Effects of degradable protein and non-fibre carbohydrates on microbial growth and fermentation in the rumen simulating fermenter (Rusitec)

Abstract

A rumen simulation technique (Rusitec) apparatus with eight 800 ml fermentation vessels was used to investigate the effects of rumen degradable protein (RDP) level and non-fibre carbohydrate (NFC) type on ruminal fermentation, microbial growth, and populations of ruminal cellulolytic bacteria. Treatments consisted of two NFC types (starch and pectin) supplemented with 0 g/d (low RDP) or 1.56 g/d (high RDP) sodium caseinate. Apparent disappearance of dry matter and organic matter was greater for pectin than for starch treatment (P<0.01) with low or high RDP. A NFC × RDP interaction was observed for neutral detergent fibre disappearance (P=0.01), which was lower for pectin than for starch only under low RDP conditions. Compared with starch, pectin treatment increased the copy numbers of Ruminococcus albus (P≤0.01) and Ruminococcus flavefaciens (P≤0.09), the molar proportion of acetate (P<0.01), the acetate:propionate ratio (P<0.01), and methane production (P<0.01), but reduced the propionate proportion (P<0.01). Increasing dietary RDP increased the production of total VFA (P=0.01), methane (P<0.01), ammonia N (P<0.01), and microbial N (P<0.01). Significant NFC × RDP interaction and interaction tendency were observed for ammonia N production (P=0.01) and daily N flow of total microorganisms (P=0.07), which did not differ under low RDP conditions, but pectin produced greater microbial N and less ammonia N than starch with increased RDP. Results showed NFC type, RDP level, and their interaction affected ruminal fermentation and microbial growth, and under sufficient ruminal degradable N pectin had greater advantage in microbial N synthesis than starch in vitro.