S. Bornstein

Effect of calorie to protein ratio on the degree of fatness in broilers fed on practical diets 1

Synopsis Three trials were carried out with broilers to compare the effect of different calorie to protein (C : P) ratios in practical‐type diets with the amount of carcass fat at 8 or 9 weeks of age. The latter was estimated on the basis of the concentration of fat or dry matter in a sample of back skin and by visually scoring the amount of abdominal fat. Rearing broilers on diets containing protein levels slightly above or below the accepted optimum did not affect growth rate. However, in most comparisons the high‐protein diets brought about better food to gain ratios, and in all comparisons they produced relatively lean carcasses. Increasing or decreasing the protein level of finisher diets resulted in a decrease or increase, respectively, in the degree of fatness. A 2‐week period was sufficient to create or reverse these trends in a pronounced manner. Dietary oil supplementation per se did not increase the amount of carcass fat as long as the C : P ratio was kept constant. If there existed any consist...

Body weight and/or fatness as potential determinants of the onset of egg production in broiler breeder hens

In four trials during consecutive years individually-caged birds were weighed at first egg, and in the first two trials they were then killed to determine abdominal and skin fat, in order to establish whether there is a minimal body weight and/or body fat pool required for the start of egg production in broiler breeder hens. There were negative correlations ranging from significant to negligible between body weight and age at first egg. For birds of the same strain on a conventional food restriction regimen, the average weight range at first egg in the four trials was 3.3 to 3.7 kg, which may be a strain characteristic. In spite of severe food restriction, all birds were very fat at first egg. The correlations between fat concentration and age at first egg were negative. In mature pullets a minimum concentration of stored, easily mobilised fat may be essential for yolk formation and ovulation.

The replacement of some of the soybean meal by the first limiting amino acids in practical broiler diets

1. Four trials were conducted to determine to what extent dietary protein concentration could be lowered while maintaining the concentrations of methionine and lysine, the first two limiting amino acids. 2. When the protein concentrations of well-balanced standard finisher diets were lowered by replacing soybean meal with sorghum grain (milo), there were progressive decreases in growth rate and increases in food consumption in spite of the substitution raising the energy content of the diets. 3. Maintaining methionine and lysine concentrations partly or completely reversed these trends. 4. Adding 0-12% methionine (above that generally considered to be the normal level in finisher diets) plus 0-20% lysine replace about 3 to 4 percentage units of soybean protein. 5. The recommended level of lysine supplementation may be exaggerated, since preliminary data indicate satisfactory results with a special supplementation of 0-10% each of methionine and lysine.

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.

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.

The replacement of some of the soybean meal by the first limiting amino acids in practical broiler diets. I. The value of special supplementation of chick diets with methionine and lysine.

1. Three trials were carried out in order to determine the amount by which dietary protein concentration can be reduced while maintaining the dietary concentrations of the first two limiting amino acids, methionine and lysine. 2. In all trials growth rate and food utilisation declined as the protein concentration of a well-balanced standard chick diet was lowered by replacing soybean meal with sorghum grain (milo), but this trend could be partly or completely prevented when methionine or methionine and lysine levels were restored. 3. Addition of 0-06 to 0-07% methionine, above that considered to be normal, is sufficient to replace approximately 0.9% soybean protein. 4. In diets containing approximately 3 percentage units less soybean protein than required, a supplementation of about 0.15% each of methionine and lysine can replace nearly 2-0% soybean protein, but cannot bring about chick performance equal to that obtained on the control ration, indicating an insufficiency of a third, or third and fourth, limiting amino acid in such low-protein diets.

The replacement of some of the soybean meal by the first limiting amino acids in practical broiler diets. 2. Special additions of methionine and lysine as partial substitutes for protein in finisher diets.

: 1. Four trials were conducted to determine to what extent dietary protein concentration could be lowered while maintaining the concentrations of methionine and lysine, the first two limiting amino acids. 2. When the protein concentrations of well-balanced standard finisher diets were lowered by replacing soybean meal with sorghum grain (milo), there were progressive decreases in growth rate and increases in food consumption in spite of the substitution raising the energy content of the diets. 3. Maintaining methionine and lysine concentrations partly or completely reversed these trends. 4. Adding 0-12% methionine (above that generally considered to be the normal level in finisher diets) plus 0-20% lysine replace about 3 to 4 percentage units of soybean protein. 5. The recommended level of lysine supplementation may be exaggerated, since preliminary data indicate satisfactory results with a special supplementation of 0-10% each of methionine and lysine.

Evaluation of methanol‐grown bacteria and hydrocarbon‐grown yeast as sources of protein for poultry: Studies with young chicks

1. In a series of five trials, conducted with broiler chicks during the starting period, two types of dietary single‐cell protein were tested: Pruteen (PR), a protein concentrate produced from methanol‐utilising bacteria, and a Lavera‐type yeast (LA) utilising the normal paraffins of heavy gas oil. 2. The inclusion of 90 to 150 g PR or LA/kg diet depressed growth rate by 14 to 16% and 9 to 10%, respectively. This effect was slightly counteracted (about 6 percentage units) by the addition of L‐arginine. 3. The growth depression can be explained completely in the case of PR or almost completely in that of LA on the basis of reduced food intake, without a decided effect on food utilisation. 4. The reduced consumption of PR‐containing diets is not due to a petroleum‐ether‐soluble factor, nor to the high and low concentrations of sodium and potassium, respectively, in PR.

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.