Effects of willow (Salix spp.) browse upon ewe reproduction and rumen microbiology under drought feeding conditions : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand

A series of grazing experiments were conducted in the summer/autumn of 2003 and 2004 at Massey University's Riverside dryland farm near Masterton in Wairarapa on the East Coast of NZ, to study the effects of grazing willow fodder blocks (6,000 stems/ha) upon the production and reproductive performance of ewes relative to ewes grazing drought pastures. Drought pastures were simulated in this study and included short drought pasture and long drought pasture. Pasture with a low pre-grazing mass of approximately 1500 kg OM/ha, a dead matter content of >50 % and a sward height of 5-7 cm was defined as short drought pasture typical of drought conditions. Long drought pasture was similar to pasture growing in the willow fodder blocks, with a pre-grazing pasture mass of >4000 kg OM/ha, a sward height of > 30cm and a dead matter content of 30-60 % . Willow fodder blocks were established on low-lying wet, marshy areas of the farm that had very low or zero productivity in the undeveloped state. Pasture development in the fodder blocks was noticed with the growth of unsown grasses and legumes, as the areas dried up following the planting of willow stakes, due to evapotranspiration from the trees. Forage in the willow fodder blocks included both trees and pasture that was grown under the trees. The nutritive value of short drought pasture was low with an ME of 8 MJ/kg O M ; long drought pasture ranged between 8- 1 0 MJ ME/kg DM; willow pasture contained 8 MJ M Elkg DM in 2003 and 1 0 MJ ME/kg OM in 2004. The nutritive value of edible willow tree (<5 mm diameter) was superior to drought pasture with an ME of > 10 MJ/kg OM. The concentrations of the secondary compounds such as condensed tannins (CT ; 30- 40 glkg OM) and phenolicglycosides ( PG ; 1 5-35 g/kg DM) were higher in willow trees compared to their concentrations (CT ; 2-3 g/kg DM) and (PG; 2-9 g/kg OM) in control drought pastures. Experiments involving short drought pasture, long drought pasture and willow fodder blocks a