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Oats Sickness in Dairy Cattle
Stephen Jagoe, BVSc, District Veterinarian, BEGA
Green oats (Avena sativa) has traditionally formed the basis of winter feed production in the Bega district until fairly recently. Being drought tolerant, areas of planting increase in drier years. However ryegrass now has replaced oats as the main pasture species in winter. One of the reasons why ryegrass has become popular is because of the risk of oats sickness, but more so because of greater feed production and feed value.
In any one year 50% of properties having oats may suffer some form of oats sickness and within these farms 5-25% of the herd is usually affected. Occasionally 80-90% can be affected. 'Oats sickness' has also occurred in cattle grazing barley and tetilla ryegrass, indicating that a change to grazing other winter cereals may not eliminate the problem. There is one record of the condition occurring in beef cattle.
BACKGROUND:
Oats sickness has been previously investigated in the Bega district by Tim Jessep and Bruce Adams. Results of these investigations include:
1. Blood calcium in affected animals can be significantly lower than in normal animals.
2. No differences have been found between affected and unaffected animals in blood phosphate, protein, albumen, magnesium, copper, alkaline phosphatase and SGOT (AST).
3. Nitrate intoxication was suspected in the 1980's - however blood, faeces, rumen content and plant nitrate levels have usually been normal. Often plant nitrate levels were found to be low.
4. Barley yellows dwarf virus [BYDV) infection appears to be more extensive on crops causing oats sickness. This virus is transmitted by certain species of aphids. BYDV does result in increased plant nitrate. However nitrate intoxication doesn't appear to play a role in oats sickness.
5. Weather conditions - heavy frosts are associated with the occurrence of the disease.
6. Length of grazing period - oats sickness is usually associated with grazing times exceeding two hours and is rarely encountered if grazing is restricted to less than one hour.
7. Rumen protozoal populations are severely depleted in affected animals. As a result rumen gas production is markedly depressed. The presence of undigested carbohydrates [from concentrate feeding) may create an altered microflora and abnormal fermentation and could induce the diarrhoea observed in affected animals.
The conclusion from previous investigations is that crops contain an agent directly toxic to rumen microflora. Only a proportion of plants or a particular area of paddock may be involved. The role of frosts, BYVD virus or possibly fungi were considered.
LITERATURE REVIEW:
A similar condition in cattle occurs in the 'once fertile' Darling Downs of Queensland and is associated with 'red-tipped' oats (Thompson and Bywater). Cattle grazing affected crops show low blood phosphate and slightly depressed blood calcium and magnesium. 'Red-tipping' results from oats grown on soils depleted of minerals and nitrogen. Zinc deficiency was suspected, but no response occurred to supplementation. Heavy nitrogen application (often at uneconomic rates) alleviates the problem in soils of adequate potassium.
'Cold cow syndrome' [Jack & others) has been reported in England and resembles oats sickness. A mycotoxin was suspected but not proven in its first season. The following season the condition recurred. Plants (ryegrass) causing the syndrome contained a significantly higher level of water soluble carbohydrate than normal plants. A state of acidosis may have resulted. Further work has not been reported.
Schneider et al. reported on field and experimental mycotoxicosis in goats, sheep and cattle grazing green oats. A fungal pathogen Dreschiera campanulata was isolated from affected plants and experimentally was toxic to ducklings, goats and sheep. Characteristic lesions included necrosis of the forestomach mucosa. In field outbreaks diarrhoea, photosensitisation and death occurred in goats, in cattle diarrhoea and reduced milk production resulted.
Investigations into conditions of sheep grazing irrigated legume crops in the Hillston district of NSW showed low plant fibre and high protein levels. Ammonia toxicity resulted in a number of syndromes including nutritional scours and dysentery (Curran).
FIELD OBSERVATIONS
1988
Three outbreaks were notified in the Bega district and one report was received from Dungog.
1. 24/07/88
3/54 Animals severely affected - in October 1987 30/60 milking animals were affected in the same paddock.
2. 30/07/88
6/230 animals affected when animals left on paddock all day. On 3/8/88, 40/230 animals were affected when left on the same crop overnight. Milk production decreased 200 litres.
3. 20/08/88
Cattle were being rotated between a ryegrass/clover crop and an oats crop. They were left longer than normal on the oats crop during the day and 12/80 animals were affected.
4. 13/09/88 (Dungog)
18/65 animals being fed greenchop ryegrass were affected with an oats sickness-like condition. 3 animals went down, all affected animals were scouring and agalactic.
No outbreaks were notified in 1989 due to excellent seasonal conditions resulting in a small hectarage only of oats being planted.
1990
Two minor outbreaks occurred in the Bega district (again reflecting good seasonal conditions) with one outbreak at Gloucester (investigated by District Veterinarian, Gloucester) and another near Camden (District Veterinarian, Camden).
1. 20/08/90
10/109 cattle were affected grazing a mixed ryegrass and oats paddock. The ryegrass component of the paddock looked healthy. The oats portion showed evidence of yellowing and was stunted in comparison to the ryegrass.
2. 31/07/90
4/50 animals were affected, and was accompanied by rapidly decreasing milk production of the herd.
3. 06/07/90 (Gloucester)
90/120 animals affected when given access to a 'rusted' oats crop overnight. The paddock showed evidence of waterlogging. Some animals were affected a few days later when allowed into the same paddock. Herd milk production dropped 25% during the outbreak.
4. (Camden]
8/135 affected animals and a herd milk production drop of 20-25% occurred on reasonably healthy looking oats crop.
RESULTS OF LABORATORY EXAMINATIONS;
| 1. | Rumen pH: | Usually less than 6; some animals approached 5 | ||||
| 2. | Protozoal counts: | [large protozoa, McMaster counting chamber, formalinised samples]. | ||||
| Affected: | 3057 [760-6060] /ml n=10 | |||||
| Controls: | 45060 [10100-86000] /ml n=10 | |||||
| 3. | Gas production: | |||||
| Affected: | 8.0 ml/50 ml rumen content/hour n=12 | |||||
| Control: | 13.3 ml/50 ml n=21 | |||||
| 4. | Carbohydrate: | |||||
| Control crops: | 33-172 ug/mg n=3 | |||||
| Affected: | 116-163 ug/mg n=3 | |||||
| 5. | Plant Analyses | |||||
| OUTBREAK | ENERGY MJ | PROTEIN % | DDM % | |||
| 1. Bega | 10.0 | 5.9 | 67 | |||
| 2.Bega | a. | 10.0 | 4.4 | 67 | ||
| b. | 9.4 | 4.5 | 63 | |||
| 3. Bega | 10.6 | 9.1 | 71 | |||
| 4. Bega | a. | 10.8 | 12.3 | 72 | Ryegrass | |
| same paddock | b. | 10.7 | 8.1 | 71 | Oats | |
| 5. Bega | a. | 10.8 | 7.8 | 72 | Re grazing | |
| b. | 10.6 | 8.2 | 71 | Re grazing | ||
| c. | 10.8 | 5.8 | 72 | At grazing | ||
| 6. Gloucester | 10.8 | 8.6 | 72 | |||
| 6. | Rumen ammonias: | |||||
| 1988 Bega - average: | 42.3 mg/litre (8.8-94.4) n=7 | |||||
| 1990 Gloucester - range: | 3-12 mg/litre n=8 | |||||
| Adequate: | 50 mg/litre | |||||
| Toxic: | 500 mg/litre | |||||
DISCUSSION
Green oats has been associated with a number of conditions:
(i) Nitrate/nitrite toxicity.
(ii) Nitrate gastroenteritis.
(iii) Water belly' (malfunctioning rumen occurring in the Gippsland region).
(iv) 'Oats sickness'.
It appears that the results of previous investigations have excluded the first two conditions and 'water-belly' appears to only affect individual animals. 'Oats sickness' has regularly occurred in the Bega district, but is now known to occur regularly on the Darling Downs and in coastal areas. Dairy cattle appear to be the only animals regularly clinically affected and this may be due to the role of supplementary concentrates.
Conditions known to result in lowered protozoal numbers and decreased rumen function include:
(i) Lactic acidosis.
(ii) Inappetence for 12-24 hours for any secondary reason e.g. TRP, displaced abomasum.
(iii) Monensin toxicity.
Again these syndromes (as primary conditions) excluded by investigations to date.
Results of investigations indicate that oats crops inducing oats sickness have a deficiency of crude protein at levels insufficient to maintain normal rumen conditions (H. Oddy, pers. comm.). Low plant nitrogen results in decreased microbial multiplication, with concurrent decreased incorporation of carbohydrate into microbial biomass. Secondary fermentation of carbohydrates fed in the dairy (usually increased in Winter) results in a relative acidosis. Altered intestinal conditions result in diarrhoea with its resultant loss of minerals (oats is low in Ca and Mg anyway).
Inappetence results due to decreased microbial digestion and agalactia is the final result. (See figures 1 and 2). A disruption of the energy cycle (principally propionate) appears to be implicated.
Predisposing conditions appear to be dry winters, dryland system of farming and inadequate application of nitrogen fertilisers. Most crops have no history of nitrogen application at, or after, crop establishment. Nitrogen was added to the crop involved in the Gloucester outbreak, but waterlogging may have caused volatilisation of available N. Superphosphate is routinely added to affected crops of establishment in the Bega district. Low soil fertility appears to be important in the condition's occurrence on the Darling Downs.
Barley yellow dwarf virus infection of the crop is routinely involved. However infection may result due to nitrogen stressed plants, as the infection can be limited by heavy application of nitrogen (E.Havilah, pers. comm.). Apparently BYDV also increases plant protein levels by 3-4% (H.Kemp, pers. comm.), so it is conceivable that without viral infection of the crop, oats sickness may be more widespread, or more debilitating to affected animals.
The condition is traditionally seen in dairy cattle. However the productivity of sheep and beef cattle grazing similar quality oats crops is likely to be limited due to inadequate protein levels. Further investigations may be indicated here.
Dairy cattle perform best consuming a balanced ration containing approximately 16% crude protein. When pasture levels of protein are as low as those in cases of oats sickness, to maintain normal rumen conditions, supplementation with high protein feeds may be necessary (see figure 3). Straight urea (46% Nitrogen) may also be considered but risks toxicity to stock.
CONTROL OF OATS SICKNESS.
(i) Don't grow oats. Ryegrass in normal seasons is a much more productive and more digestible feed than oats. However in very dry years oats can outperform ryegrass.
(ii) Attempt to have a legume component to the crop, or recently before crop establishment.
(iii) Add nitrogen fertiliser pre- and post-grazing green oats crops.
(iv) Restrict grazing time to less than two hours - however this restricts crop productivity.
(v) Feed a high protein supplement (with a component of rumen digestible protein) in the dairy. New season lupins will be economic if the management system is adapted to feeding these. (i.e. a second silo may be needed).
CONCLUSION:
Year around milk production requires a constant source of high quality pasture for dairy cattle. Seasonal conditions interfere with this supply. Certainly on the Far South Coast of NSW periods of low quality pasture occur, traditionally winter, but occasionally hot dry summers will also result in poor pasture quality. Increased supplementary feeding will not replace adequately protein supply that can be produced by pasture. Oats sickness appears to be a condition that reflects the quality of the season and can in some years severely limit milk production from a whole district. On the basis of investigations presented in this paper, hopefully agronomic advice and practices will help alleviate losses that result from this condition.
BIBLIOGRAPHY
Jessup, TM - Department of Agriculture, Bega, Files
Adams, BS - Department of Agriculture, Bega, Files
Oddy, H - NFEU, Menangle, pers. comm.
Havilah, E - Pasture Research Unit, Berry, pers. comm.
Kemp, HW - Department of Agriculture, Bega, pers. comm.
Curran, GC - 'Suspected Ammonia Toxicity in Sheep', pre-publishing draft
Schneider, DJ - Marasas, WFO; Collett, MG; Van Der Westhuizen, GCA; 'An Experimental Mycotoxicosis in Sheep and Goats caused by Dreschlera campanulata, a Fungal Pathogen of Green Oats' - Onderstepoort Journal of Veterinary Research, 52, 93 100 (1985)
Jack, EJ; Boundy, JA; Mann, JC; 'Cold Cow Syndrome' in Letters, Veterinary Record, July 9th, 1983
Veterinary Investigation Service; 'Cold Cow Syndrome in the South-West'; Veterinary Record, June 23rd, 1984
Thompson, PJM; Bywater, JW 'Red Tipped Oats'. Queensland Agricultural Journal, May - June 1987
Nocek, JE; Russell, JB; 'Protein and Energy as an Integrated System. Relationship of Ruminal Protein and Carbohydrate Availability to Microbial Synthesis and Milk Production'. Journal of Dairy Science, Vol 71, No 8, pp 2070-2107, 1988
Lean, I; Nutrition of Dairy Cattle, p 351. Post Graduate Committee in Veterinary Science, July 1987