Effects of fibre and non-fibre carbohydrate and level of intake on microbial protein yield in Sarda sheep

Three studies using Sarda dairy sheep in dry, mid-lactation and late-lactation were carried out. Forty ewes for each physiological stage were fed 8 complete pelleted diets, which differed from each other in NDF and NFC content and source. Based on their main ingredient, diets were denominated: corn meal (CM), wheat middlings (WM), corn flakes (CF), barley meal (BM), corn cobs (CC), beet pulp (BP), alfalfa (AA), and soybean hulls (SH). In each study, rumen microbial protein (MCP) synthesis was estimated measuring urinary purine derivatives. In dry sheep, MCP synthesis was not affected by diet, while in mid- and late-lactation sheep dietary effects were observed. In mid-lactation, the highest MCP production was found for BM and BP (171 and 166 g/d, respectively), while the lowest was observed with AA (63 g/d). In late-lactation, the highest MCP yield (146 g/d) was observed in BP, while the lowest were for SH and CM. MCP synthesis, for each diet, was higher in mid-lactation than in latelactation, which in turn were higher than in the dry period. Dry matter intake (DMI) was positively associated to MCP. The MCP synthesis was best predicted by dietary energy (NEL) or digestible organic matter intake (dOMI).