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Maurer, Barbara (2005): Auswirkungen von "Gentling"-Programmen auf das Verhalten von Laborratten (Wistar). Dissertation, LMU München: Faculty of Veterinary Medicine
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Abstract

The goal of this study was to investigate whether there is a “critical period” in the fourth and fifth week of life of laboratory rats, where an effect comparable to a socialisation to people can be achieved. Preliminary tests on 6 female wistar-rats at the age of six weeks have been carried out to test different methods of non-invasive stress assessment in rats, and to develop a test procedure for the main experiments. Not all investigated methods of stress assessment were applicable for the performed study. For example it could be shown that the determination of corticosterone metabolites in the faeces pointed out a distinct circadian rhythm, but no stress-related peak after performing the planned test procedure. The determination of IgA in the faeces has not been adequate to show stress-induced changes either. The developed test procedure consisted of different behaviour tests: a modified home cage emergence test, a modified open field test, and a handtest. Additionally, a neck grip and a body-surface thermometry have been carried out, and catching has been evaluated. In main experiment I, the animals have been allocated to different cages, splitting into experimental and control groups in a genetically balanced way. The rats have been housed in groups of three under standard conditions in type-IV Makrolon™ cages. 24 female wistar rats of age 21 days have been used for main experiment I (“early gentling”). The animals of the experimental group have been gentled for 10 minutes each day in the fourth and fifth week of life. All animals underwent tests to assess their behaviour towards people at the beginning of the sixth, eighth, tenth and fourteenth week of life, as well as at the age of six, six and a half and nine months. Following the tests at the beginning of the fourteenth week of life and at the age of six months the same test procedure has been carried out by a person unfamiliar to the rats (test with unfamiliar person). 12 female wistar rats, which were sisters of the animals in main experiment I and had been purchased together with them at the age of 21 days, have been used for main experiment II (“late gentling”). All animals were tested for the first time at the age of 6 months. In this test, as in the subsequent test with the unfamiliar person, they served as the zero check for the animals of main experiment I. Following these tests, the animals were allocated into experimental and control groups. The six animals of the experimental group were gentled for 10 minutes each day for two weeks. After the two weeks of gentling, at the age of six and a half months, and at the age of nine months, the rats of both groups have been tested to assess their behaviour towards people. For the main experiment III (early “intensified gentling”) 24 female wistar rats of the age of 21 days have been used. The animals of the experimental group were gentled in the fourth and fifth week of life for 10 minutes twice each day. Furthermore, the animals were talked to during the gentling and recieved a food reward. The tests have been performed analogously to the tests of main experiment I. All different parts of the test procedure have been analysed separately. Furthermore five principal target figures (PTF), summarising some results, have been defined. PTF 1 summarised the audible vocalisation and the freezing behaviour during the catching tests, PTF 2 the audible vocalisation and biting during the manipulations and the neck grip as well as the abortion of the neck grip, PTF 3 the behaviour during the handtest, PTF 4 the behaviour towards the stressor in the open field and PTF 5 summarised catching from the open field, without vocalisation. High values have been rated as “tameness”. The “early gentling” of main experiment I had a distinct effect on the behaviour towards people. The animals of the experimental group showed a significantly (p<0.05) higher tameness” than the animals of the control group in test 1 (beginning of the 6th. week of life) in PTF 3 and 4, in test 2 (beginning of the 8th week of life) in PTF 4 and 5, in test 3 (beginning of the 10th week of life) in PTF 3 and in test 5 (14th week of life, test with unfamiliar person) in PTF 1, 4 and 5. The gentling programme, conducted at the age of 6 months (main experiment II), had no noteworthy effect on the behaviour towards people. In both tests the differences between experimental and control group in the PTF were insignificant. The early “intensified gentling” in main experiment III had the most distinctive effect on the behaviour towards people. The animals of the experimental group showed in at least one PTF a significant higher “tameness” than the animals of the control group in test 1 (beginning of the 6th week of life) up to and including test 7 (6 months, test with unfamiliar person). In test 1 (beginning of the 6th week of life), the difference in PTF 3 was significant with p<0.01 and in PTF 2 with p<0.05. In test 2 (beginning of the 8th week of life) the difference in PTF 1 was significant with p<0.01 and in PTF 3 and 4 with p<0.05. Furthermore, the animals of the experimental group showed in test 3 (beginning of the 10th week of life) in PTF 4 and in test 4 (beginning of the 14th week of life) in PTF 1 and in test 5 (14th week of life, test with unfamiliar person) in PTF 1, 2 and 5, in test 6 (6 months) in PTF 1 and in test 7 (6 months, test with unfamiliar person) in PTF 2 a significant (p<0.05) higher “tameness” than the animals of the control group. Further results were that the gentling in the fourth and fifth week of life led to a significant (p<0.001) better feed utilization for the animals of the experimental groups. In parts great differences in the behaviour of the animals of the different litters occured. Not all litters were responsive to the gentling to the same extent. Furthermore, with increasing number of conducted tests, a habituation of the animals to the test procedure occurred. The gentling programmes were appropriate to reduce the fear reactions of laboratory rats towards people, when they were conducted on the animals in the fourth and fifth week of life. The animals which have been gentled at that age showed fewer fear reactions in contact with people. A more intense gentling led to longer lasting effects. Because the results of the tests with the unfamiliar person also indicated a higher “tameness” in the experimental group, this could be taken as a hint that the gentling had an effect on the behaviour towards people in general and was not limited to the experimenter. Since the gentling effects did not last a lifetime, they could not be called a “socialisation” to people. However, the results have to be regarded as hints that a “critical period” does exist in the early development of laboratory rats, in which they are particularly responsive to a gentling programme. Further studies are necessary to develop a gentling programme optimised for effort and impact, and to more accurately define the “critical period”.