Metabolizable Protein Increases Rebreeding Rates

by Nancy Carver Singleton

Using a metabolizable protein supplement can boost a herd's first-calf heifer's rebreeding rate to as much as 95 percent.

Fewer than 85 percent of heifers successfully rebreed after their first calf -- an expensive loss. Ranchers typically cull 10 to 20 percent of their cows each year, primarily because of reproductive failure. Helping heifers rebreed successfully is a high priority. "If it is not No. 1, it is high on the list," said Terry Klopfenstein, a University of Nebraska animal scientist.
NU researchers compared crude protein to a metabolizable protein made from hydrologized feather meal. Feather meal was used because it is a by-product of the poultry industry and is about 90 percent protein, Klopfenstein said. Since it is so concentrated, ranchers purchase only half as many tons to get the same amount of protein as in soybean meal.
Rebreeding rates for March-calving heifers fed metabolizable protein increased between four and 10 percent during three out of four trials in the two-year study. This translates into an average $20 a head savings by using metabolizable protein, he said.

"They (cattlemen) can, through a very small input, raise their rebreeding rate if they have problems. But if they already have a 95 percent calving rate, don't spend the money," Klopfenstein said. Few ranchers regularly achieve 95 percent.

He believes that metabolizable protein is used somewhat widely and its use has increased in recent years. The feather meal used in the study is commercially available.

Klopfenstein pointed out that NU's research was done on a commercial ranch under commercial conditions and involved approximately 1,200 heifers each year. "It takes large numbers to get reliable results. You can't do it with just 50 or 100 heifers a year," he said.
Crude protein has been used in beef nutrition for more than 100 years. "The basic assumption with crude protein is that all proteins are created equal. The assumption with metabolizable protein is that not all are equal and that accounts for differences in the proteins," he said.

The biggest difference in crude versus metabolizable is how much protein is degraded by the rumen's microrganisms. About 70 percent of soybean meal degrades, compared to 30 percent of feather meal. "That (30 percent) is a good thing. What is not degraded is digested by the animal and used as a source of protein," he said.

Because ranchers already supplement cattle in winter, metabolizable protein does not require more work. The supplement is in a cake form, similar to a crude protein based supplement, just made with different ingredients. The metabolizable protein supplement cost about $3 more per cow, but that was offset by the increased rebreeding rate.
Klopfenstein served on the National Research Council committee that recommended using a metabolizable protein system for determining the correct supplement for heifers.

Using a metabolizable protein supplement can boost rebreeding rates for first-calf heifers to as much as 95 percent. ©