Understanding the nutritive value of pasture mixtures

Abstract

An investigation of how nutritive value changes with respect to the number of species and proportions of species in pasture mixtures was carried out at Lincoln University. Tetraploid perennial ryegrass cv. Base, plantain cv. Tonic, white clover cv. Apex and red clover cv. Grasslands Sensation were all grown in monocultures, two species, three species and four species mixtures based on a simplex centroid mixture experiment design. The aim of the experiment was to quantify the nutritive value of each of these mixtures to be able to define an optimum pasture mixture based on the four species used. Allowing for the species contribution to nutritive value and diversity effects to be identified. Models have been produced to predict nutritive value attributes of a mixture involving the four species investigated. The optimal mixture was defined based on parameters of maximising annual dry matter yield and annual yields of crude protein and metabolisable energy while meeting target annual mean concentrations of metabolisable energy, acid detergent fibre, neutral detergent fibre and crude protein based on animal requirements. This mixture comprised of the following proportions: 0.43 ryegrass, 0.20 white clover and 0.37 red clover based on the number of seeds/m2. Which was equivalent to the sowing rate of 12.90 kg/ha of ryegrass, 1.50 kg/ha of white clover and 6.48 kg/ha of red clover which was equivalent to a total sowing rate of 20.88 kg/ha. This mixture would allow for the pasture to meet animal requirements while not limiting intake or stocking rate. The optimal pasture mix was expected to have an annual yield of 14,250 kg DM/ha, annual metabolisable energy yield of 160 GJ/ha and an annual crude protein yield of 2806 kg/ha. It was also expected to have metabolisable energy concentration of 11.2 MJ ME/kg DM, an acid detergent fibre concentration of 264 g/kg DM, a neutral detergent fibre concentration of 380 g/kg DM and a crude protein concentration of 195 g/kg DM. The optimal pasture mixture would allow for protein and energy requirements of livestock to be met without limiting intake. Nutritive value was found to be dependent on the species present and their proportions in each mixture. Nutritive value has shown variation across years and seasons which showed that diversity effects among species were not consistent across time. The dynamic systems of pasture mixtures show that proportions of species do not remain consistent across time. Therefore, the diversity effects were not consistent across time either. Proportions of species did not remain consistent with the sown proportions with white clover being most outcompeted within the sward often stabilised at 10% of the mixture. The proportions of ryegrass, plantain and red clover varied depending on the mixture. The nutritive value was subsequently remodelled based on the actual proportions of species in the mixtures. In conclusion, the nutritive value of the pasture mixtures were dependent on the species present and the proportions of each species. The proportions of species changed across seasons due to growth patterns and overs years as a result of the succession of species.