Developing more sustainable beef finishing strategies through improved nutrition and growth of animals

The overall objectives of this thesis were to; (i) quantify, using meta-analysis, the effect of dietary concentrate supplementation level on intake, growth, feed efficiency and carcass gain responses in growing-finishing cattle offered grass silage, and to discern how grass silage digestibility, influenced these responses (Chapter 3); and (ii) determine the intake, growth and carcass traits of steers offered grass silage ad libitum, supplemented with barley- and maize-based rations containing flaked peas, flaked beans, dried corn gluten feed or maize dried distillers grains plus solubles (animal Experiment 1), or supplemented with barley and oats with or without peas and beans (animal Experiment 2), and to ascertain the rumen fermentation pattern, apparent digestibility and nitrogen excretion of diets similar to those offered in Experiment 2 (animal Experiment 3) (Chapter 4). The meta-analysis in Chapter 3 showed that as concentrate supplement level increased, silage dry matter intake declined at progressively increasing rate and total dry matter intake and marginal growth response of cattle increased but at a diminishing rate, such that feed conversion ratio did not improve above the ‘low’ (0.25 of dietary dry matter intake) supplementation level; responses associated with silage DMD were parallel. Together with appropriate feed costs and animal live/carcass weight prices, the developed prediction models can be used to optimise concentrate feeding levels for growing-finishing beef cattle offered grass silage and maximise output income over feed costs. In Chapter 4, there were no interactions between cereal type and protein source. Intake, growth, feed efficiency and carcass traits in Experiment 1 or 2 did not differ significantly between cereal type or protein source. In Experiment 2, inclusion of a legume protein supplement with barley or oats had no effect on intake or growth performance. In Experiment 3, apparent digestibility of dry matter, organic matter and neutral detergent fibre was lower for oats compared to barley. Omitting a legume protein ingredient from the concentrate supplement decreased nitrogen intake, plasma urea concentrations and urinary and total nitrogen excretion. It was concluded that the feeding value of rolled barley was similar to rolled oats and maize meal, and flaked beans and peas were similar to corn gluten feed and maize dried distillers’ when included in the supplementary concentrate to beef cattle offered grass silage ad libitum. Omitting protein ingredients from a cereal-based concentrate did not affect animal performance and reduced nitrogen excretion. Collectively, results from this thesis will help enhance the profitability and sustainability of Irish beef cattle growing-finishing systems.