Longevity in livestock species is best defined as the length of productive life. For sows, longevity is directly related to the number of piglets produced during a sow’s productive lifetime. The longer the productive life, the higher the return on investment for the purchaser, since the initial cost of the replacement gilt cannot be overlooked. Good longevity minimizes the rate of replacement and the accompanying cost, which includes non-productive days. Other benefits of longer productive lives are that sows tend to farrow and wean more and heavier piglets than gilts do. Indeed the genetic correlations between length of productive life (longevity) and other measures of productive life are very high. The estimates of genetic correlation are greater than 0.90 for both lifetime productivity (value of saleable pigs produced in a sow’s productive life) and lifetime prolificacy (total number pigs born
or weaned during a sow’s productive life) (Serenius and Stalder, 2005).
In herds where gilts are outsourced, older sows will also have an advantage of better immunity to herd-specific diseases. The ability of a sow to stay longer in the herd without being culled from other causes directly translates to a healthier herd in general. Thus longevity translates to not only higher productivity (pigs produced) but also to more profitability due to the reduction in health costs.
Good longevity constitutes retention of a sow at the decision making stage. The antithesis of retention is of course culling, which can be either voluntary or involuntary. Sows and gilts are culled because of a variety of reasons, but several studies (Arango et. al.; 2005, Clowes; 2006 Serenius and Stalder; 2006) have shown that the primary causes of culling include: 1) reproductive failure - no heat, failure to conceive, 2) poor performance - small litters, poor milkers, 3) feet and leg
problems leading to welfare and management problems. These three main reasons can be referred to as voluntary culling. Involuntary culling may be caused by various factors including injury, accidental death, and so on. Table 1 lists the main problems leading to culling as summarized by Stalder and Serenius (2004) from various studies.
Sow longevity has been shown to be genetically associated with prolificacy and leg score or conformation traits (Serenius and Stalder, 2006). Sows with good prolificacy and few conformation problems will tend to be retained longer in a herd. The main culprit in the general
Table 1. Main reasons for sow culling from various studies. Reason | ----Percentage---- |
| | Range | Average |
Reproductive failure | 10 - 39 | 28.5 |
Poor performance (Prolificacy?) |
2 - 20 | 12.4 |
Feet/Legs & Locomotary disorders | 8 - 15 | 10.9 |
Old age | 3 - 33 | 16.7 |
Death | 3 - 12 | 7.1 |
Milking problems | 1 - 13 | 6.1 |
Health and diseases | 1 - 13 | 4.1 |
Farrowing problems | 2 - 7 | 3.3 |
Summary of studies reviewed by Stalder and Serenius (2004)
area of conformation is feet and legs. As sows get older and heavier, for example, they need good legs to support the weight. Poor legs lead to locomotion problems and this can easily lead to other complications, such as an inability to reach feed and or water, which could further lead to starvation.
Research has also shown that the one of the biggest barri
ers to sow longevity is the loss of maiden gilts and sows after the first parity (second parity crash). The loss of gilts occurs mainly when gilts are unable, for whatever reasons, to start cycling/exhibit heat and or to conceive. This can be caused by a variety of factors, some of which are management or environmental, while others could be specific to a genetic line. Traditionally gilts are bred when they achieve a certain age and, usually, on their second or third heats. According to research done at the Swine Research and Technology Centre (SRTC) at the University of Alberta (various articles), gilts should be bred on weight rather than on age. The recommended weight at first breeding should be 135 to 150 kg. In most production systems, gilts are bred at their second heat, and those that repeat more than once are culled. Culling of sows after the first parity is likewise due primarily to the inability of the sows to rebreed after weaning. Some sows exhibit an inability t
o start cycling again, and while the causes can vary, the main one is the loss of body condition due to the stresses of pregnancy and lactation. Under given management circumstances, certain genetic lines may thrive better than others.
How does Hypor address the issue of longevity in Hypor maternal lines? Direct selection for longevity would entail allowing individuals to stay in a herd for as long as they are able to and as long as they are “productive.” However, this direct selection for longevity in a nucleus breeding population would be a difficult thing to do, because one of the important factors in a selection program is the minimization of the generation interval. In other words, generation interval is the average age of parents at the birth of their offspring, and the shorter it is, the faster the rate of genetic improvement. Most breeding programs try to reduce the generation interval to the shortest biologically
possible length. This is achieved by relatively high replacement rates, meaning very few sows are allowed to stay for as long as they are productive and would otherwise be able to stay in a herd. There is a “conscious” replacement of sows with young gilts since in theory young individuals of high genetic value should be better than their parent’s generation.
With this in mind, the factors that influence longevity become crucial. As discussed above, the main factors causing culling can be reproductive (inability to breed or rebreed), poor prolificacy (litter size), and conformation. The philosophy of the Hypor breeding program is to strengthen the lines in these particular areas and, in so doing, produce sows that are less prone to culling due to failure in these particular areas.
