Beef-on-dairy calves are bringing a different set of management considerations to the feedlot as producers look for ways to capture more growth and carcass value. Growth-enhancing technologies such as implants and beta agonists can help push performance but trace mineral nutrition can influence how well cattle respond.
Research from Iowa State University is showing zinc and copper deserve a closer look when growth-enhancing technologies are part of the program. The findings were generated in native beef cattle rather than beef-on-dairy calves, but they raise important questions for a growing segment of the beef industry.
A Different Calf Enters the Feedlot
Dathan Smerchek, assistant professor of animal science at Iowa State University, has studied how trace mineral nutrition interacts with implants and beta agonists. His work suggests beef-on-dairy cattle may have some unique considerations, particularly when it comes to copper status and the amount of zinc available for growth and immune function.
Beef-on-dairy calves can arrive at the feedlot with a different mineral history than traditional beef calves.
Copper is one of the biggest concerns.
While unintentional, dairies may supplement copper above National Academies of Sciences, Engineering, and Medicine recommendations. Calves can also receive copper from multiple sources before entering the feedlot, including placental transfer, milk replacer and starter feed.
As a result, some dairy-influenced calves can enter the feedlot with liver copper concentrations of 450 parts per million or higher.
The traditional reference range for liver copper is broad, extending from about 125 to 600 ppm. Smerchek noted, however, oxidative stress may begin before cattle reach 600 ppm, potentially around 400 ppm.
For beef-on-dairy cattle, this makes understanding the calf’s mineral history more important before adding additional copper in the feedlot.
Bigger Cattle, Bigger Demands
The mineral question becomes even more interesting when growth-enhancing technologies are added to the program.
Beef cattle today grow faster, reach heavier harvest weights and use feed more efficiently than cattle did decades ago. Smerchek points to data showing growth rates increased 44% from 1977 to 2007.
“We’re dealing with an animal that’s bigger, grows faster and is more efficient,” Smerchek says.
Implants and beta agonists can push performance further. Implants improve growth rate, feed efficiency and lean tissue deposition, while beta agonists can increase growth performance and carcass weight late in the feeding period.
Both increase the animal’s demand for processes involved in protein synthesis and muscle growth.
Trace minerals support those processes.
“Proper trace mineral nutrition is essential for optimal performance if you want to get the most out of your cattle,” Smerchek says.
Zinc May Help Cattle Respond
Smerchek’s research has found a relationship between zinc supplementation and implant response.
Following implant administration, plasma zinc concentrations decline during the first 20 days. The period also corresponds with the greatest hormone payout from the implant and increased growth demand.
Several studies have found additional zinc can improve growth and hot carcass weight in implanted cattle, while responses are smaller or absent in cattle without an implant.
“By just by adding more zinc to the diet in these studies, we see we’re able to get more out of that implant, which is already an investment that results in a pretty substantial ROI,” Smerchek says. “But we can get even more out of it by optimizing our trace mineral nutrition.”
For feedlots feeding beef-on-dairy animals, the question is whether similar responses occur in dairy-influenced cattle.
Smerchek’s research did not use beef-on-dairy calves, so the exact response in those cattle still needs to be studied. But the findings provide a reason to look closely at zinc nutrition when these calves are being pushed for additional lean growth.
More Zinc is Not Always More Growth
The research does not support a blanket recommendation to keep increasing zinc.
In Smerchek’s 2022 research, cattle received 0, 30 or 100 ppm of supplemental zinc, along with either no implant or a high-potency implant. During the first 28 days, zinc supplementation improved average daily gain by about 2 kilograms and improved gain-to-feed.
The response did not continue in a linear pattern through the feeding period. Cattle also started with about 53 ppm zinc in the basal diet, already close to twice the National Academies recommendation.
“In this case it kind of looked like certainly in the beginning of the trial 83 parts per million zinc or 30 was enough to cover the extra gain we were asking of that animal with the implant,” Smerchek says.
This distinction is important for beef-on-dairy cattle. Feedlots need to consider what calves have already received before deciding how much additional mineral to provide.
Beta Agonists Add Another Layer
Zinc also appears to influence how cattle respond to beta agonists.
In a 2016 study by Olivia Gunther, cattle receiving ractopamine and a zinc amino acid complex were fed increasing amounts of supplemental zinc. As zinc increased from 30 to 60 to 90 ppm, average daily gain, final body weight and feed efficiency increased.
“As we increase zinc supplementation, we increase response directly to ractopamine growth performance,” Smerchek says.
Across the research, implants and beta agonists appear to increase tissue zinc demand and alter how cattle use zinc.
Smerchek noted approximately 100 ppm zinc may be appropriate in many production situations when cattle are receiving growth-enhancing technologies.
For beef-on-dairy, however, more research is needed to determine whether the same level produces the best response.
Copper Can Go the Other Direction
While zinc supplementation may help support the response to growth-enhancing technologies, copper requires more caution.
Copper is involved in growth, antioxidant function, iron mobilization and copper transport. But copper also becomes a pro-oxidant when tissue concentrations become too high.
Because copper is stored in the liver, continued supplementation can push liver concentrations upward. This is one reason beef-on-dairy cattle deserve special consideration.
Smerchek’s research found copper status could influence how cattle responded to ractopamine.
Cattle with adequate copper status showed a 23% improvement in average daily gain when fed ractopamine. Those with adequate-to-high copper status saw only an 8.3% improvement. Deficient cattle showed little to no response.
“We were feeding this compound and we were getting nothing out of it because these animals were deficient,” Smerchek says.
The results show copper status can affect how cattle respond to a technology designed to increase performance. Both deficiency and excessive copper status can create problems.
Beef-on-Dairy Copper Deserves Attention
The copper findings could be particularly relevant for beef-on-dairy calves because their mineral exposure starts before they reach the feedlot.
A calf may have received copper through the dam, milk replacer and starter feed before it reaches the finishing ration. If liver copper is already elevated, adding more copper in the feedlot may not provide a performance benefit.
Smerchek recommends feedlot producers avoid exceeding the National Academies recommendation for copper.
“If it’s greater than 10 parts per million, we don’t see any data that would suggest that that’s beneficial,” he says.
That makes testing and understanding liver mineral status useful when working with beef-on-dairy cattle.
Don’t Overlook Immune Function
Zinc’s role goes beyond muscle growth. The mineral is also involved in immune function, which can become important as calves move through stressful periods such as transportation, receiving and commingling.
Smerchek said he would consider feeding about 100 ppm zinc before cattle enter the feedlot, although the appropriate level can depend on intake and other factors.
Stress and disease pressure can also change how an animal uses zinc.
“If we’re overcrowding animals, if we’re increasing potentially the disease load in a pen, spending more of their zinc just to sustain an immune response may pull down their available zinc, so they don’t have that for additional growth,” Smerchek says.
For beef-on-dairy cattle, this creates another potential connection between calf health and finishing performance.
A calf dealing with health challenges may be using more of its available zinc to support the immune system, leaving less available for lean tissue growth.
Don’t Overpromise the Response
The research offers opportunities, but Smerchek cautions against taking controlled research results and assuming the same response will occur on every commercial operation.
“I’m certainly not going to go out there and advertise, hey, if you feed three times the level of zinc sulfate, you’re going to get nine additional pounds of hot carcass weight,” he says. “That’s not going to happen.”
Commercial cattle face different diets, environments, health challenges and management systems than cattle in controlled research settings.
Still, even small improvements can add up across a large group of cattle.
Rethinking Mineral Recommendations
The research also raises questions about whether today’s cattle fit neatly within mineral recommendations developed decades ago.
Modern cattle are larger, grow faster and may receive technologies designed to increase lean tissue growth. Many mineral recommendations were developed primarily to prevent deficiency rather than determine the level needed to maximize performance in cattle receiving growth-enhancing technologies.
Smerchek believes the findings could eventually contribute to updated National Academies recommendations, potentially with different recommendations for cattle receiving growth-enhancing technologies.
“I think there is a worthwhile consideration,” Smerchek says.
For feedlots raising beef-on-dairy, the message is less about adding more mineral and more about understanding what the calf already has.
Copper status can vary before the calf reaches the feedlot. Zinc demand may increase as cattle are pushed for growth. Health challenges can also change mineral use.
Getting the most from beef-on-dairy cattle may come down to making sure the mineral program supports the growth being asked of the animal without creating a new problem along the way.
For more on beef-on-dairy, read:
