Performance testing to select replacement pig breeding stocks

On-farm performance testing to select replacement breeder pigs can be a highly profitable practice.

A breeder replacement plan begins with performance testing of pigs in your herd and involves measuring and recording individual pig characteristics to find the best pigs.

If you are running on-farm, pig herd performance-testing programs and wish to implement reduced-effort variations, read about ideal performance testing conditions and performance-testing program variations to achieve the best results.

Performance testing techniques

  • Replace breeding stock uniformly throughout the year regardless of fluctuations in herd performance.
  • Replace boars after 6–12 months of work.
  • Replace sows after 4–6 farrowings or earlier if litter results are poor.
  • Performance test as many pigs as possible for each one selected as a replacement. The minimum degree of choice is 1 gilt per 10 tested (10%) and 1 boar per 20 tested (20%). Have as many litters as possible represented within each performance test group.
  • Keep the age of pigs in a performance test group within a 2 to 3-week range.
  • Compare pigs only within a live weight range of 15kg.
  • When buying in genetic material from seedstock providers, seek information about estimated breeding values. Herds in the national pig improvement program (NPIP) will provide this information.

Replacement plan

Start by creating a clear-cut plan for replacing breeding pigs and stick to this plan regardless of changes in performance during the year. Changes or fluctuations are due more to variations in environmental conditions than the genetic quality of the pigs.

The number of replacement pigs needed each year depends on the turnover of breeding animals and herd size. A herd of 100 sows may require 25–50 female and 10 male replacements per year.

Spreading the selection of replacements uniformly throughout the year in a 100-sow herd, would mean selecting 1 to 2 gilts per fortnight and 1 boar every month. This provides the highest degree of choice over the fullest possible range of genetic types within the herd.

For maximum herd productivity (pigs sold/sow/year) and rapid genetic progress, boars should work for 6 months and sows should produce between 4 and 6 litters before culling. Some animals may need to be kept longer to offset the occasional breeding failure of replacements.

Genetic traits used in selection

Traits used to select for rapid genetic improvement are:

These traits are economically important, have medium to high heritability and are easily measured before breeding age.

Traits with lower heritability, such as litter size, can be selected using information you collect about relatives and a best linear unbiased prediction (BLUP) computer program, such as PIGBLUP.

Selection differential

The selection differential is a measure of the performance superiority of selected stock over the average of the group from which they were selected. It is calculated separately for boars and sows and then averaged.

The selection differential tells you about the number of pigs chosen compared with the number available to choose from (i.e. the degree of choice). The selection differential increases as the proportion of animals selected from the group decreases.

There is not a direct relationship between the proportion selected and the selection differential. Extremely high degrees of choice are not warranted. Reasonable targets for degree of choice are 1 in 10 for gilts and 1 in 20 for boars. If selecting for growth rate alone, this would give a selection differential for boars and sows combined of about 0.1kg/day.

Generation length

The generation length is the time it takes for 1 generation to be replaced by the next. It also equals the average age of parents when their offspring are born. Genetic gains can only occur when 1 generation is replaced by the next. The more often this occurs in a given length of time, the faster progress is made. This results in the need to replace boars and sows at a young age.

There are serious disadvantages in keeping sows for too short a time. First priority must go to maintaining a high output of pigs per sow in the herd. Because the number of piglets reared per litter increases over the first few litters, the optimum age to cull sows is after their fifth litter, though there may be reasons to cull individual sows before this, such as sickness.

The best way to achieve a short generation length is to replace boars frequently. Boars should be replaced before they are 18 months old. If sows are kept for an average of 5 litters, this gives an average generation length for sows and boars of 1.8 years.

Performance testing conditions

Performance testing involves measuring the chosen characteristics (growth rate, back fat) on a group of pigs as they grow to turn-off (bacon weight). Pigs that perform best are selected as herd replacements. The greatest genetic gains are made when both boars and sows are tested, but smaller herds with superior boars can also benefit from testing homebred gilts.

All pigs must be tested under the same growing conditions to ensure that genetic differences in performance are obvious. The effects of variation in feed quality, weather conditions and disease incidence are minimised if performance comparisons are confined to pigs born within 2 or 3 weeks of each other. Even so, pigs born at the same time may grow under conditions where there are pen-to-pen differences in tail biting and scouring. Where these exist, pigs are compared not on their actual performance, but on the margins above or below the average performance of all pigs in the same pen.

Tips for testing

  • Genetic variability between pigs being tested and the number tested per pig selected must be high to give the high degree of choice for rapid genetic gains.
  • Include as many different litters from as many different sires as possible in a performance group (preferably a minimum of 4 litters). More parents contributing offspring will result in more genetic variation available for selection
  • If you have large herds that farrow uniformly throughout the year, you will naturally have groups of pigs that are large enough to give a satisfactory degree of choice.
  • If you have smaller herds, batch farrowing (a practice that has other advantages for herd management) will provide sufficient pigs of similar age for testing.