ANIMAL HEALTH
Leptospirosis
Poor calving? Lepto may be the cause BY: ANDREW ROE
B
eef cattle pregnancy testing is underway around the country and while we are out and about on the farm, it’s a good chance to have a catch up about the previous season’s calving results. Every now and then we hear about some particularly poor calving/weaning percentages, especially in first calvers. Whether it be due to abortions, stillborn calves or calves dying early in life, the end result is that, come calf marking time, a proportion of the mob fail to turn up with a calf at foot, despite being scanned pregnant earlier in the year. When investigating these cases the potential causes we have tended to consider first are bovine viral diarrhoea (BVD) and trace element deficiencies, especially selenium and iodine, as well dystocia and,
of course, bad weather at calving time. However, based on several recent cases, including one confirmed just a couple of months ago, we are now including leptospirosis (lepto) near the top of the list. Leptospirosis is a bacterial disease, with the causative organism widespread in New Zealand farmed livestock and wildlife. The bacteria live in animals’ kidneys and are shed in their urine, contaminating waterways, pasture and feed. There are six serovars (strains) of the bacteria in this country and each of them has one or more species of animal in which they largely reside. This species is referred to as the maintenance host and they act as a reservoir of the bacteria. The maintenance host species does not often suffer any significant ill effects from harbouring the lepto bacteria. Disease is seen, however, when the bug is transferred from the
maintenance host to another species of animal. A common example in NZ is Leptospira interrogans, Pomona serovar. Pigs are the maintenance host for this serovar and so they rarely get sick when carrying it. However if cattle, sheep or deer become infected with Pomona it can cause a range of problems including illness and death in young stock, and abortions in pregnant animals.
Rural workers at risk Lepto bacteria can also infect humans. Leptospirosis is regarded as our most important infectious occupational disease, with farmers, shearers, meat workers, hunters and vets being at most risk, due to their contact with animals. Nearly all NZ dairy farmers vaccinate their stock against lepto, largely to protect themselves
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May 2021