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GRASSLAND MANAGEMENT ▶▶▶


growing season a new leaf emerges every seven to eight days with the ideal time to graze being between 2.5 and 3 leaves. Summing all this information up, George adds that “manag- ing grass is not an exact science. However, measuring grass growth and basing grazing decisions on this information helps to get the best out of it.”


Timely grazing and benefits Well-managed, high-quality grass is beneficial to the animal, the sward, the environment and the farmer. Quite often cows are turned into fields to graze grass that is not at the optimum stage for grazing, which is an important factor according to Teagasc dairy adviser Tom Murphy in the Republic of Ireland. Murphy highlights that the challenge is to graze each sward when it is at, or the closest to, the correct stage for grazing in terms of the stocking rate of the farm and the time of year. “Grazing swards at higher than this can create a repetition of similar cycles, and the negative consequences are extrapola- ted,” he says. “Paddocks that are grazed too soon lead to a re- duction in overall growth, as the sward becomes exhausted. “In a typical three-week cycle, 50% of the yield is grown in the third week. When grazed at the correct stage, paddocks are grazed off better, which leads to increase tillering, better regrowth, fewer weeds, more leaf material and less stem. “Higher animal intakes, in turn, help in keeping the post-graz- ing height correct and consistent. When the grazing rotation is managed well, quicker regrowth results. “Persistency in the sward improves and the output and re- sponse to fertilisers also jumps ahead. Shorter rotations with dense swards leads to more grazings per paddock. The higher growth rate and quality leads to an additional increase in grass utilised,” he adds. Research has shown the benefit of this to be about 1.5 tonnes of grass DM for an extra grazing rotation, which is worth around € 175/ha to a dairy farmer. Good grassland management benefits the environment, as when more optimum grass is produced it is utilised better and less methane is produced compared to cows eating high fibre grass. Grazing animals redistribute their own manure, leading to less slurry production and less ammonia gasses produced. Murphy says that grazing grass at the correct stage or cover, instead of allowing five or more extra days of growth, results in a 15% reduction of greenhouse gas production.


Carbon sequestration Carbon sequestration is a natural or artificial process by which carbon dioxide is removed from the atmosphere and held in solid or liquid form. Grasslands can absorb carbon di- oxide (CO2


) during growth of grass plants and store it in dif-


ferent tissues. When cows graze the grass, the carbon will eventually return


10 ▶ DAIRY GLOBAL | Volume 8, No. 3, 2021


to the soil as manure or to the atmosphere via enteric fer- mentation. The remaining grass and roots will eventually de- compose and the carbon will then be stored in the soil. Farmers, therefore, can play a vital role in carbon sequestra- tion by managing their grassland areas well to ensure they act as good stores of carbon. Soil organic carbon (SOC) storage is of interest due to the role it can play in removing CO2


from the atmosphere. However,


grazing practices that favour SOC have benefits for farmers apart from carbon sequestration. These benefits include increasing the quality of the soil, as soils with high carbon generally have better soil structure and water-holding capacity and provide more nutrients. They also benefit farmers by reducing on-farm costs and add- ing value to the final product. Different attributes of the vari- ous grassland management techniques can increase carbon sequestration. For example, grazed pastures may sequester more carbon than grasslands used to produce silage or hay due to the recycling of organic matter and nutrients from faeces and plant residues.


Heifer grazing Rearing dairy replacement heifers is a significant cost for all dairy farmers, but applying good grass management can help mitigate these costs. Getting heifers to the right weight and stature for 24-month calving requires an average weight gain of 0.8 kg/day throughout the rearing period. Achieving this performance at grass can be a challenge but is entirely possible with the correct feeding and management. Depending on the age, weight and rearing environment of a heifer, she will require a daily energy intake of approximately 70KJ in order to achieve a 0.8 kg daily liveweight gain. Research at AHDB in England has found that using rotational grazing techniques on a heifer grazing platform not only helps train replacements for herd life, but also creates the quality leafy grass necessary for rumen development and daily liveweight gain. The advice for farmers to gain the maximum growth benefit of these heifers at grass is to ensure the grass is of good quali- ty, usually at the two-leaf stage, and to be strict about when to move the animals. In practice heifers should be moved every two to three days to prevent back-grazing. Also, farmers should ensure au- tumn-born heifers are robust enough before turnout. Although rotational grazing grows leafy, high-energy grass all year round, calves need a good start on colostrum, followed by rumen development of at least six weeks’ milk feeding be- fore a gradual weaning over 10 days to avoid any growth checks. It takes three weeks of eating concentrate, or leafy grazed grass, to grow enough bacteria for the rumen to function and produce useful energy for growth.


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