By Stephen McAulay
Pasture budgeting through the late winter period is an important consideration to start planning for in the autumn. A local dairy farmer, who used to live next door to a lifestyle farmer who was an accountant in their real life, commented that he ‘couldn’t believe that an accountant couldn’t understand that you need to divide something up before there is nothing left’. This is good advice and is essentially how large farms cope with winter grazing. Available pasture feed needs to be rationed so that the stock don’t eat all the available feed and then have nothing to eat.
Reducing stocking density is a useful tool to use to reduce feed demand. Literally, six horses eat twice as much feed per day as three horses. Most farms would reduce the number of animals carried on a property through the winter in anticipation that the grass will grow slower and, hence the total amount on farm will reduce as the winter progresses.
Peter Van Soest was the famous American ruminant nutritionist credited with creating the measurement of fibre content of grasses and relating this to digestibility, ADF & NDF. He suggested in his text (Nutritional ecology of the ruminant) that to be a good nutritionist, one should also become a good agronomist. Gaining an understanding of how pasture plants grow through the different seasons of the year, how moisture affects this growth (both too little in summer and too much in winter), when the pasture plants go through their reproductive cycles (producing seeds), how different fertilisers (especially nitrogen, phosphate, potassium and sulphur) enhance pasture growth and how animals grazing pasture affects the plants regrowth potential, will help farmers feed their animals better.
Grass has a natural growth cycle which slows down dramatically when the ground temperature is low, so target 60-day pasture rotation through the coldest months June/July. Contrast how well grass grows in the spring/early summer and autumn, when the ground temperature is warmer, so target 28-32 days pasture rotation. The low soil temperature slows down the chemical reactions which occur in the soil that convert soil minerals into plant available forms. Lower mineral availability leads to lower plant growth.
Sunlight hours change how well plants grow. This effect is noticeable when comparing south facing hill faces to similar topography facing north. The north facing land grows more plant material. This sunlight effect compounds the slow growth through the winter months.
The toughest time to feed ruminants on all grass systems is in late August/September. Fertiliser applied in the autumn will improve the pasture growth at this time. Fertiliser needs time in the soil to undergo chemical reactions before it is plant-available and the plant will physically change in size and composition during this time. Many people see the availability of grass now and think that they can avoid the expense of fertiliser, forgetting the natural changes of winter and the changing stock feed demands will change the feed availability picture.