Digestion, rumen fermentation and circulating concentrations of insulin, growth hormone and IGF-1 in steers fed diets based on different proportions of maize silage and grass silage

Replacing grass silage with maize silage results in a fundamental change in the ratio of structural to non-structural carbohydrates with commensurate changes in rumen fermentation patterns and nutrient utilisation. This study investigated the effects of feeding four forage mixtures, namely grass silage (G); 67 g/100 g grass silage133 g/100 g maize silage (GGM); 67 g/100 g maize silage133/100 g grass silage (MMG); maize silage (M) to four ruminally and duodenally canulated Holstein Friesian steers. All diets were formulated to be isonitrogenous (22.4 g N/kg DM) using a concentrate mixture. Dietary dry matter (DM) and organic matter (OM) digestibility increased with ascending maize silage inclusion (P,0.1) whereas starch and neutral detergent fibre digestibility declined (P,0.05). Ratio of non-glucogenic to glucogenic precursors in the rumen fluid increased with maize silage inclusion (P,0.01) with a commensurate reduction in rumen pH (P,0.05). Mean circulating concentrations of insulin were greatest and similar in diets MMG and GGM, lower in diet M and lowest in diet G (P,0.01). There were no effects of diet on the mean circulating concentration of growth hormone (GH), or the frequency, amplitude and duration of GH pulses, or the mean circulating concentrations of IGF-1. Increasing levels of DM, OM and starch intakes with the substitution of grass silage with maize silage affected overall digestion, nutrient partitioning and subsequent circulating concentrations of insulin

Potential of legume-based grassland - livestock systems in Europe: a review

European grassland-based livestock production systems face the challenge of producing more meat and milk to meet increasing world demands and to achieve this using fewer resources. Legumes offer great potential for achieving these objectives. They have numerous features that can act together at different stages in the soil-plant-animal-atmosphere system, and these are most effective in mixed swards with a legume proportion of 30-50%. The resulting benefits include reduced dependence on fossil energy and industrial N-fertilizer, lower quantities of harmful emissions to the environment (greenhouse gases and nitrate), lower production costs, higher productivity and increased protein self-sufficiency. Some legume species offer opportunities for improving animal health with less medication, due to the presence of bioactive secondary metabolites. In addition, legumes may offer an adaptation option to rising atmospheric CO2 concentrations and climate change. Legumes generate these benefits at the level of the managed land-area unit and also at the level of the final product unit. However, legumes suffer from some limitations, and suggestions are made for future research to exploit more fully the opportunities that legumes can offer. In conclusion, the development of legume-based grassland-livestock systems undoubtedly constitutes one of the pillars for more sustainable and competitive ruminant production systems, and it can be expected that forage legumes will become more important in the future

Meeting the protein requirements of ruminant livestock

Ruminant animals acquire their amino acids from the small intestinal digestion of ruminally derived microbial protein and dietary protein which has escaped ruminal degradation. The UK metabolizable protein system provides a framework with which the net absorption of amino acids from the small intestine is computed in relation to the animal's requirements and is based largely upon a set of criteria by which feedstuffs are evaluated. While conceptually the system has many positive features, a number of serious weaknesses have been identitled, particularly with respect to the techniques used to evaluate feedstuffs. Some of these issues are considered, particularly the over-reliance which is placed upon in vitro methodologies which have not been adequately validated against in vivo observations and have been shown to give unacceptable variation. Attention is also drawn to the inadequate representation of host tissue metabolism within such systems, for example, the importance of splanchnic metabolism with respect to overall nutrient utilization. It is concluded that improved representation of energy (i.e. carbohydrate) and protein interactions within the whole animal and not simply within the gastro-intestinal tract is urgently required; this inevitably will lead to a change in research direction. Equally, support for a mechanistic understanding rather than an empirical representation of protein metabolism in ruminant livestock is presented, given that the demands upon the ruminant industry, particularly with respect to predictability of animal response, is likely to increase as a consequence of increased consumer impact on the marketing of animal products