Barred Rock chickens were offered diets that had been pelleted at 55° or 85°C. In an 8-week feeding trial, the subjects receiving pellets processed at the higher temperature experienced significant (P ≤ .05) weight gain over those receiving the diet processed at 55°C. Although feed consumption for this treatment increased as well, the difference was not significant (P ≤ .05). Chemical investigation revealed that metabolizable energy and bioavailability of lysine of both heat treatments were similar. Starch availability as measured by in vitro enzyme susceptibility, however, was lowered by increased heat application. In a second experiment, the feeding behavior of 12-16 week old cockerels offered diets of varying particle size, resulted in significant (P ≤ .05) increases in feed consumption rate and therefore decreases in total feeding activity for birds offered pellets and crumbles as compared to mash and reground pellets. No differences were noted in meal size, meal frequency, interval between meals, or total consumption. In a parallel experiment, no differences were noted in the behavioral parameters of birds receiving diets pelleted at 55, 70, or 85°C of similar density and particle size. Mash controls, however, experienced significantly (P ≤ .05) decreased consumption rate and concurrent increase in feeding activity. The beneficial effects experienced with pelleting can therefore be attributed to the reduction in total feeding activity that allows an increased proportion of net energy to be utilized in support of growth. / M.S.

Four experiments were conducted to examine the energetic responses of chicks from lines divergently selected for 56-day body weight to caloric intake. Caloric overconsumption or calorie-protein imbalances were induced by providing glucose solutions (16% w/v) in lieu of water in the first experiment, and by force-feeding the diet to crop capacity in the subsequent trials. Feed restriction was accomplished by providing 75% of ad libitum intake each day. Both low-weight (LN) and high-weight (HN) chicks reduced their voluntary feed intake when glucose solutions were provided; caloric intake was reduced by 25% and 10% in LN and HN chicks, respectively. Weight gain and the deposition of protein and ash in the carcass were reduced by the glucose treatment, but carcass lipid deposition was increased. The efficiency of energy deposition was improved in HN but unchanged in LN chicks. Feed restriction reduced feed intake, energetic efficiency, and gain of body weight, carcass dry matter, protein, lipid and ash. The suppression of lipid deposition was more severe in the LN chicks than in the HNs. Overfeeding of a complete diet increased body weight, the deposition of all carcass constituents, and energetic efficiency. Feed restriction exerted an opposite effect, with the LN chicks exhibiting more pronounced responses than the HNs. Determined metabolizable energy values of the diet differed among feeding treatments and between lines, and line by feeding treatment interactions were observed. Body core and surface temperatures demonstrated that the LN chicks were less able than the HNs to maintain homeothermy under treatments imposed. Heat production tended to be increased by overfeeding and reduced by feed restriction. Metabolic rates were higher in LN than in HN chicks when the chicks were fed ad libitum or subjected to restricted feeding, but not when force-fed. The latter observations were attributed to differences in physical activity. Plasma triiodothyronine (T₃) of LN chicks was increased by force-feeding and reduced by restricted feeding, but no significant differences in plasma T₃ occurred in HNs. Thyroxine (T₄) and the T₃:T₄ ratios were unchanged by feed intake, although LNs exhibited higher plasma T₃ and T₃:T₄ ratios than HNs. Although endocrinological changes to caloric consumption analogous to those observed in mammals occurred, energy balance did not confirm the existence of diet-induced thermogenesis in the fowl. / Ph. D.