Response of lactating cows to three supplemental fat sources as affected by forage in the diet and stage of lactation: a meta-analysis of literature

Research on fat supplementation has demonstrated that the production response of dairy cows to supplemental fats is highly variable, both among and within fat sources. Differential responses to dietary fats that have been observed when feeding the same type of fat to cows fed different basal diets suggests fat by diet interactions occur. A summary of the available literature on the effects of fat supplementation on dry matter intake (DMI), milk yield and composition and nutrient digestion in dairy cattle since 1980 was performed. Fat sources examined were tallow, calcium salts of palm fatty acids (CaS), and selected hydrolyzed tallow fatty acids (SHTFA). Responses of lactating dairy cows to increased levels of added fat were evaluated as affected by fat source and the main forage in the basal diet. Effect of stage of lactation on the response to fat supplementation was also examined. Decreased DMI and modest milk yield increases occurred for the fat sources evaluated. Different responses to supplemental fats were observed depending on the main forage in the basal diet. Feeding tallow with diets high in corn silage decreased DMI and milk fat yield, with no effect on milk production. However, a moderate positive milk production response was observed when tallow was fed with alfalfa-based diets or diets with corn silage and alfalfa in similar proportions. Supplemental SHTFA resulted in moderate positive milk fat percentage and yield response, regardless of the main forage in the basal diet. A significant positive milk yield response was observed when CaS was fed with diets high in corn silage, but not with alfalfa-based diets or diets with alfalfa and corn silage in similar proportions. An interaction between stage of lactation and amount of supplemental fat was observed, with supplemental fat increasing milk production of early lactation cows but not that of mid lactation cows, where milk fat depression occurred. Interactions between fat type and characteristics of the basal diets must be identified in order to predict the production responses of dairy cows to supplemental dietary fats.