Response of three class‐IV major histocompatability complex haplotypes to Eimeria acervulina in meat‐type chickens

1. The importance of MHC genes and background genes in controlling disease resistance, including resistance to avian coccidiosis, has not been clarified in meat‐type chickens.

2. The role of class IV MHC genes in resistance to Eimeria acervulina was assessed in F2 progeny of a cross between 2 meat‐type lines, selected divergently for immune response to Escherichia coli.

3. Disease susceptibility was assessed by lesion score, body weight, packed cell volume and carotene absorption.

4. Chickens with the “K” class IV MHC haplotype had lower lesion scores than chickens with “F” and “A” haplotypes.

5. Plasma carotene concentrations were higher in chickens with “K” haplotype and lower in chickens with “F” and “A” haplotypes whereas body weight and packed cell volume were less sensitive measures of Eimeria infection.

6. Eimeria acervulina resistance appears to be associated with MHC class IV genes; information about MHC haplotypes may be useful in selecting for increased resistance of meat‐type chickens to coccidiosis.     

Cardiovascular effects of angiotensin‐II in chickens

1. Mature WL cockerels with permanent cannulae in brachial artery and vein were restrained in an isolated sling. Blood pressure (BP) and heart rate (HR) were continuously recorded. When the chickens were habituated to the sling, injections began. In each experiment the cockerels were injected intravenously 6 times at 6 min intervals.

2. In the first experiment 6 injections of 0.5 nmol[Aspl,Val5]ANG‐II/kg body weight were given.

3. In the second experiment oxytocin (OT) antagonist ([d(GH2)5‐O‐Me‐Tyr2,Thr4,Tyr9,Orn8]VT) at a dose of 2 nmol/kg, was injected for the first 3 and 0.5 nmol ANG‐II/kg for the last 3 injections. Such OT‐antagonist pretreatment completely abolishes the vasodepressor (VDP) response to neurohypophysial pep‐tides in chickens.

4. Injections of ANG‐II resulted in a biphasic effect on BP, an initial brief fall followed by a prolonged rise. During the hypotensive phase, tachycardia developed which turned into bradycardia as the hypertensive phase appeared. No tachyphy‐laxis of the VDP effect of ANG‐II was evident with repeated injections.

5. OT‐antagonist pretreatment had no effect on the VDP response to ANG‐II.

6. These results suggest that, unlike relaxation of chicken aortic ring in in vitro preparations, there is no tachyphylaxis of the VDP response to ANG‐II, in vivo. Furthermore, the neurohypophysial peptides are not involved in the VDP effect of ANG‐II because pretreatment with an OT‐antagonist had no effect on it. The baroreflex buffers the effects of ANG‐II on vascular tone by affecting HR.

7. As ANG‐II is secreted during hypovolaemia, the biphasic haemodynamic response peptides may have a compensatory role following volume contraction.     

Time course of oxidative phosphorylation in liver mitochondria of chickens fed on high‐protein diet

1. Progressive alterations in oxidative phosphorylation of liver mitochondria were followed for 14 d in growing chickens fed on either semi‐purified low (7%) or high (61%) protein‐energy diet. Hepatic mitochondrial oxidative phosphorylation rates were assessed polarographically with pyruvate + malate as substrates.

2. The ADP:O values were reduced significantly 4 d after the feeding of a high‐protein‐energy diet, when compared with those in chickens fed on a low‐protein‐energy diet, whereas the state 3 oxidation rates in chickens fed on a high‐protein‐energy diet from day 6 to 14 were significantly lower than those in low‐protein‐fed chickens.

3. No changes in sensitivity of mitochondrial ATPase activity to oligomycin, expressed as % of total ATPase activity, were observed among chickens fed for 21 d on diets with various protein concentrations though the FoF₁‐ATPase activity, expressed per mg protein, tended to decrease in chickens fed on high‐protein‐energy diet.

4. These results suggest that the reduced ADP:O values for liver mitochondria in the high‐protein‐fed chickens may not be involved in the degrees of integrity of the FoF₁‐ATPase.     

The incidence of breast‐blister down‐grading in broiler chickens

1. A survey was conducted into down‐grading due to breast blisters at a large processing plant.

2. The relationships between incidence of down‐grading and age, body weight, sex, size of rearing site and its distance from the processing plant, and various weather conditions during the rearing period of each flock were examined using regression analysis.

3. Age and body weight and rearing site size were the only factors significantly correlated with amount of blistering.     

Influence of diet on the intestinal microflora and meat flavour of intensively‐reared broiler chickens

1. An attempt has been made to modify the composition of the gut flora of broiler chickens by dietary means in order to determine any concurrent changes in meat flavour.

2. Birds given a diet containing an increasing proportion of whole wheat supplemented with fresh green vegetable matter (special diet) were compared with conventionally‐fed controls. At 12 weeks of age those receiving the special diet had 10 to 100‐fold higher counts of Escherichia colt and faecal streptococci in the duodenum and lower small intestine and showed differences in the intestinal incidence of species and biotypes of lactobacilli.

3. Evaluation of cooked breast‐meat samples by a trained sensory panel showed a significant difference in flavour (P < 0.01) between conventional and special‐diet birds which varied from perceptually very slight to slight. The main terms used in distinguishing special‐diet birds from conventional controls included ‘richer’, ‘meatier’ and ‘sweeter’.

4. Storage of plucked, uneviscerated birds at 4 °C for 8 d maintained the flavour difference between the dietary groups but the effect of storage on flavour was greater in both groups of birds than the influence of diet alone. The likely influence on flavour of autolytic changes occurring in the muscle during storage of the birds is discussed.     

Quantitative effects of pelleting on performance,gastrointestinal tract and behaviour of meat‐type chickens

1. In an attempt to quantify the effects of “degree” of pelleting, two experiments were conducted. Diets were prepared by mixing together a mash composed mainly of maize (experiment 1) or sorghum (experiment 2) with soft pellets, or soft pellets mixed with hard pellets.

2. The pelleting degrees (PDs) were as follows: 0 mash; 0·5 mixture of soft pellets and mash 1 to 1; 1 soft pellets pelleted once; 1·5 mixture of soft and hard pellets 1 to 1; 2 hard pellets pelleted twice.

3. In experiment 2, the weight and length of the digestive organs were determined as well as digestive enzyme activities. In both experiments, the behaviour recorded was eating, standing, sitting and drinking.

4. Food intake and body weight gain were related to the degree of pelleting in a curvilinear manner. PD had a positive effect up to a peak (1 to 1·5 PD), after which its effect decreased. Food efficiency was not related to PD. In experiment 1, food efficiency of PDs 1 to 2 were superior to PDs 0 to 0·5 and in experiment 2, PDs 1·5 to 2 were superior to PD 0.

5. The relative weight of the gizzard was reduced by pelleting, whereas pelleting increased the relative weight of abdominal fat. The content of the crop was not affected by PD, whereas that of the proventriculus was lowest in the PD 2 group. Gizzard content was inversely related to PD. Pelleting reduced the length of the jejunum and ileum: which were shortened by about 15% with PDs 1 to 2, as compared to PD 0. The weight/length ratio of the jejunum and ileum tended to increase with increasing PD to a peak at PD 1·5, and to decrease thereafter.

6. Trypsin activity in the pancreas and amylase activity in the intestinal content were reduced by pelleting.

7. Chicks fed pelleted diets were less active: they ‘sat’ more and spent less time eating than their mash‐fed counterparts.     

On estimating non‐additive genetic parameters in chickens 1

1. Several economically important traits in two Leghorn populations (over 9000 birds) were examined for additive and non‐additive components of genetic variance and sex‐linked effects. Data were analysed by two different statistical models based on least‐squares procedures.

2. Six different covariances were first calculated between relatives; i.e., full‐sibs, 3/4‐sisters, half‐sisters, dam‐daughters, grandam‐granddaughters and aunt‐nieces.

3. From the covariances, weighted least‐squares equations were used to obtain estimates of variance components for additive genetic, dominance, maternal and sex‐linkage effects.

4. The estimates of non‐additive components were highly variable but generally small compared with the additive genetic estimates.

5. In general this study suggests that for most traits, with the possible exception of rate of egg production, there is relatively little non‐additive genetic variation.

6. The consequences of possible negative correlations between additive effects and maternal effects are considered as they might apply to egg production in poultry.     

Growth,carcase composition and profitability of meat chickens given pellets,mash or free‐choice diet

1. Equal numbers of 21‐d‐old male and female meat chickens were given their dietary ingredients either mixed and presented as pellets or mash, or as separate ingredients presented on a free‐choice basis, to determine whether presentation method caused any differences in growth, carcase composition or profitability to 42 d of age.

2. The proportions of ingredients eaten by the chickens given a free choice varied widely during the first 56 h of the trial. Thereafter, the proportions did not vary widely and birds given the free choice ate approximately ½ of their intake as whole wheat, ? of their intake as concentrate (high protein meals plus vitamin and mineral premixes), and 1/7 of their intake as whole sorghum each week for the three‐week trial period.

3. The nutrient composition of the free‐choice diet selected by the birds over the trial period averaged 12.09 MJ ME/kg feed, 210 g/kg crude protein, 14 g/kg calcium and 7 g/kg phosphorus.

4. At the end of the trial the average live body weights of the birds differed significantly according to method of feeding, in the descending order of pellets > mash > free choice.

5. The empty gizzard weight of birds differed significantly according to the method of feeding, in the descending order of free choice > mash > pellets.

6. The plucked empty bodies of birds given the free choice had a significantly lower concentration of crude protein than the plucked empty bodies of birds fed on mash or pellets. There were no significant differences between the treatments in the plucked empty body concentrations of fat, calcium or phosphorus.

7. Financial analysis indicated that free‐choice feeding was more profitable than feeding mash or pelleted diets to broiler chickens by 3.6% and 33.4% respectively.     

The contribution of anorexia to reduced growth in zinc‐deficient chickens

1. It was shown, using a paired‐feeding technique, that the growth depression in zinc‐deficient chicks was largely caused by the greatly reduced consumption of the deficient diet.

2. Chicks receiving a zinc sulphate solution directly into the crop ate an amount of zinc‐deficient diet similar to that of the zinc‐sufficient diet eaten by the control chicks; palatability was thus ruled out as the cause of the anorexia.

3. Only chicks receiving the zinc‐deficient diet displayed signs of zinc deficiency.     

Selection for increased incidence of double‐yolked eggs in white leghorn chickens

1. Eleven generations of selection on two White Leghorn lines resulted in birds which, on the average, laid at least 30 double‐yolked eggs to 40 weeks of age.

2. The total number of yolks laid to 40 weeks was comparable with that of a control line selected for high egg number.

3. At peak production an F₁ cross of the two inbred lines laid 140 yolks per hundred hens per day.

4. Double‐yolk selected lines when crossed produced hens with a 20% increased body weight.

5. By the 10th and 11th generations the incidence of eggs with three or four yolks was increasing.     

Effectiveness of dietary 25‐ and 1‐hydroxycholecalciferol in combating tibial dyschondroplasia in broiler chickens

1. Three experiments were carried out to determine the effects of feeding diets containing different concentrations of cholecalciferol, 1 a‐hydroxychole‐calciferol (1‐HCC), 25‐hydroxycholecalciferol (25‐HCC), 1,25‐dihydroxycholecalcif‐erol (1,25‐DHCC) and ascorbic acid on the incidences and severities of tibial dyschondroplasia (TD) at 3 weeks of age in male broiler chicks.

2. In experiment 1, replacing 75 μg cholecalciferol/kg with the same weight of 25‐HCC decreased significantly (P<0.01) the incidence of TD from 65 to 10%.

3. In experiment 2, the incidence of TD in the control group was lower, but feeding amounts of 25‐HCC up to 250 μg/kg had a linear effect on the incidence of TD that was significant at P=0.06. There was no effect or interactions with dietary addition of 250 mg ascorbic acid/kg. Dietary addition of 5 μg 1‐HCC/kg decreased TD incidence from 21 to 5%, though the effect was not significant (P>0.1).

4. TD incidence in experiment 3 was too low to determine an effect of 25‐HCC or 1,25‐DHCC on TD incidence, though in this, as in both other experiments, the severities of TD lesions were always lower with diets containing cholecalciferol metabolites.

5. Hypercalcaemia was not observed after feeding up to 250 μg 25‐HCC/kg in either experiments 2 or 3.

6. It is concluded that 25‐HCC may be an effective practical means of improving broiler leg health by alleviating the incidence and severity of TD.     

Chemical composition and nutritional value in vitro of mechanically‐deboned poultry meat

1. The composition by proximate analysis, amino acid content and digestibility by mammalian proteolytic enzymes of pastes from mechanically‐deboned chicken breasts wings, necks and backs, and hand‐deboned breast were measured. Values obtained were used to calculate indices of nutritional value.

2. All pastes compared favourably with similar protein materials used for human food. Mechanical deboning did not alter the nutritional indices.

3. The protein quality and digestibility of the breast were somewhat higher than those for other parts.     

Alteration of fatty acid profile and nucleotide-related substances in post-mortem breast meat of α-lipoic acid-fed broiler chickens

1. The present study was conducted to determine the effects of α-lipoic acid supplementation on post-mortem changes in the fatty acid profile and concentrations of nucleotide-related substances, especially those of a taste-active compound, inosine 5?-monophosphate, in chicken meat.

2. Mixed-sex broiler chicks aged 14 d were divided into three groups of 16 birds each and were fed on diets supplemented with α-lipoic acid at levels of 0, 100 or 200 mg/kg for 4 weeks. Blood and breast muscle samples were taken at 42 d of age under the fed condition and then after fasting for 18 h. The breast muscle obtained from fasted chickens was subsequently refrigerated at 2°C for one and 3 d.

3. α-Lipoic acid supplementation did not affect any plasma metabolite concentration independently of feeding condition, while a slight increase in plasma glucose concentration was shown with both administration levels of α-lipoic acid. In early post-mortem breast muscle under the fed condition, α-lipoic acid had no effect on concentrations of fatty acids or nucleotides of ATP, ADP, and AMP.

4. In post-mortem breast tissues obtained from fasted chickens, total fatty acid concentrations were markedly increased by α-lipoic acid feeding at 200 mg/kg irrespective of length of refrigeration. This effect was dependent on stearic acid, oleic acid, linoleic acid and linolenic acid. However, among fatty acids, the only predominantly increased unsaturated fatty acid was oleic acid.

5. Dietary supplementation with α-lipoic acid at 200 mg/kg increased the inosine 5?-monophosphate concentration in breast meat and, in contrast, reduced the subsequent catabolites, inosine and xanthine, regardless of the length of refrigeration.

6. Therefore, the present study suggests that α-lipoic acid administration altered the fatty acid profile and improved meat quality by increasing taste-active substances in the post-mortem meat obtained from fasted chickens.

     

Performance,breast meat yield and abdominal fat deposition of male broiler chickens fed diets supplemented with DL‐xnethionine or DL‐xnethionine hydroxy analogue free acid

1. An experiment was conducted to compare the relative bioefficacy of DL‐methionine hydroxy analogue free acid (DL‐MHA‐FA) with DL‐methionine in broiler chickens. Responses used for comparison were weight gain and food efficiency between 7 and 35 d of age, and breast meat deposition, food cost per kg of breast meat, and abdominal fat at 41 d of age.

2. A total of 2160 seven‐day‐old male broiler chicks were used. The feeding programme consisted of a starter diet from 7 to 21 d, and a finisher diet till the end of the experiment. The starter basal diet contained 6.1 g/kg total sulphur‐containing amino acids (TSAA), and an estimated metabolisable energy (ME) content of 13.2 MJ/kg. The finisher diet contained 5.8 g/kg TSAA and an estimated ME content of 13.6 MJ/kg. Four concentrations of DL‐methionine and DL‐MHA‐FA were added at 0.5g/kg increments on an equimolar basis. Therefore, there were 9 experimental treatments which were each applied to 6 replicates of 40 chicks. Weight gain and food efficiency were determined at 35 d of age. Breast yield and carcase fat were measured at 41 d.

3. Significant responses to graded amounts of both methionine sources were observed in weight gain, food efficiency, breast meat percentage, and food cost per kg of breast meat. The responses fitted exponential regression curves. Based on the regression coefficients, equimolar bioefficacy of DL‐MHA‐FA relative to DL‐methionine was 80% for daily gain, 83% for food efficiency, 51% for breast meat yield, and 66% for food cost per kg of breast meat. Differences between the 2 sources were significant (P< 0.05) for breast meat yield and food cost per kg of meat and (P< 0.10) for food efficiency.     

Increased small intestinal fermentation is partly responsible for the anti‐nutritive activity of non‐starch polysaccharides in chickens

1. The mechanism of the anti‐nutritive activities of soluble non‐starch polysaccharides (NSPs) in broiler diets was investigated with emphasis on the inter‐relationship between viscosity and fermentation along the gut. Isolated soluble NSP were added to a control diet to effect high gut viscosity, and in vivo depolymerisation of the NSP was achieved using a commercial glycanase.

2. Addition of soluble NSPs significantly (P<0.01) increased gut viscosity, reduced the AME of the diet and depressed the growth and FCE of the birds. Enzyme supplementation of the NSP‐enriched diet reversed the adverse effects, increasing (P< 0.01) weight gain, FCE and AME. Comparisons of the viscosities (mPa) in birds fed on the NSP‐enriched diet and the same diet supplemented with enzyme were respectively: 11–9 v. 2–3 in the duodenum; 78–3 v. 4–4 in the jejunum and 409–3 v. 10–8 in the ileum.

3. Caecal volatile fatty acid concentration was markedly (P<0.01) elevated by enzyme supplementation, whereas ileal fermentation was inhibited.

4. Microscopic examination revealed that, among birds fed on the NSP‐enriched diet, there had been extensive small intestinal fermentation, which was eliminated by the enzyme supplementation.

5. Addition of a synthetic antibiotic (Amoxil) had no beneficial effects.

6. The current study demonstrated that increased fermentation occurs in the small intestine when a large amount of viscous NSPs is present in the diet and this is detrimental to the performance and well‐being of poultry.     

Physiological inhibition of growth hormone secretion by both insulin‐like growth factors‐I and ‐II in chickens

1. The role of both insulin‐like growth factors (IGF)‐I and ‐II in regulation of growth hormone (GH) secretion in chickens was examined. Seven‐week‐old male broiler chickens were injected intravenously (iv) with recombinant human IGF‐I or IGF‐II or specific anti‐IGF‐I or IGF‐II immunoglobulins. Blood samples were taken before treatment and at 15 min intervals afterwards for 1 h. Controls received saline iv.

2. Both IGF‐I and IGF‐II administration resulted in a rapid, significant decrease in plasma GH concentrations, but the concentrations of both triiodothyronine and thyroxine remained unchanged.

3. Immunisation against both IGF‐I and IGF‐II produced a significant elevation in plasma GH.

4. These data show that both IGFs can regulate GH concentrations in birds. Furthermore, the immunoneu‐tralisation data suggest that these hormones have a physiological role in the regulation of GH secretion.     

Response of broiler chickens to well‐balanced protein mixtures

1. Four experiments were conducted on broiler chickens between one and three weeks of age to determine their response to dietary protein concentrations.

2. Diets prepared by serial dilution of a concentrated protein mixture, well‐balanced with respect to all essential amino acids, were fed in three experiments, while in a fourth experiment, a lysine‐deficient protein mixture was used.

3. Response curves relating body‐weight gain to increasing concentrations of protein and of lysine intake are presented.

4. A table is presented from which optimum protein intakes can be calculated according to changes in input and output costs and changes in growth potential of the chickens.     

A note on the shelf‐life and spoilage of commercially‐processed chicken giblets

1. When chicken giblet tissues wrapped individually in polythene were stored at 1 °C, “ off” odours were detected in 11 to 14 d with necks (mean 12.3 d) tending to spoil before gizzards, hearts and livers (means 13.0 to 13.7 d).

2. In all cases, the predominant organisms at spoilage were Pseudo‐monas spp. with lower numbers of Acinetobacter spp.

3. Chlorination of process water at about 50 mg total residual chlorine/1 (including 0.1 to 0.9 mg free chlorine/1) extended the shelf‐life of giblets held at 1 °C by up to 3 d, and prior freezing of these tissues gave an extension of 1 to 2 d but combining the two treatments did not have an additive effect.

4. Immersing giblets for 1 min in a solution containing 100 g potassium sorbate/1 (pH 8.0) doubled the shelf‐life of each type of tissue by retarding growth of the normal spoilage microflora.     

The use of n‐paraffin‐grown yeast as the main source of protein in diets for chicks

1. n‐Paraffin‐grown yeast and a mixture of soyabean meal and fish meal were compared in the net protein utilisation (NPU) test, and as protein supplements in diets for broilers up to 4 weeks of age.

2. The difference between the NPU values, 0.66 for yeast and 0.80 for the soyabean meal and fish meal mixture, could largely be attributed to the high nucleic acid content of the yeast.

3. Chicks given the diet containing yeast (190 g/kg) did not grow as rapidly as those given the soyabean meal and fish meal reference diet, and the reduced growth could only partly be explained by a marginal deficiency of methionine.

4. Food conversion efficiency with the yeast diet was improved by maize oil while responses to α‐tocopheryl acetate and sodium selenite were inconsistent.

5. Chicks grew well when yeast replaced fish meal in the mixture of soyabean meal and fish meal, and when fish meal (194 g/kg diet) was the sole protein supplement.