Combined effect of shortened photoperiod and low crude protein diet on liver triglyceride accumulation and lipid-related gene expression in quail

A short photoperiod is reported to promote body weight gain in quail, and might therefore influence lipid metabolism and induce liver steatosis. Protein deficiency or malnutrition can also cause hepatic steatosis in mammals, but the effect in birds has not previously been investigated. In order to determine the influence of a shortened photoperiod and low crude protein diet on avian hepatic lipid metabolism, 10-day-old male Japanese quail (Coturnix coturnix japonica) were assigned to a 2 × 2 factorial arrangement of treatments in four groups, each of eight birds, and fed for three days, after which liver triglyceride (TG) accumulation and lipid-related gene expression were measured. Experimental factors included two dietary protein levels of 24% or 10% crude protein (CP), and two photoperiod conditions of a 12:12 h light/dark cycle (12L:12D) or a 1:23 h light/dark cycle (1L:23D). The liver TG level in quail fed the 10% CP diet under 1L:23D was higher than in birds maintained on either the 10% CP diet under 12L:12D (15.86 vs. 10.56 mg/g liver, P < 0.01) or 24% CP diet under 1L:23D (7.95 mg/g liver, P < 0.01). The sterol regulatory element-binding protein 1 mRNA, which is involved in TG synthesis, was more highly expressed in quail on the 10% CP diet under 1L:23D than in those maintained on the 24% CP diet under 12L:12D (2.2 vs. 7.9, P < 0.01), whereas the mRNA level of very low-density apolipoprotein II (apoVLDLII), which encodes a VLDL structural protein, was lower (157.3 vs. 12.5, P < 0.01). To our knowledge, this is the first report of a selective protein restriction and shorter photoperiod, alone and in combination, inducing a fatty liver state in an avian species. Our study provides insight into factors that govern lipid metabolism in birds, and the efficiency of domestic fowl production.