Organ mass and composition in growing dairy goat wethers fed different levels of poultry fat and protein

Abstract

Growing castrated dairy goats (n=20; BW=30±3.3kg) were used in an 82d growing experiment to assess effects of protein and fat levels on performance and splanchnic tissue mass and composition. Animals were individually housed in elevated pens (1.2m×1.2m), stratified by body weight, and randomly assigned to four dietary treatments. In a second experiment, four mature dairy bucks were used in a 4×4 Latin square design with 21d periods (14d adjustment and 7d collection) to evaluate nutrient digestibility. Diets were formulated to provide, either 2.5Mcal/kg DM DE and 12% CP (low fat low protein=LFLP, 2.5Mcal/kg DM DE and 18% CP (low fat high protein=LFHP), 2.9Mcal/kg DM DE and 12% CP (high fat low protein=HFLP), or 2.9Mcal/kg DM DE and 18% CP (high fat high protein=HFHP). The low and high fat diets contained 3 and 15% poultry fat, respectively. At the end of the 82d growing experiment, the animals were weighed and sacrificed. Immediately after evisceration, the digestive tract segments were tied at junctions, separated, and weighed with and without digesta. The weight of the liver and other organs of the abdominal and thoracic cavities were also recorded. Blood samples were analyzed for glucose, non-esterified fatty acids, and plasma urea nitrogen. On day 14 of each period of the digestibility experiment, total urine and feces outputs were collected and weighed. These samples were composited across days for each animal (10% of daily excretion). Fecal composites were dried at 55°C for 48h to determine dry fecal output. Dry fecal and feed samples were ground and analyzed for DM, N, NDF, ADF, EE, and ash. Urine samples were analyzed for nitrogen. Liver, small intestinal and reticulo-rumen mucosa samples from the growing experiment were analyzed for dry matter, protein, DNA and RNA. Data from the growing experiment were analyzed as a 2×2 factorial arrangement in a completely randomized experiment, using fat, protein and fat×protein interaction in the model. Daily DM intakes and daily urinary outputs were similar among treatments. Dry matter, nitrogen, and fiber digestibilities were not affected by dietary treatments. Goats fed low fat diets consumed more feed than those fed high fat diets but was not affected by protein or fat by protein interaction. Average daily gains were greater for animals fed the low than high fat diets. Blood glucose and NEFA were similar among treatments, but plasma urea nitrogen increased in animal fed high protein diets. There were no differences in liver, heart, lungs, kidneys, and spleen weights. Small intestine weights (full or empty), as a percent of slaughter weight (SWT), were lower for the animals fed low fat as compared to high fat diets (1.9 vs. 2.7 and 1.5 vs. 1.9 for full or empty, respectively). Small intestinal weight (% SWT) tended to decrease with high protein diets. Liver DNA increased with high fat diet. Small intestinal epithelial DM contents were high (P<0.05) in animals fed low than high fat diets. Protein concentration in small intestinal epithelium increased with high protein diets. Splanchnic tissue weights (except omasum and abomasum) were not affected in growing goats when fed diets differing in the proportion of energy coming from poultry fat.