Microalgae Supplementation in Sheep Nutrition: Impact on Wool Production and Quality

Introduction

Sheep (Ovis aries) are domesticated ruminants raised for meat, milk, and wool, providing essential protein and fiber globally (Woolley et al., 2023). However, poor nutrition hinders wool growth, and inconsistent feeding affects its quality (Pattie, 2021). Consistent, good nutrition maximizes fleece yield and quality. Sheep can be supplemented to maximize growth and wool production, and in this article, we will explore microalgae supplementation (McKee, 2022).

Microalgae

Microalgae are photosynthetic organisms that use carbon dioxide, sunlight, and water to produce biomass rich in essential nutrients like fatty acids, amino acids, vitamins, and antioxidants (Safi et al., 2014; Saadaoui et al., 2021; Gadzama, 2024). Chlorella vulgaris is a type of green algae that can grow in both light and dark environments (Little et al., 1953), needing only carbon dioxide, water, sunlight, and small amounts of minerals (Montoya et al., 2014; Liu and Chen, 2016). It has a high growth rate, doubling in less than 20 hours (Griffiths and Harrison, 2008), and is considered a valuable animal feed due to its high nutritional content and photosynthetic efficiency (Safi et al., 2014; Saadaoui et al., 2021; Spínola et al., 2023). Its primary fatty acids include palmitic, oleic, linoleic, and alpha-linolenic acids, which can make up over 80% of its total fatty acids depending on cultivation conditions (Zhang et al., 2014; Jahromi et al., 2022; Gadzama et al., 2024). It also contains bioactive compounds like chlorophyll, carotenoids, vitamins, and minerals that enhance animal health and performance (Madeira et al., 2017). Chlorella vulgaris supplementation has improved growth performance, nutrient utilization, intestinal health, and antioxidant status in poultry, rabbits, pigs, and fish (Safi et al., 2014; Madeira et al., 2017; Martins et al., 2021). However, microalgae did not affect sheep growth performance, wool production, and quality (Gadzama et al., 2024).

What is Wool 

Wool is a natural fiber from sheep (Ovis aries; Figure 1) harvested by shearing. It's renewable and biodegradable, unlike synthetic fibers made from non-renewable oil. Wool is produced in over 100 countries, with Australia leading in Merino wool, producing 60% of all apparel wool and 90% of fine apparel wool (The Woolmark Company, 2017). At the end of its life, wool decomposes, returning nutrients to the soil. A sheep's ability to produce wool and its fiber quality is determined by genetics (Plowman et al., 2020; Doyle et al., 2021). However, nutrition plays a crucial role in expressing this potential. Feeding sheep well leads to more wool production, but the fibers are a bit coarse. Poor nutrition results in less wool, with fibers so thin that they break easily thereby reducing the fleece's value (Hinch, 2013). Szigeti et al. (2020) demonstrated that wool can be a sensitive indicator of low selenium and high zinc intake in sheep.

Factors Influencing Wool Quality  

Overall wool quality is influenced by:

• Sheep genotype
• Nutrition 
• Physiological conditions
• Presence of parasites
• Disease
• Environmental conditions
• Management strategies

Wool Fibre Diameter

Wool fiber diameter (FD) is the most important characteristic for assessing the quality and value of wool (Rowe, 2010; Holman and Malau-Aduli, 2012). It makes up 75% of the raw wool price (Mortimer et al., 2010). It also determines the fineness at which wool can be spun (Warn et al., 2006), thus influencing post-processing wool value (Rowe, 2010). Wool with an FD of less than 30 µm is comfortable and doesn't irritate the skin (Figure 1; Rogers et al., 2010; Tester, 2010), making it ideal for high-value textiles (Greeff, 2006). On the other hand, wool with an FD greater than 30 µm can cause discomfort (Naylor, 2010; Rogers et al., 2010; Tester, 2010). 

Wool Stable Strength

Stable strength is the second most important trait in determining the quality and value of wool (Friend and Robards, 2005; Botha and Hunter, 2010). Longer staple lengths are more desirable for spinning into strong, even yarns (Angel et al., 1990; Wood, 2010; Holman and Malau-Aduli, 2012). Wool with a staple strength below 25 N/ktex is considered "tender" and more prone to breakage (Reis, 1992), reducing its quality and value (Hansford & Kennedy, 1998; Adam & Briegel, 1998). Wool with higher staple strength is more valuable and less likely to break during processing (International Wool Secretariat, 1996). 

Characteristics of wool as influenced by Chlorella vulgaris 

Gadzama et al. (2024) examined the effects of live microalgae (Chlorella vulgaris) on wool production and quality in Merino x Dorper wether lambs (Figure 2; Table 1). The researchers reported that:

• Microalgae supplementation did not affect wool yield (Gadzama et al., 2024). 
• The wool yield ranged from 56.25% to 57.68%, as reported by Gadzama et al. (2024), which is slightly lower than the 61.40% to 64.50% reported in previous studies (Meale et al., 2014, 2015).
• Similarly, wool quality parameters such as fiber diameter, fiber diameter variation, fibers above 30 mm, staple length, staple strength, spinning fineness, comfort factor, and fiber curvature showed no differences among treatments (Table 1; Gadzama et al., 2024).
• The range of wool fiber diameter 22.90 to 23.90 µm reported by Gadzama et al. (2024) is similar to that of other breeds, as reported in other studies (Schlink et al., 1999; Peterson et al., 2000; Malau-Aduli et al., 2014).

Numerical Trends

• Lambs supplemented with high algae (1%DM) diet had slightly more wool fibers above 30 mm (9.26%) than the control group (7.73%) (Gadzama et al., 2024).
• Lambs on high and medium algae diets had higher wool staple strength (34.54 N/ktex) and comfort factor (94.03%) compared to the control group (25.64 N/ktex and 90.61%) (Gadzama et al., 2024).
• Medium algae diet lambs had higher wool curvature (88.34 deg/mm) compared to the control (83.70 deg/mm) (Gadzama et al., 2024).

While there were no significant differences, some numerical trends suggest the potential benefits of algae diets on wool quality (Gadzama et al., 2024). In the studies below, (Meale et al., 2013, 2014, 2015) found that different microalgae and oil supplements did not affect wool yield and quality in sheep.

• Schizochytrium spp. (DHA-Gold) Diet: Canadian Arcott lambs are fed diets with 0%, 1%, 2%, and 3% Schizochytrium spp. showed wool growth and quality comparable to control groups (Meale et al., 2014).
• Oil Supplements: Canadian Arcott ewe and ram lambs fed diets with 2% canola oil, flax oil, high-linoleic safflower oil, and Tasco (Ascophyllum nodosum) had similar wool production and quality (Meale et al., 2015).
• Crude Glycerine: Merino ewes fed diets with 0%, 6%, and 12% crude glycerine as a replacement for whole wheat grain for 70 days showed similar wool production and quality traits (Meale et al., 2013).

These studies indicate that various dietary supplements, including microalgae and oils, do not negatively impact wool yield and quality in sheep.

Impact of nutrition on wool production and quality

Feed intake significantly affects wool production, but wool growth does not heavily drain body energy. Studies have shown that dry matter intake is positively correlated with wool growth (Rook, 2003; Hynd & Masters, 2002; Rangel & Gardiner, 2009; Gadzama et al., 2024). Sheep bred for higher wool production may consume more feed, and their genetic potential for wool production does not rely on diverting nutrients from body tissues (Piper & Dollin, 1969). However, young sheep might use body reserves for wool production, and during restricted feeding, nutrients might be prioritized for body growth over wool (Doyle & Egan, 1983; Adams et al., 2000, 2002).

Figure 2. Lamb feeding on microalgae in feedlot diet. Photo by Ishaya Gadzama, 2022)

The Role of Dietary Protein on Wool Production in Sheep

Wool production in sheep is influenced by the amount and quality of dietary protein, especially amino acids like cysteine and methionine (Plowman, 2003; Holman & Malau-Aduli, 2014; Malau-Aduli et al., 2019). When protein is limited, sheep eat more to meet their protein needs, especially those bred for high wool production (Millward, 1995). This mechanism ensures they get enough protein for wool growth even on low-protein diets (Adams et al., 2002). Even with good diets, over half of the amino acids for wool growth come from breaking down body proteins (Harris et al., 1992). Sheep with high wool growth rates break down their body protein faster (Adams & Liu, 2003). 

The Role of Dietary Energy on Wool Production 

Wool growth uses little energy (Adams & Liu, 2003). The skin uses only one-sixth the energy of muscles, so it doesn’t significantly affect overall metabolism, except during fasting when wool growth continues but other functions slow down (Harris et al., 1990). Muscles hold the most protein but break down slower than skin or gut. During undernutrition, skin and gut protein decrease faster than muscle (Murray & Slezacek, 1994).

Conclusion

With climate change and a growing global population, sheep production's role in food supply will become more critical, requiring animal health and welfare attention. While microalgae supplementation did not significantly affect wool yield or quality, consistent nutrition is crucial for maximizing wool production and quality. Wool yield and quality are key factors when buying or selling wool.

Keywords: Microalgae, Supplementation, Sheep, Nutrition, Wool.

References

• Adams, N. R., & Briegel, J. R. (1998). Liveweight and wool growth responses to a Mediterranean environment in three strains of Merino sheep. Australian Journal of Agricultural Research, 49(8), 1187-1194.
• Adams, N. R., & Liu, S. M. (2003). Principles of nutrient partitioning for wool, growth and reproduction: implications for nematode parasitism. Australian Journal of Experimental Agriculture, 43(12), 1399-1407.
• Adams, N.R., Briegel, J.R. and Blache, D. (2002). Feed intake, liveweight and wool growth rate in Merino sheep with different responsiveness to low- and high-quality feed. Australian Journal of Experimental Agriculture, 42: 399-405.
• Adams, N.R., Liu, S.M., Briegel, J.R. and Greeff, J.C. (2000). Protein metabolism in skin and muscle of sheep selected for or against staple strength. Australian Journal of Agricultural Research, 51: 541-546.
• Angel, C., Beare, S., & Zwart, A. C. (1990). Product characteristics and arbitrage in the Australian and New Zealand wool markets. Australian Journal of Agricultural Economics, 34(1), 67-79.
• Botha, A.F. and Hunter, L. (2010). The measurement of wool fibre properties and their effect on worsted processing performance and product quality. Part 1: The objective measurement of wool fibre properties. Textile Progress., 42: 227-339.
• Doyle, E. K., Preston, J. W., McGregor, B. A., & Hynd, P. I. (2021). The science behind the wool industry. The importance and value of wool production from sheep. Animal Frontiers, 11(2), 15-23.
• Doyle, P.T. and Egan, J.K. (1983). The utilization of nitrogen and sulfur by weaner and mature sheep. Australian Journal of Agricultural Research 34: 433-439.
• Friend, M. A., & Robards, G. E. (2005). Fibre diameter and staple strength of sheep selected for divergent clean fleece weight when subjected to an increase in intake or an increase in intake and diet change. Australian Journal of Agricultural Research, 56(2), 195-201.
• Gadzama, I. U. (2024). Evaluation of fresh microalgae in ruminant nutrition: impact on rumen fermentation, productive performance and meat quality. MPhil Thesis, School of Agriculture and Food Sustainability, The University of Queensland. https://www.researchgate.net/publication/383121676_Evaluation_of_fresh_microalgae_in_ruminant_nutrition_impact_on_rumen_fermentation_productive_performance_and_meat_quality
• Gadzama, I. U., Hoffman, L. C., Holman, B. W. B., Chaves, A. V., & Meale, S. J. (2024). Effects of supplementing a feedlot diet with microalgae (Chlorella vulgaris) on the performance, carcass traits and meat quality of lambs. Livestock Science, 288, 105552. https://www.researchgate.net/publication/383309053_Effects_of_supplementing_a_feedlot_diet_with_microalgae_Chlorella_vulgaris_on_the_performance_carcass_traits_and_meat_quality_of_lambs
• Greeff, J. C. (2006). Coefficient of variation of wool fibre diameter in Merino breeding programs. Farmnote. Western Australian Department of Agriculture, Perth, 1-4.
• Griffiths, M.J., & Harrison, S.T.L. (2008). Lipid productivity as a key characteristic for choosing algal species for biodiesel production. Journal of Applied Phycology, 21(5), 493–507. https://doi.org/10.1007/s10811-008-9392-7
• Hansford, K. A., & Kennedy, J. P. (1988). Relationship between the rate of change in fibre diameter and staple strength. Proceedings of the Australian Society of Animal Production, 17, 415.
• Harris, P. M., Waghorn, G. C., & Lee, J. (1990). Nutritional partitioning of growth for productive gain. Proceedings of the New Zealand Society of Animal Production, 50, 81–90.
• Hinch, G. (2013). Lecture 5: Managing Weaners and Breeding Ewes for Wool Production. Retrieved from https://www.woolwise.com/wp-content/uploads/2017/07/WOOL-412-512-12-T-05.pdf
• Holman, B. W. B., & Malau-Aduli, A. E. O. (2014). Effect of Spirulina (Arthrospira plantensis) supplementation on wool quality in purebred and crossbred Merino lambs fed pasture and lucerne hay basal diets. Journal of Agricultural Science, 6(7), 120-127.
• Holman, B., & Malau-Aduli, A. E. O. (2012). A review of sheep wool quality traits. Annual Research & Review in Biology, 2 (1):1-14.
• Hynd, P. I., & Masters, D. G. (2002). Nutrition and wool growth. In Sheep Nutrition (pp. 165-187). Wallingford UK: CABI Publishing. https://www.cabidigitallibrary.org/doi/pdf/10.5555/20023139756
• International Wool Secretariat (1996). Wool Premiums and Discounts: First Quarter 1996/97 Season. (International Wool Secretariat: Melbourne).
• Jahromi, K.G., Koochi, Z.H., Kavoosi, G., & Shahsavar, A. (2022). Manipulation of fatty acid profile and nutritional quality of Chlorella vulgaris by supplementing with citrus peel fatty acid. Scientific Reports, 12(1), 8151.
• Little, H., & Brown, R.M. (1953). The culture of Chlorella vulgaris in synthetic media of varying composition with special reference to heterotrophic growth on organic compounds. Annals of Botany, 17(3), 433–454.
• Liu, J., & Chen, F. (2016). Biology and Industrial Applications of Chlorella: Advances and Prospects. Advances in Biochemical Engineering/Biotechnology, 153, 1–35. 
• Madeira, M.S., Cardoso, C., Lopes, P.A., Coelho, D., Afonso, C., Bandarra, N.M., & Prates, J.A. (2017). Microalgae as feed ingredients for livestock production and meat quality: A review. Livestock Science, 205, 111–121. 
• Malau-Aduli, A. E. O., McEvoy, P. D., Parsons, D., & Lane, P. A. (2014). Breed variation in wool quality, growth and plasma metabolites of prime lambs fed degummed canola. In Proceedings of the 10th World Congress on Genetics Applied to Livestock Production (pp. 908-910). Vancouver, Canada.
• Malau-Aduli, A. E., Nguyen, D. V., Le, H. V., Nguyen, Q. V., Otto, J. R., Malau-Aduli, B. S., & Nichols, P. D. (2019). Correlations between growth and wool quality traits of genetically divergent Australian lambs in response to canola or flaxseed oil supplementation. PLoS One, 14(1), e0208229.
• Martins, C.F., Ribeiro, D.M., Costa, M., Coelho, D., Alfaia, C.M., Lordelo, M., Almeida, A.M., Freire, J.P.B., & Prates, J.A.M. (2021). Using Microalgae as a Sustainable Feed Resource to Enhance Quality and Nutritional Value of Pork and Poultry Meat. Foods (Basel, Switzerland), 10(12), 2933. https://doi.org/10.3390/foods10122933
• McKee, P. (2022). Supplementation for improved wool production. Top Country. Retrieved from https://topcountry.com.au/blog/animal-nutrition/supplementation-for-improved-wool-production
• Meale, S. J., Chaves, A. V., Ding, S., Bush, R. D., & McAllister, T. A. (2013). Effects of crude glycerin supplementation on wool production, feeding behaviour, and body condition of Merino ewes. Journal of Animal Science, 91(2), 878-885.
• Meale, S.J., Chaves, A.V., He, M.L., & McAllister, T.A. (2014). Dose-response of supplementing marine algae (Schizochytrium spp.) on production performance, fatty acid profiles, and wool parameters of growing lambs. Journal of Animal Science, 92(5), 2202–2213. https://doi.org/10.2527/jas.2013-7024
• Meale, S.J., Chaves, A.V., He, M.L., Guan, L.L. and McAllister, T.A. (2015). Effects of various dietary lipid additives on lamb performance, carcass characteristics, adipose tissue fatty acid composition, and wool characteristics. Journal of Animal Science, 93(6):3110–3120. 
• Merino sheep from selection combining visually assessed and measured traits. Anim.
• Millward, D.J. (1995) A protein-stat mechanism for regulating growth and maintenance of the lean body mass. Nutrition Research Reviews 8: 93-120.
• Montoya, J.D., Weathers, P.J., & McCabe, J.G. (2014). Engineering challenges in high-density algal production: A critical review of existing methods and future needs. Journal of Applied Phycology, 26(4), 1519-1538.
• Mortimer, S. I., Atkins, K. D., Semple, S. J., & Fogarty, N. M. (2010). Predicted responses in Merino sheep from selection combining visually assessed and measured traits. Animal Production Science, 50(10), 976-982.
• Murray, D. M., & Slezacek, O. (1994). Effects of a 50-day period of slow live weight loss on the body composition of crossbred wethers. Proceedings of the Australian Society for Animal Production, 20, 397-397.
• Naylor, G. R. S., Phillips, D. G., & Veitch, C. J. (1995). The relative importance of mean diameter and coefficient of variation of sale lots in determining the potential skin comfort of wool fabrics. Wool Technology and Sheep Breeding (Australia), 43(1), 69-82.
• Pattie, L. (2021). Wool news: How nutrition improves wool quality. PGG Wrightson. Retrieved from https://www.pggwrightson.co.nz/news/wool-news-how-nutrition-improves-wool-quality
• Peterson, A. D., Gherardi, S. G., & Ellis, M. R. (2000). Managing the diameter profile leads to increased staple strength of young Merino sheep shorn in spring in South Western Australia. Asian Australasian Journal of Animal Sciences, 13, 469-472.
• Piper, L.R. and Dolling, C.H.S. (1969). Efficiency of conversion of food to wool. V. Comparison of the apparent digestive ability of sheep selected for high clean wool weight with that of sheep from a random control group. Australian Journal of Agricultural Research, 20: 579-587.
• Plowman, J. E. (2003). Proteomic database of wool components. Journal of Chromatography B, 787(1), 63-76.
• Plowman, J. E., Harland, D. P., Campos, A. M., e Silva, S. R., Thomas, A., Vernon, J. A., ... & de Almeida, A. M. (2020). The wool proteome and fibre characteristics of three distinct genetic ovine breeds from Portugal. Journal of Proteomics, 225, 103853.
• Rangel, J. H. D. A., & Gardiner, C. P. (2009). Stimulation of wool growth by Desmanthus spp. as a supplement to a diet of Mitchell grass hay. Tropical Grasslands, 43(2), 106-111.
• Reis, P.J. (1992). Variations in the strength of wool fibres – A review (Sheep). Australian Journal of Agricultural Research, 43(6), 1337-1351.
• Rogers, G. E., Schlink, A. C., & Cottle, D. J. (2010). Wool growth and production. International Sheep and Wool Handbook. Nottingham University Press, Nottingham, 373-394.
• Rook, J. S. (2003). Feedlot lamb nutrition. Veterinary Extension, Michigan State University of Veterinary Medicine. Retrieved October 31, 2006, from http://cvm.msu.edu/extension/Rook/ROOKpdf/Feedlot2.PDF
• Saadaoui, I., Rasheed, R., Aguilar, A., Cherif, M., Al Jabri, H., Sayadi, S., & Manning, S. R. (2021). Microalgal-based feed: promising alternative feedstocks for livestock and poultry production. Journal of Animal Science and Biotechnology, 12(1), 76.
• Safi, C., Zebib, B., Merah, O., Pontalier, P.Y., & Vaca-Garcia, C. (2014). Morphology, composition, production, processing and applications of Chlorella vulgaris: A Review. Renewable and Sustainable Energy Reviews, 35, 265-278. 
• Schlink, A. C., Mata, G., Lea, J. M., & Ritchie, A. J. M. (1999). Seasonal variation in fibre diameter and length in wool of grazing Merino sheep with low or high staple strength. Australian Journal of Experimental Agriculture, 39(5), 507-517.
• Spínola, M.P., Costa, M.M., & Prates, J.A.M. (2023). Enhancing Digestibility of Chlorella vulgaris Biomass in Monogastric Diets: Strategies and Insights. Animals, 13(6), 1017. MDPI AG. Retrieved from http://dx.doi.org/10.3390/ani13061017
• Szigeti, E., Kátai, J., Komlósi, I., Oláh, J., & Szabó, C. (2020). Newly Grown Wool Mineral Content Response to Dietary Supplementation in Sheep. Animals, 10(8), 1390.
• Tester, D. H. (2010). Relationship between comfort meter values and the prickle rating of garments in wearer trials. Animal Production Science, 50(12), 1077-1081.
• The Woolmark Company Pty Ltd. (2017). Wool is 100% natural and renewable. https://www.woolmark.com/globalassets/_06-new-woolmark/_industry/research/factsheets/wool-is-natural-renewable-131217.pdf
• Warn, L. K., Geenty, K. G., & McEachern, S. (2006). What is the optimum wool-meat enterprise mix. International Journal of Sheep and Wool Science, 54(1), 40-49.
• Wood, E. J. (2010). Wool processing. In D. J. Cottle (Ed.), International Sheep and Wool Handbook (pp. 619-646). Nottingham University Press.
• Woolley, S. A., Salavati, M., & Clark, E. L. (2023). Recent advances in the genomic resources for sheep. Mammalian Genome, 34(4), 545-558.
• Zhang, K., Sun, B., She, X., Zhao, F., Cao, Y., Ren, D., & Lu, J. (2014). Lipid production and composition of fatty acids in Chlorella vulgaris cultured using different methods: photoautotrophic, heterotrophic, and pure and mixed conditions. Annals of Microbiology, 64, 1239-1246.