{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,8]],"date-time":"2026-09-08T16:36:22Z","timestamp":1788885382985,"version":"build-2803163510"},"reference-count":26,"publisher":"MDPI AG","issue":"15","license":[{"start":{"date-parts":[[2026,8,4]],"date-time":"2026-08-04T00:00:00Z","timestamp":1785801600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Guangdong Feed Industry Technology System","award":["2024CXTD14"],"award-info":[{"award-number":["2024CXTD14"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Animals"],"abstract":"<jats:p>Optimizing protein nutrition in ruminants is vital for enhancing growth performance, meat quality, and overall production efficiency. However, the precise protein requirement for ruminants remains unclear. Two experimental trials were conducted to investigate the impact of varying levels of rumen-undegradable protein (RUP) on in situ feed degradability, growth performance, meat quality, and rumen fermentation parameters in fattening Hu sheep. In EXP 1, six Hu sheep were fitted with rumen fistulas to measure rumen degradation characteristics of diets varying levels of crude protein (CP) (13%, 14%, 15%, and 16% X RUP: CP 40%, 45%, 50%). The results showed that the ruminal DM and GE degradation had no difference between the experimental diets (p &gt; 0.05). However, the CP degradation rate gradually decreased as the dietary RUP proportion increased (p &lt; 0.05). In EXP 2, a double factorial experiment was conducted using 720 male Hu sheep, divided into twelve dietary treatments with varying levels of crude protein (CP) (13%, 14%, 15%, and 16%) and RUP (40%, 45%, and 50%). Key performance indicators such as body weight gain (BWG), average daily gain (ADG), average daily feed intake (ADFI), and feed conversion ratio (FCR) were measured at the beginning and end of the trial. Post-slaughter, meat quality attributes, including drip loss and initial pH of the longissimus dorsi muscle, were assessed after 40 days of the trial. Rumen fluid samples were analyzed for volatile fatty acid (VFA) profiles to evaluate rumen fermentation efficiency. The results demonstrated that increasing RUP levels significantly improved BWG and ADG (p &lt; 0.05) without affecting ADFI and FCR. Although dietary protein levels had minimal impact, higher RUP levels were associated with a trend toward increased final body weight (p = 0.09). Dietary protein levels and the RUP: CP ratio had no significant effect on meat quality (p &gt; 0.05). Ruminal acetate, valerate, and iso-valerate concentrations were reduced as RUP: CP increased (p &lt; 0.05), and propionate concentration showed a similar trend (p = 0.062). In conclusion, optimizing RUP levels in the diets of fattening Hu sheep significantly enhances growth performance without compromising feed efficiency or the overall rumen fermentation process. These findings provide a foundation for developing feeding strategies that maximize production efficiency in sheep farming.<\/jats:p>","DOI":"10.3390\/ani16152407","type":"journal-article","created":{"date-parts":[[2026,8,4]],"date-time":"2026-08-04T12:32:43Z","timestamp":1785846763000},"page":"2407","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Effects of Dietary Rumen-Undegradable Protein and Protein Levels on Growth Performance, Fermentation Parameters, Slaughter Performance, and Meat Quality on Fattening Hu Sheep"],"prefix":"10.3390","volume":"16","author":[{"given":"Changxin","family":"Tian","sequence":"first","affiliation":[{"name":"Animal Husbandry and Fisheries Research Center of Guangdong Haid Group Co., Ltd., Guangzhou 511400, China"},{"name":"National Engineering Laboratory for Pollution Control and Waste Utilization in Livestock and Poultry Production, Hunan Provincial Key Laboratory of Animal Nutrition & Physiology and Metabolism, Scientific Observing and Experimental Station of Animal Nutrition and Feed Science in South-Central, Ministry of Agriculture, Institute of Subtropical Agriculture, The Chinese Academy of Sciences, Changsha 410125, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Zhibo","family":"Wang","sequence":"additional","affiliation":[{"name":"Animal Husbandry and Fisheries Research Center of Guangdong Haid Group Co., Ltd., Guangzhou 511400, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Shengdi","family":"Hu","sequence":"additional","affiliation":[{"name":"Animal Husbandry and Fisheries Research Center of Guangdong Haid Group Co., Ltd., Guangzhou 511400, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Biao","family":"Yun","sequence":"additional","affiliation":[{"name":"Animal Husbandry and Fisheries Research Center of Guangdong Haid Group Co., Ltd., Guangzhou 511400, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Zhaojin","family":"Liu","sequence":"additional","affiliation":[{"name":"Animal Husbandry and Fisheries Research Center of Guangdong Haid Group Co., Ltd., Guangzhou 511400, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Xueqiao","family":"Qian","sequence":"additional","affiliation":[{"name":"Animal Husbandry and Fisheries Research Center of Guangdong Haid Group Co., Ltd., Guangzhou 511400, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4802-3506","authenticated-orcid":false,"given":"Zhixiong","family":"He","sequence":"additional","affiliation":[{"name":"National Engineering Laboratory for Pollution Control and Waste Utilization in Livestock and Poultry Production, Hunan Provincial Key Laboratory of Animal Nutrition & Physiology and Metabolism, Scientific Observing and Experimental Station of Animal Nutrition and Feed Science in South-Central, Ministry of Agriculture, Institute of Subtropical Agriculture, The Chinese Academy of Sciences, Changsha 410125, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,8,4]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"E1","DOI":"10.3168\/jds.2006-518","article-title":"Ruminal nitrogen metabolism: Perspectives for integration of microbiology and nutrition for dairy","volume":"90","author":"Firkins","year":"2007","journal-title":"J. Dairy Sci."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"3219","DOI":"10.2527\/2004.82113219x","article-title":"Effect of dietary crude protein level and degradability on ruminal fermentation and nitrogen utilization in lactating dairy cows","volume":"82","author":"Hristov","year":"2004","journal-title":"J. Anim. Sci."},{"key":"ref_3","doi-asserted-by":"crossref","unstructured":"Chen, P.L., Li, Y., Wang, M.M., Shen, Y.Z., Liu, M.C., Xu, H.J., Ma, N., Cao, Y.F., Li, Q.F., and Abdelsattar, M.M. (2024). Optimizing dietary rumen-degradable starch to rumen-degradable protein ratio improves lactation performance and nitrogen utilization efficiency in mid-lactating Holstein dairy cows. Front. Vet. Sci., 11.","DOI":"10.3389\/fvets.2024.1330876"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"181","DOI":"10.5713\/ajas.2006.181","article-title":"Effects of synchronizing the rate of dietary energy and nitrogen release on ruminal fermentation, microbial protein synthesis, blood urea nitrogen and nutrient digestibility in beef cattle","volume":"19","author":"Chumpawadee","year":"2006","journal-title":"Asian-Australas. J. Anim. Sci."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"47","DOI":"10.1016\/j.smallrumres.2009.12.044","article-title":"Effects of pelleted total mixed rations with different rumen degradable protein on milk yield and composition of Jonica dairy goat","volume":"90","author":"Laudadio","year":"2010","journal-title":"Small Rumin. Res."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"718","DOI":"10.2527\/jas.2009-2245","article-title":"Effects of ruminal protein degradability and frequency of supplementation on site and extent of digestion and ruminal fermentation characteristics in lambs fed low-quality forage","volume":"88","author":"Atkinson","year":"2010","journal-title":"J. Anim. Sci."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"231","DOI":"10.1016\/j.smallrumres.2004.10.005","article-title":"Effect of varying levels of dietary undegradable protein on nutrient intake, digestibility and growth performance of Awassi lambs fed on high wheat straw diets","volume":"58","author":"Haddad","year":"2005","journal-title":"Small Rumin. Res."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"1247","DOI":"10.1017\/S0007114520000586","article-title":"Effects of linseed oil and rumen undegradable protein:rumen degradable protein ratio on performance of Holstein dairy calves","volume":"123","author":"Fattahnia","year":"2020","journal-title":"Br. J. Nutr."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"114646","DOI":"10.1016\/j.anifeedsci.2020.114646","article-title":"Effects of corn grain processing method (ground versus steam-flaked) with rumen undegradable to degradable protein ratio on growth performance, ruminal fermentation, and microbial protein yield in Holstein dairy calves","volume":"269","author":"Rastgoo","year":"2020","journal-title":"Anim. Feed Sci. Technol."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"38","DOI":"10.1016\/j.livsci.2006.03.002","article-title":"Effect of NDF\/undegradable crude protein ratio on in vivo digestibility, particle passage rate in riverine buffaloes compared with sheep","volume":"104","author":"Bartocci","year":"2006","journal-title":"Livest. Sci."},{"key":"ref_11","unstructured":"NRC (2001). Nutrient Requirements of Dairy Cattle, The National Academies Press."},{"key":"ref_12","unstructured":"Latimer, G.W. (2016). Official Methods of Analysis of AOAC International, AOAC International. [20th ed.]."},{"key":"ref_13","unstructured":"Horwitz, W., and Latimer, G.W. (2005). Official Methods of Analysis of AOAC International, AOAC International. [18th ed.]."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"3583","DOI":"10.3168\/jds.S0022-0302(91)78551-2","article-title":"Methods for Dietary Fiber, Neutral Detergent Fiber, and Nonstarch Polysaccharides in Relation to Animal Nutrition","volume":"74","author":"Robertson","year":"1991","journal-title":"J. Dairy Sci."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"447","DOI":"10.1016\/S0309-1740(98)00034-5","article-title":"Reference methods for the assessment of physical characteristics of meat","volume":"49","author":"Honikel","year":"1998","journal-title":"Meat Sci."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"1058","DOI":"10.2527\/jas.2008-1069","article-title":"Influence of different levels of concentrate and ruminally undegraded protein on digestive variables in beef heifers","volume":"87","author":"Pina","year":"2009","journal-title":"J. Anim. Sci."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"3317","DOI":"10.2527\/jas.2009-1779","article-title":"Board Invited Review: The hepatic oxidation theory of the control of feed intake and its application to ruminants","volume":"87","author":"Allen","year":"2009","journal-title":"J. Anim. Sci."},{"key":"ref_18","first-page":"309","article-title":"Effect of Different Protein Levels on Fattening Performance, Digestibility and Rumen Parameters in Finishing Lambs","volume":"8","author":"Kaya","year":"2009","journal-title":"J. Anim. Vet. Adv."},{"key":"ref_19","doi-asserted-by":"crossref","unstructured":"Wang, X., Xu, T., Zhang, X., Geng, Y., Kang, S., and Xu, S. (2020). Effects of Dietary Protein Levels on Growth Performance, Carcass Traits, Serum Metabolites, and Meat Composition of Tibetan Sheep during the Cold Season on the Qinghai-Tibetan Plateau. Animals, 10.","DOI":"10.3390\/ani10050801"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"325","DOI":"10.2527\/jas1974.392325x","article-title":"Effect of Protein and Energy Levels on Lamb Carcass Composition","volume":"39","author":"Craddock","year":"1974","journal-title":"J. Anim. Sci."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"1423","DOI":"10.1017\/S1751731115000580","article-title":"Effects of castration age, protein level and lysine\/methionine ratio in the diet on colour, lipid oxidation and meat acceptability of intensively reared Friesian steers","volume":"9","author":"Prado","year":"2015","journal-title":"Animal"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"107964","DOI":"10.1016\/j.meatsci.2019.107964","article-title":"Effects of alfalfa particle size and starch content in diets on feeding behaviour, intake, rumen parameters, animal performance and meat quality of growing lambs","volume":"161","author":"Francisco","year":"2020","journal-title":"Meat Sci."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"88","DOI":"10.1111\/jpn.13250","article-title":"Influence of elevated protein and tannin-rich peanut skin supplementation on growth performance, blood metabolites, carcass traits and immune-related gene expression of grazing meat goats","volume":"104","author":"McTear","year":"2020","journal-title":"J. Anim. Physiol. Anim. Nutr."},{"key":"ref_24","doi-asserted-by":"crossref","unstructured":"Saro, C., Mateo, J., Caro, I., Carballo, D.E., Fern\u00e1ndez, M., Vald\u00e9s, C., Bodas, R., and Gir\u00e1ldez, F.J. (2020). Effect of Dietary Crude Protein on Animal Performance, Blood Biochemistry Profile, Ruminal Fermentation Parameters and Carcass and Meat Quality of Heavy Fattening Assaf Lambs. Animals, 10.","DOI":"10.3390\/ani10112177"},{"key":"ref_25","doi-asserted-by":"crossref","unstructured":"Jo, Y.-H., Kim, W.-S., Kim, Y.-R., Ju, M.-S., Nejad, J.G., and Lee, H.-G. (2024). Impacts of Protein and Energy Levels on Rumen Fermentation and Microbial Activity Under Different Incubation Temperatures. Animals, 14.","DOI":"10.3390\/ani14213093"},{"key":"ref_26","doi-asserted-by":"crossref","unstructured":"Soliva, C.R., Amelchanka, S.L., and Kreuzer, M. (2015). The requirements for rumen-degradable protein per unit of fermentable organic matter differ between fibrous feed sources. Front. Microbiol., 6.","DOI":"10.3389\/fmicb.2015.00715"}],"container-title":["Animals"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2076-2615\/16\/15\/2407\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,8,4]],"date-time":"2026-08-04T12:47:13Z","timestamp":1785847633000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2076-2615\/16\/15\/2407"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,8,4]]},"references-count":26,"journal-issue":{"issue":"15","published-online":{"date-parts":[[2026,8]]}},"alternative-id":["ani16152407"],"URL":"https:\/\/doi.org\/10.3390\/ani16152407","relation":{},"ISSN":["2076-2615"],"issn-type":[{"value":"2076-2615","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,8,4]]}}}