NADIS is a network of 40 veterinary practices and six veterinary colleges monitoring diseases of cattle, sheep and pigs in the
NADIS disease bulletins are written specifically for farmers, to increase awareness of prevalent conditions and promote disease prevention and control, in order to benefit animal health and welfare. Farmers are advised to discuss their individual farm circumstances with their veterinary surgeon.
Fertility reports continued to decline in August and are now back below average. This year the number of fertility reports has been over 10% less than last year, primarily because of the very low number of reports of anoestrus recorded at the beginning of the year, although reports of the latter been above average for the last three months.
Indeed both anoestrus and non-detected heats have been above average this summer. This might, at first thought, be linked to the warm dry summer however the total number of cases reported this summer have been less than last year despite 2005 being significantly cooler!
The number of abortion problems reported in August remained below average (as it has been for most of the year). However comments from NADIS vets have provided interesting food for thought.
One abortion storm reported in August was thought to be due to feeding frosty barley straw earlier in the year, and there were continued reports of outbreaks of abortion involving both BVDV and Neospora.
The latter, despite only being recognised for a short period of time, is now probably the most commonly diagnosed cause of abortion in cattle. The link between Neospora and BVD has not been closely examined but there is definitely increasing evidence of a strong link
Several NADIS vets reported significant endometritis problems in August; overall the number of cases reported was similar to that reported in July, continuing the trend of above average numbers of cases for every month in 2006.
One NADIS vet linked the increases that he was seeing to subclinical hypocalcaemia; there certainly appears to be no link to clinical milk fever as the number of reports of that disease has been below average. We need more data!.
Figure 1: Seasonality of reports of endometritis so far this year compared to previous years, showing that every month this year has had more reports than the long-term average
Overall the number of cases of metabolic disease reported by NADIS veterinarians was well below average in August with hypomagnesaemia, milk fever and acetonaemia all showing significant drops from the previous month.
In particular there was no evidence of any of the normal seasonal increase in milk fever cases. Indeed the number of cases seen so far this year is lower than any year except for 2000 and 2001. Does this indicate a true reduction in incidence or increased treating by farmers?
Figure 2: Trend in milk fever reports by year since 1997 (data from January to August), showing consistent trend downwards from 1997 to 2001. Are we at the start of a similar trend now?
One disease which may provide a key is the ‘downer cow’. This disease has a strong link to hypocalcaemia (as one of its major risk factors) but unlike milk fever this disease is less susceptible to changes in the rate of veterinary rather than farmer treatment.
Thus the ratio of cases of downer cows to milk fever cases may provide evidence as to whether changes in farmer practice rather than changes in true incidence are responsible for the recent downturn in milk fever cases.
Figure 3: Change with time in the ratio of reports of downer cows to reports of milk fever.
As Figure three shows there have been major changes in the ratio of reports during the last nine years.
The reduction in the number of milk fever reports recorded at the end of the nineties was associated with a marked increase in the ratio of downer cows to milk fever cases, indicating strongly that the decline in veterinary treatments of hypocalcaemia was caused by an increase in the percentage of farmers treating their cows rather than by a true fall in the incidence of milk fever.
However the reduction seen over the past three years has been linked to a fall in the ratio, so this may indicate that we are getting better control of milk fever, with better nutrition during the dry period being found on more farms whether it’s complex DCAD diets or simply increasing the supply of magnesium chloride. We would be interested to hear comments.
August was warmer than average in most areas but also wetter but there were no signs that the change in weather led to major increases in lameness.
Of the four main diseases only foul-in-the-foot showed an increase in reports, but even foul-in-the-foot levels remained significantly below average. White line disease reports, which usually begin their late summer increase in August, fell markedly this year to the lowest number ever reported in August.
Given that the NADIS data suggest that the outside environment is a significant risk factor for white line disease the fall in combination with the increased rainfall is unexpected, but emphasises the complex web of factors which lead to lameness in dairy cattle.
Figure 5: Current trends in white line disease reports. The increase in July was followed by an unexpected fall in August but it is likely that the disease will be more commonly reported in September and October.
As predicted the high number of cases of summer mastitis reported in July was followed by a significantly lower number of reports in August.
It is not entirely clear why this should be the case; comments are welcomed! Interestingly there is no such relationship between reports in September and those in July or August with r2 being <0.01 in both cases (rather than 0.8 as in the July/August comparison
Figure 6: Relationship between number of reports of summer mastitis in July and September. Unlike the data for August the number of reports in July cannot be used to predict the number of reports in September
Again, like lameness, the increased rainfall in August was not associated with a large number of lungworm cases, which remained well below average in August. However there is absolutely no relation between the number of reports in August and those in September or October.
The figures for lungworm in August are consistent with the decline since 1997 in the number of outbreaks reported by NADIS veterinarians during the peak August – November period.
However this decline has not been matched by the change in the total number of cases which has declined less significantly (Figure 7). So even though the focus of lungworm prevention needs to be the autumn period we need to be aware of risk factors outside of that period.
Figure 7: The NADIS data show that there has been a significant decline in the number of lungworm reports from August to November, but increases in the number of reports outside this period has meant that overall the decline has not been as marked.
The number of New Forest Eye outbreaks increased in August to its usual seasonal peak. Although the actual figures were marginally less than average, based on the NADIS notes, in many cases their severity appears to have been worse than average.
If this is the case it may be worth asking the question whether a vaccine against New Forest Eye, such as the one available in Australia or similar, may be of value on UK farms.
Figure 8: Seasonal changes in the reporting of New Forest Eye by NADIS veterinarians
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