A meta-analysis was conducted which compared grazing swards containing a grass species and at least one herb species to grazing swards without herb species. Effects on milk production and urinary nitrogen excretion were determined. A literature search was completed on the online databases CAB Direct, Web of Science and Google Scholar using the search strategy ‘dairy cow’, ‘herb OR forb OR phorb’ and ‘grazing’. Studies were screened by title and abstract. They were included for further screening if they were reported in English, the population in the study was dairy cows and the treatment included at least one herb species in a grazing sward with a grass. The comparator was taken as a sward containing grass only or grass and clover. Milk yield, variance, and sample size were required for eligibility. In all, 116 studies were identified. A total of 41 duplicates were removed. After eligibility screening, 11 papers from 6 publications, published between 2006 and 2018, remained. Studies were from New Zealand (n = 7), Australia (n = 3) and the US (n = 1). The population were either HF or HFxJe with a range in mean daily milk yield from 12.05 to 34.7 kg (mean = 18.6kg). A total of 324 and 284 cows were included in treatment and control groups respectively for milk production analysis. Data analysis was conducted in R using a random effects model. Heterogeneity was reported using the I² statistic. Analysis of milk yield resulted in a point estimate = +1.04 kg/cow/day (CI = 0.64, 1.45; I² = 17%). Milk solids (fat + protein) analysis generated a point estimate of +0.03 kg/cow/day (CI = −0.01, 0.08) with significantly higher heterogeneity (I² = 68%). Urinary nitrogen was estimated from MUN when reported (n = 6). A point estimate of −34.87 mg/dL (CI = −67.15, −2.6) was generated although heterogeneity was high among studies (I² = 59%). This meta-analysis shows the potential benefits of multispecies swards. Despite heterogeneity, the negative confidence interval indicates a reduction in urinary nitrogen excretion. In addition, a potential increase in milk yield was shown.