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Grass Seed Infestation of Sheep

J.B. Kemp, B.V.Sc., Veterinary Inspector, FORBES

Grass seed problems seen in the Forbes Pastures Protection District have been due to barley grass (Hordeum leporinum).

CHARACTERISTICS OF BARLEY GRASS (Hordeum leporinum)

Barley grass was apparently introduced into Australia quite soon after settlement and it is a native of Europe, North Africa and Asia. It is a rapid growing winter annual and it has spread so that it is now ubiquitous in the annual pasture zone of southern and eastern Australia. This grass is widespread throughout New South Wales, occurring from the coast to parts of the Western Division. On the Riverina Plain, barley grass is widespread and it occurs on all soil types, particularly on sandy and loam soils.

It is prevalent in fallowed land and competes with winter cereal crops for soil moisture and plant foods. It also develops plentifully where pasture cover is thin. In inland lucerne growing districts, barley grass is prevalent from May to October and reduces the monetary and feeding values of lucerne hay made during the spring months.

In some seasons it is common in perennial pastures as well. It may be present as a few scattered plants, or dominate the pasture, and the one pasture may have a very different content from year to year. Reasons suggested for this fluctuation are the type of seasonal break, and fertility level.

The grass germinates in autumn, makes good growth during winter and flowers in early spring, maturing relatively early, usually producing seed heads copiously.

The naturally occurring young barley grass provides large quantities of valuable, nutritious feed in winter for all classes of stock before flowering, but as the seed ripens, the stiff, sharp points of the seeds cause mechanical injury to stock.

Fruiting occurs mainly from October to December. Maturity is delayed in plants grazed short and these plants are selectively eaten until October.

Barley grass is an annual grass with erect stem and heads. It grows to a height of 30 cm but is occasionally higher and it is covered with fine hairs. The seed heads are 3 to 10 cm long. The seed is carried in florets (or spikelets) which break from the head in groups of 3, which consist of a central, fertile floret flanked by two sterile florets (i.e. the group of 3 is the 'dispersal unit'). It has a sharp point and each of the florets has a sharp awn. The point and the awns are important in causing the stock damage and also in ensuring widespread dispersal.

When the seeds fall the short stalk by which they were attached to the main stem acts as a spearhead, penetration into soil or animals being assisted by the long awns, which permit forward movement only.

Factors Giving Barley Grass Preference Over Other Species

Smith in 1968 reported that as far as the seed and seedling stages are concerned, barley grass has several strengths which contribute to its success in pastures in southern Australia.

1. The awns on the seed repel animals and make ingestion unlikely.

2. Ants were found not to be able to move the large awned barley grass seeds in contrast to a very high percentage loss of Wimmera ryegrass seed by ants (McGowan, 1967).

3. Most seeds remain dormant until autumn, especially if day temperatures are high.

4. Germination occurs readily and rapidly, even on compact surfaces. The awns of barley grass seed appear to play a part in anchoring the seed on a soil surface that tends to set hard.

5. Large seedlings are produced.

BARLEY GRASS AND CROPS

A dry autumn, then lack of cultivation prior to sowing has lead to a lot of barley grass in crops which reduces yields of wheat and barley. There is no registered chemical available to control barley grass post-emergently and therefore it has become a large problem. On the other hand, Wimmera Rye and Black Oats can be killed out post-emergently with chemicals such as Hoegrass. Treflan, which is a residual incorporated pre-emergent chemical and used mainly for Wimmera Rye, is not highly effective or registered for control of barley grass. (G. Falconer - pers. comm.).

GROWTH OF BARLEY GRASS IN THE FORBES PASTURES PROTECTION DISTRICT IN 1981

During the winter of 1981, the writer noticed more barley grass in the Forbes District than had been noticed in the previous 9 years of residence in the area. The Forbes Pastures Protection District had been a drought declared district since January, 1980. However, good falls of rain were received in May, 1981 (57.4mm), June (62.3mm) and July, 1981 (81.6mm). Barley grass came away with the rains in May and it was the dominant species being the first to grow. A dry autumn and a wet winter and a dry spring is very conducive to barley grass. (G. Falconer - pers. comm.).

BARLEY GRASS-SEED PROBLEMS IN THE FORBES DISTRICT IN THE LATTER PART OF 1981

The large majority of grass-seed problems are not brought to one's attention. Owners regularly bring the sheep in to remove grass seeds from the eyes of sheep, particularly in lambs, and to treat any animals affected with pinkeye.

There were 3 cases associated with mortalities with which I was involved.

1. PROPERTY A

This property was visited on 12 November 1981. The mob affected consisted of 600 Merino wethers with 9 to 10 months wool, age 2 to 6 tooth.

Symptoms: The owner reported a staggers problem in his sheep, at least 6 were down and 8 had died. The sheep would go down, but on being lifted to their legs, they would run off with a stiff gait. The sheep were heavy in wool. The grass-seeds had packed in particularly under the shoulders, up the neck and around the belly, and the penetration of the seeds through the skin caused great discomfort.

Post-mortem: The sheep post-mortemed showed marked weakness prior to being killed. It showed a heavy grass-seed infestation of the wool and skin with numerous small abscesses subcutaneously. There were no lesions in the abdominal and thoracic organs.

Mortality: Approximately 50 wethers died. It was difficult for the owner to find recumbent sheep in the long grass. Later, the owner noticed in affected sheep, a break in the wool along the neck and around the belly wool. Losses took place up to the time of shearing (on 24 November 1981), but after shearing, there were virtually no losses. There was also a problem with fly strike in sheep affected with grass-seeds.

This owner had been on the property since 1946 and he said it was the worst season for barley grass since then. The area affected had been under wheat for some time.

Factors Considered Important in this Mortality

1. Grass-seed affected sheep heavy in wool.

2. The long barley grass made it difficult to find recumbent sheep.

2. PROPERTY B

Date of visit was 26 November 1981, which was on the day of shearing. Number in mob - 400, approximately 6 months of age, consisting of 300 Merinos and 100 crossbreds (Border Leicester by Merino cross).

The lambs were dipped 4 weeks prior to shearing using Cooper's 4 in 1 dip. The rest of the sheep on the property were shorn in mid September but the lambs were not shorn then because shearers were not available.

Mortality: 15 lambs had died over 2 weeks.

Post-mortem: One lamb was post-mortemed (killed for post-mortem) and was poor in condition. It was showing patches of Mycotic Dermatitis and numerous grass-seeds externally. On post-mortem there were numerous small subcutaneous abscesses, up to about pea size, containing Corynebacterium ovis-like pus. There were no lesions in the viscera.

Symptoms: The majority of the Merino lambs were poor in condition, and were showing a heavy grass-seed infestation. Numerous lambs were affected with Mycotic Dermatitis. Laboratory Findings: Smears of the wool and wool scabs confirmed Dermatophilus congolensis. Histopathology of liver and kidney was in keeping with a septicaemia/toxaemia that could arise in multiple grass-seed infestations.

Treatment: Any lambs affected with Mycotic Dermatitis were treated with 4 mls Streptopen injection - totalling approximately 100 Merino lambs and 3 weeks later approximately 25 were treated again. In all, another 12 lambs died after the first visit, making a total of 27 lambs.

Second visit on 8 February 1982: On this visit, only one Merino lamb was seen to be in a poor condition, being severely affected with Mycotic Dermatitis. This lamb was post-mortemed and there was no evidence of subcutaneous abscess formation. Small black spiked objects approximately 1 cm in length were present, obviously being the remnants of the grass-seeds. No visceral lesions were present. In the remainder of the lambs the Mycotic Dermatitis had lifted, or only showed on an odd tip of wool.

Eye Problems in this Flock: 75% of the lambs had eye problems. Crossbreds were also affected but not as badly. The eyes required checking from late October to mid December. The eyes were checked every second or third day initially by the owner. At least 30 blind lambs were treated by the owner.

Factors considered important in this Mortality:

1. Dipping sheep heavily affected with grass-seeds leading to subcutaneous abscessation.

2. Mycotic dermatitis would have exacerbated the condition which was presumably spread by the dip.

3. PROPERTY C

Date of visit 26 October 1981 (Monday).

A mob of 320 Merino lambs was seen, aged 6 to 8 weeks, in which 70 lambs died.

Fourteen days prior to the visit on Day 1, the lambs had been shower dipped with Vetrazin for fly control. One day later on Day 2, the lambs were mulesed and marked and 5-in-1 vaccinated and treated with Topclip Diazinon Mulesing Powder.

The lambs were in the woolshed for half an hour prior to being mulesed and marked and were mulesed and marked (off the ground) and then immediately were put over the fence onto a grassy yard. They were there for 4 to 5 hours and then put into an adjoining paddock overnight.

On Day 3. the mob was moved to another paddock ½ to ¾ mile away.

On Day 5, the lambs were inspected by the owner and 5 dead lambs were seen.

The lambs were next seen 9 days later when 70 were dead and 100 sick (day of visit).

Symptoms: Many dead lambs were seen at varying stages of decomposition. The sick lambs were listless. They were either too sick to get up, or would move away slowly when put on their feet. The lambs were poor in condition. The mulesing scab was hard to touch, and would peel away on lifting, leaving infected tissue underneath. The mulesing wounds were commonly flyblown. The lambs were affected with barley grass-seeds.

Post-mortem: Several lambs were post-mortemed. Numerous subcutaneous abscesses up to 4 cm diameter were seen from grass-seed infections, presumably after dipping. Mild to moderate jaundice was seen. Kidneys were pale and liver patchy. Fluid was present in pericardial sac, some containing clots. Some mayonnaise-like contents were present in the small intestine.

Laboratory findings: Three lambs were submitted to the laboratory and all three lambs revealed extensive grass-seed abscessation throughout the subcutaneous tissues all over the body. None of the mulesing wounds had healed, the wounds being severely infected and exuding a greenish foul smelling inflammatory exudate. All wounds were infected with blowfly maggots. Marking wounds were infected by both the multiplicity of bacteria and fly maggots. Due to the post-mortem findings, no microbiological and histological examinations were done. Diagnosis made was mortality from post-marking, post-mulesing infection, flystrike and grass-seed abscesses.

Treatment: All lambs were treated twice with Streptopen injections, at 24 hours apart. The mulesing wounds were treated with Diazinon Mulesing Powder. Deaths stopped within about 3 days of treatment. The owner later estimated at least 80% of the lambs were sick. Seventy (70) more lambs died after the initial visit making a total of 140 deaths out of the mob of 320 lambs. Another 80 lambs died out of a mob of 430 making a total of 220 deaths out of 750 lambs.

The owner was seen again on 22 February 1982 and he advised that the lamb mob was well but had remained stunted. The lambs had been shorn the week previously and the shearers had complained puncturing the subcutaneous abscesses when striking the skin with shears.

Factors considered important in this Mortality

1. Lateness in the season in mulesing and marking, i.e. late in October when flies were a problem.

2. Dipping heavily grass-seed infested animals which resulted in subcutaneous infection.

3. The owner considered that the small black flies were important in infection of mulesing and marking wounds.

The sheep dipping contractor observed that the lambs were heavily affected with grass-seed when the lambs were mulesed which made the shears blunt.

Two other properties with grass-seed problems

4. PROPERTY D

A report of a barley grass-seed problem after shearing.

A mob of 300 crossbred lambs (1st cross by Border Leicester), 6 months of age was kept out of the barley grass prior to shearing.

After shearing, they were put in a barley grass paddock in November and December. Grass-seeds in the eyes were first noticed and treated twice. Then the owner noticed grass-seeds to be causing ear trouble, every lamb being affected, being worse than the eye problem.

The ears were treated twice at 2 weekly intervals. There were up to 12 grass seeds in an ear with an average of 4 to 6 per ear, which caused an ear discharge. The grass-seeds were removed by the owner and disinfectant applied.

There was no trouble with the skin of these sheep.

5. PROPERTY E

There was another report of a severe barley grass-seed problem experienced in 40 years. One group of lambs were brought to water daily due to pinkeye for a couple of weeks, and treated for pink eye. The owner reported 12 lambs were lost from pink eye and poverty. The whole mob was brought in for removing grass-seeds from the eyes four times at weekly intervals.

REPORT OF GRASS-SEED INFESTATION OF SHEEP IN NEW SOUTH WALES BY DODD IN 1919

As far back as 1919, Dodd wrote in the Agricultural Gazette of New South Wales that the condition in sheep due to the penetration by certain grass-seeds, in parts of the State, and following good seasons was a very common one and of some economic importance. Dodd collected information from 51 Pastures Protection Districts, the districts varying considerably in extent. In all cases where it did occur, the intensity of the infestation varied with the seasons. In good seasons when grass was plentiful, it seeded freely, being generally most evident in late spring and summer.

Age and Class of Sheep Mainly Affected (Dodd, 1919)

1. Lambs and weaners are more particularly affected.
2. Merinos are more affected than other breeds. Wrinkled sheep are much more infested than plain bodied sheep. Merino wool retain grass-seeds more readily than other types of wool.
3. Crossbreds and English breeds suffer less due to open wool and clean faces.

Reasons given by Dodd (1919) as to Why Young Sheep are More Susceptible than older Sheep

1. They do not avoid long grass.
2. Their bodies are closer to the ground.
3. The skin is more tender.
4. There is more wool about the eyes.
5. They usually carry more wool.
6. Their constitution is less robust than older sheep.

SYMPTOMS (MCDONALD, 1981)

1. Affected sheep stand apart from their fellows, and are disinclined to move, but when they do, have a particular stiff gait. The stiff gait is due to the thick mass of grass-seeds embedded in the wool, and due to the pain produced by the seeds piercing the skin.
2. Irritation of the body causes biting, scratching and rubbing and deterioration of the fleece.
3. Ophthalmia and keratitis due to grass-seeds lodging under the eyelids and often followed by blindness.
4. Loss of condition and fever, resulting in a break in the wool.
5. Subcutaneous abscesses, especially after dipping. In the majority of cases, no suppuration is produced at all. Seeds mostly come to rest in the subcutaneous areolar tissue, mostly lying parallel to the surface of the skin.
6. Mouth problems - causing alveolitis, mandibular abscesses, abscesses under the skin of the jaws, penetration under the tongue and into the cheeks.
7. Feet problems - from accumulation of grass-seeds between the claws and penetration of the interdigital skin.
8. Ear problems - from packing of the ears with barley grass-seeds causing deafness and difficulty in mustering with occasional inner ear abscesses and circling.
9. Grass-seeds up the nose and vulva.
10. Secondary flystrike of irritated and infected areas from grass-seeds.
11. Specific diseases associated with grass-seeds
    a) Tetanus - following dipping (Cole, 1966)
    b) Anthrax - (Belschner, 1961)

TREATMENT

1. Grass-seeds can be removed with fingers or forceps from the eye, mouth, ear, interdigital area and vulva.
2. Pink eye or footrot antibiotic powder or aerosol aids in healing and control of infection.
3. Sheep heavily infested about the body are best shorn.
4. Remove sheep from barley grass affected paddocks.

CONTROL OF GRASS-SEEDS AFFECTING SHEEP

1. Shear sheep, particularly young sheep, early before the grass seed season occurs.
2. Keep sheep away from heavily seeded paddocks.
3. Don't dip heavily grass-seed infested sheep. If lousy, use tip spraying.
4. Wig sheep by shearing around the eyes. The wool on the face allows the seeds to work their way into the eyes.
5. Breed sheep particularly with open faces and also bare legs and plain necks.
6. Run cattle and horses in badly seeded paddocks.
7. Heavy stocking.
8. Mow tracks to dams, troughs and sheep camps.
9. Type of sheep
   a) lambs suffer more than older sheep
   b) Merinos suffer more than crossbreds and English breeds.

CONTROL OF BARLEY GRASS

There are various possible management practices which have been used for control of barley grass, such as cultivation, topping with a mower and spraying with weedicides.

1. Cultivation

For cropping, barley grass can be cultivated out, provided germination takes place. Therefore, with a fall of rain in April, it can be cultivated particularly with a rod-weeder. (G. Falconer - pers. comm.). However, if the rain is too late, and the crops are sown without sufficient cultivation, then the barley grass comes up.

2. Spraying

If it is too wet for cultivation it is worth spraying before sowing with a 'knock-down' chemical such as Gramoxone or Roundup. Otherwise, if cultivation and sowing does take place when the ground is moist, or rain follows cultivation, transplanting of seedlings will take place. (G. Falconer, pers. comm.).

I.C.I. Spray Top (Gramoxone)

This is used in the year before cropping, and it is applied at the end of the season when the grass is fully out in head. It stops plant growth and hastens the haying off process and prevents the seed from maturing and becoming viable. Grass-seed contamination of stock is reduced and it reduces its ability to adhere to and penetrate wool and skin. At least one day with-holding period from stock is required after spraying.

3. Topping with a Mower

As an example of this, a district owner from Grenfell, mows the barley grass just before it dries off as it is coming into ear at the end of September and early October when 50% in ear. This increases the grazing period by approximately 3 weeks. After rowing, the sheep eat it further off, and it ends up approximately 4 inches in height. This owner found that the mowing allowed the clovers and other species to grow underneath so the sheep could eat these when the barley grass had dried off. However, if the barley grass is dominant then the other species will not grow under it. (C. Johnson, pers. comm.).

TRIALS

1. Trial Showing the Effect of Monthly Grazings on the Production and Quality of a Barley Grass Dominant Pasture

Robards and Leigh in 1967 reported an experiment at Deniliquin which showed that monthly glazings resulted in the greatest production of barley grass stimulated mainly by grazing in August or September when the plants were approaching maturity. In the late spring, particularly in August or September, barley grass from treatments grazed regularly, retained a higher nitrogen level and had a higher in vitro digestibility than material from ungrazed or lightly grazed treatments. It was observed that the monthly grazings delayed the onset of flowering and the plants eventually flowered much closer to the ground. However, the number of fertile seed heads was not reduced.

2. Trial Showing the Effect of Stock Rates on Liveweights

In 1972, Campbell, Robards and Saville reported an experiment at Trangie on Merino wethers which suffered a marked reduction in liveweight in the spring of 1969 and 1970 coinciding with periods of heavy seed setting of barley grass and spear grass (Stipa variabilis). It was shown that there were significant correlations between liveweight loss and density of barley grass inflorescences.

High stocking rates suppressed barley grass and sheep in these treatments attained higher mean liveweights than sheep at lower stocking rates. High densities of barley grass inflorescences on maturity were associated with reduced green pasture availability, as well as causing trauma associated with the penetration of barley grass into the eyes and skin.

3. Trial showing the Effect of Shearing on Grass-Seeds in the Hide and Carcase

Lodge and Hamilton in 1981 reported an experiment on a group of 6 month old Merino wether weaners grazing natural pasture on the north-western slopes of New South Wales. The sheep were grazing on the natural pasture for 6 months from January to July 1977. They were then removed, shorn and grazed for a further 23 months on lucerne and oats pastures that were free of grass-seeds. The sheep were therefore not grazed on the natural pasture when barley grass-seeds were maturing in October and November.

The results showed that wiregrass seeds were a major cause of vegetable fault in wool and were also the major source of hide and carcase contamination (wiregrass: Aristida ramosa).

The number of grass-seeds in the hides and carcases declined over the 23 months that the animals grazed on pastures free of grass seed. The largest decrease occurred in the first 6 months after the sheep were removed from the natural pasture and shorn, with a mean of 63% of the seeds being lost from the hide, and a mean of 45% of the seeds being lost from the carcase. After 23 months, mean levels of infestation were reduced to 11% of those initially in the hide and 7% of those in the carcase. Observations indicated that this reduction in seed level was related to seed re-entering the wool from the carcase and hide. Even after 23 months no hides or carcases were seed free.

4. Trial Showing the Comparison of the Effect of, and on Merinos and Dorset Horns Grazing on Barley Grass

George at Armidale in 1972 reported an experiment comparing Merinos and Dorset Horns grazing on barley grass.

i. Effect on the Barley Grass

It was found that infestation of barley grass, as measured by inflorescence density was 250% greater when grazed by Merinos than when grazed by Dorset Horns. Dorset Horn sheep were seen to eat seed heads of barley grass, without any apparent discomfort in the mouth whereas Merinos appeared to avoid eating the awned seeds. Therefore, there was a lower density of barley grass in paddocks grazed by Dorset Horns which reduced the opportunity for the animals to become infested.

ii. Effect on the Sheep

Merino ewes and lambs were severely infested with barley grass-seed around the face and crutch, and were also common in the ears, vulva and under the legs. However, no Dorset Horn ewes and only a few lambs were infested by barley grass-seed. The virtual absence of wool on the face and crutch of Dorset Horn lambs and ewes would be an explanation for the fact that this breed was not adversely infested with barley grass-seed. The awns of barley grass-seed penetrated the skin of Merinos, but there was no evidence of damaged Dorset Horn skin in this experiment.

ECONOMIC EFFECTS OF GRASS-SEEDS

Grass-seed infestation of sheep causes losses from vegetable fault in wool, reduction in wool value, ill thrift and mechanical damage, and damage to skins and carcases, and mortality.

Grass-seed infestation of sheep is a major problem in Australia. Grass-seeds, along with vegetable faults from burrs and thistles are the most widespread problem affecting the Australian Wool Industry. Wool Board figures of the late sixties showed that 55% of Australia's Wool was affected, the prevalence in New South Wales being 71%. Penalties are imposed because of the cost of removing fault from wool during processing and the associated wastage. This penalty will range from 10 cents to $1-00 or more a fleece according to the degree of fault. Severely affected fleeces must be carbonised. Carbonised wool has less tensile strength and therefore more limited uses. (J.W. McDonald, 1981).

Mutton and lamb carcases with any degree of grass-seed are not eligible for the export market. They may be trimmed for the local market. A survey of abattoirs on the western slopes of New South Wales by Hamilton showed downgrading due to wire grass (Astridia spp.) from 35% to 55% due to grass-seeds.

Sheep skins which are lightly seeded receive a 50% penalty and heavily seeded pelts are penalised 100% as seeds penetrating the skin leave small holes, which enlarge during tanning.

M.J. Hartley in 1973 gave an estimate of an annual loss of $800,000 in New Zealand of which 70% was attributed to barley grass (Hordeum leporinun), the loss being entirely based on loss of value of wool and pelts.

Grass-Seed Infestation at Forbes Abattoir

The Senior Meat Inspector at Forbes Abattoir estimated that up to 10% of all carcases had some degree of barley grass contamination which required trimming during the months of November and December, 1981. One grass-seed in a carcase is classified as one too many and it requires removal by trimming of the carcase. There were complete runs of sheep where every carcase required trimming - from mild to excessive, and on the odd occasion there was a total condemnation.

Losses Due to Grass-Seed Infestation at the Forbes Abattoir

Office staff at Forbes Abattoir have estimated that loss on initial trim would be 10-15 cents up to $1-00 on a heavy trim during the grass-seed period and loss due to pre-trim into the boning room (which is the second trim done after the carcase sets) is estimated at 30 cents per head.

Losses Due to Grass-Seed Infestation at Saleyards

A buyer at Forbes Abattoir estimated that animals which showed a heavy grass-seed infestation resulted in a discount of $2-00 per head and animals having a moderate infestation in the wool had a 50 cent to $1-00 discount due to possible skin damage.

CONCLUSION

Barley grass (Hordeum leporinum) is the major cause of grass-seed problems in the Forbes Pastures Protection District. In the spring of 1981, it was very prevalent due to ideal seasonal conditions for its growth. Barley grass seeds were either directly or indirectly involved in the death of nearly 300 lambs and wethers on three properties in which the writer was directly involved. The most common problem caused by barley grass seeds in the Forbes district is eye irritation which owners regularly treat to prevent blindness.

Grass seeds also cause considerable economic loss.

ACKNOWLEDGEMENTS

1. Acknowledgement is given with thanks to the District Agronomist, Forbes (Mr. C.W. Falconer) for information given on barley grass and its control in crops.
2. To Mr. Clive Johnson, local property owner, for information on his experience on barley grass and its control.
3. To Mr. John Hudson, Senior Meat Inspector, Norwest Beef Industries Abattoir, Forbes.

REFERENCES

1. D.F. Smith, Aust. J. Exp. Anim. Husbandry Vol. 8 (1968), p. 478- 483
2. The Growth of Barley Grass (Hordeum leporinum) in Annual Pasture, Germination and establishment in comparison with other annual pasture species. Pastures - The Farmers' Handbook series - compiled by J.N. Whittet, H.D.A. - N.S.W. Department of Agriculture, Edition No. 1, p. 165
3. Pastoral Plants of the Riverina Plain - Leigh & Mulham, p. 19
4. Australian Grasses Vol. 3 - Nancy T. Burbidge, The East Coast from South East Queensland to Victoria, p. 166
5. E.J. McBarron - Poisonous Plants of Western New South Wales - Department of Agriculture, N.S.W., p. 9
6. Sydney Dodd, D.V.Sc., F.R.C.V.S. - Agricultural Gazette of N.S.W., April 2 1919 - Notes on infestation of the skin, etc. of sheep by grass seeds
7. J.W. McDonald - Sydney University - Post Graduate Committee in Veterinary Science Refresher Course for Veterinarians. Proceedings No. 58 - on Sheep, p. 111-113 - Grass Seed infestation
8. G.E, Robards & J.H. Leigh, Australian Journal of Experimental Agriculture Anim. Husbandry Vol. 7, 1967, p. 528-532 - the Effect of Frequency and time of cutting on the Production and Quality of a Barley Grass Dominant Pasture
9. R.J. Campbell, G.E. Robards & D.G. Saville, Proceedings of the Australian Society of Animal Production (1972) 9: 225 - The Effect of Grass Seed on Sheep Production
10. G.M. Lodge & B.A. Hamilton - Australian Journal of Experimental Agriculture Husb. (1981) 21, 382-386 - Grass Seed Contamination of the Wool and Carcases of Sheep Grazing Natural Pasture on the North-Western Slopes of N.S.W.
11. J.M. George - Proceedings of the Australian Society of Animal Production (1972) 9: 221 Effects of Grazing by Sheep on Barley Grass Infestation of Pastures
12. B.A. Hamilton - Wool Technology and Sheep Breeding Vol. 26 (1978) 15-17 - Grass Seed Contamination of Sheep Carcases
13. G.J. Warr - Ag. Gazette of N.S.W. (1981) Vol. 92 (1) 27-28 - Barley Grass Can Lower Sheep Production
14. M.J., Hartley - N.Z. J. of Ag. Vol. 127 (1973) 33-35. - Wool Types Characterise Barley Grass Damage