In February 1996, 48 Friesian and Jersey cows grazed pastures containing nominally 0, 25, 50 or 75% of dry matter (DM) as white clover with the balance mainly C4 grasses at either ad lib. (50 kg DM/cow/day) or restricted (25 kg DM/cow/day) allowances. The aim of the trial was to measure the effect of clover content on milk yield and composition, and to determine the optimum clover content for milk production. Milk yields of cows on the ad lib. allowance grazing 25% clover were 22% higher (P

Perennial ryegrass (Lolium perenne L.) infected with a novel endophyte (AR37 or AR1), Wild‐type endophyte or no endophyte (Nil) was sown with white clover (Trifolium repens L.) in autumn 2005. The pastures were rotationally grazed by dairy cows from 2005–2009. Annual dry matter (DM) yield did not differ but AR37 pastures had a higher ryegrass tiller density, especially after the 2008 summer drought (+130%), and less white clover than did AR1 pastures. Concentrations of alkaloids produced by the Wild‐type association (lolitrem B, ergovaline) followed the same seasonal trends as did the AR37 alkaloids (epoxy‐janthitrems) but summer drought reduced concentrations of lolitrem B and epoxy‐janthitrems to less than half the mid‐summer (February) peak concentrations in the other years. Insect pests were monitored annually between 2006 and 2009. Tiller damage by Argentine stem weevil (Listronotus bonariensis (Kuschel)) was significantly reduced by all endophyte treatments. African black beetle (Heteronychus arator (F.)) populations in soil samples increased during the experiment with Nil > AR1 > Wild‐type = AR37. Root aphid (Aploneura lentisci (Pass.)) infestations followed the pattern AR1 > Nil > Wild‐type = AR37. A lower pest pressure from all insect pests in AR37 pastures is likely to have contributed to this treatment having the highest ryegrass tiller densities.

Pressure on New Zealand's largely pasture-based dairy industry has grown with a drive to increase production, expansion into new regions and demand for farmers to mitigate environmental impacts e.g., leaching of excess urinary nitrogen. A 3-year trial in the Waikato investigating the use of mixed pasture (e.g. perennial ryegrass, white clover, prairie grass, lucerne, chicory and plantain) showed similar annual dry matter (DM) production to standard pasture (perennial ryegrass and white clover) with greater yields of mixed pasture during summer (December, January, February) when lucerne and chicory grew better than perennial ryegrass in the warm, dry conditions. However, this yield advantage did not persist during the winter (June, July, August). Milk yields from cows grazing the mixed and standard pasture were similar. The mixed pasture retained a high level of species diversity and, while a single "magic bullet" is an unlikely solution to the challenges facing dairy farmers, increased species diversity could reduce risks and increase pasture stability. Keywords: pasture species diversity, dry matter yield, milk, nitrogen

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Abstract Herbage accumulation, botanical composition, tiller density and insect pest populations were monitored over 6 years for four perennial ryegrass functional types grazed by dairy cows in the Waikato. The aim was to identify genotypic and environmental factors contributing to ryegrass persistence failure in the upper North Island. Perennial ryegrass content of pastures declined as low as 60% of total herbage mass (HM) in summer of the first 3 years but recovered in autumn to at least 75%. However, following two successive severe summer/autumn droughts in Years 2 and 3, and subsequent grass grub larvae populations exceeding the damage threshold of 200/m2, by 4 years after sowing (autumn 2015), ryegrass had fallen to 20% of HM. This pattern was repeated in the following 2 years, and was not prevented by any combination of ryegrass functional type, endophyte, seeding rate, or best-practice dairy cattle grazing and soil nutrient management. The abiotic and biotic environmental stresses dominated all other factors. Keywords: pasture persistence, perennial ryegrass, drought, insects, black beetle, dairy systems