Here is an interesting result which illustrates the impact of variation on the optimal selling weight of finisher pigs. The optimal weight of a single pig can be readily calculated if you know the approximate feed efficiency and adg for the last couple of weeks of finishing as well as an expected market price. In general you want to add the next lb as long as the value received for that lb is in excess of the cost.
As you add lbs each day in late finishing, adg tends to stablize around 2 lbs per day but feed efficiency begins to deteriorate. Therefore, each additional lb will cost a little more to put on. As you add weight, at some point you will begin to incur a discount to the base price and lean percent will begin to deteriorate. If you know how these things change, you can estimate the optimal selling weight of a single pig.
What about a distribution of pigs though, marketed from the finisher? They will not all have the same weight and each of them will be growing at a slightly different rate with individual feed efficiencies. Actually estimating this is somewhat difficult since we don't have the data to exactly establish these growth rates and FE's. HOWEVER, most producers aim at an average marketing weight for a load based on their previous experience with their marketing distributions.
The interesting implication however, is that the wider the variance of the distribution of pigs on the load, the lower the optimal average weight of the load will be (even if you could calculate it). This indicates that producers who have larger variances in loads through poor sorting and because of culls and lights mixed in with the load (as well as fast growing pigs) will be choosing a lower average weight (than is optimal for an individual pig) even when they optimize the average sale weight of the load. The narrower the variance, the closer the average can come to the single pig optimal. This illustrates the double penalty (or bonus!) of a wide variation (narrow variation). As you reduce variation in finishing pigs, you can both increase revenue due to less sort loss and discounting AND increase the average weight of the load.
Lots of money left on the table due to variation. No doubt about it.
