Effects of grazing Trifolium subterraneum and Lolium multiflorum in various proportions on forage intake and milk production of dairy ewes

The aim of this research was to evaluate the effects of grazing Trifolium subterraneum (T) and Lolium multiflorum (L), as pure or associated crops, on forage intake and milk yield and composition in Comisana ewes. The four following fenced subplots, each of 2500 m2, were used for grazing: T, 100% of surface; L, 100% of surface; TL, T and L on 66.6 and 33.3 % of surface; LT, T and L on 33.3 and 66.6% of surface, respectively. Each subplot was divided into two parcels in order to have two replicates. Forty ewes were divided into eight homogeneous groups, with regard to milk yield, days in milk and live weight. In spring for 70 days, each group grazed daily for 8 h one of the fenced parcels. Measurements, sampling and analyses regarded the available forage, dry matter (DM) intake (assessed by the n-alkane technique) and milk yield of ewes. Data were analysed for the effect of grazed forage using the GLM procedure of SAS. The clover produced a higher amount of biomass than ryegrass, due also to the higher ryegrass intake of the ewes. Herbage DM intake was lower for the L group than the other (1090 vs 1552, 1520 and 1427 g/d for L, T, TL and LT, respectively; P<0.01). Consequently, the diet affected milk yield which was lower for L ewes than for T, TL and LT groups (740 vs 924, 964 and 898 g/d; P<0.05). The exclusive use of ryegrass in the diet led to a tendency to decrease protein, casein and urea contents in milk. Moreover, L milk was higher in curd firming time (k20: 3.39, 1.68, 1.85 and 2.20 min for L, T, TL and LT, respectively; P<0.05) and lower in curd firmness (a30: 20.4, 40.3, 42.6 and 35.2 mm for L, T, TL and LT, respectively; P<0.05). In conclusion, the use in any proportion of Trifolium subterraneum showed to increase both DM intake and milk production of dairy ewes.