Studies to determine the nutritive characteristics of perennial rye-grass are helping Agriculture Victoria research scientist Meaghan Douglas develop grain rations that will optimise milk production.
Fine-tuning supplement mixes and amounts could minimise the need to feed high amounts of protein during spring, which could help farm profitability.
Ms Douglas is a research scientist at the National Centre for Dairy Research, Ellinbank. She is completing a PhD focusing on optimising the supply of nutrients from pasture and supplements to grazing dairy cows through a joint agreement with Agriculture Victoria and the University of Sydney.
Her primary focus is investigating the nutritive characteristics of perennial rye-grass cultivars grown on farms in Gippsland, northern Victoria and south-west Victoria.
Eighteen cultivars of perennial rye-grass have been collected from each region during early and late spring, summer, autumn and winter by Agriculture Victoria staff at Ellinbank, Tatura and Warrnambool, and analysed for their nutritive characteristics.
To complement this information, Ms Douglas conducted two experiments to determine the degradation characteristics of different perennial rye-grass cultivars in the rumen of dairy cows over 72 hours.
“These experiments investigated the ruminal degradation characteristics of protein and fibre in three perennial rye-grass cultivars harvested in early spring when the pasture is vegetative, and in summer during the reproductive phase of the plant life cycle,” she said.
Ms Douglas said there were differences in the amount of protein degraded in the rumen between the early spring perennial rye-grass cultivars within regions of Victoria.
“The later flowering, tetraploid cultivar had the greatest amount of total protein available for degradation in the rumen in northern Victoria, while the early flowering, diploid cultivar had the greatest amount in south-west Victoria,” she said.
Using the large knowledge base of perennial rye-grass nutritive characteristics created during this work, Ms Douglas hopes to optimise supplementary grain rations for pasture-based dairy cattle during each season of the year that can be fed in the dairy to increase milk production by complementing the nutrition the cows receive from pasture.
The diets will be formulated using nutrition model CPM Dairy, and during Ms Douglas’ PhD this model will be used to formulate optimal grain rations for use in pasture-based systems.
“The model will be evaluated by undertaking grazing experiments and using the nutritive characteristics of perennial rye-grass during each season to formulate supplementary grain rations,” she said.
“These grazing experiments will be conducted at Ellinbank using the rye-grass data from Gippsland.
“If the model is able to successfully formulate a ration for grazing dairy cows in Gippsland when compared to the results of the grazing experiment, then it could be applied to farms in northern and south-western Victoria where the perennial rye-grass data will be known.”
To evaluate the model, two grazing experiments have been conducted at Ellinbank, one in late spring and one in autumn.
Four supplementary grain diets fed in the dairy during milking were tested: a control diet consisting of wheat and barley; a formulated grain mix used in previous grazing research at Ellinbank, which consisted of wheat, barley, maize grain and canola meal; and two “designer grain mix” diets, which were formulated using CPM Dairy.
“The first mix consisted of the same ingredients as the formulated grain mix, however the purpose of this grain mix was to provide nutrients that complemented those that the cows were receiving from the pasture in order to optimise milk production, therefore the amounts of each ingredient were in different proportions to the formulated grain mix,” Ms Douglas said.
“The second mix consisted of wheat, barley, maize grain and replaced canola meal with urea and a fat supplement to determine whether the observed responses to feeding canola meal were due to some intrinsic feature of canola meal, or whether a similar outcome could be achieved using similar nutrients from different sources.”
Measurements taken during the experiments included milk production, body weight and condition score, rumen pH measurements as well as total dry matter intake of both pasture and grain.
Ms Douglas said results from the late spring grazing experiment demonstrated that cows could achieve a similar milk yield when fed a designer grain mix with half the amount of canola meal as the formulated grain mix.
“This work has shown that knowing the nutritive characteristics of perennial rye-grass in late spring can assist in formulating grain rations to optimise milk production.”