Epsilon Open Archive

Abstract

The purpose of the four studies that form the basis for this thesis was to extend the knowledge about how to utilize the domestic protein feeds in Swedish dairy production. To optimize the use of nitrogen (N) from both concentrates and forages into milk product, and thereby improving the profitability and the resilience of the domestic dairy farms.

In a study where soybean meal was replaced with solvent-extracted, heat-moisture-treated rapeseed meal, milk yield and milk protein yield increased and nitrogen use efficiency was higher with rapeseed meal supplementation. Methane yield (g CH4/kg dry matter intake) and methane intensity (g CH4/kg energy-corrected milk) decreased quadratically with increased dietary crude protein concentration.

Increasing the proportion of red clover silage in the diet did not reduce the need for protein supplementation. While the cows were still responsive to protein supplementation as heat-moisture-treated rapeseed expeller, incremental protein intake from red clover did not increase feed intake or milk yield. The changes observed with increased red clover silage intake were attributed to decreased nitrogen use efficiency and increased milk urea nitrogen. Increased protein supplementation decreased methane yield.

Replacing crimped barley with solvent-extracted, heat-moisture-treated rapeseed meal to increase dietary crude protein concentration was associated with greater total neutral detergent fibre digestibility and potentially digestible detergent fibre digestibility. The digestion rate of potentially digestible detergent fibre also increased. Omasal flow of non-ammonia nitrogen increased with increased protein supplementation, but simultaneously the flow of microbial non-ammonia nitrogen and microbial efficiency tended to decrease, with the calculated proportion of milk protein originating from rumen microbial protein showing a marked decline.

Omasal crude protein flow and milk protein yield were positively related to in vitro-estimated utilisable crude protein flow at the duodenum. Moreover, there was a strong correlation between estimated utilisable crude protein (g/kg DM) at 16, 20 and 24 hours of incubation, but results at 16 hours resulted in the best mixed model fit.

Overall, these findings show that with grass silage-based diets Swedish dairy cows could theoretically maintain or even increase milk yield when fed only domestic rapeseed meal as protein feed.