Commercial pig herd operators differ in the degree to which they rely on purchased breeding stock.
Some buy all their replacement gilts and boars while others select gilts from within existing herds and purchase only boars.
A third option is to select both male and female breeding stock from within the herd, with either regular use of artificial insemination or the occasional introduction of a boar to introduce new genes.
There are a number of breeding companies that specialise in selling gilt and young boar replacements. As these breeding companies are doing all the genetic improvement and must recoup the cost of maintaining the purebred herds and carrying out the selection program, buying all replacement breeding stock is one of the more expensive options.
Since all your herd’s genes will come from purchased stock, it is important to select stock from breeding companies that have a rigorous selection program that achieves a fast rate of genetic improvement. This means that your breeding stock provider should be running the best linear unbiased prediction (BLUP) software.
BLUP software is particularly useful in selecting traits with low heritability such as litter size or number weaned. BLUP can also improve the estimated breeding values (EBVs) for traits with medium heritability such as growth, feed conversion efficiency and carcase quality.
Most breeding companies will only sell crossbred lines as a way of protecting their investment in the nucleus purebred and to exploit hybrid vigour. Gilts produced from crossbred dams may produce a smaller litter size than their parents, as some loss in hybrid vigour may occur.
The value of hybrid vigour may be over-promoted compared with maintaining a healthy, well-managed herd. Purebred large white herds in a genetic improvement group consistently produced more pigs born per litter than the average recorded in Pig Stats over a five-year period.
In times of financial difficulty, producers who obtain stock from a breeding company may be tempted to select gilts from their own herd to reduce costs. An important consideration is whether these gilts are suitable for breeding.
The prime example is where a producer has been using a terminal sire line that incorporates the stress or halothane gene. Some of the gilts would be carriers of the gene and could produce actual stress reactors (not just carriers) after being mated to carrier boars.
Selecting own herd’s gilts and purchasing boars
It is possible to have a successful breeding program by purchasing boars or using artificial insemination (AI) while selecting all gilts from on-farm. To reduce the risks of disease through live animal introductions, AI is preferable, with possibly a boar on-hand for backup.
Purebred or mixed semen may be available at a cheaper price.
If mixed semen is used, a synthetic herd would be formed from a mixture of different breeds. Mixed semen from large white and landrace could maintain most hybrid vigour for reproductive performance. It may be a good idea to avoid using Duroc genes in gilts as this breed has a lower reproductive performance than the two white breeds.
One way of reducing the cost of AI is to use contract semen collection – herd operators can group together and purchase elite boars which would be too expensive for an individual herd. The cost of AI can be less than natural mating.
Selecting gilts and young boars from within your own herd
If all boars and gilts are bred on-farm, it is advisable to introduce genes periodically to avoid loss of productivity through inbreeding depression. With fewer introductions, it is important to select the very best boars as their genes will remain in the herd longer. Probably the best source is purebred stock with a national ranking.
The frequency of periodic ‘top-ups’ will depend on the efficiency of your selection program. For larger herds using BLUP, fewer introductions may be required; however with high selection intensities and the possibility of inbreeding depression, periodic gene introductions from highscoring EBV boars is recommended.
AI offers a safer method of introducing elite genes because there is less risk of disease than with live animals. AI has become popular for this and other reasons such as its availability, ease of use and that fewer boars are needed on-farm.
Genetic improvement programs concentrate on improving reproductive performance, growth rate, carcass quality and feed conversion ratio.
Buying replacement stock is the simplest genetic improvement option.
Disadvantages of buying all replacement stock include cost and potential for adaptation problems and disease introduction.
AI may be cheaper than buying all replacement stock.