A practitioner's guide to pasture quality

Abstract

Pasture quality has a major effect on performance of grazing animals. Intake and nutritive value of pasture are major determinants of liveweight gain, milk production, health and reproductive performance of livestock. Digestibility and metabolisable energy concentration are the two most commonly used measures of nutritive value in New Zealand. In some situations protein, soluble carbohydrate, and mineral and trace element concentrations are also important. Fungal toxins, parasite larvae or other deleterious compounds lower pasture quality by compromising animal health. Potential intake of high nutritive value herbage is also greater because of rapid speed of passage through the animal. The major determinants of nutritive value are botanical and morphological composition, the environment in which the pasture is growing, and the regrowth period (i.e., herbage age). Legume leaf has higher nutritive value than grass leaf, leaf has higher quality than stem, and dead material has very low quality. Herbage grown at cooler times of the year has higher nutritive value than when grown in warmer conditions, and quality declines with age more slowly. Grass leaf declines in nutritive value as it ages, as does stem to an even greater extent. Soil moisture has only minor direct effects on nutritive value. Fertiliser application has direct effects such as increasing protein (by fertiliser nitrogen use) or trace element concentrations (if added to the fertiliser). It also has indirect effects through changing botanical and morphological composition. Keywords: digestibility, metabolisable energy, nutritive value, pasture quality