PLANTAIN (Plantago lanceolata) NITROGEN USE AND EXCRETION BY LACTATING DAIRY COWS

The incorporation of plantain (Plantago lanceolata) in cows’ diets can reduce the urinary N concentration (UNc) and potentially reduce dairying’s environmental footprint. However, to provide farmers with confidence in using plantain-based swards, research needs to demonstrate that these environmental benefits are not at the expense of milk production and farm profit. This research examined the effect of grazing plantain on milk production and urine-N excretion by cows in an experiment conducted at Massey University’s Dairy 4 Farm throughout two lactation seasons (2017-2018 and 2018-2019). Three mobs of 20 cows were matched for age, weight and milk production, and assigned to graze three pasture treatments: (i) plantain, (ii) plantainclovers mix, (plantain, red [Trifolium pratense] and white clover [T. repens]), or (iii) ryegrass (Lolium perenne)-white clover (wc). The pastures were established (1 December 2016) in a complete randomised design with five replicate plots (800 m) for each treatment that were grazed from spring (September) to autumn (May). Cows were acclimatised to each pasture treatment for 6 days (adaptation period) before grazing the experimental plots (4 cows/plot) for 2 days (experimental period). Pasture intake, diet quality, and animal N (milk, urine and faeces) were measured during the experimental period in spring (September 2017, December 2017/18), summer (February 2018/19), and autumn (March 2018, May 2019) for both lactations. The cows grazing the plantain and plantain-clover mix pastures produced the same quantity of milk solids (P>0.05) as cows grazing ryegrass-wc pasture throughout both lactation seasons. Both plantain and the plantain-clover mix reduced (P<0.01) the UNc by 36 and 40% in the summer and autumn 2017-18, respectively, when compared with ryegrass-wc. However, the UNc in cows grazing plantain was 10 and 21% lower (P<0.01) during the summer and autumn 201819, respectively, when compared to those grazing the plantain-clover mix and ryegrass-wc pastures. The results demonstrate that plantain pastures do not diminish milk solids production from cows and the lower UNc from summer to autumn could reduce N being lost to the environment.