Effects of replacing grain feed with rumen-protected fat on feedlot performance, ruminal parameters and blood metabolites in growing Merino lambs’ diets during the hot season

Abstract

In this study, the effects of rumen-protected fat (RPF) were evaluated as an energy source for partial replacement of grain feed in the diets of Merino male lambs during the hot season. Fourteen six months old Merino male lambs weighing average of 29.59 kg were randomly allocated into two groups: control diet (CON) and diets supplemented with 30 g/kg RPF. Live weight (LW), dry matter intake (DMI) and average daily gain (ADG) were recorded, and the feed conversion ratio (FCR) was then calculated. The ruminal pH, the ruminal ammonia nitrogen concentrations (NH3-N) value, the molar proportion of volatile fatty acid (VFA), blood serum as well as hematological parameters were determined and protozoa numbers were counted. While the live weight and daily gain of the lambs were not influenced by dietary treatments, DMI was increased with RPF supplementation. The ruminal pH, VFA and ruminal NH3-N concentrations were unchanged, but the protozoa numbers decreased significantly by RPF supplementation (P<0.05). RPF supplementation significantly affected some serum and hematological parameters in comparison to the control group. In conclusion, RPF may be added to concentrate mixture lamb feed at the level of 30 g/kg to enhance the diet energy density without negatively changing the animal’s performance.