Miriam van der Meer, Patrizia Costa, Vera Baumans, Berend Olivier and Bert van Zutphen

Four groups of mice of the same inbred strain, but with different transgenic backgrounds (no treatment; integration of a functional corticotrophin-releasing factor [CRF] gene construct; integration of a non-functional CRF gene construct; transgenic technique without integration of a DNA construct) were compared, in order to identify and quantify indicators of discomfort in transgenic animals. This approach enables us to differentiate between the effects of the technique of transgenesis and the effects caused by the expression of the transgene. This paper emphasises the search for differences in the early post-natal development of the animals. To this end, newborn mice have been subjected to various behavioural tests; moreover, their growth and morphological characteristics were measured from birth up to the age of 3 weeks.
The results indicate that the presence of the microinjected DNA-construct influences the survival rate during the first 2–3 days after birth. The average loss of pups was about 10%, in contrast to the groups without the DNA construct, in which none of the pups died. The increase in the relative body weight of pups with a functional CRF construct was significantly lower than in the other groups, but only during the first 11 days. No significant differences in morphological characteristics or behavioural development were observed between the four groups. This approach was found to be adequate for detecting a broad variety of behavioural and morphological characteristics. Before general conclusions about the extent to which the technique of transgenesis affects animal welfare can be drawn, more transgenic lines should be studied in this way.
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