Fermentation properties and nutritive value of plantain (Plantago lanceolata) silage: A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy in Agricultural Science at Lincoln University

Abstract

Plantain (Plantago lanceolata) is a perennial herb from the plantaginaceae family. The increasing adoption of P. lanceolata by pastoral farmers reflects the growing interest in alternative forages to increase biodiversity and reduce nutrient losses from farm systems. However, adaptation of alternative pasture species requires understanding of how they will respond to typical management practises used for conventional pastures. Conservation of pastures by ensiling is an important forage management practise in any pastoral system. Information is required about the ensiling properties of plantain and subsequent animal response to that product. The objectives of this study, therefore, were to investigate the ensiling properties of plantain, in vitro digestibility and in vivo digestibility, and to compare the impact of pre and post ensiling management on plantain ensiling properties. Four experiments were carried out in Canterbury New Zealand between November 2016 - March 2018. In the first experiment, the effect of regrowth stage and storage duration on ensiling properties of plantain harvested in late spring were compared using replicated mini-silos (500 g FW) of plantain. Monocultures of plantain were harvested and ensiled at either 4-leaf appearance (4L), 5-leaf appearance (5L) and 6-leaf appearance (6L) and were stored for 90, 120, 150, or 180 days. In spring harvested silage, seed head made up a considerable proportion of the biomass, with increasing seed head numbers from 4L to 6L. This resulted in flow on effects with more fibre and less sugars in the 6L treatment. Pre and post harvest management had significant effects on ensiling properties with later harvesting (6L) having higher pH and lower lactic acid than earlier harvests (4L or 5L). The effect of post harvest storage duration on fermentation characteristics were variable with few consistent trends for pH, fatty acids or ammonia. However, extended storage duration resulted in loss of soluble material increasing overall mean fibre concentrations. Ensiling plantain at earlier regrowth stage resulted in silages with improved quality characteristics compared with plantain ensiled at 6L. This experiment suggests that silage made from the early regrowth stage and stored as long as 90 days produced the best quality. In the second experiment, the effect of regrowth stage (4L, 5L and 6L) and storage duration (90, 120, 150, 180 days) on plantain silage produced from autumn was tested. The results obtained were in contrast to the results obtained of experiment 1, because plantain harvested in the late regrowth stage produced silage with improved nutritional characteristics compared with early regrowth. Almost all the variables in fermentation characteristics of plantain 6L were inferior compared with the silage of plantain from the early regrowth stage, though the percentage of mould was the lowest (P=0.01). It is noteworthy that the in vitro digestibility of plantain 6L silage was higher than that of silage from the early regrowth stage (76% vs. 71.5%) and also its ME (10.4 MJ/ kg DM vs. 9.3 MJ/kgDM). In this trial, storage duration had no effect on the nutritive value and fermentative characteristics of the silage. This experiment suggests that during autumn, harvesting plantain in the late regrowth stage would be more beneficial than harvesting at an early stage of growth. In the third experiment, the effectiveness of fertilisers and additives on fermentation and nutritive characteristics were compared for spring harvested plantain at mature harvest (6L) and stored for 180 days. The various fertilisers tested were 20N; 20:1:15 NPK, 40:1:15 NPK; whereas, the additives tested were cellulase, biosil and molasses. The results suggested that there were no interactions between N fertiliser and additive on the fermentation characteristics and nutritive value of the plantain silage. However, the higher N fertiliser resulted in better fermentation characteristics of the plantain silage. Molasses also resulted in better fermentation characteristics for plantain silage, and it decreased NDF, ADF content of plantain silage. Neither the fertiliser nor the additives affected in vitro digestibility of the silage. In the fourth experiment, an in vivo DM digestibility study using lambs was conducted to confirm the results from experiments 1 and 3 by using commercially produced baleage silage that had been stored for 90 days. Four treatments: ryegrass silage, plantain silage made from an early harvest (4L), plantain silage made from a late harvest (6L) and plantain silage made from late harvest-treated molasses (plantain 6L+mol), were fed to sheep. Thirty-two male lambs aged 6-12 months with body weights of 36 kg were used for this metabolism stall study. This experiment was conducted in two runs of ten days where each run used 16 animals. Lambs consumed all silages with no evidence that novel plantain silages were less acceptable then conventional ryegrass silage. The results indicated that plantain 4L silage had high in vivo DM digestibility compared with other plantain 6L silages, although the digestibility was still inferior compared with ryegrass silage. The in vivo DM digestibility influenced the animal performance where sheep fed plantain 4L silage had better weight gains, although the greatest weight gain was still in sheep fed ryegrass silage. Plantain silage had lower crude protein then ryegrass silage at the same regrowth stage, in spite of similar crude protein at time of harvest. This resulted in lower nitrogen excretion from lambs fed plantain silage (P<0.01). The reduction in N excretion could not be explained by plant secondary compounds which were consistently absent from silages throughout all of the experiments. These studies demonstrated that plantain has some unusual ensiling characteristics in so far as the ensiled plantain does not represent well fermented forage with regards to pH, and low anaerobic stability stability due to high buffering capacity. However it has low butyric acid and in feeding trials animals found it acceptable were able to maintain weight when pre harvest management practises encouraged high nutritive value. Plantain harvested in autumn was more vegetative than that harvested in spring which led to better nutritive value, but vegetative plantain had a high buffering capacity and appeared to have a longer fermentation phase so recommendations for ensiling autumn harvest plantain are to delay harvest to allow maturity and prolong storage to allow fermentation to complete.