Introduction

With the use of all-in:all-out production and the increased pressure to minimize, if not eliminate, hold-backs, there is an expanding frustration with the existence of lightweight pigs in groups. Furthermore, packers are, in many cases, increasing the demerits for light weights and adding pressure on producers to avoid the delivery of these pigs. It can be argued that variation of weights within a group is natural and that the pursuit of "cookie cutter pigs" is unrealistic. However, we do have ways of controlling the variation in the groups that we produce. This includes the historic methods of sorting back pigs, but also controlling outside sources of variation such as consistency of breeding programs and disease control programs. Finally, we should look closely at some of the lightweight pigs and decide whether or not they are worth retaining within the group.

Measuring the effect of weight

Though we often view every pig kept alive as a benefit, keeping some of our slow growing pigs may be detrimental. Several studies have shown this in the farrowing house. Some lightweight pigs have been shown to have mortality rates much higher than other pigs as well as being weaned at a lower weight. In one study it was estimated that the lightest 10% of pigs at birth had a mortality rate that was four times the rest of the pigs. These pigs were weaned at 50% of the weaning weight of the rest of the group. Furthermore, they probably carry a higher level of disease into the nursery.

Less information is available on the performance of small pigs in the nursery and thee grow/finish barn as to the effects of retaining lightweight pigs. The effects are not as marked as in the farrowing house, but present nonetheless. It is difficult to generalize the effects across different farms as weaning ages, environment and diet vary greatly. A further complication in the analysis is the fact that this is not an all or none situation but different levels of problems for pigs of different weights. As well, beginning weight is not the only factor that determines weight at closeout. Genetics, health, and management all play into the development of the end weight.

Figure 1.Relationship of individual beginning and end weights

Thus, we cannot eliminate all lightweight pigs. Beginning weight is the best prediction of end weight and the value of a pig, however. In Figure 1, we see the weights of pigs at entry and exit from a nursery. These were within a week of age as they were put into the nursery. As can be seen, the lightweight pigs are at a lighter weight at exit as well. The middle bar shows the average and the outside bars show the expected range of weights for 95% of pigs at a specific entry weight. For instance, a pig entering at 10 pounds is expected to exit between 18 and 40 pounds. Another way to look at the graph is that a ten pound pig will average 30 lbs at exit. Figure 2 shows the average weights on a pen basis, when the pens are sorted by weight. The average weights are more predictable, with a pen averaging 10 pounds at entry resulting in a pen with a range of 21 to 34 pounds. It should be emphasized that these are the results for one farm and not applicable to all farms. Yet, it is probably more important to know the growth rates of slow-growing pigs than the group as a whole.

Figure 2. Relationship of average beginning and end weights by pen

Thus a good exercise for all hog farms to perform is to measure the growth rates of lightweight pigs entering the facility. Such an exercise involves identifying and, in three to four groups, tag and weigh the lightest 5% of the pigs at entry. If a tagged pig dies after that, weigh it and record the date and weight of that mortality. Finally, record the pigs when they are shipped. In a grow/finish barn, if they gain the required weight in the grow/finish barn, they will be shipped during the early pulls. In this case, this pig is a success. However, if it is retained until the closeout, or the feeder pig does not meet specifications, weigh these pigs and calculate the value of these lightweight pigs.

If you do such a project, you will probably find that the lighter the pig the less likely it is to survive. Furthermore, it is more likely to be marketed at a light weight. In some cases, you will find it is not advantageous to retain the pig. If this is the case, the alternative should be to raise it in an alternative environment or euthanize it.

For instance, in our case, a pig weighing 7 pounds at entry has a 50% chance of weighing less than 20 lbs and a five percent chance of exceeding 30 pounds after 35 days. Moreover, it has a 15% chance of dying during this period. The pig is worth considerably less than a 12 pound pig. If it can only be marketed above 30 pounds, the chance of marketing is only 42.5%.

Once we have recognized the value we can make logical decisions about these pigs. First of all, if too many lightweight pigs are entering a nursery, look at birthweights. The earlier we can identify a problem pig, the better. Though moving the pig back has been an alternative, recognize the effects it has on disease levels. Decide whether it is worth keeping the pig. If it is likely that it cannot be sold, it may be best to destroy it. Finally, look at your management techniques. If you do retain small pigs, try to make it as comfortable as possible for theses pigs by sorting and providing adequate heat and nutrition.

Take-home Message