(a) To obtain information concerning the sexual activity of cattle under the environmental conditions prevailing in the north western, semi-arid, summer rainfall areas of the Union of South Africa, a series of sex-physiological researches are being carried out at the Veterinary Research Station, Armoedsvlakte, near the town of Vryburg, in the Cape Province.
(b) This article reports upon the sexual activity of groups of 2 year old, 7/8th bred, Afrikaner, Fries, Redpoll and Sussex heifers, which were tested for oestrus day and night at one hourly intervals from January 3rd to February 15th, 1940, i.e., during full summer conditions.
(c) The experimental animals, the prevailing environmental conditions and the technique employed to record sexual activity, are described.
(d) The results of the investigation show that the bonemeal fed heifers were sexually much more active than the heifers which received no phosphutic supplement. Nutritional deficiency therefore affected sexual activity.
(e) The duration of the ovarian cycle, not only of the groups, but also of the individual experimental heifers, fell within the standard range of 17 to 24 days, as found in textbooks. The Armoedsvlakte environment did not influence the duration of the ovarian cycle.
(f) The standard range for the duration of oestrus proper is given in textbooks as 18 to 24 hours. During the investigation, the average duration for the Afrikaner group was 7.88 hours; for the Fries 11.67 hours; for the Redpolls 14.00 hours, and for the Sussex 9.00 hours; for the exogenous breed groups together it was 11.74 hours. Of the 86 oestrous periods recorded no less than 81, or
94 per cent. were shorter than 18 hours. At Armoedsvlakte the environment shortened the duration of oestrus to a very significant degree, i.e. compared with the accepted standard range.
(g) The results indicate, but do not prove, a difference in duration of oestrus proper between indigenous and exogenous types of heifers.
With more information it is probable that such a type difference will be demonstrated.
(h) The available data show that the oestrus proper of the Afrikaners was shorter than that of the Fries and Redpolls, and that the Redpolls have a longer duration than the Sussex. With more data, other significant breed differences will probably emerge.
(j) Observations on the reactions of heifers to actual services by "teaser" bulls and on the use of aproned bulls (which cannot serve the heifers) suggests that oestrus proper is shortened in duration by the former method.
(k) Oestrus proper was preceded by a period during which sexual activity waxed and was succeeded by a phase during which activity waned. The period of "onset" of oestrus varied from 5.19 to 8.78 hours in the individual breed groups, and the average period of "disappearance" from 5.00 to 7.45 hours. No breed group differences were found. In both phases, the frequency distribution showed a dominant tendency to short durations.
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