The grazing rotation length will be determined by the leaf appearance rate.
In a challenging season, many dairy farmers will be focusing on gaining the best return from the resources available.
Grazing management of pastures can be used to maximise pasture growth and utilisation.
The aim of good grazing management is to balance the requirements of the pasture and herd.
Grazing ryegrass pastures between the two to three-leaf stage allows the pasture to reach its best potential production.
By the two-leaf stage the tiller has restored its energy reserves required to regrow after the last grazing and the pasture becomes nutritionally balanced for the diet of the herd. Allowing the tiller to reach the three-leaf stage before grazing is a bonus, as the third leaf is an extra 30-40 per cent larger than the second leaf. If we go beyond the three-leaf stage the first leaf begins to die and increases wastage.
The grazing rotation length will be determined by the leaf appearance rate.
As the temperature declines and day length shortens as we head into winter, the leaf appearance rate slows.
This means grazing rotation needs to be lengthened to allow the pasture to continue to reach the two to three-leaf stage target.
To achieve a longer rotation length, say 50 days, the pasture area on offer per day will decrease, in this case to 1/50th of the total milking area. This will result in a decreased area of pasture on offer per grazing.
Leave a post grazing residual of 4-6 centimetres (cm) between clumps. This is where the tiller stores its energy or ’fuel’ to re-grow.
Grazing below 4 cm will reduce the amount of energy reserves available resulting in smaller tillers, slower regrowth and less pasture at the next grazing. Grazing above 6 cm has no benefit to growth and increases pasture wastage.
Allowing the herd to have access to the pasture for longer than 2-3 days will result in new shoots being grazed and a reduction in growth.
Increasing the rotation length often decreases the amount of pasture available, leading to lower post grazing residuals.
Supplements e.g. grain, silage and hay, are used to manage the residual height. If post grazing residuals are below 4 cm more supplements should be offered to the herd to increase the residual. If residuals are above 6 cm, less supplement should be offered to the herd to minimise pasture and supplement wastage.
Remember, keep an eye on the leaf stage of the pasture you are offering to the herd and the post grazing residual as the cows leave the paddock each day to see if you are reaching your target leaf stage and post grazing residuals.
For some, feed may be tight, and the rotation may be shorter and not reaching the two to three-leaf stage.
If this is your situation, there is still benefit in lengthening the rotation to gain more pasture growth and restore more energy in the base of the tillers but keep an eye on those post grazing residuals.
Completing a feed budget may assist in managing feed supply by assessing herd requirements, what is available on hand and what is required to be purchased.
Lengthening or shortening the grazing rotation is about reaching the desired leaf stage, ideally two to three-leaf stage.
The post grazing residual, a measure of feeding level including supplementary feeding, is used to maintain a residual height of 4-6 cm.
For more information please contact Sarah Clack, Dairy Extension Officer, at Agriculture Victoria Tatura on (03) 5824 5502 or sarah.clack@ecodev.vic.gov.au.