M.S.

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.

The effects of intragastrically administered tryptophan and tyrosine, which are direct precursors of brain neurotransmitters affecting food intake, were investigated. Differences in sensitivities and/or responses in relatively fast-growing and slow-growing strains of chickens were also tested. The amino acids were intubated intragastrically in a series of four experiments. Food consumption following tryptophan intubation decreased in both the slow and fast-growing strains. Increased food intake was observed in the slow-growing birds as a result of tyrosine treatment suggesting that food consumption can be altered by manipulation of dietary amino acids. Tyrosine treatment did not stimulate food intake in the fast-growing strain, implying that chickens in this population were in a state of maximal or near maximal stimulation, and thus relatively incapable of increasing food intake. To determine whether the changes observed in feeding behavior were perhaps due to some general inhibition or stimulation of the central nervous system rather than the result of mediation of feeding mechanisms in the brain, the effects of intragastrically administered tyrosine and tryptophan on tonic immobility (TI) were also tested. Duration and susceptibility of TI were unaffected by tyrosine and tryptophan, suggesting that these amino acids acted upon mechanisms specifically involved in the regulation of food intake. / Master of Science

Four experiments were conducted to compare adipocyte dynamics and body composition among adult chickens from lines differing in growth rate and feed consumption. In Experiment I, forced caloric overconsumption increased weight gain and fat deposition, with concomitant increases in the total adipocyte DNA content of the assayed fat depots. Injections of DNA-specific [methyl³H] thymidine resulted in higher radioactivity levels in the fat depots of forced versus ad libitum or restricted-fed birds. Evidently, stimulation of fat deposition in adult chickens can be associated with adipocyte hyperplasia. A second experiment was conducted to histologically examine the effects of forced caloric overconsumption on adipocyte size, number, and distribution in the retroperitoneal fat depot of adult weight-line birds. Similarly to Experiment I, force feeding increased fat deposition, resulting in increases in the retroperitoneal fat depot total adipocyte DNA content. The lipid/adipocyte DNA ratio also decreased during rapid depot expansion. This resulted in an increase in the small adipocyte population of the force fed birds when adipocyte diameter was increasing. Subsequently, when the constraints of force feeding were removed, adipose depot reduction occurred, with the mobilization of lipid from small as well as large adipocytes. In a third experiment, the effects of estrogen administration and partial lipectomy were examined. In addition to the weight-line birds, a commercial broiler breeder stock was utilized. Estrogen administration depressed body weight gain and abdominal fat deposition when compared to placebo implanted birds. Partial lipectomy depressed body weight, fat deposition, and abdominal fat total adipocyte DNA content. Lipectomy modified several components of carcass composition without altering feed intake. No indication of a compensatory hyperplastic response to lipectomy was indicated. A final experiment was conducted examining the effects of forced body weight fluctuations on body composition of male and females from the weight-selected lines. Although numerous first-order interactions were detected, force-feeding resulted in transient modifications in carcass composition and fat deposition which were more apparent in the high than low weight line, in females than males. After release to ad Iibitum feeding, the differences resulting from force feeding were reduced. / Ph. D. / incomplete_metadata

The heritable variation of body weight in two lines of chickens divergently selected for high and low juvenile body weight, as determined from parental line, F₁, F₂ and backcross generations, was principally additive. Feed intake during the first few weeks post hatching was influenced by potence in the direction of the high-weight line, while no comparable pattern was noted for early water intake. Heterosis was observed for feed efficiency which was associated with an equivalent negative heterosis for percentage carcass fat. Feed intake of chicks from the high-weight line and reciprocal crosses were restricted to that of chicks from the low-weight line. This restriction resulted in a greater depression in body weight of the high-weight line than of cross chicks. In contrast, a comparable restriction of water consumption resulted in a similar (10%) depression of body weight among both high-weight line and cross chicks. The effect of feed and water restriction on feed:water ratios was dependent upon mating type. The amount of feed introduced into the crop of chicks from the high-weight line via overfeeding was similar to their ad libitum intake. Chicks from the low-weight line could be overfed at earlier ages and to a greater degree than either high-weight or cross chicks. The degree of overfeeding was associated with the relative size of certain gastrointestinal components. Differences among populations were reflected in concomitant changes in body weight and carcass fat. Comparisons among the parental line and F₁ progeny provided evidence for nonadditive genetic variation for hedonic sensitivity towards quinine sulfate and dextrose, though in opposite directions. Additive genetic variation appeared to influence the preference ratios for both stimuli at super-threshold concentrations. These data suggest the absence of a simple relationship among growth, feed intake control and body composition. It is hypothesized that in addition to their commonality, different genetic systems exist for the expression of high and low body weight as well as their various correlates. The implications of these systems are discussed within the context of feed intake control and future genetic changes in growth. / Ph. D.

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.

A procedure was developed to examine factors contributing to skin strength of meat-type chickens. Skin breaking strength was initially measured in lines of chickens divergently selected for high (H) and low (L) juvenile body weight, their reciprocal crosses (HL and LH), and an F₂ generation derived from HL and LH matings. Skin of chicks from the LL line was weakest, that from the HH and LH matings strongest, and that from HL and F₂ matings was intermediate. Percentage heterosis for breaking strength was significantly positive while percentage recombination was not significant. Skin breaking strength and protein, fat, moisture, and total collagen concentrations of skin from the breast, thigh, and back of male and female commercial broilers were then examined in response to diets containing relatively wide or narrow ratios of calories to protein (C:P). Comparisons were made at 28, 42, and 56 days of age. Chickens fed diets containing wider C:P ratios had weaker skin than those fed diets with narrower C:P ratios, with the differences being greater at older than at younger ages. Males had stronger skin than females. Among body sites, breast skin was stronger than thigh skin with that from the back being intermediate in strength. Skin breaking strength did not appear to be consistently associated with either the protein, fat, or collagen concentrations in the skin. Skin from broiler chicks fed diets with differing C:P ratios was also examined histologically. Males had stronger and thinner skin than females, with the differences in thickness due primarily to differences in the thickness of the hypodermis. Regardless of sex, feeding diets containing wider C:P ratios resulted in weaker and thicker skin. The thicker skin was associated with an increase in the thickness of the hypodermis and a decrease in the thickness of the dermis and epidermis. With the exception of differences between back and thigh skin, increases in breaking strength occurring between skin from different sites were associated with a reduction in total skin thickness and in the thickness of the hypodermis. It was concluded that increased hypodermis thickness and/or decreased thickness of the dermis and epidermis reduced skin strength. Two experiments were conducted in which skin strength was examined in relation to heat stress and supplemental ascorbic acid. In the first experiment, chicks fed diets containing 0 or 100 mg of ascorbic acid per kg of diet were subjected to either a constant ambient temperature of 23C, a constant ambient temperature of 32C, or a treatment consisting of 32C from 1600 to 1200 hr and 400 from 1200 to 1600 hr (32/400). Both heat stress and supplemental ascorbic acid tended to increase collagen concentrations in the skin, but differences in breaking strength were inconsistent in response to these treatments. Supplemental ascorbic acid, however, partially alleviated reductions in body weight due to heat stress but did not decrease body temperatures of heat-stressed chicks. In the final experiment, diets containing either 0, 200, or 400 mg/kg of supplemental ascorbic acid were fed to chicks maintained at ambient temperatures of 23 and 34C. Contrary to previous observations, ascorbic acid failed to ameliorate the depressive effect of heat stress on body weight. Supplemental ascorbic acid tended to reduce adrenal, bursa of Fabricius, and spleen weights but had no effect on heterophil and lymphocyte numbers or ratios. Adrenal ascorbic acid concentrations were not significantly affected by supplemental ascorbic acid and plasma ascorbic acid levels were inconsistent among treatment groups. Neither supplemental ascorbic acid nor heat stress significantly influenced skin strength. It was concluded that supplemental ascorbic acid was not beneficial in improving skin strength in commercial broiler chicks. / Ph. D.

No abstract available. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.

This research reported here was carried out to examine alternatives to antibiotic growth promoters as a result of their being banned in the animal feed industry. Four experiments were conducted to evaluate the efficacy of non-medicated feed additives as replacements for antibiotic growth promoters in broiler feeds. The additives used were enzymes (a new thermo-tolerant powder enzyme called TXAP, phytase, lipase and a new phytase enzyme derived from E. coli called phyzyme XP), organic acid (Acid Pak), prebiotic (Bio-Mos®) and probiotic (All-Lac XCL). Mashed maize-soya based feeds were used in all the experiments, which were conducted in litter-floor pens. The first experiment was a dose-response trial. Broilers in eight replicate pens of 50 males and 50 females were fed unsupplemented feeds and five additional feeds containing increasing levels of TXAP, from 0.5 to 2.5 g/kg to 42 d. The second experiment used enzyme TXAP with two different enzymes (phytase and lipase), individually or in combination. Six replicate pens of 50 males and 50 females were fed either unsupplemented feeds or one of six additional feeds treated with TXAP, lipase, phytase , a combination of TXAP and lipase, a combination of TXAP and phytase or a combination of all the three enzymes . This trial continued for 42 d. In the third experiment three types of TXAP (Lot 1, 2 and 3) were used, with fixed levels of xylanase and amylase but varying levels of protease activities (4000, 2000 and 1000 U/kg for Lot 1, 2 and 3, respectively) in combination with phyzyme XP for 35 d. The fourth experiment used mannan-oligosaccharide (Bio-Mos®), organic acid (Acid pak 2x), probiotic (All Lac XCL 5x), individually or in combination and an antibiotic growth promoter (Zinc bacitracin) for 42 d. The chickens in this experiment were challenged with Clostridium perfringens (CP) at 21, 22 and 23 d to determine the efficacy of these additives for replacing antibiotics in hindering the effects of CP on the villus surface area. The dose-response trial did not show any significant improvement in broiler performance with any level of inclusion of enzyme TXAP. The results from this study showed some beneficial effects with the use of enzyme TXAP when fed alone and at a young age. Its use when combined with other enzymes and at later stages of growth needs further investigation. Feed additives in experiment 4 prevented the negative effects of CP as the treated chickens did not have lesions on their villus surfaces. The conditions under which these trials were conducted appeared to be such that little benefit was derived from the use of any of the feed additives used. It is possible that under less-hygienic conditions such as those in commercial operations greater benefits from these additives may be realised. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.

Thesis (MScAgric (Animal Sciences))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: In recent years, the aim of the production of broilers became more focused on the increase of the performance of the birds in order to increase profit. To obtain an increased performance with broiler chicks, it is necessary to look at the development of their gastrointestinal tract, the feed requirements and the ability to digest certain nutrients in the period post hatch. Research have shown clear evidence of increased performance of chicks by the inclusion of certain carbohydrate and protein sources in the prestarter diets, but in contrast to this there are also some research that found no significant effects on the performance of broilers when certain carbohydrate and protein sources were included in the pre-starter diet. Therefore, the purpose of this study was to investigate the effect that a product containing specific carbohydrate and protein sources, included in the pre-starter diets of broiler chicks, would have on their performance. It was believed that the products to be tested would result in increased performance of the chicks in the following growth phases. Special emphasis was placed on the average daily gain (ADG), feed intake, cumulative feed intake, feed conversion ratio (FCR), European production efficiency factor (EPEF) and the protein efficiency ratio. Different inclusion levels of the different raw materials were investigated in the first trial. Three raw materials and a control were compared using a summit dilution process at 100:0, 66:34, 50:50, 34:66 and 0:100. Specific production parameters such as ADG total live weight gain, feed intake per week, cumulative feed intake, FCR, EPEF and PER were measured and calculated in order to determine if there were any significant differences between the treatments with the different raw material inclusions on the performance of the chicks. No significant differences (P>0.05) were found between the 13 treatments for the ADG, total live weight gain, feed intake per week, cumulative feed intake, FCR, EPEF and PER. The results therefore indicated that there were no significant differences between the different inclusion levels of the different raw materials and no significant differences for the production parameters for animals receiving diets with various levels of the three raw materials. It is thus concluded that these raw materials can be successfully utilised in pre-starter diets of broiler chicks. The effect of the contribution of sugar to the metabolisable energy (ME) of the raw materials was tested in a commercial grower trial. The three raw materials had inclusion levels leading to supply of either 12% or 18% of the ME in the form of sugar. No significant differences were found between the seven treatments for ADG, total live weight gain, feed intake per week, cumulative feed intake, FCR, EPEF or the PER. It was concluded that the percentage in contribution of sugars between 12 and 18% to the ME of the prestarter diets had no significant effects on the production parameters tested. / AFRIKAANSE OPSOMMING: Met die produksie van braaikuikens word daar deesdae al hoe meer klem gelê op die verhoging van die produksie van die kuikens om dan dus ‘n verhoging in die wins te bewerkstellig. Om hierdie verhoogde produksie by braaikuikens te kan bereik, is dit nodig om na eienskappe van die kuiken soos die ontwikkeling van die spysvertering stelsel, die nutrient- behoeftes van die kuiken en die vermoë om sekere nutriënte te kan verteer in die periode na uitbroei. Sommige navorsing het gewys dat die insluiting van sekere koolhidraat – en proteïen bronne in die voor-aanvangs diëete van braaikuikens, lei tot ‘n positiewe effek op die produksie van die kuikens, waar ander navorsing geen effek gevind het nie. Daarom was die doel van die huidige navorsing gewees om te toets wat die effek van die insluiting in die voor-aanvangs dieet van braaikuikens ‘n sekere produk met ‘n spesifieke koolhidraat –en proteïen bron samestelling op die produksie van die kuikens sal wees in die daaropvolgende fases. Dit was verwag dat die insluiting van hierdie produkte in die voor-aanvangs diëte van braaikuikens ‘n positiewe effek sou hê op die produksie van die kuikens. Spesiale klem was gelê op die parameters soos gemiddelde daaglikse toename (GDT) voer inname, kumulatiewe voer inname, voeromset verhoudings (VOV) Europese produksie doeltreffendheids- faktor (EPEF) en die proteïen doeltreffendheids faktor (PER). Verskillende insluitings vlakke van die verskillende produkte wat getoets is, is in die eerste proef ondersoek. Die drie produkte is deur middel van ‘n piek verdunnings proses by verhoudings van 100:0, 66:34, 50:50, 34:66 en 0:100 met mekaar vergelyk. Spesifieke produksie- parameters soos die GDT, lewende massa, weeklikse voer- inname, kumulatiewe voer- inname, VOV, EPEF en die PER is gemeet. Geen betekenisvolle verskille (P>0.05) was vir die 13 behandelings verkry nie. Die resultate het derhalwe getoon dat daar geen betekenisvolle verskille tussen die verskillende insluitings vlakke van die onderskeie produkte was nie en dat daar geen betekenisvolle tussen die produksieparameters van die kuikens wat die diëte met die verskillende insluitingspeile van die drie roumateriale ontvand het, was nie. Daarom is tot die slotsom gekom dat hierdie roumateriale suksesvol in die vooraanvangsdieet van braaikuikens aangewend kan word. Die effek van die bydrae van die suiker tot die metaboliseerbare energie (ME) van die produkte was in ‘n kommersiële groei proef getoets. Die drie rou materiale was by beide 12- en 18% ingesluit. Geen betekenisvolle verskille (P>0.05) was vir die sewe behandelings vir GDT, lewende massa, weeklikse voer- inname, kumulatiewe voer- inname, VOV, EPEF en PEF verkry nie.