Breeding performance and welfare outcomes of laboratory mouse breeding schemes: A protocol for a systematic review

This is a protocol for a systematic review titled “Breeding performance and welfare outcomes of laboratory mouse breeding schemes.” Common breeding schemes for mice used in research include pairs (where one female is paired with one male), trios (two females and one male mouse), and harems (three or more females with one male). Some strategies additionally employ rotational mating (where males and females are together only temporarily rather than permanently). Several studies have investigated the impact of mouse breeding schemes on various outcomes such as litter size, offspring health, maternal behavior, and overall breeding productivity. Trio breeding is often presented as resulting in higher productivity either through increased per-cage production, and/or increasing pup survival through alloparenting. Some examples of small or non-significant increases in pup production have been reported, which are often highlighted as evidence by proponents of trio breeding. Other studies have found no significant differences between breeding systems. A meta-analysis should help to establish which results are meaningful. Trio or harem breeding poses additional animal welfare and reproductive challenges such as crowding, trampling, increased ammonia levels, and reproductive suppression in females. Rotational mating (i.e., temporary introduction of males and separation of female mice upon pregnancy or birth) has different welfare risks, such as stress related to the frequent introduction and removal of conspecifics. If these schemes do not reliably produce significantly more offspring, risks to animal welfare are not justified. By systematically analyzing the available data, the review will provide researchers and animal care professionals with a more complete picture of potential advantages and drawbacks of each breeding method. The findings of this review will help to inform best practices in laboratory animal husbandry, with implications for regulatory guidelines and standards related to responsible laboratory animal care.