A study on the replacement of soybean meal by rapeseed meal in rations for high yielding dairy cows

Feedstuffs with a high proportion of undegradable protein (UDP) are important suppliers of utilisable crude protein (nXP) in rations for high yielding dairy cows. Recent studies indicate an nXP content for solvent extracted rapeseed meal (RES) higher than often assumed and equal to the nXP content of solvent extracted soybean meal (SES). This study was undertaken to study the effects of a complete replacement of SES by RES in rations for dairy cows in the first third of lactation. On the basis of standardised digestibility trials the net energy (NEL) contents of the two meals were determined to be 8.9 (SES) and 7.1 MJ/kg DM (RES), this difference mainly due to a higher content in conjunction with a lower digestibility of crude fibre in RES. On the basis of a chemical crude protein fractionation, nXP values of 319 (SES) and 326 g/kg DM (RES) were estimated for the two meals. Total mixed rations (TMR) were calculated to be equal in NEL (7.1 MJ/kg DM) and nXP (162 g/kg DM) content, using either SES or RES as the main nXP source. On the basis of digestible crude nutrients, NEL was lower in the RES (7.0) than in the SES containing TMR (7.3 MJ/kg DM). Both TMR were fed for 91 days to a total of 163 cows which were in their first third of lacation. DM intake was higher by 1 kg/d when RES was fed (23.5 kg/d). High RES inclusion did not negatively affect yield and composition of milk. Milk yield was 40.0 (SES) and 40.5 kg/d (RES) with 3.34 % milk protein (in both groups) and 3.79 (SES) and 3.85 % milk fat (RES). When RES was included in the TMR, milk urea was significantly lower but milk acetone was significantly higher in comparison with the SES including TMR. It was concluded that high yielding dairy cows can be fed up to 4 kg RES per day if the relatively low energy value is accounted for in diet formulation.

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