Grass seed can be controlled using a variety of pasture and animal management techniques. Grasses, such as barley grass, brome grass and spear grass, cause problems when the seed is mature. Infestation is most severe when seasonal conditions favour high production or long retention of seed.
In any breed of sheep with wool, the lambs, weaners and hoggets are more severely affected than mature sheep. Young sheep are smaller, their bodies, eyes and bare skin are in closer contact with seed heads. Sheep can learn through experience to avoid contact with seed heads; this experience can be utilised by running older wethers with young lambs. Mature stock may also be affected in years when large quantities of damaging seed are produced. Merino and Merino-cross sheep appear to be most affected by grass seeds, primarily due to wool on the face and crutch.
Effects of grass seeds on sheep
Grass seed infestations in sheep and lambs have the following effects:
- Eye infection and inflammation attracts flies and may contribute to weight loss and depressed growth associated with reduced grazing and feed intake.
- Lower bodyweight and growth rate, possibly due to infection, with liveweight losses of 6-10 kilograms (kg) being reported.
- Small, low-quality and low-value carcasses often 2.5-11kg less in weight and presence of infected abscesses. These carcasses may be discounted up to $1/kg or $20 per lamb carcass.
- Reduced skin quality and value. Seeds penetrating the skin leave abscesses and small permanent holes, which enlarge during tanning. These skins are discounted.
- Increased prevalence of diseases, worm infestations and flystrike. Diseases (cheesy gland, tetanus, anthrax, pink eye, scabby mouth, lumpy wool, footrot, etc.) and flystrike enter easily through skin that is damaged by seeds, particularly after wetting. Worms build up because of the higher self-enforced stocking rates, as sheep only graze limited areas of the paddock.
- Ill thrift in sheep may be due to unidentified grass seed problems.
- Reduced feed intake and water intake (up to 1kg dry matter per day) from grass seed irritation of mouth, eyes, skin and feet of sheep. This may be compounded by poor quality pasture and the low intakes due to this.
Effects on wool and meat
Vegetable matter (which includes grass seeds) is found in all Australian wool in varying amounts depending on season and locality. Raw wool with vegetable matter is discounted as it can cause discolouration and cotting (matting of wool), it costs more to remove it during processing and wool is lost during its removal. Wool with vegetable matter is discounted. At the abattoir, carcasses with grass seeds require trimming, cause reduced throughput, a downgraded carcass and loss of export status for the carcass.