Thirty-seven Minnesota dairy herds were utilized in field studies to determine the impact of an exogenous fibrolytic and amylolytic enzyme blend (ENZ) on dairy cow performance. Each study consisted of two 21-d periods with cows offered their standard diet for 21 d, followed by a 21-d period with ENZ added to the diet at a rate of 10 g/hd/d. The majority of herds were fed a 50–65% roughage diet based on corn silage, haylage, and corn. Dry matter intake, milk yield, milk fat, milk protein, and MUN were determined by period for each herd. Daily temperature, humidity, and the temperature-humidity index were collected and averaged across period for each herd. Manure, feed ingredient, and TMR samples were collected once per period for nutrient analysis. A meta-analysis was conducted with the data from each field study. Dry matter intake was reduced (P-value < 0.0001) from 24.2 kg to 23.5 kg while milk: feed was improved (P-value < 0.0001) from 1.37 to 1.41 when ENZ was added to the diet. Milk yield, milk fat, milk protein, and MUN were not impacted by the addition of ENZ to the diet. Potentially digestible NDFD was reduced (P-value = 0.02) from 72.3 to 62.7% and NDFD was reduced (P-value = 0.03) from 41.69 to 36.19% when ENZ was added to the diet. During the study temperature increased (P-value < 0.0001) from 25.1 to 26.9°C and THI increased (P-value < 0.0001) from 76.5 to 79.4 for periods 1 and 2 respectively. Literature would suggest that as temperature and THI increase, DMI and milk yield decrease linearly. The average change in DMI and milk yield observed in this study was less than expected based upon calculations derived from the literature when ENZ was included in the diet. Therefore, it can be concluded that ENZ improved the efficiency of milk production by mitigating the drop in DMI and milk yield due to the increase in THI.