Food Grinding Behavior: A Review of Causality and Influential Factors

Food waste is a common issue arising from grinding of food by experimental animals, leading to excessive food scraps falling into cages. In the wild, animals grind food by gnawing vegetation and seeds, potentially damaging the ecological environment. However, limited ecology studies have focused on food grinding behavior since the last century, with even fewer on rodent food grinding, particularly recently. Although food grinding's function is partially understood, its biological purposes remain under-investigated and driving factors unclear. This review aims to explain potential causes of animal food grinding, identify influencing factors, and discuss contexts and limitations. Specifically, we emphasize recent progress on gut microbiota significance for food grinding. Moreover, we show abnormal food grinding is determined by degree of excess normal behavior, emphasizing food grinding is not meaningless. Findings from this review promote comprehensive research on the myriad factors, multifaceted roles, and intricate evolution underlying food grinding behavior, benefiting laboratory animal husbandry and ecological environment protection, and identifying potential physiological benefits yet undiscovered.

Effect of Food Restriction on Food Grinding in Brandt's Voles

Food grinding is supposed to be influenced by multiple factors. However, how those factors affecting this behavior remain unclear. In this study, we investigated the effect of food restriction on food grinding in Brandt's voles (Lasiopodomys brandtii), as well as the potential role of the gut microbiota in this process, through a comparison of the variations between voles with different food supplies. Food restriction reduced the relative amount of ground food to a greater extent than it lowered the relative food consumption, and altered the abundance of Staphylococcus, Aerococcus, Jeotgalicoccus, and Un--s-Clostridiaceae bacterium GM1. Fecal acetate content for the 7.5 g-food supply group was lower than that for the 15 g-food supply group. Our study indicated that food restriction could effectively inhibit food grinding. Further, Un--s-Clostridiaceae bacterium GM1 abundance, Aerococcus abundance, and acetate content were strongly related to food grinding. Variations in gut microbial abundance and short-chain fatty acid content induced by food restriction likely promote the inhibition of food grinding. These results could potentially provide guidance for reducing food waste during laboratory rodent maintenance.

Effects of Various Commercially Available Enrichment Options on Handling and Chronic Stress Markers in Female ICR Mice

Although social housing of mice generally is preferred, mice must be individually housed in some situations. In these cases, enhanced attention to environmental enrichment is encouraged, but few studies assess the wellbeing of mice provided various enrichments. In this study, we used female ICR mice to evaluate enrichment strategies that encouraged natural behaviors including foraging, exercise, sheltering, and socialization. After 3 mo of exposure to the assigned enrichment strategy, wellbeing was assessed by evaluating behavioral and physiologic differences between groups. The results suggested that the use of red-tinted igloos may decrease markers of mouse wellbeing. However, none of the selected strategies yielded measures of wellbeing indicating improvement as compared to individually housed mice with no enrichment (negative control). Furthermore, measures were not significantly different between paired mice and individually housed mice with no enrichment.

Effects of Nesting Material on the Toxicologic Assessment of Cyclophosphamide in Crl:CD1(ICR) Mice

The provision of nesting material benefits mice by reducing cold stress, improving feed conversion, increasing litter size, and improving adaptive immunity. The effects of toxins are sensitive to environmental changes, and the introduction of novel items can alter results in some toxicologic studies. We hypothesized that nesting material would reduce stress and positively alter immunologic parameters in Crl:CD1(ICR) mice, thus changing typical results from a well-studied immunomodulating drug, cyclophosphamide. A 13-wk study assessed the following treatments in a factorial design (n = 4; 32 cages total): nesting (0 or 10 g) and drug (50 mg/kg cyclophosphamide or 10 mL/kg saline; IP weekly). Detailed examinations and body weights were recorded weekly, and nests were scored twice weekly. Fecal pellets were collected at 0, 4, 6, and 12 wk for analysis of corticosterone metabolites. At study termination, clinical pathology and immune parameters were collected, a necropsy performed, and lymphoid organs and adrenal glands were submitted for histopathology. All expected results due to cyclophosphamide were observed. Nesting reduced the proportion of mice with piloerection, and body weights were highest in saline-nested male mice. No differences in hematology, clinical chemistry, or absolute lymphocyte counts were observed. Corticosterone metabolites in all nested groups were not different from baseline levels but all nonnested groups had higher levels than baseline. Nested cyclophosphamide-treated groups had significantly lower corticosterone levels than nonnested cyclophosphamide-treated groups. This study illustrates that nesting material does not alter the results of a standard toxicology study of cyclophosphamide but alleviates study-related stress and improves mouse welfare.

'Cyclical Bias' in Microbiome Research Revealed by A Portable Germ-Free Housing System Using Nested Isolation

Germ-Free (GF) research has required highly technical pressurized HEPA-ventilation anchored systems for decades. Herein, we validated a GF system that can be easily implemented and portable using Nested Isolation (NesTiso). GF-standards can be achieved housing mice in non-HEPA-static cages, which only need to be nested 'one-cage-inside-another' resembling 'Russian dolls'. After 2 years of monitoring ~100,000 GF-mouse-days, NesTiso showed mice can be maintained GF for life (>1.3 years), with low animal daily-contamination-probability risk (1 every 867 days), allowing the expansion of GF research with unprecedented freedom and mobility. At the cage level, with 23,360 GF cage-days, the probability of having a cage contamination in NesTiso cages opened in biosafety hoods was statistically identical to that of opening cages inside (the 'gold standard') multi-cage pressurized GF isolators. When validating the benefits of using NesTiso in mouse microbiome research, our experiments unexpectedly revealed that the mouse fecal microbiota composition within the 'bedding material' of conventional SPF-cages suffers cyclical selection bias as moist/feces/diet/organic content ('soiledness') increases over time (e.g., favoring microbiome abundances of Bacillales, Burkholderiales, Pseudomonadales; and cultivable Enterococcus faecalis over Lactobacillus murinus and Escherichia coli), which in turn cyclically influences the gut microbiome dynamics of caged mice. Culture 'co-streaking' assays showed that cohoused mice exhibiting different fecal microbiota/hemolytic profiles in clean bedding (high-within-cage individual diversity) 'cyclically and transiently appear identical' (less diverse) as bedding soiledness increases, and recurs. Strategies are proposed to minimize this novel functional form of cyclical bedding-dependent microbiome selection bias.

Cooking increases net energy gain from a lipid-rich food

Starch, protein, and lipid are three major sources of calories in the human diet. The unique and universal human practice of cooking has been demonstrated to increase the energy gained from foods rich in starch or protein. Yet no studies have tested whether cooking has equivalent effects on the energy gained from lipid-rich foods. Using mice as a model, we addressed this question by examining the impact of cooking on the energy gained from peanuts, a lipid-rich oilseed, and compared this impact against that of nonthermal processing (blending). We found that cooking consistently increased the energy gained per calorie, whereas blending had no detectable energetic benefits. Assessment of fecal fat excretion showed increases in lipid digestibility when peanuts were cooked, and examination of diet microstructure revealed concomitant alterations to the integrity of cell walls and the oleosin layer of proteins that otherwise shield lipids from digestive lipases. Both effects were consistent with the greater energy gain observed with cooking. Our findings highlight the importance of cooking in increasing dietary energy returns for humans, both past and present.

Effects of price and pellet type on food waste in mice

When laboratory mice are provided with free access to food, they often fragment their food such that it collects on the cage floor - wasted. An operant analysis of food waste, however, has not yet been conducted. The purpose of the present study was to evaluate the effect of response requirement and pellet type on food waste using a behavioral economic paradigm. Sixteen mice responded under a series of escalating fixed ratio schedules. Nose pokes were reinforced with either a grain-based pellet or a fiber-based pellet (diluted with non-digestible cellulose) across conditions. We found that mice spilled a greater percent of the total earned pellets at low response requirements. Additionally, mice spilled more fiber-based pellets relative to grain-based pellets. This difference was most pronounced when the fixed ratio requirement was low and was attenuated as the fixed ratio was increased, and this decrease in food waste across prices was well accounted for by an exponential model. Mice may have been extracting the calorically dense components of the fiber-based pellets only when the schedule of reinforcement was rich. When the schedule of reinforcement was lean, responding for a new pellet likely was a more functional behavior than fragmenting a pellet and discarding portions.