EFFECT OF OVERHEATING ON THE NUTRITIONAL QUALITY OF COTTONSEED MEAL

The effect of overheating on the nutritive value of cottonseed meal (CSM) for chicks and protein solubility in .2% KOH was evaluated. One-week-old male chicks were assigned to seven diets consisting primarily of corn and unautoclaved commercial CSM (expander-solvent extracted) or CSM that had been autoclaved for 20, 40, 60, 90, or 120 min at 121 C and 105 kPa. The protein level of the diets was either 21 or 22%, and FeSO4.7H2O was added to bind any free gossypol in the CSM. A control corn-soybean meal diet was included for comparison. A sample of full-fat cotton seeds extracted with a mixture of water-acetone-hexane without heating (DFCS) was also evaluated. The true digestibility of amino acids in cecectomized cockerels was determined for DFCS, three samples of unautoclaved commercial CSM, and the commercial CSM that had been autoclaved for 60 or 120 min. Growth performance of chicks was depressed (P < .05) by feeding CSM autoclaved for 40 to 60 min or more. Growth performance of chicks fed CSM diets was inferior (P < .05) to that obtained from the corn-soybean meal diet. Protein solubility for the unautoclaved commercial CSM was less than for DFCS (70 vs 60%) and did not decrease until 90 min of autoclaving. Average amino acid digestibility was higher for DFCS than in CSM (85 vs 74%). The mean true digestibilities of lysine, methionine, and cystine in the three unautoclaved commercial CSM were 64, 72, and 72%, respectively. Digestibilities of amino acids in CSM were reduced by 60 and 120 min of autoclaving. The results of this study indicated that the protein quality of CSM was affected only by extensive overheating and that protein solubility in .2% KOH was not a sensitive indicator of overheating of CSM.