Dietary chitosan improves nitrogen use and feed conversion in diets for mid-lactation dairy cows

Feed additives and fat sources have been used to meet high productive dairy cow energy requirements. This study aimed to evaluate dietary chitosan and soybean oil effects on mid-lactation dairy cow intake, digestibility, metabolism and productive performance. Twenty-four Holstein cows (134.7 +/- 53.1 days in milk, 36.14 +/- 5.32 kg/day of milk yield, and 581.2 +/- 73.6 kg of body weight, Mean +/- SD) were used in a replicated 4 x 4 Latin square design with 21-d periods, with 14 d of adaptation and 7 d for data collection. The treatment arrangement was a 2 x 2 factorial design with two levels of chitosan (0 and 4 g/kg of dietary dry matter - DM) and two levels of soybean oil (0 and 33 g/kg of dietary DM). Chitosan decreased intake only in diets without oil (P < 0.05). Regardless of fat addition, chitosan increased DM and CP digestibility (P < 0.05). Soybean oil and chitosan increased total serum cholesterol (P < 0.05). Chitosan diet had higher urea plasma concentration than control diet (CON) (P < 0.05). Over all, soybean oil increased propionate and decreased acetate ruminal molar proportion, and therefore decreased acetate:propionate ratio (P < 0.05). Chitosan decreased milk yield, nitrogen use and feed conversion efficiencies in oil-diets (P < 0.05). Soybean oil decreased short and medium milk fatty acids concentration (P < 0.05). Chitosan had no effect on long-chain milk fatty acids in diets with soybean oil (P > 0.05). However, in free oil-diets, chitosan increased milk polyunsaturated fatty adds concentration, nitrogen and energy efficiency. Chitosan addition in free-fat diets improved feed efficiency, increased milk unsaturated fatty acids concentration and association with soybean oil negatively affect animal performance.