Variation in the duration of gestation in the goat

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Abstract
(1) A large series of data on the duration of gestation in the goat has been analysed and the constants calculated. (2) The frequency curve is unimodal and symmetrical, suggesting a single factor or a variety of factors acting simultaneously as the cause for birth. (3) Slight breed differences exist in the duration of gestation in the goat as in other species examined. (4) There is a continuous variation in the duration of gestation with the time of year at which conception occurs. Spring conceptions give shorter gestations than autumn conceptions. (5) There is a distinct difference in the duration of gestation for young and older dams. This is related to the age of the dams and not to the order of the births. Gestation is shorter in the young animal than in the older. (6) In the goat the size of litter has little or no effect on the duration of gestation. (7) Constants for duration of gestation in other species have been obtained. Variability increases with the duration of oestrus and about half the variability in any species with a long oestrous period may be ascribed to this cause. (8) The factors involved in fixing the duration of gestation in the species examined are evidently the same in all cases, and probably culminate in a single agency responsible for terminating gestation.

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