Components of litter size in mice after 110 generations of selection

Abstract

The aim of the present study was to evaluate how ovulation rate and survival rate through pregnancy had been affected by more than 110 generations of upwards selection on litter size in mice. The mean number of pups born alive was 22 in the high line (selected line) and 11 in the control line (an increase in 2.6 standard deviations). Selection on litter size increased ovulation rate by 4.6 standard deviations, and it is suggested that selection also increased embryonic mortality in late pregnancy. Embryo survival from ovulation until birth was 66% in the selected line and 69% in the control line, and the observed loss in litter size from day 16 of pregnancy until birth was possibly higher in the high line compared with the control line. Selection for higher litter size has significantly increased body weight in both males and females, as the mean weight at mating for the females was 46 g in the high line and 33 g in the control line respectively.

Relationships between quantitative and reproductive fitness traits in animals

“…Two very long-term selection experiments were carried out, one (experiment 1) without LS standardization (Dummerstorf, Germany;Schü ler 1982;Renne et al 1998;Langhammer & Renne submitted), and the other (experiment 2) with LS standardization (Å s, Norway; Joakimsen & Baker 1977;Vangen 1993;Holt et al 2004). In experiment 1, selection occurred for more than 130 generations (G) using an index combining LS0 and litter weight (LW0) at birth (IZ1.6 LS0CLW0).…”

High-fertility phenotypes: two outbred mouse models exhibit substantially different molecular and physiological strategies warranting improved fertility

“…As the selection aimed toward large litters, it can be suggested that an overall growth in body weight of the dams might be helpful for proper delivery. A rise in dam body weight during the selection period has also been noticed in the Norwegian high-FL (Holt et al 2004).…”

“…Nevertheless, independent of the fertility strategy selected by the particular mouse line, the improved fecundity lines deliver a substantially higher number of offspring per litter in comparison with Ctrl animals (Table 1). Interestingly, a significantly increased rate of gestational losses (as observed for FL1) has also been described for the Norwegian high-FL (Holt et al 2004). Moreover, the majority of gestational losses in FL1 animals occur during the first 4 days of pregnancy (Spitschak et al 2007).…”

“…Such protocols have been conducted in several animal species so far, e.g. mouse, pig, and rabbit (Johnson et al 1999, Holt et al 2004, Su et al 2007, Ziadi et al 2013.…”

“…Admittedly, a similar long-term breeding approach in mice has been followed by Odd Vangen et al from the Agricultural University of Norway in Å s with high-fertility mice selected for more than 110 generations (Holt et al 2004(Holt et al , 2005 (Wei et al 2013). These mice are distinguished by an average litter size of 13.4 animals.…”