This weeks blog takes a look at a paper published in 2023 in the New Zealand Journal of Grasslands, titled ‘Five-year old, diversified pasture supports greater lamb liveweight gain than a standard perennial ryegrass-white clover pasture’.
The focus of this study by Maxwell et al. (2023) was to investigate the liveweight gain of lambs grazing five-year old pasture of either diverse pasture of Italian ryegrass, red clover and plantain, or standard pasture of perennial ryegrass and white clover. There have been many studies into animal performance on herb and clover mixes in New Zealand, however these have largely been focused on a pasture age of up to 3 years. Therefore, this study sought to investigate animal performance on older pastures, and it was of particular interest due to diverse pastures commonly being made up of short-lived perennial species.
The study was undertaken on a 3.6 ha farmlet in Canterbury that was split into two blocks – one of diverse pasture (Italian ryegrass, red clover and plantain) and one of standard pasture (perennial ryegrass and white clover). The farmlet was partially irrigated, receiving 40mm of irrigation every 10 days from November to March, with no irrigation during most of autumn. During spring, ewes and their lambs were continuously stocked with 30 ewes per pasture type until weaning on 3rd December 2020. At weaning, Coopworth ram lambs were allocated back to the pasture type that they were reared on, for the period of summer and autumn (December to May). These lambs were rotationally grazed across their respective blocks of pasture, moved every 10-15 days. The lambs were also weighted at every shift, as well as either side of shearing.
In addition to liveweight, pre-graze herbage samples were taken within 24 hours before lambs were shifted onto fresh pasture. Post-graze cuts were also taken from the paddocks the lambs had vacated, allowing for dry matter intake to be calculated as a way to estimate feed utilisation. Herbage samples were also taken, as well as nutritional composition samples.
Tailing to Weaning Liveweight Gain
The study found that there was no statistically significant difference in lamb liveweight at tailing between lambs on diverse and standard pasture. However, during the six-week period between tailing and weaning, there was a 23% higher liveweight gain for the lambs on the diverse pasture compared to that of the standard pasture. Lambs on the diverse pasture grew at an average gain of 0.335 kg/lamb/day compared to 0.272 kg/lamb/day for those on standard pasture.
As a result of the increased liveweight gain for lambs on diverse pastures, the average weaning liveweight of lambs on diverse pasture was 19% higher than that of lambs from the standard pasture. Lambs on the diverse pasture had an average weaning liveweight of 28.5 kg/lamb compared to standard pasture of 24 kg/lamb. These results suggest that there is a positive influence of the diverse components in pasture on the early liveweight gain of lambs (Maxwell et al. 2023). The study states that this showed there is an evident pre-weaning effect for the lambs reared on diverse pasture and that this potentially could be explained by how much of the lambs nutrient requirements were fulfilled by suckled milk from a nursing ewe on diverse pasture (Maxwell et al. 2023).
Post-weaning Liveweight Gain
While there was a significant difference between the average liveweight gain for lambs on diverse and standard pastures pre-weaning, the study found that there was no significant difference in the liveweight gain between lambs on the two pasture types post-weaning. This was reinforced by no significant difference in average dry matter intake or average feed conversion efficiency between the lambs on diverse and standard pastures.
Despite this, the higher liveweight for the lambs on diverse pasture from pre-weaning was maintained and resulted in an average final liveweight that was 9.6% higher for lambs on diverse pasture compared to standard pasture. The average final liveweight of lambs on diverse pasture was 50.3 kg/lamb compared to 46.1 kg/lamb for those on standard pasture.
Pasture Performance
Maxwell et al. (2023) state that it would be expected that after five years that a standard pasture would have greater production due to perennial ryegrass and white clover pasture performance persisting 5-10 years. This is in comparison to the components of diverse pasture that tend to persist for only 2-4 years as they are short-lived perennials. The study found that averaged over the whole summer-autumn period that the pre- and post-graze mass between standard and diverse pasture was not significantly different, which indicated the same yield production from both pasture types.
Overall, the botanical proportions of the sown species in the five-year-old diverse pasture was higher than expected, with high proportions of Italian ryegrass and red clover in early summer before dropping off in Autumn (Maxwell et al. 2023). Plantain was low to begin with but maintained approximately 10% over the summer-autumn period. These results indicate that it wasn’t evident that the standard pasture outperformed the diverse pasture, with the diverse pasture mix able to maintain a functional proportion of Italian ryegrass, red clover and plantain after five years (Maxwell et al. 2023). This, along with overall similar nutritive value of the two pasture types over the summer-autumn period, adds further explanation as to why there was similar liveweight gain for the two pasture types post-weaning.