Two studies were conducted on sheep in the high tropics of Colombia to study reproductive and fertility parameters associated with animal growth in this ecological zone. In the first trial, 1,389 records were used to analyze, through descriptive statistics, the fertility parameters, the birth rate, and the yield per multiple births of three genetic groups of sheep: the native Criolla and Manchada Paramuna breeds, and they were compared with the imported race Blackface. In the second study, the duration of the estrous cycle was determined and serum progesterone values were determined during the estrous cycle in 19 Criolla x Romney Marsh crossbred ewes, in this experiment, five moments of the cycle were analyzed. The fertility rates found in the Criolla and Manchada Paramuna breeds were 73.1 and 72 %, respectively, and were higher than those of the Blackface sheep (65 %). Blackface ewes showed the highest incidence of multiple births (29 %) and Manchada Paramuna ewes had the highest birth rates (93.7 %). Criolla x Romney Marsh crossbred ewes recorded a mean duration of the estrous cycle of 17.8 d. The highest progesterone secretion (11.5 nmol/L) occurred on day 9 of the estrous cycle, while in the estrus phases, its value was 0.32 nmol/L. This study contributes to the knowledge of the reproductive aspects of Colombian native sheep