Review/Oorsig Volume 22, Issue 05 - Page 24

Oorsig/Review overall prevalence of EBL in the country, but it certainly seems likely that it is high amongst dairy herds. If the within herd prevalence is very high (more than around 70%) it is very difficult to eradicate the disease as a certain degree of transmission still occurs even if you do all you can to reduce the spread. If a herd has a lower prevalence it is certainly possible to eradicate the disease if you can reduce the spread (by not re- using needles, rectal gloves etc) and ensure that EBL free heifers are introduced into the herd, while gradually culling out the infected cows. If a herd is lucky enough to be free from the disease (and we don't know how many of these there are, especially in the big dairy areas) it is well worth them taking care to prevent its introduction by either buying from EBL free herds or quarantine and testing of brought in cattle. In terms of the cost of the disease, a large study in the US found a 3% reduction of milk yield in infected herds as well as increased culling so it is certainly worth eradicating if possible. NYSCHAP has some useful resources on reducing BLV spread (google NYSCHAP BLV). There is a very sensitive BLV ELISA which can detect a single infected cow in 250 and is a useful screen to find out if herds are negative, but as far as I know it is not currently available in South Africa, although if awareness of the disease and demand for testing were to increase then maybe that might change? TC - 4 May 2017 In KZN and especially our inland dairy herds, the incidence of EBL positive titres is anything between 20 and 80% of a herd!! With herds milking between 400 and 2000 cows we are daunted by the idea of initiating a culling programme. Our practice also wonders just how effective the single-glove approach is when there are so many other possible fomites. In tiny European herds the elimination of EBL is another ballgame. I recall sitting alongside a German colleague and his looking at me “extremely skeef” when I told him our herd sizes and the number of rectals (yes some of us still palpate!) a day/week/ lifetime. Frankly we aren’t convinced – despite some stern papers and lectures by illustrious colleagues – that the EBL disease warrants too much attention, especially when compared to several far more costly conditions. Nevertheless, were someone to market a vaccine, we’ll be near the front of the queue! ECONOMIC IMPACT PI - 21 Aug 2002 A decent analysis of the disease under SA circumstances needs to be done before this 24 question can be answered. This must take into account economic impact of the disease (data from elsewhere in the world), plus the demographics and economics of the industry/herd plus the epidemiology of the disease (including what we know about it in SA). What I can say is that I looked at the available literature a few years ago when we were designing the new BSE certificate, and there was a spectrum of opinion from “severe economic impact” to “no discernible impact” to “you can't do anything about it anyway”. There was enough evidence there to convince us that some consideration of the disease is warranted, thus its inclusion for insurance and AI bulls. Ernst Arndt felt very strongly about the latter if I remember correctly. My gut feel at this stage is that it's too late for our dairy industry as a whole to 'nip it in the bud', and that it would take a major eradication campaign. We have bigger fish to fry at the moment, so I just can't see this happening. However, your question was on a specific herd. One approach which I see getting quite a lot of support is simply to eliminate transmission opportunities wherever possible. With the high turnover rate of most high-producing herds this can lead to a marked reduction in the disease incidence within 2 to 4 years. Practical steps would be: • • • • • Use needles only once Use rectal gloves only once (or disinfect between cows) Disinfect all dehorning, tagging, claw trimming and other similar equipment between uses Break transmission via colostrum: This one's controversial, but recommendations are to test cows and only use colostrum from negative cows, or use some commercial substitute (Any available in SA??) Segregating the herd into neg and positives would also help, but may not be possible. AH - 21 Aug 2002 I tend to agree that there is much more EBL out there than we think (my opinion). The feedback from the KZN will be interesting. What we need to ask is what economic impact does it have? Once an economic impact/value is tagged to it, the importance can be quantified. Embrio Plus, Taurus and other semen exporters will put a different value on EBL than a dairy. For example, I have seen it clinically in Dairy breed bulls >7 yrs old. Most of the time one sees it clinically in older (7-8 yrs) animals and I don’t know if most dairy cows last that long. I think one needs to consider the insect/biting flies as well.