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The Veterinary Journal 176 (2008) 44–49

TheVeterinary Journal

Subacute ruminal acidosis (SARA) in grazing Irish dairy cows

Luke O’Grady *, Michael L. Doherty, Finbar J. Mulligan

School of Agriculture, Food Science and Veterinary Medicine, Unit of Herd and Veterinary Public Health, University College Dublin,

Belfield, Dublin 4, Ireland

Accepted 18 December 2007

Abstract

Subacute ruminal acidosis (SARA) is a significant production disease of dairy cattle. Previous concerns have been raised over theoccurrence of SARA in pasture-fed dairy cattle and the potential consequences of laminitis and lameness. Highly digestible perennialrye grass contains high concentrations of rapidly fermentable carbohydrate and low concentrations of physical effective fibre thatmay result in SARA. This study conducted a point prevalence survey of rumen health status in grazing Irish dairy cattle fed predom-inantly perennial rye grass-based pasture. The survey assessed rumen fluid, animal health status, milk production data and pasture com-position. A total of 144 cows between 80 and 150 days in milk were sampled on 12 farms. Eleven percent of cows were classified asaffected with SARA (pH 6 5.5), 42% were marginal (pH 5.6–5.8) and 47% were normal (pH > 5.8). The study showed that low rumenpH is prevalent in grazing Irish dairy cattle consuming perennial rye grass-based pasture and raises concerns regarding effective pastureutilisation and possible consequences for animal health.� 2008 Elsevier Ltd. All rights reserved.

Keywords: Subacute ruminal acidosis; Dairy cow; Pasture; Rumen pH; Rumenocentesis

Introduction

Subacute ruminal acidosis (SARA) is a production dis-ease that is difficult to diagnose in the field due to the var-iable and subtle clinical signs associated with the syndrome.Many signs do not present until several months after theinitial insult or are masked by other common ailments ofdairy cows, such as lameness and excessive loss of bodycondition. Several studies have linked SARA to conditionsof dairy cattle such as laminitis (Oetzel, 2000; Enemarket al., 2002) decreased dry matter intake (DMI) (Garrett,1996), poor body condition score (Oetzel, 2000), loose fae-cal consistency (Nordlund et al., 1995; Oetzel, 2000), lowmilk fat syndrome (Nordlund et al., 1995; Oetzel, 2000),caudal vena cava syndrome (Nordlund et al., 1995) andabomasal displacement/ulceration (Olson, 1991).

Nordlund et al. (1995) identified two production groupsin dairy herds that are at greatest risk of SARA. These are

1090-0233/$ - see front matter � 2008 Elsevier Ltd. All rights reserved.

doi:10.1016/j.tvjl.2007.12.017

* Corresponding author. Tel.: +353 1 716 6075; fax: +353 1 716 6005.E-mail address: luke.ogrady@ucd.ie (L. O’Grady).

early lactation cows (within the first 3 weeks after calving)and cows at peak DMI (10–14 weeks post calving). Earlylactation cows are at higher risk due to a reduced absorp-tive capacity of the rumen epithelium, poorly adaptedrumen microflora, and the rapid introduction to high-energy dense diets. Cows at peak DMI are at risk due tothe high levels of volatile fatty acids produced by microbialfermentation, which overwhelm the buffering and absorp-tive capacity of the rumen. Oetzel (2005) reported a higherprevalence of SARA in cows 80–150 days in milk than forcows of <80 days in milk for total mixed ration fed herds.

The specific definition for the alteration in rumen pHthat constitutes a diagnosis of SARA in an individualcow is a subject of debate. The lack of accurate diagnostictest strategies, combined with the variable nature of rumenpH in healthy cows has contributed to this uncertainty andhas hampered agreement on the criteria for diagnosis. In arecent review, Enemark et al. (2002) defined affected cowsas having a rumen pH in the range 5.0–5.5. Nordlundand Garrett (1994) characterised affected cows as havinga rumen pH of <5.8. Oetzel (2003) proposed definitions

L. O’Grady et al. / The Veterinary Journal 176 (2008) 44–49 45

for a farm-level diagnosis, based on sampling 12 cows atrisk. A herd was classified as positive if more than threecows tested had a rumen pH of <5.5. Kleen et al. (2003)stated that studies recording the prevalence of SARA areuncommon. However, a small number of studies haveshown SARA to be prevalent in dairy cattle. Garrettet al. (1997), in a study of 15 dairy herds in the USA,revealed that in one-third of the herds investigated >40%of animals had a low rumen pH. More recently, a studyby Morgante et al. (2007) revealed that in 3/10 herds exam-ined, more than one-third of the randomly chosen animalswere found to have a rumen pH < 5.5. A further five herdshad more than one-third of the animals with a rumenpH < 5.8.

Westwood et al. (2003) raised concerns over the occur-rence of SARA in pasture-fed dairy cattle in New Zealandand identified possible links to laminitis and lameness. Thesuggested reasons for pasture-based diets contributing toSARA included high concentrations of rapidly fermentablecarbohydrates and low levels of physically effective fibre inlush pastures. It is the experience of the University CollegeDublin (UCD) Herd Health Group that SARA has beendiagnosed on individual farms contributing to low milkfat syndrome and laminitis in grazing Irish dairy herds(L. O’Grady et al., unpublished observations). The aimof the present study was to conduct a point prevalencesurvey of rumen health status in grazing Irish dairy cattle.

Materials and methods

The study took the form of single, on-farm investigations gatheringdata on rumen fluid pH and volatile fatty acid concentration, togetherwith an assessment of animal health factors, herd risk factors and anyconcurrent diseases.

Farm selection

Twelve commercial farms were selected for the survey. All of thefarms were predominantly spring calving pasture-fed Holstein-Friesiandairy herds containing at least 12 cows between 80 and 150 days inmilk at the time of sampling. To be included in the study all herds hadto be feeding <2 kg of supplementary feed per milking. The averagemilking herd size of the herds sampled was 95 ± 38 cows (mean ± SD)with an average milk yield of 8114 ± 733 kg/cow (mean ± SD).The herds were located in the Counties Wicklow and Meath and werevisited during the month of June 2006. All of the herds involved in thestudy conducted monthly milk recording and agreed to make thisdata available via the Irish Cattle Breeding Federation (ICBF)database.

Animal selection

Prior to each farm visit, data were gathered on cow identity, lac-tation number, calving date, most recent milk yield, milk fat and proteinpercentages, using the most recent milk recording. From these data,days in milk and milk fat-to-protein ratios were calculated for individualcows. The data were also analysed to identify cows between 80 and 150days in milk on each farm. These cows were selected as it was assumedthat DMI would be maximal at this time. From this group of eligiblecows, 12 animals were selected at random from each herd, irrespectiveof herd size, for sampling by rumenocentesis as suggested by Oetzel(2004).

Rumen fluid collection and analysis

Access to pasture ad libitum was considered to resemble most closely atotal mixed ration feeding-pattern. Each farm visit was timed to allow therumenocentesis to be performed 6 h post turn-out to pasture after themorning milking, as this point coincided with the predicted daily nadir inrumen pH in total mixed ration fed herds (Oetzel, 2003).

Rumenocentesis was conducted as described by Nordlund and Garrett(1994) using a needle from a 14-gauge, 80 mm long, intravenous catheter(Intraflon 2, Vycon) and a 20 mL syringe. The rumen fluid pH was mea-sured immediately on farm using a calibrated electronic pH meter (HannaInstruments pH 210 Microprocessor pH meter). Ten millilitres of rumenfluid were then transferred into a universal container containing 0.5 mL of70 mM mercuric chloride to prevent further fermentation. Samples werestored on ice during transport, before being frozen at �20 �C in the lab-oratory. The frozen samples were thawed and analysed for volatile fattyacid concentrations. After thawing, the samples were diluted 1:5 withdistilled water, mixed and centrifuged at 1400 g for 4 min (Sorvall GLC 2Blaboratory centrifuge). Then, 1 mL of the subsequent supernatant and1 mL of internal standard (0.5 g 3-methyl-m-valeric acid in 1 log0.15 mol/L oxalic acid) were mixed with 3 mL of distilled water.

Following centrifugation to remove the precipitate, the sample wasfiltered through Whatman 0.45 lm polyethersulphone membrane filtersinto a chromatographic sample vial. Finally, 1 lL of sample was injectedinto a model 3800 Varian gas chromatography instrument with a25 m � 0.53 mm i.d. megabore column (coating CP-Wax 58 (FFAP) – CB(no. CP7614)) (Varian).

Clinical scoring

The selected animals were scored for rumen fill, faecal fibre and faecalconsistency, as described by Zaaijer and Noordhuizen (2003). In addition,all animals in the herd were locomotion scored and body condition scoredby two experienced independent observers. Locomotion scores were gra-ded using the five-point scale described by Sprecher et al. (1997). Bodycondition scores were graded using the five-point scale as described byEdmondson et al. (1989).

Pasture analysis

Assessment of herd diets was performed by recording dietary man-agement, including the composition of concentrate fed, and by samplingthe pasture that the herd would graze subsequently. Grass samples werefrozen on farm for analysis at a future date. For dry matter determinationand for routine chemical analysis, pasture samples were dried at 104 �C for16 h. Pasture samples were ground in a hammer mill fitted with a 1 mmscreen. The nitrogen (N) content of the pasture samples was determinedusing a Leco FP-528N Analyser. Crude protein was determined as Ncontent 6.25�. The methods used for analysis of acid detergent fibre,neutral detergent fibre, ether extract and ash were as described by Mul-ligan et al. (2002).

Farm questionnaire

A questionnaire survey was performed to gather details on farm sizeand production level, herd and pasture management and estimated inci-dences of lameness and production diseases.

Statistical analysis

Descriptive data analysis was performed using Microsoft Office Excel2003 for Windows. Statistical analysis of the rumen sample data togetherwith the associated cow data was performed using the Proc General LinearModelling function of SAS Version 9.13 (SAS Institute) to examine thedata for the effects of farm, lactation number and days in milk. Herds wereclassified as affected (at least 25% with rumen pH 6 5.5), high risk (greaterthan 33% with pH 6 5.8) or normal. A Kruskal–Wallis test was performed

46 L. O’Grady et al. / The Veterinary Journal 176 (2008) 44–49

on these data to examine the effects of farm classification on any pro-duction, clinical score, rumen fluid or dietary factors.

Results

The 144 cows sampled were classified, based on theresults of the rumenocentesis pH data, into affected(<5.5), marginal (5.6–5.8) and normal animals. Using thesecriteria, 11% (16) of cows were classified as affected (i.e.having SARA), 42% (60) were classed as having marginalrumen pH and 47% (68) were classed as normal (Table 1).

Table 1Percentage of sampled cows classified as affected (pH 6 5.5), marginal (pH < 5(total sampled, n = 12/herd)

Herd number

1 2 3 4 5

Percentage of cows affected(rumen pH 6 5.5) (%)

0 0 8 17 25

Percentage of cows marginal(rumen pH < 5.8) (%)

33 75 25 50 67

Percentage of cows normal(rumen pH P 5.8) (%)

67 25 67 33 8

Herd risk classification Normal High Normal High Affected

Affected herds classified as containing P25% of sampled cows with a rumen pHrumen pH 6 5.8. Normal herds classified as containing 633% of cows with a

Table 2

Production and clinical score data by herd (means ± SE) for the 144 cows sampled by r

Herd

number

Lactation Milk yield

(kg/day)

Milk fat

(%)

Milk

protein (%)

Days in milk Milk

fat:protei

1 3.0 ± 1.7 33.7 ± 7.0 3.24 ± 0.44 3.11 ± 0.11 123.8 ± 14.4 1.04 ± 0.

2 2.6 ± 0.9 29.5 ± 4.2 2.84 ± 0.77 3.07 ± 0.16 113.3 ± 11.1 0.93 ± 0.

3 1.9 ± 1.3 28.5 ± 3.9 3.48 ± 0.32 3.04 ± 0.14 120.3 ± 21.1 1.15 ± 0.

4 2.7 ± 2.0 29.4 ± 6.5 3.95 ± 0.89 2.94 ± 0.23 106.7 ± 17.1 1.35 ± 0.

5 3.4 ± 2.3 35.0 ± 4.0 3.65 ± 0.72 3.15 ± 0.15 123.6 ± 19.9 1.15 ± 0.

6 3.4 ± 1.5 39.1 ± 5.0 3.57 ± 0.70 3.01 ± 0.16 106.5 ± 21.9 1.19 ± 0.

7 2.6 ± 1.4 26.4 ± 4.6 3.28 ± 0.44 3.16 ± 0.23 105.3 ± 20.2 1.04 ± 0.

8 2.4 ± 1.8 29.6 ± 6.2 2.79 ± 0.64 3.07 ± 0.20 115.8 ± 17.9 0.91 ± 0.

9 2.4 ± 2.2 24.6 ± 5.2 3.54 ± 0.35 3.17 ± 0.16 100.3 ± 16.7 1.12 ± 0.

10 2.9 ± 1.2 33.3 ± 5.7 2.74 ± 0.60 3.26 ± 0.19 110.0 ± 22.2 0.84 ± 0.

11 3.3 ± 2.3 27.7 ± 4.3 3.50 ± 0.40 3.08 ± 0.27 108.7 ± 18.5 1.14 ± 0

12 1.9 ± 1.1 25.7 ± 5.9 4.32 ± 0.52 3.30 ± 0.11 117.0 ± 25.2 1.31 ± 0.

Table 3Rumen fluid volatile fatty acid composition by herd (means ± SE) for the 144

Herdnumber

RumenpH

Rumenacetate(mmol/L)

Rumenpropionate(mmol/L)

Acetate:propionate

Iso-butyrate(mmol/L

1 6.0 ± 0.3 84.71 ± 15.28 19.20 ± 3.05 4.40 ± 0.37 0.57 ± 02 5.8 ± 0.2 122.83 ± 37.71 30.02 ± 10.03 4.13 ± 0.32 0.88 ± 03 6.0 ± 0.4 64.03 ± 10.12 20.08 ± 3.70 3.21 ± 0.26 0.65 ± 04 5.8 ± 0.3 47.73 ± 5.13 13.51 ± 2.58 3.62 ± 0.58 0.25 ± 05 5.7 ± 0.2 79.92 ± 12.48 25.98 ± 4.76 3.10 ± 0.21 0.85 ± 06 5.8 ± 0.2 82.91 ± 27.24 26.24 ± 8.65 3.17 ± 0.22 1.26 ± 17 6.0 ± 0.4 65.60 ± 15.14 19.69 ± 5.54 3.40 ± 0.41 0.60 ± 08 5.8 ± 0.2 125.96 ± 37.79 30.28 ± 8.47 4.16 ± 0.45 2.07 ± 19 5.9 ± 0.4 102.53 ± 36.31 31.61 ± 13.23 3.32 ± 0.38 0.71 ± 010 5.7 ± 0.3 123.40 ± 42.27 43.89 ± 17.50 2.89 ± 0.42 1.39 ± 011 5.8 ± 0.2 99.34 ± 10.02 28.16 ± 6.29 3.68 ± 0.79 1.68 ± 112 6.6 ± 0.7 86.80 ± 30.04 24.72 ± 8.88 3.54 ± 0.41 0.55 ± 0

Individual cow results

Data from the 144 individual cow samples are presentedin Tables 2 and 3. These data were analysed for the effectsof farm, lactation number, days in milk (Table 4) and forany significant relationship between high (>5.8) or low(65.8) rumen pH grouping and cow milk yield, milk fatand protein percentages, milk fat-to-protein ratio, bodycondition score, rumen fill, locomotion score, faecal fibreand consistency score, rumen fluid volatile fatty acidcomposition (Table 5). From the general linear modelling,

.8) and normal (pH P 5.8) based on individual cow rumen fluid pH data

Total(n = 144)6 7 8 9 10 11 12

0 25 8 17 25 8 0 11

75 50 67 42 67 67 17 42

25 25 25 41 8 25 83 47

High Affected High High Affected High Normal N/A

of 65.5. High-risk herds classified as containing >33% of the cows with arumen pH 6 5.8.

umenocentesis (n = 12 for all parameters)

n

Body

condition

score

Rumen

fill score

Locomotion

score

Rumen

pH

Faecal

consistency

score

Faecal

fibre

score

14 2.92 ± 0.16 3.5 ± 0.7 2.3 ± 0.8 6.0 ± 0.3 2.6 ± 1.0 3.0 ± 0.9

26 2.81 ± 0.19 3.9 ± 0.5 2.2 ± 0.7 5.8 ± 0.2 2.4 ± 0.8 2.9 ± 0.7

10 2.90 ± 0.33 3.9 ± 0.3 2.2 ± 0.9 6.0 ± 0.4 2.5 ± 0.5 2.4 ± 0.8

29 2.88 ± 0.17 3.9 ± 0.3 2.0 ± 1.0 5.8 ± 0.3 2.1 ± 0.5 2.7 ± 0.8

19 2.98 ± 0.46 3.9 ± 0.3 1.6 ± 0.8 5.7 ± 0.2 2.8 ± 0.8 2.0 ± 0.7

24 2.65 ± 0.31 3.7 ± 0.5 2.3 ± 0.6 5.8 ± 0.2 2.8 ± 0.9 2.6 ± 0.9

11 2.71 ± 0.14 4.0 ± 0.0 1.8 ± 1.0 6.0 ± 0.4 2.1 ± 0.7 2.4 ± 0.7

18 2.83 ± 0.22 4.0 ± 0.0 1.8 ± 0.8 5.8 ± 0.2 2.6 ± 0.5 3.3 ± 0.7

11 3.00 ± 0.15 3.8 ± 0.8 1.4 ± 0.7 5.9 ± 0.4 2.5 ± 0.7 1.8 ± 0.6

19 2.81 ± 0.19 3.9 ± 0.3 2.2 ± 0.8 5.7 ± 0.3 2.2 ± 0.6 2.0 ± 0.6

.10 2.71 ± 0.18 4.3 ± 0.7 2.0 ± 0.7 5.8 ± 0.2 1.8 ± 0.6 2.0 ± 0.4

16 3.02 ± 0.49 1.4 ± 0.7 3.3 ± 0.5 6.6 ± 0.7 2.3 ± 0.7 2.9 ± 0.7

cows sampled by rumenocentesis (n = 12 for all parameters)

)

N-butyrate(mmol/L)

Iso-valerate(mmol/L)

N-valerate(mmol/L)

Total volatile fatty acidconcentration (mmol/L)

.28 12.19 ± 2.11 1.83 ± 0.17 1.82 ± 0.32 120.33 ± 20.37

.11 18.07 ± 5.44 2.81 ± 0.58 2.58 ± 0.77 177.23 ± 54.21

.38 11.33 ± 2.41 1.31 ± 0.61 1.78 ± 0.73 99.18 ± 17.39

.04 9.07 ± 1.10 0.42 ± 0.11 0.88 ± 0.17 71.87 ± 8.28

.20 16.27 ± 2.33 1.96 ± 0.45 2.45 ± 0.38 127.44 ± 19.47

.29 18.29 ± 6.25 2.53 ± 1.40 3.84 ± 1.84 135.08 ± 42.78

.14 12.56 ± 3.24 1.44 ± 0.34 1.92 ± 0.53 101.81 ± 23.88

.58 18.64 ± 4.85 3.81 ± 1.63 4.52 ± 2.55 185.28 ± 52.80

.22 20.34 ± 6.59 1.74 ± 0.73 2.53 ± 1.37 159.46 ± 56.99

.39 26.08 ± 10.49 2.52 ± 0.97 4.34 ± 2.62 201.64 ± 71.37

.41 17.56 ± 5.01 2.94 ± 1.37 3.81 ± 2.23 153.50 ± 20.44

.12 15.25 ± 5.84 1.22 ± 0.20 1.37 ± 0.39 129.92 ± 44.70

Table 4Overall production, clinical score and rumen fluid data for the 144 cowssampled by rumenocentesis

Mean Minimum Maximum Standarderror

Lactation number 2.7 1 9 ±1.7Days in milk 115 80 150 ±42.7Milk yield (kg/day)a,b 30.2 15 49.6 ±6.6Milk fat%a 3.41 1.57 6.1 ±0.73Milk protein%a 3.11 2.43 3.7 ±0.2Fat: protein ratioa 1.10 0.47 2.11 ±0.23Body condition score a,b 2.85 2.25 4.25 ±0.29Rumen filla 3.69 1 5 ±0.9Locomotion scorea,b 2.08 1 4 ±0.9Rumen pHa 5.9 5.4 8.5 ±0.4Faecal consistency score a 2.4 1 4 ±0.7Faecal fibre scorea 2.5 1 4 ±0.8Rumen acetate (mmol/L)a 90.48 34.94 193.36 ±35.15Rumen Propionate

(mmol/L)a26.11 8.87 70.54 ±11.30

Acetate:propionate ratioa 3.55 2.31 5.18 ±0.61Iso-butyrate (mmol/L)a 0.95 0 6.41 ±0.88N-butyrate (mmol/L)a 16.30 6.74 45.29 ±6.73Iso-valerate (mmol/L)a 2.04 0.31 8.27 ±1.22N-valerate (mmol/L)a 2.65 0.62 11.09 ±1.81Total volatile fatty acid

concentration (mmol/L)a138.56 53.97 293.87 ±53.87

a Significant effect (<0.01) of farm.b Significant effect (<0.01) of lactation number.

Table 6Herd risk categorisation of production, clinical score and rumen fluid datafor the 144 cows sampled by rumenocentesis (mean ± standard error)

Affected herds(n = 3)

High riskherds (n = 6)

Normal herds(n = 3)

Lactation 2.97 ± 0.42 2.79 ± 0.43 2.28 ± 0.63Milk yield (kg/day) 31.54 ± 4.57 29.98 ± 4.89 29.28 ± 4.05Milk fat% 3.22 ± 0.46 3.37 ± 0.46 3.68 ± 0.56Milk protein% 3.19 ± 0.06 3.05 ± 0.08 3.15 ± 0.14Days in milk 112.97 ± 9.48 108.56 ± 5.50 120.33 ± 3.38Milk fat: protein 1.01 ± 0.16 1.11 ± 0.17 1.17 ± 0.13Body condition score 2.83 ± 0.14 2.81 ± 0.13 2.94 ± 0.07Rumen fill score 3.94 ± 0.05 3.94 ± 0.22 2.94 ± 1.34Locomotion score 1.84 ± 0.31 1.93 ± 0.32 2.58 ± 0.65Rumen pH 5.81 ± 0.16a 5.82 ± 0.05a 6.19 ± 0.31b

Faecal consistencyscore

2.33 ± 0.36 2.37 ± 0.36 2.46 ± 0.13

Faecal fibre score 2.14 ± 0.24 2.54 ± 0.58 2.76 ± 0.35

L. O’Grady et al. / The Veterinary Journal 176 (2008) 44–49 47

a strongly significant effect (P < 0.01) of farm was found onall variables, except days in milk (Table 4). Lactation num-ber also had a significant influence on milk yield, body con-

Table 5Production, clinical score and rumen fluid data for the 144 cows sampledby rumenocentesis (means ± SE) grouped by rumen pH value

Group 1: lowrumen pH (<5.8)

Group 2: normalrumen pH (P5.8)

Rumen pHa 5.63 ± 0.06 6.10 ± 0.05Lactation number 2.53 ± 1.35 2.87 ± 1.98Days in milk 119.96 ± 9.60 110.48 ± 8.19Milk yield (kg/day) 31.72 ± 1.01 32.96 ± 0.86Milk fat% 3.30 ± 0.12 3.19 ± 0.11Milk protein% 2.99 ± 0.04 3.03 ± 0.03Fat: protein 1.11 ± 0.04 1.06 ± 0.03Body condition score 2.80 ± 0.05 2.86 ± 0.05Rumen fill 3.93 ± 0.11 3.90 ± 0.09Locomotion score 2.31 ± 0.15 2.29 ± 0.12Faecal consistency scoreb 2.34 ± 0.15 2.60 ± 0.13Faecal fibre score 2.67 ± 0.16 2.53 ± 0.14Rumen acetate (mmol/L) 93.42 ± 3.97 97.32 ± 5.09Rumen propionate

(mmol/L)27.78 ± 1.98 25.86 ± 1.69

Acetate:propionatea 3.42 ± 0.09 3.77 ± 0.07Iso-butyrate (mmol/L) 0.91 ± 0.17 0.81 ± 0.14N-butyrate (mmol/L) 16.54 ± 1.19 15.96 ± 1.01Iso-valerate (mmol/L) 2.14 ± 0.19 1.88 ± 0.16N-valerate (mmol/L) 2.65 ± 0.32 2.25 ± 0.27Total volatile fatty acid

concentration (mmol/L)143.44 ± 9.24 144.09 ± 7.88

Group 1 (n = 76): low rumen pH (<5.8). Group 2 (n = 68): normal rumenpH (P5.8).

a Significant difference between groups (P < 0.001).b Significant difference between groups (P < 0.05).

dition score and locomotion score (P < 0.01) (Table 4).Thus, older cows had a higher milk yield, lower body con-dition score and a higher locomotion score. The low rumenpH group was associated with a significant reduction inrumen fluid acetate-to-propionate ratio (P < 0.001) and areduced cow faecal consistency (P < 0.05) (Table 5).

Herd level results

Herds were classed as SARA affected if P25% of the 12cows sampled had rumen pH of 65.5. Three (25%) herdswere categorised as affected with SARA (herds 5, 7 and

Rumen acetate(mmol/L)

89.64 ± 30.10 96.88 ± 28.87 78.51 ± 12.59

Rumen propionate(mmol/L)

29.85 ± 12.56 26.64 ± 6.70 21.34 ± 2.97

Acetate: propionate 3.13 ± 0.25 3.68 ± 0.41 3.72 ± 0.62Iso-butyrate

(mmol/L)0.95 ± 0.40 1.14 ± 0.67 0.59 ± 0.05

N-butyrate (mmol/L) 18.30 ± 6.99 17.00 ± 4.00 12.92 ± 2.06Iso-valerate (mmol/L) 1.97 ± 0.54 2.38 ± 1.17 1.45 ± 0.33N-valerate (mmol/L) 2.91 ± 1.27 3.03 ± 1.31 1.66 ± 0.25Total volatile fatty

acid concentration(mmol/L)

143.63 ± 51.84 147.07 ± 40.90 116.48 ± 15.73

Pasture dry matter(DM) (g/kg)

223.8 ± 16.8 219.6 ± 25.9 249.5 ± 53.8

Pasture crude protein(g/kg DM)

169.4 ± 37.8 181.0 ± 33.8 168.1 ± 42.5

Pasture acid detergentfibre (g/kg DM)

270.1 ± 25.9 248.4 ± 26.0 248.8 ± 28.6

Pasture neutraldetergent fibre(g/kg DM)

580.8 ± 34.0 543.0 ± 61.9 528.1 ± 68.7

Pasture water solublecarbohydrate(g/kg DM)

101.05 ± 3.61 117.55 ± 9.54 127.22 ± 63.11

Total concentrate fed(kg/day)

1.83 ± 0.29 1.67 ± 0.41 1.83 ± 0.29

Affected herds classified as containing P25% of sampled cows with arumen pH of 65.5. High-risk herds classified as containing >33% of thecows with a rumen pH 6 5.8. Normal herds classified as containing 633%of cows with a rumen pH 6 5.8.a,b Significant difference between groups denoted by different letters(P < 0.05).

48 L. O’Grady et al. / The Veterinary Journal 176 (2008) 44–49

10) (Table 1). Six (50%) of the remaining nine herds wereclassified as high risk for SARA. These herds contained>33% of the cows with a rumen pH of 5.8 or less (herds2, 4, 6, 8, 9 and 11). The remaining three (25%) herds (1,3 and 12) were classified as normal (Table 1). The analysisof these data revealed no significant effects of herd categor-isation on any of the cow, milk production, rumen fluid ordietary factors with the exception of significantly lowerrumen pH in both the affected and high risk herds in com-parison to the normal herds (P < 0.05) (Table 6).

Discussion

The study has demonstrated that grazing cows fed pre-dominantly rye grass-based pasture are potentially at riskof developing SARA and the subsequent animal healtheffects of this condition. The prevalence of low rumen pH(65.5) was lower than that reported by Garrett et al.(1997) in US total mixed ration fed cows in peak lactation(11% vs. 26%, respectively). The study found a similar pro-portion of herds affected by SARA in the high and mediumrisk categories compared to other recent studies (Morganteet al., 2007). Furthermore, it should be noted that in addi-tion to the animals that developed SARA, 80% of the cowssampled had rumen pH that was below the range of 6.0–6.1for optimal cellulolysis (Mould et al., 1983). Other authorshave reported that improvements in the digestion of fibrousdiets maybe realised in cattle at a rumen pH > 6.3 (Mulli-gan et al., 2002). Thus, the findings from this study suggestthat there maybe cause for concern regarding effective pas-ture utilisation and possible consequences for animalhealth.

Of the 12 herds surveyed in the study, three herdsreached the alarm level suggested by Oetzel (2004) in that25% of cows sampled in each herd had rumen pH valuesof 5.5 or less. Oetzel (2004) stated that in those particularherds diagnosis should be supported by clinical findingssuch as variable feed intake, lameness or increased condi-tion score loss. Other assessment criteria have been usedfor assisting herd level diagnosis. Faecal consistency, fae-cal fibre particle dimensions and rumen fill (Zaaijer andNoordhuizen, 2003; Garry, 2002) have been suggested ascow level assessments of dietary adequacy for the mainte-nance of appropriate rumen pH. Nordlund (2003) sug-gested linking ration and rumen fluid analysis andmonitoring of clinical signs of disease (e.g. laminitis) withevidence of low milk fat syndrome. However, the use oflow milk fat as an indicator of SARA remains controver-sial. While Allen (1997) summarised data from severaltrials demonstrating a relationship between milk fat per-centage and rumen pH, studies by Garrett (1996) showedpoor correlation between milk fat percentage and the pres-ence of SARA on farm, as seen in this study. Cook et al.(2005) suggested that if 10% of cows have individual milkfat percentages of 2.5 or less, then SARA may besuspected.

Although the present study did find numerically loweracetate-to-propionate ratios, milk fat percentage and faecalconsistency scores in the high risk herds, no statistically sig-nificant alteration in any of the health or production crite-ria was found in either the high or medium risk SARAherds (Table 6). Only faecal consistency was significantlylinked to low rumen pH (<5.8) in individual cows. How-ever, it should be noted in this context that a point preva-lence study does not allow for satisfactory detection ofmany problems such as lameness and condition score lossdue to the inherent dynamics of these diseases over longperiods of time.

Although rumen pH findings consistent with SARAwere detected both at an individual cow and herd level, itwas not possible to determine the length of time that therumen pH was below the cut-off value used, due to the lim-itations of a single time-point rumenocentesis sampling.Gozho et al. (2005) addressed the issue of the duration ofSARA. They defined a rumen pH threshold of between5.2 and 5.6 for >174 min/day as significant based on detect-able effects on feed intake and the presence of inflammationas evidenced by elevated peripheral concentrations of hap-toglobin and serum amyloid-A. Therefore further work willbe required to explore the duration of rumen pH depres-sion required in grazing cows for the onset of clinical dis-ease symptoms and reduced milk production.

It was not possible in the present study to identify anycausal factors for the presence of SARA on some farmsand not on others. The significant effect of a farm detectedfrom the data analysis supports the view that herd level fac-tors, such as management, may be risk factors for thedevelopment of SARA.

The present study also agreed with other reports regard-ing the safety of rumenocentesis (Morgante et al., 2007).No significant problems were noted during or after per-forming rumenocentesis. The only complication seen wasa single subcutaneous swelling in one cow, which resolvedshortly after treatment.

Conclusions

This study has shown that low and suboptimal rumenpH is prevalent in a sub-population of grazing dairy herdsin Ireland and raises questions relating to herd health inpasture-based milk production. The study has also high-lighted the difficulty in interpreting the significance ofrumen pH data with respect to making a herd level diagno-sis – this pilot study did not identify any statistical correla-tion with problems regarding animal health or reducedanimal performance in either affected or non-affectedherds. However, several reports do indicate an associationbetween low rumen pH and ailments such as lameness, neg-ative energy balance, and infertility. Further studies will beneeded to investigate in greater detail the incidence andeffects of SARA in pasture-fed cattle. In particular, it willbe necessary to establish a clearer understanding of dailyrumen pH dynamics at pasture and to develop key

L. O’Grady et al. / The Veterinary Journal 176 (2008) 44–49 49

monitoring strategies and diagnostic criteria specific to pas-ture-based management systems. It would also be beneficialif further research would examine the prevalence of SARAin pasture-fed herds at other stages of lactation as thisstudy specifically focused on cattle during peak dry matterintake.

Conflict of interest statement

None of the authors (L. O’Grady, M.L. Doherty andF.J. Mulligan) has a financial or personal relationship withother people or organisations that could inappropriatelyinfluence or bias the paper entitled Subacute ruminal acido-

sis in grazing Irish dairy cows.

Acknowledgements

The authors would like to acknowledge CatherineMcCarney, William P. Lightbody, Mary Duane, JamesCallan for their assistance during farm visits and in theanalysis of the sample material used in this study.

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