Volume 10, Issue 6: 302-312; November 27, 2020  
Professor and Head, Department of Animal Science and Nutrition, Faculty of Veterinary Medicine, Chattogram Veterinary and Animal Sciences  
University, Zakir Hossain Road, Khulshi, Chattogram-4225, Bangladesh  
Email: emran@cvasu.ac.bd;  
Supporting Information  
ABSTRACT: Current feeding programs for cattle prescribe concentrate rich diets to meet their ever increasing  
demands for high levels of milk production. These diets, however, can impair rumen health and thus cattle  
production, milk yield and welfare. High energy diets are rapidly fermented in the rumen because they are high  
in fermentable starch, low in NDF and contain finely chopped digestible forages. Feeding rapidly fermentable  
diet to the cows predominantly adapted to digest and metabolize forage based total mixed ration (TMR)  
substantially increases short term milk yield, but the risk of sub- acute ruminal acidosis (SARA) increases.  
Additionally, too high concentrate to forage ratio, too fast a switch from high forage to high concentrate, diet  
composed of highly fermented feeds, improperly mixed TMR and mycotoxins in feed also increases the  
incidence of SARA in dairy herds. SARA causes depressed feed intake, cycling feeding, reduced cud chewing,  
poor fibre digestion, rumenitis, mastitis, metritis, dehydration, diarrhoea, abomasal displacement, pulmonary  
bacterial emboli, systemic inflammation, liver abscesses, low milk fat, low milk protein, sore hooves, laminitis  
and low fertility. Therefore, SARA is a major challenge for animal health, productivity, economic efficiency and  
welfare issue even in well managed dairy herds. Feeding higher amounts of forages, supplying adequate peNDF,  
processing grains less thoroughly, reducing fermentability of the carbohydrate fraction and adapting rumen to  
the dietary changes are the key factors to be considered for preventing SARA. Continued research for accurate  
quantification of peNDF in diet, grain processing, optimization of meal size, dietary cation-anion balance, narrow-  
spectrum rumen modifier, inoculation of lactate utilizing microbes, inhibition of lactate producing microbes and  
innovation of the unique fermentability characteristics of feed ingredients to promote sufficient buffering and  
rapid absorption of VFA from rumen will explore new horizon for reducing incidence of SARA in future.  
Keywords: Acidosis, Cattle, Dairy herd, Rumen, Total mixed ration.  
The sub-acute ruminal acidosis (SARA) is a global threat which causes reduced dry matter intake and digestibility (Coon et  
al., 2019), change in bacterial density, assorted variety and community structure of the microorganism in the rumen  
(Plaizier et al., 2017), reduced microbial protein synthesis (de Veth and Kolver, 2001), decreased milk yield (Stone, 1999),  
reduced milk fat substance (Coon et al., 2019), modified lipid profile of milk (Jing et al., 2018), decreased conception rate  
(Khalouei et al., 2016), liver abscess (Wiese et al., 2017) and laminitis (Nocek, 1997). SARA has been characterized as a  
condition portrayed by critical ruminal pH and increased accumulation of short chain unsaturated fatty acids (SCFA)  
because of an imbalance between the production of fermentation acids by rumen microorganisms and the retention,  
absorption and buffering of those acids (Allen et al., 2006). SARA results altered volatile fatty acids, i.e., acidic, propionic  
and butyric acids towards elevated butyric and propionic acids and increased lactic acids in the rumen in 5-10 mmol/l  
Wilson, 1996). SARA is a result of feeding highly fermentable carbohydrate to the cows adjusted to process and use  
dominatingly forage based diets (Krause and Oetzel, 2006). However, it might likewise happen in pasture fed dairy cows  
when digestibility of the field forages are substantially high.  
SARA is a typical issue in practically all the dairy herds not just for animal health, profitability and productivity  
(Plaizier et al., 2008), yet additionally for animal welfare issues (Krause and Oetzel, 2006). It was accounted for that,  
hazard factor for laminitis (Nocek, 1997). Lameness is normally the most important purpose behind untimely culling of  
Citation: Hossain ME (2020). Sub-acute ruminal acidosis in dairy cows: Its causes, consequences and preventive measures. Online J. Anim. Feed Res., 10(1): 302-312.  
cows in a dairy herd. Furthermore, SARA has an immediate human health concern. Low ruminal and intestinal pH due to  
SARA expands the hazard for shedding enterohemorrhagic E. coli, for example, 0157:H7 (Russell and Rychlik, 2001).  
Dairy cows require high energy diets to fulfill their elevated needs for increased levels of milk production. However, high  
energy diets are quickly fermented in the rumen and magnify the danger of SARA. Accordingly, this is a significant  
challenge for dairy owners to improve animal health, profitability and financial effectiveness without challenging SARA.  
Feeding rapidly fermentable carbohydrate  
Feeding quickly fermentable diets to the cows recently adjusted to digest and utilize forage based diet is the most  
agreed explanation of SARA in dairy herds. In any case, all in all, too high concentrate to forage proportion, too quick a  
change from high forage to high concentrate and low peNDF content in diet are generally regular to SARA. SARA is  
brought about by the accumulation of VFAs and lactic acid in the rumen. As feed is digested in rumen, VFAs are produced,  
consumed or buffered in rumen. However, pH in the rumen drops if production of VFAs are quick and ingestion or  
buffering is low which surpasses the limit of the rumen to keep up harmony and at last a cyclic example of SARA  
happens. In a normal healthy rumen, lactic acid production normally rises to lactic acid use. In this manner, lactic acid  
focus is in every case brief and infrequently discernible. Under typical rumen pH, lactate-using microscopic organisms, for  
example, Megasphaera elsdenii and Selenomonas ruminantium, proceed to multiply and begin processing lactate to  
change over in different VFAs, which are then effectively protonated and retained (Goad et al., 1998). Most of the lactate  
produced can be used by these microbes. In any case, because of feeding overabundance fermentable carbohydrate,  
abundance propionate gathers in the rumen, lower ruminal pH, restrain multiplication of cellulolytic microscopic  
organisms and favor the development of lactateproducing microorganisms. As lactate delivering microscopic organisms  
multiply, pH pointedly dips under 6.0 and hinders the development of useful lactate using microbes. The turnover time of  
lactate using microscopic organisms is much slower than lactate creating microorganisms. Thus, lactate production  
quickly surpasses lactate use (Russell and Allen, 1984). Lactic acid is around multiple times more grounded than the  
other rumen acids and makes rumen pH drop forcefully. As an outcome, there is an imbalance of lactic acid digestion  
alongside expansion of VFAs coming about in SARA.  
Inadequate peNDF in diet  
In ruminant animal, salivary buffer production relies upon length and force of cud chewing. Chewing time is  
influenced by the substance of coarse fiber in the diet. The measure of genuine coarse fiber is evaluated by estimating the  
peNDF which has been characterized as the capacity of a feed to invigorate chewing and buffering of salivation in the  
rumen (Mertens, 1997). The fundamental factor that decides dietary peNDF content is the particle size appropriation and  
NDF substance of the diet, however different elements, for example, particle delicacy can likewise assume a purpose.  
Mature forages of appropriate chop length are a decent source of peNDF in contrast with cereal grains and crop residues  
(Krause and Combs, 2003). Besides invigorate saliva production, they add to rumen buffering through their inborn  
buffering component. Accordingly, as the measure of peNDF reduces in diet, chewing time just as salivary buffer  
production likewise reduces proportionately and causes frequency of SARA (Yang and Beauchemin, 2006).  
Insufficient rumen buffering  
Ruminant animals have restricted framework for buffering natural acids produced from ruminal fermentation of  
carbohydrates (Oetzel, 2015). In saliva the fact that, the genuine impact of buffering on ruminal pH is substantial in a  
forage based diet, in any case, it is moderately little on diets enhanced with quickly fermentable carbohydrate. There are  
two unique sorts of buffering i.e., exogenous and endogenous buffering. Dietary buffering is the exogenous buffering  
framework which decides real dietary cation-anion contrast (DCAD). Thusly, diets high in Na and K comparative with Cl  
and S have higher DCAD edge to kill higher ruminal pH for keeping up normal health and milk yield (Hu and Murphy,  
2007). Forages normally have higher DCAD, however, concentrates have extremely low DCAD potential and consequently,  
diets wealthy in concentrate are consistently helpless to SARA (Oetzel, 2015). Endogenous buffers produced in vivo by  
cow are discharged into the rumen through the salivation. Coarse, stringy feeds contain progressively viable fiber and  
invigorate more salivation production during eating than do finely ground TMR and concentrate work. Therefore, as the  
degrees of quickly fermentable carbohydrate increments in diet, cows become increasingly inclined to SARA.  
Inadequate adaptation  
A fast increment of highly fermentable concentrate in diet of the cows adjusted to process forage based diets  
expands the hazard for SARA since rumen microorganisms and the rumen wall can't adjust proportionately to the abrupt  
dietary changes. Deficient concentrate feeding during dry off period may likewise expand the danger of SARA due to  
damage of the ruminal papillae to build as needs be and disruption of rumen microbial population to adjust to  
unexpected high concentrate diets took care of later on (Dirksen et al., 1984). The short chain unsaturated fatty acids  
(SCFA) are generally viewed as luminal development factors and expanding their production modifies expansion of  
alimentary tract in ruminants. In light of gradually elevated SCFA fixation got from progressively expanding quickly  
Citation: Hossain ME (2020). Sub-acute ruminal acidosis in dairy cows: Its causes, consequences and preventive measures. Online J. Anim. Feed Res., 10(1): 302-312.  
fermentable diet, the ruminal epithelium endeavor to adjust slowly by expanding epithelial expansion, cell capacity and  
tissue penetrability (Penner et al., 2011). In any case, out of nowhere elevated quickly fermentable carbohydrate of the  
diet suddenly changes the rate of production of SCFA, for the most part acetic acid, propionate and butyrate (Plaizier et  
al., 2008). The rumen microorganisms and the rumen walls can't adjust proportionately to these abrupt dietary changes  
and at last SARA happens.  
Sorting of TMR particle  
Specifically sorting relatively progressively tasteful medium size forage particles even from a homogenous TMR is a  
typical inclination among dairy cows which lead them to expend a real imbalanced fiber consumption (Leonardi and  
Armentano, 2003) than determined in TMR. Ongoing examination shows that, lactating dairy cows exhibit higher degrees  
of sorting for medium size forage and concentrate particle against longer forage and smaller grain particles when taken  
care of a low forage diet. This kind of sorting conduct altogether reduces intake of sufficient peNDF from the TMR which  
continuously contributes to the occurrence of SARA in dairy herds.  
Other causes  
Dry matter intake in primiparous cows is lower than the older cows. In this way, apparently, the primiparous cows  
are at lower danger of SARA than the older cows. Nonetheless, consequences of a few examinations demonstrate that,  
primiparous cows are at higher hazard for SARA (Krause and Oetzel, 2006). Primiparous cows may require time to  
become acclimated to learn control their feed consumption when acquainted with a high-energy diet just because in the  
wake of calving. They may likewise endure experiencing issues accessing feed bunks when older cows are available in a  
Milk fat depression  
The relationship between SARA and milk fat depression is not consistent and it is really difficult to determine if a  
herd has a low milk fat test or not (Oetzel, 2015). Milk fat percentage generally depends on feed, breed, season and days  
in milk (Palmquist et al., 1993). According to the most popular substrate supply limitation theories, milk fat synthesis is  
limited by poor acetate supply since acetate is the principal precursor for biosynthesis of milk fat (Thomas and Martin,  
1988). However, the reduced ratio of acetate to propionate with highly fermentable diet is predominantly due to increased  
ruminal production of propionate. Additionally, ruminal infusion of acetate to cows suffering from SARA has only a  
marginal or no impact on milk fat synthesis (Bauman and Griinari, 2001). Therefore, substrate limitation theory appears  
almost immaterial (Bauman et al., 2011).  
According to recent research, excessive intake of unsaturated fat is the most predictable reason of milk fat  
depression in dairy cows (Vargas-Bello-Pérez and Garnsworthy, 2013). Ruminant’s diets are mostly consisting of  
unsaturated fatty acids that are extensively bio-hydrogenated in rumen. Conjugated linoleic acids are the unique  
intermediates in the biohydrogenation process and represent a mixture of positional and geometric isomers of  
octadecadienoic acid with variable conjugated double bonds (e.g., 7-9, 8-10, 9-11, 10-12) and can exist in different  
configurations (cis-trans, trans-cis, cis-cis, or trans-trans (Bauman et al., 1999). However, the major isomer of CLA in milk  
fat is cis-9, trans-11 which represents 80 to 90% of the total CLA (Parodi, 1977). Recent studies have demonstrated that,  
the cis-9, trans-11 isomers are produced in normal proportion only under healthy ruminal condition and they can prevent  
Under certain dietary conditions, such as high-concentrate, low-fiber diets, lower acetate to propionate molar ratio  
and decreased rumen pH, typical pathways of rumen biohydrogenation are altered to produce some unique fatty acid  
intermediates so that the concentration of the trans-10, cis-12 isomer increases in milk fat (Griinari and Bauman, 1999).  
These fatty acids are absorbed at the small intestine, taken up by the mammary gland and ultimately inhibit milk fat  
synthesis (Oetzel, 2015). Studies with pure isomers have ascertained that, the trans-10, cis-12 CLA is a potent inhibitor of  
milk fat synthesis. The inhibition mechanism involves a coordinated reduction in mRNA abundance decreasing the Δ9-  
desaturase activity in the biochemical pathways of fat synthesis (Bauman et al., 2011).  
In a series of studies, administration of CLA supplements to lactating dairy cows exhibited a dramatic reduction in  
the content and yield of milk fat. In a study, abomasal infusion of 60% CLA resulted greater than 50% reduction in milk  
fat (Giesy et al., 1999). In another study, abomasal infusion of the pure isomers of trans-10, cis-12 CLA reduced milk fat  
percentage and yield by 42 and 44%, respectively (Bauman et al., 1999). However, similar amount of cis-9, trans-11 CLA  
infusion had no effect on milk fat depression (Baumgard et al., 2000). Additionally, SARA may increase trans fatty acid  
uptake of host animals, perhaps by inhibiting certain bacteria which are responsible for complete biohydrogenation of  
fatty acids in the rumen (Plaizier et al., 2008).  
When the microvasculature of the corium is affected by vasoactive substances, then vascular destruction is  
inevitable. When blood is not returned to circulation by the musculature of the vascular system, then seepage and  
Citation: Hossain ME (2020). Sub-acute ruminal acidosis in dairy cows: Its causes, consequences and preventive measures. Online J. Anim. Feed Res., 10(1): 302-312.  
hemorrhage result. Laminitis is associated with inflammation of local corium which involves vascular breakdown,  
hemorrhage and exudation of the serum from capillary beds. As the horn tissue of the sole grows, the hemorrhage moves  
to the external surface and ultimately, external tissue of the sole exhibits internal hemorrhage which is the visual  
symptom of laminitis (Nocek, 1997).  
The progression from SARA to laminitis is associated with several systemic phenomena. However, the most  
common strategic and critical apex in the entire process is the reduction of ruminal pH which results metabolic and  
digestive disorders, localized trauma and vascular destruction. Destruction of the hemodynamics of the peripheral  
microvasculature due to SARA has been identified as a major etiological factor associated with development of laminitis  
(Nocek, 1997). Various theories have been developed to explain the pathogenesis of laminitis. Elevation of vasoactive  
substances especially histamine and endotoxins have been reported during occurrence of laminitis (Nocek, 1997).  
Elevated serum histamine concentration was related with corium tissue breakdown and elevated endotoxins were related  
with bacteriolysis due to decline of ruminal pH (Nocek, 1997)..  
Histamine has long been identified as a potent vasodilator and arterial constrictor (Chavance, 1946). Brent (1976)  
indicated that, histamine increases capillary permeability and arteriolar dilatation. Windholz et al. (1976) identified  
histamine as a potent vasodilator and Chavance (1946) identified histamine as a potent arterial constrictor. If histamine  
is an arterial constrictor and vassal dilator, blood pressure and flow would increase to the capillary beds (Nocek, 1997). As  
a result, pooling, vessel rupture, serum seepage and hemorrhage will occur. However, if the reverse is the case, then  
pooling would also occur because of constriction of veins rather than arteries. In any event, the impedance of blood flow  
and pressure build up within capillaries will force fluid through the vessels into the interstitial tissue spaces setting up  
In equine research, endotoxin administration resulted in vasoconstriction and arteriovenous shunting, which lead to  
poor perfusion of the digit and laminitis (Hunt, 1990). Boosman et al. (1991) administered endotoxin to cattle and  
created histopathologic lesions in the digit consistent with laminitis.  
Liver abscess  
SARA is associated with a chain of events that liberate Fusiformis necrophorus, Fusobacterium necrophorum, gram-  
negative, obligate anaerobic bacterium which is the primary etiologic agent of liver abscess (Oetzel, 2015). Low ruminal  
pH damages the surface of the rumen wall and causes ulceration of the epithelium. Once the ruminal epithelium is  
damaged, bacteria transported to the liver through portal circulation, causing liver abscesses. Infection in the liver  
originates from a necrobacillary rumenitis. Two biovars have been identified. Biovar A (F necrophorum necrophorum) the  
more virulent and predominant biovar in the rumen microflora isolated in pure culture from liver abscess. Biovar B (F  
necrophorum funduliforme) is isolated from microabscesses in rumen wall and less commonly isolated from liver  
abscesses. Arcanobacterium pyogenes, streptococci, staphylococci and Bacteroides spp are most frequently recovered  
from mixed cultures. F necrophorum, alone or with other bacteria, colonizes through the area of superficial necrosis  
produced in rumen under condition of SARA. Leukotoxin facilitate resistance to phagocytosis. Bacterial emboli from the  
lesions invade the hepatic portal venous system and transported to the liver, where they establish infectious foci of  
necrobacillosis which eventually develop liver abscesses (Krause and Oetzel, 2006).  
Reduced feed intake  
Reduced dry matter intake is supposed to be a reliable clinical sign and a few examinations have indicated a  
depressed hunger (Shinozaki, 1959), lower rumen motility (Ash, 1959), decreased fiber digestibility (Hoover, 1986) and  
reduced feed consumption (Fairfield et al., 2007) due to SARA. The depression in feed intake may have been because of  
elevated production of unstable unsaturated fats, particularly propionate and changes in the osmolarity in the rumen  
(Allen, 2000). It was accounted for that, grain induced SARA decreased in situ fiber digestibility in the rumen because of  
increased rumen acidity (Krajcarski-Hunt et al., 2002) and increased VFA production in rumen (Khafipoor et al., 2007). In  
any case, SARA prompted by feeding horse feed pellets came about no adjustment in DMI. The dissimilarity between the  
impacts of grain initiated SARA and pellet induced proposes that there may have different variables answerable for intake  
depression. A few examinations have demonstrated that grain-instigated SARA causes an expansion in acute stage  
proteins in blood, which is a marker of aggravation (Gozho et al., 2007). It has been indicated that irritation of different  
organs of the cow decreases feed intake (Andersen et al., 2003). Subsequently, the irritation coming about because of  
grain actuated SARA could add to the feed intake depression. This supposition that is fortified by the perception that  
enlistment of SARA by supplanting hay feed with hay pellets did not bring about aggravation and furthermore did not  
bring about feed intake depression (Khafipoor et al., 2007).  
Cyclic feeding  
Cyclic feeding design has been portrayed as the most reliable manifestation of SARA (Britton and Stock, 1987).  
Normally, the image is one of cyclic feed intake as the cow eats its proportion and subsequently declines further feed  
because of an uncommon fall in rumen pH coming about increased osmolality of the rumen liquid. Upon reestablishment  
of normal rumen conditions, appetite is often regained (Fulton et al., 1979). The course proceeds and subsequently, cyclic  
feeding creates.  
Citation: Hossain ME (2020). Sub-acute ruminal acidosis in dairy cows: Its causes, consequences and preventive measures. Online J. Anim. Feed Res., 10(1): 302-312.  
Feed sorting  
It has been accounted for that, whenever given chance, ruminants select diet trying to reduce the impacts of low  
ruminal pH to help keep up a sound ruminal condition. It has additionally been accounted for that, lactating dairy cows  
experiencing SARA favored long forage particles (Yang and Beauchemin, 2006) perhaps in endeavor to address their  
issue for peNDF. It was detailed that, feed sorting was influenced by the extents of purposefully induced acidosis of the  
cows. Both high and safe cows change their sorting conduct in light of acidosis difficulties and acidosis was related with  
elevated sorting for the longer particles against the shorter one.  
Poor feed efficiency  
Low ruminal pH disrupts ruminal mucosa causing ulceration of the epithelium (Krause and Oetzel, 2006). Moreover,  
over the top keratinization of the ruminal epithelium happened as an outcome of SARA results decreased absorptive limit  
(Krehbiel et al., 1995), reduced profitability and increased feed costs because of poor digestibility and lower feed  
effectiveness. It was accounted for that, ruminal NDF digestion declined from 52% for cows with a mean ruminal pH of  
6.4 to 44% for cows encountering rehashed scene of SARA with a mean ruminal pH of 5.8.  
Impaired microbial protein synthesis  
SARA reduces digestibility of organic matter subsequently brings down the productivity of microbial protein  
amalgamation in rumen which at last declines the yield of microbial protein except if increasingly fermentable  
carbohydrate is provided. The reduced microbial protein blend expands the requirement for increasingly supplemental  
feed protein in the diet of the host animal (Beauchemin et al. 2003).  
Abomasal displacement  
progression of ruminal gasses among stomach and the front stomachs are accepted to bring about abomasal atony and  
dilatation and subsequent removal (Sarashina et al., 1990). The hypothesis is upheld by the finding that a low fiber  
content in the feed proportion is the most important single factor in the event of abomasal dislodging (Shaver, 1997) and  
that the foundation of a practical fiber tangle in the drifting layer is accepted to be of significance in the more continuous  
production and ingestion of VFA in the forestomachs (Enemark, 2008). The event of abomasal ulcers has been connected  
to management and feeding of acidic diets comprising of concentrates and silage.  
Rumenitis is one of the most incessant spin-offs of rumen acidosis. The pathogenesis is not plainly seen, however,  
an increased production of VFA especially butyrate and propionate just as a brief ascent in ruminal lactate focus and  
variances in the osmolality of the rumen liquid may confuse advancement of rumenitis (Krehbiel et al., 1995).  
Parakeratosis is an outcome of increased lactate production which results mucosal sore. Mucosal injuries in rumenitis  
encourage passageway of Fusobacterium necrophorum and once in a while Acanobacterium pyogenes and help their  
subsequent colonization in the submucosa. Embolic spread to the liver makes development of hepatic boil with  
metastasis the aspiratory course by means of back vena cava causing burst of minor pneumonic corridors into the  
bronchi. Clinically these scenes may prompt epistaxis and haemoptysis portrayed by bleeding, frothing expectorate  
around the gag and nostrils showing indications of lethal rumenitis (Nordlund et al., 1995; Enemark, 2008).  
Swell is of specific issue in dairy herds kept up on high concentrate diet. The genuine connections have not yet been  
built up however the mix of decreased rumen motility brought about by a low fiber ration and subsequently a low rumen  
pH, extreme production of mucopolysaccharides and arrival of obscure macromolecules from rumen microorganisms  
because of bacterial crumbling should bring about the development of a steady froth upsetting eructation of gases from  
rumen (Cheng et al., 1998). In any case, rumen balance because of low rumen pH may likewise contribute accumulation  
of free gases coming about swell.  
The diarrhoea has been related with SARA in dairy herds (Oetzel, 2015). It was accounted for that, cows expending  
low fiber diets and experiencing SARA had more fluid excrement than cows on high forage diet. Excrement from cows  
with SARA seemed more brilliant and more yellowish than the dung of cows without SARA (Kleen et al., 2003). Frothy  
dung and loose bowels propose poor ruminal and broad hindgut fermentation related with SARA. Fermentation in the  
hindgut produces VFA and carbon dioxide. These VFAs can be consumed, yet gas is gotten away in hindgut and produces  
rises in dung giving them the 'frothy' appearance. Hindgut fermentation likewise brings about increased acidity of the  
hindgut substance. The increased acidity prompts sloughing of the epithelial cells in the digestive organ discharged with  
faces. As hindgut gets serious acidic, more water from epithelial cells come to neutralize it. As a result, poor consistency  
of the ingesta and at last the runs happens.  
Citation: Hossain ME (2020). Sub-acute ruminal acidosis in dairy cows: Its causes, consequences and preventive measures. Online J. Anim. Feed Res., 10(1): 302-312.  
SARA may influence fertility of dairy cows in a roundabout way Besides calving and potentially the health of the  
infant calf (Enemark, 2008). Cycling feeding is an outcome of SARA which may diminish accessibility of energy and some  
other indispensable supplements to the cows and the infant by diminishing DMI during early lactation. This condition is  
related with fertility in cows during post-partum and deficient development of the ova (Britt, 1995).  
Economic loss  
SARA has extraordinary financial result to the dairy ventures everywhere throughout the world. The monetary lose  
due to SARA results from reduced milk production, poor proficiency of milk production, untimely automatic separating  
and increased passing loss (Krause and Oetzel, 2005). It was assessed to be US$1.12/day per cow monetary loss in herds  
determined to have SARA (Stone, 1999). It was likewise revealed that, decreased feed consumption due to SARA came  
about impeded development in calves and evaluated in lost US$10-13 for each animal alongside extra loss from liver sore  
happened in 15% of the cases.  
Physically effective fiber (peNDF)  
The peNDF identifies with the physical attributes of a feed which shows its capability to animate chewing (Mertens,  
1997). Extended fodder particles in the feeding regimen contain adequate peNDF which advances chewing and salivary  
emission that support the acids coming about because of feed processing. In this manner, particle length of forages and  
the measure of forage fiber in the diet assume huge purpose on rumen pH through salivary buffering. Moreover, long  
forage fiber makes a skimming mat in the rumen, which animates reticulo-ruminal compressions to expel VFA by means  
of ingestion and section of liquid from rumen to bring down gut and in this manner decrease the danger of SARA.  
Fibres are digested gradually than starch and sugar. In this way, incorporating peNDF in the diet hinders the rate of  
carbohydrate processing in the rumen. Reduced rate of carbohydrate absorption reduces the rate of VFA production,  
consequently, forestalls enormous drops in rumen pH. Feeding long particle fiber can likewise move the site of starch  
dairy cows ought to be longer than 8 mm in size.  
The peNDF substance of the diet can be increased either by expanding NDF content or by expanding cleave length of  
forages (Beauchemin and Penner, 2009). Whichever way of expanding the peNDF substance of the diet at last builds  
chewing time and salivary discharge. The expanding peNDF substance of the diet by expanding the NDF content is  
generally more powerful as far as forestalling SARA than expanding forage particle length. In any case, more exploration  
is expected to more readily characterize the connections between dry matter intake, peNDF content and ruminal  
fermentability of diet.  
Preparation of diet  
Diets devoured by cows may contrast as often as possible from those that have been detailed because of mistakes  
in blending and feed sorting. It was accounted for that, cows favor littler feed particles than bigger ones (Leonardi and  
Armentano, 2003) which demonstrates that, regardless of whether the diet contains adequate peNDF, the bit that is really  
devoured may not. Some dairy ranchers add water to TMR to diminish dry matter substance so as to abstain from sorting.  
Adding water is intended to tie proportion particles together and make it hard to sorting against bigger forage particles. It  
was accounted for that, adding water to diminish a TMR dry matter from 80 to 64% decreased sorting for the littlest  
particles. Adding water to the rations can conceivably bring down dry matter intake in view of the filling impact of higher  
dampness proportions. Adding molasses to a dry TMR has been fairly appeared to forestall sorting by restricting activity  
(DeVries and Gill, 2012). Moreover, sorting can be limited by keeping away from over the top measures of long material in  
the TMR. It has been recommended that, additional roughage or straw ought not be longer than 2.5-5.0 cm (Shaver,  
Fermentability of feed  
The carbohydrate divisions inside diet contrast in their rate of absorption. Sugars and starches are digested quicker  
than fiber. Dietary starch is provided basically by grains and its rate of absorption in the rumen relies upon the sort of  
grain and how it is prepared. One way to deal with hinder the rate of fermentation is to supplant a bit of the grain with  
non-forage fiber sources, for example, beet mash, soybean structures, horse feed feast, distiller's grains, brewer's grains  
and corn gluten feed (Grant, 1997). Utilization of non-forage fiber sources decreases the measure of starch digested in the  
rumen. Besides, the best technique to decrease fermentation rate in the rumen is to expand the extent of forage in the  
diet. Adding forage to the diet not just builds chewing time and saliva emission, it additionally reduces VFA production  
round the day (Beauchemin et al., 2003). However, as the measure of forage increments in TMR, energy content declines  
Citation: Hossain ME (2020). Sub-acute ruminal acidosis in dairy cows: Its causes, consequences and preventive measures. Online J. Anim. Feed Res., 10(1): 302-312.  
Partitioning of carbohydrate  
It has been suggested that, for lactating dairy cows creating in excess of 30 kg of milk general rules for carbohydrate  
portion can be considered as CF=15-17%, ADF=19-21%, NDF (TMR) =27-30%, NDF (Forage) =21-22%, nonstructural  
carbohydrates, 35 to 40% and starch, 28 to 30%, sugar 6% (Beauchemin and Penner, 2009). The ruminally degradable  
starch, NDF and carbohydrate ought to be 60 to 70%, 50 to 60% and 50 to 55% of the absolute starch, NDF and  
carbohydrate substance of the diet. These rules should just be considered without bargaining energy prerequisites of the  
cows being referred to. Different rules in regards to physical structure and the proportions of auxiliary to nonstructural  
carbohydrate incorporate forage NDF to ruminally degradable starch >1:1; NDF: nonstructural carbohydrates >0.9 and  
<1.2 and 15 to 20% eNDF with particle size >3.8 cm long.  
Dietary protein  
Dietary protein levels have been accounted for to impact the occurrence of laminitis. Manson and Leaver (1988)  
contrasted diets and 16.1 versus 19.8% crude protein. The high protein diet fundamentally affected motion during clinical  
weakness for dairy cows somewhere in the range of 3 and 26 wk baby blues. It was considered the impact of 15.3 versus  
18% dietary unrefined protein on solid calves and on those influenced with laminitis. It was seen that, high rates of  
ruminally degradable protein were answerable for faltering and laminitis. In any case, little data is accessible with respect  
to purpose of protein in the improvement of weakness. A few propositions include unfavorably susceptible histaminic  
responses to specific kinds of proteins (Nilsson, 1963) or a connection between high protein supplementation (Bazeley  
Dietary yeast  
Utilization of microorganism to forestall neurotic changes in dairy cow is notable. Nocek et al. (2002a,b) announced  
that, inoculation of microorganisms into rumen was viable against SARA. Three kinds of lactate using microorganisms i.e.,  
Enterococcus faeccium, Lactobacillus plantarum and Sacchoromyces cerevisae were applied intraruminaly. These  
microorganisms after immunization, viably forestalled collection of lactic acid and lead to high ruminal pH. However,  
direct immunization of Selenomonas ruminantium and Megasphaera elsdenii was sketchy since their endurance was  
short (Owens et al., 1998). In vitro examinations proposed that, Saccharomyces cerevisiae communicated with rumen  
microorganisms to diminish lactate collection. It infers that, yeast supplement might be helpful to the cows experiencing  
ruminal acidosis. In any case, Saccharomyces cerevisiae reduced the impact of a grain-put together ruminal acidosis  
challenge with respect to rumen fermentation. Conversely, Li et al. (2013) revealed that, assembly of short chain fatty  
acid settled ruminal pH. Hereditary control of lactolytic microscopic organisms is a generally new thought with the point of  
expanding the lactate transformation limit and acid opposition of the microorganisms yet no industrially accessible item  
has yet been produced (Martin and Dean, 1989). Supplementation of dicarboxylic acids, for example, fumarate and  
maleate may likewise act along these lines however documentation is not yet accessible (Owens et al., 1998).  
Chewing activity  
The dairy cows normally burn through 2 to 6 h/d for eating, 3 to 9 h/d for ruminating and a limit of around 14 h/d  
for chewing relying on the diet. Expanding peNDF of the diet either by expanding the NDF content or expanding the slash  
length of forages builds chewing time and thus salivary discharge. It was accounted for that, each extra kilogram of  
peNDF in a peNDF lacking diet can expand chewing time by up to 5-7 h/d contrasted with the diets containing satisfactory  
peNDF. In this manner, a little increment in peNDF substance of the diet can be successful when diets are low in fiber.  
Vegetable forages and high protein feeds have more buffering limit than grains (Jasaitis et al., 1987). Forages having little  
particles are less viable in invigorating rumination which brings about less saliva production. For instance, rate of  
salivation production for new grass, silage and grass feed was 0.94 ml, 1.13 ml and 3.25 ml/g individually (Bailey, 1958).  
Although, expanding peNDF substance of diet builds chewing time, however the expansion in saliva yield because of  
increased chewing is not as incredible as expected since the increased progression of salivation during chewing is joined  
by a reduction in resting salivation discharge (Maekawa et al., 2002). It was accounted for that, the net increment  
altogether salivary emission because of 1 h/d additionally chewing is around 7 L which may support just around 0.5 kg of  
ground grain. Consequently, the net impact of the steady saliva production on mean rumen pH is moderately little  
although an expansion in salivation emission during eating can help decrease the degree to which pH dips under 5.8 after  
Fermentation modifiers  
Feed added substances that help change the microbial environment of the rumen, for example, sodium bicarbonate,  
yeast, bacterial direct took care of microbials and monensin can help limit acidosis. Buffers might be added to most  
lactating cow's diet as a prudent step in avoidance of acidosis (Garry, 2002). They might be included situations where the  
fiber content in the feed is excessively low. It has been accounted for that, the expansion of 150 g of sodium bicarbonate  
to the lactation feed every day positively affected the milk yield (Downer and Cummings, 1985). Thus, a beneficial  
outcome has been shown on feed intake and milk fat rate. Sodium bicarbonate at 0.5 to 0.75% of DMI might be brought  
into the proportion progressively because of their low attractiveness. Buffers might be offered free decision to cattle  
Citation: Hossain ME (2020). Sub-acute ruminal acidosis in dairy cows: Its causes, consequences and preventive measures. Online J. Anim. Feed Res., 10(1): 302-312.  
dependent on the presumption that, ruminants will promptly expend the sum expected to reduce the impacts of SARA.  
Sodium bicarbonate can be given either blended into the ration or free choice. In any case, blending the bicarbonate into  
the ration was more compelling than giving it free decision.  
Surface zone of ruminal papillae is influenced by diet (Xu and Allen, 1999). Offering high roughage diets during dry  
period may diminish papillae surface territory which reduces rate of VFA absorption (Allen et al., 2006). It was accounted  
for that, rumen papillae altogether increased in size and capacity to assimilate VFA was increased when animals were  
changed from roughage and straw based diet to a high energy diet containing a blend of grass feed and grain two wk  
preceding refreshing (Mertens, 1992). Dirksen et al. (1985) stressed the significance of versatile changes of the rumen  
mucosa for anticipation of acidosis. It was seen that, rumen papillae increased from 10 mm2 to 60 mm2 when cows  
were presented to high concentrate diets from four to six wks. Rumen papillae seemed to arrive at their most extreme  
length at 4 to 5 wk post-calving. In vivo VFA absorption rates performed at 14 wk post-calving were substantially more  
prominent around then contrasted and when cows were taken care of the feed straw diet. In another investigation, Stone  
et al. (2003) assessed papillae size and their capacity to retain valerate in 4 Holstein calves and watched substantial  
changeability in papillae size and ruminal ingestion of valerate.  
Of the SCFAs, butyrate has been accounted for to be the most powerful trigger of epithelial expansion in colonic  
epithelial cells. Intra-ruminal mixture of butyrate has for some time been known to incite ruminal epithelial expansion in  
vivo. However, rather than in vivo investigations, butyrate has been appeared to evoke an inhibitory impact on ruminal  
epithelial multiplication in vitro. These differentiating results demonstrate that, butyrate alone can't advance epithelial  
expansion legitimately, rather acts through the arrival of certain hormones and development factors. It was accounted for  
that, EGF, IGF-1, GH, insulin and glucagon fixation increased in a portion subordinate way because of ruminal mixtures of  
blended SCFA which animated multiplication of ruminal epithelium for adjustment to the subsequent changes.  
There exist positive relationships between the counter Streptococcus bovis and hostile to Lactobacillus IgG in serum  
and salivation and pervasiveness of SARA (Shu et al., 1999). Contrasted with control group, guides in the vaccinated  
group had higher (P<0.05) feed consumption, lower (P<0.05) ruminal concentrations of lactate and lower quantities of  
Streptococcus bovis and Lactobacillus. So also, polyclonal antibodies arranged against S. bovis or Fusobacterium  
necrophorum when applied to calves, substantially decreased rumen concentrations of target microscopic organisms and  
increased pH in steers took care of high-grain diets (Calsamiglia et al., 2012). These investigations recommend that, the  
danger of lactic acidosis can be decreased by inoculation against S. bovis and Lactobacillus (Gill et al., 2000). In another  
examination, the danger of lactic acidosis in sheep was reduced by inoculation with a live Streptococcus bovis antibody  
Bunk management  
Congestion, rivalry for bunk space, constrained access to feed, rare TMR push-up in the bunk, segment feeding, stall  
comfort and long milking parlor time increment the danger of SARA (Stone, 2004). In this way, the components of the  
stall must be sufficient for the size of animal that is being housed, particularly stall length, width and jump space.  
Moreover, satisfactory stall space ought to be given to permit ruminating to roughly 12 to 14 h/d. Ideal materials ought to  
be given for cow comfort.  
Sub-acute ruminal acidosis (SARA) is a multi-factorial silent threat for financial issue, animal health and welfare even in  
well managed dairy herds. As efficiency builds up, the interest for quickly fermentable carbohydrate increments  
proportionately which makes high yielding cows increasingly prone to SARA. Along these lines, planning high energy diet  
with satisfactory peNDF is a reliable predictor under traditional feeding framework. Moreover, subclinical course of the  
disease with complex etiology and pathogenesis confound its outline, analysis, monitoring and avoidance. Cautiously  
adjusting rumen to changes in diet, reducing fermentability of carbohydrate part, providing adequate peNDF to keep up  
ideal digesta pool that invigorate satisfactory salivary buffer course through rumination and elevate ruminal motility to  
expand VFA absorption are the fundamental variables to be considered in controlling SARA.  
Corresponding Author  
E-mail: emran@cvasu.ac.bd  
Authors’ Contribution  
I am the sole contributor of the manuscript.  
Citation: Hossain ME (2020). Sub-acute ruminal acidosis in dairy cows: Its causes, consequences and preventive measures. Online J. Anim. Feed Res., 10(1): 302-312.  
Conflict of interests  
The author acknowledges Department of Animal Science and Nutrition, Chattogram Veterinary and Animal Sciences  
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