NADIS Cattle Report and Forecast – September 2006

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
 

Metabolic disease

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.

Lameness

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.

 Mastitis

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

Calves

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