If you look at the research that Rick Funston and his University of Nebraska colleagues have done on the affect of supplementation on cows grazing winter range and corn stalks, the take-home message is a bit confusing. Even in cows not supplemented with protein in the third trimester of pregnancy, body condition score and rebreeding percent were acceptable.

“But what have you done to that unborn calf?” Funston asks. That’s the real story in the value of providing a protein supplement to cows grazing winter forage, he says.

The three-year study looked at the value of providing 1 lb./day of 28% protein supplement to cows grazing both dormant winter forage and corn stalks. The supplementation was provided three times a week from Dec. 1 to Feb. 28, the last trimester of pregnancy. Following the winter grazing period, the cows were managed in a common group and fed hay and a protein supplement. During the trial, half the cows grazing winter pasture were given a supplement and half weren’t. Likewise, half the cows grazing corn stalks were supplemented and half weren’t.

The effect of protein supplementation on the cows was minimal, with a few notable exceptions, Funston reports. For cows grazing winter range, a significant percent of the supplemented cows calved in the first 21 days of the calving season compared with the non-supplemented cows – 83% vs. 62%. Cows on stalks showed no difference – 78% of the cows in both the supplemented and non-supplemented groups calved in the first 21 days.

But, calf birth weight was greater for cows grazing stalks compared with winter range and tended to increase with supplementation. “This is somewhat surprising,” Funston says, “because previous research using the same cow herd did not find differences in calf birth body weight due to supplementation of dams grazing winter range.”

In addition, pre-breeding cow body weight and body condition scores (BCS) increased in the cows grazing corn residue and receiving supplementation. Cow body weight at weaning and BCS were not affected by supplementation, but cows that grazed corn stalks the previous winter were heavier at weaning than those that grazed winter range, despite similar BCS.

The real affect of protein supplementation was seen in the calves, and that began while the calves were still unborn, Funston says. Steers from supplemented cows tended to have heavier final weights in the feedlot and heavier hot carcass weights in the packing plant.

This was particularly true with steers from cows on winter range; there, steers from supplemented cows hung an average hot carcass weight of 825 lbs., compared with 789 lbs. for steers from non-supplemented cows. Meanwhile, steers from cows on corn stalks were very similar, with an average hot carcass weight of 820 lbs. from supplemented cows, and 819 lbs. in steers from non-supplemented cows.

The big difference was in quality grade. Steers from cows given a protein supplement on winter range graded 82.5% Choice, compared with 77.8% of the steers from non-supplemented cows. The difference was even greater from cows on corn stalks. There, 86.8% of the steers graded Choice from the supplemented cows compared with 64.4% from the non-supplemented cows. “We’re impacting marbling before that calf’s even born,” Funston says, depending on the nutritional plane of the cow during late pregnancy.

The heifer mates showed some interesting trends, as well. Actual weaning weights tended to be heavier for heifers on supplemented cows. On winter range, heifers from supplemented cows weighed an average of 509 lbs. at weaning, compared with 480 lbs. for heifers from non-supplemented cows. And, cows grazing corn residue and fed a supplement weaned heifers averaging 513 lbs., compared with 505 lbs. from cows on stalks but no supplement.

The big difference was seen in pregnancy rates. Of the heifers from cows fed a supplement on winter range, 90.5% settled in a 45-day breeding season, compared with 77.1% of the heifers from non-supplemented cows. Of the heifers from supplemented cows on corn stalks, 87.8% settled, compared with 83.3% from cows that didn’t receive any supplement.

The reason for the more pronounced difference between winter range and corn stalks is likely because corn residue has a higher nutritional value than dormant native grass, Funston says. “The quality of the forage appears to be higher in energy and probably most parts are higher in protein than winter range.”

Grazing crop residue is a long-standing winter production option in areas where stalks are available. But Funston was surprised at how little research had been done to quantify just how valuable it can be compared with other winter-grazing systems.

“Both systems can be very cost-effective ways to decrease production costs, which is very important in today’s economy, by reducing the amount of harvested feedstuffs you feed,” Funston says.

Based on his data, it’s probably advisable to supplement your cows, especially during the last trimester of pregnancy, to prevent adverse effects on the unborn calf and to make sure your cows maintain body condition.

“But it doesn’t take a lot,” he says. “We only supplemented 1 lb./day of a 28% distillers-based cube,” yet in a few very important areas, saw a significant response.

Providing a protein supplement for cows on winter range has long been an accepted practice. But its real value may surprise you.