Milk Yield, Somatic Cell Counts, and Risk of Removal from the Herd for Dairy Cows After Covered Teat Canal Injury

The objective of this study was to evaluate milk yield, somatic cell count (SCC), and risk of removal of a cow from the herd after covered teat injury. Teat injuries were diagnosed and treated by using endoscopy. After treatment, teats were rested for 3 × 3 d. Eighty-one cows referred to the Veterinary Clinic Babenhausen were used for this study. Each cow was matched to three herdmates by breed, age, and calving date. Data on milk yield and SCC were available from the records of the Bavarian milk control board. Test day milk yields and lactational milk yields were equal for cows with covered teat injury and herd-mates in the lactation when the injury was diagnosed and in the subsequent lactation. Calving interval in the year the injury was diagnosed and the time cows lived in the herd were also equal. However, covered teat injuries significantly increased test day SCC by 128,000 cells/ml of milk. These injuries also significantly increased the odds of subclinical mastitis (SCC >100,000 on test day) and the odds of violating European milk shipping regulations (SCC >400,000 on test day). Because increased SCC was significantly associated with decreased milk yield, cows may not have fully utilized their milk yield capacity after covered teat injury.


INTRODUCTION
Covered teat injuries are lesions of the teat canal skin, the teat cistern lining, and underlying muscle and connective tissue in which the outer teat skin is relatively undamaged (13).Teat injury in dairy cows has been reported to increase the risk of mastitis (1,5,26,27) and the risk of removal from the herd (4,5,9).Recently, new methods have been developed to restitute udder health after teat injury.These methods include teat endoscopy for diagnosis and treatment of covered teat injuries and resting the injured teat by temporary cessation of milking (10,16).The objective of this study was to evaluate milk yield; SCC, risk of removal of cows from the herd after diagnosis, and treatment of covered teat injuries using endoscopy; and resting the injured teat by temporary cessation of milking.

MATERIALS AND METHODS
For this study, 81 cows were used, which had been referred to the Veterinary Clinic Babenhausen between January 1, and June 13, 1996 because of milk flow disturbances in one teat.These cows originated from 64 herds: 1 cow from each of 51 herds, 2 cows from each of 10 herds, and 3 cows from three herds.Case history was determined, and cows were clinically examined (11).Diagnosis and carefully directed surgical treatment of the milk flow disturbances were performed using endoscopy (16).All milk flow disturbances were consequences of covered teat injuries.After surgical treatment an intramammary antibiotic was administered, a teat dilator ( 1 8 ) was inserted into the teat canal, the teat was bandaged and rested by temporary cessation of milking for three intervals of 3 d with one draining off of milk between ( 3 × 3 d).
Resting teat for 3 × 3 d means cessation of milking for 9 d.It also means draining off milk; administering an intramammary antibiotic; inserting a teat insert and bandaging the injured teat on d 1, 4, and 7; and resuming milking on d 10.All cases were reexamined 1 mo after treatment.If milk flow was still disturbed, the teat was retreated (Table 1).
These case cows were each matched to 3 control cows by herd, age, and calving date.Data for milk yield and SCC were collected from the records of the Bavarian milk control board (Table 2, Figures 1 to  4).The days of life in the herd from calving prior to the teat injury until January 1, 1998 were determined (Table 2).The probability of remaining in the herd in that period was graphed (Figure 5).The effect of teat injury on lactational milk yield, test day   milk yield, test day SCC, subclinical mastitis risk (>100,000 cells/ml of milk on test day) ( 3 ) , risk of violating European milk shipping regulations (>400,000 cells/ml of milk on test day) ( 2 ) , and the risk of removal from the herd was evaluated.The effect of teat injury on calving interval in the year that the teat injury was diagnosed was also studied as was the effect of lactational milk yield prior to the teat injury on the risk of teat injury.The effects of herd, breed, age, and calving period were adjusted for in each model.Because matching may introduce bias, matching variables were controlled for in the analysis (22).Other factors were considered in the model if their effects seemed biologically reasonable and if they significantly added to the model ( P a was < 0.1).
The outcome variables lactational milk yield, test day milk yield, test day SCC, risk of >100,000 cells/ml of milk on test day, risk of >400,000 cells/ml of milk on test day, calving interval, and teat injury were studied using generalized linear models.Calculations were performed using PROC GENMOD of SAS (24).Continous outcome variables were studied by using the identity link.Binary outcome variables were studied by using the log link.Repeated subject was the herd; the correlation structure used was exchan-   gable.For continuous outcome variables, the number of units (liters, cells, and days) is reported that the outcome variable changes per unit change of the continuous explanatory variable or with the presence of the binary explanatory variable compared with their absence (17).In binary outcome variables (0,1) a risk is reported.This risk is given as the log odds (logit).From the logit, the probability (expected value) of the outcome variable ( Y ) can be calculated.tory variables.In binary explanatory variables, the odds ratio is reported.The odds ratio is a measure of how much more likely (or unlikely) the outcome is among observations with a given risk factor compared with those without the risk factor (12). Risk of removal from the herd was studied by using survival analysis (15).The outcome variable was the time (days) in the herd from calving prior to teat injury until January 1, 1998, adjusting for the presence of the cow on January 1, 1998.Not present in the herd on January 1, 1998 was the censoring variable.Calculations were performed using PROC PHREG in SAS (24).The effect of herd was adjusted for using the SAS macro PH-LEV.The effect of explanatory variables on the hazard rate ( 1 5 ) of removal from the herd is reported.

RESULTS
Case cows with covered teat injuries were predominantly young Brown Bavarian cows housed in tie-stall facilities.Most cases were presented to the Veterinary Clinic Babenhausen during the first months in milk, and most were pretreated.Usually hind teats were acutely affected by ruptures in the area of the teat canal with lengthening of the teat canal.Signs of inflammation were often present in the milk from these teats (increased SCC, pathogens detected) during clinical examination and reexamination (Table 1).
Covered teat injuries, diagnosed and treated as described, did not significantly affect test day milk yield (Table 3 ) or lactational milk yield (Table 4).However, they increased test day SCC by 128,000 ± 25,000/ml of milk (Table 5).The odds of >100,000 cells/ml of milk on test day were 1.9 times higher for case cows than for control cows (Table 6).The odds of >400,000 cells/ml of milk on test day were 2.4 times higher for case cows than for control cows (Table 7).Only one quarter with covered teat injury developed signs of clinical mastitis.Covered teat injuries, diagnosed and treated as described, did not significantly affect the hazard rate of removal from the herd (Ta-TABLE 6. Model of the odds (logit) of >100,000 cells/ml of milk on test day of the lactation when teat injury was diagnosed and in the subsequent lactation. 1  1 Variables, estimates, standard errors, probability values, and odds ratios are given.Odds ratios of variables that were used for matching are not reported.teat injury lactation 0.37 0.13 0.00 1.5 ble 8).The injuries did not affect the calving interval in the year that the teat injury was diagnosed (Table 9).The odds of teat injury tended to increase with increasing lactational milk yield in the previous lactation (Table 10).These results are adjusted for the effects of herd, breed, age, and calving period as well as for the effects of the variables that were also in the model.This study also yielded some additional information.In general, test day milk yield decreased by 1.4 ± 0.1 L/mo throughout lactation and was 2.0 ± 0.3 L higher in the lactation subsequent to the lactation in which the injury was diagnosed (Table 3).Test day milk yield decreased with increasing SCC.Somatic cell counts >400,000/ml lowered milk yield by 1.3 ± 0.3 L on test day compared with an SCC of <400,000 (Table 3).Lactational milk yield increased with the number of days in milk and decreased with test day SCC (Table 4).Test day SCC increased by 6000 ± 3000/ml per month throughout lactation and was 42,000 ± 19,000 cells/ml higher in the subsequent lactation (Table 5).Similarly the odds of >100,000 cells/ml milk and the odds of >400,000 cells/ml milk on test day increased per month and were 1.7 times and 1.5 times higher, respectively, in subsequent lactations (Tables 6 and 7).The risk of removal from the herd decreased with increasing lactational milk yield (Table 8).Calving interval increased with increasing test day milk yield (Table 9).These results are adjusted for the effects of herd, breed, age, and calving period and for the effects of variables that were also in the model.

DISCUSSION
From the results of this study, we concluded that cows with covered teat injuries that were diagnosed and treated as described yield as much milk and remain in the herd as long as their herdmates.These results differ from other studies (4, 5, 9 ) that report increased risk of removal from the herd after teat injury.However, those studies did not specify the nature of the teat injury or how the injuries were diagnosed and treated.We also concluded from our study that covered teat injuries, managed as described, permanently increase SCC, the risk of subclincal mastitis (>100,000 cells/ml of milk) ( 3 ) , and the risk of producing milk above the violative level of European milk shipping regulations (>400,000 cells/ ml of milk) ( 2 ) .Because subclinical mastitis is associated with decreased milk yield (21), milk losses may be expected after covered teat injury.Subclinical mastitis following covered teat injury hinders utiliza-TABLE 8. Model of the risk (hazard rate) of removal from the herd of the lactation when teat injury was diagnosed and in the subsequent lactation. 1  1 Variables, estimates, standard errors, and probability values are given. 2For the lactation that teat injury was diagnosed.(20,25).Thus, silicone implants or natural teat inserts rather than dilators are now recommended to prevent adhesions in the teat canal following teat injury (10,25).This study also yielded some additional information.High milk yield in the previous lactation is suspected to be associated with an increased risk of covered teat injuries.This association is in accordance with the findings of others ( 6 ) .Covered teat injuries that were managed as described did not significantly affect calving interval, which suggests that fertility was not affected under these conditions.In both normal cows and in cows with teat injury, three major outcome parameters increased as the lactation progressed.Somatic cell counts, the risk of developing subclinical mastitis, and the risk of producing milk that violates European milk shipping regulations all increased with increasing months in milk.This result agrees with those of others (8,14) reporting an increase of SCC throughout lactation.

Figure 1 .
Figure 1.Test day milk yield (liters) of patients with covered teat injury or in herdmates.Medians are given for mo 1 to 10 of the lactation when the injury was diagnosed.

Figure 2 .
Figure 2. Test day SCC (1000 cells/ml of milk) of patients with covered teat injury or in herdmates.Medians are given for mo 1 to 10 of the lactation when the injury was diagnosed.

Figure 3 .
Figure 3. Percentage of patients with covered teat injury or of herdmates showing >100,000 cells/ml of milk on test day in mo 1 to 10 of the lactation when the injury was diagnosed.

Figure 4 .
Figure 4. Percentage of patients with covered teat injury or of herdmates showing >400,000 cells/ml of milk on test day in mo 1 to 10 of the lactation when the injury was diagnosed.

Figure 5 .
Figure 5. Probability of remaining in the herd for patients with covered teat injury (thick line) and for herdmates (thin line).

TABLE 1 .
Findings for patients (case history, clinical examination, and reexamination) 1Compared with the lateral neighboring teat.2In the milk from the injured teat.

TABLE 2 .
Parameters of patients with teat injury and in herdmates without teat injury.

TABLE 3 .
Model of test day milk yield (liters) of the lactation when teat injury was diagnosed and in the subsequent lactation.1   1Variables, estimates, standard errors, and probability values are given.

TABLE 4 .
Model of lactational milk yield (liters) of the lactation when teat injury was diagnosed and in the subsequent lactation.1   1Variables, estimates, standard errors, and probability values are given.

TABLE 7 .
Model of the odds (logit) of >400,000 cells/ml of milk on test day of the lactation when teat injury was diagnosed and in the subsequent lactation.11Variables, estimates, standard errors, probability values, and odds ratios are given.Odds ratios of variables that were used for matching are not reported.

TABLE 10 .
(1,7,23,26,27)dds (logit) of covered teat injury. 1 milk yield capacity. Others have reported(1,7,23,26,27)that teat injury permanently increases the risk of subclinical and clinical mastitis.In our study only one quarter with teat injury developed signs of clinical mastitis.The extent to which teat dilators contributed to increased SCC in our study has not been investigated.A recent study ( 1 8 ) indicated that the use of teat dilators may injure the teat canal and teat cistern epithelium and increase SCC and the risk of finding bacteria in the milk