Sahiwal cows ( n = 12 ) in early lactation were used to investigate effects of adding fibrolytic enzymes produced from fungus Humicola insolens on their milk production and weight gain. Cows were randomly assigned to two treatments: control and enzyme added to concentrate. The enzyme used was a blend that contained high xylanase and low cellulase activities. The crude enzyme from H. insolens was produced under inducing conditions in a 100 L bioreactor and used for feed applications. The results of present study showed that there was significant increase in weight gain of all the enzyme fed Sahiwal cows with the passage of time. The results showed an increase of 60 kg (19.33%) weight in Samosi 92/01 (Sahiwal cow) by enzyme supplementation. In other words one kg daily weight gain was observed in this cow. There was overall 286 kg (15.07%) enhancement in weight in the all enzyme fed Sahiwal cows in 60 days. In other words 0.795 kg/day weight was enhanced in each enzyme supplemented Sahiwal cow. Growing evidence indicates that treating a diet with fibrolytic enzymes improved weight gain with no marked effects on milk production.