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Corrigenda inserted behind title page. / Bibliography: leaves 275-306. / xxxv, 306 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The pattern of body growth and intestinal development of an Australian strain of broiler chicken, the Steggles x Ross (F1) in response to different diets was studied. Five experiments were designed to examine the pattern of growth and mechanisms involved. In four other experiments, the mechanisms underlying the gross response of the broiler chicks to dietary ingredients, anti-nutritive factors and growth enhancers were examined. Results indicated that a rapid development of the small intestine preceded significant overall body growth. Body growth would, however, depend more on the various physiological events such as those related to mucosal growth and renewal, digestive enzyme function, and nutrient transport. Some of the differences observed in productivity of broiler chickens on different diets were traced to events at the intestinal level. / Thesis (Ph.D.)--University of Adelaide, Dept. of Animal Sciences, 1999

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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

Chickens, being open thermodynamic systems, maintain a constant exchange of energy and matter with their surrounding environment. In order to avoid reaching thermodynamic equilibrium with the environment the bird makes use of homeostatic mechanisms. These ensure the reduction of the entropy of the system to values that guarantee its integrality. The thermoregulatory response is a major component of the homeostatic machinery of living systems. This induces modifications of physiological parameters of the bird, taking the system “bird” to a new steady state. The achievement of this new state is possible only if the thermoregulatory mechanisms of the birds are able to counteract the environmental demand/burden. A successful thermoregulatory response depends not only on the achievement of that steady state, but also on the compatibility of the value of those parameters with life (especially regarding the value achieved by body temperature) as well as on the time of exposure to the environmental perturbation. Based on those premises, this thesis presents a mechanistic analysis of the thermal interaction between a broiler and its surroundings. The first section of the document introduces the reader to the general concepts of thermodynamics of living systems and physics of heat exchange. The second use mechanistic simulation techniques to represent the environment, the thermal and thermoregulatory properties of a broiler chicken and the interaction between bird and environment. Finally, the third section describes a conceptual simulation model able to predict, over a given period of time, the response of a bird to environmental conditions above those associated with least thermoregulatory effort. Various simulation exercises are reported, the objectives being to study the behaviour of certain variables and to question the validity of current theories of thermoregulation in environmental physiology. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

The effect of forced molt on pituitary function and other endocrine parameters was investigated in three year old hens subjected to a dietary forced molting procedure. In addition to molting, fasting caused cessation of egg production, body and organ weight loss, alterations in hormone secretion and morphological changes in some endocrine glands. Body and ovary weights decreased but returned to normal with ad libitum feeding. Pituitary, thyroid and adrenal weights were not affected but serum hormone levels measured by RIA revealed a decrease in LH, FSH and PRL and increases in TSH, T₃ and GH all of which returned to higher levels with ad libitum feeding. Serum P₄ levels remained low (and egg-laying stopped) until ad libitum feeding was resumed and then increased and egg-laying returned to a typically productive level. Serum ACTH and T₄ increased with fasting and remained elevated. Gonadotrophs and corticotrophs increased in numbers with fasting and/or food restriction but thyrotrophs, somatotrophs and lactotrophs decreased. Correlations between cell populations and serum hormone levels was quite common. Colloid-filled follicles resembling a hypertrophic thyroid gland occurred throughout the pituitary pars distalis. Granules appear to be discharged into the follicular lumen through exocytotic pores in the apical plasmalemma of follicular cells. Lactotrophs, corticotrophs and somatotrophs are commonly arranged in follicles or clusters. PRL-containing granules are in the center of some follicles and are concentrated near pituitary cysts. Pituitary cysts, lined with ciliated epithelium and sparse mucous cells, are more prevalent in fasted hens and decline with the resumption of feeding. Reduced lactotroph populations and presumptively degenerated lactotrophs in cyst lumens are correlated with reduced serum PRL levels. Necrotic cells occurred in the pituitary parenchyma of fasted birds but dilated RER in the thyrotrophs of fasted hens indicate enhanced activity of these cells. Ultrastructural evidence presented here indicates that pituitary secretion by lactotrophs occurs both intraluminally and perivascularly.

Genetic Variation influencing reproduction and growth of White Rock chickens was studied. The populations used were lines high (HH) and low (LL) selected for 56-day body weight, reciprocal F₁ crosses (HL and LH), F₂ crosses of the F₁ and dwarf populations (HD and LD) originating from lines HH and LL. Inheritance of egg production and egg composition was examined (Experiment 1). Although reciprocal effects were generally unimportant, nonadditive genetic variation was evident for reproductive traits and egg component measures of shell and yolk. Comparisons in Experiment 2 involved dwarf and normal chickens from lines HH and LL. Yolk weight increased while the ratio of albumen to yolk decreased with age. Line and genotype differences were evident for egg shell and yolk traits while line by genotype interactions showed that genetic background influenced expression of dw. Embryo growth of dwarfs was similar to that of nondwarfs at all ages (Experiment 3). Reduced egg size of dwarf pullets did not reduce embryonic weights. Embryo length and weight and yolk sac weight were greater for line HH than LL. In Experiment 4, allometric growth and cellular content of brains were measured in normal and dwarf chickens from lines HH and LL and reciprocal F₁ crosses from hatch to maturity. Allometric slopes were similar for lines HH and LL with significant heterosis. Within an age, DNA, RNA and protein content (mg/g) were similar for all populations. Brain weight differences were due to equal filling of a greater number cells for line HH than LL. Final brain size was influenced more by embryonic hyperplasia than postembryonic hypertrophy. The final experiment measured growth and cellular content of pectoralis and gastrocnemius muscles in populations HH, LL and F₁ from hatch to day 273. HH chicks had a smaller DNA unit size and a greater unit number than LL chicks at hatch. During rapid muscle growth, cell size was larger for HH than LL chickens. Pectoralis muscle grew at a faster rate than gastrocnemius muscle. Also cellular filling as measured by the DNA unit size was higher for pectoralis than gastrocnemius muscle through day 4. By day 10 the pattern reversed with values greater for gastrocnemius than pectoralis muscle. / Ph. D.

Broilers are nearing their genetic potential and nutritional strategies are the primary means to improve their performance. Improving raw material quality, especially soybean meal, could improve broiler performance, health and welfare. Inadequate processing of soybean meal leads to high residual anti-nutritional factors (ANF) which has a negative influence on broiler performance. High trypsin inhibitor content in low- quality soybean meal causes decreased protein digestion and absorption. The main aim of this study was to evaluate the optimal quality of soybean meal for commercial use to promote performance and welfare parameters of broiler chickens. Ten dietary treatments were formulated to the same nutritional specifications, but with different soybean meals that ranged from very high-quality (Treatment 1) to the lowest quality (Treatment 10). The quality of soybean meal was determined using Table 2.1 as target values for each soybean meal quality parameter. Soybean meal quality was evaluated using urease levels (pH change), TIA (trypsin inhibitor activity), Evonik TIA, KOH (potassium hydroxide solubility), Evonik KOH, Evonik PDI (protein dispersibility index) and Evonik PCI (processing conditions indicator). The treatment diets were fed to 4800 broilers that were randomly allocated to 80 pens, each with 60 birds and eight replicates. Over a 35-day growth trial, broiler performance, welfare and physiological traits were measured on a weekly basis. Overall, improved performance was observed with higher-quality soybean meal outperforming the lower-quality soybean meal. High-quality soybean meal showed significantly better feed conversion ratio’s (FCR) and European performance efficiency factor (PEF) throughout the 35-day period, and significantly higher average daily gain (ADG) up until day 21. Bodyweight (BW), feed intake (FI) and mortality showed no significant differences irrespective of soybean meal quality. No significant differences were found in physiological traits namely: pancreas weight as a percentage of bodyweight, pancreas length to bodyweight ratio, gizzard and proventriculus weight as a percentage of bodyweight and gizzard erosion score, (PW%BW, PL:BW, GPV%BW, GE score) irrespective of soybean meal quality. High quality soybean meal showed lower incidence and lower severity of rapid feed passage (RFP) and foot pad dermatitis (FPD). Evonik PCI and urease levels (pH change) showed the strongest correlation to broiler performance, health and welfare. This study suggests using soybean meal with the following quality parameters: urease levels of around 0.05, TIA levels of below 4mg/g, KOH levels of 78-80%, PDI levels of around 15 and PCI levels of around 11. The Evonik PCI and urease (pH change) analyses for soybean meal quality was found to be the easiest and cheapest method and can be recommended as the primary quality assays for commercial feed companies in the future. / Dissertation (BSc (Agric) Animal Science)--University of Pretoria, 2020. / AFGRI / Animal and Wildlife Sciences / BSc (Agric) Animal Science / Restricted