Comparison of the effects of pectin and starch on the rumen fermentation, growth performance and microbial populations in sheep

Abstract Text: Supply of available energy is important for microbial synthesis in the rumen. Pectin and starch are two primary sources of soluble carbohydrates, but remarkably different in digestion and fermentation characteristics. This study was conducted to compare the effects of pectin and starch on rumen metabolism, growth performance, and microbial populations in sheep. Forty-five male sheep (40.2 ± 3.16 kg) were divided into five groups of nine animals each according to body weight, with three pens of three sheep in each group, and then assigned to five dietary treatments with supplementation of 0, 2.5 and 5% pectin or corn starch, respectively, to a basal diet consisted of corn stover and concentrate mixture (50:50, DM basis). The trial lasted 5 wk, and feeds offered and refused were recorded for two consecutive days every week. Body weights were measured at the beginning and end of the feeding trial for two consecutive days. At the end of the trial, two thirds of experimental sheep were slaughtered before morning feeding to collect samples of rumen contents. Dry matter intake was increased quadratically or decreased linearly with the increasing level of pectin or starch, respectively. Increasing level of pectin led to a linear increase (P<0.01) in microbial protein synthesis and daily weight gain, with highest values at 5% pectin among all treatments (P<0.01). Total volatile fatty acids concentration in the rumen was linearly increased (P<0.01) by inclusion of either pectin or starch, but the ratio of acetate to propionate was not affected. Abundances of Treponema genus and Treponema saccharophilum quantified by real-time PCR were positively stimulated (P<0.01) only by pectin, suggesting their specific role on pectin digestion. On the contrary, abundances of typical rumen amylolytic bacteria such as Succinivibrio dextrinosolvens, Ruminobacter amylophilus, Succnimonas amylolytica were higher (P<0.05) when starch was supplemented. Both pectin and starch increased (P<0.01) the population of Treponema bryantii. Increasing the level of pectin led to a linear decrease (P<0.01) of the rumen lipolytic bacterium Anaerovi briolipolytica, whereas starch stimulated the growth of the species. Because A. lipolytica can not utilize starch but lactate as substrate, thus, the growth of A. lipolyticain starch treatments may be attributed to the lactate accumulation. A better understanding of microbial populations that accompany dietary differences will expand our knowledge of ecological importance of bacteria in the rumen and may further lead to beneficial strategies to improve ruminant production performance.

Keywords: soluble carbohydrate, microbial protein synthesis, bacterial populations