Impacto da mastite subclínica na chance de cura durante o período seco de vacas leiteiras
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2019-09-09
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Universidade Federal de Goiás
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Mastitis is the most important factor to increase somatic cell count (SCC) in cow milk; this increase causes numerous losses to dairy farmers and industries. Several studies measuring cure rates of subclinical mastitis during dry-off have been conducted for several decades with different results depending on the type of pathogen involved in the infection, the age and immunity of the cow, the duration of the dry period, and the protocols used in the dry cow therapy. Few studies in Brazil consider infection time and SCC level before dry-off because of the difficulty in accessing or controlling this information. The aim of this study was to evaluate the occurrence of chronic subclinical mastitis in dairy cows before dry-off, the somatic cell count (SCC) values in this period and the odds of subclinical mastitis in the first test day of a new lactation. 2,455 lactations from 2,064 cows were evaluated in 14 farms that included 9,820 individual tests. Lactations were grouped into four categories based on the number of test days ≥ 200,000 cells/mL in the three months prior to dry-off, and were also grouped by the geometric mean SCC of the last three months into five categories. The binary response variable was based on the first test day of the next lactation and was grouped as “healthy” (<200.000 cells/mL) or “subclinical” (≥200.000 cells/mL). Three mixed logistic regression models were created, and also included the explanatory variables parity, duration of dry period, season of calving, season of dry-off. Data set evaluation (model1) showed that 850 (34.5%) of lactations returned with subclinical mastitis in the next lactation. There was a wide variation between the herds and, except for duration of dry period, all variables used influenced the postpartum SCC result. The rate of new cases (Model2) was 20.9% (152/729) and was more influenced by parity, where cows of four or more lactation were more than twice as likely to have a new case compared to second lactation cows (OR=2,40 IC 95% 1,27~4,46). The season of dry-off did not influence the new cases. The cure rate during the dry period was 59.6% (1,028 / 1,726) and ranged from 20.0 to 83.3% between herds. Cows that dry-off with geometric mean SCC below 200,000 cells / mL in the last three months of lactation were six times more likely to cure than cows that dry-off with geometric mean above 1,600,000 cells/mL (OR = 6.41-95% CI). 3.17-13,15). Systematic evaluation of the end lactation SCC can help farmers to make decisions to prevent chronic mastitis and also to establish protocols for management for chronic cows at dry-off, culling must be considered.
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BARBOSA, William Marota. Impacto da mastite subclínica na chance de cura durante o período seco de vacas leiteiras. 2019. 43 f. Dissertação (Mestrado em Zootecnia) - Universidade Federal de Goiás, Goiânia, 2019.