Effect of amount and degradability of dietary starch on animal performanceand meat quality in beef bulls

Twenty-four non-double-muscled Belgian Blue bulls, divided into four analog ous groups, were given nd libitum access to a finishing diet based on a low starch content (LS), or a high starch content with a low (HSLD), an interm ediate (HSID), or a high rumen degradability (HSHD), respectively. The diet s were isoenergetic and isonitrogenous, and consisted of 70% concentrate an d 30% maize silage. Ar slaughter, approximately 4 ru 5 h after the last fee d distribution, blood was sampled for the determination of the concentratio ns of lactate, glucose, non-esterified fatty acids and urea. Meat quality p arameters of the longissimus muscle and fatty acid composition of the intra muscular fat were also investigated. The HSLD diet resulted in a higher dai ly growth rate and dry matter intake (1.65 and 10.54 kg) than the HSHD diet (1.45 and 9.52 kg), with intermediate rates of gain and intake for LS (1.4 9 and 9.92 kg) and HSID (1.50 and 9.86 kg). From the blued metabolites, onl y urea was affected, amounting to 2.97 mmol/l for HSHD compared to 2.31, 2. 11 and 2.30 mmol/l, respectively for LS, HSLD and HSID (p < 0.05). Meat col our was darker for HSID and HSHD compared with HSLD, with higher shear forc e values for HSHD than for LS. Significant differences in concentrations of myristic acid (C14:0), palmitic acid (C16:0), and stearic acid (C18:0) wer e found, but differences in C16:0 could nor be explained by the fatty acid composition of the concentrate. High-concentrate diets with either a low st arch content or a high starch content coupled with a high rumen degradabili ty may reduce animal performance due to chronic acidosis.