Gas Endeavour Device for the Real-Time In Vitro Measurement of Carbon Dioxide and Methane Emissions Associated with Sheep Diets with Prickly Pear By-Products

Prickly pear by-products contain dietary fibre and bioactive components like polyphenols and flavonols, which can reduce total gas and methane emissions. To this end, an in vitro trial was carried out in duplicate utilizing three diets containing hay, concentrate, and two prickly pear by-products obtained after grinding the fruit peel and pastazzo (pulp + peel + seeds), which were ensiled with the addition of 12% wheat bran (raw weight). Based on the ingredient intake recorded in the in vivo study for 12 lactating ewes fed the three diets, an in vitro rumen fermentation study with the innovative Gas Endeavour system (GES) was performed, and the Gage R&R statistical method was used to evaluate the accuracy of the total gas and methane production detected by the GES device. Fermented liquor samples for each diet were used to calculate the disappearance of organic matter and neutral detergent fibre. Shotgun metagenome sequencing analysis was used to evaluate the effect of diet on the rumen fluid microbiota, and it was found that the parameters of repeatability and reproducibility of the total gas and the methane produced after 24 h were satisfactory. Prickly pear by-products display high fermentability for the peel and low fermentability for pastazzo silage, which generates lower total gas and methane emissions. This diminished methane gas production is not correlated with the relative abundance of methanogens. The different chemical and nutritional composition of the three diets altered the rumen bacteria, albeit only slightly, with particular reference to the Succinivibrio and Selenomonas genera. In conclusion, prickly pear peel silage displayed acceptable fermentation traits, which could support its utilization in sheep diets.