Control of intramammary infections in goats: impact on somatic cell counts.

Udder-half infections were recorded throughout a lactation for 1,060 goats belonging to eight commercial herds. Bacteriological examination from aseptic milk samples and somatic cell counts (SCC) determined by Fossomatic cell counting were performed at the beginning, the middle, and the end of lactation. Coagulase-negative staphylococci (CNS) were the prevalent microorganisms isolated. Geometric means of SCC for uninfected halves or halves infected by CNS or major pathogens were 272 x 10(3) cells/mL, 932,000 x 10(3) cells/mL and 2,443,000 x 10(3) cells/mL, respectively. Two field trials were carried out for evaluation of effectiveness of systematic treatment at drying-off (1 syringe by half) by a combination of penicillin, nafcillin, and dihydrostreptomycin labeled for bovines. In the first trial, all goats (n = 217) of two herds were treated immediately after the last milking, and two herds (n = 196) were used as untreated controls. In the second trial, 215 goats were treated at drying-off. There were no untreated controls. Dry period cures were determined by bacteriological examination of udder-half milk samples collected aseptically at drying-off and 2 wk after parturition. Impact of treatment on SCC was determined from composite milk samples collected monthly after kidding. At parturition, in the first trial, 40 of 202 (19.8%) udder halves were spontaneously cured in the control group vs 169 of 217 (77.9%) in the treatment group. In the second trial, 141 out of 215 treated halves were cured. During the first 75 d in lactation, geometric mean SCC was significantly lower for treated goats than for control goats. After 75 d, SCC for treated and control goats were similar. These data suggest that other methods are required to prevent new intramammary infections throughout the lactation in order to keep a low SCC in goat milk. To determine whether this could be accomplished through teat dipping, half of the goats in five commercial herds were dipped (n = 294) after morning and evening milkings through the lactation (10 mo) with a teat dip product containing nisin. Undipped goats (n = 292) served as a control group. No difference was found for SCC in milk between the dipped and undipped groups. It was concluded that systematic treatment of goats at drying-off is an efficient method for the cure of subclinical mastitis and control of SCC at the beginning of the following lactation and that effectiveness of postmilking teat disinfection remains to be demonstrated.