Effects of using thermally treated lupins instead of soybean meal and rapeseed meal in total mixed rations on in vitro microbial yield and performance of dairy cows.

The objective was to study whether thermally treated lupins (TTL) can replace solvent-extracted soybean meal (SBM) and rapeseed meal (RSM) in dairy cow rations. Three total mixed rations (TMR) were used. They differed in the inclusion of the main protein feeds (TTL alone, TTL + RSM and RSM + SBM) but were equal in organic matter digestibility and metabolizable energy content. In vitro organic matter fermentation was not significantly different between the TMR. Efficiency of microbial crude protein (MCP) synthesis was significantly higher for TMR RSM + SBM than for TTL. In vitro gas production potential was similar for the three TMR. The maximal rate of gas production was achieved later in TMR TTL than in RSM + SBM. Feed intake of dairy cows was significantly lower when TMR TTL was fed than when TMR TTL + RSM or RSM + SBM were fed. Milk yield was significantly lower with the high inclusion rate of TTL in comparison with the other TMR. The contents of milk protein and milk fat were significantly lower when the two TTL containing TMR were fed in comparison with the RSM + SBM ration. Effects of TTL inclusion on MCP synthesis may affect the amino acid supply to the duodenum of cows to a greater extent than differences in the degradability of feed proteins.