Effect of maize silage to grass silage ratio and feed particle size on ruminal fermentation in vitro

Abstract

The effect of the forage source on ruminal fermentation in vitro was investigated for fine (F) and coarse (C) milled diets, using a modified Hohenheim gas production test and a semi-continuous rumen simulation technique (Rusitec). It was hypothesised that the replacement of maize silage by grass silage might lead to associative effects and that interactions related to particle size variation could occur. Five diets with a maize silage to grass silage ratio of 100 : 0, 79 : 21, 52 : 48, 24 : 76 and 0 : 100 differed in their content of CP and carbohydrate fractions, as well as digestible crude nutrients, derived from a digestibility trial with wether sheep. For in vitro investigations, the diets were ground to pass a sieve of either 1 mm (F) or 4 mm (C) perforation. Cumulative gas production was recorded during 93 h of incubation and its capacity decreased with increasing proportion of grass silage in the diet. Across all diets, gas production was delayed in C treatments compared with F treatments. Degradation of crude nutrients and detergent fibre fractions was determined in a Rusitec system. Daily amounts of NH 3 -N and short-chain fatty acids (SCFA) were measured in the effluent. Degradation of organic matter (OM) and fibre fractions, as well as amounts of NH 3 -N, increased with stepwise replacement of maize silage by grass silage. Degradability of CP was unaffected by diet composition, as well as total SCFA production. In contrast to the results of the gas production test, degradation of OM and CP was higher in C than in F treatments, accompanied by higher amounts of NH 3 -N and SCFA. Interactions of silage ratio and particle size were rare. It was concluded that the stepwise replacement of maize silage by grass silage might lead to a linear response of most fermentation characteristics in vitro. This linear effect was also supported by total tract digestibility data. However, further investigations with silages of variable quality seem to be necessary. Keywords: silage, particle size, associative effects, ruminal fermentation, in vitro ImplicationsWhen grass silage and maize silage are incubated together but in different ratios in vitro, the associative effects on criteria of fermentation are unlikely to occur. Fermentation values for the individual silages are additive in these mixtures. However, the effect of variation in silage chemical composition remains to be investigated. The effects of feed particle size should be taken into account when comparing results of studies conducted with a Rusitec system. Further research investigating the effect of feed particle size, larger than particles produced by milling feeds with a 4-mm sieve, on degradation rates measured in rumen simulations is needed.

Effect of maize silage to grass silage ratio and feed particle size on protein synthesis and amino acid profile in different microbial fractions in a semi-continuous rumen simulation

“…High proportions of concentrate in the diet (Ranilla and Carro, 2003) and supplementation of maize starch to grass pasture (Bach et al, 1999) were reported to reduce the N content in the microbial mass. Changes in the availability of nutrients, as described between treatments F and C (Hildebrand et al, 2010), did not affect N contents of the microbial fractions. Changes in the availability of nutrients, as described between treatments F and C (Hildebrand et al, 2010), did not affect N contents of the microbial fractions.…”

“…Similar amounts of total short-chain fatty acids indicated that the amount of fermented carbohydrates was similar between diets of different maize silage to grass silage ratio (Hildebrand et al, 2010). The amount of ATP derived from Sum of the 15 analysed AA.…”

“…The degradation of OM and CP, as well as the daily amounts of NH 3 -N and short-chain fatty acids in the effluent were higher in coarse-milled than in fine-milled treatments (Hildebrand et al, 2010). The degradation of OM and CP, as well as the daily amounts of NH 3 -N and short-chain fatty acids in the effluent were higher in coarse-milled than in fine-milled treatments (Hildebrand et al, 2010).…”

“…The in vitro procedure, using a semi-continuous Rusitec (Czerkawski and Breckenridge, 1977) is described in more detail in a companion study (Hildebrand et al, 2010) and in general followed the procedures as described by Boguhn et al (2006a). In brief, six fermenters, with a volume of 800 ml each, were used per period.…”

“…Crude nutrients, fibre fractions and starch in feed and feed residues were analysed according to the official methods in Germany (Verband Deutscher Landwirtschaftlicher Untersuchungs-und Forschungsanstalten, VDLUFA, 2006), and specifications as described in the companion study (Hildebrand et al, 2010). Supernatants obtained during LAM-E isolation were analysed for NH 3 -N (Hildebrand et al, 2010).…”