PHOTO: SHUTTERSTOCK
Dairy farmer Adam Shorten has quite a bit of experience man- aging pasture use while reduc- ing environmen- tal impact on his Murragh Farm in Ireland.
Steps to success In the end, success in achieving good levels of grass intake and milk production is very much about synchronising grass supply with the nutritional demands of the cow, but this is easier said than done. Both change throughout the season and can depend on geographical location, yearly weather patterns and cow genetics. Use of pasture, like many aspects of farming, therefore takes time to get good at and presents different scenarios every year. Among others, experts at the College of Agriculture, Food and Rural Enterprise in Northern Ireland believe grass height of 8–10 cm is ideal for dairy cows in a rotational grazing sys- tem (paddocks or strip-grazing). This height can sustain a high level of milk production with good compositional quali- ty. In spring, grass should only be grazed after the third-leaf stage because before then the plant does not have enough reserves to regrow after being trimmed by cows.
To continually measure pasture height/mass, farmers can use a rising plate meter, cut-and-weigh or visual assessment. Some farmers can also access high-tech tools that forecast pasture growth such as that developed by DairyNZ; this app provides five-day grass growth rate forecasts for various districts of New Zealand.
Fresh grass allowance To ensure adequate grass intake, the right amount of fresh grass has to be allocated to the herd, and this requires reliable estimation of the fresh grass allowance. Dr Cindy Klootwijk and her colleagues at Wageningen University (WUR) have evaluated the effect of grazing system on rising plate meter calibration to estimate fresh grass allowance and found that one region-specific calibration equation could be used across grazing systems, despite relatively large differences in pre- and post-grazing heights and period of regrowth. The equation has been calibrated for use in various regions of the world, and Klootwijk notes that the use of such a re- gion-specific equation is critical for farmers since the relation- ship between grass height and herbage mass is influenced by climate, season, grass variety and soil type. To account for the patches of pasture around manure that are rejected by cows, farmers should exclude the rejected patches from the meas- urements with the rising plate meter and subtract the per- centage of grassland area covered with rejected patches from the total area available for grazing.
Moving cows with technology In order to move cows around efficiently, balancing their grass intake with the need for the grass to regrow, there are many technological aids now available. “PastureBase Ireland” and INRA (the French National Institute for Agricultural Re- search), for example, have both developed pasture use tools. There are also several semi- or fully automated systems that monitor dairy cow grazing behaviour in order to properly allo- cate pasture and move them according to preset parameters. University of Minnesota researchers recently evaluated the use of an ear-tag accelerometer called CowManager SensOor which requires a number of solar-powered routers placed in
40 ▶DAIRY GLOBAL | Volume 7, No. 3, 2020
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