ADULTS

Metabolic disease

The number of reports of displaced abomasums (DAs) in March increased by almost 100% following the same pattern as seen last year. It will be interesting to see whether the number of cases will peak in March as they did last year in contrast to previous years when April and May were the peak months. Is there an association with the weather or with turnout? We would be very interested to hear any ideas. High DA levels seem here to stay. Is the industry just accepting this as there appears to be little active effort to investigate and reduce the problem?

Figure 1: Number of monthly reports of DA in 2007 and 2006 compared to mean of 1997-2005.

After a fall to very low levels in February, reports of acetonaemia increased by over 200% in March. Levels were not unusually high (being very close to the long term average) but the large change suggests that there were major changes in cow metabolism during this month. Hypomagnesaemia and milk fever both remained low in March, particularly the latter. The low figures suggest that like last year it will be a good spring for staggers with around 50% of the long term average number of cases. So far this year the number of milk fever reports has been lower than any previous year except for 2001. It might be thought that milk fever treatment would be of gradually reducing importance, at least from a veterinary perspective, as more farmers treat their own cases. However the picture painted by the NADIS data is more complex. Although the general trend is downwards, the slope is slow (at just over 2% per year) and the individual variation between years is very large. This is particularly the case for the first three months of the year where the evidence for any reduction is poor. We would like to hear your thoughts on what’s driving the slow decline in total numbers and whether you’ve seen a change in seasonality of the disease. The data so far this year suggest that milk fever levels will remain low until at least July so farms with higher than average cases or with outbreaks should be closely investigated.

Figure 2: Changes since 1997 in the number of reports of milk fever over the whole year and in the first three months

Fertility

Although both increased the number of reports of both non-detected oestrus and anoestrus remained low in March; another record low (excluding 2001) for anoestrus and an almost record for non-detected oestrus (beaten only by March 2003). These low March figures following low January and February figures suggest that fertility has been good since the turn of the year. Is this another indication of cows having good quality feed in front of them? The only major fertility problem to be significantly above average in March was ovarian cysts. However in comparison to last month the number missed heats per ovarian cysts increased from around 6 to just below the long term average of around 8.5. There doesn’t appear to be any long term consistent trend (see Figure 2) but the data clearly show that there are different risk factors for ovarian cysts and missed heats. We would be interested to hear what factors you think are keeping ovarian cysts rates relatively high.

Figure 2: Effect of year on the number of non-detected oestrus cases per report of ovarian cysts (Winter figures based on data from November to March)

An interesting endometritis problem was reported by aGloucestershire vet. He reported that a 150-animal dairy farm with an ongoing endometritis problem had Mycoplasma bovis and Histophilus somni identified from swabs. Neither of these bacteria are the typical bacteria associated with endometritis. Investigation is ongoing.

Cattle lameness

The OTMS scheme has been effectively dismantled for over one year. Lame cattle that are not fit for transport are thus worthless unless they fit the criteria for the OCDS. It might have been thought that this would mean that there would be more veterinary treatment of lame cows however this has clearly not been the case with the overall number of lameness cases continuing to decline. Overall lameness reports in 2006 were lower than in any previous year and 2007 has continued this trend with overall figures so far this year being less than 80% of the already low 2006 figures to the same date. We need to know whether this reduction reflects the situation on the ground or whether it reflects reduced veterinary involvement. The first is good news, the second is not! Lameness is the most important welfare problem in dairy cattle and the NADIS data are the most current and widest ranging data we have on its prevalence. With a bit more support from government the data could identify clearly whether the reduction in lameness is real.

Even if the NADIS data are taken at face value they still show that significant lameness is occurring on UK dairy farms. This is highlighted by individual vet reports with one NADIS vet reporting that after an investigation instigated by a Defra vet they found that 15% of a 320-cow herd was affected by digital dermatitis despite routine foot bathing. Even with rose-tinted spectacles the battle is far from won.

Fig 3: Number of reports of lameness in January to March from 1997 to 2007.

Mastitis

Sand bedding is currently very popular in the US because of its impact on lameness and mastitis. A Lincolnshire vet reported that one of his dairy farms has seen a massive reduction in mastitis cases since changing cubicle bedding from straw to sand in 2004, with cases reducing from 104 in 110 cows in 2004 to 45 cases in 135 cows in 2006. We would like to hear of other reports of using sand, as except for the disposal problem, sand-bedded cubicles seem to offer significant benefits over conventionally bedded versions. The vet above reported that he believes that some of the improvement was due to the use of internal teat sealants throughout the herd, with those that require antibiotics also getting teat sealants. This combined therapy has proved very popular with around 50% teat sealants being used in combination with antibiotics, despite the obvious increase in cost of the combined therapy. Reports of the use of teat sealants would be very welcome, particularly the process of how combined therapy is chosen. Interestingly on the same farm megasupplementation with vitamin E has been used to control retained fetal membranes (RFM) with 1500 IU of Vitamin E being given per cow per day via the dry cow minerals. Current UK recommendations are equivalent to less than one tenth of this figure! More recent American (NRC) recommendations suggest a higher figure of around 1000 IU for dry cows. The primary effects of vitamin E appear to be on mastitis and RFM, with the evidence for the latter being a lot stronger than the former. The response of the herd will be further monitored. Is anybody else using vitamin E megasupplementation?

Other diseases

Bovine iritis (silage eye) cases usually peak in March as the final silage of winter is fed out. However this year’s figures have been much lower than normal and lower than 2006 which was already very low. These low figures suggest that the quality of baleage is probably better this year than average, although it cannot be discounted that the reduction in cases is due to vets being less likely to be called out to see such cases. Again with a bit of additional support the NADIS data would provide even more valuable information on an important and painful disease (it is the most commonly reported disease caused by Listeria in cattle).

Figure 4: Reports of bovine iritis by month showing that the peak of cases has been much lower in 2006/7 than average.

A Yorkshire vet reported confirming persistent infection (PI) with BVDV in a three-year-old milking cow, highlighting the fact that not all PIs are scrawny calves which get mucosal disease. They can persist in the herd and have several calves (which will almost invariably be PIs), whilst causing significant economic loss to the farm.

CALVES

In March both calf scour and enzootic pneumonia remained at levels well below the long term average, with the number of pneumonia outbreaks being the lowest ever recorded by NADIS except for March 2001 and the number of scour outbreaks (less than half the number reported in March 2001). Again it’s unclear whether these reductions are due to better disease control or less use of vets. As seems to be the theme of this month’s report additional support to collect more data, such as that from sentinel farms, would greatly enhance the value of the NADIS data. We would be very interested to hear all opinions on how much of the low level of calf disease is due to it being actually less common or less commonly seen by vets.

Figure 4: Change with time relative to 1997 cases in the number of reports of calf scour between January and March

Further Reading

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