Feeding System Effects on Dairy Cow Rumen Function and Milk Production

SIMPLE SUMMARY: In ruminants, diet has a significant effect on rumen function. Hence, this study was conducted to see if changing the normal grass-based diet of cows could change rumen function and milk production. Therefore, we compared three diets: Grass (cows grazing grass-only), Grass-Clover (cows grazing grass-white clover only) and cows fed a total mixed ration (TMR) diet indoors. We monitored the cows over the course of a full lactation cycle in a spring-calving system. In order to examine rumen function, some of the cows had a cannula placed in their rumen so that we could collect rumen contents samples. After we collected the samples and analysed the data we found that the type of diet the cows were offered did significantly affect milk production; milk yield and milk solids yield were generally highest on the TMR diet. When we looked at the rumen sample data we found that diet also affected rumen function; it altered the rumen volatile fatty acid (VFA), and ammonia and lactic acid profiles significantly but did not effect on rumen pH. Clover inclusion in the diet led to higher total rumen VFA and ammonia concentrations and higher milk urea nitrogen compared to the grass and TMR diets. We suggest this indicates a higher protein intake on that diet. Given these findings, we concluded that a clover-based diet could significantly alter rumen function, milk composition and milk yield in dairy cows. ABSTRACT: Good rumen function, which is largely influenced by the diet of the cow, is essential to optimise animal performance. This study, conducted over the course of a full lactation in a spring-calving milk production system, compared the rumen function and milk production of cows offered one of three dietary treatments: (1) Cows grazing grass-only swards receiving 250 kg nitrogen (N)/ha/year (Grass), (2) Cows grazing grass-white clover swards receiving 250 kg N/ha/year (Grass-Clover), and (3) Cows offered a total mixed ration diet and housed indoors (TMR). Treatment significantly affected milk production; milk yield and milk solids yield were generally highest on the TMR treatment. There was no effect of treatment on rumen pH. However, treatment significantly altered the rumen volatile fatty acid (VFA), and ammonia and lactic acid profiles. Clover inclusion in the sward led to higher (p < 0.05) total VFA and ammonia concentrations compared to the Grass and TMR treatments. The increased rumen ammonia concentration was associated with a significantly greater milk urea nitrogen (MUN) content in the milk from cows fed on Grass-Clover, indicating a greater excess of dietary protein in that treatment. It was concluded that a clover-based dairy cow feeding system could significantly alter rumen function, milk composition and milk yield.