Effect of oral administration of diisopropyl 1, 3-dithiolan-2-ylidenemalonate (NKK-100) on the components of mixed function oxidase system in hepatic microsomes was investigated in male broiler chicks. Feeding NKK-100 increased relative liver weight and microsomal protein content of the liver. Contents of cytochrome P 450 and b 5 per mg microsomal protein and g liver increased with NKK-100 levels. The activities of NADPH-cytochrome c reductase and NADH-cytochrome b 5 reductase per g liver were enhanced by feeding NKK-100, while those activities per mg microsomal protein remained unchanged. Pretreatment with clopidol (an anticoccidial agent) and colistin (an antibiotic) did not affect the components of MFO. These results suggests that NKK-100 has a property to activate the hepatic microsomal MFO and the effect of NKK-100 are more prominent in the increases in specific activities of cytochrome P 450 and b 5 rather than in those of NADPH-cytochrome c reductase or NADH-cytochrome b 5 reductase.

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Concentrations of progesterone, estradiol and testosterone in peripheral blood plasma of pullets were measured from 13 to 19 weeks of age, and the relationships between the ages of first egg laying and fluctuations in these peripheral steroids before and after the onset of laying were investigated.
1. The average age in days and body weight at the first egg laying were found to be 136.7±0.96 days and 1, 475±13.1g, respectively.
2. The egg production rate in the first weeks after the onset of laying showed 61.1%, 73.6%, 75.0% and 81.3% in the group exhibiting the first egg laying at 17, 18, 19 and 20 weeks of age, respectively.
3. The concentrations of progesterone in blood plasma were found to remain at a low level (less than 70pg/ml) until 3 weeks before the onset of laying, and then rose sharply 1 to 2 weeks before the onset of laying. In the group exhibiting earlier first egg laying, later increases of concentrations of progesterone was observed.
4. The concentrations of estradiol in blood plasma showed a prepubertal peak (more than 320pg/ml) in every group. The earlist and highest observation of this peak was made in the group exhibiting later first egg laying.
5. The concentrations of testosterone in blood plasma tended to increase gradually with the onset of laying, and more remarkable changes were observed in the group of later first egg laying.

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Ninety Harvard-comet laying hens at 49 weeks of age were used to examine the egg weight and the egg shell qualities under two kinds of the 28-hour ahemeral light-dark cycles. In the experment 1, they were divided into three groups and all of them were exposed to 15L: 9D cycles for one week of preliminary period. Each of the three groups was then, exposed to the normal 15L: 9D as control, the ahemeral 19L: 9D and the ahemeral 15L: 13D cycles, respectively. In the preliminary period, as well as in 1st, 5th and 9th week after the exposure to ahemeral LD cycles, the eggs were collected every 4 hours and the egg weight, the albumen weight, the shell thickness, the shell weight and the shell breaking strength were measured. At 84 weeks of age, the experiment 2 was started in the same method with the experiment 1.
In the experiment 1, the egg, the egg yolk and the egg albumen weight increased in 1st, 5th and 9th week after exposure to ahemeral LD cycles. The differences between the normal group and the ahemeral groups in 1st week were not significant but those in 5th and 9th week were highly significant. Exposure to ahemeral LD cycles also increased the shell thickness, the shell weight and the shell breaking strength. And the significant differences were observed even in 1st week. In Experiment 2, similar tendency to experiment 1 was observed in all measurements, while the differences between the normal and the ahemeral groups were not so clear as in experiment 1. There was no clear differences in all measurements between two ahemeral groups in both experiments.

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Experimental diets containing 16% of brewer's yeast in place of soybean and fish meal in a control diet were fed to hens for 12 weeks, fertile eggs were collected and the offspring obtained. The offspring were reared for 212 weeks feeding the same diets as their parents were. Though the experiment was continued for 212 weeks, the data of laying period for 80 weeks, i.e., from 20 to 100 weeks of age, were presented in this paper, because in practical poultry farms hens are replaced by pullets at a much younger age than 212 weeks. Two kinds of brewer's yeast were tested, one designated as N from Kirin Brewery Co., Ltd., and the other designated as O from Sapporo Breweries Ltd..
The hens started to lay in the spring, 1976. No significant difference was observed in the egg production between the control hens and those fed the yeast in the initial 16 weeks after the start of laying. The egg production of the control decreased in the summer and fall, while that of the hens fed the yeasts decreased more slowly than the control. The difference in these periods was significant statistically (p<0.05). In the next spring, when the egg production recovered after the drop in the winter, the recovery of the hens fed the yeasts was rapid, resulting in a significant difference in the egg production between the control and the hens fed the yeasts. Summing up the data for 80 weeks, the average egg production of the hens fed the yeasts was about 7% higher than that of the control hens. Little difference was observed in the feed intake between the hens. Average egg weight of the hens fed the yeasts was slightly lower than that of the control, but their daily egg production (average egg production×average egg weight) was about 3g i.e., 8%, greater than the control.
Presence of an unidentified factor, which may activate the egg production was suggested in the yeast. The factor may have little effect when the hens are young, healthy and productive, but have an effect to keep higher egg production than the control hens when the egg production of the latter decrease for some reason. At the later stage of the egg production, usually at about 80 weeks of age, the production of the hens decreases gradually, and finally come to such a low level that the income from their eggs didn't cover the expense for their feed, so that the hens must be replaced by pullets. At this time, the hens fed the yeast keep about 10% higher egg production than that of the control. The findings are meaningful economically for poultry farmers, because the hens fed the yeasts could be kept further, without being replaced.

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