Effects of mixing red clover and maize silages on milk production and whole-body N partitioning in dairy cows

Twenty-four multiparous Holstein-Friesian dairy cows in mid lactation were used in a 33 Latin square changeover experiment with three 4-week periods to investigate the effect of altering the ratios of red clover (RC) silage and maize silage in the forage component of their diet. Ratios (in the dry matter (DM)) were: RC10, 0.1 RC:0.9 maize; RC50, 0.5 RC:0.5 maize; RC90, 0.9 RC:0.1 maize. All cows received ad libitum access to their allocated forage with 4 kg of a standard concentrate per day. Whole-body N partitioning and whole-tract diet digestibility measurements were carried out using a subset of cows (n=9). Results are presented in order of RC10, RC50 and RC90 respectively. Feed DM intakes (19.6, 20.5, 19.5 kg DM d-1, s.e.d. 0.32, P<0.01) and milk yields (26.1, 27.3, 25.7 kg milk d-1, s.e.d. 0.54, P<0.01) were highest on diet RC50. Milk protein concentrations decreased (P<0.001) as forage RC proportion increased, and protein yields were significantly (P<0.01) higher on diet RC50. Urine N excretion was lowest (as a ratio to N intake), and milk N secretion was highest, on diet RC10. It is concluded that milk and protein yields can be improved by feeding RC silage as 1:1 mix with maize silage, but that the efficiency of utilisation of forage N was reduced when diets contained more than 0.1 RC silage.