Biochemical,physiological and production indices related to fat metabolism in the laying fowl at various stages of physiological development

1. The significance of fat accumulation during physiological development of layers was studied using White Leghorn x Australorp pullets from 12 weeks of age.

2. Liver fat, carcass fat, liver weight and body weight increased markedly at the onset of sexual maturity.

3. Within the liver, the protein to DNA ratio did not alter significantly during development; glycogen was not consistently depleted by egg production.

4. Liver fat content was significantly correlated with carcass fat, liver weight and DNA concentration, and plasma total lipid and cholesterol, independent of stage of development; with body weight, liver protein, moisture, and protein to DNA ratio, excluding the period prior to commencement of sexual maturation; and with plasma phospholipid during lay.

5. Obesity was a feature of faster growing fowls which matured earlier, consumed more, utilised food less efficiently for egg production and produced fewer saleable eggs.     

Agonistic interactions in developed and undeveloped breeds of chickens

1. Agonistic interactions were observed over a 24‐week period in Rhode Island Red and in Nigerian local fowl aged 32 weeks or 12 weeks at the start of the experiments.

2. Agonistic interactions were both more numerous and more severe (fights and peck avoidances) in groups of the local breed than in those of Rhode Island Reds.

3. The outcome of severe interactions favoured local males and Rhode Island females in the first experiment and Rhode Island males in the second.

4. Small body and comb size might account for the relatively high number of agonistic interactions and the submissiveness of local females and young males while physical strength or some other breed characteristic might account for the high number of agonistic interactions of local males as well as their dominance in breed encounters.     

Rapeseed meal and egg taint: Treatment of rapeseed meal to reduce tainting potential

1. Treatment of rapeseed meal with calcium hydroxide suspension decreased the sinapine content by up to 90%. Smaller decreases were obtained by autolysis, steaming and treatment with ammonia.

2. When this treated meal was fed to susceptible ("tainting") hens the concentration of trimethylamine in the eggs was decreased to much less than that required to cause taint.     

Effect of light,vitamin d and dietary phosphorus on egg‐shell quality late in the pullet laying year

1. Eighteen diets supplying all combinations of three phosphorus contents (3.1, 4.0 and 4.8 g non‐phytate P/kg) and six vitamin D supplements (37.5 or 150 μg cholecalciferol/kg; or 16 or 24 μg 25‐hydroxy‐cholecalciferol/kg; or 37.5 μg cholecalciferol/kg with either 16 or 24 μg 25‐hydroxycholecalciferol/kg) were fed to 2 880 pullets of two stocks from 64 to 74 weeks of age. The birds were housed in eight light‐proof rooms, four of which had 24‐h light‐dark cycles (16L : 8D) and four had 28‐h cycles (20L : 8D).

2. The dietary treatments had no significant effect upon food intake, egg output, shell thickness, shell deformation or specific gravity of the eggs.

3. The 28‐h cycle reduced mean rate of lay by 4.5%, increased egg weight by 5.8% and increased shell thickness by 9.4%. The proportion of eggs with shell faults revealed on candling was reduced from 4.1 % to 2.8%.

4. It is concluded from this and other sources that decreasing dietary phosphorus or modifying vitamin D supplements may sometimes lead to increases in shell thickness of the order of 1 to 2%, but that these changes are unlikely to result in a measurable reduction in the proportion of cracked eggs late in the laying year.

5. A 28‐h light‐dark cycle results in a longer and more uniform interval between consecutive ovipositions and thus gives reliable increases in shell thickness which are large enough to reduce the proportion of cracked eggs in many practical situations. Whether it is profitable to use an ahemeral cycle will depend upon the relative prices paid for eggs of different sizes.     

A diet formulated from by‐products and indigenous foodstuffs for laying hens

1. The performance of six commercial stocks of laying hens fed on a diet composed of home‐produced foodstuffs, not usually used for human consumption, was compared with that of birds fed on a conventional diet.

2. The experimental diet was calculated to be low in energy and methionine and high in fibre by conventional standards. Birds ate up to 12% more of this diet, but the calculated intakes of energy and methionine were less than those of the corresponding controls.

3. White stocks fed on the experimental diet produced seven eggs less per bird than controls while the production of brown stocks was essentially unaffected.

4. The gross efficiency of energy utilisation for egg production was better with the experimental diet.     

Habituation by the immature fowl in response to repeated injections of corticotrophin.

1. Immature birds treated for 7 d with corticotrophin (30 IU/kg, one injection per day) had significantly poorer growth rates and decreased adrenal cholesterol concentrations. Plasma glucose, corticosterone and cholesterol concentrations and adrenal weight were within the normal range 24 h after the last injection.

2. The responses of birds pretreated as described above to a single injection of corticotrophin (30 IU/kg) were determined.

3. A similar degree of hyperglycaemia had developed in both groups after 2 h but thereafter the responses differed: the concentration of plasma glucose did not increase further in those pretreated with corticotrophin and had begun to decrease at 6 h, whereas that of the birds pretreated with saline increased progressively.

4. The concentrations of plasma corticosterone had increased similarly in the two groups to a peak at 2 h but there was a significantly more rapid decrease in the birds pretreated with corticotrophin.

5. Both groups showed a transient hypercholesteraemia but the increase was significant only in the group that had previously received saline.

6. There were decreases in the concentrations of adrenal cholesterol in both groups. The decrease, in absolute terms, was 2–4 times greater in the group receiving corticotrophin for the first time: percentage changes were similar, however.     

Selection for food conversion in broilers: Direct and correlated responses to selection for body‐weight gain,food consumption and food conversion ratio

1. Direct and correlated responses were determined after five generations in four lines of chickens selected either for increased body‐weight gain (line W), for increased food consumption (line F), for decreased food conversion ratio (line E), or at random (line C).

2. Realised heritability estimates calculated after five generations of selection were : 0–37 + 0.04 for weight gain (WG); 0.44 + 0.05 for food consumption (FC); 0.21 + 0.04 for food conversion ratio (FCR).

3. Realised genetic correlation estimates were: WG and FC, +0.71 ±006; WG and FCR, ‐0.40±0.09; FC and FCR, +0.27 + 0.09.

4. Zero‐generation heritability and genetic correlation estimates were greater than the realised estimates, and sex linkage appeared to be important in the expression of all three traits.

5. The genetic correlation between FC and FCR was asymmetrical with considerable positive response in FCR in line F (r_g = +0.79) but negligible response in FC in line E (r_g = —0.01).

6. There was an apparent plateau in response in FCR in line E from the third to the fifth selected generations.