Feed protein solubility as an indicator of digestibility and availability of nutrients in the diets of bulls

Abstract

The research was conducted on steppe red bulls with duodenal and ileocecal anastomoses when feeding isoenergetic, isoprotein hay-concentrate diets with different levels of soluble protein (SP) and rumen degradable protein (RDP). We studied the transformation of dry matter (DM), organic matter (OM), crude protein (CP), crude ash (CA), crude fat (CF), crude fiber (CF) and nitrogen-free extractives (NFE) separately in a complex stomach, small (SI) and large (LI) parts of the intestine. Assimilation of protein by animals was assessed by the amount of it digested in SI, and unproductive costs — by the part of nitrogen in the urine. Diets consisted of hay, peas and mineral supplements. Different amounts of SP in the diets were achieved by feeding natural pea (control) or pea grilled at a temperature of +105°C (experiment). When feeding a diet with a reduced level of SP and RDP, the apparent intensity of digestion decreased, which was manifested in a slightly smaller amount of feed consumed, and in a smaller number of duodenal and ileocecal chyme. In a complex stomach, the CP digestibility of the experimental diet with a reduced level of SP was 10% lower. In the control diet with a high level of SP, more CP was degraded in rumen and more ammonium nitrogen was supplied to SI. The availability of CP for digestion in SI on the experimental diet was 5.8% higher, against control, with 8–10% higher digestibility of DM, OM and CP, but lower digestibility of CA and CF. In LI, the digestibility of nutrients in the studied diets was multidirectional. A significant amount of dietary protein was depreciated in the control diet with a high level of SP due to a 40% increase in urinary nitrogen excretion.