Effects of tallow supplementation on dietary nutrient and minimal amino acid utilization in the laying hen were studied in two experiments. In the first experiment diets contained six levels of animal tallow ranging from 0 to 10%. Percent egg production and egg mass were not significantly affected by tallow. Body weight was significantly increased by 2% tallow was maximum at 6%. Addition of up to 6% fat improved feed conversion without adversely affecting other production characteristics. Metabolizable energy (ME) intake increased from 305.1 to 322.4 kcal/hen/d over the range of 0 to 6% tallow with no further improvement at higher tallow levels. Maximum net energetic efficiency was obtained with 2 and 4% tallow. Ability to digest tallow declined significantly with hen age. Higher tallow ME values were obtained from calorimetry data than from digestibility measurements due to beneficial effects of tallow on digestibilities of fat and protein in the basal diet. No improvement in starch retention was observed with tallow supplementation. In the second experiment, diets containing four levels of protein (15.0, 13.6, 15.0 + methionine and 17.0%) without and with 3% tallow were fed to hens housed in an open cage house or an insulated, evaporatively cooled house. Egg production and egg mass were significantly higher in the insulated house. This study indicates that reducing total protein below the National Research Council (NRC, 1984) recommended level significantly reduced egg production by birds housed in an open house. Supplemental methionine to provide .60% TSAA was required for maximum egg production. Egg production was significantly improved with the low protein diet when 3% tallow was added; however, egg production rate supported by this combination was significantly below that obtained with the 17% protein diet either with or without added tallow. For birds housed in the insulated, evaporatively cooled house the diet based on the NRC amino acid recommendations appeared to be optimal for performance, even with a lower protein level. No additional benefits were obtained in egg production with 3% tallow in any of the diets under these housing conditions.
Poultry -- Feeding and feeds., Poultry -- Feed utilization efficiency., Tallow., poultry, FAT, PERFORMANCE, AMINO ACIDS
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