Beyond the drought

Many North Island farms experienced moderate to severe drought over the summer months. Much needed rain and lack of feed in most areas put a hold on the sale and transportation of stock and supplementary feed. This essentially left many farms hanging by a thread desperately praying for the heavens to open.

We know that when nutritional needs are not being met that stock lose body condition score, have reduced liveweight gains, lowered reproductive success, reduced milk production, and they become more prone to disease due to a weakened immunity.

Hence many animal health problems may surface as a result of a drought… viral pneumonia, ryegrass staggers, facial eczema, pink eye and excessive tooth wear to name a few. Also, as feed becomes limited, stock may be forced to browse plants that they would not normally consume. This is the reason why we often see plant poisonings during a dry period.

During these dry months, worm eggs and free-living stages (L1, L2 and L3 larvae) will shelter inside the dung on pasture, remain low down in the pasture sward (if you have grass), and even survive beneath the top layer of soil. In the days following rain, the presence of moisture activates worm egg hatching and larval development on pasture. This explains why we often see outbreaks of worms a few weeks after a drought has broken because the rain triggers an ‘en masse’ migration of larvae onto pasture from these areas.

Also, many worms will adapt in different ways to enhance their survivability during a dry period so that when the rain finally arrives, their life cycle can resume. For instance, on pasture, Barbers Pole worm eggs (lambs/hoggets) have a unique ability to be able to take in more water as they dry, and the hatched larvae will hold in water as their skin dries. Trichostrongylus columbriformis (black scour worm in lambs/hoggets) can coil up to slow their water loss in a dry environment, whilst lungworm (disease is common in weaner deer and dairy calves) and Ostertagia ostertagi (brown stomach worm in cattle) can inhibit within the animal during these times.

Over the summer months, stock are often also forced to graze around areas near water where grass is more plentiful. These are often areas where young liver fluke encyst on pasture. Once eaten, the young fluke migrate to the liver of the host to mature into adults. Severe, acute disease may be seen in the late summer/early autumn, but more commonly, the chronic form of the disease is seen in two-tooth and mixed-aged ewes and young cattle in the winter (following infection over the summer) coinciding with the stress of winter, late pregnancy and often inadequate nutrition.

Sudden deaths due to salmonellosis typically occur in two-tooth/mixed-aged ewes often coinciding with the autumn flush following a dry spell. Outbreaks typically occur as a result of stress e.g. change in feeding level, prolonged yarding/droving, heavy stocking rates etc. Two to three deaths a day is not uncommon (up to 6 % deaths) with most ewes found dead next to water. A khaki coloured diarrhoea with mucus and flecks of blood staining the crutch and down hind limbs may be observed. Preventative vaccination programmes are the best way to control disease. Two vaccinations with Salvexin®+B four weeks apart prior to the risk period is recommended.

Following a drought, active growth (or regrowth) in plants after rain or irrigation leads to rapid uptake of nitrate from the soil. If sunny weather follows, the nitrate is utilised by the plant and is quickly converted to plant proteins. However, if overcast weather continues, the nitrate from the soil is not utilised efficiently by the plant and accumulates in the leaf. This is why nitrate poisoning is frequently seen in cattle after periods of dull, overcast weather. Nitrate poisoning is common in cattle grazing brassica crops (rape, chou, turnips), green feed oats, ryegrass (perennial, tama) and can also occur with various thistles and weeds. Crops and pasture can simply be tested for nitrate levels prior to grazing so that if toxic can be avoided until the levels decline.

If you have any questions regarding management of any of these or any other issues, please do not hesitate to contact your vet.


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