Abstract
The data used in this survey were obtained from the calving record of Japanese cattle in Akita Prefecture, during the years 196871.
The sex ratio of offsprings was 52.2±0.43 in the Japanese Black, 47.1±0.85 in the Japanese Brown and 51.2±1.23 in the Japanese Shorthorn. The total sex ratio combined these three breeds was 51.2±0.37. The ratio in the Brown breed was significantly lower than those in the other two breeds.
Of a total of 117 bulls, each produced 10 to 2, 484 offsprings, 13 showed a high (shifting to male) or low (shifting to female) sex ratio of their offsprings. Especially, two bulls of the Brown breed exhibited lower sex ratios (40.1±3.0 and 31.0±4.3).
In the Black and Brown breeds, the sex ratios in artificial insemination were lower than those in natural mating. The differences, however, were insignificant in both the breeds.
Seasonal difference in sex ratio was significant only in the Brown breed with a low ratio (43.5) in summer.
