Weighing Pigs Without a Scale: A Simple Tool for Estimating Pig Weight

By Dr. Mark Knauer, North Carolina State University

Pig farmers recognize the importance of pig weight. The economics of marketing decisions, dietary phase changes, deciding when to mate gilts, etc., are all closely tied to an approximation of pig weight. However, available tools to capture pig weight, without the use of a scale, are limited.

In relation to simple body measurements, heart girth circumference is perhaps the most accurate way to estimate pig weight. Yet anyone who has tried to measure the heart girth of a pig knows that using a weigh tape can be challenging. Hence we have developed an improved method of measuring heart girth circumference by using a 3/8 inch polyethylene tube as an alternative to using a weigh tape. The tubing balances the durability and flexibility needed to increase ease of measurement.

We collected data to validate the accuracy of the heart girth tube. Data were collected from pigs (n=101) in a commercial farm at an average weight of 256 pounds. Both pig weight and heart girth circumference were measured once. The correlation between pig weight and heart girth was 0.93, indicating that heart girth circumference is a very good predictor of pig body weight. Heart girth accurately predicted 50% of the pigs within 9 pounds and 80% of the pigs within 16 pounds of their live weight. We hypothesize the correlation between heart girth and carcass weight may be greater than that with live weight due to differences in pig gut fill. The equation developed for estimating live weight was:

1. Niche farms or youth projects where it is not cost effective to own a weigh scale.

2. Ensuring proper gilt weight at first mating in sow units.

3. Identifying pigs for market in farms that have excessive sort loss. We do not suggest measuring every pig in the finisher, but there may be value to using the heart girth tube on a few pigs per pen, writing the estimated weight on the pigs, and using them to calibrate one's eye. It is perhaps easier to use the heart girth tube standing on the outside of the pen as pigs are generally more accustomed to people in the alleyways than in the pen.

4. Evaluating a farm's stockmanship. We have been in gilt development units and commercial finishers where we were able to capture heart girth measures pretty easily and other farms where it was quite challenging. Given the genetics and nutrition among farms were identical, docility differences between farms indicate how often people saw the pigs and/or how people interacted with the pigs.

Learn more information on constructing and using the heart girth tube.

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