Milk: Benefit or Burden
Increasing milk EPD can increase calf weaning weight, but it comes at a cost.
DES MOINES, Iowa (June 23, 2021) — Be careful what you ask for. University of Kentucky researcher Ben Crites reminded beef cattle breeders to be careful about selection for increased milk. Making a presentation during the 2021 Beef Improvement Federation Research Symposium & Convention hosted June 22-25 in Des Moines, Iowa, Crites said selection emphasis on milk expected progeny difference (EPD) values typically delivers more than heavier-milking cows. More milk can mean heavier weaning weights, but it can also come at significant cost.
To illustrate the point, Crites reviewed Angus genetic trends from 1972 to 2020, showing how average weaning weight EPD increased from -20 to +60 pounds (lb.). That huge change in weaning weight accompanied an increase in average milk EPD from +9 to +26 lb. Cows became bigger during that same span of years, however, as reflected by an increase in mature weight EPD — from -90 to +60 lb.
Crites encouraged his audience to think about what a milk EPD really is. It is designed to be a predictor of a sire’s genetic merit for milk and mothering ability, as expressed in his daughters and compared to the daughters of other sires. Crites emphasized that it’s not just about milk production.
“It’s about the pounds of calf they wean,” Crites added. “It’s commonly referred to as ‘milk,’ but it’s actually a measurement of maternal weaning weight.”
According to Crites, for the breeder seeking to increase weaning weight through milk, it takes an average of 42 lb. of increased milk to achieve 1 lb. of additional calf weaning weight. The cost of producing more milk comes from increased feed requirements. If the additional feed energy needed to produce an extra 42 lb. of milk came from corn purchased at the current price, the additional 1 lb. of weaning weight gained would cost $1.85.
Crites noted that failing to provide the required feed energy for milk production will likely result in loss of body condition score and an increased number of cows that fail to rebreed. That represents lost revenue.
“We need to revisit milk and the relationship of milk EPDs and daughters’ milk characterized in the ’80s and ’90s,” stated Crites, adding that insufficient data are available to fully characterize the effects of age and breed of cow, stage of lactation, nutritional status and other factors influencing milk composition in cows. “We need to understand the energetic costs to produce more milk.”
Crites described a collaborative field study by the University of Kentucky, Virginia Tech and North Carolina State University. Now under way, the study’s objectives include:
- Determine the association of milk EPD and total maternal index with daughters’ milk production.
- Calculate and appropriate economic factor for milking ability in selection indexes.
- Evaluate the milk components of current genetics.
- Investigate the relationships of milk EPD and total maternal index with adjusted 205-day weaning weight.
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