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Baiting methods against rats may fail because the bait chosen is less attractive to the rodent than pig feed, or due to the use of insufficient amounts during a control campaign.
on July 1, 2009

Fine-tune your rat campaign

Start baiting when fresh rat activity is observed and repeat the treatment 2-3 weeks later to take account of the surviving animals' ability to restore population size

Routine audits for farm assurance schemes in Europe are finding some deficiencies in meeting the requirement for effective rodent control on pig units. A few of the criticisms pinpoint mistakes in construction or maintenance. More of them relate to the management of the baiting technique used against rats.

Constructional concerns have led mainly to the on-farm kitchen where feeds are stored and prepared. In one instance, the building erected for this purpose was discovered to have a space between its perimeter wall and the steel cladding attached to it which, in effect created a perfect corridor for rats to use as their trackway to and from a favourite feed source. The door of the store was also at fault for failing to seal correctly when closed and for lacking a gnaw-proof strip along its lower edge, such as from metal.

Every-day errors identified at other places have included stacking bags of feed against the wall. Rats can hide or even nest behind the stack, the auditors explained. This is less likely to happen if bags are placed even just a short distance from the wall surface.

By contrast, the farm-assured units had taken note of the need to avoid previous untidy practices such as simply throwing empty bags into a corner and leaving piles of spilled feed on the floor. Action had also been taken to remove vegetation away from the sides of buildings so that the rodents were denied cover or burrowing places nearby.

Their baiting procedures could still be improved, however. Most common among the errors was under-estimating the numbers of rats in the vicinity, followed by a frequent failure to renew baits once the first amount had been put down.

Numbers are notoriously difficult to estimate, comment specialists in rodent control. A sign of damage to housing, equipment or materials tells you only that rats have been there, not when and certainly not how many. Examining tracks and droppings is hardly more indicative, even for an expert.

At the end of last year, a commentary prepared by British rodenticide manufacturer Sorex emphasised the fact that rats are active almost exclusively at night, making it all too easy to under-estimate population. It also warned about putting too little priority on achieving early and effective control once a rat problem had been identified. Technical specialist Sharon Hughes, who runs the company's farm rodent control research and development programme, calculated that the rat's high rate of breeding could allow the population to be restored to its former size only one month after the end of a baiting programme that removed 80% of the rodents present initially.

The species most commonly found in Europe, the brown rat Rattus norvegicus, is sexually mature at just 2 months old and afterwards the female can have 8-10 offspring in each of 7 litters annually. This omnivorous animal may eat up to 30 grams of food daily and especially likes mixed feed, so it is likely to remain living and breeding around a feed store or pig-house even when there are ample food supplies in the fields outside the unit.

The choice of bait needs to reflect this behaviour. It must compete with feed for its attractiveness to the animal. Also, it will be selected exclusively on smell, texture and taste rats have poor eyesight and it must be put in close proximity to the feed or it will not be found. According to Sharon Hughes at Sorex, their natural wariness of new objects and the wide availability of alternative foods will restrict rats' consumption of all but the most attractive and arresting baits. Moreover, their intake starts sooner and stays higher where they are offered the bait in a variety of forms rather than as a pellet of uniform characteristics.

Rats are creatures of habit, however, so baiting points can be located on their most obvious routes. The standard advice is to put them along the tracks defined next to the walls of buildings. But this fails to underline a frequent error made by producers, which is to assume that bait can be left in such places permanently. The control procedure recommended by the experts is to start a new baiting campaign each time new signs of rat activity are detected and to keep topping up the bait until it is no longer being taken.

"Most rodent control programmes fail because farmers bait once and then give up," says Dr Jonathon Wade, technical director at rodenticides company PelGar International in the UK. "Follow-up treatments are essential for complete control."

He advises following up 2-3 weeks after the initial baiting. A final campaign after another 2-3 weeks is desirable, to take account of new rats coming in to fill the gap left by a population just wiped out.

His company recommends marking the location of each baiting point on a simple plan of the unit and also recording the date. In addition it says these points should be checked at least every 2-3 days if not on a daily basis and replenished as necessary. At the same time, it adds, untouched bait stations can be moved to a place where greater activity has been observed.

A further aspect discussed by its recommendations refers to the safe disposal of spoiled bait as well as of dead rats. Waste baits should be sealed in a secure container before being put with the non-hazardous materials for disposal, it says. Dead rats collected during and after baiting also are classified as non-hazardous waste, but burning or burying them is illegal in most European countries. Equally important, keep the carcases securely covered so they cannot be reached by scavengers before their disposal is completed. PIGI

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