A Meta-Analysis to Understand the Relationship between Pig Body Weight and Variation from Birth to Market

Abstract

This meta-analysis aims to understand the changes in pig body weight (BW) variation from birth to market and develop prediction equations for coefficient of variation (CV) and standard deviation (SD) as a function of BW. Standard deviation is the measure of dispersion of a set of values from the mean and CV is the SD expressed as a percentage of the mean. Data collected from 16 papers and data sets yielded 117,268 individually weighed pigs with sample size ranging from 120 to 4108 pigs. Polynomial regression analysis was conducted separately for each variation measurement. The resulting prediction equations (CV (%) = 20.04 - 0.135 × (BW) + 0.00043 × (BW)², R² = 0.79; SD = 0.41 + 0.150 × (BW) - 0.00041 × (BW)², R² = 0.95) suggest that there is a quadratic decreasing relationship between the CV of a population and BW, the slope gets smaller as mean BW increases from birth to market. A quadratic increasing relationship is observed for SD, with slope being smaller as mean BW of pigs increases from birth to market. These prediction equations can be used by swine producers to estimate expected CV and SD of BW among a population of pigs.

Keywords: coefficient of variation; meta-analysis; pigs; standard deviation.

Figure 1

Plots of coefficient of variation (CV) and standard deviation (SD) as a function of body weight (BW) from birth to market. Gray area represents the 95% confidence interval on CV and SD of BW, respectively. (a) Relationship between CV and BW (CV = 20.04 − 0.135 BW + 0.00043 BW²; standard error of regression coefficients, 0.253, 0.0112, 0.000078, respectively; R² = 0.79, all terms p < 0.05). (b) Relationship between SD and BW (SD = 0.41 + 0.150 BW − 0.00041 BW²; standard error of regression coefficients, 0.133, 0.0059, 0.000041, respectively; R² = 0.95, all terms p < 0.05).