The productivity of lactating dairy cows fed irrigated Persian clover (Trifolium resupinatum)

A number of experiments were undertaken to establish the productivity of lactating dairy cows when offered green, vegetative Persian clover (Trifolium resupinatum) herbage and to study its utilization by these cows. The research included indoor feeding and grazing experiments and intensive metabolism studies. Levels of daily intake varied from 1.3 to 4.5 kg DM/100 kg liveweight and in early-to-mid lactation, milk yields as high as 30 kg/day were sustained. In early-to-mid lactation, marginal returns to additional feeding were 1.24 kg milk, 0.046 kg fat and 0.034 kg protein for each additional kg DM of Persian clover eaten by cows weighing 500 kg. In late lactation, marginal returns were 1.10, 0.050 and 0.035 kg/kg DM for milk, fat and protein, respectively. In a grazing experiment, utilization of herbage on offer was very high, ranging from 58-88% as grazing intensity increased. Consideration of the products of digestion suggested that fermentation of Persian clover herbage in the rumen resulted in a balance of metabolites that is unlikely to be detrimental to animal production. However, there were two aspects of rumen fermentation that could influence the potential utilization of the herbage. First, for much of the year, levels of ammonia in rumen fluid (up to 500 mg/L) were much higher than microbial requirements. Second, rumen fluid pH often dropped to about 5.5, a level which may inhibit cellulolysis. The implications of manipulating these aspects of rumen fermentation are discussed. It was concluded that, while few problems exist with the use of vegetative Persian clover for lactating dairy cows, this herbage may be used more efficiently if fed in conjunction with supplements that provide a better balance of nutrients for fermentation in the reticulorumen.