The effect of pasture species on pasture and animal performances in irrigated systems

Abstract

The effect of two contrasting forage supply options on forage and sheep production was evaluated on irrigated farmlet systems at Winchmore, mid Canterbury, over 3 years. One system was based on perennial ryegrass pastures (Control), and the other on hybrid ryegrass, tall fescue, and chicory pastures (Improved). Pasture growth rates were similar for all pasture types, however, pasture cover was on occasion, higher on the Control than Improved systems ensuring this system was self-sufficient in feed while the Improved system had a deficit averaging 714 kgDM/ha/yr. Swards on both systems contained similar proportions of legume but the Improved system contained less grass and more chicory before lamb grazing. Despite the apparent improvement in feed quality of the Improved system, its lamb performance was greater than that from the Control system for the first year only, when swards were newly established and contained greater proportions of chicory and legume. Although pasture production was similar between years there was considerable variation in lamb growth rates. This was most pronounced in the Improved system where pre-weaning rates averaged 266 and 216 g/d in years 1 and 3 respectively, and post-weaning rates 190 and 108 in years 1 and 2 respectively. The post-weaning variation appeared to coincide with fluctuations in clover and to an even greater extent, the chicory content of swards, the proportion of which declined as seasons progressed and pastures aged. The Improved system gave financial returns from lamb that were $49/ha higher than the Control in year 1 but offered no advantage in subsequent years. Compared to the Control, the Improved system had the added costs of more frequent pasture renewal and was further disadvantaged by a feed deficit necessitating buying-in supplies. Improvements anticipated to accrue from the inclusion of higher quality swards in an irrigated animal production system, were not supported by findings from this study. Keywords: irrigation, lamb production, pasture production, pasture quality, pasture species