Demand driven approach to pasture allocation

A demand-driven approach to pasture allocation has enabled the FutureDairy team to consistently achieve 18-20 tonnes dry matter (DM)/hectare pasture utilisation under full irrigation. This approach involves systematic monitoring of pasture growth and has the potential to achieve higher pasture utilisation than the industry average. The approach is based on physiological principles similar to the three-leaf stage approach, so it is not a case of one approach versus another. Grazing at the three-leaf stage is a simple and effective approach that is quite easy to put into practice. For many, it will continue to be the preferred way to make pasture allocation decisions. But the demand-driven approach based on monitoring may suit for those wishing to increase pasture utilisation even further. FutureDairy’s demand-driven approach is based on creating enough demand for pasture and monitoring pasture growth systematically. A cow can eat a maximum of 5-7t DM/ha/year (pasture plus supplements), but the farmer needs to create enough demand (stocking rate) to harvest about 20t DM/ha. Decisions about pasture allocation are based on matching demand (pasture removal by grazing or harvest) to pasture growth rate. As long as the basic inputs (water and nutrients) are provided, there’s not a lot that can be done to change pasture growth rates. But the farmer can change total demand for pasture per hectare to avoid over-grazing and under-grazing. That’s the tool used to balance pasture removal with growth rates in FutureDairy’s whole sys- tem studies. The Future Dairy team calculates the herd’s feed requirements and then meets them first with pasture, using supplements only to meet real feed gaps when pasture quality or quantity is truly limiting. It aims to feed the minimum possible level of concentrates all year round to balance the herd’s diet, increase animal production and improve reproductive performance. But the level of supplementary feeding is adjusted according to changes in pasture growth rate and quality. This approach can be used for a range of dairy feeding systems, including those based mainly on pasture, pastures plus supplements and the many variations of complementary forage systems (CFS), which involve a combination of pasture, cropping and supplements. FutureDairy has identified four basic steps to achieving high pasture utilisation: • maximising pasture growth; • monitoring pasture cover; • allocating pasture according to growth rate; and • using supplements to cover the true pasture deficit. While many good dairy managers follow these steps intuitively, the key to FutureDairy’s consistently high pasture utilisation has been getting each step right, most of the time. The reality is this approach requires more work and time. Maximising growth Pasture growth can be maximised by growing more grass and utilising more of it. As long as the basic inputs (water, nutrients, temperature and sunlight) are not limiting, growing more grass comes down to having enough green leaf area for photosynthesis to occur. Utilising more grass means minimising decay. Green leaves need to be removed (by grazing or harvesting) before they decay and die. Grazing management decisions influence the amount of green leaf area avail- able and how many green leaves are removed before they start decaying. That’s the basis of the traditional three-leaf stage approach to pasture allocation. The FutureDairy approach takes this a bit further. It aims to maintain pasture cover over the whole farm area within a relatively narrow range around a given tar- get (see figure). The actual target depends on the pasture species, region and the tools used (for example, rising plate meter, rapid pasture meter etc.) but the average of the desired levels of pre- and post-grazing pro- vide a good approximation. For example, if the target pre-grazing pasture cover is 2500 kilograms DM/ha and the target post-grazing cover is 1500kg DM/ha, then the target pasture cover should be somewhere around 2000kg DM/ha. The target pasture cover may be a little lower in winter and autumn when pasture growth is slower and a little higher in spring and summer when growth is faster. For seasonal calving systems it is desirable to deliberately build up pasture cover before calving to ‘buffer’ the system. Generally Future Dairy aims to keep seasonal variations in pasture cover to a minimum. Figure 1 shows the contrast between the desirable situation (with pasture cover moving up and down within a narrow range around the target) and what happens if pasture growth gets out of control in spring and summer due to poor pasture allocation (the red line). The way pasture cover is maintained around a target range ensures the amount of pasture removed by grazing or harvesting balances out the amount of pasture grown. This is achieved by adjusting pasture allocation, rotation length and the level of supplements according to pasture growth. Monitoring pasture cover Maintaining this balance involves avoiding over-grazing and under-grazing, avoiding grazing too soon and avoiding grazing too late. The only way to get this right consistently is by monitoring pasture cover systematically. Monitoring pasture cover allows Future Dairy to track growth rates and to balance the average rate of pasture removal with average growth rates. Pasture cover should be assessed in some way, preferably using a rising plate meter or an automatic bike pasture meter. Ideally the monitoring should be weekly, particularly during the fast-growing periods in spring and summer. The difference in pasture covers for each (ungrazed) paddock between two weeks gives an estimate of pasture growth rate. As all paddocks are measured, the same monitoring of pasture will give a good indication of pre- and post-grazing covers. During the same monitoring the Future Dairy team also assesses leaf stage on those paddocks closer to being grazed to help fine-tune the grazing roster for the next week. Allocating pasture With an estimate of pasture cover and growth rates, the team can decide the area to allocate for grazing. Logically, pasture growth rate estimated in this way needs to be considered with other factors such as weather, soil conditions and experience. With the FutureDairy approach, rotation length is not ignored, but it does not drive grazing decisions. It is more of a consequence of the grazing decisions, and it can be used as a ‘checking factor’ to ensure that decisions fit within the expected range. For example, rotation length will be shortest in spring when pasture growth is fast and longer in winter when pasture growth is slower. Supplements Next the team calculates the difference between the cows’ requirements and the pasture available in the allocated area. In spring there may be more pasture available than the cows require, in which case pad- docks may be taken out of the rotation for silage. The same rate of demand-driven pasture intake and pasture growth rate will indicate the size of the area to be shut down for silage. At other times of the year there will be a shortfall, which will be met by increasing supplements. The level of supplements is adjusted to achieve the balance between pasture growth rates and removal (by grazing or harvest). If less supplementary feed is fed than required, the cows will tend to compensate by grazing harder. This affects total dry matter intake because the amount of dry matter per bite decreases dramatically with lower post-grazing cover. It also affects the pasture regrowth rate (the pasture will take much longer to achieve the desired pre-grazing cover target) and total pasture utilisation. Leaving residuals (post-grazing cover) at less than 1300kg DM/ha compared with about 1500kg DM/ha can reduce average pasture growth by more than 10-12kg DM/ha per day. If this was done at each grazing, 3-4t DM/ha of pasture growth a year could be lost. And even worse, the farmer wouldn’t see it happen (see Figure 2). Adjusting the level of supplements is the main way to prevent over-grazing. Other strategies to prevent over-grazing include: • the timing and physical placement of feeding supplements; • the number of grazing’s each day (day and night paddocks or a single paddock); and • the time of moving cows into and out of the paddock. Customise rules for each farm The principles outlined here have worked consistently for the FutureDairy team. However, farmers who want to achieve the highest possible pasture utilisation on their farm should consider these principles in the context of their own system and goals. The key factors that influence the way these principles are applied on a farm include: • region and pasture types; • herd size and production system; • farm infrastructure; and • cow type and genetic merit.