Timed Pregnant Mice & Rats

What to Expect for Timed Pregnant Animal Orders

How long is gestation in the rat and mouse? Counting the day the plug is detected as Day 1, parturition (birth) occurs most often on Day 20 in mice and Day 22 in rats. However, variability is normal and will occur between individuals, as well as between species and strains. As a result, not all rats and mice will deliver on the same day. For untimed pregnant orders, a variation of 2-3 days gestation can be expected. The actual gestation and/or exact day of littering cannot be guaranteed, nor can the number of pups born in a litter.

What day does implantation occur? Implantation occurs about Day 4-5 in mice and Day 5-6 in rats. We recommend that whenever possible, customers avoid orders which would ship animals during the time of implantation. In both mice and rats, a phenomenon called embryonic diapause is possible. In this condition, the female halts the development of the embryos as hatched blastocysts. They can be held in the uterus for up to 13 days. Although this phenomenon is normally associated with physiological stress of lactation, it is possible that failure or delay of implantation may occur under other stressful conditions. Please see the table below to understand the guarantees that apply for time-mated rats and mice.

Are all "plugged" animals pregnant? Not all females in which a plug is observed will become pregnant. However, for timed pregnant rat orders of 13 days or greater in gestation, the stage at which fetuses can be palpated, most rats received by customers should be pregnant.

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Pregnant Animal Policy

Charles River only uses the most up-to-date techniques and technology in producing pregnant animals for your order. Rats can be safely and accurately palpated after 13 days of gestation. Prior to that, determination of pregnancy (in both rats and mice) is made by the observation of a vaginal plug. More than 99% of our timed pregnant orders are filled successfully. We strive to continuously improve our ability to prevent all problems that may arise, especially those associated with the more difficult orders, such as inbred mice in early stages of gestation.

Percent Guaranteed Pregnant at Time of Shipment

Note: Weekend timed pregnant orders may incur surcharges. Please call customer service at 1-800-522-7287 for details.

We do not guarantee the number of offspring per litter. Due to natural variations in the length of gestation, the exact day of parturition is not guaranteed. To avoid charges, cancellations for pregnant animals must be received prior to the scheduled mating day. 

How to Report Problems with Charles River Laboratories' Pregnant Orders

Charles River stands behind all its orders. If you experience a problem with your timed pregnant animal order, contact Customer Service at 1-800-LAB-RATS (1-800-522-7287) or send an email to [email protected].

In order for our specialists to help serve you better, please have the following information ready:

• The actual number of animals received (including any extras)
• The number of animals that were pregnant.
• If the animals were not pregnant, were implantation or resorption sites observed?
• If the animals were pregnant, but the stage of gestation appeared to be incorrect, what day did it appear to be?
• How was this determined?

This information, coupled with the specifics on your order we’ll have on file, will help resolve your problem in a quick, satisfactory manner.