Live weight gain of ewes and lambs grazing subterranean clover-based pastures : A thesis submitted in partial fulfilment of the requirement for the Degree of Master of Agricultural Science at Lincoln University

Abstract

The performance of four dryland pastures grown at Ashley Dene, Canterbury, was compared over the last two years of the five-year ‘MaxAnnuals’ grazing experiment. The pastures were sown in March 2013 with cocksfoot with sub clover, or a ryegrass/fescue hybrid with sub clover, both with and without balansa clover. ‘MaxAnnuals’ follows on from the previous ‘MaxClover’ experiment which found cocksfoot with subterranean clover was persistent and high yielding over the nine years. There was limited live weight gain data from ‘MaxClover’, so this paddock scale experiment was initiated. Ryegrass or plantain were also included in with clover in this ‘MaxAnnuals’ experiment to extend the range of species tested. Balansa clover was added to the subterranean clover-based pastures to see if the overall animal and pasture yields and clover content could be increased by the inclusion of a second legume. Each of the four pasture types were assigned a mob of ewes and lambs during spring and weaned lambs during summer, when pasture growth allowed. Grazer ewes were used to ‘clean-up’ pastures in autumn. The main measurement period was the live weight gain of ewes and lambs in spring. Differences between years or among treatments were related to seasonal pasture yield, composition, and feed intake. The total live weight production was not different among treatments of each year, but there were differences between years. Live weight gain averaged 511 kg/ha in 2016 and 635 kg/ha in 2017. During 2016, there was both spring and summer live weight production periods, but soil water deficits in late spring 2017 did not allow grazing over summer. Thus, the live weight production achieved solely from the spring of 2017, was greater than the 2016 spring and summer periods combined. During spring, ewe live weight decreased by 6 kg/ha across all treatments in 2016, but increased by 61 kg/ha in 2017. Lamb live weight gain averaged 402 kg/ha in spring 2016 which was less than the 574 kg/ha in 2017. The higher live weight gain in spring 2017 is due to the differences in clover content between years. The average clover content at the beginning of spring was 5% in 2016, and 75% in 2017, which led to 90% greater intake. Thus, the higher content of the winter-active sub clover meant that pasture growth was greater and began 281 °C days earlier in 2017 resulting in opening spring pasture covers of 2065 kg DM/ha, more than double that of the 931 kg DM/ha achieved at the start of spring 2016. The lower clover content in 2016 meant that spring pasture accumulation averaged 6.4 kg DM/ha/°C day, which was less than the 10.4 kg DM/ha/°C day in spring 2017. Across both springs, yields from plantain pastures averaged 5021 kg DM/ha, which was higher than the average of 4284 kg DM/ha from cocksfoot pastures. Although lower yielding, cocksfoot pastures were the most persistent with an average weed content of only ~1% at the end of the experiment. The poorer persistence of ryegrass in the initial mix meant that plantain took advantage and increased its presence in the ryegrass pastures so they were referred to as plantain pastures. Throughout the last two years, the weed content of the plantain pastures increased from ~4% to ~38% of the sward. This suggests plantain pastures may be an option for short-term (3-4 years) in dryland environments, but weed invasion is likely to compromise their production and persistence. The addition of balansa clover did not increase live weight gains, but did increase total clover content. Across both springs, clover content averaged ~37% from sub clover, which was lower than the ~45% from sub clover plus balansa pastures. Balansa together with subterranean clover in the mix caused management complications because the top flowering balansa needed time to reseed when ewes and lambs were grazing. Thus, it is recommended to concentrate on the management of the most dominant legume in any pasture to maximise clover content.