Alternatives for the redesign of beef cattle productiondietary protein, forage intake and feed efficiency

Resumen

The present thesis aimed at identifying and assessing strategies to redesign beef cattle intensive fattening systems in order to increase their profitability and decrease their environmental burden. Moreover, the potential role of ruminal microbiota in the outcome of the tested strategies was evaluated, focusing on their link with ruminal microbiota robustness, defined as the community’s ability to cope with disturbances. First, the impact of reducing dietary crude protein from 14 % to 12 % (on a dry matter basis) was assessed, observing that it did not have major impacts on either dry matter intake or animal performance and that it significantly reduced nitrogen waste. Second, the effects of improving forage quality were evaluated and it was seen that replacing barley straw by oats haylage as forage source did not modify dry matter intake, performance or nutrient apparent digestibility, while vetch haylage feeding reduced concentrate intake, slaughter body weight and nutrient apparent digestibility. Both reducing dietary protein and providing high-quality haylage as forage source did increase ruminal microbiota alpha diversity and network complexity, suggesting that these dietary strategies can enhance rumen microbial community robustness. Third, the potential relationship between animals’ feed utilization efficiency, and ruminal microbiota composition and associative patterns was explored, revealing increased nutrient apparent digestibility rates and a fermentation pattern oriented towards the production of propionate in high-efficiency animals. Beside, alpha diversity and genera network complexity increased with time in low-efficiency bulls, highlighting a possible trade-off between feed efficiency and ruminal microbiota robustness. In conclusion, moderate restriction in dietary protein supply, increasing forage quality and intake and improving feed efficiency were all proved to be feasible options to redesign intensive beef cattle production. The potential link between ruminal microbiota robustness, animal health and system’s economic profitability deserves to be further studied.