Weather, herbage quality and milk production in pastoral systems. 3. Inter-relationships and associations between weather variables and herbage growth rate, quality and mineral concentration.

Prevailing weather conditions influence herbage growth and quality, and therefore may have a substantial impact on animal production. Before investigating relationships between weather factors, herbage quality and animal production, it is beneficial to first quantify interactions between herbage quality characteristics and mineral concentrations. The objective of the present study was to investigate the association between weather and herbage growth rate, quality and mineral concentration under rotational grazing systems. Daily weather data and weekly records of herbage quality and mineral concentration from a research dairy farm were available across the years 1995 to 2001, inclusive. Herbage growth rates were also recorded on a monthly basis. Results imply moderate correlations between some weather variables and herbage quality and mineral concentration. Generally, the strength of the absolute correlations between weather and herbage-related variables decreased following adjustment of the herbage-related variables for month of year and research farmlet. Negative correlations existed between rainfall and herbage water-soluble carbohydrate (r = –0.19) and organic matter digestibility concentration (r = –0.13) and metabolisable energy content (r = –0.14), independent of time of year and farmlet. Weather explained up to 14% of the variation in herbage nutrient content over and above that explained by time of year and farmlet. Significantly different correlations existed across time between some weather and herbage-related variables, indicating that the relationships may differ across seasons. Results from the present study, in conjunction with information on the effect of herbage quality and/or mineral concentration on animal production, will be valuable in improving our understanding of weather influences on herbage growth, quality and mineral concentration.