these problems. Both the effects of the technologies themselves and their likely ramifications are addressed.
The applications of biotechnology can have adverse effects on the welfare of animals. For example, ruminants produced by in vitro culture or nuclear cell transfer methods—whether or not they carry a transgene—tend to have higher birth weights and longer gestation lengths than calves or lambs produced by artificial insemination. Large offspring syndrome (LOS) is much more frequent in cattle produced by in vitro techniques. Because of LOS, difficult calvings can be a problem and might require special husbandry or veterinary procedures such as caesarian sections. Additional health and welfare problems requiring special attention include respiratory distress, lack of suckling reflex, and a variety of pathologic conditions.
Some of the techniques in use are extremely inefficient in the production of transgenic animals. Efficiencies of production range from 0 to 4 percent in pigs, cattle, sheep, and goats, with about 80 to 90 percent of the mortality occurring during early development. Of the transgenic animals that survive, many do not express the inserted gene properly, often resulting in anatomical, physiologic, or behavioral abnormalities. The variability and subtly of response makes assessment difficult.
Unexpected phenotypic effects—especially on behavioral traits of genetically altered animals—might occur. Work with knockout and cloned mice has demonstrated, in some instances, elevated levels of aggression and impairment of learning and motor tasks, suggesting additional studies of cloned livestock are warranted. Although there generally are fewer potential animal welfare concerns associated with the production of transgenic farm animals for biomedical purposes than for agricultural purposes, some concerns remain. A common method to produce pharmaceuticals in animal tissues or fluids is to produce transgenic cattle or goats that express the protein of interest in mammary tissue. The recombinant protein then is secreted in milk when the female lactates. Those proteins either might be expressed in non-mammary tissues, or might “leak” out of the mammary gland into the circulation. If the protein is biologically active in the species in which it is produced, it could cause pathologies and other severe systemic effects.
An important animal welfare concern related to xenotransplantation is the management and housing of pigs intended for use as organ source animals. The pigs are maintained in sterile, often isolated environments to minimize transmission of disease to human recipients, but this environment might lead to abnormal behavioral development.