Can plantain maintain milk production of dairy cows whilst reducing urinary N losses?
Nitrogen (N) from urine patches is a major contributor to N leaching, due to the high loading rate of N in urine patches compared with the capacity of many plant species to take up N. This study aimed to determine milk production and urinary N excretion from dairy cows grazing a single alternative forage; plantain; to compare the effect of time of day and N fertiliser inputs on the chemical composition of alternative forages which may prove useful in reducing the supply of N to the grazing animal and; to investigate management strategies around time of day allocation which allow for at least 50% of the animals diet to be plantain. Five experiments were conducted in Canterbury, New Zealand which compared forages in grazing, small plot and in sacco studies. In the first experiment, the effects of 50% or 100% of a herbage diet of plantain on milk production and urinary N concentration were measured in two experiments for late (autumn 2015) and early (spring 2015) lactation spring calving cows. Three groups of 12 mixed age Friesian × Jersey dairy cows were offered a perennial ryegrass-white clover pasture, pure plantain or 50% perennial ryegrass-white clover and 50% pure plantain by ground area (50–50 pasture–plantain). Cows were blocked according to milksolids, age, days in milk and liveweight. The experiment was conducted for 10 days with a 3 day transition period and 7 day experimental period. Urine N concentration was lower in the late and early lactation experiments (P <0.001) for plantain (2.4 and 2.2 g N/L respectively) and 50–50 pasture–plantain (3.6 and 3.4 g N/L respectively) than pasture (5.4 and 4.7 g N/L respectively). There was an increase in urine output in late lactation from cows on plantain (73.8 L/cow/day) and 50-50 pasture-plantain (59.1 L/cow/day) compared with those on perennial ryegrass-white clover (46.5 L/cow/day). In early lactation urine volume was similar among treatments averaging 43.8 L/cow/day. The increase in urine volume in late lactation did not offset the large reduction in urinary N concentration, resulting in a 30% reduction in urinary N output from cows grazing 100% plantain (177 and 119 g N/cow/day in late and early lactation respectively) and 15-30% reduction for those on 50% plantain (213 and 114 g N/cow/day in late and early lactation respectively) compared with those grazing perennial ryegrass-white clover (251 and 205 g N/cow/day in late and early lactation respectively). An increase in urine frequency was observed in both experiments for cows on 50% or 100% plantain compared with those on pasture which may result in a better spread of urine when cows are fed plantain. Milk solids produced per cow in late lactation were greatest for cows grazing plantain (1.67 kg/day) compared to pasture (1.50 kg/day) with 50–50 pasture–plantain intermediate (1.60 kg/day). Milk solids production was similar among treatments in early lactation averaging 2.41 kg/cow/day. This experiment suggests plantain may offer environmental benefits to dairy systems by reducing the N concentration of urine deposited on the soil from grazing cows without impeding production. In the second experimental chapter, a plot experiment was carried out to examine the effects of nitrogen inputs (low (180 kg N/ha/year for grasses and herbs and 156 kg N/ha/year for legumes) and high (450 kg N/ha/year for grasses and herbs and 389 kg N/ha/year for legumes)) and harvesting time (0700 h (AM) vs 1600 h (PM)) on the chemical composition of six forages (perennial and Italian ryegrass, plantain, chicory and red and white clover). The experiment was managed as a cut and carry system with forages harvested when they reached grazing height. Nitrogen fertiliser was applied following each harvest in the form of calcium ammonium nitrate (CAN 27-0-0-0). The effect of harvest time was greater (P<0.001) than the effects of N fertiliser on chemical composition for all forages. Perennial and Italian ryegrass showed the largest increase in WSC from morning to afternoon, at the expense of NDF and to a lesser extent CP. This suggests afternoon allocation of perennial or Italian ryegrass may be beneficial to improve the nutritive value of pasture on offer and allocation timing is less important for white clover, chicory and plantain. Chicory and plantain, maintained a greater CP concentration at low N fertiliser inputs (averaging 15.3 g CP/kg DM) than the grasses (averaging 12.6 g CP/kg DM) in summer and autumn. Where N fertiliser use is limited herbs may provide a suitable alternative to meet an animal CP requirements. The higher CP of chicory and plantain may lead to greater N intake per unit DM consumed for herbs compared with perennial and Italian ryegrass. This indicates that factors other than N intake may be driving the lower N excretion seen for cows grazing plantain in Chapter 3. The third experiment, was an in sacco experiment which evaluated the effects of harvesting perennial ryegrass-white clover or plantain in the morning (0700 h) or afternoon (1600 h) on the degradation characteristics in the rumen of dairy cows. The experiment was a 2 × 2 factorial design. There were two pasture treatments of either plantain or perennial ryegrass-white clover which were harvested at two times of the day; 0700 hrs or 1600 hours. This created four treatments. Four rumen cannulated multiparous Jersey × Friesian lactating dairy cows were used. Each cow received one treatment, repeated four times until all cows received each treatment. Forages harvested in the afternoon had a greater (P<0.001) concentration of WSC (20.2 and 13.2% DM for plantain and perennial ryegrass-white clover respectively) compared with those harvested in the morning (14.9 and 8.36% DM for plantain and perennial ryegrass-white clover respectively). This came at the expense of NDF and to a lesser extent CP. However, the difference in NDF between forage types (averaging 26.1% for plantain and 40.9% for perennial ryegrass-white clover) was greater (P=0.012) than effect of harvest time. Overall the effect of altering the forage type was greater than the diurnal effect on rumen degradation characteristics. Plantain had faster (P<0.001) DM degradation rates than perennial ryegrass-white clover which resulted in faster (P=0.004) N degradation rates. Faster DM degradation rates are correlated with improved voluntary feed intakes. As a result the use of plantain as pasture for dairy systems may be useful to increase total voluntary intake. The fourth experiment compared milk production and urinary N from late lactation cows using allocation methods which provided a 50% perennial ryegrass-white clover and 50% plantain diet. Using results from the plot and in sacco experiments, three replicated groups of four late lactation, Holstein Friesian x Jersey dairy cows were blocked according to milksolids, age, days in milk and liveweight and assigned to one of two treatments of 50% plantain and 50% perennial ryegrass either as (1) spatially separated monocultures in the same paddock (spatial separation), or (2) plantain allocated following morning milking and perennial ryegrass allocated following afternoon milking (temporal separation). The experiment was conducted for 14 days comprised of a 7 day adaptation period and 7 day experimental period. Milksolids production was greater (P=0.001) for cows grazing spatial (1.53 kg MS/cow/d) than temporal (1.37 kg MS/cow/d) separation treatments. Apparent DM intake (15.0 kg DM/cow) and urine N concentration (2.6 %) was similar (P>0.05) between treatments. Under the conditions of the experiment, allocating plantain temporally resulted in lower milk production. When offering a diet of 50% plantain - 50% perennial ryegrass, this experiment suggested allocation for greatest milk production is best achieved through spatial separation. A feature of the results from the grazing experiment of this study was the reduction in urinary N concentration when cows grazed plantain, despite similar N intake to cows grazing perennial ryegrass-white clover. Other research suggests this may be due to plant secondary metabolites aucubin, acteoside and catalpol. A final experiment aimed to characterise the concentration of secondary metabolites in plantain herbage. This was a two year experiment using plantain from the plot experiment. The experiment was a randomised block design with three replicated treatments. Treatments were two N fertiliser rates (180 kg N/ha/year and 450 kg N/ha/year) and two harvest times (0700 h and 1600 h). Samples were taken seasonally when plantain had reached grazing height. Concentrations of the metabolites were varied. Acteoside consistently had the greatest concentration (ranging from 36.0-1.77 mg/g DM), aucubin intermediate (range 5.85-0.566 mg/g DM) and catalpol lowest (<0.390 mg/g DM). The concentration of metabolites was not be altered by N fertiliser and typically did not show diurnal fluctuations. There was a strong seasonal effect on the metabolites with peaks in concentration occurring in spring. This experiment suggests N fertiliser and time of day harvesting cannot be used as strategies to increase the concentration of secondary metabolites in plantain. This study confirmed that plantain has similar feed value and milk production potential to perennial ryegrass-white clover when offered as green leafy herbage to dairy cows. However, feeding plantain at 50 or 100% of 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 an appealing opportunities to reduce the environmental impact of dairy farming. This was not attributed to a lower CP of plantain but may be related to the secondary metabolites in plantain herbage.... [Show full abstract]