_1703650494 20231227041454000 Rovedar Daryoushbabazadeh@gmail.com Rovedar Farm Animal Health and Nutrition Farm Anim. Health Nutr. 2980-7905 12 21 2023 2 4 Sayyed Mahmoud Nasrollahi https://orcid.org/0000-0002-5348-1106 Subacute ruminal acidosis can be defined as a depression of rumen pH, which affects animal health and production. Although researchers have tried to find a solution for this disorder, it is a prevalent problem that causes considerable losses in commercial dairy cow production. This review aims to reveal critical points in current knowledge about subacute ruminal acidosis and suggest solutions for future research. The first challenging issue in subacute ruminal acidosis is the diagnosis method of this disorder, which requires appropriate statistical evaluation and modeling. In addition, biological factors should be considered to define subacute ruminal acidosis since some roles have recently been observed for different CO2 species in the rumen as a direct cause of the events. These CO2 species are sometimes more accurate than rumen pH in explaining the decrease in feed intake, milk yield, milk fat percentage, and inflammation responses. In the future, the measuring of the CO2 species in the rumen may be a replacement for pH measurement or become a factor that can greatly explain ruminal acidosis. Compared to basic methods, another challenging point is the reliability of rumen pH measurements as well as the accuracy of newly developed sensors. The reticular pH with current boluses could be measured by monitoring cows on-farm or a large number of animals in research. In conclusion, a thorough definition and precise application of new measurement devices can reveal some unknown factors for subacute ruminal acidosis in dairy cows.   12 21 2023 63 70 https://creativecommons.org/licenses/by/4.0 10.58803/fahn.v2i4.32 https://fahn.rovedar.com/index.php/FAHN/article/view/32 10.1016/j.tvjl.2007.12.016 10.1017/S1751731118001921 10.7591/9781501732355 10.3168/jds.2022-22571 Kitkas GC, Valergakis GE, Karatzias H, and Panousis N. Subacute ruminal acidosis: prevalence and risk factors in Greek dairy herds. Iranian J Vet Res. 2013; 14, 183-189. 10.1186/1751-0147-55-48 10.1515/pjvs-2017-0067 10.1016/j.livsci.2018.02.001 10.22271/j.ento.2021.v9.i2i.8537 Laporte-Uribe JA. Rumen CO2 species equilibrium might influence performance and be a factor in the pathogenesis of subacute 10.1093/tas/txz144 Sun YY, Cheng M, Xu M, Song LW, Gao M, and Hu HL. The effects of subacute ruminal acidosis on rumen epithelium barrier function 10.1016/j.smallrumres.2018.09.017 10.3168/jds.2017-13191 10.3168/jds.2015-9671 10.1016/j.anifeedsci.2016.06.012 10.3168/jds.2019-17760 10.1016/j.anifeedsci.2016.06.026 Neubauer V, Humer E, Kröger I, Braid T, Wagner M, and Zebeli Q. Differences between pH of indwelling sensors and the pH of fluid and solid phase in the rumen of dairy cows fed varying concentrate 10.1111/jpn.12675 10.1016/j.anifeedsci.2017.03.007 10.3168/jds.2015-9725 Hungate R, Dougherty R, Bryant M, and Cello R. Microbiological and physiological changes associated with acute indigestion in sheep. Cornell Vet. 1952; 42: 423-449. Available at: https://www.cabdirect.org/cabdirect/abstract/19531402099 10.3168/jds.S0022-0302(96)76510-4 10.3168/jds.2008-1389 10.3168/jds.2011-4447 10.3168/jds.2008-1656 10.3168/jds.2017-13706 10.1128/AEM.00739-09 10.1017/S175173110999111X Plaizier JC, Li S, Tun HM, and Khafipour E. Nutritional models of experimentally-induced subacute ruminal acidosis (SARA) differ in their impact on rumen and hindgut bacterial communities 10.3389/fmicb.2016.02128 10.1093/jas/skaa248 10.3390/ani11010195 10.1016/j.anifeedsci.2011.12.007 10.3168/jds.S0022-0302(05)73048-4 10.1186/s12917-018-1463-7 10.1016/j.livsci.2016.07.003 10.1016/j.tvjl.2007.12.017 10.21423/bovine-vol1994no28p109-112 10.3168/jds.S0022-0302(99)75340-3 10.1017/S1751731119003112 10.3168/jds.S0022-0302(04)70057-0 Hollberg W. Comparative studies of rumen fluid samples obtained by using the Schambye-Sorensen sonde or by puncture of the caudoventral rumen sac. Dtsch Tierarztl Wochenschr. 1984; 91: 317-320. Available at: https://pubmed.ncbi.nlm.nih.gov/6386421/ Aceto H, Simeone A, and Fergusson J. Effect of rumenocentesis on health and productivity in dairy cows. J Anim Sci. 2000; 83(Suppl. 1): 40. 10.1016/j.livsci.2019.103822 10.4061/2010/392371 10.12681/jhvms.18886 10.1016/j.compag.2008.05.015 10.1111/asj.12415 10.3390/s5040209 10.1016/j.anifeedsci.2011.12.005 10.3168/jds.S0022-0302(97)76074-0 10.1021/acs.chemrev.5b00736 10.1351/pac198557030531 Valsaraj KT, and Melvin EM. Elements of environmental engineering: thermodynamics and kinetics, CRC Press; 2000. 10.2527/1998.7661702x 10.3168/jds.2015-9486 10.1139/m76-071 10.1016/j.livsci.2009.09.003 10.1128/aem.57.10.3013-3019.1991 10.1002/bit.21530 10.3168/jds.S0022-0302(01)74651-6 10.3168/jds.S0022-0302(02)74111-8 National research council. (NRC) I. Nutrient requirements of dairy cattle. 2001. 10.1128/jb.149.3.1034-1040.1982 10.1071/AR9550115 10.3389/fphys.2013.00382 10.1093/jn/118.11.1366 10.1113/expphysiol.1972.sp002136 10.1099/00221287-19-1-130 10.1021/bi00140a026 10.1111/jpn.12752 10.1016/j.cyto.2008.06.016 10.1152/ajplung.90460.2008 10.1161/01.RES.0000075601.95738.6D 10.1007/s00408-010-9234-7 10.3844/ajavsp.2013.8.27 Wang R, Wang M, Zhang XM, Wen JN, Ma ZY, Long DL et al. Effects of rumen cannulation on dissolved gases and methanogen community 10.3168/jds.2018-15187 10.1016/j.bej.2014.06.007 10.1093/jas/skaa228 10.3168/jds.2012-6109 10.1016/j.anifeedsci.2005.08.004 Nasrollahi S. The new fundamentals for sub acute ruminal acidosis occurrence and their effects on dairy cow health and productivity: Behavioral responses, molecular changes and individual variations. PhD Thesis, University of Tehran. 2017. 10.1016/j.heliyon.2020.e03712 10.3168/jds.2018-14903 10.3168/jds.2018-15064 10.3168/jds.2021-21115 10.3168/jds.2006-534 10.3168/jds.2014-8212 10.3168/jds.2007-0572 10.3168/jds.2011-4465 10.2527/jas.2015-9605 ‏