THE LONG-TERM EFFECTS OF A RANGE OF PASTURE TREATMENTS APPLIED TO 3 SEMINATURAL HILL GRASSLAND COMMUNITIES .2. ANIMAL PERFORMANCE

Five pasture treatments were applied to three semi-natural hill grassland communities. The pasture treatments were: (1) controlled grazing, (2) controlled grazing + lime, (3) controlled grazing + lime + phosphate, (4) controlled grazing + lime + phosphate + oversown white clover and (5) controlled grazing + lime + phosphate + oversown white clover + oversown perennial ryegrass. The communities were dominated by Agrostis/Festuca (site 1), Molinia (site 2) and Nardus (site 3). The Nardus at site 3 was substantially reduced by herbicide before treatments were applied. All treatments were grazed simultaneously by mature wether sheep on three occasions each year to a residual herbage mass of 560 kg DM ha-1. There were two grazing periods, each of 4 weeks duration beginning in mid-May and mid-July respectively and a further grazing period of 3 weeks duration beginning in mid-October. The number of sheep grazing days and liveweight gain of sheep were recorded during each grazing period for 13 years at each site. Organic matter intake (OMI) and digestibility (OMD) of ingested herbage were measured in years 2, 5 and 13. Mean daily OMI per head ranged from 1290 g for treatment 1 to over 1400 g for treatment 4 and 5. OMI values were higher for the Agrostis/Festuca site (mean OMI 1450 g) than for the Molinia and Nardus sites (1310 g and 1370 g respectively) largely owing to differences in the values for treatments 1, 2 and 3. OMI values for each treatment decreased by around 300 g between May and October. Mean OMD values from treatments 1, 2 and 3 were higher for the Agrostis/Festuca site (0.66) than for the Molinia and Nardus sites (0.63 and 0.64 respectively). The OMD values for treatments 1, 2 and 3 at the Molinia and Nardus sites declined by between 0.05 and 0.02 between years 2 and 13 and also showed the greatest decrease between May and October (0.08). OMD values for treatments 4 and 5 (0.67 and 0.69 respectively) were higher than for treatments 1, 2 and 3 at all sites and levels were maintained over 13 years. Individual liveweight gains of sheep increased from treatment 1 (-18 g d-1) to treatment 5 (82 g d-1), but they decreased over time on all treatments. The Agrostis/Festuca site gave 17% more annual sheep grazing days than the Molinia site and 33% more than the Nardus site. The mean number of annual sheep grazing days for each treatment ranged from 2250 for treatment 1 to 3640 for treatment 5. Annual sheep grazing days increased over 13 years by between 35 and 45% for treatment 1 and 55 and 70% for treatment 5. The results are described in relation to the changes in pasture composition and herbage accumulation.