Effect of replacing barley with corn or sorghum grain on rumen fermentation characteristics and performance of Iranian Baluchi lamb fed high concentrate rations

The present study, conducted in Iran, was aimed to evaluate the effects of partial substitution of barley with corn or sorghum (slowly fermenting grains) on in situ dry matter (DM) and starch degradability and in vivo digestion characteristics and performance in finishing Iranian Baluchi lambs. In the first experiment, samples of ground barley (B), corn (C), sorghum (S) and their combinations [%: 70 barley:30 corn (LC), 70 barley:30 sorghum (LS), 30 barley:70 corn (HC) and 30 barley:70 sorghum (HS)] were incubated in nylon bags in rumen of three fistulated Holstein steers. Effective degradability (ED) for DM and starch were different (P < 0.05) among treatments. In both cases, ED was higher (P < 0.05) for B than that for C, S, HC and HS. Results of the present study confirmed previous reports that ruminal degradability of barley is higher than that of corn and sorghum, and further suggested that there may be benefits in replacing barley with ~70% of corn or sorghum. In Experiment 2, 30 Iranian Baluchi male lambs weaned at 65 days of age (BW 32 ± 2.3 kg) were divided into five equal weight groups (6 animals per group) in a complete randomised design. Lambs received a mixed diet in the form of total mixed rations (TMR), consisting of 32.5% alfalfa hay [89% DM, 43% natural detergent fibre (NDF) and 16% crude protein (CP) in diet DM basis] and 67.5% of the respective concentrates. The five iso-caloric (10.73 MJ ME/kg) and iso-nitrogenous (14% CP/kg DM) concentrates with different sources of starch used in the study were (1) barley, as the control cereal source for starch, and in the other treatments barley substituted with (2) 30% corn (LC), (3) 30% sorghum (LS), (4) 70% corn (HC) and (5) 70% sorghum (HS). Lambs in HC and HS diets recorded increases of 20 and 50 g/day in average daily gain, respectively, compared with lambs in B. Substitution of B with 70% C and S significantly (P < 0.01) improved ruminal pH and, presumably, resulted in higher starch outflow for post-ruminal digestion, as reflected by a higher blood glucose concentration, particularly for lambs in the HS diet. Results of the present study reaffirmed the advantages of feeding a mixture of grains with differing fermentation rates and, as previously reported, also suggested that the inclusion rate of slowly degradable grains should be ~70% so as to enhance animal performance.