Exogenous fibrolytic enzymes promoted energy and nitrogen utilization and decreased CH4 emission per unit dry matter intake of tan sheep grazed a typical steppe by enhancing nutrient digestibility on China loess plateau

Exogenous fibrolytic enzyme (EFE) products in ruminant nutrition may be an important alternative to meet the increased demands for animal products in the future with reduced environmental impacts. This study aimed to evaluate the dose-response of EFE supplementation on the nutrient digestibility, nitrogen and energy utilization, and methane (CH4) emissions of Tan sheep grazed in summer and winter. A total of 20 Tan wether sheep with an initial body weight of 23.170.24 kg were used in a randomized complete block design and categorized into two groups. Animals fed orally with 1 g of EFE (10,000 U/g) mixed with 30 mL of water using a drencher constituted the EFE group. For experimental accuracy, the control (CON) group was orally administered with 30 mL of normal saline daily before grazing. The following results were obtained: EFE in the diet increased dry matter intake (DMI) (P<0.05), average daily gain (ADG) (P<0.05), and digestibility (P<0.05) compared with CON in summer and winter. DMI increased but ADG and digestibility decreased in winter compared with those in summer. Sheep fed with the EFE diet increased the concentrations of rumen ammonia nitrogen (P<0.05) and total volatile fatty acids (P>0.05), but reduced pH (P>0.05), compared with CON in summer and winter. EFE increased nitrogen (N) intake, digestible N, retained N, and retained N/digestible N (P<0.05) but reduced fecal N/N intake, urinary N/N intake, and excretion N/N intake in summer and winter (P<0.05), compared with CON. Retained N/N intake was reduced and excretion N/N intake increased in winter relative to those in summer. In winter, gross energy (GE), manure E/GE, CH4 emissions, CH4/DMI, and CH4/GE increased but digestion energy and metabolic energy decreased compared with those in summer. Sheep fed with the EFE diet had a greater GE intake than those fed with the CON diet (P<0.05) but had lesser CH4/DMI and CH4E/GE (P<0.05) than those fed with the CON diet in both summer and winter. In conclusion, EFE supplementation increased DMI, apparent digestibility, and N deposition rate. These effects were beneficial for animal production. The CH4 emission per unit DMI of grazing Tan sheep was lesser and conducive for augmenting the environmental benefits. Exogenous fibrolytic enzymes can effectively degrade forage fibers, thereby enhancing the digestibility of nutrients in sheep and improving animal performance without adversely affecting their health. Lay Summary Globally, the supply-demand relationship between grassland and livestock is mainly mediated by the optimization of pasture management. The interaction between grassland and livestock is one of the fundamental drivers of grassland occurrence and development. Natural grassland yields and quality are affected by precipitation, heat, and grazing, and their dynamics vary seasonally with distinct peaks and troughs. The use of exogenous fibrolytic enzymes during troughs can improve the growth performance, digestion, and metabolism of grazing sheep. The exogenous fibrolytic enzyme supplement used in this research may aid in improving the health and overall productivity of grazing sheep.

Automated summary

This study evaluated the dose-response of exogenous fibrolytic enzyme (EFE) supplementation on the nutrient digestibility, nitrogen and energy utilization, and methane emissions of grazing Tan sheep in summer and winter. The results showed that EFE supplementation increased dry matter intake, average daily gain, and digestibility, while reducing methane emissions. These findings are important for meeting the increased demand for animal products and reducing environmental impacts in the future.