Data on sex ratio in swine were obtained from the Ibaragi Experiment Station of Animal Industry (Ib) and the Livestock Farm, University of Tokyo (Tb), and compared with those given in the authors' three preceding reports
13). They were collected from 3, 269 head (from 1962 to 1969) at Ib and 1, 509 head (from 1959 to 1971) at Tb and analyzed for sex ratio by the methods described in reportI
1). (The classes which showed a shift of sex ratio to either sex were presented mainly in tables.) The results obtained from all the groups of breed as a whole are summarized as follows.
1) The total sex ratio (Table 1) was significantly high at Ib. No shift of sex ratio was found at Tb. There were significant differences between Tb and Ta, To, Tk or Ib of the nine farms studied.
2) One boar showed a high sex ratio of his offspring at Ib, but another showed a low sex ratio at Tb. Four sows at Ib and three at Tb exhibited high sex ratios. Three sows at Ib and two at Tb, however, showed low sex ratios (Table 2).
3) The sex ratios of litter series (Table 3) were high in two classes at Ib. Two groups of litter series presented high sex ratios, but there was (no significant difference between either of them and any other group. No such shift of sex ratio, however, was seen at Tb.
4) Only one class of litter size (Table 4) showed a high sex ratio at Tb. A shift to male was observed in the grouping of litter size at Ib.
5) A shift of sex ratio to male was seen in summer and winter for primary sex ratio, and in autumn for secondary at Ib. A significant seasonal difference was noticed in secondary sex ratio between autumn and winter at Ib (Table 5).
6) Artificial insenmination induced a shift to male at Ib, but there was no significant difference in sex ratio between it and natural mating at Ib or Tb (Table 6).
7) A high sex ratio was found in only one age class of boars at Ib, but there was no significant difference between age groups of boars at Ib. A shift to male was observed in two age classes of sows at Ib. A shift to male was found in one age group of sows at Ib, but no significant dif-ference was observed between any two age groups of sows (Table 7).
8) No shift of sex ratio was present in any age group of breed as a whole at Ib or Tb. A shift to the sex or the opposite sex of the older parent was seen in some groups of breed at both stations (Table 8).
9) A shift of annual sex ratio to female was observed in only one year at Tb (Table 9).
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