Somatic cell counts in bovine milk: relationships to production and clinical episodes of mastitis

The relationships between somatic cell counts, milk production and episodes of clinical mastitis were evaluated using data collected between 1979 and 1981 in 32 southern Ontario Holstein herds. Somatic cell counts were logarithmically transformed and the distribution of the resulting counts is presented. The seasonal pattern in cell counts was evaluated using a formal statistical procedure. Counts were lowest in the winter and spring and highest in the early fall but the differences amongst monthly geometric mean cell counts were small. Assuming a linear relationship between log somatic cell counts and test day milk production it was found that a unit increase in the log count resulted in a loss of 1.44 kg of milk. Regression analyses within specific log cell count ranges indicated that the previous estimate may underestimate losses at low cell counts and overestimate losses at higher cell counts. The relationships between cell counts and episodes of mild or acute clinical mastitis were evaluated by comparing counts preceding and following the clinical episodes to comparable counts in matched control cows. Mild cases of mastitis were preceded by higher cell counts than were found in control cows but the same phenomenon was not observed in acute cases of mastitis. Both mild and acute cases were followed by higher cell counts than were found in control cows.

Antimicrobial use in feedlot calves: its association with culture rates and antimicrobial susceptibility

Data were collected on anti-microbial usage and health problems, in beef feedlot calves. Although the association between them was not significant, many feedlot owners did not use recommended dosages or duration of treatment and this may have led to a reduced recovery rate.Injectable tetracyclines were the most frequent antimicrobial for primary treatment of sick calves; whereas chloramphenicol was selected most frequently when the primary treatment appeared to be ineffective. Treatment with anti-microbials reduced the likelihood of isolating both Pasteurella multocida and Haemophilus somnus. Chloramphenicol therapy reduced the likelihood of isolating Pasteurella haemolytica. Therapy with a particular antimicrobial, in the week prior to death, increased the level of resistance in P. haemolytica to that antimicrobial. Treatment with other antimicrobials also increased the level of resistance to that antimicrobial; although to a lesser degree. The lowest levels of resistance were observed in Pasteurella isolated from nontreated cattle. After adjustment for antimicrobial exposure, resistance to penicillin, tetracyclines and chloramphenicol occurred together more frequently than expected by chance alone.

An observational study of Corynebacterium bovis in selected Ontario dairy herds

An observational study of Corynebacterium bovis was conducted in 74 Ontario dairy herds. The levels of infection with C. bovis were 19.9, 36.2 and 85.6% at the quarter, cow and herd level, respectively. Teat disinfection was found to be the variable best able to distinguish between herds with a high or low C. bovis quarter infection rate. Mean total milk somatic cell counts for 1103 quarters and 107 cows infected with only C. bovis ranged between 150,000 and 200,000/mL and were significantly higher than for uninfected quarters or cows. The rate of infection with mastitis pathogens was not significantly different in quarters previously colonized with only C. bovis compared to previously uninfected quarters.

Factors associated with mortality and treatment costs in feedlot calves: the Bruce County Beef Project, years 1978, 1979, 1980

Three years of data on factors associated with death losses and health costs in Ontario feedlot calves were analyzed. The results support the previously reported findings; however, significant differences in the third year (1980-81) of the study were noted. Calf groups that were "mixed" after arrival in the feedlot or had a larger than average number of calves (means = 142) had increased death losses and health costs. Calf groups whose ration was changed from dry hay to hay silage or corn silage as the major component of the ration during the first month after arrival had higher death losses and health costs. Feeding grain (barley/oats/corn) prior to, or concurrent with, the change to silage appeared to decrease the harmful effects. Cattle groups vaccinated against respiratory disease within two weeks of arrival experienced increased death losses and health costs. These effects were ameliorated by delaying vaccination in groups switched to silage; however, no benefits from delaying vaccination were noted in dry hay fed groups. Prophylactic antimicrobials in the water supply during the first week after arrival appeared particularly deleterious to the health of calf groups. The effects of prophylactic antimicrobials in the starter ration were unclear. During 1980-81, there was a marked decrease in the relative importance of fibrinous pneumonia as a cause of death and the feeding of silage was not significantly associated with mortality. Both these events may have arisen from the drastic decrease in the percentage of groups fed silage by two weeks postarrival (from 32% in previous years to 7% in 1980-81).

A survey of mastitis in selected ontario dairy herds

A mastitis survey involving 74 Ontario dairy herds was conducted. The prevalence of infection at the quarter level was found to be 4.1% with Streptococcus agalactiae, 4.5% with other streptococcal species and 8.0% with Staphylococcus aureus. Regardless of the infection status, the geometric mean somatic cell count was found to increase with age of the cow but no increase was observed with increasing stage of lactation. The percentage of cows from which a bacterial pathogen was isolated increased with age but not with stage of lactation.

Somatic cell counts in bovine milk

Factors which influence somatic cell counts in bovine milk are reviewed and guidelines for their interpretation are presented. It is suggested that the thresholds of 300 000 and 250 000 cells/mL be used to identify infected quarters and cows respectively. However, it is stressed that somatic cell counts are general indicators of udder health which are subject to the influence of many factors. Therefore the evaluation of several successive counts is preferable to the interpretation of an individual count.Relationships between somatic cell counts and both milk production and milk composition are discussed. Subclinical mastitis reduces milk quality and decreases yield although the relationship between production loss and somatic cell count requires clarification. Finally the availability of somatic cell counting programs in Canada is presented.

The application of bulk tank somatic cell counts to monitoring mastitis levels in dairy herds

The objective of this study was to investigate the feasibility of developing a system whereby measurements taken on bulk tank milk samples could be used to monitor the level of subclinical mastitis in dairy herds. The variables that were examined were the logarithmically transformed total somatic cell counts and percentages of cell volume in channel 8 (volumes from 89.2 to 178.3 microm(3)), the presence or absence of Streptococcus agalactiae and various husbandry/management factors including herdsize and the use of teat dips. Each of the use of actual monthly and rolling average bulk tank cell count determinations was investigated. It was found that the inclusion of all variables resulted in a correct classification of approximately 85% of herds and that no improvement was achieved by the use of rolling as opposed to actual monthly values. The inclusion of various husbandry/management practices improved the percentage correct classification to some extent over that achieved by the sole use of total somatic cell counts and percentages of cell volume in channel 8 when the herds were grouped on the basis of quarter infection rate (<10%, >10%) but not in the case of the cow infection rate categories (<20%, >20%). The use of both total cell counts and percentages of cell volume in channel 8 did not improve the overall predictive value over that achieved by the sole use of percentage of cell volume in channel 8 in the case of the quarter infection rate groupings but did to some extent in the case of the cow infection rate groupings. When the classification functions were applied prospectively and considering combinations of the two cell count determinations only, it was found that they were able to correctly classify, on the basis of the quarter infection rate groupings, approximately 75% of the study herds. It is concluded that the system described herein has limited application as a basis for selecting problem herds.

Somatic cell counts, mastitis and milk production in selected Ontario dairy herds

Somatic cell counts were performed monthly on bulk tank milk samples for all producers in the Ontario counties of Hastings, Lennox/Addington and Prince Edward throughout 1978 and 1979. Other data were obtained via a structured questionnaire and from the records of the Ontario Milk Marketing Board. Many producers have not adopted practices that have been advocated for the integrated control of mastitis. For example, 43.3% of producers surveyed used single service paper towels, 63.3% regularly used teat dip and 56.5% dry cow therapy. The mean of the average monthly somatic cell count for all producers for 1978 was 621.1 x 10(3) cells/mL. This latter value was used to divide the producers into case (higher than average) and control (lower than average) groups. Control herds averaged 95.9 liters more shipped milk per cow per month than case herds. Milk from control herds averaged 0.22 percentage points higher than case herds for each of average fat and lactose, and 0.16 percentage points higher for protein. The linear regression of monthly shipped milk on the respective monthly bulk tank somatic cell count indicated a loss of 13.26 L/cow/month for each 100,000 increase in somatic cell count.

The effects of storage and method of fixation on somatic cell counts in bovine milk

Fresh milk samples and potassium dichromate preserved milk samples were stored at both ambient, approximately 21 degree C, and refrigerator temperatures, 3-5 degree C, for varying lengths of time before somatic cell counts were performed on an electronic particle counter. Fresh milk samples stored at ambient temperatures became unacceptable for somatic cell counting by 16 hours while those stored in the refrigerator were acceptable for up to three days. Once dichromate had been added to the milk no difference in cell counts attributable to temperature of storage were detected and there was very little change with time up to 14 days. On the average the addition of the dichromate elevated the cell counts/mL. As well a method of rapid fixation of milk involving the addition of glutaraldehyde prior to counting was evaluated. In fresh milk samples the use of glutaraldehyde as a fixative required adjustment of the threshold setting on the cell counter in order to produce results comparable to those obtained from formalin fixed samples. With dichromate preserved milk samples, glutaraldehyde fixation generally elevated the cell counts but the results were variable.

The interpretation of antimicrobial susceptibility patterns

The results of a computer model designed to demonstrate the effect of antimicrobial exposure (therapy) on the likelihood of isolating putative pathogens and on the proportion of successfully isolated organisms resistant to specific antimicrobials are presented. The results indicate that the observed percentage resistant is not a reliable indicator of the actual percentage resistant in the source population. Data from the Bruce County Beef Project in 1979-80 are used to verify some of the assumptions used in the model.

Factors associated with morbidity and mortality in feedlot calves: the Bruce County beef project, year two

The results of the second year of the project confirmed most of the major findings from the initial year. Feeding cornsilage, particularly as the major roughage in the first month after arrival was associated with excess mortality. Mixing of cattle from different sources and vaccinating against respiratory disease appeared to be the most important additional factors that increased mortality rates. Delaying vaccination at least two days postarrival may have prevented the negative effects of vaccination but only in calves fed cornsilage. Morbidity rates were highly variable among farms but were positively correlated with mortality rates and treatment costs. The occurrence of infectious thromboembolic meningoencephalitis appeared to share some of the same risk factors as mortality; whereas, urolithiasis did not. Water deprivation may be a risk factor in the occurrence of urolithiasis. Fibrinous pneumonia was again the most frequent cause of death. Relative to year one, infectious thromboembolic meningoencephalitis increased in frequency and only one death was attributed to bovine virus diarrhea.

Bovine mastitis: a survey of Ontario dairy producers, 1978

A survey to assess the knowledge and perception regarding mastitis of 1200 randomly selected Ontario dairy producers was conducted using a mailed questionnaire. Other data were provided by the Ontario Milk Marketing Board and the Dairy Herd Improvement Association. In general, producers were less aware of subclinical than clinical mastitis and did not appreciate the losses in production associated with it. Approximately 40% of producers were not familiar with mastitis in its subclinical form.Many producers have not adopted practices that have been advocated for the integrated control of mastitis. For example, 35.5% of producers surveyed used single service paper towels and 38% regularly used teat dips and dry cow antibiotic therapy.

Use of total and differential somatic cell counts from composite milk samples to detect mastitis in individual cows

The objective of this study was to ascertain the value of variables measured on composite milk samples as predictors of mastitis in individual cows. The standard of comparison was the results obtained from the bacteriological examination of individual quarter foremilk samples. Cows were classified as negative or positive with regard to mastitis on the basis of one quarter sampling only and cows which were impossible to classify in this manner were omitted from subsequent analyses. The variables that were examined were: the presence or absence of specific bacteria, demographic data, and logarithmically transformed total somatic cell counts and percentages of cell volume in channels 7 through 12 of a Coulter Counter. It was found that the inclusion of all variables resulted in correct classification of 95.9% of cows with regard to their mastitis status. Sequential elimination of individual variables or groups of variables in an attempt to simplify the procedure reduced the correct classification to 86.8% when only the log transformation of the total somatic cell count and the demographic data were included. The ability of a function which included the logarithm of the total somatic cell count, the logarithm of the percentage in channel 8 and demographic data, to classify cows was examined in detail and the sensitivity and specificity of the function also discussed. It is also shown that with increasing age the minimum total somatic cell count required to classify a cow as positive increased and possible explanations of this phenomenon are discussed.

Factors associated with mastitis in Ontario dairy herds: a case control study

Data from Ontario dairy cattle herds which had had a high average milk gel index for 1978 (cases) and from other herds which had had a low average during the same period (controls) were collected and analyzed using case control techniques. The purpose of the study was to contrast factors of husbandry and management between the two groups and to determine the relative contribution of each of these factors on mastitis (as determined indirectly by the milk gel index) at the herd level. Control herds had higher average production levels than did case herds, shipping 1807 litres more milk per cow per year. Milk from control herds averaged 0.06 percentage points higher in butterfat, 0.19 percentage points higher in lactose and 0.05 percentage points lower in total protein. However, many factors can influence production, therefore these latter differences, in both shipped milk and composition, can not be attributed solely to differences in the prevalence of mastitis between the two groups. Control herds were more likely to use teat dip, receive regular veterinary service, use dry cow antibiotic preparations and have knowledge concerning subclinical mastitis than were case herds. Control herds also tended to raise more of their own replacements, have a higher culling rate for reasons of low production and have a more modernized dairy operation. Case herds, on the other hand, were more likely to scrutinize foremilk, use more milking units per operator and wait longer between the start of stimulation and attachment of the milking unit. The study confirms, under natural field conditions, the importance of integrated mastitis control practices and also reaffirms the relative importance of practices such as the use of teat dips and dry cow antibiotic preparations.

Use of Total and Differential Somatic Cell Counts to Differentiate Potentially Infected from Potentially Non-infected Quarters and Cows and Between Herds of Various Levels of Infection

The objective of this study was to ascertain the value of variables measured on bulk tank and composite milk samples as predictors, respectively, of the level of mastitis in herds and individual cows. The standard of comparison was the results obtained by bacteriological examination of the secretion from individual mammary quarters. It was found, whether sampling at the herd or cow level, that of the three variables measured on each sample, namely somatic cell count, percentage of cell volume in channel 8 (includes cells with individual volumes from 89.2 to 178.3 μm³) and presence or absence of Streptococcus agalactiae , that the ability of the first two variables to discriminate (predict) was not significantly improved by the inclusion of the latter variable. Using values for the former two variables as measured on bulk tank milk and collected at the time of quarter sampling, it was possible to correctly classify 45.5% of the study herds into one of the three quarter infection rate categories considered, namely, < 10, 10-25 or > 25%. The percentage of herds correctly classified was increased to over 80% by inclusion of five monthly counts recorded previous to the time of quarter sampling. Using the same two variables but measured on composite milk samples, 79.4% of cows were correctly classified as being either positive or negative when a positive cow was defined as one having at least one positive quarter. The overall percentage of cows correctly classified decreased from 79.4 to 77.9% when an attempt was made to distinguish between negative cows and cows with one positive quarter. However, this overall percentage progressively increased to 92.7% as the definition of a positive cow was changed from one having one positive quarter to one having two, three or four positive quarters. The procedure shows promise for monitoring the level of mastitis infection in either dairy herds or cows but requires further refinement before consideration could be given to its implementation.

Factors associated with mortality in feedlot cattle: the Bruce County Beef Cattle Project

The design of and the analysis of data from the Bruch County Beef Cattle Project, particularity the field study, are presented and discussed. A major value of the study may lie in its ability to relate laboratory findings to events in the field. The factor most strongly related to mortality was ration, with cattle on hay based rations having a much lower mortality on average than cattle on corn based rations. In general, management activities associated with growing cattle (as opposed to fattening) over the first winter were sparing for mortality. Groups of cattle given prophylactic vaccines or drugs within two days of arrival tended to experience higher mortality (not statistically higher) than those cattle not receiving those measures, or cattle groups recieving the same prophylactics more than 48 hours after arrival. However, these results require validation in the remaining years of the study. Fibrinous pneumonia was the most frequent diagnosis in the calves on postmortem examination.

The longevity of Fasciola hepatica metacercariae encysted on herbage

An experiment was described in which guinea pigs were used as tracer animals in an attempt to assess the longevity of Fasciola hepatic metacercariae on pasture at Werribee, Victoria. The metacercariae had been encysted on both an irrigated and non-irrigated area at various times during 1976. It was determined that, under the conditions of the experiment, metacercariae can survive and remain viable for up to 10 weeks during the winter. It was also determined that longevity during the summer was greatly reduced, and was of the order of only 1 week. The significance of these findings, with respect to the epidemiology of the disease, was discussed.

The effect of prior infection with Fasciola hepatica on the resistance of sheep to the same parasite

The development of flukes that resulted from a challenge dose of 175 F. hepatica metacercariae was compared in 4 groups of sheep that were maintained under grazing conditions on fluke-free pasture. One group had been previously uninfected and all subgroups of each of the other 3 groups had been exposed to one of a range of previous doses of metacercariae. The preliminary infections of 2 of the 3 groups had been terminated respectively after 7 and 14 weeks. The third previously infected group had received its preliminary infection as 2 doses of metacercariae, 7 weeks apart. The latter infection had been terminated after 14 weeks. No appreciable differences in the mean numbers, length, prepatent period or fecundity of flukes, established as a result of the challenge dose of metacercariae, were detected between the control group and the 3 previously infected groups. It was concluded that under the conditions of the present experiment no evidence was detected that would suggest that previous infection with F. hepatica conferred any significant resistance to a future challenge.