Effect of heat stress on reproductive performance of an imported dorper ram: a case study in Thailand

Abstract

The aim of this study was to observe the possible influence of seasonal and environmental conditions on ejaculated semen qualities and male reproductive traits in an imported ram under tropical conditions. A Dorper ram was imported from South Africa and raised in Nakhon Pathom province. Semen was collected monthly by an artificial vagina over a period of one year. Semen picture and other parameters were evaluated in each sample. Climatic data (temperature, relative humidity and day length) were provided by the Meteorological Department of the Ministry of Communications of Thailand. Results showed that semen characteristics (volume, concentration, mass motility, motility and percentage of normal spermatozoa) of this ram significantly varied according to temperature, temperature-humidity index (THI) and day length, while scrotal circumference was only significantly associated with day length. Characteristic peak of the Dorper ram’s reproductive traits was shown during the cool season from December to March.