The nutritional value and palatability of Ulva lactuca as ruminant feed ingredient

Thesis (MScAgric)--Stellenbosch University, 2024.

ENGLISH ABSTRACT: The increasing global warming and climate change continues to cause problems for livestock farmers. Along with this they also face challenges such as droughts and increasing desertification, which puts more pressure on sustainable daily farming operations. The increasing human population, need for livestock derived protein (LDP) and food security means that innovative ways to farm are sought after. This leads to an increased interest in alternative raw materials that can be used in ruminant diets which does not use arable land and fresh water for cultivation. One such alternative raw material is a seaweed; Ulva lactuca. It has been proven that this seaweed has the potential to be included in ruminant diets as it has a favourable nutritional profile and while also produce high amounts of biomass, uses salt water for cultivation, does not require arable land and is readily available in marine environments making it free to harvest. This seaweed has been reported to have a high protein, ash and fibre content. The high ash content is linked to their ability to accumulate minerals from their environment, leading to an increased concentration of minerals. This in turn might limit the energy potential of this seaweed, especially since seaweeds in general have very low concentrations of fat. This is supported by their very low total fatty acid content found in the seaweed. However, their relatively high protein content indicates that they have the potential to be used as a supplementary source of protein. The amino acid content of U. lactuca is unbalanced, meaning that this seaweed should not be used as the only protein source. Even though some studies reported a good nutritional profile for U. lactuca , it has been shown that the nutritional profile varies between seaweeds collected from different locations. This is due to factors such as time of harvest, geographical location, environment it is found in, water quality and pollution. It was suggested by previous authors that this seaweed can be compared to a medium to low quality forage like lucerne hay. A study was therefore conducted to determine the nutritional profile and palatability of U. lactuca harvested at location in Cape coast of South Africa. In the first part of the current study the nutritional profile of Ulva lactuca harvested on the Coast of Southern Africa was determined. Six different batches of U. lactuca was harvested during an 8 month period and air dried in forced-air oven whereafter an proximate analysis was conducted to determine the salt content, bromoform content, amino acid (AA) content and fatty acid (FA) content. An in vitro analysis was performed to determine the extent of crude protein (CP)- and neutral detergent fibre (NDF) degradability. Descriptive statistics were subsequently performed. The proximate analysis supported previously cited literature, as it was reported that the CP value of Ulva lactuca was 235.5 g/kg DM, which is higher than lucerne hay proving the potential of this seaweed as a supplementary protein source. It can also be considered a fibre source since it contains a high fibre content of 224 g/kg DM. It also had a high ash content of 318 g/kg DM, a low ether extract (EE) content of 6.04 g/kg DM and a relatively high salt content of 102 g/kg DM. The high ash and low fat content supports the hypothesis that the energy potential of this seaweed might be limited due to the higher amount of minerals. The gross energy (GE) value of 11.48 MJ/kg is relatively good compared to that of lucerne hay. No bromoform was detected during the quantification of the air-dried sample. Thus, Ulva lactuca could be considered as a viable alternative ruminant feed source provided that a proper nutritional analysis is performed before being included in maintenance diets of ruminant animals. This is supported by the in vitro results, based on the high NDF degradability and relatively high RUP content. The amino acid (AA) profile of Ulva lactuca was unbalanced, therefore it is suggested that other protein sources or individual AAs should be supplemented to accommodate for any AA shortfalls. The high salt content needs to be considered during the rinsing at harvesting, as this high salt content might limit the use of the seaweed in animal diets. The high salt content will have a negative influence on the dry matter intake, and subsequently a negative influence will be observed on the production parameters. The second part of the study was conducted to evaluate the palatability of Ulva lactuca for ruminants, with the goal of establishing a maximum inclusion level of this seaweed in maintenance diets for sheep (Ovis aries). This trial consisted of an in vivo palatability trial conducted at the Welgevallen Experimental Farm of the University of Stellenbosch. A randomised block trial design was used where 40 Dohne Merino ewes were blocked according to initial weight and randomly allocated to treatment and pens resulting in 8 replications (n=8) per dietary treatment. After an initial two-day adaptation period from consuming pasture-based diets, the ewes were given pelleted diets of 0 g/kg (C), 50 g/kg (U5), 100 g/kg (U10), 200 g/kg (U20) and 400 g/kg (U40) ad libitum for a period of 14 whole days. All animals showing below 3% of body weight feed intake per day for 3 consecutive days and who lost more than 10% of body weight were removed from the trial. It was assumed that significant lower feed intake and/or body weight loss suggest poorer feed palatably. All of the U40 and U20 animals were removed from the trial at 3 and 5 days after data collection commencement due to excessive weight loss and poor intake (P < 0.05), respectively. The inclusion of U. lactuca up to 10% of maintenance diets to sheep did not affect palatability, dry matter intake (DMI), body weight change (BWΔ), water intake (WI), growth, feed conversion ratio (FCR) or faecal score. Based on the results of the current trial, U. lactuca inclusion up to 10 % can successfully be included in sheep maintenance diets, without affecting the overall production parameters and palatability of the diet. Ulva lactuca could potentially be included up to 20 % levels, with higher levels proving to be too unpalatable. It is hypothesized that the inclusion of seaweed at 20 % levels could possibly be achieved given that the feed is made more palatable with the inclusion of molasses or artificial sweeteners, however this is still to be proven.

AFRIKAANSE OPSOMMING: Toenemende aardverwarming en klimaatverandering veroorsaak daagliks probleme vir veeboere. Veeboere moet ook uitdagings soos droogtes en toenemende woestynvorming wat daagliks druk op die boerderybedrywighede hanteer. Toenemende menslike bevolking, die behoefte vir protein vanaf dierlike oorsprong en voedselsekuriteit dra alles by tot die soeke na innoverende maniere om meer volhoubaar te boer. Hierdie faktore dra by tot die toenemende belangstelling in alternatiewe grondstowwe wat in herkouerdiëte, wat nie gebruik maak van bewerkbare grond of vars water vir produksiedoeleindes benodig, gebruik kan word. ‘n Seewier, Ulva lactuca, is een potensiële grondstof wat aan die bogenoemde vereistes voldoen. Hierdie seewier het die potentiaal om in herkouerdiëte gebruik te kan word omdat dit ‘n gunstige nutriëntinhoud bevat terwyl dit ook oor ander byvoordele soos hoë produksiepotensiaal, die gebruik van soutwater vir produksie doeleindes, die verlaging in afhanklikheid van bewerkbare grond en dat dit geredelik beskikbaar is in mariene omgewings wat dit ‘n betreklik goedkoop bron maak, beskik. In deel een van die huidige studie is bevind dat hierdie seewier 'n hoë proteïen-, as- en veselinhoud bevat. Die hoë as-inhoud is gekoppel aan die plant se vermoë om minerale uit die mariene omgewing te versamel. Laasgenoemde kan egter die energiepotensiaal van U. lactuca beperk, aangesien seewier in die algemeen reeds betreklik lae konsentrasies van vet bevat. Laasgenoemde word ondersteun deur baie lae totale vetsuurinhoud wat in die seewier voorkom. Hul relatiewe hoë proteïeninhoud dui egter daarop aan dat hierdie plante die potensiaal het om as 'n aanvullende bron van proteïen vir diere gebruik te kan word. Die aminosuurinhoud van U. lactuca is egter ongebalanseerd, wat beteken dat hierdie seewier nie as die enigste proteïenbron gebruik kan word nie. Alhoewel sommige studies 'n goeie voedingsprofiel vir U. lactuca aangeteken het, is daar aangetoon dat die voedingsprofiel verskil tussen seewiere wat van verskillende plekke van oorsprong versamel is. Laasgenoemde kan aan faktore soos seisoen van oes, geografiese ligging, habitat, waterkwaliteit en besoedeling toegeskryf word. Verskeie outeurs stel voor dat hierdie seewier met lusernhooi vergelyk kan word. In die eerste deel van hierdie verhandeling is die voedingswaarde van Ulva lactuca, wat aan die Kaapse kus van Suider-Afrika geoes is, se voedingswaarde evalueer. Ses verskillede opbrengste van U. lactuca is gedurende ‘n 8 maande periode geoes en in ‘n warmlugoond gedroog waarna die voedingswaardebepaling met ‘n Weende ontleding ontleed is om die sout-, bromovorm-, aminosuur (AA)- en vetsuur (FA) inhoud van Ulva lactuca te bepaal. 'n In vitro fermentasie om die mate van ruproteïen (CP)- en nutraalbestande vesel (NDF) degradering te bepaal, is verder uitgevoer. Beskrywende statistiek is daarna uitgevoer. Die resultate van die Weende ontleding het voorheen gepubliseerde data ondersteun, synde die huidige voedingswaardebepaling ‘n CP- waarde van Ulva lactuca 235.5 g/kg DM getoon het, wat hoër is as lusernhooi wat die potensiaal van hierdie seewier as 'n aanvullende proteïenbron rugsteun. U. lactuca kan ook as 'n veselbron beskou word aangesien dit 'n hoë veselinhoud van 224 g/kg DM bevat. Dit bevat verder ook 'n hoë asinhoud van 318 g/kg DM, 'n lae eterekstrak (EE) inhoud van 6.04 g/kg DM en 'n relatiewe hoë soutinhoud van 102 g/kg DM. Die hoë as- en lae vetinhoud ondersteun die hipotese dat die energiepotensiaal van hierdie seewier dalk beperk kan word as gevolg van die groter hoeveelheid minerale wat hierdie seewier versamel. Die bruto energie (GE) waarde van 11.48 MJ/kg vergelyk relatief goed met dié van lusernhooi. Geen bromovorm is tydens die kwantifisering van die luggedroogde monster waargeneem nie. Ulva lactuca kan dus as 'n moontlike alternatiewe herkouervoerbron beskou word mits 'n behoorlike voedingsanalise uitgevoer word voordat dit ingesluit word in onderhoudsdiëte van herkouerdiere. Laasgenoemde word ondersteun deur die in vitro resultate, aangesien ‘n hoë NDF degradeerbaarheid en relatief hoë deurvloeiproteïenfraksie (RUP) van U. lactuca bevestig is. Die aminosuurprofiel van Ulva lactuca is egter ongebalanseerd en daarom word daar voorgestel dat ander proteïenbronne of individuele aminosure (AA) aangevul moet word om vir enige AA-tekorte te korrigeer. Die hoë soutinhoud moet verder in ag geneem word tydens die afspoel van die seewier tydens die oesproses, aangesien hierdie hoë soutinhoud die gebruik van die seewier in dierediëte kan beperk. Die hoë soutinhoud sal 'n negatiewe invloed op die droëmateriaalinname hê, wat weer tot verlaagde produksieparameters van diere sal lei. In die tweede deel van hierdie studie is die smaaklikheid van Ulva lactuca vir herkouers evalueer, met die doel om 'n maksimale insluitingsvlak van hierdie seewier in onderhoudsdiëte vir skape (Ovis aries) te bepaal. Hierdie proef het bestaan uit 'n in vivo smaaklikheidsproef wat by die Welgevallen-proefplaas van die Universiteit van Stellenbosch uitgevoer is. 'n Ewekansige blok ontwerp is gebruik waar 40 Dohne Merino ooie volgens aanvanklike massa geblok is en ewekansig aan behandeling en krale toegedeel is, wat tot 8 herhalings (n=8) per dieetbehandeling gelei het. Na 'n aanvanklike aanpassingsperiode van twee dae vanaf voorheen ad libitum weidinggebaseerde dieet, is die ooie ad libitum vir ‘n tydperk van 14 hele dae van verpilde diëte; 0 g/kg (C), 50 g/kg (U5), 100 g/kg (U10), 200 g/kg (U20) and 400 g/kg (U40) voorsien. Alle diere wat minder as 3 % van liggaamsmassa voerinname per dag vir 3 opeenvolgende dae gevreet het en wat meer as 10 % van liggaamsmassa verloor het, is uit die proef verwyder. Daar is verder aangeneem dat ‘n betekenisvolle lae voerinname en/of liggaamsmassaverlies ‘n aanduiding van lae voersmaaklikheid sal aandui. Al die U40 en U20 diere is na 3 and 5 dae nadat datakolleksie begin het verwyder weens uitermate lae inname en massaverlies (P < 0.05) onderskeidelik. Die insluiting van U. lactuca tot 10 % van onderhoudsdiëte aan skape het nie smaaklikheid, droëmateriaalinname (DMI), ligaamsmassaverandering (BWΔ), waterinname (WI), groei, voeromsetverhouding (VOV) of mistelling beïnvloed nie. Gebaseer op die resultate van die huidige proef, kan U. lactuca tot 10 % suksesvol by skaaponderhoudsdiëte ingesluit word, sonder om produksieparameters en smaaklikheid van die dieet te beïnvloed. Daar word wel bespiegel dat Ulva lactuca wel moontlik tot 20 % ingesluit kan word, terwyl hoër vlakke egter te onsmaaklik blyk te wees. Die hipotese dat U. lactuca tot 20 % in herkouerdiëte ingesluit kan word, mits die voer meer smaakliker met die insluiting van melasse of kunsmatige versoeters gemaak word, lyk teoreties moontlik. Hierdie hipotese moet egter nog getoets word.

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