Ruminal fermentation characteristics and microbial nitrogen assimilation in sheep fed differently composed grass silages

Abstract

The investigation aimed at examining if the composition of grassland silage affects the microbial nitrogen assimilation in the rumen of sheep. The silages were made of vegetative summer re-growths consisting of 48% grasses, 28% legumes and 24% other forbs (GCF) or of pure grass (G). Silage GCF contained more intermediately degradable non-structural and less slowly degradable carbohydrates, more crude protein (CP), a narrower ratio between slow and very slow degradable nitrogen (N), and exhibited higher in situ degradability of organic matter and CP than Silage G. Four adult wethers equipped with rumen fistulae were used in a two factorial trial. Feed was offered either as silage alone or as a mixture of silage and barley (60:40). Microbial N was estimated using continuous intraruminal 15N infusion and measurement of 15N-enrichment in microbes isolated from rumen liquor samples. With the exception of trends for ruminal butyrate concentrations, no interactions were detected between silage and barley feeding. Sheep receiving Silage GCF exhibited larger diurnal fluctuations of ammonia, and produced more microbial N (p < 0.05) than sheep on Silage G. Feeding the silages with barley decreased ruminal pH and elevated the concentrations of butyrate (p < 0.05). The 15N incorporation into microbial N was reduced by barley feeding (p < 0.05) along with a trend to accelerated rumen fluid turnover, resulting in similar microbial N yields as found in sheep receiving silage without barley. It is concluded that the larger and better balanced amounts of intermediately degradable carbohydrate- and N-containing fractions favoured the ruminal microbial protein synthesis in sheep consuming Silage GCF instead of Silage G.

Diverse Swards and Mixed-Grazing of Cattle and Sheep for Improved Productivity

“…This may be attributed to their slower rate of maturation and greater digestibility, relative to grasses, throughout the year (Bruinenberg et al, 2002;White et al, 2004;Petersen et al, 2013). In addition, CP concentrations were higher on diverse swards (Figure 2D), in line with previous studies (Hofmann and Isselstein, 2005;Seip et al, 2012;Seither et al, 2012). The positive effect of species richness can be attributed to either a legume effect or a functional group effect.…”

“…Phytodiversity has also been shown to affect forage quality, although reports are inconsistent (Bullock et al, 2001;Tracy and Faulkner, 2006). For example, White et al (2004) found a negative effect, while other studies (Hofmann and Isselstein, 2005;Isselstein, 2005;Seip et al, 2012;Petersen et al, 2013) have suggested that the herbage of more diverse-swards contains higher concentrations of crude protein, particularly in late season.…”