It has been established that nutritional management through pregnancy and the rearing phase is of vital importance in allowing a lamb to reach its growth potential and a replacement ewe lamb to reach her reproductive potential.
Ewe Nutrition
Throughout the gestation period, good management of nutrition for pregnant ewes is essential to make sure they are in the right condition to meet the demands of the growing lambs through to lambing and lactation.
The correct balance of protein in the diet, both quantity and quality, is needed from the last third of pregnancy for adequate udder development to take place. These requirements increasing as lambs near term and colostrum production starts.
With demand on protein resources at its peak, there is less available for the immune system and, unless there is adequate dietary protein supplementation, immunity against internal parasites will usually decline. This allows the periparturient rise in worm egg output to occur.
The degree and duration of this relaxation of the ewe’s immune response to internal parasites will depend on the degree and duration of the shortfall in dietary protein. Along with this is the influence of other stress factors such as adverse weather conditions and inter-current disease.
Parasite Burdens
Managing parasite burdens effectively is also a pre-requisite if the flock is to make best use of the nutrition available.
Gastrointestinal worms and liver fluke are the two most common parasite problems for most farms, but require quite different approaches for effective control.
Gastro-Intestinal Worms
Gastrointestinal worms are, in general, species specific – i.e. sheep worms do not infect cattle and vice versa. This means that rotational grazing systems, with different grazing species, can be a useful tool in managing worm burdens on a farm.
Sheep will generally mount an effective, protective immune response to gastrointestinal worms in response to exposure over the first one or two grazing seasons. When it comes to managing worms in ewe lambs this has to be an important consideration.
Managing worms in ewes at lambing time is an important part of any gastrointestinal worm control policy. As discussed above, the ewe’s protein balance around lambing time has a major impact on her ability to control faecal worm egg output.
On a flock level, and for most individuals in the flock, the aim of anthelmintic treatment of ewes at lambing time is to minimise the worm egg contamination of pasture. This reduces the level of challenge experienced by their lambs.
On many farms, most of the worm population overwinters in ewes; therefore, treatment of whole flock exposes a large percentage of the worm population to treatment at the same time, increasing the selection pressure for resistance.
Treating ewes when their immune system is functioning well has little impact in overall worm egg output. So, targeting treatment to those that are likely to be under nutritional stress will give the same benefit on pasture contamination as treating the whole flock, while minimising the selection pressure for resistant worms.
Suppressive dosing strategies around lambing time may give a short-term benefit in terms of lowering pasture worm challenge but, as explained above, can exert a high selection pressure for resistant worms.
This is exacerbated if ewes are treated repeatedly, as the treated ewes continue to remove any susceptible worms from the pasture while grazing, leaving only resistant worms to produce the next generation of worms.
Targeting treatment of ewes at lambing time to those likely to be under nutritional stress (i.e. thin ewes, ewes carrying triplets, or ewes that are lame or sick) with a single treatment around the time of lambing, will have a similar impact on reducing pasture contamination, while minimising the selection pressure for resistance.
Suppressive dosing regimes such as the frequent, repeated use of drenches, or the repeated use of persistent products, can eliminate the worm challenge in the short term and may prevent sheep from developing or maintaining their immunity to these parasites.
This may appear to give effective control in the short term. However, it may also leave some animals without immunity to worms and, therefore, vulnerable to disease, if faced with a worm challenge later on.
Suppressive dosing strategies (i.e. killing as many worms as often as possible) also exert a strong selection pressure for anthelmintic resistance. This allows resistant worms to survive and multiply, while susceptible worms are suppressed, ultimately leading to a largely resistant worm population.
Suppressive dosing strategies are therefore not sustainable in the medium to long term. For ewe lambs then, the best approach is to have a grazing management plan that allows for a low level, controlled exposure to parasites. Back this up with a program to monitor worm burdens, which allows targeted treatments to prevent disease or negative impacts on growth rates.
Liver Fluke
The opposite is true for liver fluke. This parasite (Fasciola hepatica) affects both cattle and sheep, and neither species mount an effective, protective immune response to liver fluke.
Minimising or eliminating exposure to the infective stages of the parasite is the aim, rather than controlled low-level exposure. As liver fluke affects both cattle and sheep, any control measures for the replacement ewe lambs have to be part of an overall ‘whole farm’ control plan.
Effective fluke control plans have four component parts:
Reducing fluke egg output from grazing animals to reduce the pasture contamination for the following season;
Reducing the available habitat for the intermediate host, the mud snail;
Minimising exposure to the infective stages (metacercaria) on pasture;
Effective, strategic treatment of ‘at risk’ animals.
The key point for ewes in late pregnancy is to minimise fluke burdens – to minimise the drain on nutritional resources – by strategic treatment of ewes that have been grazing fluke-risk pastures.
After lambing, a targeted adulticide treatment to remove any fluke that may have survived previous treatment, will greatly reduce the number of fluke eggs landing on the pasture to generate the fluke challenge for the following autumn.
The key point for lambs is to avoid metacercarial exposure, as even low levels of liver fluke infection will have a negative impact on health. For this to be possible, ‘safe’ or low risk areas have to be identified for the ewe lambs at high risk times of year (autumn and winter).
Effective monitoring programmes can be set up with little effort, that will show if/when ewe lambs meet a fluke challenge, and allow the most effective use of the flukicides.
Effective control of both GI worms and liver fluke rely on factors specific to the individual farm. One size does not fit all, so speaking to your vet or advisor to ensure the best possible nutrition for ewes in late pregnancy and to develop a plan specific to your own farm is the best approach to managing GI worms and liver fluke in your flock.
Contact Jaguza Support