Twenty-four multiparous Holstein-Friesian dairy cows were used in a replicated 4 × 4 Latin square changeover design experiment to test the effects of changing from ryegrass (Lolium perenne) silage to red clover (Trifolium pratense) silage in graded proportions on feed intakes, milk production, milk organoleptic qualities, and whole-body nitrogen partitioning. Four dietary treatments, comprising ad libitum access to 1 of 4 forage mixtures plus a standard allowance of 4 kg/d dairy concentrates, were offered. The 4 forage mixtures were, on a dry matter (DM) basis: 1) 100% grass silage, 2) 66% grass silage: 34% red clover silage, 3) 34% grass silage: 66% red clover silage, and 4) 100% red clover silage. In each of 4 experimental periods, there were 21 d for adaptation to diets and 7 d for measurements. There was an increase in both DM intakes and milk yields as the proportion of red clover in the diet increased. However, the increase in milk yield was not as great as the increase in DM intake, so that the efficiency of milk production, in terms of yield (kg) of milk per kg of DM intake, decreased. The concentrations of protein, milk fat, and the shorter chain saturated fatty acids decreased, whereas C18 polyunsaturated fatty acids (PUFA) and long-chain PUFA (C20+) increased as the proportion of red clover in the diet increased. There was little effect of dietary treatment on the organoleptic qualities of milk as assessed by taste panel analysis. There were no effects on the aroma of milk, on aftertaste, or overall liking of the milk. Milk was thicker and creamier in color when cows were fed grass silage compared with red clover silage. The flavor of milk was largely unaffected by dietary treatment. In conclusion, increasing the proportion of red clover in the diet of dairy cows increased feed intakes and milk yields, decreased the concentration of fat and protein in milk, increased PUFA for healthiness, and had little effect on milk organoleptic characteristics.

Fresh forages may result in the loss of up to 40% of dietary nitrogen as rumen ammonia, as the microbial population is unable to utilise all the non-protein nitrogen released from rapidly degradable plant proteins. This may be due to the characteristically low levels of readily available energy released in the rumen, primarily as a result of the low levels of water soluble carbohydrate (WSC) in traditional forages. In a previous experiment Lee et al, (1999) found an increase in liveweight gain of pre-weaned lambs grazing Lolium perenne selected for high WSC concentrations. This study examined whether the enhanced performance on high WSC grass may be related to increased supply of nitrogen to the small intestine.

Belanche, A., Lee, M.R.F., Moorby, J.M., Scott, M., Newbold, C. J. (2010). Effect of forage species, ryegrass water soluble carbohydrate concentration, and red clover polyphenol oxidase activity on in vitro rumen efficiency of nitrogen utilization. Advances in Animal Biosciences. Proceedings of the British Society of Animal Science Annual Conference, 'Food, Feed, Energy and Fibre from Land - A Vision for 2020', Queen's University, Belfast, Northern Ireland, 12-14 April 2010, p203. RONO: 06628CGC Sponsorship: Commission of the European Communities FP7, KBB-2007-1.A relatively small proportion of the nitrogen (N) consumed by the ruminant is transferred into meat (5-15%) or milk (15-30%), and most of the rest is excreted, with potential impacts on water, soil and air quality. Many fresh forage diets used for dairy cows present an imbalance between the rapidly available N and the slowly available energy in the rumen, which can limit microbial protein synthesis and increase excretion losses. In this experiment two strategies to improve the dietary energy/protein balance and their effects on microbial synthesis were studied. The first was to use perennial ryegrass (Lolium perenne) bred to express high water soluble carbohydrate (HWSC) concentrations. The second was to reduce and/or delay protein degradation in the rumen, to improve the energy/N synchronisation, by employing the activity of the enzyme polyphenol oxidase (PPO) in red clover (Trifolium pratense; RC). The latter promotes the formation of protease resistant cross-linked protein complexes (Lee et al., 2004).Non peer reviewe

Novel lines of high sugar ryegrass have been shown to increase the efficiency of N use and milk production in zero-grazed cattle (Miller et al., 1999). An experiment was carried out to determine whether this was in part due to an increase in the efficiency of microbial protein synthesis in response to the amount and availability of water soluble carbohydrate (WSC) increasing the balance between energy and nitrogen supply to the rumen microbial population.