Editor’s note: The following assessment is provided by Maurice Zarate, a master’s candidate in swine production at Southern Illinois University and herdsman on an Indiana pork operation. He has had his theory reviewed by, Gary Apgar, assistant professor of swine nutrition Southern Illinois University, and Max Rodibaugh, DVM, among others. PigChamp was contacted but did not comment.

Many producers use the PigChamp recordkeeping system to calculate performance of grow/finish pigs. This article will demonstrate that PigChamp underestimates Rate of Gain for surviving pigs, by over-
estimating both the days that pigs spend in the finisher and their total starting weight.

Following is an example that demonstrates this problem.

Assume we move 850 pigs into a finisher when they average 70 pounds in bodyweight, and 810 of those pigs are sold at an average 270-pound market weight. Forty pigs were lost, due to a 4.7 percent mortality during this turn. These pigs died at an average of 72 days in the finisher. Total pig-days for PigChamp were calculated using 850 pigs on feed for an average of 111.29 days.

According to PigChamp: Rate of Gain = Ending pounds - Starting pounds ÷ Total pig days  = (810 x 270) - (850 x 70) ÷ 94,600 = 1.68

Note: Total starting weight includes the 40 losses, which overestimates the total pig starting weight, and reduces total gain of survivors. Also by using the total-group pig days, including those 40 losses, it penalizes the surviving group, and over-estimates the pig days. Both of these scenarios result in a lower than expected average daily gain.

Following is a proposed manner of calculating average daily gain for data derived from the same finisher. Rate of Gain = (Market hogs x 270)- (Market hogs x 70) ÷ (Total pig days - pig days from losses) = (810 x 270) - (810 x 70) ÷ 91,720  = 1.77. The difference between the two calculations is 0.09 pounds of gain per day. This number could increase in cases of higher mortality or if losses occur later in the turn. This difference can be significant, if data generated from PigChamp are used to estimate performance and diet changes.

By underestimating the pigs’ true performance, there is a great potential that high-priced feeds may be over-used in the finisher, resulting in higher costs per turn.

The performance estimate could get cloudier when gilts, lightweight pigs or any other removal occurs other than for market sales.

One way to solve this miscalculation would be to record the weight when a loss occurs, and account for this gain. It would be useful only to estimate the rate of gain, and should not be used to calculate feed efficiency