Reproduction and Body Weight of Mice after Long-Term Selection for Large Litter Size

ABSTRACT:Alternative methods of selection to increase litter size in mice have been practiced for 21 generations followed by six generations of relaxed selection. Three replicates were used with four selection criteria: index of components (IX: I = 1.21 x total ovulation rate + 9.05 x ova success), uterine capacity (UT), litter size (LS), and an unselected control (LC). In IX, ovulation rate and ova success were measured by number of corpora lutea and number of pups bornlnumber of corpora lutea, respectively. In UT, uterine capacity was measured and defined as number of pups born to unilaterally ovariectomized (right ovary excised) females. Selection in LS was based on number born to unaltered dams. In all cases, number born was fully formed, live or dead pups. Pups from 16 randomly chosen LC dams and from the top 16 dams in IX, UT, and LS were selected to produce the next generation in each criterion-replicate line.

Section: Resultsmentioning

confidence: 73%

“…J. Eisen, personal communication) or 29 generations (Bakker et al, 1978) in other experiments with mice. Response in number born (uterine capacity) to the UT selection criterion also was positive, but smaller (.09 pups per generation), as might be expected when selecting for increased number of embryos in a more crowded uterine environment.…”

Section: Resultsmentioning

confidence: 99%

Alternative methods of selection for litter size in mice: III. Response to 21 generations of selection

Kirby

Nielsen

1993

“…Improvements in litter size in mice have occurred from direct selection (Falconer, 1955(Falconer, , 1965(Falconer, , 1971Bradford, 1968Bradford, , 1979Joakimsen and Baker, 1977;Bakker et al 1978;Eisen and Durrant, 1980) and from selection for embryo (fetal) survival rate (Bradford, 1969(Bradford, , 1979. Responses from direct selection have been attributed largely to increased ovulation rate and stable or increasing survival rate (Bakker et al, 1978;Bradford, 1979).…”

Section: Discussionmentioning

confidence: 99%

Index Selection for Components of Litter Size in Swine: Response to Five Generations of Selection

Neal

Johnson

Kittok

1989

Selection for an index of ovulation rate (OR) and embryo (fetal) survival rate (ES) to 50 d of gestation (I = 10.6 x OR + 72.6 x ES) was practiced for five generations in a line that was a composite population of the Large White and Landrace breeds of swine. A control line sampled from the same population was selected randomly and mated. Ovulation rate and number of fetuses (FETS) were measured by laparotomy and ES was calculated as FETS/OR. The select line averaged 43 litters by 18 sires and the control line averaged 42 litters by 15 sires per generation. Each generation, all females available in the select line (average of 147) were mated and laparotomized, but only selected females were farrowed. One-half of the females underwent laparotomy in the control line. Inbreeding coefficients at generation five averaged 5.34% for the select line and 4.59% for the control line. Regressions of the difference between means of the lines on generation number were .57 ± .11 for OR, -.013 ± .0096 for ES, .20 ± .20 for FETS and 5.10 ± 1.76 for I. Realized heritability for I was .30 ± .09. Heritabilities estimated by regression of daughter on dam were .17 ± .07 for OR, .18 ± .09 for ES and .08 ± .10 for FETS, and the genetic correlation between OR and ES was estimated to be -.56 ± .24. The increase in number of pigs per litter at birth was .19 ± .14 per generation. INDEX SELECTION FOR COMPONENTS OF LITTER SIZE IN SWINE: RESPONSE TO FIVE

“…Response to selection for increased litter size is realized in part through an increase in number of ova shed (Falconer, 1960;Joakimsen and Baker, 1977;Bakker et al, 1978). Bakker et al (1978) also observed an improvement in survival before and after implantation.…”

Section: Introductionmentioning

confidence: 98%

“…Litter size has been successfully increased through direct selection on increased number born (Falconer, 1960;Joakimsen and Baker, 1977;Bakker et al, 1978;Eisen, 1978;Kirby and Nielsen, 1993) or on its components: ovulation rate (Land and Falconer, 1969), prenatal survival (Bradford, 1969(Bradford, , 1979, uterine capacity (Kirby and Nielsen, 1993), and an index of components (Kirby and Nielsen, 1993).…”

Section: Introductionmentioning

confidence: 99%

Embryonal survival to 6 days in mice selected on different criteria for litter size.

Ribeiro

Engelen²,

Nielsen

1996

Embryonal survival was compared in mice resulting from four criteria of selection: LS = selection on number born; IX = selection on an index of ovulation rate and ova success; UT = selection on number born to unilaterally ovariectomized females; and LC = unselected control. Selection occurred for 21 generations with three replicates of the four criteria; thereafter, relaxed selection was practiced. The evaluation was performed using mice of two replicates at Generation 35 and one replicate at Generation 36. Data on a total of 289 female mice were recorded. Females, at an average age of 9 wk, were mated to males of the same line. Six days after mating, each female was killed, ovaries were excised, corpora lutea were counted and equated to number of ova shed, and the numbers of implantation sites in each uterine horn were recorded. Least squares means were .84, .91, .85, and .82 for left embryonal survival (left implantations/left ova) and .91, .90, .86, and .87 for right embryonal survival for LS, IX, UT, and LC, respectively. The right side had greater ovulation rate ( P < .001) and number of implantations ( P < .001). For embryonal survival, the criterion × side interaction was possibly important ( P < .09). Selection for litter size by different criteria increased ovulation rate ( P < .003) and embryonal survival ( P < .05) to 6 d. However, responses in embryonal survival were not greater after UT selection compared with LS or IX selection.