Variation: You Can Manage It, But You Can't Avoid It

Apr 15, 2008 12:00 PM, By John F. Patience Prairie Swine Centre Saskatoon, Saskatchewan

In the third scenario, performance is poor but variability is low, indicating an overall impairment due to a poor environment. Crowding could be the problem in this scenario, because crowding, unless severe, will uniformly depress growth, but not increase variability.

Addressing Variability

The challenge of variability can be addressed in two ways ? reducing variability and managing variability.

If variability within a barn is already quite low, producers are more likely to achieve success by seeking ways to manage variability. But if variability is high, then clearly there are deficiencies within the barn that are impairing performance and should be addressed. In this instance, it should be possible to reduce variability.

Reasonable targets for variability in a barn can be based on CV as described above. Although information on “normal” variability is admittedly limited, I would offer the following thresholds for CV:

20% of weaning weights;
12 to 15% for nursery exit weights; and
8 to 12% for weight at first pull from the finishing barn.

In other words, if the CV for body weight at weaning is around 20%, at nursery exit is 12-15%, or at first pull is 8-12%, then it makes sense for barn managers to seek ways to manage variability rather than reduce it because it is already close to the lower practical limit.

These targets may change in the future as we develop more information on CVs under commercial conditions.

Topic of Interest

Variability is becoming a topic of increased interest in the pig industry due to its substantive impact on net income. This has become more obvious in all-in, all-out systems, where tail-end pigs are more obvious than they would be in a continuous-flow system.

Although variability has earned extra attention, there is much to learn, such as how much variability is inherent and must therefore be accepted, and how much is excessive and therefore, at least theoretically, can be reduced.

Poor herd health, itself a poorly defined term, is believed to be a major contributor to variability. But we also know that inadequate access to feed and water can contribute.

Managing variability will be the focus of most farms, requiring imaginative strategies based on facts and not specious logic to be successful.

Unfortunately, many procedures known to effectively manage variation require either changes in physical facilities or increased labor, neither of which is viewed with much enthusiasm at this point in the pork production cycle.

Nonetheless, there are substantial rewards to producers who reduce or manage variability effectively, because the costs of not doing so are also substantial.

Table 1. Example Variation in Body Weight of Pigs at Three Ages1
		Average age, days
		19	68	140
No. of pigs	1,264	700	632M
Weight, lb.
	Mean	11.9	64.1	228.2
	Median	11.9	64.0	229.7
	Minimum	5.3	52.4	163.7
	Maximum	20.2	90.0	274.8
	Range	14.9	37.6	111.1
	Range, % of mean	121	59	48
Standard deviation, lb.	2.7	8.2	18.3
Coefficient of variation, %	22.4	12.82	8.02
1Body weights were determined on whole groups of animals without pre-selection at weaning (19 days), nursery exit (68 days of age) and at 20 weeks of age before the first market pull. All were collected at the Prairie Swine Centre Elstow Research Farm. The weights were collected at different times, so the three groups of pigs are not related to each other. The ages represent means, although the range in ages would be plus/minus three or four days.