Abstract Assessment of the existence of macroalgae and revealing the chemical composition to investigate the potential usage for feed to support sustainable beef production has been conducted in Indonesian prominent livestock production area specifically Lombok, Bali, Yogyakarta, Lampung and Bengkulu. These regions host numerous seaweed production centres, while others hold the capacity to develop into seaweed cultivation zones. To assess the existence, utilisation, and accessibility of macroalgae in each region, observations and interviews were conducted. Subsequently, dominant macroalgae species were sampled and subjected to proximate analysis to determine their nutritional profiles. The results showed that the dominant macroalgae observed included red algae (Rhodophyta) like Eucheuma sp., Gracilaria sp., and Acanthophora sp., green algae (Chlorophyta) such as Ulva sp. and Caulerpa sp., and the brown alga (Phaeophyta) Sargassum sp. The dominant macroalgae found in all five observation sites with high abundance were Sargassum sp., Gracilaria sp., and Eucheuma cottonii. Ulva sp. and Eucheuma spinosum were present at four sites, while Acanthophora sp. and Caulerpa sp. were found at three sites. The dry matter content of the macroalgae ranged from 9.92% to 17.01%, with the highest values observed in the Eucheuma group (14.11%-17.01%). This was followed by Sargassum sp. (12.55 ± 2.40%), Ulva sp. (12.28 ± 2.33%), and Gracilaria sp. (11.09 ± 3.79%). Caulerpa sp. exhibited the lowest dry matter content (9.92 ± 1.29%). The crude protein (CP) content varied both within and between groups of algae species and observation sites. Gracilaria sp. exhibited the highest CP content (13.55 ± 0.16%), followed by Caulerpa sp. (11.87 ± 2.22%), Sargassum sp. (8.98 ± 0.42%), and Ulva sp. (6.98 ± 0.94%). The mineral content of the macroalgae was noticeably high, which is reflected in the low organic matter content. Ulva sp. had the highest organic matter content (80.17%), followed by Sargassum sp. (70.55%), Gracilaria sp. (66.53%), Caulerpa sp. (47.61%), and Eucheuma cottonii (43.50%). The readily available seaweed in this study tend to exhibit moderate to high protein and mineral content, making it a promising partial replacement or supplement for conventional feed, potentially contributing to sustainable beef production. Gracilaria sp., the most readily available seaweed, high in nutrient content with the potential to partially replace conventional feed protein sources. Its abundance of vitamins and minerals may enrich the overall value of the feed.
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