Effects of High Calcium and Phosphorus Administrations on Secondary Sex Ratio in Pigs

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When 19, 025 sows were administered with a calcium (Ca) and phosphorus (P) preparation containing 2.55-fold Ca and 1.54-fold P of the respective standardized mineral contents for breeders, a significantly (P<0.01) higher litter male/female ratio (secondary) was indicated in the calcium and phosphorus (Ca/P) treatment period compared to that of pre-treatment (control) interval. During the pre-treatment period, the litter sex ratio of sows indicated a value similar to previous findings. By supplementing this Ca/P preparation in breeders for a 2-year period, the male/female ratio was significantly enhanced without any apparent influences from the breed, mating pattern, seasonal variation and parity history. Further, effects on gestation period and litter size were negligible with supplementation of high Ca/P levels. On comparing the male ratio (1.395; taking the female ratio as 1) in the post-treatment (1.066) and pre-treatment (0.992) periods, the former interval manifested a significantly higher value, indicating favorable effects of the high Ca/P supplementary diet on the male/female ratio. Further, the longer the sows were supplemented with this Ca/P preparation, the higher was the male/female ratio. Terminating supplementation of the high Ca/P preparation during the post-treatment period manifested a recovery tendency of the male/female ratio to pre-treatment values.