brucellosis epidemic and negative herd growth in a dairy farm in fars province, iran

In dairy farms, brucellosis would have a small or zero contribution to the annual culling and will not be a limit for expansion of herds, if the preventive protocols are exactly pursued. however, if even one case of brucellosis is reported, the herd will be prevented from selling animals and buying new stock, until it is cleared-off the disease. in a survey on growth rates of 32 dairy herds in iran (provinces of khorasan-razavi, yazd, isfahan, fars, khuzestan, kohgiluyeh and boyer-ahmad), from a total of 25,267 culls in a 5-year period (2018-2022), 136 cases (0.5% of total culls) were culled of brucellosis. while most farms did not have any brucellosis report, 75 cases were reported only in one farm in fars during 2021 and 2022. both parts of the herd were affected: 41 cases in milking herd and 34 cases in replacement heifers. during these years, the total culling rate of the herd exceeded the maximum recommended level, which is 35% for milking cows and 30% for heifers (sum of stillbirths, mortality and culling). the culling rates approached to 39% and 46% in milking cows and 39% and 49% in replacement heifers, respectively in two years. the herd showed negative growth (-11% and -9.5%) in the corresponding years (decrease in the number of milking cows) and as much as 32.2% and 50.5% of total culls were due to brucellosis. the farm had fallen behind its scheduled plans despite investing for expansion in the same years. it was believed that the farm was managed as a closed herd because no new stock was bought for several years. however, other critical control points for prevention of the disease appeared to be ignored. traffic control, boosting the immune system of animals through nutrition and regular vaccination, regular serologic testing and rapid slaughter of positive cases, not borrowing equipment from other farms, having hygienic maternity stalls, etc. are among the requirements of biosecurity in dairy farms.