Grazed pastures based on ryegrass species provide most of the feed for dairy cattle in New Zealand. There are many cultivars of perennial (Lolium perenne), annual and Italian (L. multiflorum), and hybrid (L. boucheanum) ryegrasses available for dairy farmers to use in pasture renewal. This study describes an index which ranks ryegrass cultivars relative to a genetic base according to the estimated economic value (EV) of seasonal dry matter (DM) traits. A farm system model was used to derive EVs ($ ha−1 calculated as change in operating profit divided by unit change of the trait) for additional DM produced in different seasons of the year in four regions. The EV of early spring DM was consistently high across all regions, whereas EV for late spring DM was moderate to low. Genotype × environment analysis revealed significant reranking of DM yield among ryegrass cultivars across regions. Hence, separate performance values (PVs) were calculated for two mega‐environments and then combined with the corresponding season and region EV to calculate the overall EV for twenty‐three perennial ryegrass and fifteen short‐term ryegrass cultivars. The difference in operating profit between the highest ranked and lowest ranked perennial ryegrass cultivar ranged from $556 ha−1 to $863 ha−1 year−1 depending on region. For short‐term ryegrasses used for winter feed, the corresponding range was $394 to $478 ha−1 year−1. Using PV for DM yield, it was estimated that plant improvement in perennial ryegrass has added $12–$18 ha−1 year−1 (depending on region) operating profit on dairy farms since the mid‐1960s.

Economic values (EVs) are an estimate of the change in farm system profit per unit of change in a defined plant trait. Cultivars within species such as perennial ryegrass differ in the major production traits of dry matter yield, nutritive value and persistence, but the impact of those differences on farm financial performance is seldom calculated and reported. This paper explains what EVs are, describes how they can be calculated, and discusses some of the associated methodological issues. EVs have been derived for seasonal dry matter yield in New Zealand dairy systems. Extra feed produced in late spring has consistently low economic value, while extra feed produced in early spring has consistently high value. There have been no systematic investigations into the EVs of nutritive value and persistence in New Zealand pastures; this is a clear opportunity for future research. The lack of data on cultivar differences in these traits will restrict the application of EVs to pasture cultivar evaluation. This gap is now being addressed by new industry initiatives. Keywords: pasture cultivars, evaluation, traits, economic values, performance values

Two experiments were carried out to determine the effect of slope on lamb mortality. In Experiment 1, 166 Marshall Romney (MR), 170 conventional Romney (CR), and 59 MR X CR ewes were allocated to one of 17 lambing areas of 0.2-0.4 ha and uniform slope. Mean slopes ranged from 3 to 44 ° and each area was surrounded by electric netting fences. Ewes entered their respective lambing areas 2 days before the expected lambing date and remained there for 4-5 days. In Experiment 2, two 1 ha plots selected on the basis of conformity of slope (36--44°) and 100-120 m long were each divided into three equal lambing areas by fences down the slope. Barriers either 15 or 30 m apart were constructed of 33-cm-high woven polyethylene mesh across the slope on two of the three lambing areas in both plots. Lamb mortality in Experiment 1 was not affected by slopes up to 30° but there was a large increase in lamb mortality with slopes of 36--44° (19.4% lamb mortality for less than 30° versus 50.1 % lamb mortality for more than 30°). In Experiment 2, 83-90% of lambs slipped off the birth site and 68-70% of ewes followed their lambs down the slope. The barriers stopped only 60% of the lambs encountering them. The other 40% passed under or over the barriers. Barriers increased separation of twin lambs (39% no barriers versus 65% barriers). The incidence of ewes rearing both twins when the co-twins were separated soon after birth by 0-1 m, 2-4 m ,or greater than 4 m was 15/16, 1/5, and 0/18, respectively. MR ewes had a lower lamb mortality than CR ewes (17 versus 43%). Although there were no differences in the incidence oflambs slipping off the birth site (83% MR versus 89% CR), the MR ewes had a lower incidence of abandonment of lambs (20% MR versus 41% CR).