Supplementing pregnant cows with protein can enhance genetic potential of calfWritten by Gayle Smith
Supplementing a cow with protein during the winter can be a big boost to the growing fetus, according to Aaron Stalker, University of Nebraska beef range systems specialist.
The researcher said they just completed a four-year study evaluating the need for protein supplementation in pregnant cows during the winter months.
A look at results
According to this study, cows that received protein supplementation during pregnancy weaned bigger calves. In some instances, it also increased carcass weight and quality grade.
Stalker thinks the growing fetus is sensitive to the uterine nutritional environment.
“If the cow is consuming sufficient nutrients, the fetus gets a signal that the environment outside the uterus is a good source of nutrients, and the fetus will grow to its genetic potential,” he said.
However, if the cow didn’t receive supplement during gestation, the fetus received a signal that the environment outside the uterus is nutrient-poor, and the calf will better adapt to that environment if it has a slower growth rate and a smaller mature size, Stalker explained.
“We found that the nutrient environment of the dam influences the lifetime performance of the calf based on the signal the calf perceives during gestation,” Stalker said.
What they didn’t find was any change in pregnancy rates based on feeding the cows a supplement during the winter months.
“During the course of this study, we never supplemented the cows with more than one pound of protein, and mostly it was 0.35 to 0.4 pounds per cow per day during the winter,” he said. “During this four-year study, we made 576 cow observations.”
Stalker said cows can meet the nutritional needs for themselves and their growing fetus by grazing winter range with up to two pounds of protein supplement per day like distiller’s grain or alfalfa.
He also said different protein supplements are available, and ranchers should select a least-cost supplement that is available in their area and easy for them to feed.
A simpler way to meet the cow’s protein requirements through the winter is by grazing cornstalks. Stalker said the most important thing to consider when grazing cows on a cornfield is to use the correct stocking rate.
Based on a 1,200-pound cow and 175-bushel-per-acre corn, Stalker said 1.5 animal unit months (AUMs) per acre or 45 grazing days per acre on irrigated cornstalks should be sufficient.
He added that producers who are utilizing a cornfield that yielded differently or a smaller or larger cow can utilize the cornstalk grazing calculator at beef.unl.edu under learning modules to determine the correct stocking rate.
The cornstalk calculator is also capable of determining the total cost per head per day of grazing a cornfield, so ranchers can easily compare it to other feeding methods.
At 1.5 AUM per acre, Stalker said it isn’t necessary for ranchers to supplement their cattle on the cornfield.
“There is a big difference in nutrient content of the corn plant,” he explained. “The corn grain is the most nutritional part of the corn plant, which is why cows will go through a field and eat all the downed corn first.”
“The husks are the next most nutritional part of the plant, followed by the leaves, the cobs and finally the stems,” he said.
Husks are about 58 percent total digestible nutrients (TDN), Stalker said.
“We have to cut our meadow pretty early to get 58 percent TDN in grass hay,” he explained. “That is pretty good quality and about what they need to maintain their weight.”
Length of grazing
The problem producers run into, Stalker continued, is grazing the cornfield too long.
“Cows selectively choose the higher quality parts of the plant first,” he said. “Only about 12 percent of a cornfield is husks. The leaves make up a third.”
“What happens is the cow starts out with a higher quality diet, and as time progresses, the quality of that diet decreases,” he explained. “If we stock that cornfield even heavier, the decline will occur even faster. That is why stocking rate is so important.”
The amount of leaves and husks in a field is a function of corn grain yield. Stalker said about 16 pounds of leaf and husk will be produced per bushel of corn. From there, the cows will walk on some of the residue and defecate on some, so he figures the harvest efficiency for the cow at about 50 percent.
Since harvesting machinery has become more efficient, cattle have suffered fewer problems with acidosis from consuming too much corn, Stalker said. However, if more than eight bushels of corn per acre are left in the field or if there is spillage from the grain cart, producers may want to consider some type of intervention like cross-fencing or adding sodium bicarbonate to the water.