Impact of heat stress, nutritional restriction and combined stresses (heat and nutritional) on growth and reproductive performance of Malpura rams under semi-arid tropical environment.

Abstract

A study was conducted to assess the combined effect of heat stress and nutritional restriction on growth and reproductive performances in Malpura rams. Twenty-eight adult Malpura rams (average body weight (BW) 66.0kg) were used in this study. The rams were divided into four groups: CON (n=7; control), HES (n=7; heat stress), NUS (n=7; nutritional stress) and COS (n=7; combined stress). The study was conducted for a period of 2months. CON and HES rams had adlibitum access to their feed while NUS and COS rams were under restricted feed (30% intake of CON rams) to induce nutritional stress. The HES and COS rams were kept in climatic chamber at 42°C and 55% relative humidity for 6h a day between 10:00h and 16:00h to induce heat stress. Body weight increased significantly (p<0.05) in CON as compared to NUS and COS. When compared within groups, scrotal width morning, scrotal width afternoon, scrotal circumference morning and scrotal circumference afternoon were significantly (p<0.05) larger in CON while smaller in COS rams. The higher testicular length was recorded both during morning (p<0.05) and afternoon (p<0.01) in COS rams while the lowest in NUS rams. The highest plasma testosterone concentration was recorded in CON and lowest in COS rams. Semen volume and mass motility also differed significantly (p<0.05) between the groups. The highest semen volume and mass motility was recorded in CON and NUS while lowest in both HES and COS rams. It can be concluded from this study that when two stressors occur simultaneously, they may have severe impact on reproductive performance of rams.