Response of lactating dairy ewes to various levels of dietary calcium soaps of fatty acids

Two experiments were completed to assess lactational effects of feeding calcium soaps of fatty acids (CSFA) to lactating sheep. In the first experiment, 50 Manchega ewes were blocked into groups of 10 to which the treatments were applied. Ewes grazed and were supplemented indoors with hay and a concentrate. Treatments consisted of different levels of CSFA in the concentrate, being: control, 50, 100, 150 or 200 g CSFA/kg as fed. Concentrates were fed individually at fixed amounts depending on lactation period: nursing (weeks 1–4; 1.0 kg/day), and early (weeks 5–7; 1.0 kg/day), mid (weeks 8–14; 0.8 kg/day) and late milking (weeks 15–21; 0.6 kg/day). Level of CSFA did not affect milk yield, and effects on milk composition varied by lacation period. The biggest effects occurred during nursing, when milk fat content (P<0.05) and yield (P<0.001), as well as milk total solids content (P<0.001) and yield (P<0.05), increased linearly with CSFA dose. Milk fat content increased at a decreasing rate (linear and quadratic P<0.05) with CSFA dose during milking, but milk protein content decreased (P<0.05) linearly in mid and late (P<0.01) lactation. Relative milk fat yield response to CSFA fat was bigger (P<0.01) during nursing than in milking (55% and 20%, respectively) and decreased linearly (P<0.001) with increasing CSFA feeding at the end of lactation. Findings from the first experiment were applied in a second experiment to the total mixed ration of a flock of 94 Manchega ewes. Treatments consisted of control and CSFA added (42 g CSFA/kg DM) total mixed rations. Diets were compared during mid lactation (weeks 7–16) by using a switch-back design of three periods of 20 days each (1, control; 2, CSFA; 3, control). Contents of milk fat and milk total solids, as well as their yields, increased (P<0.05) in the CSFA diet, but milk protein did not vary. Milk from CSFA fed ewes had less saturated fatty acids (FA) and more monounsaturated FA than the control. The C14:1/C14:0 Δ9–desaturase index was not modified by CSFA. Overall, feeding CSFA to dairy ewes increased milk fat content and modified the FA profile of milk fat. Although FA from dietary CSFA were efficiently transferred to milk at the beginning of lactation, use of moderate amounts of CSFA is recommended, particularly at the end of lactation in order to avoid negative effects on milk protein concentration.