by Lilly Platts
Cow size is a constant topic of conversation in the beef industry, and the ideal weight varies by environment and program.
The energy required to sustain a female throughout each yearly cycle not only matters for the cow herself, but also for the calf she produces. When resources are tight due to drought or the economy, producers are faced with tough decisions. A pregnant cow can withstand a lot, but it is imperative that her energy requirements are always met in order for her to produce the highest-performing calf possible. Dr. Allison Meyer, Associate Professor of Physiology and Ruminant Nutrition at the University of Missouri, shared about the relationship between cow size, nutrition, and calf needs during the 2025 Fall Focus Educational Symposium in Columbia, Missouri.
Meyer first challenged producers to figure out what their own females weigh, and to consider that muscle — which is often more present in crossbred cattle like SimAngus — is heavier than fat. “As we consider cow size, I want to challenge everyone, before throwing the first stone, to figure out what your mature cows weigh,” she said. “Your cows weigh probably more than you think they do if you don’t weigh them a lot, or your customer’s cattle weigh more than they think they do, because your breed still has muscle in it. That’s why we like them.”
Finding the ideal cow weight, which strikes the balance between input and output, can be tricky. Thriftiness is often prioritized, but if cow size is too small, calf size at weaning will also decrease. Meyer explained that by thinking about cows like factories, producers can determine whether or not their females are too big for their environment. “A cow’s job is to hang around for a long time and make as many products, or calves, as she can. When we think of it in terms of a factory, we don’t necessarily think that a big factory that makes a lot is a bad thing. It depends on what you are making,” she explained. Evaluating the obvious external measures, like weight or frame size, doesn’t offer the full picture of cow efficiency. Muscle mass and nutrient utilization are also important. Muscle adds weight, and more weight requires more nutrient intake; however, muscle is also critical in times of stress. “Muscle is the place where you can put extra protein,” Meyer shared. “We can’t store protein just anywhere in the body, but when cows are hungry or go through periods of time where they don’t get enough nutrients, they can pull from their muscle.”
During pregnancy and lactation, this nutrient reservoir can be critical. “They can give their little fetus, or their udder, those amino acids,” Meyer added.
In her research, Meyer has found that cattle with thin muscle cannot withstand stress. Because of this, she encourages producers to keep in mind that the pendulum
on cow size can swing too far in either direction. “I think that cows can get way too little, just as they can get way too big,” she said.
Cow-calf producers are beholden to the weather, and in many areas of the US, drought has greatly diminished resources. Too much moisture can also create challenges for females — grass might look abundant, but the protein in forages is often diluted with excess moisture. Across the country, volatile weather creates nutritional challenges for beef cows. “We have to keep in mind that a cow is regularly in situations where she is stressed because of the amount of nutrients she gets,” Meyer said.
Despite this challenge, producers are consistently working to maximize genetic potential, which can only be realized if a female isn’t stretched too far nutritionally. “Her calf has the genetics to do so much, and that can only happen if it has nutrients,” Meyer shared. “Her job as a factory is to give nutrients to her calf, and the only period of the calf’s life that she can do that is from the time it’s conceived to the time it’s weaned.”
Meyer shared that while individual seedstock producers may do everything they can to meet their cow herd’s nutritional needs, and ultimately maximize the genetic potential of calves, there are many producers who either aren’t able to do so, or who do not have the knowledge to do so. Testing hay is an easy, affordable step that many producers skip. “We’re currently dealing with really weird conditions, so sometimes we think that our forage is great when it isn’t. Many people have genetic information on every animal on the place, but haven’t done a hay test in decades,” Meyer said. “Not every hay bale that looks good actually has the right numbers.”
Often, producers don’t realize they aren’t fully meeting the nutritional needs of their cow herd during gestation. “I know that many times when we don’t feed cows well, it’s by accident. I’m not casting blame on this situation, but I want us to think about the nutrients a calf needs from the time it’s conceived until the time that it’s weaned.”
Much of Meyer’s research focuses on cow needs in the late stages of pregnancy. Nutritional requirements increase during this time, but don’t always align with the standard yearly schedule many producers follow. “The problem with that is that we’ve actually selected calving seasons primarily to give more nutrients to that cow actually when she’s milking, and when we need to get her rebred, which means that many times she doesn’t have as much of an opportunity to eat as many nutrients when she’s in her late pregnancy,” Meyer explained.
Physical appearance can also skew feeding decisions, and producers often don’t realize that a cow was underconditioned until after she has calved. “Sometimes we also imagine that when she’s full and she has a big fetus in her, that she has a little more condition on her than she does,” Meyer said.
This mistake can be hard to reverse, especially in the resulting calf. Cows naturally prioritize where nutrients go, and while the cow will sacrifice herself for as long as possible, a fetus may be shortchanged in order for a cow to continue maintaining her own body. “Now, we know that cows generally pull from themselves first,” Meyer said. “They’re kind of the ultimate martyr, but there is a limit because they need to keep themselves alive. It is bad for their calf if they are dead or if they can’t make milk, so they do start to limit their calf and their ability to make milk.”
In a USDA-funded study, heifers were either fed to their nutrient requirements during pregnancy, or only to 70% of their protein and energy needs. The females and their offspring were evaluated based on a number of criteria. Overall, if cows were not given enough to eat, their calves didn’t receive enough nutrition. Decreased birthweights were also observed, which is not a positive outcome when the lower weight is due to nutrition.
“If we change the fetal growth trajectory, bad things can happen. We can change fetal development, their vigor, their cold tolerance, and all kinds of things like that,” Meyer explained.
Meyer emphasized that the only correct way to decrease birthweight is through genetics, not nutrition. There is a misconception that feeding a cow “too well” can cause calves to have large birthweights, but Meyer shared that this cannot happen. “You actually cannot feed birth weight into a calf that its genetics didn’t have the potential for,” she said.
In the experiment, calf vigor was measured in the two groups of females based on the amount of time it took for calves to stand up after birth. Meyer shared, “We found that if the dams were nutrient restricted in this study [their calves] took longer to attempt to stand, and longer to stand.”
These calves weighed less through weaning, and Meyer shared that skeletal differences and a smaller ribeye area were also observed. These changes could be attributed to a number of factors — from getting less nutrients in utero, to the lower-quality colostrum their mothers produced; the females fed at 70% were put on a diet that met their nutritional needs at 100% after giving birth, but colostrum is produced before birth. Even on a full diet, these cows and calves weren’t able to catch up to their counterparts. Differences were observed in the restricted females well past the first calf cycle. “We found that even though we had been managing them together since we weaned their first calf, and really we were feeding them similarly since they gave birth to their first calf, that they still were smaller if they had been nutrient restricted in the first pregnancy. They weighed less throughout their second pregnancy, the rest of their second pregnancy, and through their second lactation,” Meyer explained.
These females also had less muscle mass and smaller frame scores, which could be viewed as beneficial in certain programs, but Meyer cautioned that low muscle means these females won’t have the reserves to withstand environmental challenges. “What we do to a heifer, especially during her first pregnancy and lactation, does affect her forever. We expect her to grow about 20% of her mature body weight while she’s pregnant. But many times we think she’s developed because she’s pregnant, and I think that’s really wrong. I think we need to consider that she’s still being developed all the way through her first pregnancy, and probably until we’ve weaned her first calf,” Meyer shared.
Meyer also explored the implications of the current cattle market. Even newborn calves are worth a substantial amount, which means that getting them through the first three weeks of life isn’t only important from an animal husbandry standpoint, but also because of value. Additionally, because feedyards are asking more of cattle with the goal of larger finished weights, making sure calves are healthy from the beginning is more important than ever. Meyer concluded, “We don’t necessarily have to make cows bigger to make their calves have the potential to be bigger. We can just manage them better so that their calves can meet their genetic potential to do those things. What is the point of having great genetics if you don’t realize that genetic potential because a cow didn’t have the inputs she needed?” .
