Effect of sodium bicarbonate supplementation and variation in the proportion of barley and sugar beet pulp on growth performance and rumen, blood and carcass characteristics of young entire male lambs

Abstract

Forty-eight Suffolk × Mule entire male lambs (22.3 kg average live weight, two months old) were used to study the effects of addition of sodium bicarbonate and increasing quantities of molassed sugar beet pulp (MSBP) to diets based on barley grain (780 g kg −1 fresh weight and approximately iso-energetic and iso-nitrogenous). Measurements were made of dry matter (DM) intake, growth, some ruminal and blood plasma metabolites and hormone profiles and body composition. The animals were allocated by randomised block design on the basis of live weight to one of six dietary treatments and an initial slaughter control group ( n = 7 and mean live weight = 22.3 kg per treatment). Animals in the initial slaughter control group were slaughtered on Day 1 of the study in which barley was supplemented with sodium bicarbonate (15 g kg −1 fresh weight) (Experiment A) or replaced with increasing quantities of MSBP in a separate experiment (B) to provide diets containing 75, 50, 25 and 0% of the maximum quantity of barley (Experiment B). The diets had similar in vitro dry matter digestibility and contained similar estimated values for metabolisable energy concentration. In Experiment A, the inclusion of sodium bicarbonate had no significant effect on live weight gain, DM intake, feed utilisation efficiency, ammonia concentration and the molar proportion of ruminal volatile fatty acids, rumen fluid, carcass and soft tissue characteristics and composition. In Experiment B, increases in level of barley in the diet had no effect on ruminal pH, but linearly increased the molar proportion of propionate in rumen fluid ( p < 0.01), hot- and cold-carcass weights ( p < 0.01), empty body weight ( p < 0.01), perirenal and retroperitoneal fat ( p < 0.05) and gain of crude protein in cold carcass ( p < 0.01). Evidence was also obtained for decreases in concentrations of ruminal ammonia and plasma area associated with increasing concentrations of dietary MSBP. Certain significant quadratic effects on plasma insulin concentration, which were not associated with indices of carcass and digesta-free body growth, were also recorded. It is concluded that the diet based on MSBP alone was not utilised as effectively for growth and body weight gain as MSBP-based diets also containing barley grain. The results suggest that any limitations in growth performance by entire male lambs fed a diet containing high levels of MSBP may be effectively abolished by the replacement with barley at a substitution rate of 25% or greater.