Forage plantain (Plantago lanceolata L.): Meta-analysis quantifying the decrease in nitrogen excretion, the increase in milk production, and the changes in milk composition of dairy cows grazing pastures containing plantain

Plantain (Plantago lanceolata L.) has been increasingly used as a forage component in dairy grazing systems due to its capacity to reduce nitrogen (N) losses, while improving or maintaining milk production. A meta-analysis was conducted to quantify the effect of plantain on milk production and urinary nitrogen (UN) excretion by dairy cows. The main outcomes of this analysis included the yield, solids (fat + protein), protein and fat components of milk, and N concentration in urine, daily urine volume, and total UN excretion by dairy cows. Overall, grazing pastures containing plantain significantly increased milk yield (weighted mean difference (WMD) = 1.02 kg/cow/day, 95% confidence interval (CI) = 0.55–1.46), milk solids yield (WMD = 0.07 kg/cow/day, 95% CI = 0.02–0.12), and milk protein yield (WMD = 23.4 g/cow/day, 95% CI = 11.3–35.5), maintained milk protein concentration and milk fat yield, but reduced milk fat concentration (WMD = −0.24%, 95% CI = −0.31 to −0.17). Feeding pastures containing plantain reduced total UN excretion by 22% (95% CI = 15–28), which was associated with a decrease of 30% in UN concentration (95% CI = 20–38) and an increase of 17% in daily urine volume (95% CI = 7–29). Subgroup analysis showed that cows grazing pastures containing plantain had a significantly higher milk yield in late lactation (WMD = 1.4 kg/cow/day, 95% CI = 0.8–1.9), but a similar milk yield in early lactation, compared to grazing control pastures. In addition, meta-regression analysis found statistical associations between the content of plantain in the diet and N concentration in urine (P < 0.001), daily urine volume (P < 0.001), and total UN excretion (P = 0.036). The results suggest that incorporating plantain into grazing pastures is a potential strategy for improving farm productivity, while reducing the environmental impact of dairy farms.