ABAH Bioflux, 2016, Volume 8, Issue 1. http://www.abah.bioflux.com.ro 1 Follicular hierarchy evaluation of pateros ducks ( Anas platyrhynchos domestica ) from semi free- range farms of Zamboanga del Sur and Misamis Occidental, Mindanao, Philippines Leocris S. Batucan Jr., Bryan G. D. Belleza, Henry I. Rivero, Olga M. Nuñeza Department of Biological Sciences, Mindanao State University – Iligan Institute of Technology, Tibanga, Iligan City, Philippines. Corresponding author: O. M. Nuñeza, olgamnuneza@yahoo.com Abstract . The egg-type pateros ducks, Anas platyrhynchos domestica, in the Philippines are raised in the traditional semi free-range management system which allows farmers to keep the ducks in flocks as extra activities in between their crop farming routines. This study assessed the follicular development in ducks grown from farms in semi free-range system and evaluated the different conditions of the gonads using the follicular ranks and the frequency of occurrence of follicular atresia. Nineteen ducks from Zamboanga del Sur (9 aged 6-12 months; 10 aged 13-24 months) and 20 ducks from Misamis Occidental (10 each for 6-12 and 13-24 months age group) were dissected and evaluated (n=39). Results showed that the gonadosomatic index (GSI) of 6-12 month-old ducks from Zamboanga del Sur (Group 1) was 0.367% while GSI of the 6-12 month-old ducks from Misamis Occidental (Group 2) was 0.323%. Lower GSI of 0.298% was observed for Group III (13-24 month-old ducks from Zamboanga del Sur) and Group IV with 0.222% (13-24 month-old ducks from Misamis Occidental). Results also revealed atretic, unresponsive, and undeveloped follicles in almost all of the ducks sampled which appear to be affected by the type of feeding management by the farmers. Key Words: Endocrine disruptor, feeding, follicles, gonads, gonadosomatic index, management. Introduction . The Philippine duck industry is dominated by balut (partially hatched embryos) production and by smallholder production that accounts for more than 75 percent of total duck output (Dagaas & Chang 2004). The demand for duck products in the Philippines continually rises indicating that the duck industry can be a lucrative enterprise. The pateros ducks, Anas platyrhynchos domestica, are raised under two farm management systems – complete confinement and semi free-range system (Lambio et al 1988). In the latter, ducks are allowed to range freely the whole day usually in rice fields and are then herded back to their shelter at night time or during severe weather. Semi free-range management system allows the ducks to have varying food sources as compared to the commercial management system wherein the food they eat depends on the farmer’s choice. However, semi free-range management system exposes the ducks to a number of ecological factors which could alter their egg-laying capacity. Data over a 10-year period (2003-2013) showed that there is stagnation, if not contraction, in the duck inventory of five out of six regions of Mindanao (Philippine Statistics Authority 2014). The low egg productivity must be taken into account in order to help the farmers overcome decline in marketing as well as low-quality breeding stocks. One of the ways duck egg production fitness can be assessed is by checking on its follicular hierarchy and occurrences of follicular atresia on the ranks of rapidly growing follicles. Birds have unique characteristic in their ovaries wherein follicles from all stages of development exist at the same time once they reach egg-laying stage (Johnson & Woods 2007). Examination of the preovulatory follicles (POF) may provide a viable method to estimate