|dc.description.abstract||Expansion and intensification of dairy in pasture based systems whilst economic, creates environmental challenges through nitrate leaching and degradation of water quality. With pressure to reduce nitrate leaching and simultaneously increase pasture productivity and milk production, studies have been carried out to develop management strategies to reduce N surpluses. At the animal level an effective way to reduce the environmental impacts is through nutritional interventions. Inclusion of plantain (Plantago lanceolata L.), in the traditional perennial ryegrass-white clover pastures has shown potential to reduce nitrogen concentration in urine. Most studies including plantain however, grew it in diverse pastures where it is difficult to manage persistence due to different grazing requirements compared with perennial ryegrass. Further its contribution to N loss when sown in a mix with other plant species was not clear.
This research evaluated the effect of grazing increasing proportions of spatially planted plantain and perennial ryegrass-white clover pastures species on N excretion, milk production, urinary and feeding behaviour in Canterbury, New Zealand. The experiment was carried out at Lincoln University Research Dairy Farm, Canterbury, New Zealand in April 2016. Forty eight late lactating primi and multi-parous Friesian x Jersey cows were blocked according to pre-experimental average (mean, ± s.e.m) liveweight (499.21 ± 6.44 kg), milk solids (1.41 ± 0.02 kg), milk yield (14.14 ± 0.29 kg) and age (5.42 ± 0.19). Four cows were randomly allocated to 3 replicates of 4 treatments (0% plantain, 15% plantain, 30% plantain, 60% plantain) of proportions of spatially separated perennial ryegrass-white clover and pure plantain.
Pre-grazing herbage mass (kg/ha DM ± sem) for pasture and plantain were similar across treatments (3857.9 ± 46.5 and 4973.1 ± 74.5 respectively) whilst the cows grazed the two monocultures to the same post-grazing herbage mass (1504.8 ± 36.1 vs. 1510.5 ± 79.3). Chemical composition was similar between perennial ryegrass-white clover and plantain across treatments. Pre-grazing pasture had similar CP and ME (23.6 ± 0.61%, 12.3 ± 0.03 ME/kg DM and 20.5 ± 0.24% and 12.77 ± 0.04 ME/kg DM for perennial ryegrass-white clover and plantain respectively. Dry matter intake (DMI) estimated from pre- and post-grazing herbage mass was lower (P=0.003) for PL0 than PL15, PL30 and PL60 and similar between PL15, PL30 and PL60 (14.74 vs. 15.96, 16.00, 15.97kg respectively). Milk yield (16.1 L/cow/day ), milk solids (1.6 L/cow/day), protein ( 4.5%) and fat (5.8%) were unaffected by percent proportion increase of plantain in the diet. Urine N concentration and urine N output had 33% lower N (P=0.012) in the PL60 than PL0 (0.30 vs. 0.45 g N/L and 431.3 g N /day vs. 545.4 g N/day respectively). The effect was mainly related to the difference derived from 30% to 60% plantain in the diet with the difference in N concentration and N output between PL0 and PL30 being 13%. Milk, urea and milk urea N declined (P=0.004) by 18% in PL60 compared with PL0. The urine volume (2.3 litres/urination) and patch area (0.34m2) were unaffected by the percent increase of plantain proportions in the diet. Based on urine volume, patch size and N concentration, there was a 40% decline from 316 to 190 kg N/ha in urine patch loading from 0% to 60% proportion of plantain in the diet indicating the key potential of plantain to reduce N loading in pastures. As urine loading is critical for determining N leaching, this is likely to contribute to reduced leaching even if urine frequency is marginally higher. The cows allocated more time (47.3 minutes) to plantain than pasture (43.54 minutes) during the morning grazing, but in the afternoon grazing bout, the reverse was true with more time spent grazing pasture than plantain (62.1 vs. 34.9 minutes/cow respectively). Animal bite rates were similar in the morning and afternoon grazing bouts (46 vs. 39 and 49 vs. 44 bites/minute/cow respectively).
This study confirmed that plantain has similar feed value and milk production potential to perennial ryegrass-white clover and when offered as green leafy herbage to dairy cows. However, feeding greater than 30% plantain in the diet resulted in significant reduction in both urine N concentration and urine N excretion. As these are key components of determining N loading of urine patches, the study indicates that plantain may present appealing opportunities to reduce environmental impact of dairy farming.||en