Monitoring udder health status using somatic cell counts in Holstein dairy herds located in north-east of Iran and effectiveness of 10-point mastitis control program

Background: The somatic cell count (SCC) of individual cow samples is a useful proxy for monitoring udder health status. Aims: The present study aimed to provide updated information about udder health in Iranian Holstein dairy cattle, and to quantify the effectiveness of the mastitis control program. Methods: A total of 17,990 monthly test-day records from 1,663 Holstein dairy cattle in 10 “regular” herds and 2,389 test-day records from 386 Holstein dairy cattle in 2 herds that were assigned to the 10-point mastitis control program (“controlled” herds) were included. Each test-day record comprised the date of recording, daily milk production (kg), fat and protein (%), days in milk, parity, and SCC. Results: Median (Q1-Q3) SCC × 10^3 for “regular” and “controlled” herds were 136 (52-391) and 64 (24-204) cells/ml, respectively. Also, the percentage of records containing SCC 200,000 cells/ml (elevated SCC) for these groups were 40.3% and 25.5%, respectively. Mixed effects logistic analysis revealed that milk records from cows in the first lactation, early lactation, and with 40 kg daily milk yield had lower odds of elevated SCC. The odds of elevated SCC were lower in summer and autumn than in winter. Conclusion: Host and environmental characteristics influence SCC. This should be considered for the interpretation of SCC results. Mastitis control programs can support dairy producers to reach a standard level of udder health.