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PASTURE TYPES
Improved pasture usually comprises a mix of introduced perennial grass species (such as various rye grasses, phalaris and fescues) plus clover. It requires regular applications of superphosphate and if overgrazed becomes highly susceptible to weed invasion. Both types of pasture are important to good horse management. Thoroughbreds and Warmblood horses must be grazed in pasture-improved paddocks. If they are put in paddocks which only have native pasture they will lose condition quite quickly, particularly in winter. On the other hand, ponies will founder very easily during spring in pasture-improved paddocks and generally can be kept in native pasture all year round without risk of foundering. Other breeds, such as Arabs Appaloosas Quarter Horses and Stock Horses seem to thrive on either type of pasture, unless they are in heavy work, when they will need supplementary feeding.
WEEDSThere are 12 species of weeds declared 'noxious' in the ACT in accordance with the Noxious Weeds Act 1990 (see Table below). Those most commonly seen in horse paddocks include thistles, Paterson's Curse, Bathurst Burr, St John's Wort and Serrated Tussock. In addition, there are quite a number of other weeds seen in horse paddocks including Mustard Weed (Skeleton Weed), Deadly Nightshade, Nettles, Horehound, Flatweed (False Dandelion), and Sorrel. Weeds Declared Noxious in the ACT
Under the Noxious Weeds Act, landowners are responsible for the eradication of weeds and most people owning horse agistment properties make some effort to control weeds. However, for a variety of reasons, mainly relating to logistics and cost, weed control in horse paddocks is very difficult. Once weeds infest a paddock the only way to really get rid of them is to completely repasture the paddock - a very expensive and lengthy procedure. Most land holders rely on a combination of methods to keep the number of weeds to a manageable level. This includes spraying with herbicides in spring and autumn, and in summer slashing any weeds that have not been sprayed. Horses are fussy eaters and unless pastures are kept in perfect condition, most paddocks end up having a fairly high weed burden. Although this may look unsightly, a paddock with lots of weeds is not necessarily dangerous to horses. Most of the time they will ignore the weeds, particularly if there is plenty of grass, simply because they are fussy eaters. So while the paddock next door that has sheep in it may look better, remember the sheep are eating the weeds as well. However, while horses generally don't eat weeds, there are two species to watch out for when choosing a paddock for your horse because they are particularly noxious if your horse does eat them; one is Paterson's Curse and the other is St John's Wort. A third weed, Flatweed (or False Dandelion) has been implicated in stringhalt and is also discussed below.
Paterson's CurseThe ability of this weed to spread rampantly throughout pasture, its particularly toxic nature and the difficulty of eradicating it, indeed makes it a curse. There are two plants that are commonly called Paterson's Curse and both belong to the Echium genus. Paterson's Curse (E. plantagineum) is the most common on the Southern Tablelands and the other is Viper's Bugloss (E. vulgare). Both are similar in appearance having broad spreading leaves growing outwards and upwards to about 30cm. A tall stem of purple flowers follows, with the flower head curling over as it ages. The weed spreads to cover entire paddocks which in late spring canturn whole valleys and hillsides into a purple carpet. Both species require similar control measures. People often confuse Paterson's Curse with lucerne because they both have purple flowers. However, lucerne has much smaller leaves which grow out from the stem, which is much thinner than that of Paterson's Curse. Paterson's Curse poisoning in horses generally results from long-term consumption of the plant. The toxin stops cellular division in the liver which results in chronic hepatic fibrosis (sclerosis of the liver). Given good pasture, horses don't usually eat Paterson's Curse. However, they will do so under two conditions. Firstly, if the paddock is so badly infested with weed that they have no choice. They then develop a taste for it and actually then seek it out if moved to a paddock with only a small amount. Secondly, when Paterson's Curse is sprayed with a selective herbicide such as MCPA or 2-4-D, it reacts by producing sugars. This makes the plant much more palatable and attractive for horses to eat. If a paddock is boom sprayed with either of these chemicals, horses should be removed until either the weeds die or the 'withhold' period for the chemical is over. How quickly the plants die after spraying depends on the concentration of chemical used, the size of the plants and the weather conditions, but it usually takes a couple of weeks. An absolute minimum of two weeks and preferably 4-6 weeks should be allowed before horses are put back into the paddock. From the horse owner's point of view this means two things: don't agist your horse in a paddock with a thick growth of Paterson's Curse (i.e. covering more than about 50% of the ground); and if the owner of the property sprays the pasture with herbicide, insist that your horse is moved out of the paddock for at least two weeks, even if the herbicide used is non-toxic to horses (such as Brush-Oft).
St John's WortSt John's Wort is rather pretty, having a ferny ground cover and a tall stem of small yellow flowers. In medieval times it was favoured as a herb for treating dysentery, rheumatism, gout and hypochondria, and as a charm against witchcraft. It was introduced to Australia as a garden plant in 1875. However, because of its toxicity to livestock, it has now been declared noxious over all parts of NSW and the ACT. The toxicity of St John's Wort is caused by the chemical hypericin, a fluorescent red pigment which is contained in oil glands in the leaves. When eaten, this chemical causes the lighter parts of a grazing animal's skin to become sensitive to sunlight, leading to sunburn and irritation (photosensitivity). Secondary infections may then set in. While symptoms in cattle and sheep can be extremely acute and lead to death, horses rarely eat enough of the weed to be seriously affected. Horses having no white markings may not show any effect and animals which are accustomed to the weed are less susceptible to its effect than horses which have never been exposed to it. Horses which do react readily to St John's Wort are those which have white legs and/or white noses. The affected skin becomes dry and scaly and on the lower legs a secondary infection will often take over, creating a far greater problem than the original reaction. If you find your horse with a skin condition which you otherwise can't account for, check the pasture to see if you can find any St John's Wort. In summer and autumn there will be a profusion of yellow flowers, standing on long leafy stems, 30-60cm high. In winter and spring these stems will persist as dead stalks. If your horse has eaten enough to cause a reaction, the plants will usually be quite abundant. If possible, remove the horse from the paddock and put it in a covered yard or stable for a few days to reduce exposure to sunlight. If you cannot move your horse out of the sun, provide some cover such as a summer rug, a mesh fly veil and a canvas flap hanging down from the nose band of the halter. If there is a secondary infection, treat as described in Chapter 13. If the skin condition is severe, call a vet. Just because there is St John's Wort growing in your horse's paddock is not necessarily cause for alarm. The weed is widespread throughout the ACT and many horses, even white skinned horses do not react to it (i.e. they don't eat it). The critical factor is the availability of palatable grasses. As with other noxious weeds, if there is nothing much else to eat but St John's Wort in your horse's paddock, you are clearly going to have problems.
FlatweedFlatweed looks very much like dandelion and grows abundantly in both native and improved pastures. The plant itself is not particularly toxic but it has been implicated in stringhalt, a condition that can severely debilitate horses. Stringhalt predominantly occurs in autumn, but may also occur if there are very moist conditions during summer. There was a widespread outbreak of stringhalt in the Canberra region in late January 1995 after a period of unseasonally heavy rain, followed by hot weather which resulted in higher than normal levels of humidity. It is not the Flatweed itself with causes stringhalt but a fungus that is thought to grow in association with it. Mustard Weed (also known as Skeleton Weed) has also been implicated in this condition. The toxic nature of the fungus causes damage to the two long nerves in a horse (one which travels from the brain to the heart and the other which travels from the sacro illiac region of the spine down the back of the hind leg). Horses havihg stringhalt can be recognised by the puppet-like action of their hind legs. Very mild cases may go unnoticed, especially if the horse is not worked at all, and mild cases may only be noticed when the horse is asked to back up and then the leg action becomes unnaturally pronounced. In severe cases the horse walks with extreme awkwardness or may not be able to walk at all. Horses will almost always recover from stringhalt, with mild cases taking about 2-3 months. These horses can be put back into light work when their gait is again normal and when they have no trouble going backwards. In severe cases recovery may take as long as two years. There is little that can be done to hasten the rate of recovery, although removing the horse from pasture and hand feeding along with vitamin supplements seems to help.
Other Problem WeedsThere are several other weeds that can cause problems with horses, or their owners. These include the thistles (saffron and scotch) and Bathurst Burr. Saffron thistles can grow so thickly that you may have problems in late summer just walking through a paddock to catch your horse. In addition, your horse may proceed at a very bouncy trot or canter if ridden through a paddock that has lots of thistles. By far the worst of the prickly weeds is Bathurst Burr. This weed is quite common in the ACT region and occurs mainly around old sheep camps and yards. It has a severe thorn which is very painful if you touch the plant with bare hands, and a burr which makes a tangled mess of manes, tails and forelocks. If you find burrs tangled in your horse's hair do the landowner a big favour. When you pull the burrs out put them into a bag and take them home to your rubbish bin. The burrs last for many years in the ground and a few dropped around yards can wash into a paddock and sprout years later. Similarly, if you see Bathurst Burr growing on someone else's land, either tell the owner where it is so they can pull it out, or pull it out yourself and put it in a rubbish bin. If you don't have gloves, use the heel of your boot to bend the stem over at ground level then carefully pull it out by the base of the plant. |
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Solutions
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The are two main types of pasture in the ACT region, native and improved.
Native pasture generally comprises the plant species that were growing in the
district before agricultural practices began. It can be poor in quality (wire
grass and spear grass) or good quality (red grass and wallaby grass) and it can
be improved with . the application of subterranean clover and superphosphate.
