Objective: To determine the prolificacy and weight of lambs at birth (BW) in two genotypes of hair sheep within an agropastoral system on the coast of Oaxaca, Mexico, and to evaluate the effect of two sources of selenium on the performance of lambs from said system during the fattening phase. Design/Methodology/Approach: The study was carried out in an agropastoral system (coconut palm and Cynodon dactylon grass) in Río Grande, Oaxaca. Two experiments were conducted; the first studied 58 ewes distributed in a completely randomized design (CRD) with factorial arrangement of 223, and focused on the following fixed effects: genotype, number of births, and body condition (BC). The measured variables were prolificacy and BW. The second experiment studied 23 lambs of 4 months in age that were offspring of the females in experiment 1. They were distributed in a CRD with three treatments: T1, without selenium provided; T2, with barium selenate provided; T3, with selenomethionine provided. The dependent variables were daily weight gain (DWG), dry material consumption (DMC), and feed conversion (FC). Results: The Pelibuey ewes with one and two births and the Black Belly ewes with one birth demonstrated the highest averages in prolificacy (P0.05). The lowest averages (P0.05) were detected in ewes with BC 4 irrespective of number of births. The BW was affected (P0.05) by genotype; Black Belly lambs weighed 680 g (P0.05) more that Pelibuey lambs. The DWG, DMC and FC behaved similarly (P0.05) between treatments and their general averages were 0.114 kg day1, 0.679 kg day1, and 6.18, respectively. Study Limitations/Implications: In the agropastoral system, the BC of ewes limits their reproductive performance. The weight of the lambs at the start of fattening determines their performance during fattening. Findings/Conclusions: In the agropastoral system, Pelibuey and Black Belly females present adequate prolificacy averages and BW; however, it is very important that they remain within BC 3. Neither of the two sources of selenium improves DWG, DMC, and FC of lambs fattened in pens in the agropastoral system