Seasonal changes in energy economy of farmed polecat as evaluated by body weight, food intake and behavioural strategy

Seasonal weight changes in laboratory ferrets

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.

Response to Fasting in an Unnaturally Obese Carnivore, the Captive European Polecat Mustela putorius

The European polecat ( Mustela putorius) is a naturally lean carnivore prone to excessive weight gain in captivity. This study assessed its suitability to investigate the natural history of the obese phenotype displayed in overweight humans, domestic animals, and seasonally obese wild mammals. Ten farm-bred polecats were subjected to a 5-day fast with 10 controls. Obesity (40% body fat) was associated with an unfavorable plasma lipid profile and high glucose and insulin concentrations. The polecats were in phase II of fasting with normoglycemia, low liver carbohydrate stores, and decreased plasma concentrations of urea and most amino acids. Although the plasma nonesterified fatty acid (NEFA) levels were elevated, the adipose tissue lipase activities suggested a blunted lipolytic response. Lipid mobilization was more efficient from intraabdominal fat. The animals developed hepatic lipidosis with elevated NEFA influx into the liver and losses of n-3 polyunsaturated fatty acids and arginine as hypothetical etiological factors. The plasma leptin, insulin, and triiodothyronine levels decreased but were not accompanied by reduced sex steroid or increased stress hormone concentrations. The blunted lipolytic response often encountered in obesity suggests that the organism is trying to defend the obese phenotype. Liver lipidosis and decreased insulin and triiodothyronine levels seem to be among the most consistent responses to fasting manifested in diverse mammalian orders and different levels of body fatness. The polecat could be recommended as an easily accessible carnivorean model to study the natural history of the obese phenotype and its comorbidities.

Seasonal energetics of northern phocid seals

The metabolic rate of harp (Pagophilus groenlandicus), harbor (Phoca vitulina), and ringed seals (Pusa hispida) was measured at various temperatures in air and water to estimate basal metabolic rates (BMRs) in these species. The basal rate and body composition of three harp seals were also measured throughout the year to examine the extent to which they vary seasonally. Marine mammalian carnivores generally have BMRs that are over three times the rates expected from body mass in mammals generally, both as a response to a cold-water distribution and to carnivorous food habits with the basal rates of terrestrial carnivores averaging about 1.8 times the mean of mammals. Phocid seals, however, have basal rates of metabolism that are 30% lower than other marine carnivores. Captive seals undergo profound changes in body mass and food consumption throughout the year, and after accounting for changes in body mass, the lowest rate of food intake occurs in summer. Contrary to earlier observations, harp seals also have lower basal rates during summer than during winter, but the variation in BMR, relative to mass expectations, was not associated with changes in the size of fat deposits. The summer reduction in energy expenditure and food consumption correlated with a reduction in BMR. That is, changes in BMR account for a significant portion of the seasonal variation in energy expenditure in the harp seal. Changes in body mass of harp seals throughout the year were due not only to changes in the size of body fat deposits, but also to changes in lean body mass. These results suggest that bioenergetics models used to predict prey consumption by seals should include time-variant energy requirements.

Phytosterols act as endocrine and metabolic disruptors in the European polecat (Mustela putorius)

Phytosterols or plant sterols (PS) are consumed as natural remedies and margarines by the general population in developed countries to lower elevated serum cholesterol levels. They are also present in high concentrations in pulp mill effluents. The aim of the study was to screen the endocrine and metabolic parameters of the European polecat (Mustela putorius) for the effects of PS. The results showed an increase in the plasma estradiol and TH levels with no effects on the hypophyseal regulatory hormones. The plasma ghrelin levels decreased. PS also affected intermediary metabolism. The liver glycogen content increased as did the kidney glucose-6-phosphatase activity. The liver lipase esterase activity, on the other hand, decreased due to PS. In serum lipids the total cholesterol did not change, but the low-density lipoprotein levels increased and the high-density lipoprotein-cholesterol ratio decreased. PS had widespread previously unreported effects on the physiology of the polecat. The multiple effects indicate the need of a thorough risk assessment of the effects and interactions of PS.

Regulation of weight loss in male farm mink

1. Regulation of weight loss was studied in wild mink (Mustela vision) under farm conditions. 2. Body weight of male minks was already adjusted to a low level before the mating season. 3. Weight loss was a result of changes in energy expenditure and energy intake. 4. This study emphasizes the dynamic nature of seasonal energy regulation.

Regulation of energy economy in raccoon dogs and blue foxes: a process of dynamic interactions

1. Seasonal regulation of energy economy was studied in farm-raised blue foxes (Alopex lagopus) and raccoon dogs (Nyctereutes procyonoides; Gray, 1834). 2. Both species exhibited marked seasonal changes in body weight, body energy content, food intake and locomotor activity. Seasonal changes in food efficiency were also evident. 3. The results emphasize the important role of both energy intake and energy expenditure in the regulation process. 4. It can be concluded that regulation of seasonal energy balance is a dynamic process with various interactions between different factors.

Voluntary regulation of energy balance in farmed raccoon dogs

1. Seasonal changes in body mass and voluntary feed intake were studied in juvenile raccoon dogs (Nyctereutes procyonoides, Gray 1834) under farm conditions. 2. The body weight maximum was achieved in mid-November. Thereafter, body weight gradually declined towards summer. This pattern was closely connected to voluntary regulation of feed consumption. During autumn, appetite of the animals was good enhancing gradual deposition of excessive fat reserves. 3. Excessive adiposity itself, together with factors like shortening daylength and decreasing air temperature, seemed to play as a trigger for starting of winter rest. 4. The results support the endogenic nature of energy balance regulation.

Seasonal changes in hepatic activity of G-6-phosphate and alpha-glycerophosphate dehydrogenase in farmed polecats and raccoon dogs

Liver weight of both male and female polecats was significantly higher in winter than in summer. There were no seasonal or sex differences in the liver weight of raccoon dogs. Body weight of male polecats was highest in winter. No marked seasonal changes in body weight of female polecats, or raccoon dogs of both sexes were found. Total hepatic glucose-6-phosphate dehydrogenase activity of polecats and raccoon dogs was higher in winter than in summer. Specific activity of alpha-glycerophosphate dehydrogenase was highest in summer, but total hepatic activity did not show any seasonal changes.