A comparison of methods for the diagnosis of bovine subclinical mastitis within New Zealand dairy herds : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in veterinary clinical science at Massey University

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Copyright is owned by the Author of the thesis. Permission is given for

a copy to be downloaded by an individual for the purpose of research and

private study only. The thesis may not be reproduced elsewhere without

the permission of the Author.

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A COMPARISON OF METHODS _----'1?

(,4-f\.o

FOR THE DIAGNOSIS OF BOVINE SUBCLINICAL MASTITIS WITHIN NEW ZEALAND DAIRY HERDS

A thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Clinical Science

at Massey University.

Robert John Holdaway

1990

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ii

ABSTRACT

During the 1986-1987 and 1987-1988 dairy seasons, milk samples were taken from cows within three New Zealand dairy herds. Individual quarter foremilk samples were taken using aseptic precautions, and whole udder, composite samples were obtained using a milk meter, at monthly intervals.

The three herds differed with respect to herd size, milking shed design, use of teat spraying, and the incidence of mastitis, both past and present.

The bacteriological status of each quarter was determined, and the ability of the following parameters to distinguish between infected and uninfected quarters, and between infected and uninfected cows was ascertained.

(1) Somatic cell count (2) Sodium concentration (3) Potassium concentration (4) Electrical conductivity (5) pH

(6) Lactose concentration

(7) N-acetyl-B-d-glucosaminidase activity (8) a1-antitrypsin concentration

With the exception of the antitrypsin concentration, the concentration of each parameter in the milk changed during the course of milk removal. The effect of this variation on the composition of the composite milk sample is discussed.

The stage of lactation at which the sample was taken exerted a significant effect on the level of each parameter in quarter foremilk samples. Similar effects were observed with composite samples, although statistical significance was not reached in every instance.

Both infected and uninfected udder quarters were affected by the stage of lactation.

The age of the cow exerted a significant effect on the levels of a number of the parameters within quarter foremilk samples. The effect of age of the cow on the level of each parameter within composite milk samples was generally not significant.

The bacteriological status of the udder quarter exerted a significant effect on the level of each parameter in at least one of the three herds. The effect of the bacteriological status on the pH and on the

po

tassium concentration of the milk was smaller in degree than was the effect on the remaining parameters.

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iii The herds differed with respect to bacteriological findings. Herd A showed a lower incidence of infection than did herds

B

or C. The incidence of infection with minor pathogens was highest within herd

B,

while the incidence of infection with major pathogens was highest within herd C. The incidence of infection tended to increase with the age of the cow.

While each of the eight parameters showed high specificity, the sensitivity was generally lower. An exception to this finding was the somatic cell count which showed both high sensitivity and high specifidty.

The somatic cell count was able to correctly classify more than 75 % of quarter foremilk samples in each of the three herds, being more consistent in this respect than were any of the other parameters, the diagnostic abilities of which varied between herds.

The addition of second parameter to a model containing the somatic cell count generally did not increase the diagnostic accuracy of the system.

The threshold value was found to vary both between herds, and between stages of the lactation, this variation being greatest for the somatic cell count. Providing that the threshold is adjusted for the stage of lactation, the somatic cell count is able to accurately predict the infection status throughout the dairy season. The selected threshold should take into account the level of bacterial infection within the particular herd to which it will be applied.

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iv

ACKNOWLEDGEMENTS

The work reported in this thesis was carried out with the generous financial assistance of the Livestock Improvement Corporation of the New Zealand Dairy Board.

Sincere thanks are due to the following persons:

Mr Ian Steffert and Dr Colin Holmes, my two supervisors, provided invaluable advice, constructive criticism and support during the course of the project.

Members of the Somatic Cell Counting Subcommittee of the Livestock Improvement Corporation, including Mr Harry Brown, Dr Graeme Morris, Mr Ian Hook and Dr Brian Wickham were very supportive.

Professor Robert Anderson and Dr John Rendel offered advice regarding the application of statistical procedures, and the use of the Massey University

mainframe computer.

Professor Robert Jolly was very supportive throughout the project, and was responsible for supervising a course on the anatomy and pathology of the mammary gland. Similarly, Dr Duncan McKenzie is resp�:msible for my knowledge of lacta tional physiology.

Cheryl Cooper and Jenny Wickham helped with the milk sampling, often under t rying circumstances. Dr Bob Greenway, Geraldine Borrie, Janice Rumbal and Margaret Scott provided technical advice concerning the various assays, and were always very patient.

The somatic cell counting was carried out b y Chris Bedford, Raewyn Smith and Joanne Jeffrey at the Wellington-Hawkes Bay Livestock Improvement Corporation,

and latterly by the staff of the Hillcrest Testing Center in Hamilton.

Lynne Cullinane provided advice, encouragement, and invaluable assistance with

w ord-processing and printing of the thesis, while Jan Schrama spent many hours

making the bacteriological media, often at short notice, but always in good

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V

humour. Rose Law and Peter Wildbore assisted with the ordering of chemicals and media.

The staff of the Massey University Computer Center provided a very professional, yet friendly service.

Special thanks are due to the owners and managers of the three dairy farms without whose co-operation this project would not have been possible. The sampling procedures caused disruption to the normal milking routine, and their tolerance and patience was sincerely appreciated.

Finally, a huge debt of gratitude is due to my family for their patience and support during the course of the project.

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TABLE OF CONTENTS

PAGE

ACKNOWLEDGEMENTS _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _.iv

TABLE OF CONTENTS _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _.vi

LIST OF TABLES _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _.viii

LIST OF GRAPHS _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _.xiii

CHAPTER ONE THE SIGNIFICANCE OF BOVINE MASTITIS . . . . . . . . . . . . . . . . 1

CHAPTER TWO THE DIAGNOSIS OF SUBCLINICAL MASTITIS: A REVIEW OF THE LITERATURE . . . . . . . . . . . . . . . . . . . . . . . . 13

CHAPTER THREE MATERIALS AND METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60

CHAPTER FOUR THE EFFECTS OF STAGE OF MILKING ( MILK FRACTION ) ON THE LEVEL OF SELECTED PARAMETERS IN MILK . . . . . . . . . . . . . . . . . . . .73

CHAP.TER FIVE A DESCRIPTION OF THE BACTERIOLOGICAL STATUS OF QUARTERS AND OF COWS DURING THE TRIAL PERIOD . . . . . . . . . . . . . . . . . . . . . . . . . . 103

CHAPTER SIX THE EFFECTS OF BACTERIOLOGICAL STATUS, STAGE OF LACTATION AND AGE OF COW ON LEVELS OF PARAMETERS IN MILK FROM INDIVIDUAL QUARTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .139

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.,---^- ^.

TABLE OF CONTENTS ( CONTINUED )

CHAPTER SEVEN

THE DIAGNOSIS OF INFECTION IN QUARTER SAMPLES . . . . 206

CHAPTER EIGHT

THE EFFECTS OF AGE OF COW, STAGE OF LACTATION AND BACTERIOLOGICAL STATUS ON THE LEVEL

OF EACH PARAMETER IN COMPOSITE MILK SAMPLES . . . . . . 25 1

CHAPTER NINE

THE DIAGNOSIS OF INFECTED UDDERS USING

COMPOSITE MILK SAMPLES . . . . . . . . . . . . . . . . . . . . . . . . . . .295

CHAPTER TEN

SUMMARY AND GENERAL DISCUSSION . . . . . . . . . . . . . . . . . . .330

BIBLIOGRAPHY _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _.351

APPENDIX _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _. _.390

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TABLE

2.1

LIST OF TABLES

TITLE

RELATIONSHIP BETWEEN THE CALIFORNIA MASTITIS TEST AND THE SOMATIC CELL COUNT.

PAGE

21

2.2 COMPARISON OF TESTS WITH RESPECT TO THE SENSITIVITY, SPECIFICITY, REPEATABILITY,

RAPIDITY AND OPERATING COSTS. 59

3.1 DESCRIPTION OF THE THREE SELECTED FARMS. 61 3_.2 RESULTS OF STORAGE TRIAL: SOMATIC CELL COUNT. 66

4.1 STAGE OF MILKING TRIAL: BACTERIOLOGICAL

STATUS OF UDDER QUARTERS. 93

4.2 4.3 4.4 4.5

4.6

4.7 4.8

4.9 4.10

5.1

5.2a

5.2b

5.2c

STAGE OF MILKING TRIAL: MEAN SOMATIC CELL COUNT. 94 MEAN SODIUM CONCENTRATION. 95 MEAN POTASSIUM CONCENTRATION. 96 MEAN ELECTRICAL CONDUCTIVITY. 97

MEAN pH. 98

MEAN LACTOSE CONCENTRATION. 99 MEAN NAGase ACTIVITY. 100 MEAN ANTITRYPSIN CONCENTRATION. 101 STAGE OF MILKING TRIAL: ANALYSIS OF VARIANCE. 102

NUMBER OF COWS AND OF QUARTERS ANALYZED. 126 INCIDENCE, DURATION AND LEVEL OF INFECTION: HERD A. 127

· HERD B. 128 HERD C. 129

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LIST OF TABLES ( CONTINUED

TABLE TITLE

5.3 BACTERIOLOGICAL FINDINGS AT A SUBSEQUENT SAMPLING

PAGE

GIVEN A SPECIFIC FINDING AT AN ARBITRARY SAMPLING. 130 5.4a NO. OF BACTERIAL SPECIES ISOLATED PER QUARTER: HERD A. 131

5.4b _{HERD B.} 132

5. 4c _{HERD C.} 133

5.5 PREVALENCE OF INFECTION IN PREVIOUS SURVEYS. 134

5.5 _key KEY TO TABLE 5.5. 135

6.1 ANALYSIS OF VARIANCE: INDIVIDUAL QUARTERS. 172 6.2 CONTRAST ANALYSIS BETWEEN BACTERIOLOGICAL STATUSES. 173 6.3a CONTRAST ANALYSIS BETWEEN AGE GROUPS: HERD A. 174

6 _•3 b _{HERD B}. 17 5

6. 3 c _{HERD C.} 176

6.4a CONTRAST ANALYSIS BETWEEN STAGES OF LACTATION: HERD A. 177

6 . 4 b _{HERD B}_. 17 8

6 . 4 c ^{HERD C}^. 17 9

6.5a CONTRAST ANALYSIS BETWEEN STAGES OF LACTATION UNINFECTED QUARTERS ONLY:

6.5b

6.5c

7.11 RESULTS FOR ALL HERDS:

7.1ii

BACTERIOLOGICAL CLASSIFICATION 1.

RESULTS WITHIN INDIVIDUAL HERDS BACTERIOLOGICAL CLASSIFICATION 1

HERD A. 180 HERD B. 181 HERD C. 182

239

24 0

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TABLE

7.1iii

7.1iv

7 .1v

7.1vi

LIST OF TABLES ( CONTINUED )

TITLE

RESULTS BY STAGE OF LACTATION, BACTERIOLOGICAL CLASSIFICATION 1.

RESULTS OF SOMATIC CELL COUNT WITHIN HERDS, BY STAGE OF LACTATION,

BACTERIOLOGICAL CLASSIFICATION 1 .

RESULTS FOR TOTAL DATA,

BACTERIOLOGICAL CLASSIFICATION 2.

RESULTS WITHIN INDIVIDUAL HERDS, BACTERIOLOGICAL CLASSIFICATION 2.

7.2i DISCRIMINANT FUNCTION ANALYSIS FOR ALL HERDS.

7.2ii

7.2iii

7.2iv

DISCRIMINANT FUNCTION ANALYSIS WITHIN INDIVIDUAL HERDS.

DISCRIMINANT FUNCTION ANALYSIS FOR ALL HERDS, SOMATIC CELL COUNT PLUS ONE OTHER PARAMETER.

DISCRIMINANT FUNCTION ANALYSIS

WITHIN INDIVIDUAL HERDS, SOMATIC CELL COUNT PLUS ONE OTHER PARAMETER.

7.3 CORRELATION BETWEEN THE SOMATIC CELL COUNT AND EACH SELECTED PARAMETER.

7.4 EFFECT OF USING CRITICAL THRESHOLD VALUES, '

OR SET THRESHOLD VALUES, ON THE DIAGNOSIS OF INFECTION WITHIN INDIVIDUAL UDDER QUARTERS.

8.1 EFFECTS OF BACTERIOLOGICAL STATUS, STAGE OF LACTATION AND AGE OF COW ON THE LEVELS OF THE SELECTED

PARAMETERS IN COMPOSITE MILK SAMPLES.

8.2

8.3a

CONTRAST ANALYSIS BETWEEN EACH BACTERIOLOGICAL STATUS, IN COMPOSITE MILK SAMPLES.

CONTRAST ANALYSIS BETWEEN STAGES

OF LACTATION FOR COMPOSITE MILK SAMPLES: HERD A.

PAGE

241

242

243

244

245

246

247

248

249

250

277

278

279

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LIST OF TABLES ( CONTINUED )

TABLE TITLE

8.3b CONTRAST ANALYSIS BETWEEN STAGES

OF LACTATION FOR COMPOSITE MILK SAMPLES: HERD B.

8.3c _{HERD C.}

8.4 NUMBER OF INFECTED QUARTERS PER INFECTED UDDER.

9.1i RESULTS OF THE THRESHOLD PROGRAM WITHIN THE TOTAL DATA SET: COMPOSITE MILK SAMPLES, BACTERIOLOGICAL CLASSIFICATION 1.

9.1ii

9.1iii

RESULTS OF THE THRESHOLD PROGRAM WITHIN INDIVIDUAL HERDS: COMPOSITE MILK SAMPLES, BACTERIOLOGICAL CLASSIFICATION 1.

RESULTS OF THE THRESHOLD PROGRAM BY STAGE OF LACTATION WITHIN THE TOTAL DATA SET: COMPOSITE MILK SAMPLES, BACTERIOLOGICAL CLASSIFICATION 1.

9.2i DISCRIMINANT FUNCTION ANALYSIS FOR THE TOTAL DATA SET, USING EACH PARAMETER ALONE: COMPOSITE MILK SAMPLES, BACTERIOLOGICAL CLASSIFICATION 1.

9.2ii

9.2iii

9.2iv

DISCRIMINANT FUNCTION ANALYSIS WITHIN INDIVIDUAL HERDS, USING EACH PARAMETER ALONE: COMPOSITE MILK SAMPLES, BACTERIOLOGICAL CLASSIFICATION 1 .

DISCRIMINANT FUNCTION ANALYSIS FOR THE TOTAL DATA SET, USI�G THE SOMATIC CELL COUNT PLUS ONE OTHER PARAMETER: COMPOSITE MILK SAMPLES, BACTERIOLOGICAL CLASSIFICATION 1.

DISCRIMINANT FUNCTION ANALYSIS WITHIN INDIVIDUAL HERDS, USING THE SOMATIC CELL COUNT PLUS ONE OTHER PARAMETER: COMPOSITE MILK SAMPLES,

BACTERIOLOGICAL CLASSIFICATION 1 .

9.3 CORRELATION BETWEEN THE SOMATIC CELL COUNT

AND EACH OTHER PARAMETER: COMPOSITE MILK SAMPLES.

PAGE

280

281 282

320

321

322

323

324

325

326

327

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LIST OF TABLES ( ^CONTINUED )

TABLE TITLE

9.4 SUMMARY OF PREVIOUS STUDIES INTO THE ABILITY OF THE SOMATIC CELL COUNT TO DISTINGUISH BETWEEN INFECTED AND UNINFECTED COWS.

9.5 EFFECT OF USING A FIXED THRESHOLD VALUE ON THE DIAGNOSTIC ACCURACY OF THE SOMATIC CELL COUNT FOR COMPOSITE MILK SAMPLES.

10.1 INTERNATIONAL DAIRY FEDERATION GUIDELINES FOR THE DIAGNOSIS OF SUBCLINICAL MASTITIS.

10.2 EFFECT OF INFECTION OF THE UDDER AND OF THE TEAT CANAL ON THE SOMATIC CELL COUNT OF MILK: RESULTS OF A PREVIOUS TRIAL.

PAGE

328

329

349

350

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GRAPH

5.1a

5.2a

5.1b

5.2b

5.1c 5.2c

6 .1ai.

6.1ai.i.

6 .1bi.

6 .1bi.i.

6 .1ci.

6.1ci.i.

6. 2ai.

LIST OF GRAPHS

TITLE

PREVALENCE OF INFECTION WITHIN UDDER QUARTERS: HERD A PREVALENCE OF INFECTION WITHIN COWS: HERD A PREVALENCE OF INFECTION WITHIN UDDER QUARTERS: HERD B PREVALENCE OF INFECTION WITHIN COWS: HERD B PREVALENCE OF INFECTION WITHIN UDDER QUARTERS: HERD C PREVALENCE OF INFECTION WITHIN COWS:

LOG(lO) SOMATIC CELL COUNT VS STAGE OF LACTATION,

BY BACTERIOLOGICAL STATUS: QUARTER SAMPLES.

LOG(l0) SOMATIC CELL COUNT·

VS STAGE OF LACTATION,

BY AGE OF COW: QUARTER SAMPLES.

LOG(10) SOMATIC CELL COUNT VS STAGE OF LACTATION,

LOG(lQ) SOMATIC CELL COUNT VS STAGE OF LACTATION,

LOG(lO) SODIUM CONCENTRATION VS STAGE OF LACTATION,

HERD C

HERD A

HERD B

HERD C

HERD A

PAGE

136

137

138 138

183

184

185

186

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LIST OF GRAPHS (CONTrNUED )

GRAPH TITLE PAGE

6.2aii _LOG(10) SODIUM CONCENTRATION vs STAGE OF LACTATION,

BY AGE OF COW: QUARTER SAMPLES. HERD A 186

6.2bi _LOG( 10) ^SODIUM CONCENTRATION VS STAGE OF LACTATION,

BY BACTERIOLOGICAL STATUS: QUARTER SAMPLES. HERD B 187

6.2bii _LOG( 10) SODIUM CONCENTRATION VS STAGE OF LACTATION,

BY AGE OF COW: QUARTER SAMPLES. HERD B 187

6.2ci _LOG( 10) ^SODIUM CONCENTRATION vs STAGE OF LACTATION,

BY BACTERIOLOGICAL STATUS: QUARTER SAMPLES. HERD C 188

6.2cii _LOG(10) SODIUM CONCENTRATION VS STAGE OF LACTATION,

BY AGE OF COW: QUARTER SAMPLES. HERD C 188

6.3ai _LOG( 10) POTASSIUM CONCENTRATION vs STAGE OF LACTATION,

BY BACTERIOLOGICAL STATUS: QUARTER SAMPLES. HERD A 189

6.3aii _LOG(10) POTASSIUM CONCENTRATION vs STAGE OF LACTATION,

BY AGE OF COW: QUARTER SAMPLES. HERD A 18 9

6.3bi _LOG( 10) POTASSIUM CONCENTRATION VS STAGE OF LACTATION,

BY BACTERIOLOGICAL STATUS: QUARTER SAMPLES. HERD B 190

6.3bii _LOG(10) POTASSIUM CONCENTRATION VS STAGE OF LACTATION,

BY AGE OF COW: QUARTER SAMPLES. HERD B 190

6.3ci _LOG(10) POTASSIUM CONCENTRATION VS STAGE OF LACTATION,

BY BACTERIOLOGICAL STATUS: QUARTER SAMPLES. HERD C 191

6.3cii _LOG(10) POTASSIUM CONCENTRATION vs STAGE OF LACTATION,

BY AGE OF COW: QUARTER SAMPLES. HERD C 191

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GRAPH

6.4ai.

6.4ai.i.

6. 4bi.

6.4bi.i.

6.5ai.

6.5ai.i

6.5bi

6.5bii

6.6ai

6.6aii

LIST OF GRAPHS ( CONTINUED )

TITLE

LOG(lO) ELECTRICAL CONDUCTIVITY VS STAGE OF LACTATION,

LOG(10) ELECTRICAL CONDUCTIVITY VS STAGE OF LACTATION,

LOG (10) pH

LOG(l0) pH

LOG(10) pH

LOG(lO) pH

LOG(lO) LACTOSE CONCENTRATION VS STAGE OF LACTATION,

PAGE

HERD A 192

HERD B 193

HERD A 194

HERD B 195

HERD A 196

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jJ*'

GRAPH

6. 6bi

6. 6bii

6. 6ci

6. 6cii

6. 7ai

6. 7aii

6. 7bi

6.7bii

6. 7ci

6. 7cii

6. 8ai

.. ----·· ---

LIST OF GRAPHS ( CONTrNUED )

TITLE

LOG (10) LACTOSE CONCENTRATION VS STAGE OF LACTATION,

LOG (10) LACTOSE CONCENTRATION vs STAGE OF LACTATION,

BY AGE OF COW: QUARTER SAMPLES .

LOG (10) LACTOSE CONCENTRATION VS STAGE OF LACTATION,

LOG(10) LACTOSE CONCENTRATION vs STAGE OF LACTATION,

LOG (10) NAGase ACTIVITY VS STAGE OF LACTATION,

LOG(10) NAGase ACTIVITY VS STAGE OF LACTATION,

LOG (10) ANTITRYPSIN CONCENTRATION VS STAGE OF LACTATION,

PAGE

HERD B 197

HERD C 198

HERD A 199

HERD B 200

HERD C 201

HERD A 202

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GRAPH

6.8a11

6.8b1

6. 8b11

6.8c1

6.8c11

LIST OF GRAPHS ( ^CONTINUED

TITLE

LOG(10) ANTITRYPSIN CONCENTRATION VS STAGE OF LACTATION,

6.9 COMPOSITE MILK YIELD DURING LACTATION, WITHIN INDIVIDUAL HERDS.

8.11 _{LOG (10)} SOMATIC CELL COUNT BY STATUS, WITHIN HERDS: COMPOSITE SAMPLES.

8.111 _{LOG (10)} SOMATIC CELL COUNT BY AGE, WITHIN HERDS: COMPOSITE SAMPLES.

8.21 _{LOG (10)} SODIUM CONCENTRATION BY STATUS, WITHIN HERDS: COMPOSITE SAMPLES.

8.2i.1 _{LOG (10)} SODIUM CONCENTRATION BY AGE, WITHIN HERDS: COMPOSITE SAMPLES.

8.31 _{LOG (10)} POTASSIUM CONCENTRATION BY STATUS, WITHIN HERDS: COMPOSITE SAMPLES.

8.311 _{LOG (10)} POTASSIUM CONCENTRATION BY AGE, WITHIN HERDS: COMPOSITE SAMPLES.

PAGE

HERD A 202

HERD B 203

HERD C 204

205

283

284

285

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LIST OF GRAPHS ( ^CONTINUED )

GRAPH TITLE

8.41 LOG(l0) ELECTRICAL CONDUCTIVITY BY STATUS, WITHIN HERDS: COMPOSITE SAMPLES.

8.411

8.51

8.511

LOG(lO) ELECTRICAL CONDUCTIVITY BY AGE, WITHIN HERDS: COMPOSITE SAMPLES.

LOG(l0) pH BY STATUS,

WITHIN HERDS: COMPOSITE SAMPLES.

LOG(lO) pH BY AGE,

WITHIN HERDS: COMPOSITE SAMPLES.

8.61 LOG(l0) LACTOSE CONCENTRATION BY STATUS, WITHIN HERDS: COMPOSITE SAMPLES.

8.611

8.71

8.711

LOG(lO) LACTOSE CONCENTRATION BY AGE, WITHIN HERDS: COMPOSITE SAMPLES.

LOG(lO) NAGase ACTIVITY BY STATUS, WITHIN HERDS: COMPOSITE SAMPLES.

LOG(l0) NAGase ACTIVITY BY AGE, WITHIN HERDS: COMPOSITE SAMPLES.

8.81 LOG(lO) ANTITRYPSIN CONCENTRATION BY STATUS, WITHIN HERDS: COMPOSITE SAMPLES.

8.811

8.1111

8.2111

8.3111

8.4111

LOG(10) ANTITRYPSIN CONCENTRATION BY AGE, WITHIN HERDS: COMPOSITE SAMPLES.

LOG(l0) SOMATIC CELL COUNT VS STAGE

OF LACTATION, WITHIN HERDS: COMPOSITE SAMPLES.

LOG(lO) SODIUM CONCENTRATION VS STAGE

LOG(lO) POTASSIUM CONCENTRATION VS STAGE

LOG(lO) ELECTRICAL CONDUCTIVITY VS STAGE

PAGE

286

287

288

289

290

291

292

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LIST OF GRAPHS ( CONTINUED )

GRAPH TITLE PAGE

8 .5iii LOG(lO) pH VS STAGE

OF LACTATION, WITHIN HERDS: COMPOSITE SAMPLES. 293

8.6iii LOG(l0) LACTOSE CONCENTRATION VS STAGE

8.7iii LOG(lO) NAGase ACTIVITY VS STAGE

OF LACTATION, WITHIN HERDS: COMPOSITE SAMPLES. 294 8.8iii LOG(l0) ANTITRYPSIN CONCENTRATION VS STAGE