Feeding value of dryland lupin/cocksfoot pasture compared to lucerne pasture for sheep

Abstract

New Zealand South Island high country farms are typically nitrogen (N) deficient with environmental challenges that limit the production and persistence of traditional legumes like white clover (Trifolium repens) and lucerne (Medicago sativa). The perennial Russell lupin (Lupinus polyphyllus) has thrived on the roadsides of the high country since its introduction in 1952. Lupin is capable of growth in acidic, low fertility soils with high levels of Al, and well suited to moderate to high rainfall areas of the high country. Agricultural stands of perennial lupin are present on some high country farms, including Glenmore Station and Sawdon Station, but are generally utilised as a mature plant. While recent work on perennial lupin has looked at quantifying liveweight gain from pasture production, there is a lack of published knowledge on the feeding value of lupin as a pasture component of a pasture mix within a rotational grazing system and its contribution to the feeding value of cocksfoot (Dactylis glomerata)-based pasture mixtures in dryland environments. The objective of this study was to compare the feeding value of dryland cocksfoot/lupin pasture for sheep in comparison to pure lucerne pasture as a control. The two pasture types were compared in a grazed experiment at Lincoln University, using data collected during the complete 2016/17 growing season. This growing season was the fourth year of the experiment after the two pasture types were sown in December 2013. A group of young Coopworth ewe sheep were rotationally grazed on each pasture type (six 0.13 ha paddocks per pasture type) from August 17th 2016 to June 1st 2017 (288 days), spending 7 - 11 days in each paddock. There was no significant difference in herbage allowance between each group, and all sheep were shifted to the next paddock on the same day. Liveweight gain of sheep, herbage mass, herbage height, botanical and morphological composition of herbage and nutritive value were recorded throughout the trial period. Sheep grazing cocksfoot/lupin pasture gained 60% as much liveweight per hectare as sheep grazing lucerne pasture over the over the year (P<0.001). Herbage intake was 1.496 kg DM/sheep/day on lucerne pasture, higher than the 0.986 kg DM/sheep/day gained by sheep on cocksfoot/lupin pasture (P<0.001). Pre-grazing herbage mass was higher on lucerne pasture than cocksfoot/lupin pasture, allowing for a higher stocking rate on lucerne pasture at 20.8 head/ha compared with 13.6 head/ha on cocksfoot/lupin pasture. Leaf was the most rapidly consumed morphological pasture component, followed by petiole/pseudostem, and stem for both pasture types. The lupin fraction of the cocksfoot/lupin pasture was consumed within the first 4 days of the 10 day grazing period. Dead material was avoided by sheep grazing both pasture types. There was no significant difference in annual ME between cocksfoot/lupin and lucerne pasture, but lucerne pasture had greater ME FCE. Pre-grazing herbage mass and pasture composition indicated more opportunity for sheep to select high ME components on lucerne pasture than cocksfoot/lupin pasture. With adequate soil moisture lucerne pasture has the potential for high liveweight gain per hectare, making it a better pasture option for young lambs than cocksfoot/lupin pasture. However the feeding value of cocksfoot/lupin pasture is adequate for liveweight gain in young sheep. In the high country environment where the rooting depth of lucerne is restricted by high Al soils, limiting lucerne growth, cocksfoot/lupin pasture can be used as an alternative forage crop.