The effect of Ulva lactuca on in vitro ruminal gas production kinetics, intrinsic methane production and the performance of Dohne Merino ewes

Thesis (MScAgric)--Stellenbosch University, 2023.

ENGLISH ABSTRACT: Marine macroalgae present a compelling avenue for mitigating the methane emissions originating from ruminant livestock, which is of disreputable concern. This potential stems from their significant bromoform content, a haloalkane that effectively inhibits the methanogenic pathway. While Asparagopsis taxiformis, a red seaweed, has shown to nearly eliminate methane emissions from ruminants, the use of a seaweed practical in the South African context has yet to be studied. The present study investigated whether Ulva lactuca, a green marine algae abundantly available in South Africa, can reduce in vitro total gas and methane production when replacing lucerne hay in a mixed sheep feed. Furthermore, the production performance and methane emissions from feedlot lambs were investigated to determine whether the substitution of lucerne hay with U. lactuca may result in reduced methane emissions while maintaining animal performance. Four treatment diets were milled through a 1 mm sieve and were incubated using bovine rumen fluid as inoculum: (1) 0 g U. lactuca kg⁻¹ feed dry matter (DM) (0U); (2) 25 g U. lactuca kg⁻¹ feed DM (25U); (3) 50 g U. lactuca kg⁻¹ feed DM (50U); and (4) 100 g U. lactuca kg⁻¹ feed DM (100U). Total gas and CO2 production was determined with the aid of an automated system and methane production was estimated by difference. Cumulative gas production data were fitted to a non-linear model (Y = b(1-exp⁻ᶜ⁽ᵗ⁻L⁾)) to estimate values for total gas production (b, ml), rate of gas production (c, ml/h), and a discrete lag time (L, hours). The extent of total gas production (b) was significantly (P < 0.05) lower for 100U than for 25U, but neither differed from 0U or 50U. The lag time observed (L) was significantly (P < 0.05) lower for 50U than 0U, but neither differed from 25U or 100U. No significant differences were found for rate of gas production (c). No significant differences in rate (c) and extent (b) of methane production were observed between treatments and lag times (L) did not differ either. The ratio between methane and total gas production was highest for 100U which differed significantly (P < 0.05) from 25U, but not from 0U or 50U. The higher methane ratio observed in the 100U treatment may be attributed to the lower total gas production in this treatment due to the lower fermentability of U. lactuca compared to lucerne. In the second trial, 40 Dohne Merino ewes were randomly allocated to the four treatment groups used in the first trial to investigate the effect of U. lactuca on production parameters and methane emissions of feedlot lambs. Methane emissions were measured using a handheld laser methane detector that measures the methane concentration between the device and the target using infrared absorption spectroscopy. The addition of U. lactuca up to 50 g kg⁻¹ DM had no effect on dry matter intake, average daily gain or feed conversion ratio but negatively impacted these parameters when included at a rate of 100 g kg⁻¹ DM. No significant differences were observed between treatments for methane production, in either grams per day, grams per kilogram bodyweight per day or grams per kilogram DM intake per day. Methane reductions by seaweeds are largely attributed to a haloalkane, bromoform. The volatility of bromoform and the drying technique used resulted in no bromoform being detectable in the sample used in this study. This study concluded that U. lactuca can successfully be used to replace lucerne at a rate of up to 50 g kg⁻¹ DM without negative impacts on animal performance but is unsuccessful in reducing methane emissions when included in the diet at a rate of up to 100 g kg⁻¹ and dried under forced air oven conditions. Further research into suitable preservation techniques of U. lactuca is needed to investigate the potential of the alga in reducing methane emissions from ruminants.

AFRIKAANSE OPSOMMING: Mariene makroalge bied ‘n goeie geleentheid om metaanvrystelling afkomstig vanaf herkouervee, wat van groot kommer is, te verminder. Hierdie potensiaal spruit uit die beduidende bromoforminhoud, ‘n haloalkaan wat die metanogeniese proses effektief inhibeer. Hoewel Asparagopsis taxiformis, ‘n rooi seewier, reeds bewys is om metaanvrystellings vanaf herkouers in sommige gevalle byna uit te wis, moet die praktiese gebruik van ‘n seewier in die Suid-Afrikaanse konteks nog bestudeer word. Hierdie studie het ondersoek ingestel na die moontlikheid of Ulva lactuca, ‘n groen seewier wat welig groei in Suid-Afrika, in vitro totale gas- en metaanproduksie sal verminder wanneer dit lusernhooi gedeeltelik in ‘n gemengde skaapvoer vervang. Die produksieparamters en metaanvrystellings van voerkraallammers is ook ondersoek om vas te stel of die gedeeltelike vervanging van lusernhooi met U. lactuca sal lei tot verminderde metaanvrystelling terwyl prestasie van die dier gehandhaaf word. Vier behandelingsdieëte is deur ‘n 1 mm sif gemaal en met bees-rumenvloeistof geïnkubeer: 1) 0 g U. lactuca kg⁻¹ voer droëmateriaal (DM) (0U); (2) 25 g U. lactuca kg⁻¹ voer DM (25U); (3) 50 g U. lactuca kg⁻¹ voer DM (50U); en (4) 100 g U. lactuca kg⁻¹ voer DM (100U). Totale gas- en CO2-produksie is bepaal met behulp van ‘n outomatiese sisteem en metaanproduksie is bereken as die verskil. Kumulatiewe gasproduksiedata is met behulp van ‘n nie-liniêre model (Y = b(1-exp⁻ᶜ⁽ᵗ⁻L⁾)) bepaal om totale gasproduksie (b; mL), tempo van gasproduksie (c; mL/h) en ‘n diskrete vertragingsfase (L; ure) te bepaal. Die totale gasproduksie (b) was betekenisvol laer (P < 0.05) vir 50U as vir 0U, maar nie een van die twee het van 25U of 100U verskil nie. Die tempo van gasproduksie (c) het nie tussen behandelings verskil nie. Wat metaanproduksie betref, is geen betekenisvolle verskille in tempo (c), totale hoeveelheid (b) of in die vertragingsfase (L) tussen behandelings waargeneem nie. Die verhouding tussen metaan- en totale gasproduksie was die hoogste vir 100U, wat betekenisvol hoër (P < 0.05) was as vir 25U, maar nie verskillend van 0U of 50U nie. Dié hoër verhouding kan toegeskryf word aan die laer totale gasproduksie van hierdie behandeling (100U) as gevolg van die laer fermenteerbaarheid van U. lactuca in vergelyking met lusern. In die tweede eksperiment is 40 Dohne Merino-ooie toegeken aan dieselfde vier behandelings van die eerste proef om die invloed van U. lactuca op produksieparameters en metaanvrystelling van voerkraallammers te ondersoek. Metaanvrystellings is gemeet met die gebruik van ‘n draagbare laser metaan detektor wat die metaan konsentrasie tussen die toestel en die teiken meet met die gebruik van infrarooi absorpsie spektroskopie. Die insluiting van U. lactuca tot en met 50 g kg⁻¹ DM het geen betekenisvolle invloed op droëmateriaalinname, gemiddelde daaglikse toenname of voeromsetverhouding gehad nie. Hierdie parameters is egter negatief beïnvloed waar U. lactuca teen 100 g kg⁻¹ DM in die ransoen ingesluit is. Geen betekenisvolle verskille is tussen behandelings waargeneem ten opsigte van metaanvrystelling nie. Die verlaging in metaanvrystelling as gevolg van die inname van seewiere kan grootliks toegeskryf word aan die haloalkaan, bromoform. Die vlugtigheid van bromoform en die drogingstegniek wat gebruik was het waarskynlik gelei tot die totale afwesigheid van bromoform in die monsters wat in hierdie studie gebruik was. Hierdie studie het bevind dat U. lactuca lusernhooi effektief kan vervang tot en met 50 g kg⁻¹ DM sonder enige negatiewe invloed op prestasie, maar dat dit onsuksesvol is in die verlaging van metaanvrystelling tot en met 100 g kg⁻¹ DM met die drogingstegniek wat gebruik is om die seewier te preserver. Verdere navorsing is nodig om toepaslike preserveringstegnieke vir U. lactuca te ondersoek om die potensiaal van die seewier om metaanvrystellings te verlaag, te bepaal.

Masters