The response of liver enzymes to feed restriction and subsequent ad lib. feeding in the laying hen.

1. The effects of restricted feeding, and ad lib. feeding following food restriction, on hepatic carbohydrate and lipid metabolism in the laying hen were studied. 2. The birds were allocated to four groups and given either 92, 84 or 75 g/d or allowed ad lib. access to food. 3. Food restriction significantly reduced liver total lipid content compared with ad lib.-fed control birds and this was reflected in reduced hepatic lipogenic enzyme activities. 4. When birds from the restricted regimens were allowed free access to food they initially consumed more food than the control group but after 2 weeks of ad lib. feeding the food consumptions of the birds in all the groups were similar. 5. Concomitant with the increase in food intake there were also increases in liver lipid content and hepatic lipogenic enzyme activities. After 18 d of ad lib. feeding these measurements were similar in the previously restricted birds and the ad lib.-fed control group. 6. Despite these effects on lipid metabolism, food restrictio, and the subsequent release from food restriction, had no significant effects on the specific activities of the glycolytic enzymes examined. 7. Although there were large increases in liver lipid content following release from feed restriction no birds died from, or showed any of the symptoms of, fatty liver-haemorrhagic syndrome. This suggests that, in the absence of any other factor which may be involved in the syndrome, these high liver lipid contents were not, alone, sufficient to cause FLHS. The results also indicate that free access to food following food restriction is unlikely to be a major factor in initiating the syndrome.