I. Bartov

Effects of dietary protein concentration and corticosterone injections on energy and nitrogen balances and fat deposition in broiler chicks

Reducing dietary protein concentration in isocaloric diets consistently decreased nitrogen and energy excretion, and increased dry matter (DM), non-protein DM (NPDM), energy retention and fatness. There were significant correlations, negative between dietary energy-to-protein (E:P) ratio and nitrogen excretion and positive between the E:P ratio and the retention of DM, NPDM and energy. Nitrogen excretion was correlated with energy excretion, and NPDM retention with energy retention. Corticosterone injections increased fatness despite significantly increasing nitrogen and energy excretion. A positive relationship was observed in corticosterone-treated birds between nitrogen excretion on the one hand and the retention of DM and NPDM on the other. Increased food intake because of a low dietary protein concentration was not evident when a sorghum-based diet was used. Moreover, corticosterone injections increased neither the food intake nor the fatness of chicks fed this diet. Decreasing the protein concentration in diets containing identical metabolisable energy (ME) levels slightly, but significantly increased apparent ME values in three out of four experiments. Corticosterone injection did not affect this variable.

Stability of abdominal fat and meat of broilers: Relative effects of vitamin E, butylated hydroxytoluene and ethoxyquin 1

1. α‐Tocopheryl acetate (ATA) and ethoxyquin (EQ) markedly improved the stability of fat and meat of broilers fed on diets not supplemented with fat, while butylated hydroxytoluene (BHT) improved fat stability only. 2. The stability of carcass fat of broilers fed on diets supplemented with acidulated soyabean‐oil soapstock was improved by all three anti‐oxidants, but BHT and EQ were more effective than ATA. Meat stability was improved only by EQ. 3. The relationship between dietary EQ concentrations and the stability of carcass fat was logarithmic, whereas with that of thigh meat it was linear, irrespective of the degree of saturation of the carcass fat.

Corticosterone and fat deposition in broiler chicks: Effect of injection time, breed, sex and age

1. Corticosterone (680 micrograms/kg body weight per day) given as six daily injections to 3- or 7-week-old chicks decreased weight gain, but increased food consumption, abdominal fat pad weight, skin dry matter, relative liver size and liver fat concentration. 2. Time of day of injection did not modify the response to corticosterone of 3-week-old chicks kept under natural daylight nor of 7-week-old broilers receiving additional illumination. 3. Pure White Rock chicks and Cornish X White Rock crossbred chicks responded similarly to corticosterone at 3 weeks of age. 4. Seven-week-old female birds treated with corticosterone had significantly larger abdominal fat pads than similarly treated males. 5. Corticosterone injection was more effective in increasing the proportion of liver fat in 7-week-old birds than in 3-week-old chicks. 6. The increased amount of abdominal and liver fat due to corticosterone injections administered at 3 weeks of age disappeared after 3 weeks, but growth depression was still evident.

Effects of degree of fatness in broilers on other carcass characteristics: Relationship between fatness and the composition of carcass fat1

1. Three trials were performed to examine the effect of degree of fatness in broilers on the composition of carcass fat. The various degrees of fatness were obtained by varying the energy to protein (E :P) ratios in conventional diets. 2. Increasing the E : P ratio caused increased fat deposition with increases in the proportions of palmitic and oleic acids and a decrease in linoleic acid. 3. Highly significant negative correlations were obtained between the degree of fatness (expressed as percentage of dry matter of the skin) and of unsaturation of abdominal fat (expressed as iodine value). 4. The same negative correlations were obtained for individuals within the same dietary treatment, especially those producing lean birds.

Effects of high concentrations of dietary vitamin E and ethoxyquin on the performance of laying hens.

1. Three experiments were carried out with light strain laying hens to evaluate the effects of relatively high doses of dietary vitamin E (125 mg/kg food) or ethoxyquin (EQ) (250 mg/kg food) on their laying performance. The control diet contained 5 and 125 mg/kg vitamin E and EQ, respectively. The experimental diets were fed either from one or 32 weeks until 88 or 89 weeks of age. 2. The two antioxidants did not affect the growth of the pullets, age at first egg, final body weight, average egg weight or relative abdominal fat pad size and liver weight at the termination of the experiments. In two out of three experiments, vitamin E and EQ did not affect egg production, food efficiency or mortality; in the third experiment vitamin E significantly (P less than 0.05) improved egg production and food efficiency after an outbreak of Newcastle disease which occurred at 34 weeks of age. EQ significantly reduced mortality during the course of this experiment, but did affect the variables of performance. In two experiments vitamin E consistently improved shell density, although a significant effect was observed in only one of the eight determinations carried out. EQ did not affect this variable. 3. The uterine muscle was more susceptible to oxidation than the drumstick meat, as evaluated by TBA values. In both tissues, vitamin E significantly and consistently decreased TBA values and restricted their increase during incubation, while EQ was less effective, particularly in the drumstick meat. 4. It is concluded that increasing vitamin E and EQ concentrations in diets of laying hens have no effect on the decrease in egg production due to aging. However, vitamin E may minimize the decline in egg production and food efficiency following the outbreaks of some diseases and slightly improve--under certain yet undefined conditions--shell density.

Effects of energy concentration and duration of feeding on the response of broiler chicks to growth promoters 1

Abstract 1. Two experiments were carried out with male broiler chicks from 7 to 49 d of age to evaluate the combined effect of the growth promoters (GPs) avoparcin (AVO, 20 mg/kg), Zn bacitracin (BAC, 25 mg/kg) and nitrovin (NIT, 18 mg/kg), and dietary energy concentration (EC) (experiment 1) and the effect of age of feeding AVO (experiment 2) on performance, utilisation of dietary nutrients, yield of defeathered eviscerated carcases (DEC) and size of various organs. 2. AVO, in contrast to BAC and NIT, significantly (P<0–05) decreased fat excretion and increased dry matter, fat and nitrogen retention, dietary AMEn content, weight gain and food efficiency. AVO also significantly decreased the size of the liver and the small intestine (SI), the length of the SI and its specific weight. The effect of BAC and NIT on the variables of the SI was less pronounced than that of AVO. Although the effect of AVO on increasing fat retention, growth and food efficiency was more pronounced with the high EC diet, neither ...

Effects of degree of fatness in broilers on other carcass characteristics: Relationship between fatness and the stability of meat and adipose tissue1

1. Three trials were carried out to compare the effects of different degrees of fatness in broilers and of dietary a‐tocopherol (AT) concentrations on the stability of meat and adipose tissue at 5 to 9 weeks of age. 2. In spite of higher concentrations of AT in carcass fat, the meat and abdominal fat of lean broilers were less stable than those of obese birds, apparently due to an increase in the unsaturation of their carcass fat. 3. Dietary AT improved significantly the stability of meat and adipose tissue, irrespective of the degree of fatness. However, the difference in the stability of these tissues between obese and lean broilers remained apparent even with 60 mg AT/kg of the diet. 4. A linear relationship was observed between dietary AT and the stability of adipose tissue, whereas the relationship between AT intake and meat stability was logarithmic.

Stability of abdominal fat and meat of broilers: Effect of duration of feeding antioxidants 1

1. The α‐tocopherol (AT) content of abdominal fat and fat stability increased as a function of the duration of α‐tocopheryl acetate (ATA) feeding in broilers fed on diets containing either 40 g acidulated soyabean‐oil soapstock (ASS) or tallow/kg. A linear relationship was observed between AT content of the adipose tissue and its stability with both types of fat supplements. 2. The stabilities of carcass fat and meat of 9‐week‐old broilers fed on diets containing ASS with 300 mg ethoxyquin (EQ)/kg or diets containing tallow with 20 mg ATA/kg from weeks 5 to 9 were comparable with those obtained by feeding these antioxidants and fats throughout the growth period. 3. ATA added to a diet containing ASS, and EQ, added to a diet containing tallow did not improve meat stability despite such an effect on adipose tissue when fed for 9 weeks. The results emphasise the importance of using the dietary antioxidant appropriate to the fat supplement to improve carcass stability.

Lack of effect of dietary energy‐to‐protein ratio and energy concentration on the response of broiler chickens to virginiamycin

1. Two factorial experiments were carried out with male broiler chicks from 6 to 28 (experiment 1) and from 7 to 49 (experiment 2) d of age to evaluate the combined effect of virginiamycin (VIR), dietary energy concentration, and energy-to-protein (E:P) ratio on performance and the utilisation of dietary nutrients. 2. VIR had no significant effect in either experiment on food intake or weight gain, but significantly improved food efficiency up to 28 d of age (P less than 0.001 and P less than 0.05 in experiments 1 and 2, respectively). 3. VIR consistently and significantly (P less than 0.01) decreased fat excretion, improved fat relative retention and increased dietary AMEn. VIR also significantly (P less than 0.01) increased relative retention of dry matter, while it did not affect nitrogen balance. 4. Neither of the variables of performance and utilisation of dietary nutrients was affected by the interactions between VIR and either dietary E:P ratio or energy concentration. It is concluded, therefore, that the effect of VIR in increasing the utilisation of dietary energy does not depend on the above factors.

Effect of early nutrition on fattening and growth of broiler chicks at 7 weeks of age 1

1. Six experiments were carried out with male and female broiler chicks in a factorial arrangement to evaluate the combined effects of fat concentration or energy-to-protein (E:P) ratio in diets fed from 1 to 7 or 14 d of age, and of the E:P ratio in diets fed from 1 or 2 to 7 weeks of age on fattening and performance of the birds. 2. Diets with a wide E:P ratio fed from 1 or 2 to 7 weeks consistently and significantly increased abdominal fat pad size at 7 weeks of age. On the other hand, in 5 of the experiments, the nutritional treatments from 1 to 7 or 14 d did not significantly affect this variable in chicks fed on diets with either the narrow or the wide E:P ratio. 3. Body weights and food utilisation at 7 or 14 d were consistently and significantly improved by increasing dietary fat concentration and using diets with a narrow E:P ratio. However, at 7 weeks of age, in only two of the experiments were body weights still significantly affected by early nutrition. 4. Diets with a wide E:P ratio consistently and significantly reduced the performance of chicks up to 4 weeks of age. Nevertheless, at 7 weeks of age the performance of these chicks tended to be better (at times significantly so) in most of the experiments, despite their excess fattening.