Two feather digestion processes to remove the feathers from the carcasses of dead hens were evaluated for their impact on the nutritional quality of the resulting feather meal. There were three treatments: control (untreated feathers), a feather-digesting enzyme, and NaOH treatment. Both enzyme- and NaOH-treated feathers were easily separated from the hen carcasses. The CP level of enzyme-treated feathers after autoclaving (49.90%) was significantly less than the control and NaOH-treated feathers (94.48 and 87.31%, respectively) because of elevated ether extract levels resulting from skin and abdominal fat release during the 12-h enzyme incubation. Before autoclaving, pepsin digestibilities of enzyme- and NaOH-treated feathers were significantly higher than the control. However, after autoclaving, no significant difference was found in pepsin digestibility between the control and enzyme treatments or control and NaOH treatments. The typical limiting amino acids, methionine, lysine, and histidine, in feathers were present at greater levels in the resulting enzyme-feather meal (E-FM) compared with the NaOH-feather meal (N-FM) or control-feather meal (C-FM) on a percentage of CP basis. Cystine levels, however, were significantly lower in the E-FM and N-FM compared with that of the C-FM. In chick bioassays, no significant differences were found in protein efficiency ratio (PER) and net protein ratio (NPR) among C-FM, E-FM, and N-FM. The AMEn of E-FM (4.52 kcal/g) was significantly higher than the C-FM (3.58) or N-FM (2.79). These findings indicated that although enzyme treatment could improve the nutritional quality of feathers from dead hens, NaOH treatment was a more rapid means of separating feathers from the carcass.

This study was designed to evaluate the effect of chemical and enzymatic approaches to digest poultry feathers from dead birds for the purpose of recycling their nutrients as animal feeds. The experimental treatments were as follows: 1) control, 2) 24-h enzyme, 3) 24-h NaOH, 4) 2-h NaOH, and 5) 2-h NaOH and 24-h enzyme. The feather N solubilities of the control, 24-h enzyme, 24-h NaOH, 2-h NaOH, and 2-h NaOH and 24-h enzyme treatments were 0.91, 2.55, 78.83, 30.03, and 50.34%, respectively. The pepsin digestibilities of unsolubilized feather residues from the control, 24-h enzyme, 2-h NaOH, and 2-h NaOH and 24-h enzyme treatments were 4.67, 13.19, 55.83, and 59.08%, respectively. The in vitro amino acid digestibilities of the 2-h NaOH and 24-h enzyme treatment were significantly higher than the 24-h enzyme or 2-h NaOH (P < 0.05), except for alanine, whereas the 2-h NaOH treatment had significantly higher amino acid digestibility than the 24-h enzyme treatment (P < 0.05), except for methionine and histidine. Costs per kilogram of solubilized feather for the 24-h enzyme, 24-h NaOH, 2-h NaOH, and 2-h NaOH and 24-h enzyme treatments were $9.64, 4.72, 12.39, and 22.97, respectively. The results indicated that prolonged incubation with NaOH improved feather solubility, whereas further enzyme treatment after NaOH treatment increased feather solubility, pepsin digestibility, and in vitro amino acid digestibility.

This study was conducted to evaluate the recycling of whole dead hens into feed ingredients by enzyme or sodium hydroxide pretreatment and fermentation. Evaluation criteria included nutrient preservation, pathogenic microorganism elimination, and assays of nutritional quality. The pH levels of enzyme- and NaOH-treated hen carcasses decreased from 6.01 and 7.66 to 4.18 and 4.24, respectively, during the 21-d fermentation. Hydrogen sulfide levels were not detected on Days 1 and 3 from the enzyme treatment; however, high levels (800 ppm) were measured from the NaOH treatments. By Day 21, H2S levels of both treatments had decreased to 78 ppm. The control, enzyme, and NaOH treatments before fermentation contained high levels of Escherichia coli and Staphylococcus aureus; however, after fermentation, these potential pathogens were eliminated in the enzyme and NaOH treatments. Levels of CP, EE, and ash of the control product were higher than either the enzyme or NaOH treatment. NaOH reduced pepsin digestibility by 11% compared to the enzyme treatment. In a bioassay, the chicks fed control autoclaved hen meal (CHM) had higher (P < 0.05) feed intake, weight gain, protein efficiency ratio (PER), and net protein ratio (NPR) than enzyme-treated, fermented, and autoclaved hen meal (EHM) or NaOH-treated, fermented, and autoclaved hen meal (NHM). However, the AMEn of the CHM and EHM were higher than the NHM (P < 0.05) when evaluated using mature cockerels. These results indicated that fermentation processing of dead hens reduced the concentration of some nutrients and depressed growth performance when hen meals were fed to young chicks.