In our Animal Breeding series, we introduce new information about mouse breeding and health every week to provide education for aspiring mouse care experts. The topic of today's article is the common problem in mouse breeding of female mice eating pups, also known as infanticide in rodents.
Read on to explore the reasons why female mice eat their infants, the ways this may be prevented, and some common questions and answers about this issue.
Why Are Mice Eating Their Babies?
There are three main reasons why mother mice eat their offspring, related to the nutrition, environment, and other contributing factors, described below:
(1) Insufficient milk production
Lack of nutrition or high temperature during lactation will lead to insufficient milk production; large litter size also leads to reduced milk production, which will cause the mice pup to compete for milk and bite the nipples of the female mouse. Thus, the female mice refuse to breastfeed because of pain and even bite their baby. In a situation where there are too many pups and insufficient milk production, the female mouse may eat part of the litter to ensure the survival of the majority of the pups.
Lack of certain nutrients will cause female mice to cannibalize and devour their pups. Studies have found that when the protein content of the feed is less than or equal to 16%, it contributes to the phenomenon of eating pups and reduces reproductive efficiency.
(1) Crowded environment
Crowded environment means high stocking densities, tight spaces, and high temperatures. Strong light or noise stimulate the female mice during lactation and cause neurological disorders. Stress from crowding can cause symptoms such as panic and irritability in female mice, and it can cause female mice to bite and eat pups.
Animals rely on scent cues and norepinephrine to form strong memories of other animals and to determine whether their pups are biological. When animals smell special odors, such as the peculiar smell caused by the replacement of the mice cage bedding, or the odor of the pups is altered by human contact, it may cause the pups to be eaten.
(1) Stillbirth and weak pups
Some female mice will eat the stillbirth as soon as they find it, and develop the bad habit of cannibalism. When there are too many pups, some pups will become weak due to stunted development. In order to ensure the survival of the next generation, the female mice usually eat the weak pups to ensure the survival of the healthy pups.
(2) Male mice eat pups
During the breeding period, both male and female animals have higher aggression, and the aggression level of male animals is higher than female animals. Aggressive behavior in both males and females decreased with increasing familiarity.
(3) Tasting blood
Generally, mice are docile, but if they have tasted blood, it may induce brutal animalism and they may develop the bad habit of eating pups. Therefore, mice that have bitten their pups will generally become habitual offenders.
(4) Motherhood instinct not developed
Female mice that give birth for the first time are inexperienced and their motherhood instinct has yet to mature, which may lead to negative emotions such as anger and impatience, resulting in the phenomenon of eating pups.
How to Prevent Infanticide in Rodents?
☑ Select the feed suitable for this strain of mice and strictly sterilize.
☑ After the feed is sterilized by high temperature and high pressure, some nutrients will be damaged to varying degrees.
☑ Provide the mice with suitable light, temperature, humidity, and quiet environment (refer to the national standard for details), control the stocking density, and do not move the mice at will within three days after giving birth. For some strains, you can consider changing the cage 7 days after giving birth.
☑ The frequency of changing cages and bedding of lactating female mice can be appropriately reduced.
☑ The light should not be too bright, especially for the white and albino mice, which should be located in the lower layer of the cage racks.
☑ It is best to choose the 2nd to 4th parity of female mice in a co-cage, which has strong reproductive ability and motherhood, and is less likely to eat pups.
☑ When the abdomen of the female mouse is obviously distended and it is confirmed that she is pregnant, put the pregnant mouse in a cage alone. Pay attention to gentle handling and movements, in order to prevent the pregnant mice from being stressed and increase the possibility of eating babies after giving birth.
☑ It is recommended not to change cages 3 days before delivery and 3 days after birth.
☑ If milk replacement is required, it is best to make the milk replacer smear with the smell of the lactating mother, such as smearing the mother's urine on the milk replacer before feeding.
☑ Once the dead pups are found, they should be dealt with in time. If there are too many pups (one female mouse with 8 pups is appropriate), the weak and thin pups should be eliminated before the female mouse eats the pups. Otherwise, after the weak pups are bitten, other healthy pups may also be at risk of being eaten.
Related Questions and Answers
Q1: Mother mice are prone to eating pups after surgery. How to solve this problem?
A: A case-by-case analysis is required. For example, what operation was performed, at what stage of motherhood, whether effective analgesia was given, and whether the smell in the cage was affected.
There may be the following reasons for the female mouse to eat the pups:
Stress response. Does surgery stress female mice? If the female mouse feels unsafe in the environment and has a lot of pressure, it will eat pups.
Effective pain relief. Pain relief before and after surgery ameliorates stress response, often recommended are tilidine, ibuprofen.
Odor, whether there are other odors in the mouse cage.
Q2: How many weeks are neonatal mice on the C57BL/6 background at risk of being eaten?
A: Generally, within 1 week of age, the mice pups are more likely to be eaten. After 1 week of age, the probability of being eaten will be lower.
However, if the 5-7day-old mice have the operation of clipping their claws, they may also be eaten after the claws are clipped. This type of procedure introduces stress and foreign odors that substantially increase the probability of infanticide.