Mastitis in Dairy

Coliforms and environmental streptococci were the most prevalent pathogens in clinical mastitis samples. The incidence of clinical mastitis in the first 100 days of lactation was significantly lower for the combination treatment than for the antibiotic treatment alone during both drought and rainy weather dry period. However, the reduction on incidence of clinical mastitis was significantly higher during rainy weather dry period (63.26%), compared with the drought weather dry period (33.33%). Benefits/cost ratios for the combination treatment based on the increase in saleable milk were 2.03 and 5.08 during drought and rainy weather dry period, respectively. The use of an internal teat sealant in combination with a long-acting antibiotic at dry off was associated with significantly lower clinical mastitis in the first 100 days of lactation, with a greater difference found during rainy weather dry period.

Introduction

Environmental mastitis has become a major problem, particularly in low bulk tank somatic cell count dairy farms that have successfully controlled contagious pathogens (Hogan et al., 1989). Over the past five years, the incidence and etiology of mastitis in Argentina has changed. Increasing intensification of milk production systems in Argentina, will further increase environmental mastitis. The most frequently isolated pathogens in clinical mastitis samples during early lactation in Argentina were Streptococcus uberis and coliforms (Izak et al., 2010). Bargo et al. (2009), showed a mean incidence rate of clinical mastitis of 24.4 cases per 100 cows between dry off and 90 days in milk. Green et al. (2002) demonstrated that intramammary infections (IMI) during the dry period is an important influence on subsequent clinical mastitis, with a 50% of the cases of environmental mastitis diagnosed within 100 days of calving being attributed to dry period infection. A major factor allowing the invasion of pathogens into the gland during the dry period is often a significant delay in the formation of a complete keratin plug in the teat canal (Williamson et al., 1995; Dingwell et al., 2003), The recognition of the protective effect of the keratin plug and the increasing importance of the environmental pathogens had increased interest in the potential value of internal teat sealants in Argentina. The use of an internal teat sealant in combination with antibiotic dry cow therapy reported significant reductions in the prevalence of IMI after calving and the incidence of clinical mastitis in the first 100 days of lactation (Cook et al., 2004; Newton et al., 2008; Runciman et al., 2010). However, neither of these studies investigated the use of an internal teat sealant in combination with a longacting antibiotic at dry off during drought and rainy weather dry period on incidence of clinical mastitis in the first 100 days of lactation. The aim of this study was to evaluate the efficacy of an internal teat sealant during drought and rainy weather dry period on incidence of clinical mastitis in the first 100 days of lactation.

Materials and Methods

A total of 80 cows in two commercial dairy herds in the Province of Santa Fe, Argentina, with an average of 350 milking cows, were enrolled in the study from January 2009 to December 2010. Dairy farms selected had a bulk tank somatic cell count less than 250,000 cells/ml, were free of Streptococcus agalactiae, and controlled Staphylococcus aureus. Cows eligible for enrollment were in good health, had 4 functional quarters free of teat lesions with no clinical mastitis present on the day of dry off. The cows not have received systemic or intramammary antibiotics or antiinflammatory treatments within 30 days prior to dry off and had an expected dry period length of at least 45 days. All eligible cows were dried off abruptly at the end of the designated milking. At dry off, cows were randomly allocated to receive either an intramammary infusion of 600 mg of benzathine cloxacillin (Orbenin Extra Dry Cow; Pfizer Animal Health) in all four quarters of each cow alone or the same antibiotic combined with an internal teat sealant (TeatSeal; Pfizer Animal Health) in all four quarters of each cow. Dry cows were housed in a pasture-based management system using a concentrate supplement. Clinical cases of mastitis were recorded and sampled throughout the dry period and for the first 100 days of lactation. Clinical mastitis was defined as the presence of visibly abnormal milk and/or abnormal quarter or signs of systemic illness. Isolates were identified according to the procedures of the National Mastitis Council. Chi-square analysis was used to evaluate the differences between the two treatment groups for clinical mastitis. Benefits/cost ratios for the combination treatment were based on the increase in saleable milk of production losses associated with clinical mastitis during the first 90 days of lactation (Bargo et al., 2009). The cost of treatment and labor costs were not included in the assessment. The average milk yield losses for mastitis cases occurring during the first 90 days of lactation (Bargo et al., 2009) was calculated to be 959 lb per case (435 kg per case). The milk price was $0.35/kg and the cost of the teat sealant was $7.5 per cow.

Results and Discussion

Of the 80 cows enrolled in the study during drought dry period in 2009, 40 cows received the internal teat sealant in combination with antibiotic dry cow therapy and the remaining 40 received the antibiotic alone at dry off. Of the 78 cows enrolled in the study during rainy weather dry period in 2010, 42 cows received the internal teat sealant in combination with antibiotic dry cow therapy and the remaining 36 received the antibiotic alone at dry off. During the drought dry period, in the cows given the combined treatment there were 4 cases of clinical mastitis (10% of cows) in 4 quarters (2.5% of quarters) between dry off and 100 days in milk, compared with 6 cases of clinical mastitis (15% of cows) in 6 quarters (3.75% of quarters) in the group treated with antibiotic alone. The proportion of quarters experiencing a clinical mastitis event between dry off and 100 days in milk was significantly lower for combination treatment vs. antibiotic alone (P<0.05). The reduction in the proportion of cows treated for mastitis during the first 100 days of lactation was 33.33%. During the rainy weather dry period, in the cows given the combined treatment there were 6 cases of clinical mastitis (14.29% of cows) in 6 quarters (3.57% of quarters) between dry off and 100 days in milk, compared with 14 cases of clinical mastitis (38.89% of cows) in 14 quarters (9.72% of quarters) in the group treated with antibiotic alone. The proportion of quarters experiencing a clinical mastitis event between dry off and 100 days in milk was significantly lower for combination treatment vs. antibiotic alone (P<0.01). The reduction in the proportion of cows treated for mastitis during the first 100 days of lactation was 63.26%. Coliforms and environmental streptococci were the most prevalent pathogens in clinical mastitis samples. Prevalence of bacterial isolates from quarters with clinical mastitis between dry off and 100 days of lactation during drought and rainy weather dry period is shown in tables 1 and 2.

TABLE 1. PREVALENCE OF BACTERIAL ISOLATES FROM QUARTERS WITH CLINICAL MASTITIS BETWEEN DROUGHT DRY PERIOD AND 100 DAYS OF LACTATION.

TABLE 2. PREVALENCE OF BACTERIAL ISOLATES FROM QUARTERS WITH CLINICAL MASTITIS BETWEEN RAINY WEATHER DRY PERIOD AND 100 DAYS OF LACTATION.

The average milk yield losses for mastitis cases occurring during the first 90 days of lactation (Bargo et al., 2009) was 959 lb per case (435 kg per case). Based in the reduction on incidence of clinical mastitis, 23,975 lb (10,875 kg) more saleable milk per 100 cows was available in the combination treatment group during rainy weather dry period. With a value of $0.35/kg of milk sold and the cost of the teat sealant of $7.5 per cow, the benefits/cost ratio of adding the internal teat sealant per 100 cows were 2.03 and 5.08 during drought and rainy weather dry period, respectively.

This study is in agreement with other trials (Cook et al., 2005; Newton et al., 2008; Runciman et al., 2010), which have shown that there is benefit in using an internal teat sealant in combination with dry cow antibiotics compared with antibiotic dry cow therapy alone, in reducing clinical mastitis during the first 100 days of lactation. During the drought dry period, there was a reduction in the proportion of cows treated for clinical mastitis during the first 100 days of lactation, with 15% of cows and 3.75% of quarters in the antibiotic alone group and 10% of cows and 2.5% of quarters in the combined treatment group. During the rainy weather dry period, there was a reduction in the proportion of cows treated for clinical mastitis during the first 100 days of lactation, with 38.89% of cows and 9.72% of quarters in the antibiotic alone group and 14.29% of cows and 3.57% of quarters in the combined treatment group. The incidence of clinical mastitis in the first 100 days of lactation was significantly lower for the combination treatment than for the antibiotic treatment alone during both drought and rainy weather dry period. However, the reduction on incidence of clinical mastitis was significantly higher during rainy weather dry period (63.26%), compared with the drought weather dry period (33.33%). The reduction in the proportion of cows treated for mastitis during the first 100 days of lactation during drought dry period was similar to the study by Godden et al. (2003), which reported a reduction of 33% in the incidence of clinical mastitis between dry off and 60 days of lactation. The reduction in the proportion of cows treated for mastitis during the first 100 days of lactation during rainy weather dry period was higher compared with other trials (Cook et al., 2005; Newton et al., 2008; Runciman et al., 2010). However, the effect of weather during dry period has not been explored in these studies using an internal teat sealant. Godden et al. (2003), observed that quarters dried off during the months of May, June, or July were at significantly higher risk for clinical mastitis between dry off and 60 days of lactation, than for the referent month of August. However, Baillargeon et al. (2010), observed that the combination treatment had no interactions with season of dry off; although the effect was greatest for cows that were dried off in summer, the direction of the effect was the same in all seasons. This study clearly demonstrates that for cows during a rainy weather dry period, the combination of dry cow antibiotic and internal teat sealant resulted in significantly fewer clinical mastitis cases in the first 100 days of lactation. Lopez-Benavidez et al. (2005), reported associations between soil moisture conditions during rainy weather and Streptococcus uberis contamination. In Argentina during rainy seasons, muddy conditions in pastures contribute significantly to environmental mastitis in a dairy herd. Management practices that minimizing exposure to muddy conditions during dry period, may decrease the probability of mastitis at calving. Therefore, in periods of high susceptibility to IMI, such as the dry and calving periods, cows should be managed to prevent the contact of cow teats to environmental pathogens. Coliforms and environmental streptococci were the most prevalent pathogens in clinical mastitis samples. This is in agreement with other reports (Godden et al., 2003; Newton et al., 2008; Izak et al., 2010). Economic justification of adding the internal teat sealant in this study and other reports (Cook et al., 2005; Baillargeon et al., 2010), comes from the reduction in the incidence of clinical mastitis and increase in saleable milk.

Conclusions

The current study demonstrated that the use of an internal teat sealant in combination with antibiotic dry cow therapy is effective in reducing the incidence of clinical mastitis in the first 100 days of lactation during both drought and rainy weather dry period. However, the reduction on incidence of clinical mastitis and benefit/cost ratio were significantly higher during rainy weather dry period. Increasing intensification of milk production systems in Argentina, will further increase environmental mastitis. Therefore, the use of combination treatment with an internal teat sealant at dry off is a practical option to reduce the incidence of clinical mastitis caused by the environmental pathogens.

References

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