The effect of treatment with long-acting antibiotic at postweaning movement on respiratory disease and on growth in commercial dairy calves.

Bovine respiratory disease (BRD) is a major concern when raising replacement heifers because of the high incidence and long-term effects of this disease, such as decreased growth and increased time to first calving. The objective of this study was to determine the effect of tulathromycin (TUL) treatment at postweaning movement on the incidence of BRD in dairy replacement heifers. A total of 1,395 heifers were enrolled between November 2006 and June 2007 at a commercial heifer-raising facility. Calves were randomly assigned either to treatment with TUL or to a positive control group treated with oxytetracycline (TET). Calves treated with TUL were 0.5 times (95% CI: 0.4 to 0.7) less likely to be treated for BRD in the 60 d following enrollment than calves treated with TET. For calves that had no history of BRD in the pre-enrollment period, TET calves weighed 4.9+/-0.5kg less than TUL calves after 6 wk in group housing. If calves were treated for BRD in the pre-enrollment period, there was no treatment effect on growth. Calves with clinical BRD in the 60 d following movement weighed 7.9+/-0.6kg less than calves without BRD after 6 wk in group housing. Treatment with TUL at the time of movement to group housing had a beneficial effect on the health and performance through the prevention of BRD in dairy calves with no prior history of the disease. Moreover, BRD after movement to group housing after weaning had a significant effect on the growth of dairy calves.

Microbiological quality of bulk tank raw milk in Prince Edward Island dairy herds.

The objectives of this study were to evaluate microbiological quality of bulk tank milk in Prince Edward Island, to evaluate correlation among milk quality criteria, and to determine seasonal effects on milk quality parameters. Bulk tank raw milk quality was evaluated on all Prince Edward Island dairy herds (n = 235) over a 2-yr period (March 2005 to March 2007). Biweekly total aerobic (TAC), preliminary incubation (PIC), laboratory pasteurization, and coliform (CC) counts were determined using a Petrifilm culture system. Additionally, bulk tank somatic cell count was determined weekly. The mean and median values were 12.8 x 10(3) and 4.9 x 10(3) cfu/mL for TAC, 29.6 x 10(3) and 13 x 10(3) cfu/mL for PIC, 87 and 12 cfu/mL for laboratory pasteurization count, 21 and 5 cfu/mL for CC, and 218 x 10(3) and 187 x 10(3) cells/mL for somatic cell count. There was moderate correlation (0.57) between TAC and PIC. All other correlation coefficients were low (<0.26). Correlation results suggest that a single quality parameter could not predict others used in this study. Seasonal data indicate that 1) in general, all counts tended to be low in winter, 2) the CC and somatic cell count were always high in summer, and 3) TAC tended to be high during summer.

Adherence and efficacy of an external teat sealant to prevent new intramammary infections in the dry period.

The efficacy and adherence of an external teat sealant applied at drying off was evaluated in 2 studies between 1997 and 1999. At drying off, 2 quarters were randomized to receive intramammary dry-cow antibiotic therapy, and the remaining 2 quarters were treated with either a single or double application of external teat sealant. Approximately 3 d before calving, all teats that had been dipped at drying off were redipped in a single coating of teat sealant. Adherence of the teat sealant was scored for the first 2 wk after drying off, and physical traits of the teat skin and teat ends were recorded. Quarter milk samples were collected 1 wk before drying off, at drying off, 0 to 7 d, and 14 to 21 d postcalving. Somatic cell counts were determined from quarter samples taken at d 7 and 14 to 21 d after calving. Data were analyzed from 172 dry periods of 162 cows. The mean time of sealant adherence following drying off application was 3 +/- 0.13 d. Double sealant application significantly increased the duration of adherence by 0.67 d. Teats that had teat sealant applied twice at drying off and that had up to 3 d of adherence had the lowest linear score (LS) at 14 to 21 d (1.89 +/- 0.31) of all quarters. The LS of quarters that received antibiotic therapy only was 2.27 +/- 0.19. The majority of intramammary infections identified at drying off were caused by the minor pathogens, coagulase-negative staphylococci and Corynebacterium bovis (51 and 23%, respectively). The results from this study indicate that duration of sealant adherence to the teat-end should be considered when evaluating the impact of teat sealant treatment at drying off on the level of infection after calving. Double sealant application, cooler seasons, and longer teat lengths were associated with a significant increase in the duration of sealant adherence to the teat-end.

Herd management factors that affect duration and variation of adherence of an external teat sealant.

During 1998 and 1999, a purposive sample of Ontario dairy herds was enrolled in a study to examine management factors associated with adherence of an external teat sealant. A total of 74 herds were recruited that had previously complied with a provincial Sentinel Herd mastitis study. All herds were sent a management survey and a commercially available external teat sealant product. The sealant was applied to all cows in first lactation or greater that were scheduled to go dry. Adherence of the teat sealant was scored on a scale of 1 to 5 (1 = sealant completely removed) for the first 12 d following dry off. Complete data were analyzed from 806 cows in 48 herds (mean of 17 cows/herd). Mean duration of adherence of the teat sealant was 4 d (range 1 to 7 d). Of the management factors recorded, only changing the feed to reduce milk production prior to drying off was significantly associated with 0.78-d prolonged adherence. No factors related to dry cow housing, bedding material, or floor surface were associated with the duration of adherence. The variance around the duration of adherence was examined. The median variance of adherence was 3.0 d(2), which was equivalent to a standard deviation of 2.6 d. Herds in which dry cows were housed in tie-stall barns, and the herds that used a penicillin and novobiocin combination dry cow antibiotic had the greatest variation. We concluded that modifying the ration to reduce milk production enhanced adherence of an external teat sealant. Teat-end preparation prior to application of the teat sealant is an important factor to consider when choosing to adopt this dry period mastitis prevention strategy. This study demonstrates that beyond cow- and quarter-level factors, herd management factors can influence the duration and variation of sealant adherence experienced among different herds.

Test characteristics from latent-class models of the California Mastitis Test.

We evaluated (using latent-class models) the ability of the California Mastitis Test (CMT) to identify cows with intramammary infections on the day of dry-off. The positive and negative predictive values of this test to identify cows requiring dry-cow antibiotics (i.e. infected) was also assessed. We used 752 Holstein-Friesian cows from 11 herds for this investigation. Milk samples were collected for bacteriology, and the CMT was performed cow-side, prior to milking on the day of dry-off. At the cow-level, the sensitivity and specificity of the CMT (using the four quarter results interpreted in parallel) for identifying all pathogens were estimated at 70 and 48%, respectively. If only major pathogens were considered the sensitivity of the CMT increased to 86%. The negative predictive value of the CMT was >95% for herds with major-pathogen intramammary-infection prevalence <15%, so that selective dry-cow therapy might be reasonable for such herds if cows were screened with the CMT.

Efficacy of two hydrogen peroxide teat disinfectants against Staphylococcus aureus and Streptococcus agalactiae.

An experimental teat dip containing 0.5% hydrogen peroxide as the active ingredient was compared with a teat disinfectant also containing 0.5% hydrogen peroxide that is commercially available throughout North America. The study was conducted under conditions of experimental challenge with a positive control following the guidelines recommended by the National Mastitis Council. The efficacy of the test product and the positive control product were compared in 45 cows, with 89 total teats receiving each product after milking during a 10-wk study period. There was no significant difference between the experimental hydrogen peroxide product and the positive control in new intramammary infections caused by Staphylococcus aureus (27.0 and 18.0% in the treatment groups, respectively). Additionally, there was no significant difference between the experimental product (6.7%) and the positive control groups (4.5%) in new intramammary infections caused by Streptococcus agalactiae. Traditional analysis of teat skin condition changes supported improved teat skin condition with the test disinfectant. After accounting for the correlation of teats within cow, significant differences were also observed between the treatment groups for teat skin condition. The experimental hydrogen peroxide-based teat disinfectant provided efficacy similar to that of the positive control teat disinfectant, with significant improvement in teat skin condition and no adverse effects on teat end condition.

An evaluation of two indirect methods of estimating body weight in Holstein calves and heifers.

Monitoring the growth of replacement heifers is a useful management tool to assist producers in achieving a reasonable goal for age at first calving. Standard growth curves have been established, and heart girth tapes are widely available to estimate body weight (BW). Probably the easiest, and undoubtedly the most accurate, means of determining the actual BW of heifers is by using a calibrated electronic scale. However, if an electronic scale is not available, indirect methods of BW estimation are required. The hipometer is a new indirect tool that uses the external width between the greater trochanters of the left and right femurs to estimate BW. The purpose of this observational study was to evaluate the hipometer and the heart girth tape to estimate the BW of Holstein heifers, as compared with their actual weight recorded by an electronic scale. A total of 311 Holstein heifers in 4 research herds, ranging in age from 1 wk old to immediately prior to calving (24 mo), were used in this comparison. The mean BW of all heifers was 261 +/- 124 kg. The Pearson values of the correlation between the scale and hipometer weights, and the scale and tape weights were 0.92 and 0.94, respectively. The concordance correlations of scale weight with hipometer and tape weights were 0.98 and 0.99, respectively. The agreement among the 3 methods, as assessed by the kappa statistic, was substantial for heifers aged 3 to 15 mo. However, poor to no agreement was observed in heifers younger than 3 mo, as well as at 15 mo of age or greater (kappa 0 to 0.18). This is of particular concern because these groups represent the age when dairy heifers would be weaned (< 3 mo) and the age when breeding would normally commence (> 15 mo). We concluded that the hipometer is an easy and useful alternative method of estimating the BW of Holstein heifers, particularly in heifers aged 3 to 15 mo.

Association of cow and quarter-level factors at drying-off with new intramammary infections during the dry period.

Our objective was to describe cow and quarter-level factors associated with drying-off, and to evaluate their impacts on new intramammary infections (IMI) during the dry period. Data from 300 cows in five research herds were collected starting 2 weeks prior to scheduled drying-off. Variables of interest included daily milk production, teat-end integrity, formation of the teat-canal keratin plug, and quarter-milk bacteriological culture results. Overall, 11% of quarters developed new IMI in the dry period; this varied by herd, parity and time of the study. Most new IMI were caused by environmental streptococci and coliform organisms (34 and 30%, respectively). Quarters that had a cracked teat-end had higher odds of developing new infections than those without cracks (15 and 10%, respectively). Quarters that formed a keratin plug early in the dry period had a lower odds than those that did not close (10 and 14%, respectively). After 6 dry weeks, 23% of quarters were still open. The hazard of quarters closing if milk production on the day prior to drying-off was >21 kg 1.8-times less.

The association between bulk tank milk analysis for raw milk quality and on-farm management practices.

Our objective was to determine the risk factors associated with bacteriological quality of bulk tank milk. Bulk tank milk samples were collected from all Prince Edward Island dairy herds (n=235) from March 2005 to March 2007. Biweekly total bacterial, preliminary incubation, laboratory pasteurization, and coliform counts were conducted using a Petrifilm culture system. Data for on-farm risk factors were collected via a mail-out survey which consisted of 4 main sections: (1) general farm demographics and management, (2) cow cleanliness and hygiene, (3) milking procedures and mastitis control, and (4) equipment maintenance and cleaning. Of 235 producers, 153 completed the mail-out survey giving a response rate of 65%. Both total aerobic and preliminary incubation counts were positively associated with the amount of soiling on the teats prior to udder preparation, manual cleaning of the bulk tank, and the use of a specific type of detergent. Additionally, various methods of premilking udder preparation were important, with pre-dip followed by drying being superior to other methods in reducing the bacterial counts. The laboratory pasteurization count was positively associated with the presence of a plate cooler and inadequate frequency of acid wash, whereas having a water purification system was negatively associated with laboratory pasteurization count. Finally, coliform count was negatively associated with clipping udder hair and automated washing of the bulk tank, whereas increasing herd size and inadequate frequency of acid wash were risk factors. Season was a significant predictor for all bacterial counts with the lowest counts tending to occur in winter.

Efficacy of intramammary tilmicosin and risk factors for cure of Staphylococcus aureus infection in the dry period.

The objective ofthis study was to evaluate the efficacy of intramammary tilmicosin, administered at drying-off, for eliminating Staphylococcus aureus infection, and to identify risk factors for S. aureus cure during the dry period. A total of 219 naturally infected cows, representing 308 quarters, were randomized to receive either one of two treatments at drying-off. Cows received either an intramammary infusion of 500 mg of benzathine cloxacillin, or a sterile solution containing 1,500 mg of tilmicosin. All cows had quarter milk samples taken aseptically three times before dry-off, and at wk 1, 2, and 4 of the subsequent lactation. Overall, 62% of cows and 67.5% of quarters infected with S. aureus cured during the dry period. The cure following administraton of tilmicosin was 67.3 and 72.5% for cows and quarters, respectively. By comparison, the cure achieved with cloxacillin was 56.9 and 62.9% of cows and quarters. Cows receiving tilmicosin were 2.1 times more likely to cure. The cure rate for cows decreased as the linear score on the last DHI test increased, and as the amount of S. aureus being shed increased. Quarters that cultured positive multiple times before drying-off were less likely to cure. Staphylococcus aureus infections located in front quarters of the udder were 2 times more likely to cure than those in hind quarters. Results of this study demonstrate that intramammary tilmicosin at drying-off is efficacious in curing existing S. aureus during the dry period. Risk factors associated with the cure of S. aureus were identified.

The efficacy of intramammary tilmicosin at drying-off, and other risk factors for the prevention of new intramammary infections during the dry period.

The objective of this study was to compare the efficacy of an intramammary infusion, containing tilmicosin phosphate, to an infusion of a negative control intramammary placebo for preventing new intramammary infections (IMI) during the dry period. Cows were enrolled from 24 dairy herds from three geographical regions of Canada. Data from 248 cows and 938 bacteriologically negative quarters at drying-off are summarized. Overall, the rate of new IMI during the dry period was 16.7% of quarters. The new infection rates for quarters that received intramammary tilmicosin compared with the intramammary placebo were 14.4 and 19.4%, respectively. The majority of new IMI was caused by coagulase-negative staphylococci (49%) and environmental streptococcal organisms (26.8%). The probability for quarters to develop new IMI in the dry period was significantly increased when cows had higher milk production before drying-off (P = 0.04), when cows had longer dry periods (P = 0.02), and when dry cows were housed in tie-stall barns (P = 0.002). Higher parity cows and those that had a linear score somatic cell count (SCC) above 4 on the last DHI test were also at increased risk for new IMI (P < 0.10). Administration of intramammary tilmicosin appears to be an efficacious therapy for prevention of new IMI; however, there is currently no approved intramammary formulation of this product available. Use of blanket dry cow antibiotic therapy compared to selective dry cow therapy, as well as the importance of identifying risk factors and managing the environment of dry cows are discussed.