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重要，因为它可以提高生产者的盈利能力，降低牛肉生产的环境足迹。由于饲料通常比精料更昂贵，每单位可用能量，并且牛饲料效率和性能随着饲料中饲料含量的增加而降低，因此大多数饲养场饲喂高精料、低饲料的饲料（10%或更少的DM作为饲料; Samuelson等人，2016）。然而，此类饮食可增加消化系统疾病的发生率和严重程度（即酸中毒、瘤胃角化不全、肝肿胀和腹胀; Vasconcelos和Galyean，2008）。为了减轻这些疾病的风险并提高饲料效率，通常在饲养场饮食中添加饲料抗菌剂，如离子载体和抗生素。随着越来越多的法规限制在饲料中使用抗菌剂，重要的是要开发新的策略，可以保持或提高饲料效率和生产者的盈利能力，同时改善动物的健康和福利。如果可以提高饲料来源的纤维消化效率，则可以通过增加饲养场饮食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效率，从而提高肉牛的生产性能和健康。在今后5年的研究中，我将主要完成4个短期目标：1）研究动物生理和瘤胃微生物学参数与牛纤维消化能力的关系; 2）研究瘤胃接种物对不同纤维消化能力牛瘤胃发酵参数的影响; 3）调查当饲喂高浓缩物饮食时，以及当饲喂不同的草料来源时，选择在高干草饮食上具有更大纤维消化率的牛是否也具有更大的纤维消化率;以及4）调查选择具有更大消化纤维能力的小牛是否实际上具有改善的生长性能和饲料效率。我有兴趣了解微生物-宿主相互作用对消化纤维更有效的肉牛胃肠道生理学的影响。最大限度地提高牛使用草料和消化纤维的能力，可以减少可用于喂养人类的谷物的使用，提高可用草料来源和低质量谷物残留物的利用率，并提高饲料效率，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柠檬酸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.