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Incidence of Clinical Mastitis in a Herd of Jersey Cattle
Incidence of Clinical Mastitis in a Herd of Jersey Cattle R. H. M I L L E R , J. R. OWEN l, and E. D. MOORE 1,2 U. S. Department of Agriculture, ARS Animal Physiology and Genetics Institute Genetics and Management Laboratory Beltsville, MD 20705 ABSTRACT
Incidence of clinical mastitis in 1278 lactations of 390 Jersey cows was studied for effects of lactation number, quarter of udder, month of calving, sire, and milk yield. Results for quarter did not conflict with the usual finding that incidence is higher in rear quarters. A mastitis index based on stage of lactation at which infection occurred had less variation, greater variation among sires, and a continuous distribution, in contrast to the traits porportion infected and number of cases. Mastitis increased with advancing lactation number subsequent to second lactations. Fall calvers may have less mastitis since they would be dry or in late lactation during summer. Incidence of mastitis increased at a decreasing rate as total milk yield in the lactation affected increased. INTRODUCTION
A wide variety of factors influences the frequency of mastitis in dairy cattle. Those in our report are lactation number (parity), quarter, month of calving, milk yield, and sire. Increased frequency of mastitis at older ages is well documented. Rendel and Sundberg (14) reported an incidence of 14.9% in first lactation compared to 37.7% in fourth lactations. Legates and Grinnells (7) found a frequency of 16.7% in 215 heifers and 51.1% in 959 older cows. Schmidt and Van Vleck (15) reported a correlation of .39 between age and number of infected quarters. Braund et al. (3) stated that the incidence of mastitis increased with age as judged by positive California Mastitis Test
Received March 17, 1975. 1USDA, ARS, Dairy Experiment Station, Lewisburg, TN. 2This work was in cooperation with the Agricultural Experiment Station, University of Tennessee, Knoxville.
reactions. Miller et al. (11) reported that number of quarter cases increased from 1.14 for first lactations to 4.0 for fourth lactations. The literature suggests a higher frequency of infection in rear quarters but no consistent difference between right and left halves. Rendel and Sundberg (14) suggested that front quarters are more protected and, therefore, less likely to be injured and to contract mastitis. They reported a small but nonsignificant excess of infections (1.4%) in rear quarters. There was no difference between right and left sides. Neave et al. (12) observed a 12% excess of mastitis in rear quarters. Arthur (2) also found more mastitis in rear quarters. Braund et al. (3) detected little difference in infection (as judged by cell counts) between front and rear but did find a higher rate of infection on the right side as compared to the left. Miller et al. (11) reported a small excess of infection (4.2%) in the rear, as compared to the front, but only a 1% excess of the right side over the left side. McDowetl and McDaniel (9) reported a higher frequency of mastitis in summer with twice as many treatments in July to September compared to April to June. Afifi (1) found higher cell counts in November in Dutch herds, but this may have been confounded with stage of lactation. Wilton et al. (18) reported that year-seasons accounted for little variation in udder infections. Miller et al. (11) found no significant difference between months of calving. Reports on the relationship between milk production and mastitis conflict. One reason, as pointed out by Wilton et al. (18), is that several counteracting tendencies may be involved. Mastitis infection causes a reduction in subsequent milk production in the quarter infected (6, 8, 17) although there may be some compensation by the uninfected quarters (4). On the other hand, some have suggested that high-producing cows contract mastitis more frequently, particularly in early lactation. Wilton et al. (18) reported that milk yield in a lactation was associated negatively with the extent of udder 113
114
MILLER ET AL.
infection although all correlations were - . 10 or less. When Wilton et al. (18) related infection frequency in one lactation to milk yield in the preceding lactation, the two were correlated only slightly. Legates and Grinnells (7) found that milk yield in first lactation was related positively to udder infections in later lactations though only to a small degree. Legates and Grinnells (7) reported a moderate degree of genetic association between first lactation milk yield and infection in later lactations. Afifi (1) found a negative relationship between cell count and milk yield on day sampled for first lactations. O'Bleness et al. (13) reported that high milk production was associated with increased infection. Differences for sire and cow in measures of mastitis incidence have been small. Wilton et al. (18) reported that regressions of second lactation incidence on first lactation and of incidence in later lactation on second lactation were moderately high and larger than the regressions of frequency in later lactation on incidence in first lactation. Miller (10) summarized heritabilities by a mean of .16 for measures of clinical mastitis. Our objectives were (a) to assess the frequency of clinical mastitis in a dairy herd and (b) to determine the effects of lactation number, quarter of udder, month of calving, milk yield, and sire on the frequency of clinical mastitis.
in a strip cup before milking. Cows were milked twice daily in a milking parlor. Ten basic traits were derived: 1) total number of separate quarter cases, 2 to 5) number of separate cases in each quarter, 6) presence or absence of infection in any quarter, 7 to 10) presence or absence of infection in each of the four quarters (the latter five traits subsequently will be referred to as "proportion infected"). In addition to these, four indices of mastitis were based on the criterion of Smith and Schultze (16). These indices reflect the stage of lactation in which the first case of mastitis is observed in each of the four quarters of a cow. For example:
DATA AND METHODS
YijkQ = ~ + si + cij + Pk + m~ +/3(Xijk~ -X) + eijk~
The data were complete lifetime histories of clinical mastitis for all cows 1959 to 1972 in the Jersey herd at the Dairy Experiment Station, Lewisburg, TN. Date of the first incidence of mastitis (if any) in each of a cow's quarters in each lactation was recorded. Also recorded was the total number of separate cases in each quarter during the lactation. A case of mastitis was defined as any intramammary antibiotic treatment. A separate case was defined as one in which at least 7 days had elapsed since any previous treatment in the same quarter. Since clinical treatment was the criterion, many instances of treatment without actual bacterial infections were no doubt present. Management procedures for the prevention of mastitis were standard. Beginning in 1970, each cow's teats were dipped in a teat-dip solution after each milking. Presence of mastitis requiring treatment was judged by clotty milk Journal of Dairy Science Vol. 59, No. 1
I1 = (no. days to 1st case in any quarter) + total days in milk = D1/DIM. (D 1 + no. days to 1st case in any of the other 3 quarters) + (2 x total days in milk). 12 =
These indices, therefore, range from 0 (calved with mastitis) to 1.0 (no mastitis during lactation). In contrast with the other measures of mastitis, these indices have the advantage of being continuous variables. However, their distributions ~till are characterized by large uninfected classes. There were 1278 lactations available on 390 cows. The data were analyzed by the following least squares model:
where si is a random effect of the i th sire, cij is a residual random effect for the jth daughter of the ith sire, Pk is an effect peculiar to the k th lactation number (parity), mQ is an effect common to all observations in the ~th month of calving, Xijk~ is the average milk yield per day of lactation (kg), /3 is the regression of the mastitis trait Yijk~ on milk yield per day of lactation, and eijk~ is a random error term representing unexplained variation between observations on the same cow. A preliminary analysis indicated that it was impossible to fit a model including cows, years, and parity simultaneously due to confounding. Therefore, effects of year were ignored. R ESU LTS
Means and standard deviations are in Table 1. Frequency of infection was relatively low.
115
MASTITIS INCIDENCE T A B L E 1. Arithmetic means and standard deviations•
Trait Proportion infected Prop ortion infected, Proportion infected, Proportion infected, Proportion infected, Number Number Number Number Number Index Index Index Index
-1 -2 -3 -4
of of of of of
cases cases, cases, cases, cases,
LF LR RF RR
LF LR RF RR
Mean
SD
.290 .105 .121 .119 .140
.454 .306 .326 .324 .347
.77 .18 .19 .19 .20 .820 .850 .872 .888
. . . . .
,'dl',
. . . . .
.
.
.
.
.
- i • d ,
.
.
.
.
.
.
d
,
~
z
z
Z
.
.
.
.
1.91 .85 .75 .67 .62
.
•
d
.
.
.
.
.
.331 .281 .245 .218
Twenty-nine percent of the lactations had at least one infection, and the mean number of cases per lactation was .77. Frequency of infection was higher in the rear quarters than in the front, and higher in the right side of the udder compared to the left. Proportion infected was .224 for the front, .261 for the rear quarters; .226 for the left side, .259 for the right. None of the differences were statistically significant by Student's t-test. The mean lndex-1 (11) was .82. Intracow phenotypic correlations are in "Fable 2. The correlation between proportion infected and number of cases was .57, indicating that only about 32% of the variation in number of cases is accounted for by division of cows into infected and uninfected categories. Correlations between the mastitis indices and number of cases ranged from .55 to - . 6 1 ; those between the indices and proportions infected ranged from - . 7 8 to - . 8 4 . There was a tendency in both number of cases and proportion infected for a higher correlation between left-front and right-front quarters and between front and rear quarter combinations. However, all such correlations were .40 or less. All correlations relating number of cases in one quarter to number in other quarters, and between proportion infected in one quarter and proportion infected in others, were positive. This indicates that occurrence of mastitis in one quarter increases the chance of occurrence in another quarter. Analysis of variance is in Table 3. Differ-
..~ .~
,,~ ~
-~. ?~o °
.
.
gggg
." X Journal of Dairy Science Vol. 59, No. 1
116
MILLER ET AL.
ences between sires were significant only for the four mastitis index traits and number of cases in left-rear. Differences of parity were significant for every trait with F-values being largest
for number of cases and proportion
infccted. Month of calving was significant for all traits, except number of cases in left-rear,
number of cases in right-front, total proportion infected, and proportions infected in left-front and left-rear; F values were small, however. The
~ m
quadratic regression of mastitis on daily milk yield was significant for all traits except number of cases in left-rear, number of cases in right-rear, and proportions infected in left-rear, right-front, and right-rear; F-values were largest for the mastitis indices.
mm ~
Table 4 gives least-squares constants for effccts of parity for proportion infected, total number of cases, and 11. Seventh and later lactations were p o o l e d together as one group. M a x i m u m susceptibility to mastitis occurred in
tile seventh and later lactations, which had 2.84 more cases of mastitis than first lactations. Mean infection rates were reached in the fourth
m
to fifth parities. Constants for month of calving for number of cases and I~ are in Table 5. While the trends
are erratic, it appears that mastitis was more frequent for cows calving in February to July than in August to January. However, cows calving in June w o u l d have .24 fewer cases than average. The results for both n u m b e r of cases and the mastitis index agree that April calvers have m o s t mastitis and September to December calvers the least.
e.
m
~
Regressions of percent infected, number of cases, and l i on daily milk yield are in Table 6. The quadratic term was significant at .05 or .01 for all three traits. Milk yields at which maximum (or minimum in case of 11) occurred were: 31.7 kg for proportion infected, 29.8 kg for number of cases, and 27.6 kg for I 1 .
t~
DISCUSSIONS A N D CONCLUSIONS
m
~
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o
Journal of Dairy Science Vol. 59, No. 1
,~ ug C)
O
Our results do not contradict the general finding of a higher proportion of mastitis infection in rear quarters. Since rear quarters normally produce more milk than front quarters (5), this fits a pattern of increased incidence of mastitis accompanying higher milk production. This differential rate of infection within udder has a bearing on the design of
MASTITIS INCIDENCE
117
TABLE 4. Least-squares parity constants and standard errors. Constants SIS Parity
N
Proportion infected
Number of cases
1 2 3 4 5 6
388 292 189 137 103 77 92
-.24 -.24 -.12 -.01 .12 .15 .33
-1.O1 -.95 -.67 -.16 .32 .65 1.83
7
.03 .03 .03 .03 .04 .04 .04
mastitis e x p e r i m e n t s . Where h a l f - u d d e r designs with t w o t r e a t m e n t s arc e m p l o y e d , t r e a t m e n t s s h o u l d be balanced b e t w e e n f r o n t and rear quarters. Three kinds o f measures of mastitis were e x a m i n e d : n u m b e r o f separate cases during a lactation, p r o p o r t i o n i n f e c t e d (binomial), and an i n d e x based o n stage o f lactation at which i n f e c t i o n occurs. P r o p o r t i o n i n f e c t e d a n d mastiffs i n d e x w e r e closely related w h e r e a s n u m b e r o f cases p r o v i d e d s o m e w h a t m o r e u n i q u e inf o r m a t i o n a b o u t mastiffs incidence. However, mastitis indices had m u c h smaller c o e f f i c i e n t s o f variation t h a n the o t h e r t w o measures. Mastiffs indices also h a d relatively large mean squares for sire. Thus, s o m e c o m b i n a t i o n o f n u m b e r o f cases and i n d e x m i g h t be desirable (I4 was related m o r e closely t o n u m b e r o f cases t h a n were the o t h e r t h r e e indices). However, b o t h measures failed t o reflect i m p a c t of mastitis on milk p r o d u c t i o n . Our results c o n f i r m the w e l l - d o c u m e n t e d
TABLE 5. Least-squares month of calving constants and standard errors. Month
Number of cases
January February March April May June July August September October November December
-.12
.20
.29
.22
.64 .88 .00 -.24 .13 -.16 -.39 -.55 -.23 -.25
.21 .23 .24 .24 .22 .20 .19 .20 .21 .21
.13 .12 .13 .14 .16 .18 .18
Index -1 .15 .14 .07 ,02 -.08 -.09 -.22
.02 .02 .02 .02 .03 .03 .03
increase in f r e q u e n c y o f mastiffs with age of cow. Seventh parities had 33% m o r e lactations x~dth mastitis i n f e c t i o n t h a n average while first parities had 24% less i n f e c t e d lactations t h a n average. Later parities also had m o r e i n f e c t i o n s per lactation, and i n f e c t i o n s t e n d e d to o c c u r earlier t h a n in y o u n g e r parities. Mastiffs was no more extensive in s e c o n d parities t h a n in first parities in this herd. Thus, w h a t e v e r factors are responsible f o r increasing t h e p r o b a b i l i t y o f c o n t r a c t i n g mastitis as c o w s grow o l d e r app a r e n t l y only c o m e i n t o play a f t e r s e c o n d lactations. ( F a c t o r s t h a t have been suggested are increased stress due to higher milk s e c r e t o r y activity and wear o f the s p h i n c t e r muscle.) Since t h e p r o b a b i l i t y of cows b e c o m i n g i n f e c t e d increases with age, mastitis experim e n t s w h i c h d e p e n d on the f r e q u e n c y o f natural i n f e c t i o n s are m o r e effective with older cows (third or later parities). Even in this case, it m a y be desirable to have e x p e r i m e n t a l assignments to t r e a t m e n t b a l a n c e d according to parities o f t h e cows. Increased mastitis with age also has implication for genetic selection. S o m e have a d v o c a t e d t h a t s e l e c t i o n s h o u l d be for length of life as a
Index -1 .022 -.077 .002 -.099 -.024 -.035 -.055 -.010 .057 .082 .094 .042
.04 .04 .04 .04 .04 .04 .04 .03 .03 .04 .04 .04
TABLE 6. Regression of mastitis traits on milk yield, a
Proportion infected Number of cases Index -1
Linear
Quadratic
.0436 c .227 b -,040 b
-.00152 c -.00837 b .001442 b
akg/day. bp<.01. Cp<.05. Journal of Dairy Science Vol. 59, No. 1
118
MILLER ET AL.
means of increasing the e c o n o m i c returns f r o m dairy cattle. Our results indicate that as the p r o p o r t i o n of the herd in third and later parities increases, the costs of mastitis treatment and subsequent losses in milk would increase markedly. Thus, any assessment of the value of increased longevity should take this into account. Results concerning m o n t h of calving were not clear. However, m o n t h was statistically significant for n u m b e r of cases and for all four mastitis indices. Tile trend indicated by n u m b e r of cases and the mastitis index did not agree completely. However, both agree that cows calving f r o m S e p t e m b e r to D e c e m b e r had less mastitis. McDowell and McDaniel (9) reported that a higher f r e q u e n c y of mastitis occurred during the summer. Our results are based on calving date rather than date of infection, and cannot be used to support or contradict McDowell and McDaniel's report. Regressions of mastitis traits on average daily milk yield were statistically significant and curvilinear. Examination of m a x i m u m and m i n i m u m showed no decrease in mastitis within the range o f daily milk yield ( m a x i m u m value was 27.6 kg/day). Thus, the range of milk yields w o u l d be characterized by increasing incidence of mastitis but at a steadily decreasing rate. Previous results regarding milk p r o d u c t i o n and mastitis conflict. One reason for this, as pointed out by Wilton et al. (18), is that at least two tendencies arc c o n f o u n d e d . Quarters infected by mastitis may have both short- and long-term reduction in subsequent milk yield. If high producers t e n d to contract mastitis more readily than low producers, these two factors would tend to cancel each other, obfuscating the relationship between observed milk yield and mastitis infection. In our results, higher producers were predicted to have m o r e mastitis at all milk yields, but to progressively smaller degrees. This could be due to a steadily increasing reduction in the subsequent milk yield occurring as the incidence and severity of mastitis increase. This would bring about a direct positive relation between milk yield and mastitis at lower production, but only a very weak positive relation at high production. To produce at m a x i m u m potential, a cow must remain free of mastitis infection. Conclusions are: 1) our results do not Journal of Dairy Science Vol. 59. No. 1
conflict with the general finding that rear quarters exceed front quarters in f r e q u e n c y of mastitis, 2) the mastitis i n d e x and n u m b e r of cases of mastitis both contain worthwhile inf o r m a t i o n about the scope of mastitis infection while p r o p o r t i o n infected is redundant, 3) the mastitis index exhibits less total variation than other measures of mastitis and has a higher degree of differences a m o n g sires, 4) the frequency' of mastitis increases with advancing lactation n u m b e r subsequent to second parity, 5) there is a t e n d e n c y for less mastitis in lactations of cows calving in the fall, possibly due to a higher f r e q u e n c y of mastitis occurring during summer, 6) f r e q u e n c y of mastitis increases at a decreasing rate as milk yield per day of the lactation affected increases. REFERENCES
1 Afifi, Y. A. 1967. Genetical and some environmental influences affecting the level of leukocyte counts in the milk of cows. Thesis, Mededelingen Lavalbouwhogeschool, Wageningen, Netherlands. 2 Arthur, G. H. 1947. Observations on the clinical aspects of bovine mastitis. Vet. Rec. 59:231. 3 Braund, D. G., and L. H. Schultz. 1963. Physiological and environmental factors affecting the California Mastitis Test under field conditions. J. Dairy Sci. 46:197. 4 Crossman, J. V., F. H. Dodd, J. M. Lee, and F. K. Neave. 1950. The effect of bacterial infection on the milk yield of individual quarters of the cow's udder. J. Dairy Res. 17:128. 5 Johansson, 1. 1957. Untersuchungen uber die variation in der Euter-und Strichform der Kuhe. Z. 1"ierz. Zuechtungsbiol. 70:233. 6 Leffler, R. 1966. The relationship between milkability and udder health in Simmental cows in Switzerland. Dairy Sci. Abstr. 28: 33. 7 Legates, J. E., and C. D. Grinnells. 1952. Genetic relationships in resistance to mastitis in dairy cattle. J. Dairy Sci. 35:829. 8 Lups, P., and H. C. Ritter. 1966. Relationship between chronic udder disease and milk yield of cows. Dairy Sci. Abstr. 28:205. 9 McDowell, R. E., and B. T. McDaniel. 1968. Interbreed matings in dairy cattle. 1I. Herd health and viability. J. Dairy Sci. 51:1275. 10 Miller, R. H. 1972. Breeding for disease resistance in dairy cattle. Proceedings, Joint Meeting NC-2 and S-49 Regional Dairy Cattle Breeding Technical Committees. 11 Miller, R. H., J. W. Smith, N. W. Hooven, Jr., and R. E. Pearson. 1973. Factors affecting variation in several measures of clinical mastitis in a herd of Holstein cattle. J. Dairy Sci. 56:666. (Abstr.) 12 Neave, F. K., F. H. Dodd, and E. Henriques. 1950. Udder infections during the dry period. J. Dairy Sci. 17:37. 13 O'Bleness, G. V., L. D. Van Vleck, and C. R.
MASTITIS INCIDENCE Henderson. 1960. Heritabilities of some type appraisal traits and their genetic and phenotypic correlations with production. J. Dairy Sci. 43:1490. 14 Rendel, J., and T. Sundberg. 1962. Factors influencing the type and incidence of mastiffs in Swedish dairy cattle. Acta Vet. Scand. 3:13. 15 Schmidt, G. H., and L. D. Van Vleck. 1965. Heritability estimates of udder disease as measured by various tests and their relationship to each other and to milk yield, age, and milking times. J. Dairy Sci. 48:51.
119
16 Smith, J. W., and W. D. Schultze. 1970. Factors related to the level of natural resistance to udder infection. Page 38 in Proc. 6th Int. C o m m i t t e e on Cattle Diseases. 17 Wheelock, J. V., J. A. F. Rook, F. K. Neave, and F. H. Dodd. 1966. The effect of bacterial infections of the udder on the yield and composition of cow's milk_ J. Dairy Res. 33:199. 18 Wilton, J. W., L. D. Van Vleck, R. W. Everett, R. S. Guthrie, and S. J. RobertS. 1972. Genetic and environmental aspectS of udder infections. J. Dairy Sci. 55:183.
Journal of Dairy Science Vol. 59, No. 1
Incidence of clinical mastitis in 1278 lactations of 390 Jersey cows was studied for effects of lactation number, quarter of udder, month of calving, sire, and milk yield. Results for quarter did not conflict with the usual finding that incidence is higher in rear quarters. A mastitis index based on stage of lactation at which infection occurred had less variation, greater variation among sires, and a continuous distribution, in contrast to the traits porportion infected and number of cases. Mastitis increased with advancing lactation number subsequent to second lactations. Fall calvers may have less mastitis since they would be dry or in late lactation during summer. Incidence of mastitis increased at a decreasing rate as total milk yield in the lactation affected increased. INTRODUCTION
A wide variety of factors influences the frequency of mastitis in dairy cattle. Those in our report are lactation number (parity), quarter, month of calving, milk yield, and sire. Increased frequency of mastitis at older ages is well documented. Rendel and Sundberg (14) reported an incidence of 14.9% in first lactation compared to 37.7% in fourth lactations. Legates and Grinnells (7) found a frequency of 16.7% in 215 heifers and 51.1% in 959 older cows. Schmidt and Van Vleck (15) reported a correlation of .39 between age and number of infected quarters. Braund et al. (3) stated that the incidence of mastitis increased with age as judged by positive California Mastitis Test
Received March 17, 1975. 1USDA, ARS, Dairy Experiment Station, Lewisburg, TN. 2This work was in cooperation with the Agricultural Experiment Station, University of Tennessee, Knoxville.
reactions. Miller et al. (11) reported that number of quarter cases increased from 1.14 for first lactations to 4.0 for fourth lactations. The literature suggests a higher frequency of infection in rear quarters but no consistent difference between right and left halves. Rendel and Sundberg (14) suggested that front quarters are more protected and, therefore, less likely to be injured and to contract mastitis. They reported a small but nonsignificant excess of infections (1.4%) in rear quarters. There was no difference between right and left sides. Neave et al. (12) observed a 12% excess of mastitis in rear quarters. Arthur (2) also found more mastitis in rear quarters. Braund et al. (3) detected little difference in infection (as judged by cell counts) between front and rear but did find a higher rate of infection on the right side as compared to the left. Miller et al. (11) reported a small excess of infection (4.2%) in the rear, as compared to the front, but only a 1% excess of the right side over the left side. McDowetl and McDaniel (9) reported a higher frequency of mastitis in summer with twice as many treatments in July to September compared to April to June. Afifi (1) found higher cell counts in November in Dutch herds, but this may have been confounded with stage of lactation. Wilton et al. (18) reported that year-seasons accounted for little variation in udder infections. Miller et al. (11) found no significant difference between months of calving. Reports on the relationship between milk production and mastitis conflict. One reason, as pointed out by Wilton et al. (18), is that several counteracting tendencies may be involved. Mastitis infection causes a reduction in subsequent milk production in the quarter infected (6, 8, 17) although there may be some compensation by the uninfected quarters (4). On the other hand, some have suggested that high-producing cows contract mastitis more frequently, particularly in early lactation. Wilton et al. (18) reported that milk yield in a lactation was associated negatively with the extent of udder 113
114
MILLER ET AL.
infection although all correlations were - . 10 or less. When Wilton et al. (18) related infection frequency in one lactation to milk yield in the preceding lactation, the two were correlated only slightly. Legates and Grinnells (7) found that milk yield in first lactation was related positively to udder infections in later lactations though only to a small degree. Legates and Grinnells (7) reported a moderate degree of genetic association between first lactation milk yield and infection in later lactations. Afifi (1) found a negative relationship between cell count and milk yield on day sampled for first lactations. O'Bleness et al. (13) reported that high milk production was associated with increased infection. Differences for sire and cow in measures of mastitis incidence have been small. Wilton et al. (18) reported that regressions of second lactation incidence on first lactation and of incidence in later lactation on second lactation were moderately high and larger than the regressions of frequency in later lactation on incidence in first lactation. Miller (10) summarized heritabilities by a mean of .16 for measures of clinical mastitis. Our objectives were (a) to assess the frequency of clinical mastitis in a dairy herd and (b) to determine the effects of lactation number, quarter of udder, month of calving, milk yield, and sire on the frequency of clinical mastitis.
in a strip cup before milking. Cows were milked twice daily in a milking parlor. Ten basic traits were derived: 1) total number of separate quarter cases, 2 to 5) number of separate cases in each quarter, 6) presence or absence of infection in any quarter, 7 to 10) presence or absence of infection in each of the four quarters (the latter five traits subsequently will be referred to as "proportion infected"). In addition to these, four indices of mastitis were based on the criterion of Smith and Schultze (16). These indices reflect the stage of lactation in which the first case of mastitis is observed in each of the four quarters of a cow. For example:
DATA AND METHODS
YijkQ = ~ + si + cij + Pk + m~ +/3(Xijk~ -X) + eijk~
The data were complete lifetime histories of clinical mastitis for all cows 1959 to 1972 in the Jersey herd at the Dairy Experiment Station, Lewisburg, TN. Date of the first incidence of mastitis (if any) in each of a cow's quarters in each lactation was recorded. Also recorded was the total number of separate cases in each quarter during the lactation. A case of mastitis was defined as any intramammary antibiotic treatment. A separate case was defined as one in which at least 7 days had elapsed since any previous treatment in the same quarter. Since clinical treatment was the criterion, many instances of treatment without actual bacterial infections were no doubt present. Management procedures for the prevention of mastitis were standard. Beginning in 1970, each cow's teats were dipped in a teat-dip solution after each milking. Presence of mastitis requiring treatment was judged by clotty milk Journal of Dairy Science Vol. 59, No. 1
I1 = (no. days to 1st case in any quarter) + total days in milk = D1/DIM. (D 1 + no. days to 1st case in any of the other 3 quarters) + (2 x total days in milk). 12 =
These indices, therefore, range from 0 (calved with mastitis) to 1.0 (no mastitis during lactation). In contrast with the other measures of mastitis, these indices have the advantage of being continuous variables. However, their distributions ~till are characterized by large uninfected classes. There were 1278 lactations available on 390 cows. The data were analyzed by the following least squares model:
where si is a random effect of the i th sire, cij is a residual random effect for the jth daughter of the ith sire, Pk is an effect peculiar to the k th lactation number (parity), mQ is an effect common to all observations in the ~th month of calving, Xijk~ is the average milk yield per day of lactation (kg), /3 is the regression of the mastitis trait Yijk~ on milk yield per day of lactation, and eijk~ is a random error term representing unexplained variation between observations on the same cow. A preliminary analysis indicated that it was impossible to fit a model including cows, years, and parity simultaneously due to confounding. Therefore, effects of year were ignored. R ESU LTS
Means and standard deviations are in Table 1. Frequency of infection was relatively low.
115
MASTITIS INCIDENCE T A B L E 1. Arithmetic means and standard deviations•
Trait Proportion infected Prop ortion infected, Proportion infected, Proportion infected, Proportion infected, Number Number Number Number Number Index Index Index Index
-1 -2 -3 -4
of of of of of
cases cases, cases, cases, cases,
LF LR RF RR
LF LR RF RR
Mean
SD
.290 .105 .121 .119 .140
.454 .306 .326 .324 .347
.77 .18 .19 .19 .20 .820 .850 .872 .888
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1.91 .85 .75 .67 .62
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.331 .281 .245 .218
Twenty-nine percent of the lactations had at least one infection, and the mean number of cases per lactation was .77. Frequency of infection was higher in the rear quarters than in the front, and higher in the right side of the udder compared to the left. Proportion infected was .224 for the front, .261 for the rear quarters; .226 for the left side, .259 for the right. None of the differences were statistically significant by Student's t-test. The mean lndex-1 (11) was .82. Intracow phenotypic correlations are in "Fable 2. The correlation between proportion infected and number of cases was .57, indicating that only about 32% of the variation in number of cases is accounted for by division of cows into infected and uninfected categories. Correlations between the mastitis indices and number of cases ranged from .55 to - . 6 1 ; those between the indices and proportions infected ranged from - . 7 8 to - . 8 4 . There was a tendency in both number of cases and proportion infected for a higher correlation between left-front and right-front quarters and between front and rear quarter combinations. However, all such correlations were .40 or less. All correlations relating number of cases in one quarter to number in other quarters, and between proportion infected in one quarter and proportion infected in others, were positive. This indicates that occurrence of mastitis in one quarter increases the chance of occurrence in another quarter. Analysis of variance is in Table 3. Differ-
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." X Journal of Dairy Science Vol. 59, No. 1
116
MILLER ET AL.
ences between sires were significant only for the four mastitis index traits and number of cases in left-rear. Differences of parity were significant for every trait with F-values being largest
for number of cases and proportion
infccted. Month of calving was significant for all traits, except number of cases in left-rear,
number of cases in right-front, total proportion infected, and proportions infected in left-front and left-rear; F values were small, however. The
~ m
quadratic regression of mastitis on daily milk yield was significant for all traits except number of cases in left-rear, number of cases in right-rear, and proportions infected in left-rear, right-front, and right-rear; F-values were largest for the mastitis indices.
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Table 4 gives least-squares constants for effccts of parity for proportion infected, total number of cases, and 11. Seventh and later lactations were p o o l e d together as one group. M a x i m u m susceptibility to mastitis occurred in
tile seventh and later lactations, which had 2.84 more cases of mastitis than first lactations. Mean infection rates were reached in the fourth
m
to fifth parities. Constants for month of calving for number of cases and I~ are in Table 5. While the trends
are erratic, it appears that mastitis was more frequent for cows calving in February to July than in August to January. However, cows calving in June w o u l d have .24 fewer cases than average. The results for both n u m b e r of cases and the mastitis index agree that April calvers have m o s t mastitis and September to December calvers the least.
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Regressions of percent infected, number of cases, and l i on daily milk yield are in Table 6. The quadratic term was significant at .05 or .01 for all three traits. Milk yields at which maximum (or minimum in case of 11) occurred were: 31.7 kg for proportion infected, 29.8 kg for number of cases, and 27.6 kg for I 1 .
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DISCUSSIONS A N D CONCLUSIONS
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Journal of Dairy Science Vol. 59, No. 1
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Our results do not contradict the general finding of a higher proportion of mastitis infection in rear quarters. Since rear quarters normally produce more milk than front quarters (5), this fits a pattern of increased incidence of mastitis accompanying higher milk production. This differential rate of infection within udder has a bearing on the design of
MASTITIS INCIDENCE
117
TABLE 4. Least-squares parity constants and standard errors. Constants SIS Parity
N
Proportion infected
Number of cases
1 2 3 4 5 6
388 292 189 137 103 77 92
-.24 -.24 -.12 -.01 .12 .15 .33
-1.O1 -.95 -.67 -.16 .32 .65 1.83
7
.03 .03 .03 .03 .04 .04 .04
mastitis e x p e r i m e n t s . Where h a l f - u d d e r designs with t w o t r e a t m e n t s arc e m p l o y e d , t r e a t m e n t s s h o u l d be balanced b e t w e e n f r o n t and rear quarters. Three kinds o f measures of mastitis were e x a m i n e d : n u m b e r o f separate cases during a lactation, p r o p o r t i o n i n f e c t e d (binomial), and an i n d e x based o n stage o f lactation at which i n f e c t i o n occurs. P r o p o r t i o n i n f e c t e d a n d mastiffs i n d e x w e r e closely related w h e r e a s n u m b e r o f cases p r o v i d e d s o m e w h a t m o r e u n i q u e inf o r m a t i o n a b o u t mastiffs incidence. However, mastitis indices had m u c h smaller c o e f f i c i e n t s o f variation t h a n the o t h e r t w o measures. Mastiffs indices also h a d relatively large mean squares for sire. Thus, s o m e c o m b i n a t i o n o f n u m b e r o f cases and i n d e x m i g h t be desirable (I4 was related m o r e closely t o n u m b e r o f cases t h a n were the o t h e r t h r e e indices). However, b o t h measures failed t o reflect i m p a c t of mastitis on milk p r o d u c t i o n . Our results c o n f i r m the w e l l - d o c u m e n t e d
TABLE 5. Least-squares month of calving constants and standard errors. Month
Number of cases
January February March April May June July August September October November December
-.12
.20
.29
.22
.64 .88 .00 -.24 .13 -.16 -.39 -.55 -.23 -.25
.21 .23 .24 .24 .22 .20 .19 .20 .21 .21
.13 .12 .13 .14 .16 .18 .18
Index -1 .15 .14 .07 ,02 -.08 -.09 -.22
.02 .02 .02 .02 .03 .03 .03
increase in f r e q u e n c y o f mastiffs with age of cow. Seventh parities had 33% m o r e lactations x~dth mastitis i n f e c t i o n t h a n average while first parities had 24% less i n f e c t e d lactations t h a n average. Later parities also had m o r e i n f e c t i o n s per lactation, and i n f e c t i o n s t e n d e d to o c c u r earlier t h a n in y o u n g e r parities. Mastiffs was no more extensive in s e c o n d parities t h a n in first parities in this herd. Thus, w h a t e v e r factors are responsible f o r increasing t h e p r o b a b i l i t y o f c o n t r a c t i n g mastitis as c o w s grow o l d e r app a r e n t l y only c o m e i n t o play a f t e r s e c o n d lactations. ( F a c t o r s t h a t have been suggested are increased stress due to higher milk s e c r e t o r y activity and wear o f the s p h i n c t e r muscle.) Since t h e p r o b a b i l i t y of cows b e c o m i n g i n f e c t e d increases with age, mastitis experim e n t s w h i c h d e p e n d on the f r e q u e n c y o f natural i n f e c t i o n s are m o r e effective with older cows (third or later parities). Even in this case, it m a y be desirable to have e x p e r i m e n t a l assignments to t r e a t m e n t b a l a n c e d according to parities o f t h e cows. Increased mastitis with age also has implication for genetic selection. S o m e have a d v o c a t e d t h a t s e l e c t i o n s h o u l d be for length of life as a
Index -1 .022 -.077 .002 -.099 -.024 -.035 -.055 -.010 .057 .082 .094 .042
.04 .04 .04 .04 .04 .04 .04 .03 .03 .04 .04 .04
TABLE 6. Regression of mastitis traits on milk yield, a
Proportion infected Number of cases Index -1
Linear
Quadratic
.0436 c .227 b -,040 b
-.00152 c -.00837 b .001442 b
akg/day. bp<.01. Cp<.05. Journal of Dairy Science Vol. 59, No. 1
118
MILLER ET AL.
means of increasing the e c o n o m i c returns f r o m dairy cattle. Our results indicate that as the p r o p o r t i o n of the herd in third and later parities increases, the costs of mastitis treatment and subsequent losses in milk would increase markedly. Thus, any assessment of the value of increased longevity should take this into account. Results concerning m o n t h of calving were not clear. However, m o n t h was statistically significant for n u m b e r of cases and for all four mastitis indices. Tile trend indicated by n u m b e r of cases and the mastitis index did not agree completely. However, both agree that cows calving f r o m S e p t e m b e r to D e c e m b e r had less mastitis. McDowell and McDaniel (9) reported that a higher f r e q u e n c y of mastitis occurred during the summer. Our results are based on calving date rather than date of infection, and cannot be used to support or contradict McDowell and McDaniel's report. Regressions of mastitis traits on average daily milk yield were statistically significant and curvilinear. Examination of m a x i m u m and m i n i m u m showed no decrease in mastitis within the range o f daily milk yield ( m a x i m u m value was 27.6 kg/day). Thus, the range of milk yields w o u l d be characterized by increasing incidence of mastitis but at a steadily decreasing rate. Previous results regarding milk p r o d u c t i o n and mastitis conflict. One reason for this, as pointed out by Wilton et al. (18), is that at least two tendencies arc c o n f o u n d e d . Quarters infected by mastitis may have both short- and long-term reduction in subsequent milk yield. If high producers t e n d to contract mastitis more readily than low producers, these two factors would tend to cancel each other, obfuscating the relationship between observed milk yield and mastitis infection. In our results, higher producers were predicted to have m o r e mastitis at all milk yields, but to progressively smaller degrees. This could be due to a steadily increasing reduction in the subsequent milk yield occurring as the incidence and severity of mastitis increase. This would bring about a direct positive relation between milk yield and mastitis at lower production, but only a very weak positive relation at high production. To produce at m a x i m u m potential, a cow must remain free of mastitis infection. Conclusions are: 1) our results do not Journal of Dairy Science Vol. 59. No. 1
conflict with the general finding that rear quarters exceed front quarters in f r e q u e n c y of mastitis, 2) the mastitis i n d e x and n u m b e r of cases of mastitis both contain worthwhile inf o r m a t i o n about the scope of mastitis infection while p r o p o r t i o n infected is redundant, 3) the mastitis index exhibits less total variation than other measures of mastitis and has a higher degree of differences a m o n g sires, 4) the frequency' of mastitis increases with advancing lactation n u m b e r subsequent to second parity, 5) there is a t e n d e n c y for less mastitis in lactations of cows calving in the fall, possibly due to a higher f r e q u e n c y of mastitis occurring during summer, 6) f r e q u e n c y of mastitis increases at a decreasing rate as milk yield per day of the lactation affected increases. REFERENCES
1 Afifi, Y. A. 1967. Genetical and some environmental influences affecting the level of leukocyte counts in the milk of cows. Thesis, Mededelingen Lavalbouwhogeschool, Wageningen, Netherlands. 2 Arthur, G. H. 1947. Observations on the clinical aspects of bovine mastitis. Vet. Rec. 59:231. 3 Braund, D. G., and L. H. Schultz. 1963. Physiological and environmental factors affecting the California Mastitis Test under field conditions. J. Dairy Sci. 46:197. 4 Crossman, J. V., F. H. Dodd, J. M. Lee, and F. K. Neave. 1950. The effect of bacterial infection on the milk yield of individual quarters of the cow's udder. J. Dairy Res. 17:128. 5 Johansson, 1. 1957. Untersuchungen uber die variation in der Euter-und Strichform der Kuhe. Z. 1"ierz. Zuechtungsbiol. 70:233. 6 Leffler, R. 1966. The relationship between milkability and udder health in Simmental cows in Switzerland. Dairy Sci. Abstr. 28: 33. 7 Legates, J. E., and C. D. Grinnells. 1952. Genetic relationships in resistance to mastitis in dairy cattle. J. Dairy Sci. 35:829. 8 Lups, P., and H. C. Ritter. 1966. Relationship between chronic udder disease and milk yield of cows. Dairy Sci. Abstr. 28:205. 9 McDowell, R. E., and B. T. McDaniel. 1968. Interbreed matings in dairy cattle. 1I. Herd health and viability. J. Dairy Sci. 51:1275. 10 Miller, R. H. 1972. Breeding for disease resistance in dairy cattle. Proceedings, Joint Meeting NC-2 and S-49 Regional Dairy Cattle Breeding Technical Committees. 11 Miller, R. H., J. W. Smith, N. W. Hooven, Jr., and R. E. Pearson. 1973. Factors affecting variation in several measures of clinical mastitis in a herd of Holstein cattle. J. Dairy Sci. 56:666. (Abstr.) 12 Neave, F. K., F. H. Dodd, and E. Henriques. 1950. Udder infections during the dry period. J. Dairy Sci. 17:37. 13 O'Bleness, G. V., L. D. Van Vleck, and C. R.
MASTITIS INCIDENCE Henderson. 1960. Heritabilities of some type appraisal traits and their genetic and phenotypic correlations with production. J. Dairy Sci. 43:1490. 14 Rendel, J., and T. Sundberg. 1962. Factors influencing the type and incidence of mastiffs in Swedish dairy cattle. Acta Vet. Scand. 3:13. 15 Schmidt, G. H., and L. D. Van Vleck. 1965. Heritability estimates of udder disease as measured by various tests and their relationship to each other and to milk yield, age, and milking times. J. Dairy Sci. 48:51.
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16 Smith, J. W., and W. D. Schultze. 1970. Factors related to the level of natural resistance to udder infection. Page 38 in Proc. 6th Int. C o m m i t t e e on Cattle Diseases. 17 Wheelock, J. V., J. A. F. Rook, F. K. Neave, and F. H. Dodd. 1966. The effect of bacterial infections of the udder on the yield and composition of cow's milk_ J. Dairy Res. 33:199. 18 Wilton, J. W., L. D. Van Vleck, R. W. Everett, R. S. Guthrie, and S. J. RobertS. 1972. Genetic and environmental aspectS of udder infections. J. Dairy Sci. 55:183.
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