• Optimisation of Nutrient Supply for Beef Cattle Fed Grass or Silage.

      Moloney, Aidan P.; O'Kiely, Padraig; Hickey, M.C.; Adams, L.A. (Teagasc, 2001-05-01)
      Since forage forms a large part of growing ruminant rations in Ireland, the trust of this project was to examine the effect of ensilage on ruminal digestion of grass and to examine ruminal microbial protein and intestinally absorbable protein supplied by grass and/or clover. A range of in vitro and in vivo techniques were employed and strategies used by commercial beef producers to optimise cattle growth (and nutrient supply) were also documented. To accomplish the aims of this project, a range of methodology developments/ modifications in vitro and in vivo was carried out. From in vitro methodology development it was concluded that : (i) Compared with fresh silage, drying per se may give artifically higher rates of dry matter (DM) digestion. (ii) Greater experimental precision can be obtained by ensuring a greater substrate surface area to reaction volume ratio in each reaction vessel. (iii) For studies where the rate of digestion is of greatest importance, pre-incubation of frozen inoculum in a nutrient medium best simulated the cellulolytic activity of unfrozen inoculum. In studies that require large volumes of inoculum for extended work, freezing directly is justified. (iv) Neutral detergent extraction altered in vitro digestion characteristics of silage. The residue after washing with water at 70°C has a high residual fibre concentration and is more representative of the structural components of silage ingested by ruminants. (v) A semi-continuous culture system developed at Grange Research Centre can successfully model in vitro ruminal digestion of fibre and starch-based diets in a controlled environment. From in vivo methodology development it was concluded that : (i) Oven drying at 60°C and correction for loss of volatiles gives a good estimation of DM concentration of ruminal particulate digesta. This procedure has the added advantage that drying at 60°C allows the residual materials to be analysed for fibre fractions without concern for heat damage which can occur at a higher drying temperature. (ii) A naso-ruminal sampling device can be used to measure the relative patterns of fermentation of contrasting diet types when in situ for up to 7 days. (ii) Application of a vacuum to withdraw samples had no negative effect on ruminal fluid variables. From in vitro studies on grass digestion, it was concluded that : (i) Ensiling of grass decreased the apparent extent of digestion of cell walls when in the presence of the whole plant and that this largely reflected an increase in the lag time before digestion commenced. (ii) Ensiling of grass did not negatively affect the digestion of isolated cell walls. (iii) There is a negative impact of ensiling on microbial protein production from the water soluble carbohydrate fraction of grass. (iv) Supplementation with the water soluble fraction of grass significantly improved the apparent extent of digestion for ensiled forages when compared with the supplementation of the post-ensiling fraction in a batch culture system. (v) There is a negative impact of maturity on the pattern of cell wall fermentation and that this impact can be decreased by ensiling method. From studies on herbage digestion in vivo it was concluded that : (i) Grass silage type had a greater effect than the rate of concentrate fermentation on ruminal microbal protein synthesis. (ii) Harvesting time had a bigger impact on nutrient supply from herbage than sward type (grass or grass/clover). (iii) Increasing clover content in the herbage decreased the biological value (g nitrogen retained/kg absorbed) of dietary protein. Diverse stratgies were used on commercial beef farms to optimise nutrient supply and animal growth. Average animal performance on individual farms was not better than would be typically recorded in a research environment. There was scope on many of the farms to improve technical performance and to decrease the costs of production.