The Wistar rat is selected at the Wistar Institute, Philadelphia, USA, prior to 1910. In 1932, from Wistar Institute to Glaxo Laboratory, UK. In 1933, from Glaxo to the Dutch Institution for Nutrition, Amsterdam. In 1941, the Unilever Company, Vlaardingen, the Netherlands, obtained a breeding stock from Dutch Institution for Nutrition. Thereafter, the Unilever stock was referred as the Wistar Unilever or WU rat.
In 1958, transferred from Unilever to TNO Central Institute for the Breeding of Laboratory Animals. To Harlan Laboratories through acquisition in 1986. Harlan became Envigo in 2015.
Envigo uses well-established techniques to successfully produce time mated rats, mice, hamsters, and rabbits. We use an Impedance Meter for determining the stage of estrus in rats prior to breeding. Time mated rats and mice are determined by observation of a vaginal plug. Plug date is considered to be day zero (0) of gestation.
Due to the natural variation in the length of gestation, the exact day of parturition cannot be guaranteed. In addition, Envigo cannot guarantee the minimum number of offspring per litter.
Please be aware that late-term pregnant animals may deliver their litter prematurely while in transit, and depending on the circumstances involved, requests for credit or replacement of these animals may be declined at our sole discretion.
If problems regarding gestational age or pregnancy are encountered, customers should immediately contact Envigo’s Customer Service Department and provide detailed information regarding the animals involved.
|Expected Pregnancy Rate|
|Stock or Strain||Timed mated <13 days gestation (at shipping)||Timed mated ≥ 13 days gestation and over (at shipping)||Untimed pregnant ≥ 13 days gestation (at shipping)|
* Plug guarantee only; no guaranteed pregnancy. Plug date = Day 0.
** Untimed pregnant rodents will be selected from our breeding colonies on the basis of palpation or visual confirmation. A variation of three to four days gestation can be expected. Therefore Envigo cannot be held responsible for actual gestation and/or exact day of littering.
To avoid charges, cancellations for timed mated animals must be received one week prior to mating date.