No description available.

No description available.

The gene encoding chicken growth hormone (GH) was isolated from a chicken genomic library. The size of the gene was 4 kb. It was digested with PstI and subcloned into pUC18. Three of the PstI fragments were used for restriction fragment length polymorphisms (RFLPs) analysis at the GH locus in two chicken strains (fat and lean line). Four polymorphic sites were detected using a PstI fragment (PII) as a probe. One polymorphism was located at a SacI restriction site (PS1), and three at MspI sites (PM1, PM2 and PM3). A method based on polymerase chain reaction (PCR) was developed for detecting polymorphisms at PM3 site. A fragment of 823 base pairs which contained the PM3 polymorphic site was amplified. Three genotypes (+/+,$-$/$-$ and +/$-$) were distinguished by examining the MspI digested PCR products in either agarose or polyacrylamide gel. / Ten anonymous cDNA clones were also isolated from a chicken liver cDNA library and used for RFLPs analysis. Three of these clones were found to be able to detected RFLPs at MspI sites in chicken strains (strain 7, 8, 9, 8R, S and K) indicating that a high frequency of genes are polymorphic and can be used as markers in mapping experiments. One of the three clones was present on a haploid genetic element. Segregation analysis showed that the inheritance of this haploid gene was determined by the genotype of the female parent.

No description available.

No description available.

Master of Science

Previous studies indicated that exposure of broiler cockerels to acute heat for 24 hr at five days of age increased their survivability when exposed to high ambient temperature prior to market. Since they were conducted at low relative humidity, the aims of the present study were to determine if higher relative humidity affected the response and to investigate the physiological basis of the response. The early, neonatal, heat stress consisted of increasing ambient temperature to between 35.0 to 37.8 C for 24 hr at five days of age in half of the pens (early heat stress) while the remaining pens were kept at 29.4 C (early control). At 6 wk of age a second, late, juvenile, heat challenge was administered. Ambient temperature in half of the early heat stressed pens and early control pens was gradually increased to between 35.0 to 37.8 C for 8 hr on two consecutive days. Significantly lower mortality during the second heat challenge was observed in the early heat stressed birds. This reduction in mortality ranged from 75 to 90% of that seen in the early control birds. Additionally, there were no deleterious effects on body weight, body weight gain or feed efficiency caused by exposure of birds to early heat stress. Feed restriction or administration of a commercially available electrolyte package to the water had no effect on the ability of the birds to withstand high ambient temperature. Water consumption, core and surface body temperature were increased upon exposure to late heat; however, there were no significant differences between the early heat stressed and early control groups. There was a significant reduction in plasma T₃ concentration in the late heat stressed birds. No significant differences in plasma glucose were observed among the heat treatment groups. A significant increase in total plasma protein occurred during the first sampling period during late heat stress, with values returning to control levels during the second sampling period. No significant differences between the early heat stressed and early control groups were observed in plasma T₄ and total plasma protein during late heat. Heterophil to lymphocyte ratio was lower in the early heat stressed group than in the early control group during the second day of late heat exposure These results indicate that thermotolerance can be induced by exposing broiler chicks to 35.0 to 37.8 C for 24 hr at 5 days of age with no adverse effects on performance. Although the mechanism by which Early, neonatal, heat exposure induces thermotolerance is unknown, it is clear that it does not resemble acclimation. / Master of Science

Four experiments were carried out with laying hens to evaluate the effects of body weight, age, dietary protein, and tallow levels on performance, nutrient intake and energy utilization. In the first experiment, Single Comb White Leghorn birds were divided into four body weight groups at the onset of egg production. Voluntary feed intake was 18% less for the lightest (1.39 kg) in comparison with the heaviest group (1.83 kg). Egg weight was directly related to body weight with the heavy birds producing an average egg weighing 65.3 g and the lightest birds having an average egg weight of 58.9 g. Feed conversion was also significantly better for the lighter birds. Maintenance requirements for the heaviest and lightest birds were 60.5 and 57.9% of metabolizable energy consumed, respectively. Metabolizable energy intakes above maintenance were 131 kcal/d for the heavy birds and only 119 kcal for the light group. A composite regression analysis indicated a maintenance requirement of 127.7 kcal/d/kg('0(.)75) and an energetic efficiency of 75.2% for the conversion of metabolizable energy to net energy. In order to evaluate the effects of age and body weight on laying hen performance, the last three experiments were designed using old, molted, and young hens which were divided into the heaviest and lightest body weight groups. The old birds were 72 weeks old, the molted birds were 106 weeks old, and the young birds were 27 weeks old at the start of the studies. In each experiment the birds were fed ten experimental diets with 12, 14, 16, 18, and 20% dietary protein in combination of 1 and 4% supplemental fat. Egg output was increased with the supplementation of tallow in only the young birds; while energy retentions were improved in the old and molted birds with fat feeding. Average energy retentions per kg physiological body weight were 58.8, 41.7, and 38.6 kcal for the young, molted, and old hens, respectively. The light-bodied birds showed 9% better gross energetic efficiencies than the heavy-bodied birds. Estimated daily protein intake requirements were 16.8, 13.3, and 12.8 g/d to support production levels of 84, 64, and 66% for the young, old, and molted birds, respectively.

Relationships among glucose tolerance, plasma insulin, and plasma glucagon were examined in chicks developed through selection for high (HW) and low (LW) body weight, and in F, crosses (HL) between HW males and LW females. At 21, 42, 63, and 84 days of age, chicks from each population were intubated with glucose (2 g/kg body weight) following a 24-hr fast. Blood was collected at 20-minute intervals up to 100 minutes postadministration. At all ages, the LW chicks were better able to metabolize glucose than their HW counterparts, while the HLs exhibited intermediate responses. Impaired glucose tolerance in the HWs and HLs was not associated with insulin insufficiency; the HWs and HLs, in comparison to the LWs, were hyperinsulinemic at 42 and 63 days of age and plasma insulin levels did not differ among populations at 21 or 84 days of age. Plasma glucagon responses to glucose administration were inconsistent, but plasma glucagon levels were consistently higher in the HWs and HLs than in the LWs. It was concluded that excessive fat deposition in chickens selected for rapid growth is associated with hyperinsulinemia and insulin resistance. / Master of Science

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.