Effects of supplementation with exhausted myrtle berries on rumen function of dairy sheep

Manipulation of the gut functions, and rumen microbiota and metabolism with feed additives, in particular those rich in polyphenols, has been recognized as promising strategy for improving feed efficiency in sheep. Aiming to evaluate the effect of the dietary supplementation of exhausted myrtle berries (EMB), as source of polyphenols, on the metabolism and microbial population in ruminal fluid of sheep, eighteen Sarda dairy ewes were used in a 11-week experiment. Ewes were allocated to three groups, homogeneous for milk production, days in milking and parity. The groups were assigned to three diets, which were individually fed: i) a control diet (CON); ii) a diet supplemented with 50 g/d per animal of EMB (EMB50); iii) a diet supplemented with 100 g/d per animal of EMB (EMB100). The basal diet (the same for all animals) consisted of dehydrated alfalfa (1.2 kg/d per animal), a commercial concentrate (0.50 kg/d per animal), a mixed meal (soybean, corn, and linseed, 0.15, 0.10 and 0.20 kg/d per animal, respectively) and beet pulp (0.25 kg/d per animal). The supplementation with EMB did not affect (P > 0.05) the rumen pH. Ammonia content was reduced (P < 0.05) by the EMB supplementation at both doses of EMB compared with CON. The total volatile fatty acids (VFA) decreased (P < 0.05) in EMB100 compared to CON and EMB50, whereas the molar proportions of acetate, propionate, butyrate and the ratio acetate:propionate were not affected by the diet. Diet did not affect (P > 0.05) the estimated production of methane. Weak effects were observed on ruminal concentration fatty acids (FA), except for the CLAcis-9,trans-11 and total CLA concentrations, that increased (P < 0.05) in EMB50 and tended to increase (P < 0.10) in EMB100 compared with CON. The abundances of the microbial groups studied in this work were, in general, influenced by the diet × sampling date interaction. The low dose of EMB increased (P < 0.05) the abundance of fungi. Butyrivibrio group was significantly lower (P < 0.05) in both EMB50 and EMB100 diets than in CON. Overall, the reduction of rumen ammonia accumulation, which could reflect the reduction of Butyrivibrio group, known as proteolytic bacteria, suggests that EMB, as source of polyphenols, might be useful to improve nitrogen balance in dairy sheep.