Effects of supplementing pomegranate peel with fatty acid sources on oxidative stress, blood metabolites, and milk production of dairy cows fed high-concentrate diets

Primiparous cows are more susceptible to oxidative stress than multiparous cows because of their lower total antioxidant capacity. The objective of this study was to evaluate the effects of fatty acid (FA) source with and without pomegranate peel (PP) as an antioxidant-rich source in the diet on oxidative stress, blood metabolites, lactation performance, and nutrient digestibility in primiparous lactating cows. Twelve Holstein dairy cows in early lactation were randomly assigned to a replicated 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments. Each period lasted 28 days with 21 days for feed adjustment and 7 days for data and sample collection. The diets were supplemented with 15 g/kg DM of palmitic acid-enriched fat (enriched in saturated FA) or fish oil (enriched in unsaturated FA) contained 0 or 87 g/kg DM of PP. Pomegranate peels increased total dietary antioxidant concentrations and fish oil reduced the ratio of n-6 to n-3 in the experimental diets. Significant interactions were observed for plasma non-esterified FA and malondialdehyde concentrations, milk fat yield, and apparent total-tract nutrient digestibility. Plasma non-esterified FA concentrations decreased in cows fed palmitic acid-enriched fat when PP was included in the diet. Diets with PP resulted in increased plasma concentrations of malondialdehyde in cows fed fish oil but not in those fed the palmitic acid-enriched fat. In addition, total plasma antioxidant capacity increased in cows fed PP containing diets, whereas blood inflammatory markers were not affected by the by inclusion of PP. Supplementing palmitic acid-enriched fat increased milk fat yield by 10% compared with fish oil, whereas a trend toward a decrease in this variable was observed when fish oil was fed without PP. Also, feed intake increased and milk protein concentration decreased in cows consuming diets containing PP, while milk yield was greater for cows fed fish oil. Cows fed palmitic acid-enriched fat had lower DM and NDF digestibility than in those fed fish oil. The molar fraction of propionate in the rumen decreased and the ratio of acetate to propionate increased in cows fed PP containing diets. Cows fed palmitic acid-enriched fat had a greater molar fraction of propionate but a lower ratio of acetate to propionate than cows fed fish oil. Overall, inclusion of PP in diets containing fish oil or palmitic acid-enriched fat contributed to improved feed intake and antioxidant capacity, while we observed no interaction on oxidative stress and inflammatory markers in dairy cows.