A. Glickman

Development of a Staphylococcus aureus vaccine against mastitis in dairy cows. I. Challenge trials.

A vaccine composed of three field isolates of Staphylococcus aureus (S. aureus) derived from cases of mastitis in cows was developed. The vaccine was administered to nine uninfected cows while 10 other cows were used as controls. All cows were challenged with a highly virulent S. aureus strain administered into two quarters of each cow. Quarters were tested for clinical signs, secretion of S. aureus, and somatic cell count (SCC). No systemic effects were observed in any of the cows, vaccinated or control. Vaccinated cows had 70% protection from infection compared with fewer than 10% in the controls. Moreover, all quarters challenged in the vaccinated cows, regardless of whether they were successfully infected or not with S. aureus, exhibited very mild inflammatory reactions, identified by their low SCCs (<100,000).

Udder disease etiology, milk somatic cell counts and NAGase activity in Israeli Assaf sheep throughout lactation.

Bacterial pathogens causing udder infections in Israeli Assaf dairy sheep were identified and changes occurring throughout lactation were monitored to study the correlation between the contaminant and the severity of the infection, as measured by somatic cell count (SCC) and NAGase tests. A total of 159 Israeli Assaf dairy sheep on one farm, in their first (69), second (13) or third and more (77) lactations were included in this study. Udder halves were tested for bacterial condition, SCC and NAGase activity 2-3 weeks post lambing and every 4 weeks after until drying-off. At first sampling, in 60.7% (193/318 quarters) of the halves no bacterial growth (NBG) was detected. Different species of coagulase negative staphylococci (CNS) were the main pathogen group in infected udders. Streptococci were isolated from 14 halves, most of them in the two udder halves. The percent of udder infection in sheep in their third or further lactations was 2.8 greater (P<0.05) than in that of sheep in their first lactation. During the lactation, 90.6% of the halves did not change their classification status, suggesting that most infections occur before lambing and/or during the following first few days. The arithmetic mean of SCC and NAGase of total half udder milk and samplings (during the lactation) were 1144+/-48x10(3)cells/ml and 49.4+/-2.5, respectively. The average SCC in the milk of halves classified as NBG was 321+/-35x10(3)cells/ml and was not significantly changed during the lactation period. In halves infected with CNS, average SCC was 1371+/-150x10(3)cells/ml at the first testing and increased to 2129+/-347x10(3)cells/ml at drying-off. No significant differences were found in SCC and NAGase activity between the different species of the CNS. The mean SCC over the types of bacteria isolated, lactation number and days in lactation was significantly different (P<0.0001). In 4% of the halves, from all samples, SCC was above 5000x10(3)cells/ml although no bacteria were detected in their milk. The higher SCC in the CNS infected halves contrasted with the more moderate SCC found in dairy cows similarly infected, suggesting that the sheep udder has a lower resistance and an augmented immunological response against this group of bacteria. Thus, this should be considered accordingly in schemes for sheeps milk quality payment.

Udder infection and milk somatic cell count, NAGase activity and milk composition—fat, protein and lactose—in Israeli-Assaf and Awassi sheep

The present study aimed to identify the pathogens that cause subclinical udder infections in Israeli dairy sheep and evaluate their influence on milk yield and composition. Eight hundred and fifteen Israeli-Assaf and Israeli-Awassi dairy sheep were surveyed. More than half of the sheep were in their third or higher lactation (513/815 sheep) and in 14 out of 20 flocks; the sheep were in their peak (second to third month) of lactation. The percentage of bacteriological infected udders in the flocks ranged from 8.6 to 64.3%. The effect of the bacteriological infection on somatic cells count (SCC) was significant ( P> 0.001). Various species of coagulase-negative staphylococci (CNS) mainly S. chromogenesand S. epidermidis, formed the main pathogen group in infected udders. Lactation number did not significantly influence either the infection rate of udder halves or the milk SCC, although the percentage of udder halves with no bacteriological findings found was higher at first lactation than at the second and third lactation. Milk yield was significantly higher in uninfected than in infected halves. Milk composition—fat, proteins and lactose—varied among flocks, with mean total protein lower in uninfected halves than in infected ones and lactose higher in uninfected than in infected halves.

Effect of subclinical intramammary infection on somatic cell counts, NAGase activity and gross composition of goats' milk

The study was aimed at identifying the pathogens causing subclinical udder infections in representative Israeli dairy goat herds and determining their effect on milk quality. Five hundred goats in ten flocks of various breeds and crossbreeds were surveyed. Of the 500 goats, 13.4% were in their first lactation, 36.4% were in their second lactation and 50.2% were in their third or higher lactation. Percentages of udder halves with subclinical intramammary infection in the flocks ranged from 35 to 71%. The effect of the bacteriological infection on somatic cells count (SCC) was significant (P<0.001). Various species of coagulase-negative staphylococci (CNS), mainly Staphylococcus caprae and Staphylococcus epidermidis, were the main pathogens in infected udder halves. Lactation number did not significantly influence either infection rate of udder halves or SCC, although the percentage of udder halves with no bacteriological findings was higher at the first lactation than at the third lactation. Milk composition (fat, protein and lactose) varied among flocks, with lower mean total protein in uninfected halves than in infected ones and higher lactose in uninfected than infected halves.

Efficacy of dry-off treatment in sheep

The efficacy of dry-off treatment of sheep in curing chronic intramammary infections and preventing new ones during the dry-off period and during the following lactation was studied in the present work. A total of 85 Israeli-Assaf dairy sheep on one farm in their first, second, third or more lactations were divided into pairs according to bacteriological condition, somatic cell count (SCC), NAGase activity and lactation number, and were then randomly allocated to one of two groups: one group to receive drying-off treatment, the second as an untreated control. At drying off, sheep in the treatment group received intramammary treatment with a commercial cattle dry-off treatment, which is a combination of penicillin, nafcillin and dihydrostreptomycin. At the first sampling (I), 15–20 days after lambing, cure rates (CR) of 64.9 and 6.5% for the treated and control groups, respectively were significantly different (P<0.001). At the second (II) sampling, 35–50 days after lambing, no change was found in the CR of the control sheep while that of the treated group decreased to 46.4%; this difference was also found to be significant (P<0.005). New infection rates (NIRs) in the treated and control groups were 15.6 and 28.6%, respectively, at sampling I and 27.3 and 42.9%, respectively, at sampling II. Although the NIRs were lower in the treated group, the difference from the control group was not significant. The new infections were mainly due to different coagulase-negative staphylococci. Overall, in both samplings SCCs and NAGase activities were significantly higher (P<0.05) in the infected than in the non-infected halves. No significant differences in these parameters were found between treated and control halves that exhibited no infection nor between those found to be infected. However, at sampling II, the mean SCC and NAGase activity in the infected halves were higher in the treated than in the control ones. Antibiotic residues were detected in five of the 25 sheep sampled on the first day, in three out of 25 on the second day and in only in two sheep on the third and fourth days after lambing. On the fifth day no antibiotic residues were detected. These data suggested that dry-off treatment could reduce intramammary infection and somatic cell count of dairy sheep, but other methods are required to both prevent new infection and maintain healthy udders in the herd.