Evaluation of animal variability in fibre digestion and strategies to improve forage use in beef cattle diets

提高饲料效率对牛肉行业非常有意义，因为它可以增加生产者的盈利能力，降低牛肉生产的环境足迹。由于饲料通常比精料单位有效能量更昂贵，而且随着饲料中饲料含量的增加，牛的饲料效率和生产性能也会降低，因此大多数饲养场采用高精料、低粗料的饲料（10%或更少的DM作为饲料；Samuelson et al., 2016）。然而，这种饮食会增加消化系统疾病的发生率和严重程度（如酸中毒、瘤胃角化不全、肝脓肿和腹胀；Vasconcelos和Galyean， 2008）。为了减轻这些疾病的风险并提高饲料效率，在饲料中，通常在饲料中添加离子载体和抗生素等抗菌剂。随着越来越多的法规限制在饲料中使用抗微生物药物，重要的是制定新的战略，以保持或提高饲料效率和生产者的盈利能力，同时改善动物健康和福利。如果能提高饲料来源的纤维消化效率，就有可能通过增加饲粮中饲料的浓度来提高饲料效率、盈利能力和动物健康。因此，我的研究计划的长期目标是提高纤维消化的效率，从而提高肉牛的生产性能和健康状况。在接下来的五年里，我的研究将有四个短期目标：1)研究动物生理和瘤胃微生物参数与牛消化纤维能力的关系；2)研究不同纤维消化能力牛瘤胃接种量与瘤胃pH值和固体通过率对瘤胃发酵参数的相互作用；3)研究高干草日粮中纤维消化率较高的牛是否在饲喂高精料日粮和饲喂不同的饲料来源时也具有较高的纤维消化率；4)研究选择消化纤维能力更强的犊牛是否真的能提高生长性能和饲料效率。我感兴趣的是了解微生物-宿主相互作用对消化纤维效率更高的肉牛胃肠道生理的影响。最大限度地提高牛利用牧草和消化纤维的能力，可以减少可用于人类饲料的谷物的使用，提高对可用饲料来源和低质量谷物残留物的利用，提高饲料效率，从而提高牛肉生产的经济和环境可持续性。此外，关于瘤胃微生物降解顽固性木质纤维素的复杂和协调作用的知识可能对其他行业如纤维素生物燃料和饲料酶的生产产生影响。

Improving feed efficiency is of great interest to the beef industry as it can increase producer profitability and lower the environmental footprint of beef production. Because forage is generally more expensive per unit of available energy than concentrates, and cattle feed efficiency and performance is reduced with the increase forage content in diets, most feedlots feed high-concentrate, low-forage diets (10% or less of DM as forage; Samuelson et al., 2016). However, such diets can increase the incidence and severity of digestive disorders (i.e. acidosis, rumen parakeratosis, liver abscesses, and bloat; Vasconcelos and Galyean, 2008). To mitigate risk for these disorders and to increase feed efficiency, in feed antimicrobials such as ionophores and antibiotics are commonly added to feedlot diets. With increasing regulations restricting the use of in feed antimicrobials, it is important to develop new strategies that can maintain or improve feed efficiency and producer profitability, and at the same time improve animal health and welfare. If the efficiency of fibre digestion of forage sources can be improved, it could be possible to improve feed efficiency, profitability, and animal health by increasing concentrations of forage in feedlot diets. Hence, the long-term goal of my research program is to improve the efficiency of fibre digestion, and consequently the performance and health of beef cattle. My research over the next five years will address four short-term objectives: 1) investigate the relationship of animal physiological and rumen microbiological parameters with the ability of cattle to digest fibre; 2) investigate the interaction of rumen inoculum of cattle with divergent ability to digest fibre with ruminal pH and with solids passage rate on ruminal fermentation parameters; 3) investigate if cattle selected for greater fibre digestibility on a high grass hay diet also has greater fibre digestibility when fed a high concentrate diet, and when fed a different forage source; and 4) investigate if calves selected for greater ability to digest fibre actually have improved growth performance and feed efficiency. I am interested in understanding the effect that microbe-host interactions have on gastrointestinal physiology in beef cattle that are more efficient at digesting fibre. Maximizing the ability of cattle to use forages and digest fibre can reduce the use of grain that could be used to feed humans, improve the utilization of available forage sources and low quality cereal residues, and increase feed efficiency, consequently increasing the economic and environmental sustainability of beef production. In addition, the knowledge generated on the complex and orchestrated action of the rumen microbes to degrade recalcitrant lignocellulose may have implications for other industries like the production of cellulosic biofuels and feed enzymes.