The grains of three sorghum varieties varying in tannin content were fed to growing chickens as 70 per cent of their diet in three experiments. Tannic acid per se was also fed as 0.1 per cent and 1.0 per cent of the grain component in one of these experiments. There was a marked growth retardation as the tannin content of the grain component rose. This retardation, whether produced by an increase in plant tannin or the addition of tannic acid per se, could only be partially alleviated by supplementation with high levels of methionine and choline. Raising the tannic acid or plant tannin level of a ration appears to have two detrimental effectsdepressing feed intake and a toxic effect. Addition of tannic acid significantly depressed liver fat content and testis weight. Additional methionine plus choline supplementation prevented the liver fat depression but did not prevent the reduction in testis weight.

The performance of pullets either fed lysine deficient diets or restricted in total feed intake in their starter (0-6 weeks), grower (6-1 2 weeks) or developer (1 2-20 weeks) phases or throughout their rearing period (0-20 weeks) were compared in separate experiments. Two levels of severity of each type of restriction were examined. No restriction treatment significantly improved the efficiency of conversion of feed to egg either measured on a chronological basis (0-68 weeks) or a physiological age basis (40 weeks from first egg). Both types of restriction applied in the starter phase tended to reduce egg size. Severe restriction throughout rearing greatly increased rearing period mortality.

No abstract

1. A realised heritability of 0.23 was obtained in an Australorp flock (S) selected for five generations for high egg specific gravity. 2. A comparison with an unselected control flock (C) over 50 weeks of lay in the final generation indicated a number of statistically significant correlated responses in commercially important traits in the S line in addition to the direct response of +0.004 in specific gravity. 3. With an increase in specific gravity, there was a decrease of 3.4 in the percentage of soft-shelled eggs laid. 4. The weight and albumen height of eggs measured within 1 hour of lay declined by 1.8 g and 2.1 Haugh units respectively. 5. There were reductions in the weight and albumen height losses of eggs stored over a 10-d period (C 0.74, S 0.62 g and C 17.9, S 15.0 Haugh units respectively), so that at the end of this period the albumen heights in both lines were the same. 6. Average body weight and daily food intake were less by 0.28 kg and 7.5 g respectively. 7. Although there was no change in egg production, the average age at first egg was reduced by 11.3 d.

The intake of the pullet was controlled in both growing and laying periods by limiting time of access to feed. Experiments examined severity of restriction and the age of lifting growing period restriction. In the growing period, severity of restriction was of less importance than the age at which restriction was lifted. Although ending restriction at 18 weeks improved the efficiency of conversion of feed to eggs, delaying the lifting of restriction gave marked further improvements. Restricting the bird's intake during lay gave additional increases in efficiency over and above those produced by growing period restriction alone. Denying the bird's access to feed from 7.30 a.m. to 3.30 p.m. daily was the most effective of the laying period restrictions examined. The effects of treatments on carcase composition at point of lay were also examined.