livability, productive life, somatic cell score and the health composite capture the costs that do not show up in the first lactation. Heavy emphasis on yield alone will not protect you from mastitis or early culling. See our guide to somatic cell count and milk quality.

Step 4: Match calving traits to your heifers

Calving ability and stillbirth numbers matter most on first-calf heifers. Choose a more conservative tier of sires for heifers than for mature cows.

Step 5: Screen for recessives and inbreeding

Check each bull's haplotype and recessive status against your cow herd, and avoid carrier-by-carrier matings for the same haplotype. Holstein USA notes that such matings show a significant drop in conception rate, and that valuable carriers can still be used with non-carrier mates. Our article on haplotypes and recessive traits goes into detail.

Step 6: Build a team

Use several bulls instead of one or two. Genomic evaluations of young bulls carry lower reliability than daughter-proven bulls, and a team averages out prediction error, limits inbreeding and keeps you from betting your herd on one pedigree. A sensible team usually mixes proven bulls with a share of genomic young sires.

Heat, methane and other emerging traits

New traits are entering evaluations, but not all of them are on standard U.S. summaries. Research evaluations for heat tolerance in Holsteins show a genetic trade-off with production, and Canada has a national methane efficiency evaluation. Treat these as tie-breakers among bulls that already pass your main screens. See our articles on selecting for heat tolerance and methane and genetics.

A short pre-purchase checklist

• Total merit above your herd's target, with fertility and livability not below your herd average.
• Calving traits appropriate to the cows or heifers he will be used on.
• Recessive and haplotype status checked against your herd.
• Relationship to your existing sire team, to limit inbreeding.
• Reliability noted, with extra bulls added when it is low.
• Semen price considered last, not first.

Bottom line

The modern Holstein is the product of dollars-based selection that now includes fertility, livability, health and feed efficiency alongside yield. Keep the index in charge, put floors under fertility and health, screen for recessives, use a team, and be skeptical of any single-trait pitch. For farm business resources, see the Agriculture Directory, and for dairy industry stories, farm.fm's dairy section. This site is independent and not affiliated with any breed association or A.I. company.