Measuring for pig herd performance testing

Measuring and recording the characteristics of your pigs is an important part of performance testing and helps you to select the best pigs for your breeding program.

Growth rate

This is normally measured from birth to bacon weight and the only information required is birthdate and live weight at bacon. Live weight is divided by the number of days from birth to bacon. Only pigs that differ in live weight by less than 15kg should be compared.

Back fat thickness

The depth of back fat over the eye muscle is the best single measurement of lean meat content. It is taken at the P2 position, which is 65mm down the left side from the midline at the level of the head of the last rib.

To locate the P2 position on live pigs:

  1. Find the rearmost edge of the last rib on the pig's left side.
  2. Mark a spot vertically above on the midline.
  3. From this spot, measure 70mm forward on the midline, and then 65mm down the left side from the midline.
  4. Mark the P2 site with a felt-tipped pen.

Back fat thickness is conveniently measured using echo sounder/ultrasound equipment designed for this purpose.

Selecting the best pigs

This example is a simple method for selecting breeders on-farm. With some additional effort, such as the provision of accurate pedigree records and computer recording, you can select breeders using your pigs' measurements through service providers, such as through computer programs PIGBLUP and the National Pig Improvement Program (NPIP). These programs consider the pigs' relatives and your herd in relation to other herds.

The selected pigs from any method are then assessed for physical soundness, such as the teat number in females.

Calculating index scores

The best way to use the performance measurements for selecting breeding stock is to combine them into a breeding value index. This simple equation combines growth rate (multiplied by an appropriate factor) and back fat thickness after each is given an appropriate weighting factor. The third item in the equation simply corrects back fat for live weight variation between pigs.

The weighting factors in the index account for variations in costs and returns in the pig industry, and need to be updated periodically as these do change.

The following in an example index that will improve growth rate, food conversion and carcass lean:

  • Index score = [60 x daily gain (kg)] − [fat P2 (mm)] + [0.1 x weight (kg)]

In this form, the index can be used to compare only individuals of the same group that were grown under the same conditions. Comparisons among pigs grown in different groups can be made by calculating a corrected score:

  • Corrected score = individual score − average score

Results from on-farm performance tests can be used to compare only animals on the same farm. With simple index selection, there is no way of knowing if the best boar tested on farm A is better or worse than the best performer on farm B, as most of the differences in performance between farms are environmental.


High levels of inbreeding depress performance in reproductive traits. The best way to reduce inbreeding is to use as many different sires (or their semen) as possible in the herd each year. This means a rapid turnover of boars (working life of 6 months), which is easier to achieve in large herds. A recommended minimum number of boars to replace in a closed herd would be 8 per year.

In small herds, it will be necessary to introduce outside boars occasionally to control inbreeding. They must be superior boars drawn only from herds conducting a performance-testing program. Superior across-herd evaluated boars, or their semen, from the National Pig Improvement Program (NPIP) are highly regarded.

Keeping records

On a test record sheet enter the pig's identification number, weight and fat measurements.

Sample on-farm performance test sheet (from birth)

Calculation of index score
Pig no. Date born Weight
Daily gain
x 60
Fat P2
x 0.1
1 30/9 83 146 .57 34.2 15 8.3 27.5  
2 2/10 84 144 .58 34.8 12 8.4 31.2 +0.5
3 2/10 80 144 .56 33.6 14 8.0 27.6  
4 2/10 85 144 .59 35.4 11 8.5 32.9 +2.2
5 11/10 80 135 .59 35.4 15 8.0 28.4  
6 2/10 86 144 .60 36.0 12 8.6 32.6 +1.9
7 24/9 83 152 .55 33.0 13 8.3 28.1  
8 24/9 91 152 .60 36.0 18 9.1 27.1  
9 2/10 94 144 .65 39.0 13 9.4 35.4 +4.7
10 24/9 94 152 .62 37.2 15 9.4 31.6  
11 24/9 95 152 .63 37.8 16 9.5 31.3  
12 2/10 81 144 .56 33.6 14 8.1 27.7  
13 30/9 91 146 .62 37.2 14 9.1 32.3  
14 11/10 86 135 .64 38.4 12 8.6 35.0 +4.3
15 30.9 88 146 .60 36.0 13 8.8 31.8 +1.1
Averages:.60 13.8 30.7