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Effect of a Fluctuating Milking Vacuum on Certain Measures of Udder Health1
EFFECT
O F A F L U C T U A T I N G M I L K I N G V A C U U M ON C E I ~ T A I N MEASURES OF UDDE~ HEALTH : D. E. STANLEY ~ AI~I) E. M. KESLER Department of Dairy Science AND
A. L. BORTREE Department of Veterinary Science The Pennsylvania State University, University Park SUI~I~ARY A floor-type milking machine was altered by substitution of a motor-driven nylon petcock for the conventional one. I n this way, the level of vacuum in the teat cups was made to vary between 7 and 15 in. of mercury at a rate of 53 vacuum fluctuations per minute. Two trials, each utilizing 12 cows, were conducted. The test periods were of 21 and 26 days' duration, and each followed preliminary standardization periods. I n each trial, two cases of clinical mastitis developed among the six cows milked with the altered machine. California Mastitis Test scores on milk produced by the experimental cows rose significantly, as compared with scores on milk front control animals. Direct leucocyte count of the milk also increased, due mainly to the mastitic cows. Hotis tests, on milks produced in Trial II, indicated little change in reactions, other than ~ marked increase in alkalinity of the milk from experimental cows. There was little difference in amounts of milk produced by control and experimental animals. A longer time was required to milk with the variable vacuum machine.
I n spite of considerable experimental evidence (1, 2), opinion is still divided as to the effect of the level of milking vacuum on udder health. Wilson (6) claimed that an inadequate reserve of vacuum, resulting in wide fluctuations during' milking, was an important predisposing cause of mastitis. I n some machines, particularly those in which the milk has to be raised several feet, inefficient removal may result in the formation of a milk lock in the milk tube. This results in a marked drop in the level of vacuum at the teat (1). I n addition, the vacuum level fluctuates because of movement of the milk within the milk tube. I n contrast, Sehalm and Noorlander (5) have incorporated a vacumn fluctuating mechanism into the design of a milking machine. The present work was conducted to study the effect of a fluctuating milking vacuum on
udder health, on the level of production, and on the length of time required to milk. :EXPERI~ENTAL PROCEDURE A floor-type milking machine was used as the basic unit upon which a vacuum fluctuating mechanism was attached, Figure 1. This machine has a vacuum-controlling petcoek incorporated into the manufacturer's design. During
Received for publication August 30, 1962. : Authorized for pub]ieatlon as Paper I~o. 2696 in the Journal series of the Pennsylvania Agricultural Experiment Station. Present address: Department of Dairy Science,
l~utgers, The State University, New Brunswick, FI~. 1. ~lilking machine with attached vacuum New Jersey. fluctuating mechanism. 1343
]344
D , E . STANLEY, E. M. K E S L E R , AND A . L . B O R T R E E
the preliminary investigation, it was noted that continuous rotation of the peteock created a fluctuating vacuum within the teat cups. The peteock was replaced with a cylindical nylon stopcock, designed to rotate in the milker head. The power necessary to rotate the stopcock was provided by a Dayton gear-head electric motor. A round rubber belt was used to connect the pulley on top of the nylon stopcock with the motor. To establish evidence of the vacuum fluctuation, a graphic representation of the vacuum level at the teat was made using a Detco vacuum recorder, s A vacuum gauge was connected to the mouth of one teat cup while the milking machine was in operation, with the three other teat cups in place and actively nfilking a cow. By this means it was determined that with each rotation of the stopcock the level of vacuum in the teat cup varied from 7 to 15 in. of mercury. The stopcock was driven at approximately 53 rotations per minute. Twenty-four Holstein cows were used, 12 in each of two trials. Eleven of the total were first-calf heifers and these animals were distributed, as equally as possible', between the groups. The cows were housed in a stanchion barn, and were turned out daily for a short period of exercise. They were fed good-quality hay and corn silage ad libitum, and concentrates according to production. Details of management were uniform for both groups. Those animals used in Trial I were in an advanced stage of lactation, ranging between the fifth and seventh mo~th. Milk production during a preliminary period of 6 wk averaged 44.0 lb daily (range 31.3-64.1). California Mastitis Test (CMT) (4) scores were determined weekly on quarter samples of milk from each cow during the preliminary period. At the end of this period, the cows were divided into two groups on the basis of age, milk production, and CMT score. The test period was for 21 days. During that time the control animals were milked with a regular DeLaval machine, whereas the experimental group was milked with the altered, variable-vacuum machine. The stage of lactation of the cows in Trial I I ranged between the second and fifth month. Daily milk production averaged 53.0 lb (range 39.6-68.0) at the start of the trial. A preliminary period of 19 days was used. During the preliminary period quarter samples of milk were obtained at three-day intervals. These samples were evaluated on the basis of the CMT, Hotis test, and direct leucocyte count. The results of these 3Detco Equipment Co., San Jose, California.
tests were used, along with age of the animMs and level of milk production, to group the cows. The test period in Trial I I was for 26 days. I n Trial I criteria for evaluation of the effects of the variable vacuum milker included the CMT, the amount of milk produced, and use of the strip cup. Foremilk from each teat was drawn onto a strip cup at the morning milking and at all afternoon milkings when samples were not taken. At weekly intervals dm'ing the preliminary period and each afternoon during the test period the milk was drawn directly onto a paddle for CMT evaluation. The amount of milk produced at each milking was weighed and recorded to the nearest 0.1 lb. I n Trial I I criteria for evaluation included those used in Trial I, plus direct leucocyte counts and Hotis tests (3) on quarter samples of milk obtained at three-day intervals. The time required to milk the animals was determined at four evening milkings each during preliminalvf and test periods. To obtain reliable milk samples for the tests, a uniform procedure was followed. The side of the udder and the teats were washed thoroughly with a disinfectant solution. After discarding the first few streams, a milk sample was drawn from each teat into a snmtl strewcap bottle. These samples were used later for the direct leucocyte count. Following this initial sampling, the teats were again cleaned, using gauze sponge saturated with 70% ethanol. Milk was drawn directly into a sterile screw-cap sample bottle containing 1 ufl of a 1% aqueous solution of bromcresol purple. This was used for the Hotis test. The final sampling consisted of obtaining nfilk for the CMT. RESULTS AND DISCUSSION The cows adjusted easily to the experimental milking machine after becoming accustomed to the slight whirring noise made by the motor. The machine performed satisfactorily, but did require more attention by the operator, since the teat cups tended to fall from the udder. All cows remained healthy during the experiment, with the exception of four cases of clinical mastitis. Data on nfilk production are presented in Table 1. During the preliminary period of the first trial, the cows in the two groups produced at approximately the same rates. During the 3-wk test period, the control a n d experimental groups averaged 37.8 and 41.0 lh/day, respectively. The average decline in production between the prelinfinary and test periods was greatest in the control group; however, this
MILKING
VACUUM
A_ND U D D E I ~
HEALTH
1345
TABLE 1 Effect of fluctuating milking vacuum on milk production " (lb/cow/day) Preliminary period
Test period
Difference
Trial I Control group Experimental group
43.5 ( ~ 12.3)" 4:4.~ ( ± S.2)
37.8 ( ~ 10.7) 41.0 ( ± 8.3)
--5.7 --3.4:
Trial 1I Control group Experimental group
52.6 (+_ 11.2) 53.6 ( ± 11.1)
48.4: (+--_10.8) 46.3 ( ± 7.5)
--4.2 --7.3
"~Data are means of six cows per group. ~' Standard deviation. difference was not statistically significant (P > 0.05). The six experimental animals included in Trial I I produced an average of 53.6 lb of milk daily during the preliminary period and 46.3 lb during the test period. The controls averaged 52.6 and 48.4 lb/day during the preliminals: and test periods, respectively. The decline in milk production between preliminary and test periods averaged 4.2 lb/day for the control aninmls and 7.3 lb for the experimental. Although amounting to 3.1 lb, the difference between the two groups was not statistically significant, as measured by the "t" test (P > 0.05). Grading and interpretation of the C~{T results were as outlined by Schahn (3), with the exception that a numerical value of one was assigned to his classification of T (trace). This necessitated increasing the nmnerieal value of each of the higher grades by one. During the preliminary period of Trial I, milk produced by control cows had an average CMT score of 2.04, whereas that of the experimental group was 1.98 (Table 2). The score for the control group decreased slightly during the test period; that of the milk produced by the experimental aninmls rose. In Trial II, milk produced by the control group in the preliminary period had an average CMT score of 0.60, Table 3. The average was 0.68 during the test period. The scores fo r the experimental animals increased by an average of 0.52 during the test period. The difference in average CMT scores between preliminary and test periods was computed for individual quarters and these data were subjected to an analysis of variance. In each trial the variation due to treatment closely approached significance. When the data from both trials were combined, differences due to treatment were significant at the 2.5% level of probability. Direct leucocyte counts were made on milk samples obtained at three-day intervals through-
out Trim II. In the preliminary period, milk from control cows averaged 494,000 (+--- 439,000) leucocytes/milliliter and that from experimental animals, 307,000 (---+311,000). During the test period, the average count for the control cows increased by 189,000, with one of the six animals showing a decrease. The count f o r experimental cows increased by an average of 1,788,000~milliliter, but the increase was due largely to two animals. These two suffered severe attacks of clinical mastitis during the experimental period. Leucocyte counts varied so greatly between samplings from the same
2
TABLE Effect
of
fluetuating
milking
vacuum
on
CMT
Scores a
Trial I Preliminary period
Test period
Differenee
0.92 2.73 2.19 3.66 1.46 1.33
1.58 3.02 1.74: 3.23 1.38 0.36
+0.66 +0.29 --0.45 --0.39 --0.08 --0.97
2.04
1.88
-0.16
Experimental group 948 2.60 959 1.90 979 3.02 1014 1.94 1016 1.46 1018 0.98
3.07 3.71 3.63 1.99 2.18 1.14
+0.4:7 +1.81 b +0.6l b +0.05 +0.72 +0.16
2.62
+0.64
Cow no. Control group 944 964 10'03 JO06 1017 1020 Meav-
Mean
1.98
Data are mean values of quarter samples from each cow. There were six and 14: samplings in preliminary and test periods, respeetively. b Clinical mastitis dm'ing test period.
1346
D.E.
STANLEY, E. ~ . K E S L E R ,
TABLE 3 Effect of fluctuating milking vacuum on CMT scores a Trial I I Preliminary period
Test period
Differonce
1.62 0.36 0.00 0.82 0.20 0.59
1.78 0.4'0 0.10 0.75 0.55 0.52
+0.16 +0.04 +0.10 --0.07 +0.35 --0.07
0.60
0.68
+0.08
Experimental group 984 0.00 998 0.98 999 0.00 1022 0.33 1023 1.39 1027 0.00
0.15 1.70 1.35 0.95 1.58 0.00
+0.15 +0.72 b +1.35 b +0.72 +0.19 0.00
0.95
+0.5.2
Cow no. Control group 954 983 1000 1019 1024 1028 Mean
Mean
0.43
Data are mean values of quarter samples taken from each cow. There were seven and iive samplings in preliminary and test periods, respectively. b Clinical mastitis during test period. quarters that only limited importance could be attached to them. Hotis test data, on milk produced in Trial II, provided an indication of the presence or absence of certain types of bacteria and of the p H of the milk. There was little difference in the percentages of Hotis reactions for bacterial growth between the preliminary and the test period for either the experimental or the control animals, Table 4. The percentage of experimental animals secreting milk of abnormally high p i t increased markedly during the
TABLE 4 Incidence of positive Hotis test reactions, Trial I I Per cent of samples showing positive Hotis reaction for microorganism growth
Per cent of samples sho~ving abnormal (alkaline) pH
PrelimPreliminary Test ina.ry Test period period period period Control group 32.7 Experimental group 36.3
26.7
8.9
10.0
25.8
5.4
4`2.5
AND A . L . B O R T R E E
trial, rising from an incidence of 5.4% during the preliminary period to 42.5% during the test period. The number of alkaline reactions noted in milk from control cows did not change appreciably during the trial. I t was obseiwed that all of the experimental animals exhibited an increase in alkalinity of the milk secreted from one or more quarters during the last week of the test period. The time required to milk the control and experimental groups during the preliminary period of Trial I I was similar, averaging 5.76 and 5.78 rain per cow, respectively. During the test period, the average time required to milk the control animals was 5.96 rain, but that for the experimental animals was 7.64 min. This difference was significant at the 1% level of probability, as measured by analysis of variance. Results of this research suggest that fluctuating milking vacuum did affect udder health. Considering both trials of the study, six mature cows and six heifers were subjected to the effects of fluctuating milking vacuum. Four of the six cows exhibited unmistakable symptoms of clinical mastiffs during at least the final week of the test period. The six heifers did not develop mastitis. Seven mature cows and five first-calf heifers were used as control animals; none of them contracted mastitis. A marked increase in leukocyte counts was observed with respect to the mastitic cows. I n both trials, the CMT scores increased when the animals were subjected to the experimental milker. Considering both trials, this increase in CMT scores was statistically significant. Results of the Hotis test, conducted during the second trial, showed an appreciable increase in the alkalinity of the milk secreted by the cows milked with the experimental milker. According to Schalm (3), an increase in alkalinity of the milk is one of the first signs of irritation of the secretory tissue. The Hotis test results did not indicate a change in the percentage of milk samples containing pathogenic organisms. This lack of increase may indicate that the increased irritation of the mammary tissues was mechanical in origin rather than bacterial. These data do not indicate whether the deleterious effects of the experimental machine were due solely to variable vacuum. Additional time was required to milk cows with the machine. While milk production by control and experimental animals was not different, it is interesting to speculate whether such would have been the case if the test periods had been longer.
~IILKING YACUUM AND UDDEI~ HEALTH
RE'FERE~ OE,S
(1) MINIS~I~¥ o~ AQ~ICULTVRB, FISH~L~S AND FOOD. Machine Milking. Bull. 177. Her M a j e s t y ' s Stationery Office, London. 1959. (2) Noo~AN])]~, D. O. Milking Machines and Mastitis. Compton Press, Inc., Compton, Calif. 1960. (3) S O ~ L ~ , 0. W. A Syllabus on the Bovine Mammary Gland in Health and Disease. Dept. Clinical Pathology, School of Vet. Med., Univ. of Calif., Davis.
1347
(4) SOHAL~, O. W., A.~D N00RLANI)~, D. O. Experiments a n d Observations Leading to the Development of the California Mastitis Test. J. Am. Vet. Med. Assoc., 130: 199. 1957. (5) SC]~AL~, O. W., AN]) NOOlCLA~gF~, D. O. Milking Machine Design as an Aid to Mastitis Control. J. Am. Yet. Med. Assoc., 131: 127. 1957. (6) WILSOn, C. D. Factors t h a t Predispose to Mastitis with Special l~eference to Milking Techniques. Yet. Record, 70: 159. 1958.
O F A F L U C T U A T I N G M I L K I N G V A C U U M ON C E I ~ T A I N MEASURES OF UDDE~ HEALTH : D. E. STANLEY ~ AI~I) E. M. KESLER Department of Dairy Science AND
A. L. BORTREE Department of Veterinary Science The Pennsylvania State University, University Park SUI~I~ARY A floor-type milking machine was altered by substitution of a motor-driven nylon petcock for the conventional one. I n this way, the level of vacuum in the teat cups was made to vary between 7 and 15 in. of mercury at a rate of 53 vacuum fluctuations per minute. Two trials, each utilizing 12 cows, were conducted. The test periods were of 21 and 26 days' duration, and each followed preliminary standardization periods. I n each trial, two cases of clinical mastitis developed among the six cows milked with the altered machine. California Mastitis Test scores on milk produced by the experimental cows rose significantly, as compared with scores on milk front control animals. Direct leucocyte count of the milk also increased, due mainly to the mastitic cows. Hotis tests, on milks produced in Trial II, indicated little change in reactions, other than ~ marked increase in alkalinity of the milk from experimental cows. There was little difference in amounts of milk produced by control and experimental animals. A longer time was required to milk with the variable vacuum machine.
I n spite of considerable experimental evidence (1, 2), opinion is still divided as to the effect of the level of milking vacuum on udder health. Wilson (6) claimed that an inadequate reserve of vacuum, resulting in wide fluctuations during' milking, was an important predisposing cause of mastitis. I n some machines, particularly those in which the milk has to be raised several feet, inefficient removal may result in the formation of a milk lock in the milk tube. This results in a marked drop in the level of vacuum at the teat (1). I n addition, the vacuum level fluctuates because of movement of the milk within the milk tube. I n contrast, Sehalm and Noorlander (5) have incorporated a vacumn fluctuating mechanism into the design of a milking machine. The present work was conducted to study the effect of a fluctuating milking vacuum on
udder health, on the level of production, and on the length of time required to milk. :EXPERI~ENTAL PROCEDURE A floor-type milking machine was used as the basic unit upon which a vacuum fluctuating mechanism was attached, Figure 1. This machine has a vacuum-controlling petcoek incorporated into the manufacturer's design. During
Received for publication August 30, 1962. : Authorized for pub]ieatlon as Paper I~o. 2696 in the Journal series of the Pennsylvania Agricultural Experiment Station. Present address: Department of Dairy Science,
l~utgers, The State University, New Brunswick, FI~. 1. ~lilking machine with attached vacuum New Jersey. fluctuating mechanism. 1343
]344
D , E . STANLEY, E. M. K E S L E R , AND A . L . B O R T R E E
the preliminary investigation, it was noted that continuous rotation of the peteock created a fluctuating vacuum within the teat cups. The peteock was replaced with a cylindical nylon stopcock, designed to rotate in the milker head. The power necessary to rotate the stopcock was provided by a Dayton gear-head electric motor. A round rubber belt was used to connect the pulley on top of the nylon stopcock with the motor. To establish evidence of the vacuum fluctuation, a graphic representation of the vacuum level at the teat was made using a Detco vacuum recorder, s A vacuum gauge was connected to the mouth of one teat cup while the milking machine was in operation, with the three other teat cups in place and actively nfilking a cow. By this means it was determined that with each rotation of the stopcock the level of vacuum in the teat cup varied from 7 to 15 in. of mercury. The stopcock was driven at approximately 53 rotations per minute. Twenty-four Holstein cows were used, 12 in each of two trials. Eleven of the total were first-calf heifers and these animals were distributed, as equally as possible', between the groups. The cows were housed in a stanchion barn, and were turned out daily for a short period of exercise. They were fed good-quality hay and corn silage ad libitum, and concentrates according to production. Details of management were uniform for both groups. Those animals used in Trial I were in an advanced stage of lactation, ranging between the fifth and seventh mo~th. Milk production during a preliminary period of 6 wk averaged 44.0 lb daily (range 31.3-64.1). California Mastitis Test (CMT) (4) scores were determined weekly on quarter samples of milk from each cow during the preliminary period. At the end of this period, the cows were divided into two groups on the basis of age, milk production, and CMT score. The test period was for 21 days. During that time the control animals were milked with a regular DeLaval machine, whereas the experimental group was milked with the altered, variable-vacuum machine. The stage of lactation of the cows in Trial I I ranged between the second and fifth month. Daily milk production averaged 53.0 lb (range 39.6-68.0) at the start of the trial. A preliminary period of 19 days was used. During the preliminary period quarter samples of milk were obtained at three-day intervals. These samples were evaluated on the basis of the CMT, Hotis test, and direct leucocyte count. The results of these 3Detco Equipment Co., San Jose, California.
tests were used, along with age of the animMs and level of milk production, to group the cows. The test period in Trial I I was for 26 days. I n Trial I criteria for evaluation of the effects of the variable vacuum milker included the CMT, the amount of milk produced, and use of the strip cup. Foremilk from each teat was drawn onto a strip cup at the morning milking and at all afternoon milkings when samples were not taken. At weekly intervals dm'ing the preliminary period and each afternoon during the test period the milk was drawn directly onto a paddle for CMT evaluation. The amount of milk produced at each milking was weighed and recorded to the nearest 0.1 lb. I n Trial I I criteria for evaluation included those used in Trial I, plus direct leucocyte counts and Hotis tests (3) on quarter samples of milk obtained at three-day intervals. The time required to milk the animals was determined at four evening milkings each during preliminalvf and test periods. To obtain reliable milk samples for the tests, a uniform procedure was followed. The side of the udder and the teats were washed thoroughly with a disinfectant solution. After discarding the first few streams, a milk sample was drawn from each teat into a snmtl strewcap bottle. These samples were used later for the direct leucocyte count. Following this initial sampling, the teats were again cleaned, using gauze sponge saturated with 70% ethanol. Milk was drawn directly into a sterile screw-cap sample bottle containing 1 ufl of a 1% aqueous solution of bromcresol purple. This was used for the Hotis test. The final sampling consisted of obtaining nfilk for the CMT. RESULTS AND DISCUSSION The cows adjusted easily to the experimental milking machine after becoming accustomed to the slight whirring noise made by the motor. The machine performed satisfactorily, but did require more attention by the operator, since the teat cups tended to fall from the udder. All cows remained healthy during the experiment, with the exception of four cases of clinical mastitis. Data on nfilk production are presented in Table 1. During the preliminary period of the first trial, the cows in the two groups produced at approximately the same rates. During the 3-wk test period, the control a n d experimental groups averaged 37.8 and 41.0 lh/day, respectively. The average decline in production between the prelinfinary and test periods was greatest in the control group; however, this
MILKING
VACUUM
A_ND U D D E I ~
HEALTH
1345
TABLE 1 Effect of fluctuating milking vacuum on milk production " (lb/cow/day) Preliminary period
Test period
Difference
Trial I Control group Experimental group
43.5 ( ~ 12.3)" 4:4.~ ( ± S.2)
37.8 ( ~ 10.7) 41.0 ( ± 8.3)
--5.7 --3.4:
Trial 1I Control group Experimental group
52.6 (+_ 11.2) 53.6 ( ± 11.1)
48.4: (+--_10.8) 46.3 ( ± 7.5)
--4.2 --7.3
"~Data are means of six cows per group. ~' Standard deviation. difference was not statistically significant (P > 0.05). The six experimental animals included in Trial I I produced an average of 53.6 lb of milk daily during the preliminary period and 46.3 lb during the test period. The controls averaged 52.6 and 48.4 lb/day during the preliminals: and test periods, respectively. The decline in milk production between preliminary and test periods averaged 4.2 lb/day for the control aninmls and 7.3 lb for the experimental. Although amounting to 3.1 lb, the difference between the two groups was not statistically significant, as measured by the "t" test (P > 0.05). Grading and interpretation of the C~{T results were as outlined by Schahn (3), with the exception that a numerical value of one was assigned to his classification of T (trace). This necessitated increasing the nmnerieal value of each of the higher grades by one. During the preliminary period of Trial I, milk produced by control cows had an average CMT score of 2.04, whereas that of the experimental group was 1.98 (Table 2). The score for the control group decreased slightly during the test period; that of the milk produced by the experimental aninmls rose. In Trial II, milk produced by the control group in the preliminary period had an average CMT score of 0.60, Table 3. The average was 0.68 during the test period. The scores fo r the experimental animals increased by an average of 0.52 during the test period. The difference in average CMT scores between preliminary and test periods was computed for individual quarters and these data were subjected to an analysis of variance. In each trial the variation due to treatment closely approached significance. When the data from both trials were combined, differences due to treatment were significant at the 2.5% level of probability. Direct leucocyte counts were made on milk samples obtained at three-day intervals through-
out Trim II. In the preliminary period, milk from control cows averaged 494,000 (+--- 439,000) leucocytes/milliliter and that from experimental animals, 307,000 (---+311,000). During the test period, the average count for the control cows increased by 189,000, with one of the six animals showing a decrease. The count f o r experimental cows increased by an average of 1,788,000~milliliter, but the increase was due largely to two animals. These two suffered severe attacks of clinical mastitis during the experimental period. Leucocyte counts varied so greatly between samplings from the same
2
TABLE Effect
of
fluetuating
milking
vacuum
on
CMT
Scores a
Trial I Preliminary period
Test period
Differenee
0.92 2.73 2.19 3.66 1.46 1.33
1.58 3.02 1.74: 3.23 1.38 0.36
+0.66 +0.29 --0.45 --0.39 --0.08 --0.97
2.04
1.88
-0.16
Experimental group 948 2.60 959 1.90 979 3.02 1014 1.94 1016 1.46 1018 0.98
3.07 3.71 3.63 1.99 2.18 1.14
+0.4:7 +1.81 b +0.6l b +0.05 +0.72 +0.16
2.62
+0.64
Cow no. Control group 944 964 10'03 JO06 1017 1020 Meav-
Mean
1.98
Data are mean values of quarter samples from each cow. There were six and 14: samplings in preliminary and test periods, respeetively. b Clinical mastitis dm'ing test period.
1346
D.E.
STANLEY, E. ~ . K E S L E R ,
TABLE 3 Effect of fluctuating milking vacuum on CMT scores a Trial I I Preliminary period
Test period
Differonce
1.62 0.36 0.00 0.82 0.20 0.59
1.78 0.4'0 0.10 0.75 0.55 0.52
+0.16 +0.04 +0.10 --0.07 +0.35 --0.07
0.60
0.68
+0.08
Experimental group 984 0.00 998 0.98 999 0.00 1022 0.33 1023 1.39 1027 0.00
0.15 1.70 1.35 0.95 1.58 0.00
+0.15 +0.72 b +1.35 b +0.72 +0.19 0.00
0.95
+0.5.2
Cow no. Control group 954 983 1000 1019 1024 1028 Mean
Mean
0.43
Data are mean values of quarter samples taken from each cow. There were seven and iive samplings in preliminary and test periods, respectively. b Clinical mastitis during test period. quarters that only limited importance could be attached to them. Hotis test data, on milk produced in Trial II, provided an indication of the presence or absence of certain types of bacteria and of the p H of the milk. There was little difference in the percentages of Hotis reactions for bacterial growth between the preliminary and the test period for either the experimental or the control animals, Table 4. The percentage of experimental animals secreting milk of abnormally high p i t increased markedly during the
TABLE 4 Incidence of positive Hotis test reactions, Trial I I Per cent of samples showing positive Hotis reaction for microorganism growth
Per cent of samples sho~ving abnormal (alkaline) pH
PrelimPreliminary Test ina.ry Test period period period period Control group 32.7 Experimental group 36.3
26.7
8.9
10.0
25.8
5.4
4`2.5
AND A . L . B O R T R E E
trial, rising from an incidence of 5.4% during the preliminary period to 42.5% during the test period. The number of alkaline reactions noted in milk from control cows did not change appreciably during the trial. I t was obseiwed that all of the experimental animals exhibited an increase in alkalinity of the milk secreted from one or more quarters during the last week of the test period. The time required to milk the control and experimental groups during the preliminary period of Trial I I was similar, averaging 5.76 and 5.78 rain per cow, respectively. During the test period, the average time required to milk the control animals was 5.96 rain, but that for the experimental animals was 7.64 min. This difference was significant at the 1% level of probability, as measured by analysis of variance. Results of this research suggest that fluctuating milking vacuum did affect udder health. Considering both trials of the study, six mature cows and six heifers were subjected to the effects of fluctuating milking vacuum. Four of the six cows exhibited unmistakable symptoms of clinical mastiffs during at least the final week of the test period. The six heifers did not develop mastitis. Seven mature cows and five first-calf heifers were used as control animals; none of them contracted mastitis. A marked increase in leukocyte counts was observed with respect to the mastitic cows. I n both trials, the CMT scores increased when the animals were subjected to the experimental milker. Considering both trials, this increase in CMT scores was statistically significant. Results of the Hotis test, conducted during the second trial, showed an appreciable increase in the alkalinity of the milk secreted by the cows milked with the experimental milker. According to Schalm (3), an increase in alkalinity of the milk is one of the first signs of irritation of the secretory tissue. The Hotis test results did not indicate a change in the percentage of milk samples containing pathogenic organisms. This lack of increase may indicate that the increased irritation of the mammary tissues was mechanical in origin rather than bacterial. These data do not indicate whether the deleterious effects of the experimental machine were due solely to variable vacuum. Additional time was required to milk cows with the machine. While milk production by control and experimental animals was not different, it is interesting to speculate whether such would have been the case if the test periods had been longer.
~IILKING YACUUM AND UDDEI~ HEALTH
RE'FERE~ OE,S
(1) MINIS~I~¥ o~ AQ~ICULTVRB, FISH~L~S AND FOOD. Machine Milking. Bull. 177. Her M a j e s t y ' s Stationery Office, London. 1959. (2) Noo~AN])]~, D. O. Milking Machines and Mastitis. Compton Press, Inc., Compton, Calif. 1960. (3) S O ~ L ~ , 0. W. A Syllabus on the Bovine Mammary Gland in Health and Disease. Dept. Clinical Pathology, School of Vet. Med., Univ. of Calif., Davis.
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(4) SOHAL~, O. W., A.~D N00RLANI)~, D. O. Experiments a n d Observations Leading to the Development of the California Mastitis Test. J. Am. Vet. Med. Assoc., 130: 199. 1957. (5) SC]~AL~, O. W., AN]) NOOlCLA~gF~, D. O. Milking Machine Design as an Aid to Mastitis Control. J. Am. Yet. Med. Assoc., 131: 127. 1957. (6) WILSOn, C. D. Factors t h a t Predispose to Mastitis with Special l~eference to Milking Techniques. Yet. Record, 70: 159. 1958.