Effects of intramammary infection and dry-off treatment on the immune-metabolic profile of Alpine dairy goats

Sixty Alpine dairy goats were classified as healthy (HEAL, n = 30) or infected (INFE, n = 30) based on bacteriological culture of udder-half samples collected 7 d before dry-off. At -61 d from kidding (DFK), goats were dried off and randomly allocated to 2 homogeneous groups either receiving no treatment (15 HEAL, 15 INFE) or being treated intramammarily with 250 mg of cefazolin per half-udder (15 HEAL, 15 INFE). Milk yield, composition, and SCC were monitored at -82, 17, 45, and 80 DFK, and blood samples were collected at -66, -56, -7, and 8 DFK to assess plasma analytes. Antibiotic administration at dry-off did not affect productive performances in the new lactation or plasma analyte trends. Regardless of udder health status, lactose decreased in late lactation despite stable yield, likely due to increased SCC and mammary permeability during involution. The INFE goats had higher SCC before dry-off and higher SCS at 45 DFK. Following dry-off, plasma urea decreased across all groups, reflecting dietary changes aimed at easing milk cessation. Glucose and nonesterified fatty acids (NEFA) remained stable during the dry period. The INFE goats showed elevated plasma cholesterol at -57 DFK, suggesting transient dyslipidemia due to IMI. After kidding, all goats showed peaks in NEFA, NEFA/albumin ratio, BHB, bilirubin, and glutamate oxaloacetate transaminase, indicating body reserve mobilization and hepatic stress. Concurrently, increases in haptoglobin and ceruloplasmin, and decreases in albumin/globulin ratio and paraoxonase, reflect an acute phase response. The INFE goats showed higher reactive oxygen metabolites and thiol concentrations between -57 and 8 DFK, and elevated ceruloplasmin at -7 and 8 DFK, indicating sustained systemic inflammation. Plasma analytes could serve as effective diagnostic tools to improve the detection of subclinical mastitis in dairy goats.