A previously reported study into an apparently increasing incidence of Nephritis in lambs in the Murray- Mallee area of SA is continuing.
Unfortunately the study has been unsuccessful so far in describing a consistent likely aetiology for the condition or means of reducing the syndrome. Some on farm interviews have been conducted, and further samples collected from an abattoir, and a closer examination of spatial and temporal patterns is occurring, leading to an increasingly complex picture.
Project aims have been altered to address reporting of the condition at abattoir level and further sampling, examination of affected lines, interviews of producers and recommendations to the SA sheep industry are planned for the coming year.
The South Australian Enhanced Abattoir Surveillance program (EAS) has been in operation for 10 years and inspectors are employed to examine lines of sheep, both mutton and lambs at two major export abattoirs in South Australia. Requirements are that there must be at least 100 sheep per line, and the sheep bodies and viscera are examined by trained staff for 19 different conditions, and an estimate of incidence in the line is determined and recorded. These statistics are reported to PIRSA and if incidence exceeds a determined threshold a letter is sent to producers with the report and a factsheet on the subject. (see examples in Appendix)
Nephritis is a condition that inspectors report daily to PIRSA, these reports are consolidated and then reported to districts in SA on a monthly basis. To date all inspections have been conducted at Thomas Foods International (TFI) abattoirs at Murray Bridge and Lobethal, SA; but the program is about to be taken up by a JBS abattoir at Bordertown, SA as well. TFI slaughter about 50% of SA sheep, and JBS is a major processor as well.
A study of the data shows that semi arid cropping and grazing country with average rainfalls between 250 to 400mm per year have a higher incidence of this condition in SA with higher rates in lamb lines than older sheep.
In a previous report an objective of the study was to attempt to identify a case definition, causality and risk factors for the condition, but only the first has been achieved to date.
It is difficult to find papers on interstitial nephritis in lambs or even textbook references. “White spot kidneys” in calves may be due to ascending urinary tract infections.1 Leptospira are described as a cause in cattle also. “The aetiology of interstitial nephritis remains obscure” (p 686) was a statement made in 1966, and appears to be still the case. Textbooks and papers also refer to the fact that this type of lesion, particularly milder forms are relatively common post mortem findings, of uncertain importance.
Leptospirosis has been described as a cause of “white spotted kidneys” in lambs2 and this possibility still needs to be tested with some serological surveys.
The study is continuing in order to attempt to identify risk factors including Leptospirosis, lamb marking processes, transient rumenitis, environmental factors and an assessment of financial impacts.
Rather than a general survey of a cohort of regionally affected producers, it is intended to instead work with a small group of producers with regular and consistent reports of nephritis, and good management and records.
Since JBS allocates individual body numbers and weights it may also be possible to correlate the extent and number / percentage of nephritis lesions with decreased lamb body weights for the first time when data becomes available from this source.
In addition, another outcome of this study may be to make recommendations to abattoir staff about classification of nephritis lesions.
Results of the study are being reported to the funding body for the EAS Program, the SA Sheep Advisory Group, and to SA sheep producers.
Some initial sampling and analysis occurred on one property near Murray Bridge in order to develop a case definition at abattoir level and laboratory level.
Case definition – Inspectors: “any kidney that is misshapen, or has a visible white mark or spot on the surface. Any lesion seen on cut surface of the kidney” or as described in the Factsheet:
“Nephritis is the term used to describe damaged kidneys. The damage seen at the abattoir may have been caused:
Case definition – pathologists (quoted from pathology reports):
"Diagnosis: pyelonephritis & tubulointerstitial nephritis, multifocal, chronic, mild to marked, with interstitial fibrosis, lymphofollicular hyperplasia & focal abscessation."
Comments (partial extract):
"The chronic inflammatory lesions identified within the submitted kidney samples are essentially similar and suggest a spectrum from mild to moderately severe lesions, although, subjectively, there is not much difference between the kidneys grossly categorised as moderate vs severe. These lesions are compatible with chronic pyelonephritis and multifocal areas of cortical tubulointerstitial nephritis. This likely reflects an ascending bacterial urinary tract infection with extension of the offending agent from the pelvis into the renal parenchyma. The consistent involvement of the renal pelvis (especially in the mild category, where there are few cortical inflammatory foci) suggests that haematogenous infection of the kidneys (i.e. embolic nephritis) is a less likely route of infection. In one of the 'severe' kidneys, there is formation of a small abscess within the inner cortex.
No specific inciting cause can be identified microscopically, i.e. no bacteria, fungi, parasites, etc. Leptospiral organisms were not detected in a fresh kidney sample tested by PCR; however, this does not fully exclude this as a potential possible agent."
Results to date Part 2
On farm Surveys.
A general questionaire was developed to attempt to gather basic epidemiological data including breeds of sheep , lamb marking procedures, feedlot practice, water sources, mortalities at various ages, pasture and economic impacts observed. Although it was intended to interview 17 producers with high incidence (positive) and 19 producers with no reports (negative) in the Mallee area; to date only 5 positive and 2 negative producers have been interviewed. It was originally intended that 2 PIRSA vets and one PIRSA animal health officer conduct these surveys, but only 1 vet has been available.
From this small sample size it has been difficult to draw any conclusions except to note that all properties appear to have similar ecology and management systems, but varying levels of management input and expertise. All producers are mixed sheep / cropping enterprises, but some are predominantly one or the other. In the mainly cropping properties sheep are seen as the less important enterprise and sometimes management reflects this.
However, properties that have good or average managment all apear to have similar incidence of reported nephritis. Other observed similarities appear to be:
Hence there appears to be a disconnection between observed effects, and the PIRSA Fact Sheet and textbook statements about causes, effects and treatments.
A total of approximately 1400 kidneys, from two producers, removed by inspectors for Nephritis were examined at an abattoir and sorted into mild, medium and severe categories. Only 15% and 25% of the total number of kidneys were classed subjectively as severe. These were kidneys with marked, obvious lesions of 3-10 mm diameter, multiple white spots on external and / or cut surface, with visible clear cysts or abcesses, or grossly deformed. Some sample photographs are attached.
Literature sources state that pathological effects occur when parenchyma damage exceeds 75%, so it is reasonable to suggest that “severe” affected kidneys may be having health or production effects, although without individual body data and life history records it will be difficult to prove this.
The study has been designed as a low cost, low input study with limited resources attempting to provide practical answers to producers who have identified an issue of concern.
Although some of the original objectives of the study have not been achieved at this stage, the intention is to continue as time and resources permit.
Since only 15- 25% of kidneys classified as “nephritis” on the slaughter floor have “severe” grade lesions that could reasonably be affecting production, a new objective of the study will be to investigate whether low grade lesions should be reported at all to producers. If this occurs an expected result would be a dramatic reduction in reports, which reflect more of the real impact of the condition in the industry. The producers then affected by consistently high incidence of “severe” lesions could then be more closely investigated in order to determine risk factors and possibly aetiology.
An interesting suggestion for a contributing factor for lesions in 9 to 11 month old lambs that are described as being "pyelonephritis & tubulointerstitial nephritis, multifocal, chronic" and apparently due to ascending urinary tract infection, is that there could be a role for transient rumenitis in these lambs causing change in urine pH and growth of microorganisms3. This rumenitis may be due to inappropriate feedlot induction in some of these lambs. This hypothesis may be difficult to prove, but questions around feedlot management may be helpful in the ongoing survey.
In addition, if body weight data can be correlated with nephritis incidence in a line of sheep it may be possible to quantify losses due to this condition.
The PIRSA EAS program has been very well received by SA producers and continues to be 80% funded by SA Industry, and is seen as delivering helpful, timely and good quality advice to producers, agents, and others engaged in Industry.
Dr Elise Matthews, PIRSA EAS Program Manager, 33 Flemington St, Glenside
Mr Peter Zviedrans, PIRSA PIIMS data manager, 33 Flemington St, Glenside
Dr Cleopas Bamhare, Manager, PIRSA Disease Surveillance Program, 33 Flemington St, Glenside
Dr David Rutley, Thomas Foods International, Murray Bridge, SA