A multilocation clinical trial in lactating dairy cows affected with clinical mastitis to compare the efficacy of treatment with intramammary infusions of a lincomycin/neomycin combination with an ampicillin/cloxacillin combination

A study was conducted to compare the efficacy in lactating dairy cows of intramammary infusions in quarters affected with clinical mastitis between a formulation containing 330 mg lincomycin and 100 mg neomycin in a 10-mL aqueous solution (LINCOCIN(R) FORTE S, Pharmacia & Upjohn) and a formulation containing 75 mg ampicillin and 200 mg cloxacillin in an oil suspension (AMPICLOX(TM), Pfizer Animal Health). This study was designed as a multicentre clinical trial involving investigators in France, Germany and Belgium and carried out according to the European Commission guidelines on Good Clinical Practices. Cows in the herds were monitored for clinical mastitis. When evidence of clinical mastitis was detected in a single quarter, a pretherapy milk sample was collected from the affected quarter. After milk sampling, the cow was assigned to one of the two treatment groups at random and treated with an intramammary infusion of one syringe of either LINCOCIN(R) FORTE S or AMPICLOX(TM) for three successive milkings in the mastitic quarter. At 4-5, 13-15 and 20-22 days after first infusion, the veterinarian returned to the farm to conduct a clinical examination and collect milk samples from the affected quarter. Milk samples were cultured for the presence of mastitis organisms and somatic cell count. (SCC) was measured. Following a 10-month study period, 256 cases were enrolled in the study. A total of 232 and 189 cases were analysed for clinical cure and for clinical-plus-bacteriological cure, respectively. The proportions of cases cured clinically and cured clinically-plus-bacteriologically were compared between the two treatment groups. Somatic cell count differences between treatment groups were also tested. The clinical cure rate for LINCOCIN(R) FORTE S (62.5%) was significantly better than for AMPICLOX(TM) (51.8%) (P = 0.035). The clinical-plus-bacteriological cure rate was also significantly better for LINCOCIN(R) FORTE S (38.1%) than for AMPICLOX(TM) (21.7%) (P = 0.005). Among bacteriologically cured cases, the SCC declined in both treatment groups but the SCC was significantly higher for the AMPICLOX(TM) group than for the LINCOCIN(R) FORTE S group (P = 0.036). In conclusion, clinical cure rate, clinical-plus-bacteriological cure rate, and SCC level were significantly better with LINCOCIN(R) FORTE S than for AMPICLOX(TM).