the invention will be more clearly understood from the following description thereof given by way of example only . to prepare a batch of seal formulation the liquid paraffin is first delivered into a skerman 800l kettle . the mixer is run at 20 rpm . the alugel 30 df ( aluminum stearate ) is then added through the transfer port . the mixer is turned off between additions of the alugel powder . the steam line is opened and the temperature is allowed to rise to 160 to 165 ° c . this temperature is held for approximately 2 hours to sterilize the mixture . at the end of the sterilizing cycle , the condensate valve is opened and blown down . cooling water is then allowed into the jacket to cool the contents to less than 40 ° c . the base thus formed is then checked for quality . if necessary , the batch base may be homogenized for 10 minutes using a silverson homogeniser . the charge port is then opened and 296 kg of the bismuth sub - nitrate is added in 10 kg lots . the contents are mixed for one minute at 20 rpm between additions of each 10 kg of bismuth sub - nitrate . mixing is continued for approximately 1 hour at 45 rpm . the remaining 640 kg of bismuth sub - nitrate is then added in 10 kg lots as above and mixing is continued for 1 hour following the final additions . we have found that the addition of the bismuth sub - nitrate in two separate portions is important in producing a seal which can be processed and used effectively . if necessary , the mixture is homogenized for 15 minutes using a silverson homogeniser . the product is then transferred to a colibri filling machine for filling into injector tubes . 5 cows were infused in all four quarters at drying off with the seal formulation prepared as described in example 1 . these cows had previously been determined as uninfected in all four quarters . commencing at the first milking after calving , these cows were milked and the composite milk sample collected for analysis . this process was repeated for the first 10 milkings after calving . milk samples were also collected in the same manner from 5 untreated cows . to simulate the milk handling process within the milking system , these milk samples were passed through a fibre filter material used in milking machine filters . the milk samples were then analyzed by mass spectrometry for bismuth concentration . the average bismuth level in milk drawn at first milking was 3 . 3 ppm declining to 0 . 39 ppm at milking no . 10 . the maximum level recorded for any individual cow was 8 ppm at first milking . for untreated cows the levels fluctuated in the range 0 . 001 to 0 . 03 ppm . the seal formulation described in example 1 was administered at drying off and has been shown to reduce the incidence of new infection in the dry cow period and in the period around calving . this reduction appears to be comparable with that achieved by prophylactic antibiotic treatment . thus , the seal of the invention very surprisingly offers a non - antibiotic approach to dry cow period prophylaxis . 2 teats in each cow infused at drying - off with seal and remaining teats untreated ( day 0 ). 3 days later ( day 3 ) all teats were inoculated into the teat canal ( depth of 4 mm ; using 22 cfu of streptococcus dysgalactiae code m and an inoculum volume of 0 . 1 ml ). new infections resulting from use of the inoculum occurred in five ( 5 ) of the untreated quarters in the period day 3 to day 13 . new infections resulting from use of the inoculum occurred in two ( 2 ) of the treated quarters in the period day 3 to day 13 . resulting new infections were monitored daily for 10 consecutive days after inoculation ( to day 13 ). samples of secretion were collected in an aseptic manner from quarters showing signs of clinical mastitis prior to treatment with antibiotics . all quarters in all 4 cows were sampled in an aseptic manner on day 13 ( the last day of the trial )— these samples were used to : ( 2 ) monitor the level of str . dysgalactiae surviving in the teats after 10 days 2 teats in each cow infused at drying - off with seal and remaining teats untreated ( day 0 ). 3 days later ( day 3 ) all teats were inoculated into the teat canal ( depth of 17 mm ; using 1 , 190 cfu of streptococcus dysgalactiae code m and an inoculum volume of 0 . 1 ml ). new infections resulting from use of the inoculum occurred in twenty ( 20 ) of the untreated quarters in the period day 3 to day 13 . new infections resulting from use of the inoculum occurred in eight ( 8 ) of the treated quarters in the period day 3 to day 13 . resulting new infections were monitored daily for 10 consecutive days after inoculation ( to day 13 ). samples of secretion were collected in an aseptic manner from quarters showing signs of clinical mastitis prior to treatment with antibiotics . all quarters in all 17 cows were sampled in an aseptic manner on day 13 ( the last day of the trial )— these samples were used to : ( 2 ) monitor the level of str . dysgalactiae surviving in the teats after 10 days . * a total of 4 quarters were infected in three cows and these quarters were excluded from the study . therefore 32 quarters were assigned to each treatment . a total of 528 cows in three commercial herds were used . each herd had a general history of dry period mastitis . the breed of the herds was predominantly fresian or fresian crosses . cows with at least three uninfected quarters , immediately prior to drying off , were identified within the three herds . all individual quarters were assumed to be independent units . the treatments used were as follows 1 . negative control - untreated , no infusions at drying off , but teat ends were sanitized with alcohol soaked cotton wool swabs . 2 . positive control - treated with 250 mg cephalonium in a long - acting base , infused at drying off . this product is known as cepravin drycow . cepravin is a trademark of mallinckrodt veterinary . 3 . antibiotic with seal - cloxacillin benzathine 600 mg in a 4 g unit dose infused at drying off and followed immediately by an infusion of 4 g of a blend of bismuth sub - nitrate ( 66 %) in liquid paraffin with 8 . 5 % alugel 30df . 4 . seal - bismuth sub - nitrate 66 % w / w in liquid paraffin with 8 . 5 % alugel 30 df in a unit dose of 4g infused at drying off . these treatments were randomized among the 528 cows determined to have three or four uninfected quarters at drying off . the treatments were randomized between quarters to achieve as far as possible the same number of quarters per treatment , left and right , front and back . bacteriological results for individual quarters at drying off and at calving were compared to calculate the incidence of new intramammary infections ( imi ). chi - square testing was used to compare the incidence of new infection between quarters , treatments and controls . this experiment has demonstrated that the antiinfective - free seal formulation of the invention administered at drying off is very surprisingly equivalent in terms of prophylactic efficacy , to a long acting dry cow antibiotic . all three treatments reduced new imi during the dry period by approximately 85 %. surprisingly , there was no significant difference between the antibiotic based treatments and the antibiotic - free treatment of the invention . thus , this study has shown that by physically sealing the teat canal with a seal which has no bacteriostatic or bacterial action , the dry period imi may , surprisingly , be controlled . the invention has the potential therefore of achieving dry period prophylaxis on a wide scale , at a lower unit cost , and with no risk of antibiotic residues after calving . the invention is not limited to the embodiments hereinbefore described which may be varied in detail . new intrammary infections ( imi ) identified during the study , grouped by period and by herd .
an antiinfective - free formulation for prophylactic treatment of mastitis in dry cows comprises a seal formulation having approximately 65 % by weight of bismuth sub - nitrate in a gel based on aluminum stearate . the seal formulation is prepared by adding the bismuth sub - nitrate to the gel base in at least two separate stages .