Poor uniformity of slaughter pigs is much more than simply a research topic for university studies in the USA. It is a practical problem seen every day in the pork chains of many different countries. That was the message from speakers at the 4th European swine symposium organised recently by Elanco Animal Health.

Experience indicates that one-third of all pigs born fail to achieve their full sales value, American and European speakers declared. The most common reason for this failure seems to be a less than optimal weight at slaughter. It links to having lightweight pigs in many pen-groups at the end of finishing in all-in/all-out facilities.

Recording an average weight per batch says very little about the variability. The unit manager needs to monitor individual pig weights. Inevitably this means more work in weighing. But the effort and time are worthwhile if they allow at-risk pigs to be identified.

"The time has come to weigh pigs on a regular basis," the meeting heard. "Those who have been in favour of the idea thought that there would be resistance from the people who would have to do the weighing. In fact the response has been positive. Producers can see the sense of finding accurate weight information on the farm in order to manage it correctly."

Calling for unit management to turn out more uniform slaughter pigs should not be dismissed as an unnecessary over-complication, according to the manager of a processing operation in Spain that handles 3 million pigs/year. All slaughterhouses need greater uniformity in the pigs they receive in order to meet the strict demands of their own customers, quite apart from the fact that having less variability of animals on the slaughter line spells extra efficiency for the factory.

Representatives of Elanco reported at the meeting that experience with an advisory programme in Mexico over the last 2 years had underlined the benefit of proactive management in pork production to deliver pigs of the fullest possible value to all concerned. The same programme, being called Full Value Pigs, is also running in Canada and Asia and the symposium marked its European launch.

Pigs are defined as full-value where they have reached optimum end weight in good time, going on to achieve maximum market price and income. Remarks about the lack of uniformity in this context referred in particular to a common problem of under-performing animals that start out light in weight and never achieve their true growth potential.

Warning on weights

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But there was a surprise when speakers discussed the problem in more detail. American veterinary practitioner Dr Karen Lehe described findings that have indicated the focus of producers' attention should switch from weight at weaning to the weight of the pig when it leaves the nursery phase.

Traditionally, of course, the heavier pig at weaning has been supposed to have a head start in growing quickly through to the end of finishing. The pointer from an investigation by Dr Lehe and colleagues at Round Grove Veterinary Services in Indiana is that some adjustment of weight order can occur because of differences in individual performance while a batch of pigs is in the nursery. The exit weight then becomes more indicative. The lighter pigs at the start of the grow-out are those at most risk of staying as lightweights within the group until marketing time.

Dr Lehe referred back to a pilot study first reported in 2006, in which coloured ear-tags had been used to determine weight history. A tag of the first colour was applied at weaning to any pig found to be among the 15% lightest. The second colour of button was used to identify those in the 15%-lightest category at their exit from the nursery. By this time, therefore, the unit's pigs had been divided into 4 groupings. Some had no tag, a second contingent carried only the weaning button, a third wore the nursery identifier and the fourth was carrying tags of both colours.

Later, the same groupings were checked for their representation in the 15% lightest pigs at marketing time. The pilot study had been conducted simultaneously at 2 farms and the results differed in one respect according to unit of origin. On Farm A but not Farm B, being lightweight at weaning meant being more likely to be in the light group (weighing under 100kg, in this case) at marketing. However, the nursery exit weight on both units was a clear predictor of whether or not the particular pig was going to be a lightweight later.

Since then there has been a follow-up by Karen Lehe with her colleague Todd Wolff and University of Minnesota professor John Deen, to check if the pattern is similar also in a facility that does not have a separate nursery. Castrates in a wean-to-finish house holding 1000 pigs were ear-tagged on weaning at 3 weeks old, again at 10 weeks (equivalent to a nursery exit age) and at the end of finishing at 23 weeks. A presentation of the project to the 2007 annual general meeting of the American Association of Swine Veterinarians explained that it was designed to see whether the lightest 5%, 10%, 15% or 20% of pigs at 3 and 10 weeks old were more at risk of either dying before 23 weeks or ending as lightweights.

Once more, the investigators discovered that the end weight of the pigs corresponded more strongly to how much they weighed at 10 weeks than at weaning. The pilot study had shown the nursery exit underdogs to be 13.4 times (Farm A) or 10.5 times (Farm B) more at risk of being in the lightest 15% when the first load from the unit was marketed. This compared with only 4.5 times or 1.7 times for the lightest weaners. Now the follow-up was revealing that members of the sub-population containing the 15% lightest pigs at 10 weeks old were 12.5 times more likely than their heavier counterparts to figure among the poorest 25% at market age.

Therefore the basic indication remained the same, whether or not facilities included separate nursery accommodation. Moreover, the most recent work has verified piglet performance in the nursery phase as deserving special attention because of its impact on ending uniformity.