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Marte Holt - abstract fra doktorgradsavhandling
Ane Gro Siri SkjelfjordAbstract fra avhandlingen
Effects of long-term selection and inbreeding on litter size in mice / Effekter av lang tids seleksjon og innavl på kullstørrelse hos mus
In this thesis the effects of long-term selection and inbreeding on reproduction are evaluated based on data from two long-term selection experiments in mice. One of the selection experiments was conducted at the Agricultural University of Norway and covers 122 generations of selection on first parity litter size in mice. The other experiment was carried out at the University of Sydney, Australia and covers 50 generations of full-sib mating combined with selection for litter size and inter litter interval.
Response to selection is in the Norwegian lines described to be very high, and part of the response in the high line is achieved by crossing of selected lines. In generation 122, the mean number of pups born alive was 22 for the high line, and 11 for the control line. An overall estimate of heritability was 0.19 (±0.01). Comparisons of additive variance in different periods of the study revealed a decreased additive variance over periods in the low line but constant addivite variance over periods in the high line and the control line. Environmental variance increased over periods in all lines, probably due to increased environmental sensitivity of the animals.
Studies of the effect of selection for litter size on ovulation rate and embryonic survival revealed that selection has increased the mean numbers of ova shed in the Norwegian lines significantly. Selection has probably also resulted in an increased embryonic mortality (in percentage) in late pregnancy. The average number of ova shed was 33 in the high line and 16 in the control line. Selection on number of pups born alive has also increased body weight at mating.
Inbreeding combined with selection has been proven to be successful for the creation of an inbred line with a high reproductive capacity. Data for this analyses originated in seven Australian inbred lines, and revealed that inbreeding depression varies between lines. On average, inbreeding depression resulted in a reduction in the mean litter size of 0.9 pups per 10 % increase in the inbreeding coefficient.
The effect of new versus total inbreeding on number of pups born alive was also analysed. The results clearly indicate that newly created inbreeding has a larger effect than total level of inbreeding on number of pups born alive.
Key words: selection, mice, inbreeding, additive variance, old inbreeding
Pr. desember 2004:
Marte Holt, Aqua Gen AS, c/o Norsvin, Postboks 504, 2304 Hamar
Publisert: 01.12.08
Oppdatert: 05.01.09
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