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The present study was conducted to determine the effects of some environmental sources of variation on birth weight in Nili-Ravi buffalo calves born at Livestock Development Research Center Raroo Muzaffarabad over a period of 18 years. The data consisted of 416 calves born during the study period. Year of calf, sex of calf, birth season and parity were the main sources of variation on birth weight. The statistical analysis was carried out by using SAS statistical package program. The mean birth weight was 36.1±3.23 kg with a coefficient of variation of 8.62%. The birth weight ranged from 19 to 45 kg. The effects of calf sex, parity and birth season and birth year on birth weight were significant (P<0.01). Male calves were heavier (39.3±3.75 kg) as compared to female calves (33.2±3.21 kg). Birth weight of calves born during spring season had the highest value. The highest birth weight was recorded in 7th parity, while the lowest birth weight was recorded in first parity. Heavier dams produced heavier calves, and as body weight of the dam at calving increased with age of the dam at calving, the birth weight of calves born also increased. This study indicates that environment is a very important source of variation for birth weight. The improvement and control in birth weight is possible by taking into account the environmental sources of variation while executing a breeding plan for Nili-Ravi buffaloes.