Tailored boars give greater uniformity
Choices relating to the terminal sire can make a big difference to the proportion of slaughter pigs achieving the top carcase specification for price from the processor.
Different pig markets and different environments bring different choices. The clearest illustration of this effect in pig production is the way in which the regions of the world differ for the type of terminal sire they favour. For example, the market in North America seems to prefer mostly the Duroc, while a large part of Europe focuses on terminal boars of Pietrain and Yorkshire derivation.
Sometimes the choice has been determined by nature of the pig feeds used. Some feed ingredients require animals in the slaughter generation to have a higher intake capacity. Duroc-derived market hogs tend to perform relatively well under those circumstances, which may be the most important reason behind pig producers in North America choosing the Duroc or products based on Duroc genes.
Pig processing plant requirements also have their influence on the choice of terminal sire. Ultimately every pig producer wants to have the maximum proportion of finishing pigs within the grid of carcase measurements receiving the highest price from the processor. However, the preferred carcase description as defined by the penalties imposed for sub-optimal weight, fat depth and loin depth is difficult to achieve when the variance in the population is large. Both the producer and the processor would gain if pigs could be grown in homogeneous groups to a specific end point rather than requiring extensive sorting at slaughter.
Unfortunately, variance has a tendency to increase throughout the production cycle. Actions to limit it should therefore start by aiming to minimise initial differences. Various nutritional and management strategies for both dry and lactating sows can be implemented to promote this. Also, since a key component in achieving steady growth rates is to have regular production numbers so that stocking density remains close to optimal, mating and farrowing need to be managed to ensure an even placement of pigs.
Diseases influence individual pigs to different degrees and hence tend to magnify variance. Separating different ages in segregated production sections will limit disease transfer. Feeds and the feeding system have an equally strong influence. Inappropriate diets, abrupt changes in ingredients, poor grinding, inadequate mixing, deterioration in storage and feed separation during transport can all contribute to variation in pig performance and carcase quality.
Although both phase pig feeding and split-sex feeding have the potential to improve feed utilisation and lower the cost of production, they are difficult to apply in variable populations. Worse still, they can even extend the degree of variation by making inappropriate feed changes for those pigs furthermost removed from the mean of the population. Proper feeding by sex and careful rationing, especially the restriction of castrates at the end of the finishing phase, can lead to a more uniform slaughter pig.
All-in/all-out production systems have been shown to reduce the variation in growth rate relative to continuous-flow systems. However, where the slaughter pigs from a compartment or room are marketed as a single batch, their individual weights can be quite variable relative to situations where the group is sold over several off-takes. Sorting and weighing of pigs before slaughter is an effective way to improve the uniformity of slaughter pigs, but it is very labour-intensive.
At unit level, more variation between pigs will lead to more frequent deliveries to the slaughterhouse and therefore to a less efficient use of housing capacity.
There is the additional consideration that sorting and mixing are known to disrupt the pigs' social order. This in itself has the potential to increase variance, although its significance may relate to group size: it seems to be a factor of lesser concern in large groups. Small groups will be easier to manage and control, while big-pen systems will limit the mixing of pigs.
That then brings us back to pig genetics. A known fact is that a wide range of growth characteristics in pig breeding stock will lead to a great spread of rates of weight gain in the progeny. Using one uniformly consistent type of parent-stock sow (an F1 cross) will make the final products more uniform, whereas resorting to the use of F2 crosses as parent stock tends to give more variation in the final product, because the sow side is more variable.
