Avoiding impacts on sheep from grass seeds
Your sheep and their wool can be affected by grass seed contamination, particularly when seasonal conditions favour high seed production. It's important not to underestimate the negative effect that grass seed contamination can have on your flock's productivity.
Effects of grass seed on sheep
Grass seed infestations can have the following effects on sheep:
- lower bodyweight and growth rate, due to irritation and infection
- small, low-quality and low-value carcasses
- reduced skin quality and value, as seeds penetrating the skin leave abscesses and small permanent holes, which enlarge during tanning
- increased risk of bacterial diseases, higher parasite burden and flystrike (as a result of skin-penetrating wounds and forced changes in grazing habits when sheep attempt to avoid grass seeds)
- damage to the mouth, eyes, ears and feet, causing
- reduced feed and water intake
- lameness and listlessness
- severe pain and distress
Reducing the effects of grass seed by shearing
Shearing is the only known way to relieve the pain and discomfort that sheep suffer from high levels of grass seed in the skin and carcass.
Signs of grass seed infestation in sheep
In Queensland, grass seed usually affects sheep during summer and autumn. They are listless, with a stiff gait or a reluctance to move. Some may show skin irritation and rubbing, and cotting of the wool.
Check sheep for dehydration from grass seed
You can check if your sheep are dehydrated from grass seed by gently pinching the skin and then letting it go to see how quickly it recoils into place. If this recoil lasts longer than 2 seconds, the animal is clinically dehydrated. Seeds will be seen visually when the fleece is opened along the neck, jowl, and belly wool.
Checking a carcass for grass seed infestation
After death, if the carcass is skinned, you will see the extent of seed penetration on the underside as confirmation of the problem. Seeds will be found penetrating into the flesh and will pull through the skin during skin pull.
Identifying problem grasses
Problem grasses pose the biggest threat when the seed is mature. The main grasses that can cause grass seed problems for sheep health, wool and skins are:
- wire grass, feathertop and white spear
- spear grass and corkscrew grass
- black spear grass.
Pasture management to prevent grass seed contamination
To manage your pasture effectively and reduce the spread of grass seeds to animals you should consider the following strategies:
- Encourage other grasses as competitors - Mitchell grass, blue grass and mulga grasses will outgrow problem grasses in normal to hot, wet summer rainfall years.
- Burning - destroys problem grasses, but can have other effects on species composition and the subsequent growth of vegetation (depending on the season, amount of herbage, the frequency of burning and the intensity of the burn).
- Mechanical treatment - involves slashing tracks through tall seed-bearing plants to, for example, allow animals safe access to water from grazing areas.
- Herbicides - usually only applicable to intensive, high-rainfall areas as cost prohibits their use in other areas.
Animal management to prevent grass seed contamination
You can also alter your animal management practices to reduce the spread of seeds to your sheep:
- Shearing - shearing sheep before grass seed matures will often reduce wool vegetable matter faults and seed damage to skins. When deciding the best time for shearing, you should also consider how it may affect the spread of lice and flies.
- Stocking rate - strategic short-term heavy stocking, including cell grazing and rotational grazing, may reduce infestations of problem grasses.
- Cross-grazing - a change in stock species or ratios can assist the change back towards a summer grass pasture. Cattle are virtually immune to grass seeds, and their feeding habits can help clear access to short feed for sheep. Horses and goats can do a similar job.
- Spelling - pastures infested with problem grasses should be rested for the summer growing period (December, January and February) to provide competition and maintain a stable population of summer pasture grasses.
- Breeding and selection - Merino sheep with little face cover, or open faces, and few body wrinkles are less likely to be affected by grass seed.
- Rugging - strategic rugging at times when grass seed is mature may help to reduce vegetable matter in wool. (This is usually only feasible for intensive or small sheep operations.)