Differences in Fluid, Electrolyte, and Energy Balance in C57BL/6J Mice (Mus musculus) in Metabolic Caging at Thermoneutral or Standard Room Temperatures.

The Guide for the Care and Use of Laboratory Animals recommends mice be pair or group housed and provided with nesting materials. These provisions support social interactions and are also critical for thermoregulatory behaviors such as huddling and burrowing. However, studies of fluid and electrolyte balance and digestive function may involve use of metabolic caging (MC) systems in which mice are housed individually on wire-mesh floors that permit quantitative collection of urine and feces. MC housing prevents mice from performing their typical huddling and burrowing behaviors. Housing in MC can cause weight loss and behavioral changes in rodents. Here, we tested the hypothesis that MC housing of mice at standard room temperature (SRT, 22 to 23 °C) exposes them to cold stress, which causes metabolic changes in the mice as compared with standard housing. We hypothesized that performing MC studies at a thermoneutral temperature (TNT, 30 °C) would minimize these changes. Fluid, electrolyte, and energy balance and body composition were assessed in male and female C57BL/6J mice housed at SRT or TNT in MC, static microisolation cages, or a multiplexed metabolic phenotyping system designed to mimic static microisolation cages (Promethion, Sable Systems International). In brief, as compared with MC housing at SRT, MC housing at TNT was associated with lower food intake and energy expenditure, absence of weight loss, and lower urine and fecal corticosterone levels. These results indicate that housing in MC at SRT causes cold stress that can be mitigated if MC studies are performed at TNT.

Short-term Housing in Metabolic Caging on Measures of Energy and Fluid Balance in Male C57BL/6J Mice ( Mus musculus).

Metabolic caging is an important tool for quantitative urine and feces collection in rodents, although significant limitations and problems accompany its use. Despite strong opinions among investigators regarding the effects of metabolic caging on energy and fluid homeostasis, careful quantitative analysis of the impact of this caging type-particularly when used for mice-is lacking. The current study assessed the effects of metabolic caging, with or without modifications such as plastic platform inserts, on ingestive behaviors, energy expenditure, accuracy of urine and fecal collection, and ambulatory activities in male C57BL/6J mice. Housing mice in metabolic cages, regardless of platform inclusion, increased energy expenditure without modifying food intake, presumably due to the inability of mice to perform normal thermoregulatory behaviors (burrowing and huddling). Surprisingly, mice in metabolic cages actively avoided platforms, and the inclusion of platforms modified the behavior of the mice and had position-dependent effects that reduced the accuracy of urine collection. Moving mice from cohousing to individual housing in home cages also increased ingestive behaviors and energy expenditure. We conclude that single housing of male C57BL/6J mice increases energy expenditure, that this increase is potentiated in metabolic caging conditions, and that platforms in metabolic cages alter mouse behavior and urine collection. Additional future work is needed to determine the potential benefits of using higher ambient temperature for studies of mice in metabolic caging and whether the above effects occur in females and other strains of mice and other rodent species.

Assessing Accumulation of Organic Material on Rodent Cage Accessories.

According to the 8th edition of the Guide for the Care and Use of Laboratory Animals (the Guide), rodent cage accessories, such as filter tops, should be sanitized at least once every 2 wk. We performed a study to test the hypothesis that organic contamination (measured by ATP content, expressed as relative light units (RLU)) of cage accessories (wire bar inserts and filter top lids) does not differ at 2 wk (14 d) as compared with 30, 60, and 90-d time points after cage change even when in constant use. An additional time point for filter top lids of 180 d after cage change was also evaluated. Eight groups were studied: the wire bar inserts and filter top lids used for mice and rats, in both static and individually ventilated cages (IVC). When analyzing data from both mouse and rat static and IVC caging, we found that the mean RLU values for mouse IVC and rat static and IVC cage components were below 100,000 RLU at the 14-d time point. The mean value for the mouse static group was slightly above 100,000 RLU at this time point. Based on this observation, we considered 100,000 RLU to be an appropriate actionable level. We concluded that changing wire bar inserts at least every 14 d, as recommended in the Guide for sanitizing these components in mouse and rat static cages, may be considered acceptable. This interval could be extended for mouse and rat IVC cages up to 90 d while remaining below this limit. Filter top lids for mouse static cages should be changed at least every 30 d, but static rat and IVC mouse/rat filter top lids could be changed up to every 180 d, while still staying below this actionable level of contamination.

Effect of Nearby Construction Activity on Endothelial Function, Sensitivity to Nitric Oxide, and Potassium Channel Activity in the Middle Cerebral Arteries of Rats.

The present study assessed the effect of nearby construction activity on the responses of rat middle cerebral arteries (MCA)to the endothelium-dependent vasodilator acetylcholine and the NO donor sodium nitroprusside (SNP) and the activity of MaxiK potassium channels in MCA smooth muscle cells from male Sprague-Dawley rats. Two monitoring systems were used to assess vibrations in the animal rooms during and immediately after construction activities near the research building where the animal facility is located. One was a commercially available system; the other was a Raspberry-Pi (RPi)-based vibration monitoring system designed in our laboratory that included a small computing unit attached to a rolling sensor (low sensitivity) and a piezoelectric film sensor (high sensitivity). Both systems recorded increased levels of vibration during construction activity outside the building. During the construction period, vasodilator responses to acetylcholine and SNP were abolished, and MaxiK single-channel current opening frequency and open-state probability in cell-attached patches of isolated MCA myocytes were dramatically decreased. Recovery of acetylcholine- and SNP-induced dilation was minimal in MCA from rats studied after completion of construction but housed in the animal facility during construction, whereas responses to acetylcholine and SNP were intact in rats purchased, housed, and studied after construction. Baseline levels of vibration returned after the completion of construction, concomitant with the recovery of normal endothelium-dependent vasodilation to acetylcholine and of NO sensitivity assessed by using SNP in MCA from animals obtained after construction. The results of this study indicate that the vibration associated with nearby construction can have highly disruptive effects on crucial physiologic phenotypes.

Rat Breeding Parameters According to Floor Space Available in Cage.

The cage floor space recommended for a female rat with a litter is greater in the 8th edition of the Guide for the Care and Use of Laboratory Animals than in previous editions. As a result, research institutions using commonly available cages to house rats may not offer the recommended amount of space for a breeding pair and litter housed in the same cage. We evaluated breeding parameters in rats housed in cages with 143 in(2) (922.6 cm(2)) compared with 210 in(2) (1355 cm(2)) of floor space. Given the strains of rats typically used at our institution, a monogamous breeding pair and litter requires 164 in(2) (1058.1 cm(2)) of floor space according to the Guide. Pairs of breeding animals were housed in each type of cage; and average time between litters, number of litters born, percentage of litter weaned, numbers of pups born and weaned, and average weaning weights were evaluated. None of the breeding parameters evaluated differed according to the floor space of the cage in which the rats were housed.

IACUC Considerations for the Use of Livestock in Translational Research.

Through its program oversight function, the institutional animal care and use committee (IACUC) plays a central role in ensuring the humane use and care of animals in research. To be effective in this role, the IACUC requires explicit knowledge of the species for which it bears oversight responsibility. Owing to a variety of species-specific factors, such as their relatively large size and range of acceptable housing environments, livestock present many special considerations for the IACUC. This article reviews many of those considerations in a format intended to aid IACUCs in the review of animal care and use programs involving livestock species used in translational research.

The cost of self-imposed regulatory burden in animal research.

U.S. federal regulations and standards governing the care and use of research animals enacted in the mid- to late 1980s, while having positive effects on the welfare and quality of the animals, have resulted in dramatic increases in overall research costs. In addition to the expenses of housing and caring for animals according to the standards, establishing the requisite internal compliance bureaucracies has markedly driven up costs, in both institutional monetary expenditures and lost research effort. However, many institutions are increasing these costs even further through additional self-imposed regulatory burden, typically characterized by overly complex compliance organizations and unnecessary policies and procedures. We discuss the sources of this self-imposed burden and recommend strategies for avoiding it while preserving an appropriate focus on animal well-being and research success.

PCR testing of a ventilated caging system to detect murine fur mites.

Rodents housed in microisolation caging are commonly monitored for infectious agents by the use of soiled bedding sentinels. This strategy relies on the successful transmission of rodent pathogens from the index rodents via soiled bedding to sentinel cages and the subsequent infection or colonization of sentinel rodents. When the prevalence of a pathogen is low or the target agent is not readily transmitted by soiled bedding, alternative testing methodologies should be used. Given the continued prevalence of institutions self-reporting murine fur mites and with the advent of a new sensitive and specific PCR assay for mites, we sought to determine whether the exhaust system of an individual ventilated caging (IVC) system could be used for monitoring the rack's rodent population for mites rather than relying on the responses of sentinels. We deployed single cages of mice (Mus musculus) that were known to be infested with either Radfordia affinis or Myobia musculi on a 70-cage rack, sampled the horizontal exhaust manifolds weekly, and used the new PCR assay to test these samples for mite DNA. We detected the presence of fur mites at a 94.1% probability of detection within 4 wk of placement. Therefore, we recommend swabbing and testing the shelf exhaust manifolds of IVC racks rather than relying on soiled-bedding sentinels as an indicator of the mite status of the rodents on that rack.