Seasonal weight changes in laboratory ferrets.

Eleanor J Jones,Jennifer K Bizley,Joseph Sollini,Katarina C Poole,Stephen M Town,Shin Yamazaki

doi:10.1371/journal.pone.0232733

Abstract

Ferrets (Mustela putorius furo) are a valuable animal model used in biomedical research. Like many animals, ferrets undergo significant variation in body weight seasonally, affected by photoperiod, and these variations complicate the use weight as an indicator of health status. To overcome this requires a better understanding of these seasonal weight changes. We provide a normative weight data set for the female ferret accounting for seasonal changes, and also investigate the effect of fluid regulation on weight change. Female ferrets (n = 39) underwent behavioural testing from May 2017 to August 2019 and were weighed daily, while housed in an animal care facility with controlled light exposure. In the winter (October to March), animals experienced 10 hours of light and 14 hours of dark, while in summer (March to October), this contingency was reversed. Individual animals varied in their body weight from approximately 700 to 1200 g. However, weights fluctuated with light cycle, with animals losing weight in summer, and gaining weight in winter such that they fluctuated between approximately 80% and 120% of their long-term average. Ferrets were weighed as part of their health assessment while experiencing water regulation for behavioural training. Water regulation superimposed additional weight changes on these seasonal fluctuations, with weight loss during the 5-day water regulation period being greater in summer than winter. Analysing the data with a Generalised Linear Model confirmed that the percentage decrease in weight per week was relatively constant throughout the summer months, while the percentage increase in body weight per week in winter decreased through the season. Finally, we noted that the timing of oestrus was reliably triggered by the increase in day length in spring. These data establish a normative benchmark for seasonal weight variation in female ferrets that can be incorporated into the health assessment of an animal’s condition.

Highlights

IntroductionWeight changes in laboratory ferrets respiratory diseases such as Influenza and Severe Acute Respiratory Syndrome (SARS) [8,9] including the new coronavirus strain, SARS-CoV-2 [10]
Weight loss is a key indicator of health problems, and understanding the factors that contribute to natural variation in body weight is critical for correctly monitoring an animal’s condition
The weights of 39 female ferrets were recorded as part of their daily health monitoring through multiple cycles of summer and winter light cycles (Fig 1A)

Summary

Introduction

Weight changes in laboratory ferrets respiratory diseases such as Influenza and Severe Acute Respiratory Syndrome (SARS) [8,9] including the new coronavirus strain, SARS-CoV-2 [10]. In laboratory animals exposed to scientific procedures, a standard approach to monitoring health status is to measure body weight. Weight loss is a key indicator of health problems, and understanding the factors that contribute to natural variation in body weight is critical for correctly monitoring an animal’s condition. Ferrets undergo significant variation in their body weight seasonally; there are currently no normative data available to provide a benchmark for the expected seasonal weight changes. Seasonal variations may mask or exaggerate changes in body weight due to an experimental procedure or change in health status and must be integrated into assessments of a ferret’s health status

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