Estudo de caso do consumo de antimicrobianos, da dinâmica de produção e da carga ambiental do Leite de Descarte, um importante impasse na bovinocultura de leite

Abstract

The use of antimicrobials in dairy cows raises concerns due to their high consumption, the presence of residues in products, the development of microbial resistance, and the release of pharmaceutical residues into the environment. Clinical mastitis (CM), a recurrent and economically significant disease in dairy cattle, is one of the main reasons for the use of these drugs. During CM treatment, milk secretions containing pharmaceuticals form Waste Milk (WM), a waste product not intended for processing and generally used to feed calves, a controversial practice due to its environmental and health implications. This study analyzed the use of antimicrobials to treat CM in dairy cows from a farm in Minas Gerais, Brazil, using historical data from 2020 to 2023. Information such as occurrence date, animal identification and weight, affected mammary quarter, medication used, and treatment duration was evaluated. To understand the entry of these drugs into the environment, the excretion levels of the most commonly used antimicrobials were investigated: Ceftiofur (CEF), Cefapirin (CEPA), Kanamycin (KAN), Cephalexin (CFX), and Cefquinome (CFQ). Data on dosage, application frequency, and excretion rates were collected and analyzed using mathematical modeling. Over the 1,459 days analyzed, the average body weight of the animals was 631.30 ± 72.7 kg, an estimated value but considered very close to the real weight based on internal evaluation (ScoreP). The most affected mammary teat was the left front (29.4%), followed by the left teat (24.7%), with no clear seasonal pattern. The number of treatments per antimicrobial was: CEF = 313, CFX = 79, KAN = 79, CFQ = 73, and CEPA = 7. During the period, 86 animals were treated, with 720 CM cases in teat recorded and 551 antimicrobial treatments applied. The average treatment duration was 6.4 days (CEF), 9.4 (CFQ), 6.6 (CFX and KAN), and 9.6 (CEPA). Except for CEF, all treatments exceeded the recommendations on drug labels. The farm produced 1,509,645.5 liters of raw milk (RM) and 148,651.0 liters of WM, with an average ratio of 10.25 liters of RM per 1 liter of WM. WM was allocated to calf feeding (74.9%) and environmental disposal (25.1%). WM was identified as the primary route for antimicrobial entry into the environment. The average concentrations predicted in WM were 1.07 mg/L of CEF, 0.09 mg/L of CFX, 0.09 mg/L of CEPA, and 0.0001 mg/L of KAN, with no CFQ detected. In the urine of lactating cows, the values were 0.018 mg/L (CFX), 0.015 mg/L (KAN), 0.013 mg/L (CEF and CFQ), and 1.63×10−5 mg/L (CEPA). In feces, the values were 0.007 mg/kg (CEF), 0.001 mg/kg (CFX and KAN), 0.0005 mg/kg (CFQ), with no CEPA detected. The risks of using WM for calf feeding are discussed, with proposed alternatives such as biomaterial production, chemical treatments, and biogas production. This research presents a systematic and innovative environmental approach to understanding antimicrobial consumption, production dynamics, and the environmental burden of Waste Milk.