Lee I. Chiba, Henry W. Ivey, Keith A. Cummins, and Brian E. Gamble

As the world's population grows, sources of protein for human nutrition become more and more valuable. High-quality protein products are essential in human diets, but they also are a vital component of diets fed to pigs in the swine industry. Finding viable alternative protein sources for pigs is necessary to avoid conflicts between human food requirements and the swine industry. AAES research indicates that hydrolyzed feather meal may be a suitable alternative protein source for finisher pigs.

Feather meal, a major by-product of poultry processing, is high in protein (80-85%) but deficient in some amino acids, especially lysine. Because adequate lysine is the primary concern for most swine diets, it is generally recommended that feather meal be limited to about 5% of the diet for optimum performance. Previous AAES research demonstrated that feather meal is an effective source of extra dietary nitrogen to enhance leanness of finisher pigs. Results from that study also suggested that pigs may be able to utilize more than 5% feather meal in their diets. However, in that study, corn and soybean meal provided a fixed amount of protein and lysine, and feather meal provided additional protein and lysine.

A recent study was conducted to evaluate the value of feather meal as a source of protein supplement and to determine whether soybean meal can be completely replaced by a combination of feather meal and crystalline lysine.To determine the optimum concentration of dietary feather meal, five com-soybean meal diets were formulated to contain 0.73% lysine and 0-12% feather meal (see table). This lysine concentration is 20.8% greater than the current National Research Council (NRC) recommendation. Two additional diets containing 9% feather meal were used to test the possibility of completely replacing soybean meal with feather meal. Both of these com-feather meal diets were formulated to have the same protein content as the corn-soybean meal diet with 0% feather meal. Crystalline lysine was added to one of the corn-feather meal diets to achieve 0.73% lysine.

At an average weight of 150 pounds, pigs housed in individual pens were assigned to one of these seven diets. To assess carcass traits, all pigs were slaughtered when they weighed approximately 220 pounds. Results are summarized in the table.

Weight gain and gain-to-feed ratio (a measure of feed efficiency) decreased linearly as the dietary feather meal content increased. However, greater weight gain of pigs fed the diet containing 3% feather meal and greater feed intake of pigs fed the diet containing 12% feather meal seemed to be primarily responsible for the over-all linear decreases. These reductions were not consistent or progressive as dietary feather meal increased from 0% to 12%. The rate and efficiency of weight gain in pigs fed other soybean meal diets were relatively similar.

Carcass quality of finisher pigs was not greatly affected by the inclusion of up to 9% feather meal. However, the diet with 12% feather meal did decrease carcass quality. This is illustrated by reductions in proportion of carcass lean (48.7% vs. 51.6%) and the rate of lean growth (0.52 vs. 0.66 pounds per day), compared with pigs fed other combinations of soybean meal and feather meal.

Because of its lysine deficiency, it is recommended that feather meal should be incorporated into swine diets based on the lysine content. However, this method would increase both the amount of feather meal needed to satisfy the pig's lysine requirement and the protein content of diets. Supplementation of feather meal diets with the most deficient amino acid, lysine, is likely to decrease not only the amount of dietary feather meal required, but also the protein content of swine diets. Thus, lysine supplementation of feather meal diets could alleviate the environmental concern resulting from the increased nitrogen excretion in the urine of pigs fed highprotein diets.

As expected, pigs fed the corn-feather meal diet without lysine supplementation grew more slowly and less efficiently than those fed the soybean meal diets containing 0% or 9% feather meal. The addition of crystalline lysine to bring the lysine concentration up to 0.73% did not alleviate growth depression caused by completely replacing soybean meal with 9% feather meal.

This lack of growth response to lysine supplementation is difficult to explain. The amino acid content of this diet was at least 20.8% greater than NRC recommendations. For instance, the second most deficient amino acid, tryptophan, was 25.3% greater than the NRC requirement. Total content of all amino acids, therefore, should have been adequate. One possible explanation is that pigs may utilize not only lysine but other amino acids in feather meal less efficiently than those in soybean meal. This contention, however, does not explain the carcass data.

Carcass quality was generally lower in pigs fed the two corn-feather meal diets than those fed the corn-soybean meal diets containing 0% or 9% feather meal. However, carcass backfat, loin muscle area, and proportion of lean improved greatly with lysine supplementation, and these traits were very similar to pigs fed the soybean meal diet containing 0% or 9% feather meal.

Although lean growth rate was lower in pigs fed the lysine-supplemented feather meal diet than those fed the corn-soybean meal diet containing 0% or 9% feather meal, this decrease was caused by an extension in the feeding period (about seven days).

In conclusion, these results indicate that up to 9% feather meal can be incorporated in the finisher pig diet with no adverse effects on carcass traits and little effect on growth rate and efficiency. In addition, although weight gain may be reduced, feather meal can be used as the only source of protein supplementation without decreasing carcass quality, provided that the diet is supplemented with crystalline lysine. It is not known whether the growth depression caused by a complete replacement of soybean meal with feather meal can be alleviated by supplementation with other amino acids, thus avoiding the increase in feeding period. Further research is needed to explore the full potential of utilizing feather meal in swine diets. Nevertheless, considering the market incentives for leaner pigs and possible reduction of feed costs, feather meal may be a suitable alternative protein supplement for finisher pigs.

Chiba is an Associate Professor and Cummins is a Professor of Animal and Dairy Sciences. Ivey is Superintendent (retired), and Gamble is
an Assistant Superintendent of the Wiregrass Substation in Headland.