Reduce heat stress by adding fat and amino acids to ration

By University of Missouri researchers - When summer temperatures rise, pigs being finished for market don't eat as much. That cuts feed efficiency and increases days to market. Both are costly to pork producers. Pigs fed modified diets in environmental chambers, under heat stress, at the University of Missouri have shown a way to keep pigs growing, right on through the hot, humid days of summer.
calendar icon 24 April 2001
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Joel Spencer, graduate student in animal science, found that when the "heat increment" in swine rations was reduced and essential amino acids were added the pigs thrived.

While pigs on the modified diet improved performance, pigs on a typical ration of corn and soybeans, which are heat producers, did not do as well.

The modified diet contained 8 percent added fat over the regular diet. And, amino acids were also increased to maintain a constant lysine-to-energy ratio, which improved performance even above adding fat.

Unexpected findings.

Feed efficiency, as well as growth rate, improved. The amino acids in the fat-added diets produced better gains at less cost, under heat stress, than the regular corn-soy diet. They also produced gains similar to pigs reared in a cooler environment. The cool chamber was kept at a constant 70oF. The hot chamber was at 95oF during the day and 85 degrees F at night. "It was like a lot of days in a hot Missouri summer," Spencer said.

Another bonus was improved carcass quality in the hams and loins from pigs fed the high-fat diet during heat stress.

After success with the experiment in the MU labs, Spencer, along with his PhD advisor Gary Allee, expanded their study to a commercial hog farm, where they tried their experimental rations in two confinement-finishing barns with 600 pigs in each.

In summer on the farm, temperatures were uncontrolled. Fortunately, for the experiment, the researchers hit two weeks of very hot weather at the start of the study.

Higher average daily gain

Pigs grown on the farm had higher average daily gain, by 15 percent, during the two-week heat wave when fed the ration fortified with amino acids and 8 percent more fat. These were gains similar to those at the MU lab.

Feed efficiency also went up at the farm as it had in the lab. Although, the pigs do not eat as much during hot weather, they continue to gain when fed the supplemented diet. "Reduced feed intake combined with increased gains, leads to increased feed efficiency," Spencer said.

Another benefit of the farm study was that the researchers followed the barrows to the packing plant. There the payoff for the diet switch was found.

$2 more per pig

Pigs on the modified "hot weather" diet returned $2 more per pig than barrows fed the corn-soymeal ration. "The fat-and-lysine diet cost more per ton, but with improved performance it returned more profit after feed costs," Spencer said.

One reason for increased profit was less variation in weight of the barrows, which average 260 pounds per head when sold. "With fewer overweight hogs and fewer light hogs, there was less dockage from the packer," Spencer said.

There are problems still to be studied. Rations with high fat content, which was poultry fat in this study, are more difficult to make into pellets and to feed. Also, the animal scientists want to see if they can add less fat and achieve the same benefits.

In giving his report in Columbia at Pork Expo, sponsored by the Missouri Pork Producers Association, Spencer summed up his on-farm study.


Pigs that were fed the ration with reduced heat increment and with supplemental lysine, improved gain, reduced days to market, reduced weight variation in finished pigs, and boosted profits over feed costs.

"This shows the value of doing research in a controlled heat chamber," Spencer said, "then taking the research to the farm to test its validity."

Partial support for the study was provided by Ajinomoto Heartland Lysine of Chicago, Ill.

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