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Item Meat quality and fat characteristics of lambs finished on different summer forages : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand(Massey University, 2025-10-16) Phillips, HollyNew Zealand lamb production systems are typically based on grazing perennial ryegrass/white clover pastures; however forage quality and growth tend to be inconsistent over the summer period leading to reduced intakes and animal performance. Summer-active forage crops can be included in the farm system to provide a source of high-quality forage over this crucial finishing period. In addition to this, ensuring consistently high eating quality lamb meat is paramount to maintain and expand export markets, thus any change to production systems need to consider the impact on the meat produced. Whilst alternative forages to perennial ryegrass/white clover have been studied extensively for their agronomic characteristics and animal performance, less is known about the impact of an alternative forage on the value chain from farmer to processor and in particular characteristics that can impact the consumer such as meat quality. This is particularly the case with the relatively new forage brassica species, Raphanobrassica. This collection of studies conducted a comprehensive assessment of lambs grazing Raphanobrassica, Chicory, Perennial ryegrass/white clover (Chapters 3-7), Leafy Turnip, Red Clover and Perennial ryegrass/white clover + concentrate (Chapters 3-4). Studies utilised a replicated farmlet design and measured lamb growth, carcass production, meat quality, fat characteristics, volatile profile and conducted a consumer sensory evaluation. Lambs grazing alternative forages had increased lamb growth rates, carcass weights and dressing out percentages (Chapters 3 & 5). Using Raphanobrassica or Chicory resulted in greater per hectare lamb performance (liveweight gain and carcass weight produced per hectare) over the summer and autumn period. The two forage types had different factors driving this increase, with lambs fed Chicory having greater per head performance and Raphanobrassica able to support a larger number of grazing lambs per hectare due to superior forage growth in dry conditions (Chapter 5). Instrumental measurement of meat quality (pH, meat colour, shear force and water holding capacity) demonstrated small and inconsistent effects of forage diet (Chapters 4 & 6). Grazing alternative forages resulted in greater fat deposition (V-GR and intramuscular fat %) from faster growth and heavier carcasses. Changes in fatty acid composition were small and explained by the differences in IMF deposited (Chapters 4 & 6). Assessment of different grazing durations over summer and autumn (32, 35 or 67 days) showed that length of time grazing had a greater effect on meat quality and fat deposition than the forages themselves, with longer grazing durations associated with heavier carcasses, greater fat deposition and a fatty acid profile that was more saturated (Chapter 6). A stepwise analysis was used to assess the volatile profile of lamb meat, with 10 key volatile compounds differentiating the forage grazed and grazing duration. Aldehydes, alcohols and ketones (derived from lipid oxidation), sulphur compounds and hydrocarbons (non-lipid volatiles) were identified as potential markers for the forage treatments (Chapter 6). A consumer sensory panel identified meat from Chicory fed lamb as being less tender, however this can be explained by the larger carcass weights achieved on this forage type. Scores for overall liking for Raphanobrassica were dichotomous, potentially due to Raphanobrassica having more frequent rankings for greatest flavour intensity, indicating flavour intensity could be a stronger driver of liking for some consumers compared to others (Chapter 7). This research has shown that alternative forages to perennial ryegrass/white clover can be grazed by lambs over the summer period to improve animal production per head and per hectare without compromising the quality of meat produced for the processor or consumer.Item Investigation of tropical pasture species to improve dairying in the tropics : a dissertation presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University, Manawatū, New Zealand(Massey University, 2023) Jayasinghe Mudiyanselage, Priyanath JayasingheDespite the ever-increasing demand for dairy products, dairy production in tropical regions is often lower than in temperate regions, due to a range of factors including the lower nutritive value of pastures. The availability of high-quality tropical pastures is a key requirement to increase the productivity of dairy cows as well as manage enteric methane emissions. Warm-season perennial grasses are the dominant forages in tropical and subtropical regions, and thus exploring their nutritive characteristics and evaluating their likely performance in existing dairy production systems, is imperative in the effort to improve dairy productivity. This thesis was undertaken to investigate tropical pasture species for improving dairying in the tropics via a modelling and simulation approach. A dearth of data comparing the nutritive values of tropical pastures grown across different environments limits the selection of forages for livestock in the tropics. A database was constructed containing a total of 4750 records, with 1277 measurements of nutritive values representing 56 tropical pasture species and hybrid cultivars grown in 26 different locations in 16 countries, in order to compare the nutritive values and greenhouse gas production across different forage species, climatic zones, and defoliation management regimes. The average edaphoclimatic (with minimum and maximum values) conditions within this data set were characterized as 22.5°C temperature (range 17.5–29.30°C), 1253.9 mm rainfall (range 104.5–3390.0 mm), 582.6 m elevation (range 15–2393 m), and a soil pH of 5.6 (range 4.6–7.0). The data revealed spatial variability in nutritive metrics across bioclimatic zones and between and within species. The ranges of these nutrients were as follows: neutral detergent fibre (NDF) 50.9–79.8%, acid detergent fibre (ADF) 24.7–57.4%, crude protein (CP) 2.1–21.1%, dry matter (DM) digestibility 30.2–70.1%, metabolisable energy (ME) 3.4–9.7 MJ kg⁻¹ DM, with methane (CH₄) production at 132.9–133.3 g animal⁻¹ day⁻¹. The arid/dry zone recorded the highest DM yield, with decreased CP and high fibre components and minerals. Furthermore, the data revealed that climate, defoliation frequency and intensity, in addition to their interactions, have a significant effect on tropical pasture nutritive values and CH₄ production. Overall, hybrid and newer tropical cultivars performed well across different climates, with small variations in herbage nutritive value. Results revealed that greater pasture nutritive values and lower CH₄ production can be potentially achieved through the selection of improved pastures and subsequent management. Subsequently, the suitability of three improved tropical perennial pastures: Chloris gayana ‘Rhodes grass cv. Reclaimer’ (RR), Megathyrsus maximus ‘Gatton Panic’ (GP), and Brachiaria ruziziensis x B. decumbens x B. brizantha ‘Brachiaria Mulato II’ (BM) for tropical dairy production was evaluated using their carbon assimilation, canopy structure, herbage plant-part accumulation and nutritive value parameters under irrigated conditions. A field experiment was conducted at Gatton Research Dairy (27° 54′ S, 152°33′ E, 89 m asl) Queensland, Australia, which has a predominantly subtropical climate. Photosynthesis biochemistry, canopy structure, herbage accumulation, plant-part composition, and nutritive value were evaluated. Photosynthesis biochemistry differed between pasture species. The efficiency of CO₂ assimilation was highest for GP and quantum efficiency was highest for BM. Pasture canopy structure was significantly affected by an interaction between pasture species and harvest. Forage biomass accumulation was highest in GP, while BM produced more leaves and less stem compared to both GP and RR. A greater leafy stratum and lower stemmy stratum depth were observed in the vertical sward structure of BM. Brachiaria Mulato II showed greater carbon partitioning to leaves, leaf: stem ratio, canopy, and leaf bulk density. The BM also demonstrated greater nutritive value (Total digestible nutrients (TDN), ADF, NDF, neutral detergent insoluble protein (NDICP), starch, non-fibre carbohydrates (NFC), ME, mineral profile (Mg, P, K, Fe, Zn) and dietary cation-anion difference (DCAD)) for leaf, stem, and the whole plant. Overall, the observed greater quantum efficiency, leaf accumulation, and nutritive value of BM suggested that BM is an attractive forage option for dairying in pasture-based systems in tropical and subtropical climates. The DairyMod-SGS, a mechanistic biophysical pasture model was parametrised and robustly validated for the prediction of the growth of the three tropical pastures (BM, GP, and RR), aiming to use the model as an effective tool to explore the likely performances of newer species under different edaphoclimatic and agronomic management practices. The model was calibrated using measurements of biomass components, canopy structure, and carbon assimilation collected from the field experiment at the Gatton Research Dairy Farm. Subsequently, the model was tested extensively using the published and unpublished data (16 data sets, 32 experiments, 14 different locations across South America, North America, Australia and Africa) to ensure that the parameterised model performed well and was reliable across a diverse set of environments and management practices. In the model parameterisation stage, the model predicted the above-ground biomass with good agreement for all tropical pastures with a high R² of 0.92, 0.98, 0.74 and low RMSE of 341, 583, 848 kg DM ha⁻¹ for BM, GP, and RR, respectively. The model agreement was good for the validation data with R² of 0.86, 0.80, 0.87 and RMSE of 954.5, 790.5, and 633.2 kg DM ha⁻¹ for BM, GP, and RR, respectively. The predicted leaf and stem partitioning was relatively poor, and the model also struggled to simulate realistic pasture growth in Mediterranean and desert environments (R² < 0.50). The present study has improved the robustness and accuracy of DairyMod-SGS in relation to tropical pastures and indicated that the model can be successfully used for investigating the likely performance of improved tropical pastures under a broad range of conditions. The validated DairyMod-SGS pasture model was applied to simulate the long-term pasture production of three improved pastures (BM, GP, and RR) in major dairying regions of Sri Lanka under three management scenarios: 1) rainfed pasture production system under the industry average nitrogen (N) fertiliser rate (Yₜᵂᴺ = yield over time under water and N limitation); 2) rainfed pasture production system under non-limiting N fertilisation (Yₜᵂ = yield over time with no N limitation but water limitation); and 3) potential pasture production system under non-limiting N and irrigation (Yₜ = yield over time with no N and water limitations). Simulations were carried out for 16 sites across Sri Lanka (8 sites in the dry zone (DZ), 5 sites in the intermediate zone (IZ), and 3 sites in the wet zone (WZ)) over a 30-years period (1980–2010). The model simulated that the long-term pasture production greatly varied between climate zones, pasture species and management scenarios. Overall, the Yₜᵂᴺ scenario showed a seasonal cycle following the rainfall pattern, with a reduction in growth rates in dry seasons (May to September). Growth rate and herbage accumulation were greater in GP at Yₜᵂᴺ, and BM at Yₜᵂ and Yₜ, while RR always showed the lowest growth rate. The variability of pasture growth between climate zones was highest in DZ (May to September) whereas the variability between species was lowest in RR. Pasture accumulation of both BM and GP outperformed their standard cultivars currently grown in Sri Lanka. In general, the pasture accumulation under Yₜᵂ increased (doubled) the growth rate, while the Yₜ scenario substantially increased (nearly tripled) the growth rate. Overall, the finding of this thesis suggested that all three pasture cultivars tested (BM, GP, and RR) are suitable for growing across major dairying regions in Sri Lanka, and that appropriate fertiliser and irrigation management can greatly intensify the herbage accumulation. In particular, BM appeared to be promising in terms of nutritive value, and agronomic and physiological traits. However, regional edaphic conditions, and the management ability of the farmers with respect to inputs and defoliation management, will ultimately determine the performance of improved cultivars such as those used in this thesis. There is a need for extension activities to support farmers in the management required to achieve best performance (yield, nutritive value and persistence) from these species. Future research is recommended to: 1) validate the model under Sri Lankan conditions, using both unimproved and improved cultivars, to determine its suitability in estimating tropical pasture yield; and 2) use additional models to evaluate the performance of improved tropical pastures in the context of the whole farm system, to identify the likely impact on dairy production and economic return.Item Plantain (Plantago lanceolata L.) as a natural mitigation strategy to reduce nitrogen losses from pasture-based dairy systems : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Agricultural Sciences at Massey University, Manawatu, New Zealand(Massey University, 2020) Rodríguez Gelós, Maria JimenaThe incorporation of plantain (Plantago lanceolata) into cows’ diet can reduce urine nitrogen (N) concentrations and modify the soil N cycle in urine patches by inhibiting nitrification. The objective of this thesis was to assess the potential of plantain as a mitigation option for N loss from dairy farms to the environment by measuring N leaching (nitrate [ NO3-]), and N emissions (nitrous oxide [N2O] and ammonia [NH3]) from plantain swards on a Pallic soil, and to evaluate the inhibitor effect of aucubin, a secondary metabolite, on N losses from soil. An important aspect of this study was the evaluation of NO3- leaching at the paddock scale from three pasture treatments (plantain, plantain-clovers mix and ryegrass-white clover) throughout two grazing seasons. Pasture treatments were grazed with lactating cows approximately monthly from September 2017 to May 2019. All the drainage from the grazed plots was monitored and sampled for NO3- and total N analyses during the 2017, 2018 and 2019 drainage seasons. The effect of plantain on N2O and NH3 emissions was evaluated in two field experiments carried out in spring 2017 and autumn/winter 2018. The N2O emissions from soil were measured using the static chamber method, and NH3 losses with the dynamic chamber method. In this field experiment the effects of adding two urine types (from cows grazing plantain or ryegrass-white clover) to two swards (plantain or ryegrass-white clover) were evaluated. The ability of aucubin to reduce N losses from urine patches was studied in a lysimeter experiment where aucubin was applied along with urine from cows grazing ryegrass-white clover pasture to ryegrass-white clover and plantain swards. In a hydroponic experiment, the release of secondary metabolites from a plantain root system was quantified. The plantain pasture treatment reduced NO3- leaching by 48 and 58% (2.6 and 3.8 kg NO3--N ha–1, respectively) compared to ryegrass-white clover and plantain-clovers mix pasture treatments, in the 2018 drainage season. During the 2019 drainage season, NO3- leaching between the plantain (4.0 kg NO3--N ha–1) and ryegrass-white clover (3.1 kg NO3--N ha–1) treatments were similar, which was likely due to a lower proportion of plantain in the sward during the critical summer-autumn period. In spring 2017, even though the urea-N concentration was 45% lower in urine of cows fed plantain than in urine of cows fed ryegrass-white clover swards, the cumulative N2O emissions from urine Abstract ii of cows grazing plantain was similar to urine of cows grazing ryegrass-white clover swards. Nitrous oxide emissions were reduced 31% by the plantain sward (1.4 kg N2O-N ha–1) in spring 2017. In autumn/winter 2018, N2O emissions from urine of cows grazing plantain (urea-N concentration was 40% lower in the urine of cows fed plantain than in the urine of cows grazing ryegrass-white clover pastures) were 48% lower (4.3 kg N2O-N ha–1) than from urine of cows grazing ryegrass-white clover. However, in this season, the cumulative N2O losses were 69% (7.1 kg N2O-N ha–1) higher from the plantain sward than the ryegrass-white clover sward and were associated with an increase in the water filled pore space (WFPS) in the plantain soil. The lower urea-N concentration in urine from cows fed plantain compared to ryegrass-white clover reduced NH3 losses from plantain and ryegrass-white clover swards in both spring 2017 and in autumn/winter 2018. The lysimeter experiment also showed that plantain swards reduced N2O emissions by 50% (9.0 kg N2O-N ha–1) compared to ryegrass-white clover swards. The addition of aucubin reduced the N2O emissions from urine patches by 36% in ryegrass-white clover swards. Only small concentrations of secondary metabolites were detected in the roots exudates of plantain plants grown in the hydroponic experiment. A high aucubin concentration (12 g kg–1 DM) in plantain leaves was observed after 50 and 60 days of the hydroponic study. In conclusion, this research demonstrates the potential of plantain to mitigate N leaching from pastoral dairy systems and N2O and NH3 emissions from urine patches by reducing the N and urea-N concentrations in cow urine. There was also evidence of a plantain sward effect on N dynamics in the soil, which decreased N2O emissions, possibly through the release of aucubin into the soil via leaf litter.