Young sheep of Romanov breed: productivity and biological features at different levels of energy and protein in the diet

The experiment was performed on two groups of Romanov sheep at the age of from 3 to 10 months under different rearing and fattening conditions at the "Pokrov" sheep farm in the Tver region. An increase in metabolic energy and crude protein in the diets of animals from 3 to 7 months of age led to an increase in the growth intensity of the body weight in Group II. The live weight of rams at the age of 7 months was greater by 5.79 kg or 17.75% in Group II than in Group I, and the daily gain increased from 138 g to 186 g. In terms of the daily gain, the difference at this age was 45 g or 32.37%. According to the slaughter results, the pre-slaughter weight of the rams in Group II increased by 9.73 kg or 22.3% compared to Group I; the hot carcass weight was greater by 5.08 kg or 25.5%; the slaughter weight by 6.4 kg or 31.1 %; and the slaughter yield increased from 47.3% to 50.7%, or by 3.4 absolute percent. The histological studies of the longissimus muscle showed, that in Group II, the diameter of muscle fibers increased by 4.3 μm or 15.7%, the diameter of fat cells by 6.2 μm or 10.4%; and the numbers of muscle and fat cells per 1 cm2 of the longissimus muscle increased and amounted to 5.6 and 28.6%, respectively. The width of the connective tissue decreased by 5.2 μm or 14.7%. The difference in the amounts of wool shorn—original and clean fiber—was 0.27 and 0.20 kg or 20.1 and 21.1% in favor of Group II animals with an increased level of energy and protein in their diets. The histological studies of skin showed, that the total skin of rams in Group II (at intensive feeding) was thicker by 523 μm or 22.6% than in Group I, with the pilar layer being thicker by 231 μm or 15.1%. The thickness of the reticular layer increased by 290.5 μm or 38.8% in young animals of Group II. The 3-7 month old Romanov rams with the live weight of 16-38 kg and 186 g of the daily body weight gain had requirements for 1.45 kg of dry matter (DM), 1.50 energetic feed units (EFU) of exchange energy, and 186 g of crude protein per 1 head a day at a cost of 7.8 kg of DM, 8.06 EFU of metabolic energy, and 988 g of crude protein per 1 kg of increase.