Equine fecal inoculum optimization in in vitro fermentation assays of dehydrated roughage

ABSTRACT This study evaluated the influence of coastcross hay substrate hydration and equine fecal inoculum dilution on the parameters of fermentation and microbiology in in vitro essays. A 2 × 2 factorial block design was used. The first factor was hydration of the coastcross hay substrate 12 h before incubation or at the time of incubation, and the second factor was the dilution of fecal inoculum with a nutrient solution in a weight: weight ratio of 1:1 or 1:3. Degradation of the dry matter (DM), organic matter (OM), and neutral detergent fiber (NDF) were evaluated at 24, 48, and 72 h. Microorganisms were counted 24 h after inoculation. The ammoniacal nitrogen concentration (NH3-N), pH, and cumulative gas production were measured up to 72 h and adjusted by the non-linear Gompertz regression model. Hydration of substrate and time of incubation increased nutrient degradation of coastcross hay, as well as the final volume of gases and the concentration of Streptococcus spp. The 1:3 dilution increased the final pH and Streptococcus spp. concentration. The hydration of substrate did not have any effect on NH3-N, Lactobacillus spp., cellulolytic, and total anaerobic bacteria concentrations. In addition, no effect of hydration was observed on the fermentation rate and the maximum fermentation time on the model used. The fermentation profile of the grass substrate is not affected by dilution, and, therefore, horse feces can be used as a source of inoculum in in vitro fermentation trials. Hydration increases the gas volumes and the nutrient degradation of grass hay, renders the lag phase time insignificant and, therefore, can be irrelevant in terms of fermentation model settings.

摘要 本研究旨在评估海岸杂交禾草（coastcross hay）基质含水率与马粪便接种物（equine fecal inoculum）稀释比例，对体外试验（in vitro essays）中发酵及微生物学相关参数的影响。试验采用2×2析因区组设计（factorial block design）：其一为接种前12小时或接种即刻对海岸杂交禾草基质进行补水；其二为采用营养溶液按1:1或1:3的重量比对粪便接种物进行稀释。分别于24、48、72小时检测干物质（dry matter, DM）、有机质（organic matter, OM）及中性洗涤纤维（neutral detergent fiber, NDF）的降解率；于接种后24小时对微生物进行计数。截至72小时，测定氨态氮浓度（ammoniacal nitrogen concentration, NH₃-N）、pH值与累计产气量，并通过非线性Gompertz回归模型（non-linear Gompertz regression model）对数据进行拟合校正。研究结果显示，基质补水与接种时机均可提升海岸杂交禾草的营养物质降解率，同时提高最终产气体积与链球菌属（Streptococcus spp.）的浓度。采用1:3的稀释比例可提升发酵体系的最终pH值与链球菌属浓度。基质补水对氨态氮浓度、乳杆菌属（Lactobacillus spp.）、纤维素分解菌（cellulolytic bacteria）及总厌氧菌（total anaerobic bacteria）浓度均无显著影响；此外，在本研究所用模型中，补水对发酵速率与最大发酵时长亦无显著作用。禾草基质的发酵特性不受接种物稀释比例的影响，因此马粪便可作为体外发酵试验的接种物来源。补水可提升产气体积与禾草干草的营养物质降解率，同时使滞后期时长（lag phase time）失去统计学意义，因此在发酵模型的参数设置中可忽略该因素。