| Summary: | Effectiveness Of Land Tenure Systems Regulation In African Rural Areas. Ten cycling heifers were studied during 11 months (mo) to determine the possible influence of some environmental parameters of a high altitude and tropical zone, on estrous cycle and estrus duration, hour of estrus presentation and blood progesterone levels. The climatic variables studied were rainfall, humidity, temperature, and sunshine duration. Estrous cycle duration varied between 17 and 27 days (d) with a mean value of 21.1d. Estrus duration varied between 9 and 16 h, with a mean value of 10.64 h. The percent distribution of estrus appearance at different times of a day, was as follows : 25 % occurred between 1800 and 0600 ; 37.5 % o between 0630 and 1000 ; 29.4 % between 1030 and 1600 ; and 8.1 % between 1630 and 1730. Progesterone levels in days 0 (estrus), 5, 10, 15 and 20 of the estrous cycle had mean values of 0.0, 1.27, 3.77, 4.80 and 0.32 ng/ml, respectively. Statistical analysis showed no effect of environmental parameters on the physiological variables and on the levels of the hormones analysed throughout the period studied. It seems that Holstein cattle adapt well to the climatic conditions of Bogota.
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