Effect of grape pomace supplementation in mid-lactation dairy ewes on production and quality of milk and methane emissions

The aim of this study was to evaluate the effect of including grape pomace (GP) in the diets of ewes during mid-lactation on milk composition, milk coagulation properties (MCP), and methane emissions, using a Laser Methane Detector (LMD). Twenty-four Sarda dairy sheep, homogeneous in body weight (BW; 59.1 ± 0.75 kg), milk yield (MY; 2.4 ± 0.007 kg/day), and days in milk (DIM; 101 ± 1 days), were allocated into three treatment groups. The control group (CTR) received no GP supplementation, the GP100 group was supplemented with 100 g/day per head of GP, and the GP150 group with 150 g/day per head of GP. The trial lasted six weeks, including one week for adaptation and five for sampling. Feed intake was recorded daily using an individual automatic feeding system (Biocontrol AS, Rakkestad, Norway), and individual milk samples were collected weekly. Methane emissions were measured during the final week of the trial over three consecutive days during both morning and evening milkings, with two-minute measurements per ewe. The inclusion of GP, at both dosages, did not affect milk yield, fat content, or protein content. However, GP reduced the concentration of saturated fatty acids (SFA) while increasing monounsaturated fatty acids (MUFA) and total unsaturated fatty acids (UFA) in the milk. Notably, GP150 significantly increased the levels of CLA cis-9, trans-11 and C18:1 trans-11 compared to the CTR and GP100 groups. ME, expressed as respiration and eructation peaks, were not affected by GP supplementation. The means of concentration of methane during eructation events were 188.7, 160.64 and 185.45 ppm for CTR, GP100 and GP150, respectively. These results suggest that including 100 to 150 g of GP per day in the diet of lactating ewes can improve the fatty acid profile of milk without negatively impacting production traits, offering potential benefits for milk quality.