Digestibility and clover proportion determine milk production when silages of different grass and clover species are fed to dairy cows

Discipline: pasture/grazing; Key words: legume, organic matter digestibility, eating behaviour, drinking behaviour, faeces score 

Forages with high dry matter (DM) yields are important to sustain profitable milk production. Also, dairy cows require forages that are highly digestible to support high milk yield. In global feeding systems, grass-clover silages often constitute a major part of the feed for dairy cows, and thus a stable production of high-quality herbage is essential. Yield and quality of different grass and legume species are highly dependent on geographical location, weather conditions and management; therefore, selection of species is important for optimal forage production. Research has shown that grass-clover silages of different cuts had similar values for milk production at comparable digestibility. Similarly, milk production in cows fed different grass species, has been shown to be comparable provided that digestibility is similar. The question is how wide does this apply, since it is well documented that DM intake and milk production generally are higher in cows fed legume-based diets compared with grass-based diets. This is because legumes contain less fibre than grasses and have a higher degradation rate of fibre in the rumen. The effects of clover versus grass on eating behaviour are, however, not well researched. 

The objective of the study by Dr M. Johansen and colleagues was therefore to investigate how silages of the most relevant grass and clover species in Denmark affect DM intake, eating behaviour and milk production in dairy cows. Their results were published in the Journal of Dairy Science, Volume 100 of 2017, page 8861 to 8880, the title being:Digestibility and clover proportion determine milk production when silages of different grass and clover species are fed to dairy cows 

The primary growth of perennial ryegrass (early and late harvested), tall fescue, red clover and white clover swards were cut, wilted and ensiled without additives. Danish Holstein cows were fed ad libitum with total mixed rations containing 70% forage on a DM basis. The forage source was either one of the six pure silages or late perennial ryegrass silage mixed (50:50 on DM basis) with either red clover or white clover silage. 

Intake of DM, milk yield and milk lactose concentration were higher, whereas milk fat and protein concentrations were lower when cows were fed clover compared with grass. No differences in DM intake and milk composition were detected between cows fed red clover and white clover, but white clover resulted in higher milk yield than red clover. Cows fed early perennial ryegrass, which had the highest silage organic matter digestibility (OMD), did not produce the expected amount of energy-corrected milk (ECM) compared with the other treatments. Across all other grass species, ECM was related to OMD. Inclusion of 50% clover in the diet increased ECM with 2.3 kg/d, and the response to OMD was comparable to the response for the grass silages. Drinking and eating behaviour differed markedly in cows fed pure white clover compared with the other treatments. Water intake per drinking bout was comparable among treatments, but cows fed pure white clover had higher drinking bout duration and reduced drinking rate. Additionally, meal size was smaller for cows fed pure white clover compared with the other treatments, for which meal size was similar. 

In conclusion, differences in ECM between different species can be explained by differences in OMD, but at a given OMD level inclusion of clover in the diet will increase ECM. These results should also be of value to South African conditions where the introduction of clovers is considered.