If you look at some of the research that’s been done on the value of supplementing cows, you could get the idea that it’s not all that profitable, says Rick Funston, a University of Nebraska reproductive physiologist in North Platte.

Dig a little deeper, however, and the research reveals a different set of truths.

Funston says they’ve done studies looking at early weaning with and without supplements. Pregnancy rates between the two systems were similar. “So if we stopped at this point, we would draw a conclusion that it didn’t pay to supplement those cows,” he says.

But then they looked at the performance of the calves, both heifers and steers. For cows grazing winter range, the only advantage to supplementation was that the cows receiving a higher plane of nutrition weaned more live calves. But there was no advantage in birth weight, weaning weight or pregnancy rates.

But the heifer calves kept for replacement, born to dams supplemented during the last trimester of pregnancy, showed a distinct advantage. “If you look at the percentage of heifers calving in the first 21 days and overall pregnancy rate, we decreased fertility in these heifers before they were ever born by how we managed the dams,” Funston says.

They saw similar results in the steer calves. “If we didn’t supplement those late-weaned cows, we took 60 lbs. of carcass weight off that calf,” Funston says. Meanwhile, steers from non-supplemented cows graded lower. “So we not only impacted carcass weight and heifer fertility, we now impacted quality grade before these calves were ever born,” he says.

Longer term, not supplementing the cows led to reduced fertility. The study lasted three years and cows that weren’t supplemented while on winter range faced the most nutritionally challenging environment. “If you look at the bottom line, the percentage of calves born in the first 21 days, we were starting to erode reproduction. Those cows were getting bred, but they were getting bred later by not supplementing,” Funston says.

The only advantage they found to not supplementing cows during late pregnancy was that the heifer calves were more efficient. “Think of that heifer developing in a perceived nutrient-limited environment,” Funston says. “Maybe it was programmed to be more efficient.” In effect, the cow, through its environment, was telling the calf that nutrients are going to be scarce and you’re going to have to be efficient in how you utilize them once you’re born.

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