Wednesday, July 6, 2022

Theories being sifted

Being left with unexplained wet-dry hoggets at the end of lambing is frustrating.

The phenomenon isn’t new but the reason behind it has never been uncovered, despite many farmers working with their local vet on this.

The problem, identified as foetal loss in maiden ewes (as both hoggets and maiden two-tooths are affected), can result in a loss of between 10-30% in a year, although some farmers are reporting losses up to 40%.

Awareness of the problem has become widespread, prompting further attention and investigation by this country’s agri-research experts who have set up a working group in response. Known as the Fetal Loss in Maiden Ewes Working Group, it is headed by Dr Anne Ridler of Massey University and comprises some of the country’s leading animal-health specialists. The group held its first meeting in September, and recorded all the known information collected so far from veterinarians, laboratories and farmers.

According to Ridler the problem is often first noticed when sheep scanners identify an unusually high number of hoggets, or maiden two-tooths, either in the process of foetus re-absorption or carrying a dead foetus. If a second scanning is undertaken several weeks later, hoggets that were pregnant at the first scan may be found to be empty. Generally, no abortive material is ever noticed in the paddock and the ewe is in otherwise healthy condition and just presents as an unexplained wet-dry at the end of lambing.

The problem was also sporadic, Ridler said. A farm would have a significant issue for one or two years, then in the subsequent year the problem did not recur.

Dr Kim Kelly, of MSD Animal Health and a working group member, has been working closely on the issue with farmers and veterinarians in Southland. She described the issue as reasonably widespread and serious, with many theories about the cause.

“Vets have been testing for everything possible, ruling out common causes and left with question marks.”

Ridler said it was the working group’s goal to go through these many theories, gathering as much information as possible. As a first step a survey of farmers was planned to gather information and identify possible risk factors.

Infectious diseases will be one of the many potential causes the group will focus on.

To date, there has been a tendency to implicate neospora or helicobacter but, although not completely ruled out, it is believed neither is significantly involved as symptoms of these abortive diseases present differently.

There is a strong possibility the problem may not be from an infectious disease but from something else altogether, so nutrition (over/under feeding), genetics, stress triggers, physiological factors and the animal immune response will all be investigated.

Kelly said she was particularly interested in the physiological and immune response theories as it was possible a maiden ewe’s immune system was reacting to a stressor or management change in its environment that was causing it to “ramp up” its immune response, ultimately destroying the foetus in the process. Or, for another reason altogether, the immune system of a maiden ewe could not cope with a foetus, identifying it as a foreign body and rejecting it.

One of New Zealand’s leading researchers in hogget mating, Professor Paul Kenyon of Massey University, is interested in the theory of nutrition and said this had been investigated several times because there was some evidence that both low liveweight gains and high – above 300g/day – were risk factors.

“Also some investigations have looked at abortive disease but to date it is clear we do not have an understanding of the main cause and a confounding issue is often that there is an issue one year but then not the next on a given farm.

“If reproductive loss could be reduced to the levels seen in mature ewes it will likely mean a significant increase in the total number of lambs available for slaughter in New Zealand.”

In order to assist in building knowledge and geographical spread, the working group would like to hear from farmers who know or believe they are experiencing the problem. Email Ridler at A.L.Ridler@massey.ac.nz.

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