MATCHING SUPPLEMENTS TO PASTURE – February 2018
Uncategorized
Ellinbank research farm

By Dr Martin Auldist

UPDATE: Dr Meaghan Douglas successfully completed her PhD in May 2020 – To determine optimal supplementary feeding strategies at four key stages of pasture growth for lactating dairy cows in pasture-based systems

Experiments to determine the nutritive characteristics of perennial ryegrass are helping Agriculture Victoria research scientist, Meaghan Douglas, develop supplementary grain rations that will optimise milk production of grazing dairy cows.

There is substantial variation in the nutritive characteristics of perennial ryegrass due to time of year and geographic location, which points to an opportunity to fine-tune the composition and amount of supplement in line with the nutrients that cows are already receiving from pasture. In particular, minimising the need to feed high amounts of protein during spring and autumn, when pasture protein concentrations are also high, could improve farm profitability.

Meaghan is based at Agriculture Victoria’s Ellinbank Centre. She is currently completing a PhD at the University of Sydney and is focussing on optimising the supply of nutrients from pasture and supplements to grazing dairy cows.

Image: Dr Meaghan Douglas at Ellinbank research farm

Her primary focus is investigating the nutritive characteristics of perennial ryegrass cultivars grown on farms in Gippsland, northern Victoria and south-west Victoria.

“Eighteen cultivars of perennial ryegrass have been collected from Ellinbank, Tatura and Warrnambool region during early and late spring, summer, autumn and winter,” says Meaghan. “These will all be  analysed for their nutritive characteristics.”

To complement this information, Meaghan has conducted two experiments to determine the how different perennial ryegrass cultivars degrade in the rumen of dairy cows.

“These experiments investigated the ruminal degradation characteristics of protein and fibre in three perennial ryegrass cultivars harvested in early spring when the pasture is vegetative, and in summer during the reproductive phase of the plant life cycle,” says Meaghan.

“There were differences in the amount of protein degraded in the rumen between the perennial ryegrass cultivars harvested from Gippsland.

“The late flowering, tetraploid cultivar had more protein available for degradation in the rumen in both early spring and summer. The two diploid cultivars had lower amounts of rumen-degradable protein, but the early flowering cultivar had more protein than the late flowering cultivar in early spring”.

Using the detailed database of perennial ryegrass nutritive characteristics created as a result of this work, Meaghan formulated some tailor made grain rations using the nutrition model CPM Dairy, and then tested them in pasture-based systems.

“The grain rations were tested by undertaking grazing experiments after using the nutritive characteristics of perennial ryegrass during each season to formulate optimal diets,” says Meaghan.

“Two grazing experiments were conducted at Ellinbank using the perennial ryegrass data from Gippsland in late spring and one in autumn.”

Four supplementary grain diets fed in the dairy during milking were tested in each experiment: a control diet consisting of wheat and barley; a formulated grain mix used in previous grazing research consisting of wheat, barley, maize grain and canola meal; and two “designer grain mix” diets, which were formulated using CPM Dairy and were specific for either the late spring or autumn experiments. All diets were fed at a rate of 8 kg DM/cow/day.

“The first designer grain mix consisted of the same ingredients as the formulated grain mix, however the purpose of this mix was to provide nutrients that complemented those the cows were receiving from the pasture in order to optimise milk production…so the proportions of each ingredient of grain mix was adjusted accordingly. In particular, the amount of protein was reduced by over half compared with the formulated grain mix by removing some canola meal.

“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.”

Meaghan said results from the late spring grazing experiment demonstrated that cows can achieve a similar milk yield when fed a designer grain mix with half the amount of canola meal, because of the high protein concentration in pasture at that time. Milk production was lowest in the wheat and barley mix, even though these cows consumed the greatest amount of pasture.

Similar results were observed during autumn. The first designer grain mix in this experiment also had less canola meal, but there was an extra 1 kg of maize included in the ration. These cows produced similar amounts of milk as cows with higher amounts of canola meal in their ration.

“This work has shown that knowing the nutritive characteristics of perennial ryegrass in late spring and autumn can assist in formulating grain rations to optimise milk production, and benefit the farmer’s back pocket.”

Meaghan’s research was funded by the Department of Economic Development, Jobs, Transport and Resources and Dairy Australia.