AGUIRRE, Germán; PARDO, Carlos    GONGORA, Agustín. ONSET OF OESTRUS, PREGNACY RATE AND RELATIONSHIP OF THE INSEMINATION TIME WITH PROGESTERONE LEVELS IN COWS BRAHMAN. []. , 11, 1, pp.766-772. ISSN 0122-0268.

Objetive. To establish oestrus frecuency, fertility rate and progesterone levels in cows brahman. Materials and methods. Onset of oestrus, pregnancy rate and the P₄ levels were analyzed to the moment of AI in Brahman cows (n=160) in a farm of Cundinamarca department (Colombia). Results. The biggest frequency of oestrus was observed in the morning (68.75%) regarding the afternoon (31.25%). Average values of P₄ were of 0.22 ng/ml, with values maxima and minima of 3.035 ng/ml. and 0.000 ng/ml, respectively. The efficiency in the oestrus detection for levels of P₄ was high (96.25%). The average of time lapsed among the moment of the oestrus detection and the insemination was of (12.6 hours). An statistical association did not found among the levels from P₄ to the moment of the insemination with the fertility rate of (45%). Conclusions. The climatic conditions or the season can affect the onset of oestrus, that the levels of P₄ by itself do not explain the rates of fertility, that the P4 is useful in the handling of reproductive control and that the AI different to the scheme AM - PM could improve the fertility rates of the programs of AI in the Colombian humid tropic.

: Oestrus; progesterone; artificial insemination; brahman.

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