UNIVERSITY PARK, Pa. -- Adding fat to the food ration of beef cows will likely enhance reproduction, advises a beef specialist in Penn State's College of Agricultural Sciences.

Several studies have shown that added fat will increase the number of follicles that will be formed on the ovary of the cow, according to associate professor John Comerford, who points out that fat will increase the efficiency of rumen fermentation in producing energy for the cow.

"While not a silver bullet that will replace good overall management, evidence suggests supplementing food with fat for the breeding herd may have some economic benefits," he says. "There is considerable evidence now to suggest that adding limited fat supplements -- particularly polyunsaturated fats from plant sources -- to the diet of beef cows prior to breeding will enhance reproduction by reducing the anestrus period after calving."

Plant-derived oils have been shown to increase insulin and growth hormone levels, and LH secretion was increased with fat supplementation, according to Comerford. He points out that the optimum level of supplementation has not been determined.

"One study has shown 2 pounds of raw cottonseeds per day fed for 60 days, beginning 30 days before breeding season started, increased the number of cows cycling at the beginning of the breeding season by 18 percent," he says. "Using this level as a guide, the economics of this supplementation for Pennsylvania and the Mid-Atlantic region remains to be examined."

Whole soybeans can be used as the example since they will be more readily available in this region. When priced at $4 per bushel, this results in a total cost of $80 .for feeding 10 cows for 60 days at 2 pounds per day.

"The beans are an excellent source of energy and protein for the cows, and a conservative estimate (based on a hay price of $80 per ton) results in a substitution value of about $50 worth of hay," says Comerford. "Cows bred earlier in the breeding season result in calves being older and heavier at weaning the next year. If we actually wean nine calves from the 10 cows, we would need to increase weaning weight by about 4 pounds per calf to recover the rest of the cost of feeding the beans. This would be an average of about two to three days older when sold at weaning because of the supplementation."

Comerford believes supplementing feed with soybeans adds an excellent source of energy and protein. "Young cows can be expected to improve body condition and rebreeding rate," he says. "Cows with a higher potential for milk production may be able to produce more milk."

It will be important to watch the cost of the supplement, Comerford cautions. Farmers should optimize the amount that is fed, and remember there are a lot of issues related to reproduction; general nutrition, herd health, bull fertility, weather and several other factors.

Added fat often has been used in the diet of cattle to increase the energy density of the ration because fat has a higher number of calories per unit of weight than carbohydrates and sugars. This was particularly important for feedlot animals where above-average growth rates were expected, and for dairy cows with high levels of milk production. Excessive use of fat in the diet (more than 7 percent of the dry matter intake) can be detrimental because it may be unpalatable and cause the loss of rumen microbes.

There are several sources of fat available for use in cattle diets, including commercially prepared fat additives such as Megalac. Other sources include fishmeal, the oilseeds such as whole soybeans and whole cottonseeds, and food byproducts such as bakery wastes. The latter three often are available in this region.

Adding fat to feed will not influence the number of follicles that are present in cows that have been "superovulated" and used in embryo transfers, Comerford notes.

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EDITORS: Contact John Comerford at 814-863-3661 or e-mail jxc16@psu.edu

Contact:

Jeff Mulhollem jjm29@psu.edu 814-863-2719 814-865-1068 fax