A collaborative, multi-institutional growth standard for dam-reared infant rhesus and pigtail macaques (Macaca mulatta and Macaca nemestrina) in research settings (2026)

Haertel, A. J., Berns, K. E., Falkenstein, K. (Shelley) P. et al.

Abstract

A multicenter study was undertaken to generate new weight-for-age growth standards to monitor the growth of infant rhesus and pigtail macaques in research breeding colonies. Previously, single institutions have developed reference growth curves, under the assumption of linear growth, for infants raised in certain settings with a limited scope of benefit to outside institutions. Weight and health records from seven research institutions across the USA were used to build models of body weight by age. Linear and Box-Cox Power Exponential (BCPE) distribution models, which have been adopted from the World Health Organization’s methods, were compared to find the best fit of the models. Resultant weight percentiles and growth velocity charts were provided from the best-fit model ranked by generalized Akaike’s information criterion. Multiparameter models with the BCPE distribution fit the data better than linear models with normal distributions. The assumption that infant macaque growth is linear was challenged by our findings; growth rates appear to change over the first year of life for infant macaques. Growth standards were integrated into centile charts and a computer application in MS Excel to provide user-friendly weight-for-age percentile charts to access and analyze macaque growth data. The new growth standards provide a unified reference that best represents normal physiological growth for all infant rhesus and pigtail macaques from birth through the first year of life. These standards offer guidance on expected growth trajectories and serve as a benchmark for assessing the healthy development of macaque infants across research breeding colonies.