The nutritional status of the gestating cow and heifer has far-reaching implications, not only for her future fertility but, potentially, for the health and performance of her calves (including the fertility of her heifer offspring), and ultimately, a producer’s bottom line. To optimize long-term herd performance — and keep production costs down — it’s crucial to supplement those females in a strategic way.

Because reproduction rates and feed costs are two of the most critical factors for any beef system’s success, balancing reproduction and nutritional needs remains a hot area of research. “Reproductive traits, as we are able to measure them today, are very lowly heritable,” says Rick Funston, an associate professor and beef reproductive physiology specialist at the University of Nebraska. “Therefore, we use the other component of what influences those traits, which is management. Largely through nutrition, we manage reproduction by the timing of and the need for supplementation when nutrient availability doesn’t meet requirements.”

The question boils down to this: How can producers maximize reproduction without overspending on feed? “We’re always trying to find that optimal level,” says Scott Lake, associate professor and beef specialist at the University of Wyoming Extension. “Maximizing reproduction and optimizing reproduction, from an economic standpoint, might not be the same thing. You want to find that fine line.”

Complicating matters is the fact that there’s no one-size-fits-all answer. “That’s something producers are going to have to pencil out,” Lake says. “Generally speaking, if you’re getting 98 to 100 percent conception, you’re overfeeding probably 85 to 90 percent of the herd. If you get 90 percent conception rate and let that bottom 10 percent fall out, I think economically you’re better off, but exactly what that number is will depend on  your resources and your feed costs.” Also complicating the equation: what we’re now learning about fetal programming and the ways nutritional levels impact progeny performance.

When supplementation matters
At the University of Nebraska, they’ve looked at supplementation for cows grazing on winter range, as well as early weaning as a management tool to provide extra body condition going into winter grazing, Funston says. The results: no significant payoff for either practice. “In a spring-calving herd, it largely hasn’t benefitted the cow to either supplement or early wean, provided they’re on an increasing plane of nutrition going from calving to breeding,” he says. That last point turns out to be key — environmental conditions provided the cows with what they needed, at the time they needed it most.

But the study didn’t stop there; researchers also looked at how those management decisions impacted the future calves. That’s the idea behind “fetal programming” — the effects of the mother’s physical condition and nutritional levels on genetic expression in the off- spring. It’s a concept that came from the human medical world, introduced decades ago when a doctor first realized that babies born to malnourished mothers went on to suffer from various health problems later in life. More recently, it’s become a lens through which to consider livestock production systems: Offspring of dams that experienced nutritional stress during gestation may be more likely to exhibit reduced growth and meat quality.

That’s what Funston and his colleagues found. “Over several years of research, we saw an impact,” he says. “Those events that happen before birth affected the progeny later in life.” Especially detrimental was the decision not to supplement the cows on winter grass. That impacted the fertility of their heifer calves as well as subsequent steer carcass weights and carcass quality, along with sickness rates in the feedlot.

A few specifics: When, in one of their studies of cows grazing winter range, they fed supplemental protein to only one group (a 42 percent protein cube delivered at a rate equivalent to a pound a day, three days a week), that group increased the weaning weights of their calves by 22 pounds. Hot carcass weights increased by 87 pounds.

The long-term impacts of nutritionMay-calving heifers
Meanwhile, in a May-calving herd, it’s a whole different scenario, Funston says, especially for heifers and first-calf heifers. “We’re currently studying the need for supplementation during winter grazing on a later-calving herd because those cows would be in a different stage of gestation. We’re also supplementing heifer calves and first-calf heifers during breeding to see how that impacts their breeding rates. We don’t have enough data to make any conclusions, but preliminarily, the younger animals in that system had lower conception rates than in a spring-calving herd. We’ve seen a response to supplementing heifer calves and first-calf heifers in that May-calving herd during the breeding season.” The key in those later-calving herds is that when they’re breeding, forage quality is declining; their plane of nutrition is decreasing.

Chip Ramsay, manager of the Rex Ranch in Ashby, Neb., where the calving season began in March and April in years past, has applied some of these ideas for years. “We think we have seen what Rick’s experiments have shown,” he says. “We supplement mature cows much less than we supplement our 2- and 3-year-old females. We saw close to a 7 percent difference in pregnancy rates of heifers born to 2- and 3-year-old females than to mature cows. You’d think it would be the other way around. We’re weaning a lighter heifer from a first-calf heifer, and they were still lighter at pregnancy test than the heifers born to the mature cows — yet those progeny tend to breed up better than the mature cow progeny, even though they were developed in the same herd.

The long-term impacts of nutrition“In addition, we don’t put a lot of development costs in our replacement heifers, which has saved us a lot of money over the years,” Ramsay says.

The body-condition-score question
Because it’s becoming clearer that whether the animal’s plane of nutrition is rising or falling is important, it would seem that managing nutrition programs around body-condition scores may not be an optimal method. “Body condition, in and of itself, can be deceiving, because those cows that calve in our later-calving system tend to carry more condition than the earlier calving ones, but it’s really not just body condition. It’s the change in condition, which you can’t even see,” Funston says. “You don’t realize what’s going on metabolically; it’s not evident for some period of time.”

In their spring-calving herd, cows might be pretty thin, below a 5, but they breed fine provided they’re increasing during the time from calving to breeding, Funston says. “The opposite is true in the later-calving system. Those cows may calve in good condition, but their pregnancy rates are lower because of what’s happening during breeding season: Nutrient quality is not increasing.”

Heifers are susceptible to this, too. “Generally, we don’t think of heifers as a major challenge to get pregnant,” Funston says. “They’re still growing, but their requirements aren’t constrained by milk or anything like a first-calf heifer. But we still see later-born heifers in our May herd, if we don’t supplement during breeding, that will be 20 percent or 30 percent lower in pregnancy rate than the spring-calving herd with the same genetics.” That is likely also a function of intake; they simply can’t eat enough to meet their requirements at their age.

But for cows, too, the more we learn, the more important it seems to be that their nutritional needs be closely monitored throughout gestation. “When I was going to school, we were taught it’s okay to let cows drop off and get thin during mid-gestation and pick them up toward the end, and economically, that’s probably true,” Lake says. “But we’re learning more about fetal programming all the time. Most of organ development happens during the second trimester; most of the growth is during the third trimester. So we can really affect marbling during the third trimester and maybe even efficiency during the second.”

Now Lake wouldn’t recommend letting cows get thin during pregnancy. “You need to keep your cows in good condition, especially if you’re keeping replacements out of your herd.” Because now we know it’s not just a matter of what is happening right now with nutritional levels — the results of smart supplementation will be seen on the ground in your herd for years to come.