FREE RANGE PIGS
Pigs will gain a proportion of their food from grazing; but they DO NOT graze exclusively. Pigs that are raised on pasture need an appropriate type of pasture, and some supplemental feeding, if you are to achieve optimum productivity.
Under some farming practices though, grazing can be significant. A pasture composed of the right species and fertilised adequately will supply all of the needs of a grazing animal.
The greatest restrictions to obtaining an abundance of pasture all the year are climate, soil fertility, topography and pasture composition. Pigs will not eat so much grass. If pasture is too high or too short the animal's intake may be restricted. Young animals need plenty of feed to develop properly.
FACTORS WHICH INFLUENCE THE NUTRITIONAL VALUE OF A PASTURE
Factors which influence the nutritional value of a pasture include:
- The stage of growth of a plant - plants lose nutritive value as they mature.
- Composition of sward - ratio of grasses, legumes and herbs.
- Nutrient status of the soil - are all necessary elements present?
- Climate - imposes restrictions on growth.
- Management of sward - over/under-stocking, planning use, fertilisers.
The Stage of Growth of a Plant
Realising that as plants mature there is a loss of nutritive value, we can plan to utilise pasture while it is at its best by grazing paddocks evenly, stocking more heavily, and conserving excess fodder at the best stage of growth (silage or early cut hay).
Composition of Sward
Pastures are made up of varying ratios of grasses, legumes and herbs (edible weeds such as docks, capeweed, and wild radish). The legumes provide the bulk of the protein and the grasses provide the carbohydrates. All three provide minerals. The herbs (weeds) need not be regarded as a problem if their ratio is below 15%, they become a disadvantage by lowering the area available for more productive species.
Pigs need pasture rich in protein (the higher the better), but this cannot happen unless the soil is rich in nitrogen. Nitrogen can be supplied at considerable cost by the use of nitrogenous fertilisers, or inexpensively by the introduction of legumes. The remarkable ability of clovers and other legumes to take nitrogen from the air and change it to chemicals which can be absorbed by the plant roots is made possible by the help of bacteria. The bacteria enter the roots of legumes, and the plant forms nodules around them. The bacteria feed on sugars supplied by the plant and in return supply the plant with nitrogen.
Clovers grown in soil lacking nitrogen will rapidly provide protein enriched pasture which stock need to put on flesh and keep healthy. The decay of clovers enriches the soil with nitrogen, which in turn is used by the pasture grasses. Clovers thus raise the protein content of the whole pasture. The basis of all pasture improvement is therefore the use of clovers and other legumes.
Native pastures, in which there are no clovers, contain apart from water, 5 12% protein in weight. At the end of a dry autumn the protein content of a native pasture may fall as low as 3%. As stock need at least 7% and preferably 10 15% of protein in their diet, they cannot properly exist through the winter on low protein pastures. If protein drops to 3%, the bacteria which digest the fodder in the paunch of an animal die. Consequently, pastures low in protein cannot be easily digested. The presence of clover in a pasture will considerably increase the protein of the grasses.
Grasses vary in their productivity and their nutritional value. The nutrients are found in the leaf of the plant, and therefore the ratio of leaf to stalk will determine the nutritional value. This varies between species and stage of maturity.
The best of our imported species, the rye grasses, phalaris and cocksfoot species, are more productive and more nutritious than earlier importations such as bent, sweet vernal, crested dogs tail, fog grass and our native species.
Nutrient Status of the Soil
Fertility of the soil obviously will affect both the productivity and the nutritional value of the pasture. The level of nutrients and the soil's pH value (acidity or alkalinity) can be critical in determining the chances of success of establishing a pasture.
It is advisable, therefore, whenever you wish to sow a pasture, or even decided to apply a fertiliser to an established pasture, to contact the local district officer of the Department of Agriculture and see if his recommendations substantiate those of your neighbour or contractor.
From the results of soil tests, fertiliser trail plots and experience within the district, the local extension officer is best able to advise you on the most suitable fertiliser. In some instances, it may be advisable for the extension officer to inspect the property to make a recommendation.
Climate is the main factor restricting pasture growth. It determines the length of the growing season, and the longer the growing season the better will be the overall nutritional value of the herbage, because the plants will remain at the immature leafy stage of growth for a long time. As we mentioned earlier, this stage gives herbage of the highest feed value.
Climate also affects the supply of nutrients from the soil. High rainfall generally causes the soil to be poor in nutrients because of extensive leaching. Under dry conditions growth is restricted through lack of moisture and availability of essential nutrients. Frosts present another restricting factor in growth, particularly with early summer fodder crops.
Management of Sward
Management of pasture plays a big part in the overall management of property. The planting of species for specific purposes in certain areas is one use of pasture management. For example, planting water tolerant species in damp areas phalaris, paspalum and strawberry clover. Stock numbers, feed requirements and feed availability require careful planning to avoid overgrazing and under grazing and to meet conservation requirements. The overall objective, climatic conditions permitting, is to have the sward as leafy as possible for as much of the season as possible.
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