Influence of Hormones on the Depressing Effect of Dietary Protein for the Fat Deposition of Growing Chicks

Abstract

It has been reported that starting chicks or growing meat-type chicks become fatty or lean by simply changing dietary levels of protein, and the fat deposition may be controlled by certain hormones. This paper deals with the effects of diethylstilbestrol (DES), testosterone, thyroxine, thiouracil and prolactin in growing chicks.One hundred and forty-four meat-type chicks of both sexes were placed in growing cages at 2 weeks of age, and fed with either one of the two isocaloric diets with a different protein level (CP: 20 and 26%) up to 6 weeks of age. Hormone treatments and thiouracil feedings were started at 3 weeks of age. DES (1mg/bird), testosterone (1mg/bird) and thyroxine (30μg/100g body wt.) were injected intramusculary into the birds once daily for three weeks, prolactin (25 I.U./bird) was injected intramusculary every other day. Thiouracil was fed at 0.2% level in the basal diet. The birds were sacrificed at 6 weeks of age and the abdominal fat was removed and weighed. Percentages of the weight of the abdominal fat to the body weight were used for the comparison of the fat deposition.1) The injection of diethylstilbestrol resulted in an increase in the fat deposition in both groups of birds. However, the birds fed with the higher protein diet showed less fat deposition than the birds fed the lower protein diet, although the difference was statistically not significant at 5% level.2) The injection of testosterone did not affect the fat deposition in both groups of birds, and the less fat deposition was observed in the birds fed with the higher protein diet.3) The injection of thyroxine resulted in a decrease in the fat deposition, but the less fat deposition was still thiouracil observed in the birds with the higher protein diet.4) Feeding thiouraci caused an increase in the fat deposition, but the difference between the two groups of different protein levels was not observed.5) No appreciable effect of prolactin on the fat deposition was observed in the male birds. But, in the female birds, the depressing effect of the higher protein diet was diminished.