From the Archives, in Recognition of the 75th Anniversary of AALAS: “The Long-Evans Rat in Biomedical Research” – A Special Issue of Laboratory Animal Care (1969)

The previous article republished in this series was a review that covered some of the background, history, and genetics of the “Swiss” mouse stock. The installment in this issue is a rat-related follow-up.

For the October 1969 issue of Laboratory Animal Care, in addition to the standard journal content (published as Part I), there was a second special issue released as Part II. This was composed of papers originally presented earlier in the year at a symposium sponsored by the New York Metropolitan Branch of AALAS entitled “The Long-Evans Rat in Biomedical Research.” The 11 articles comprising the special issue were edited by Steven H. Weisbroth, MS, DVM, DACLAM. At that time, Dr. Weisbroth was employed in the Department of Laboratory Animal Medicine at the State University of New York, Stonybrook. The articles covered a broad range of topics including the origin of the Long-Evans (LE) rat stock as well as its biology, breeding, genetics, and experimental uses. Some articles compared the biologic and pathologic responses of LE rats to Sprague–Dawley and other rat stocks and strains commonly in use at the time. See the Foreword reproduced below.

Two articles have been selected for republication in this issue. The first is a brief review of the history and derivation of the LE rat including a discussion of rat coat color genetics and an explanation of how the selection for the hooded coat pattern contributed to the establishment of LE stock by Drs. Long and Evans at the University of California, Berkeley. ¹ The second article outlines the process used by a commercial breeder (Blue Spruce Farms) to establish a barrier-maintained SPF breeding nucleus of LE rats using cesarean derivation and cross-fostering onto defined-flora dams brought in from another source. ² With the use of gnotobiotic rodents on the rise, contemporary readers may be interested in the descriptions of the construction details (including plastic sheeting-clad walls) and operating practices of the barrier facility that were used in this work decades ago. Together, the 2 articles provide important background on the LE stock and give a snapshot of methods being used at the time in an attempt to improve the health status of commercially available rats.

Dr. Weisbroth’s name will be well known to those who are familiar with the history and literature of laboratory animal science and comparative medicine, since he is a very prolific scientific author who has played a part in the writing of many seminal books, articles, and guidelines that have helped shape our field. Similar to this LE meeting in 1969, he was involved in another set of early symposia that focused on the laboratory rabbit, and those presentations became the backbone of the first “blue book” in the American College of Laboratory Animal Medicine (ACLAM) series, The Biology of the Laboratory Rabbit, which he coedited with Drs. Ronald E. Flatt and Alan L. Kraus. ³ Dr. Weisbroth has a long history with AALAS and its journals, having been awarded the Griffin Award and serving at one time on the Laboratory Animal Science Editorial Board. He currently has one of the longest streaks of publishing in AALAS publications that I am aware of, with his first coauthorship found in a 1966 issue of Laboratory Animal Care and his most recent paper being published in June of this year (2024) in Comparative Medicine!

For those unfamiliar with the old term, “PPLO” as used in the second article stands for “pleuropneumonia-like organisms” and refers to microbes we now know as Mycoplasma. Interestingly, there was a follow-up article published 5 y later. It revealed that after the original rederivation, colony monitoring performed at the 9-mo interval on the original LE barrier breeding stock identified a 10% prevalence of Mycoplasma pulmonis. Efforts were made to repeat the rederivation with improved methods. Unfortunately, they continued to struggle with Mycoplasma contamination, but along the way, Dr. Weisbroth and his collaborators validated the testing of these rat colonies for Mycoplasma using nasal washings obtained from live, sedated rats within the barrier as an alternative to postmortem sampling of tissue samples taken from euthanized animals. This early Replacement, Reduction, and Refinement (3Rs)-type approach to reduce the number of animals killed for microbial monitoring was then shared with the laboratory animal science community. ⁴

Foreword

In an effort to obtain information about the characteristics of the Long-Evans stock of laboratory rats (Rattus norvegicus), a symposium was organized under the auspices of the New York Metropolitan Branch, American Association for Laboratory Animal Science. The papers were presented at the College of Physicians and Surgeons, Columbia University, New York, N.Y. in both an afternoon and evening session on the 27th of March 1969. Because of the interest that prompted this symposium, the papers were selected to either review certain aspects of the biology of Long-Evans rats or to present studies where Long-Evans rats were compared with recognized stocks of albino laboratory rats. In addition to the reviews, information was sought on the biologic response of Long-Evans rats to various stressors. The contributors to the symposium addressed themselves to these ends. The 140 registrants represented a broad spectrum of those with an interest in laboratory animals. They included investigators from universities and research institutes, representatives of pharmaceutical companies, breeders, and those engaged in laboratory animal care.

Steven H. Weisbroth