Nutritional and zootechnical consequences of variations in starch degradation rate in ruminants

Abstract

A data base was pooled with 52 comparisons between two diets containing starch fraction having either a rapid or a slow degradation rate in the reticulo-rumen. This base was treated with appropriate statistical methods to test the effects and to calculate empirical models of rumen digestion response and animal performances to these variations in starch degradation rate.

Decreasing starch degradation rate decreased the amount of fermentable organic matter and microbial growth, however, microbial growth efficiency was not affected. With slow starch sources, rumen pH and the proportion of ruminal acetate were higher while the proportion of propionate and its concentration in fluid were lower. There was a systematic decrease of total tract starch and organic matter digestibility, and thus diet energy density, with a slow versus a rapid starch degradation rate.

Nine of the published trials were based on a factorial 2 × 2 combinations of starch and nitrogen degradation rates. No interactions appeared between these two parameters for the measured items.

Decreasing the starch degradation rate was accompagnied by a systematic increase in the level of dry matter intake. In contrast, a specific analysis of trials performed on dairy cows indicated that raw milk yield was not altered by changes in the starch degradation rate. However the milk contents in fat and protein were respectively significantly increased or decreased when slow starch diets were compared to rapid ones.