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Three experiments were conducted to study changes in exocrine pancreas function in relation to age, dietary fat and digestibility in poultry. In the first experiment, 120 White Leghorn and 120 Hubbard chicks were fed a basal diet with or without 5% animal fat. Total units of lipase, amylase, trypsin and chymotrypsin activities in pancreas increased linearly with age in Hubbards from 2 to 29 days, but plateaued after 16 days in Leghorns. Hubbards showed higher total pancreatic lipase, amylase, trypsin and chymotrypsin activities compared with Leghorns. Addition of 5% dietary fat significantly increased total lipase activity in pancreas, but decreased total amylase activity. Added fat had no well defined effect on total pancreatic trypsin and chymotrypsin activities. Fat digestibility in Leghorns fed the low fat diet increased significantly from 14 to 30 days of age, but not in Leghorns fed the high fat diet; while Hubbards fed both diets showed a significant decrease in fat digestibility. Fat digestibility was increased with added fat in both breeds. No direct correlation was found between nutrient digestibility and corresponding enzyme activity. In the second experiment, 80 young White Leghorn hens were fed a basal diet with or without 5% animal fat. Fat supplementation did not generally significantly affect lipase activities, but total lipase activity in pancreas decreased after 10.6 and increased after 12.7 mo in pancreata of birds fed both diets and fed the high fat diet, respectively. Fat digestibility was not affected by age, but was higher with fat supplementation. In the third experiment, 96 older White Leghorn hens were fed a basal diet with or without 5% animal fat. Total pancreatic lipase activity showed a U-shaped curve with the lowest value at 15.7 mo and increased after 15.7 mo following either natural or force molting. Fat supplementation did not significantly affect lipase activities. Amylase, trypsin and chymotrypsin activities decreased with age from 10.2 to 15.7 mo, but were increased with fat supplementation. Fat digestibility was not affected by age, but was significantly higher with fat supplementation.

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The objective of this work was to define the effects of dietary energy intake on broiler fat deposition and metabolism. Fatty broilers are one of the major problems in the broiler industry. The effects of changing calorie to protein (Cal/Pr) ratios, and the addition of cellulose or dried distiller's byproduct (DDBP) in the diet, on abdominal fat deposition, liver lipogenesis and glucose oxidation and broiler performance indicated that the mean body weight of broilers fed narrower Cal/Pr ratio diets (124 and 143 for starter and grower, respectively) were lower (P<.01) than broilers fed diets with mid-Cal/Pr ratios (138 and 160) and wide Cal/Pr ratios (147 and 171). Feed conversion was better (P<.01) for broilers fed the diet with wide Cal/Pr ratio than the broilers fed the diet with narrow Cal/Pr ratio. Abdominal fat deposition increased (P<.001) with wide Cal/Pr ratio than narrow Cal/Pr ratio. No significant differences were found in in vitro liver lipogenesis and glucose oxidation when Cal/Pr ratio was widened. Mean body weight, feed conversion and abdominal fat levels of broilers fed 5% cellulose or 10% DDBP diets were not different when compared to broilers fed diets with the same Cal/Pr ratio without these two feed ingredients. The time-course of the deposition of abdominal fat fitted a negative exponential growth curve. The data also indicated that the highest potential for abdominal fat deposition was during the first two weeks of age. When the feed intakes of broilers were restricted for a 6 day period beginning at 1, 2, 3 and 4 weeks of age, the feed efficiencies of all the restricted broilers were significantly improved compared with broilers fed ad libitum. No significant differences were observed in mean body weight between the different treatments. The percentage of abdominal fat in broilers restricted-fed starting either at 1 or 2 weeks old for a 6-day period were lower (P<.05) than broilers fed ad libitum. Feed restriction from days 7 to 12 reduced the adipocyte size but not the number. Feed restriction decreased (P<.05) lipogenesis at 2 and 8 weeks of age. No significant effects were found in lipolysis between the restricted and ad libitum-fed broilers. These studies demonstrate that early feed restriction (days 7 to 12) reduced abdominal fat deposition which is attributed to the reduction in the adipocyte size. Smaller size adipocyte resulted from decreased activity of lipogenesis. / Graduation date: 1991

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