Raising Your Herd’s Genetic Status, Without Risking Its Health

By Dr Grant Walling, Research and Development Director JSR Genetics and Janet M Owen, Veterinary Pig Specialist, Garth Partnership. A pig producer receives significant advice from many sources. Much of it comes from the supply industry - feed companies, veterinary practices, breeding companies.
calendar icon 2 July 2007
clock icon 5 minute read

Occasionally opinions clash - creating a dilemma. Recently, to protect herd health, some vets have advised producers to close their herds to new breeding stock; how then to prevent the erosion of genetic performance? Larger producers often purchase purebred damline animals and run a miniature in-herd breeding pyramid. This takes a great deal of organisation in managing three different types of sow on the farm, and detailed record keeping, but can produce good results.

For smaller sized pig enterprises the breeding pyramid is not an option. A common alternative is rotational criss-cross breeding in which F1 parent gilts are mated to dam line semen from one of the two breeds in the F1. Their progeny are mated to the other breed present in the F1. This oscillation between the breeds continues by using the damline semen, with herd replacements selected from the progeny.

Warning signs and perimeter fencing provide good restrictions for on-farm access

This simplistic system produces a far inferior product and presents some challenges. The F1 parent gilts need to be clearly identified to prevent selection as slaughter pigs or visa versa. Selected F1 parents also need to be raised on a gilt rearing ration from approximately 60kg. Slaughter progeny produced from damline matings (which will make up 7.7% of the slaughter pigs) can be up to 14 days slower to finish and will typically grade at least 0.5mm fatter - even greater at heavier slaughter weights. Due to the selection of breeding stock alone, the herd will produce 2.5% less slaughter pigs.

The performance of the breeding herd will also be affected. Using an F1 parent maximises heterosis, which affects traits such as litter size. A criss-cross programme decreases the heterosis, initially by 50% in the parent sow, because they are no longer produced from two unrelated purebred lines; decreasing numbers born alive by up to 10%.

The selection intensity of gilts chosen for the herd is typically poor with producers selecting primarily on type rather than quantitative traits. In contrast, reputable breeding companies have trained geneticists, sophisticated hardware and dedicated software to perform the same task.

JSR calculates that a criss-cross scheme and the related inferior performance can cost around 4p/kg deadweight. Harder hit will be those with ‘all in-all out’ finishing facilities (due to slower growing damline genotypes) and those on tighter contracts less tolerant to variation in slaughter product.

Ultimately there are no shortcuts to producing good breeding stock. However, with practical and clear protocols in place alongside good communications between vets regarding unit biosecurity and stock integration pig producers can be confident in obtaining the best genetics by regularly purchasing replacement breeding gilts and boars from a reputable breeding company.

Risks that cannot be controlled include the location of the unit regarding neighbouring pig farms, roads, slaughterhouses, markets and topography.

Pig pathogens spread best in moderate temperatures, high humidity and low air turbulence. The distance airborne pathogens can travel varies but, in general, for pigs in close proximity the risks of a herd health breakdown are high. These risks can be reduced by structures to break up plumes of wind borne pathogens, and by vaccinating animals against serious health issues.

The challenges that can be controlled relate to everything that comes into the unit, ranging from stockmen and vets to food and the pigs themselves. The following guidelines are recommended:

Entrance to unit showing single staff entrance, changing and showering unit
  • A period of pig freedom before entry.

  • A change into boots and overalls belonging to the unit, even a shower.

  • Goods should be bought from reputable sources.

  • Plant and equipment must not be moved from farm to farm.

  • Disposal of deadstock preferably by incineration on site.

  • Knacker collection sites must be secure and well away from the unit.

  • Feed delivery vehicles should not enter the unit.

  • Herd replacements should be bought from a reputable breeding company with a robust health monitoring programme.

Exit loading ramp
  • The health status of the supplying unit should be discussed by the vets of both breeding company and customer.

  • Pre-delivery vaccinations can protect higher health animals.

  • Isolation and acclimatisation can minimise the risk of destabilising the resident herd.

  • The age of gilts delivered might also be adjusted.

  • Off-site isolation, including the testing of sentinels and rechecking the herd of origin after 6-8 weeks.

  • Breeders’ delivery vehicles should be fully cleaned and disinfected.

  • Two disinfectable loading docks are needed, one for incoming animals, the other for dispatches.

  • Loading docks must be immaculate.

  • Drivers must neverwalk beyond their side of the ramp.

  • Unit staffmust never step onto the vehicle or driver’s side of the ramp.
In conclusion, most pig producers will obtain the best results by the regular purchase of replacement breeding gilts and boars from a reputable breeding company with a robust health monitoring programme. Any risks can be minimised by good communications between vets and good veterinary advice regarding unit biosecurity and new stock integration.

March 2007
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