Strategic management of chicory (Cichorium intybus L.) for improved milk quality and nitrogen utilization in dairy farm systems : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University

Abstract

As consumers interest in the environment and the source and quality of their functional food increase, milk quality from pastoral grazed systems is becoming increasingly important. Additionally, strategies to diminish the loss of nitrogen (N) associated with the traditional perennial ryegrass/white clover [Lolium perenne L./Trifolium repens L.; (RGWC)] are being considered. Recent research has identified the value of forage herbs as a pathway to mitigate N losses in the environment. However, the current research has focused on the role of plantain (Plantago lanceolata L.) with little emphasis on the alternative herb chicory (Cichorium intybus L.). Chicory is known to have high palatability and healthy fatty acid (FA) profile, but little is known about the best management practices for chicory in an irrigated dairy environment or about the animal response in relation to milk quality and N partitioning. The main aim of the thesis was to investigate the effects chicory-based herbage has on urine N excretion, milk production and milk FA composition of dairy cows, as well as to understand the mechanisms leading to the variation in milk FA of cows grazing chicory-based herbage and those grazing RGWC-based herbage. A secondary aim was to investigate the effect of grazing management (defoliation intensity, severity and timing) before and after vernalisation on morphology, functional traits, herbage DM production and biochemical composition of chicory and the subsequent effect on milk production and milk FA composition. Two grazing experiments and one agronomy experiment were conducted on irrigated chicory-based pastures grazed by dairy cows.

The first experiment compared milk production, milk FA, urination patterns, and N use efficiency of cows grazing chicory, plantain, or RGWC. Fifty-four Friesian x Jersey cows in late lactation were blocked into replicated groups of six cows and offered one of three pasture types. Automated urine sensors measuring urine volume and timing were affixed to approximately 10 random cows per treatment for 24 h. Milk yield was similar for all treatments, but milk solids production (protein + fat) were greater from cows grazing chicory than RGWC (1.86 vs 1.72 kg MS/cow.day, P < 0.01) while plantain was intermediate (1.76 kg MS/cow.day). Milk produced from cows grazing chicory or plantain contained greater proportions of omega-3 FA than that from cows on RGWC (P < 0.01), despite lower omega-3 FA in herbage. The traditional RGWC increased the percentage of conjugated linoleic acid (CLA; isomer C18:2 c9 t11) and vaccenic acids in milk compared with those of milk produced from herbs (P < 0.01). This reflected the greater percentage of α-linolenic acid in RGWC (P = 0.02) than in forage herbs. There was large variation in urine event volume (0.13–11.6 L per event), though mean urine volume per event was similar for each treatment (3.01 ± 0.3 L per event; P = 0.24). Water, sodium and potassium intakes from herbage was greatest for chicory compared with plantain or RGWC. Frequency of urination increased with increasing water, sodium and potassium intakes and cows grazing chicory and plantain urinated more often (28.6 and 21.2 events/cow.day, respectively) than those grazing RGWC (13.9 events/ cow.day, P < 0.05). Consequently, cows grazing chicory excreted 1.5 and 2.4 times more urine per day (P < 0.01) than cows grazing plantain and RGWC, respectively. Apparent N intake was similar between cows grazing chicory and RGWC, but greater than cows grazing plantain. However, urinary N (UN) concentrations from cows grazing chicory and plantain were similar (P > 0.05), but substantially lower than RGWC (1.3 vs 4.8 g/kg; P < 001). The reduction in UN in cows grazing herbs was mainly attributed to increased number of urinations, which resulted in urine dilution. The combination of similar urine volume per event in all three forages, frequent urinations and substantially lower UN concentration in cows grazing the forage herbs indicate a benefit from forage herbs to reduce N load onto pasture. Overall, the findings from this first experiment demonstrated the potential benefit of chicory to alter milk FA composition, however, the mechanisms leading to the increase in beneficial FA in milk of cows offered the chicory were not clear and needed further investigations. Additionally, while the study demonstrated that sole diets of chicory elevated urination frequency and reduced UN concentration when compared with RGWC, practically however, it is unlikely that farmers will grow large areas of their farm in chicory and therefore more strategic management of chicory to alter animal response (milk production, milk FA composition and urine N excretion patterns) warranted investigation.

The second grazing experiment investigated the effects of including chicory into the traditional feeding regime of ryegrass/white clover, and time of its allocation on milk production, rumen fermentation, and FA composition of milk and rumen digesta of dairy cows. Nine groups of four cows were allocated one of three replicated feeding regimes: (1) RGWC, (2) RGWC + morning allocation of chicory (CHAM), and (3) RGWC + afternoon allocation of chicory (CHPM). One cow per group had a rumen cannulae fitted. Treatment did not affect total grazing time or estimated dry matter intake, but cows ruminated less when fed chicory than RGWC. Allocating chicory in the afternoon elevated milk production compared with RGWC and CHAM. Similar to the first grazing experiment, milk from cows grazing chicory contained greater concentrations of polyunsaturated FA (PUFA) such as C18:3 c9, 12, 15 and C18:2 c9, 12 than those on RGWC. As with milk, rumen digesta concentration of PUFA increased when cows grazed on chicory rather than RGWC, which corresponded with lower concentrations of intermediate vaccenic and biohydrogenation end-product stearic acid for cows grazing on chicory. Mean ruminal pH was lower for cows offered chicory than those on RGWC, reflecting greater rumen concentrations of volatile fatty acids (VFA) for cows fed chicory. Apparent N intake was unaffected by treatment (P = 0.151). Chicory inclusion increased urination frequency by up to 69%, resulting in a 33% mean decline in UN concentration, independently of time of allocation. A decline in UN concentration was detected following greater urination activity, with cows offered CHAM having lower UN concentration than cows offered CHPM or RGWC (P ≤ 0.05) at 2000 h. The milk FA and urine excretion results of this second grazing experiment were consistent with the previous experiment showing that strategic use of chicory can achieve desired outcomes. The basis for grazing management decisions in this second experiment was informed by detailed agronomic investigation of chicory.

Concurrent agronomy studies of chicory were conducted alongside the grazing experiments. The agronomy experiment measured functional traits, morphology, herbage production and biochemical composition of chicory under irrigated field conditions before and after vernalisation in Canterbury, New Zealand. The experimental site was laid out in a complete randomized block design with four replications where two regrowth intervals and two defoliation heights were applied. Regrowth interval had a stronger influence over functional traits and herbage production than defoliation height, with more pronounced effects after vernalisation. Plants managed under shorter regrowth intervals had narrower roots with lower concentration of sugars than plants under longer intervals, which might compromise their longevity. In addition, plants managed under shorter intervals remained mostly vegetative with heavier and longer leaves, though with reduced photosynthetic capacity than those managed under longer intervals. The thermal time to initiate stem elongation in plants managed under longer intervals was ~274 growing degree-days, with a mean stem elongation rate increasing linearly at 1.4 ± 0.08 mm/growing degree-days. In terms of nutrient and FA composition of chicory herbage, the findings showed significant interaction effects between phenology stage and regrowth interval. Before vernalisation, the FA and nutrient components exhibited little variation with regrowth interval and defoliation height irrespective of time of day. After vernalisation, concentrations of linoleic, linolenic and total FA declined, by 50, 74 and 63% respectively. Furthermore, extending the regrowth interval from 300 to 600 growing degree-days after vernalisation caused a decline of 28% of linoleic, 40% of linolenic and 33% of total FA concentrations. Generally, there were little to no diurnal changes in the main FA’s with the exception of linoleic and oleic acids after vernalisation (P < 0.01). Vernalisation decreased CP, digestibility and ME, while fibre contents increased. Between morning and afternoon there were general declines in CP and fibre contents as well as increases in soluble sugars and non-fibre carbohydrates of the herbage regardless of vernalisation. While feed quality was generally poorer in vernalised chicory, the concentration of polyunsaturated FA and digestibility can be enhanced by shortening the regrowth interval. The increase in FA and feeding value in afternoon herbage may enhance both productivity and quality of the milk while minimizing environmental risks associated with pastoral farming.

Overall, the thesis shows, for the first time, that chicory is a high moisture forage crop that increases urination frequency and dilutes the N concentration of the urine when included into that traditional grazing regime with RGWC. This demonstrates the potential role of chicory in promoting environmentally sustainable pastoral dairying systems. Timing of chicory allocation affected the diurnal patterns of urine excretion, but not the daily urine excretion output, indicating that chicory could be allocated anytime during the day without compromising the potential environmental benefits. Including chicory into a traditional grazing regime has the potential to increase milk production of dairy cows and allocating chicory during the afternoon is a useful strategy that can translate to improved milk production. The thesis further confirmed that feeding chicory to dairy cows enhanced the concentration of functional FA in milk. The lower rumen pH, lower concentration of biohydrogenation intermediate and end product vaccenic and stearic acids, respectively, and the elevated concentration of PUFA in the rumen of cows fed chicory suggested reduced biohydrogenation and may explain the elevated concentration of PUFA in the milk of cows fed chicory compared with those fed RGWC. In terms of managing chicory pastures, the experiments conducted demonstrated the potential trade-offs between herbage production and feeding value as chicory plants exposed to longer regrowth intervals accumulated larger amounts of aerial mass and reduced the highly nutritious leaf proportion of the herbage. Alternating frequent and infrequent defoliation regimes might be used to optimise vegetative growth, root reserves, and pasture persistence. A key finding from the thesis quantified the growing degree-days to initiate stem elongation post vernalisation, which provides management directive for timing of defoliation of chicory in order to maintain feed quality for grazing livestock.