Kiwi Post: The Art of Finding Disease

The International Conference on Animal Health Surveillance (ICAHS) comes to New Zealand in early May this year. This is a triennial event, and this is the third such event, so well done to everyone involved in getting us to host it.

Not the least of the roadblocks must have been the huge slab of irony that a conference on animal health surveillance should be hosted by New Zealand. This is like North Korea hosting a conference on democracy, or the Middle East hosting a conference on regional cooperation, or the White House hosting a conference on sanity.

New Zealand has many remarkable facets, but animal disease surveillance is not one of them. This in itself is quite remarkable on two fronts. First, being an island nation, heavily dependent on primary production, we are both largely safe from- and consequently at huge risk of- a devastating exotic disease coming into the country. The chances are low- although they get higher with every passing year and every increase in international travel- but the consequences are high.

Secondly, being almost exclusively pastoral with little housing and hence relatively low stocking rates, our (ruminant) stock are not exposed either to the diseases associated with housing (1), nor those associated with intensification. Our disease rates are therefore low.

Or are they? We have no compulsory disease database for individual animals. We have no national treatment recording programme or database. We have no compulsory requirement to record ‘normal’, endemic disease. And whilst we have a requirement to record and notify ‘exotic’ disease, a prerequisite for this would typically be recognising ‘normal’ disease first.

This has secondary effects all through production. Because disease is deemed insignificant or rare, its diagnosis is firstly, rarely taught, and secondly, deemed unimportant. It’s not at all uncommon to meet experienced herd managers who really have no idea what acidosis is, or milk fever, or metritis, or anything that we may take for granted. Of course, they would never admit that, being experienced, and typically full of testosterone, and so the ignorance is perpetuated.

And, given that disease is unimportant, and diagnosis even more so, a veterinary diagnosis is entirely superfluous and a waste of money. This is all very well, but it means that veterinarians’ knowledge of disease incidence and prevalence in New Zealand is highly limited, and focussed on disease incidence reported for commercial research purposes.
For example, we may cite the annual incidence of clinical mastitis as 12.7%, but this is drawn from a commercial research project looking at product evaluation (2). The incidence of hindlimb lameness has been cited as 10% for a 6 month period, but this was based on three farms chosen non- randomly in Canterbury (3).

Given that our recognition of normal disease is poor, it goes without saying that we are at risk from exotic disease recognition. If vets aren’t out on farms regularly, how many animals are missed before the sentinel case is spotted? Our data suggest that the mean number of professional (vet & tech) visits per 100 cows per year on dairy farms vary between 3 and 10, largely driven by regional variations in herd size. These data were gathered from Welfarm farms, people who have voluntarily enrolled in a national animal health and welfare programme. These farms are biased towards people who get this is important.

When we had our last major exotic disease ‘incursion’, an outbreak of disease and deaths caused by a novel variety of swedes in 2014 (4), it took an inordinate amount of (unpaid) work by local vets to pull the data together to determine the cause. And even then the first deaths were probably 6-8 weeks before the vets began to draw the lines. Thankfully it wasn’t infectious. But we still don’t know how many cows died and how many were affected.

While all this is a huge risk, it’s also a huge opportunity for New Zealand. A half- decent marketing department would have long ago recognised that our teeny incidence of, say, LDAs is well worth marketing when compared to almost all of our competitors. The current model is not fit for purpose for NZ Inc. There’s a subtle difference between passive and comatose surveillance.

In the first instance, farmers need to be engaged in the value of disease detection. Veterinarians will happily follow suit, and, if properly resourced by government, the various ministerial bodies I’m sure would be only too keen to lift the profile of disease surveillance. If not, New Zealand’s ICAHS conference would be better titled the Ironic Conference of Animal Health Surveillance.

1. Laven RA, Holmes CW. A review of the potential impact of increased use of housing on the health and welfare of dairy cattle in New Zealand. New Zealand Veterinary Journal, Volume 56, Issue 4, pp 151-157, Aug 2008
2. McDougall S, Arthur DG, Bryan MA, Vermunt JJ, Weir AM. Clinical and bacteriological response to treatment of clinical mastitis with one of three intramammary antibiotics. New Zealand Veterinary Journal, Volume 55, Issue 4, pp 161-170, Aug 2007
3. Bryan M, Tacoma H, Hoekstra F. The effect of hindclaw height differential and subsequent trimming on lameness in large dairy cattle herds in Canterbury, New Zealand. New Zealand Veterinary Journal, Volume 60, Issue 6, pp 349-355, Nov 2012
4. Bryan M, Hea S, Wilkinson S. A clinical and epidemiological analysis of swede-related deaths in Southland and Otago over winter 2014; Proceedings of the Society of Dairy Cattle Veterinarians of the NZVA Annual Conference, pp 269-286, Jan 2015. Publisher: VetLearn Foundation