Partial replacement of concentrate in the lactating ewe’s diet with silages of agro-industrial by-products – Effect on milk composition and fatty acid profile, serum metabolites and growth of suckling lambs

The purpose of this experiment was to evaluate the effect of partial replacement of concentrate feed with mixed ingredient silages (MIS) produced with agro-industrial by-products in the diets of lactating ewes on the body weight of ewes, growth performance of suckling lambs, composition and fatty acid (FA) profile of milk, and serum metabolites of the ewe. After lambing, 54 lactating ewes and their lambs were distributed to one of the following experimental diets (18 ewes/diet): C – concentrate diet; SPBG – concentrate and silage containing 200 g/kg sweet potato, 500 g/kg brewers grains and 300 g/kg alfalfa hay; and AHBG – concentrate and silage containing 200 g/kg almond hulls, 600 g/kg brewers grains and 200 g/kg alfalfa hay. Hay was provided ad libitum in all diets. In both silage diets (SPBG and AHBG) the concentrate and silage constitute 33.3 and 66.6 % DM of the diet, respectively. Every day, the ewes received the same amount of the diet, which was completely consumed. Lambs were weighed at birth and weekly during the 8 weeks of trial. In the last 4 weeks of the trial, individual milk samples were collected weekly and then pooled per each ewe for chemical analysis. At the end of the trial, a blood sample was collected from the ewes to analyse serum metabolites. SPBG and AHBG silage showed pH values of 4.00 and 4.29, respectively. Total N as NH₃-N and as soluble-N varied from 3.23 to 5.23 and from 348 to 354 g/kg total N, respectively. The animals well accepted the silages. Partial replacement of concentrate with silage of agro-industrial by-products in lactating ewe diets did not affect the growth performance of suckling lambs and the composition of milk. Both silage dietary treatments changed the milk FA composition, reducing the short-chain FA (6:0–14:0), branched-chain FA, and 18:1 trans-10, and increasing the saturated FA 16:0, 18:0, 20:0, 22:0, 23:0 and 24:0 and 18:1 trans-11. Regarding serum metabolites, silage diets increased the urea concentration and decreased the β-hydroxybutyrate concentration. Results showed that ensiling is a good approach to preserving sweet potato, almond hulls, and brewers grains, producing a good quality feed that can be introduced to diets of lactating ewes without compromising animal performance.