To achieve 600- to 700-pound weights at weaning, the trend has largely been a push for more – more milk, more growth. But what is it costing to wean those heavier calves? Is there a limit of milk production that your forage can support? And does more milk really equate to more growth?
During the annual Beef Improvement Federation (BIF) Convention held virtually this June, Travis Mulliniks, assistant professor and range cow production system specialist at the University of Nebraska – Lincoln addressed some of these questions.
“If we look at average weaning weights in commercial herds in many regions across the country, we find a stabilization of calf weaning weight,” Mulliniks told BIF viewers. “We are selecting for increased milk and increased growth, but we’re not seeing that output of increased weaning weight.”
But why? Mulliniks said it all comes down to the environment.
“When we look at the response to [increased milk selection], we get to a point where milk production didn’t increase by the given genetic potential to increase milk production. So there is a limitation of the amount of nutrients in the environment to allow that cow to milk more,” he said.
Productivity
To give viewers a better idea on how much the environment influences genetics and productivity, Mulliniks compared milk production data from cows in Tennessee and New Mexico. The cows in Tennessee had high growth potential, high milk potential, high forage growth and high feed input. The cows in New Mexico had moderate growth, low milk potential, limited forage availability and lower feed input.
“When we looked at 24-hour milk production in these cows, we go from 24 pounds at peak lactation in Tennessee and 13 pounds at peak lactation in New Mexico. There was about a 50-pound difference in calf weaning weight on average, so it’s not really an efficient system in selecting for more milk to get a higher calf weaning weight,” Mulliniks said.
Some things to note from the data:
- Tennessee cows had 25 pounds of calf weaned per 1 pound of milk, while New Mexico cows had 43 pounds of calf weaned per 1 pound of milk.
- Tennessee cows weighed 1,500 pounds and New Mexico cows weighed 1,100 pounds.
- Tennessee cows had an 88% pregnancy rate, while New Mexico cows had 96%.
- Tennessee cows had a 44% retention rate at 5 years of age, while New Mexico cows had 61%.
- And New Mexico had a lower cost of production at about $300 to $400 less.
“When you look at that from a complete production standpoint, by selecting for increased growth and increased milk, we’re really not getting that out from an entire production system. We may be weaning more calf, but we are not weaning more total pounds of production due to that pregnancy rate, and it’s costing us more to get there,” he said.
Reproduction
Pressure on milk selection can have a negative effect on reproductive efficiency, Mulliniks said. Referring to another study out of Tennessee that looked at 237 spring-calving Angus cows, fed a high-quality forage diet from calving through breeding, researchers found the cows started to lose reproductive efficiency at about 24 to 26 pounds of milk.
Mulliniks said, “If you couple this reproduction response back to calf weaning weight, the optimum cow in this more higher-quality environment in Tennessee would be a cow that produced 20 to 22 pounds of milk at peak lactation. When you get over that, you are going to start to decrease reproductive efficiency driven by this reproductive response.”
One of the reasons for this lower pregnancy rate, Mulliniks said, could be the resumption of estrus. Data from New Mexico shows that more than 14 pounds of milk puts cows at a disadvantage to cycle and breed in time. “This could be driving longevity, especially for a young female,” he said.
Another thing to pay attention to, is the energy balance at calving. For example, in Nebraska with mostly spring- and summer-calving herds, Mulliniks will often get calls from producers with lower pregnancy rates or strung-out calving seasons. He attributes this to the level of milk production and when the cows are lactating.
“When we look at a May-calving herd, we look at cows that before we even get into the breeding season in August, who are already in a negative energy balance. So the cow that would fit this May-calving herd would be totally different then the type of cow that would fit that March-calving herd due to the forage quality difference,” he said. “It’s the same environment, it’s just forage quality is driving some of these differences between March and May calving. We’ve really got to focus on the resources we have and selecting animals that fit best within that season.”
Feedlot performance
Lastly, how does this fit into the feedlot? Referring to data out of Nebraska and Tennessee that looked at low, moderate and high milk potential in feedlot performance, Mulliniks pointed out that offspring from lower milking animals are a little more efficient from a growth aspect post-weaning than their counterparts.
Mulliniks went on to explain that offspring from high-milking animals have increased requirements, increased organ mass and size, and with that, an increase in energy requirement and a decrease in feedlot efficiency. So what is selected for on the cow-calf side can really influence some post-weaning performance as well, he said.
To watch the full presentation and view the data charts, visit the Beef Improvement Federation website. 
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Cassidy Woolsey
- Editor
- Progressive Cattle
- Email Cassidy Woolsey
