Milking machine test survey of UK herds.
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Animals↗
Biomedical subjects
J E Hillerton
Publications and source records attributed to J E Hillerton.
Treating mastitis in the cow--a tradition or an archaism.
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Animals↗
Errors associated with milk cell counting.
The accuracy of somatic cell counts in milk samples was investigated in four studies. First, the counts recorded by one milk buyer in one supply over six months ranged from 105,000 to 401,000 cells/ml with no apparent changes in the volume of milk consigned or the level of mastitis in the herd that would explain this wide range. Secondly, the counts in daily samples from one bulk milk supply for 28 days ranged from 84,000 to 282,000 cells/ml, again with no apparent changes in the performance of the herd to explain the wide range. Thirdly, the replicated counts recorded for one sample by three separate laboratories agreed closely; however, when a sample with a high cell count was interspersed then two of the three laboratories reported high cell counts suggestive of 'carry-over' in excess of the 2 per cent 'allowable' Finally, cell count data from three separate laboratories on samples from 21 cows for 33 days revealed problems with the misidentification of samples on the farm in 1 per cent of the samples, and misidentification and mishandling of 1 to 2.6 per cent of the samples in the laboratories. All three laboratories differentiated samples from cows with subclinical and clinical mastitis, but the mean cell count of the uninfected cows varied between the laboratories with one of them recording statistically significantly higher counts over the period.
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Streptococcus agalactiae infection in dairy cows.
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Animals↗
Prophylactic effects of two selective dry cow strategies accounting for interdependence of quarter.
Infusion of a long-acting antibiotic preparation at drying off in dairy cows as a prophylactic therapy is usually recommended for all quarters where it is in use. Studying the effectiveness of such treatment using quarter as the unit of analysis assumes that each quarter within a cow has a risk of being infected independent of the other quarters of the cow. Failure to account for interdependence of quarters within a cow may lead to inaccurate variance estimates and errors in assessing treatment effects. Data from two trials assessing different dry-cow strategies were examined for interdependence of infection between quarters. Logistic regression with a variance inflation factor or a multilevel analysis was used to assess the effect of antibiotic and internal teat-sealant dry cow strategies. Parity and infection status at drying off were covariates in the analysis. Interdependence of the risk of quarter infections within control-group cows was demonstrated in both dry-cow antibiotic and teat-seal trials. However, cows that received either of these treatments did not demonstrate interdependence. Treated quarters in both trials were 3.0 times less likely to acquire a new infection at calving compared with the untreated controls. Quarters in cows of parity 3 or greater were also at an increased risk in the antibiotic treatment trial. In both trials, quarters with either Corynebacterium spp. or coagulase-negative staphylococci infections at drying off had an increased risk of a new intramammary infection at calving. This study has demonstrated the beneficial and comparable effects of antibiotic and teat seal dry cow strategies; both decreased the risk of intramammary infection at calving. The application of dry-cow strategies at the cow level and not the quarter level is also supported.
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Evaluation of measurements of the conductivity of quarter milk samples for the early diagnosis of mastitis.
Measurements of the conductivity of quarter milk samples were made in 31 cows in a 70-cow herd in southeast England, for a period of 15 weeks. Over this period, 42 per cent of cow-weeks and 20 per cent of quarter-weeks had an increase in quarter milk conductivity of 10 per cent of more compared with the mean conductivity of the previous 14 milkings. Fourteen per cent of quarter-weeks had an increase in conductivity of 15 per cent or more. The geometric mean somatic cell count (cell count) was higher in quarter-weeks with a 10 per cent or greater increase in conductivity than in quarter-weeks with a conductivity change of less than 10 per cent. At a conductivity threshold of 10 or 15 per cent and a cell count threshold of 200,000 or 400,000 cells/ml the specificity of this system was estimated to be 85 to 92 per cent, the sensitivity 40 to 54 per cent, the negative predictive value 87 to 93 per cent and the positive predictive value 33 to 55 per cent. The positive predictive value of the individual quarter milk conductivity was insufficiently accurate to be used as the sole criterion for the selection of quarters for early antibiotic treatment.
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The effect of selective dry cow treatment on new intramammary infections.
Dry cow therapy, or antibiotic treatment at end of lactation, is used to eliminate intramammary infections and prevent new infections during the dry period. It is one part of a total management system recommended in controlling intramammary infections in the dairy cow. Public health concerns advise prudent use of antibiotics, as their use may promote bacterial antibiotic resistance and leave antibiotic residues in the food chain. The effects of dry cow treatment and no treatment were compared, on new intramammary infections and clinical mastitis within two low cell count herds and two herds undergoing conversion to organic farming. The results will inform those restricting their use of dry cow therapy on the additional risk of new intramammary infection and aid in development of alternative management strategies. No cases of clinical mastitis in the dry period were observed in treated cows, whereas in the untreated groups a significant number were observed. Significantly more new infections at calving were found in the untreated group in all herds. In those quarters where infections were first detected at calving, the incidence of clinical mastitis was significantly greater in the untreated group in all herds. Clinical mastitis detection was significantly lower in organic herds. Untreated quarters infected at drying with Corynebacterium spp. or coagulase-negative staphylococci were found to have an increased risk of new infection by Streptococcus uberis or coliform bacteria. It can be concluded that dry cow therapy continues to lower significantly the rate of new dry period intramammary infection in herds with elevated somatic cell counts and a high prevalence of infection.
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The effect of an intramammary teat seal on new intramammary infections.
As concern over the possible overuse of antibacterials increases, attention has focused on reduction of antibiotic usage and on nonantibiotic alternatives. A nonantibiotic intramammary teat sealant, Teat Seal (Cross Vetpharm Group Ltd., Tallaght, Dublin, Ireland), has been available in Ireland, in combination with an intramammary tube of cloxacillin. Teat Seal has been reformulated for use in cows with low cell counts as an alternative to antibiotic dry cow therapy at the end of lactation. The product is now marketed as Orbeseal (Pfizer Animal Health). A comparison between this teat sealant and no treatment was made on new intramammary infections and clinical mastitis, on all cows within four herds, and on low cell count cows in three herds. No cases of clinical mastitis in the dry period were observed in cows treated with Teat Seal (n = 197), whereas a significant number (6 cows) were observed in the untreated cows (n = 204). In all herds, significantly more new infections at calving were found in the untreated group (62 cows in the untreated group compared with 21 cows in the Teat Seal group). In those quarters where infections were first detected at calving, the incidence of clinical mastitis was significantly greater in the untreated group. Quarters in both treatment groups that were infected at drying off with Corynebacterium spp. or coagulase-negative staphylococci were not protected against new infections and had an increased risk of new infection by Streptococcus uberis. The results will inform those restricting their use of antibiotic dry cow therapy in alternative management strategies and the additional risk of new intramammary infection.
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Changes in cow teat tissue created by two types of milking cluster.
We have investigated the responses of cow teats to machine milking in a study of relatively newly installed commercial milking parlours fitted with one of two types of milking cluster. The first was a common type with a large claw volume (> 200 ml), 15-16 mm i.d. long milk tube, 10 mm short pulse tube, cluster weight < 3-2 kg and used alternate pulsation. The second was a more traditional type with a 150 ml claw bowl volume, 13.5 mm i.d. long milk tube, 8 mm short pulse tube, cluster weight approximately 3.5 kg and used simultaneous pulsation. We scored approximately 50 cows in each of 20 herds, all within 60 s of cluster removal, for changes from the premilking teat condition: teat colour (creation of reddening or blueness), firmness, thickening at the base of the teat associated with the position of the liner mouthpiece, and whether the teat duct orifice was open. There were statistically significant differences in the proportion of cows displaying these four alterations in teat condition between herds using the two types of cluster. The more common type of cluster was always associated with better teat condition. The cause and effect of poorer teat condition have not been fully established and are likely to be multifactorial. The principal risk factors may be cluster weight, overmilking, vacuum applied during the overmilking phase and the design of the liner mouthpiece.
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Models of temporal variation in questing activity in individuals of Ixodes ricinus (Acari: Ixodidae).
Intensive observations of the questing activity of Ixodes ricinus ticks in the field were made to provide data on the range of durations of periods of continuous questing activity, and of the variation in questing activity between individuals. Continuous periods of questing were observed to extend to a maximum of 28 hours. Substantial variation in questing activity between individuals was observed. Models fitted to the distribution of durations of bouts of questing activity provide insights into the questing ecology of I. ricinus. Results suggest that questing duration may not be solely dependent on the state of hydration of the tick. A function fitted to the frequency distribution of the proportions of active life that individuals spend on questing, provides an empirically-based model that can be used to generate a stochastic expression of variation of questing activity in individuals in a questing population.
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Comparison of treatment of mastitis by oxytocin or antibiotics following detection according to changes in milk electrical conductivity prior to visible signs.
Mastitis was induced in dairy cows by infusion of 500 cfu of Streptococcus uberis into the mammary gland. Most infections developed to clinical disease, and the majority were predicted by changes in the electrical conductivity of the foremilk. The benefits of clinical prognosis and bacteriological cure were determined for cases that were treated when predicted to develop into clinical mastitis and compared with cases that were allowed to develop until milk clotted or until pyrexia before intramammary antibiotic treatment was used. Treatment prior to clinical mastitis included use of intramammary antibiotic or intramuscular oxytocin to allow stripping of residual milk to remove bacteria. All infections in which treatment was delayed resulted in clinical mastitis that was cured clinically and bacteriologically by sustained treatment using a broad-spectrum intramammary antibiotic preparation once daily but requiring a mean treatment time of 10 d. It was possible to prevent clinical mastitis from developing and to eliminate all infections in cows that were treated early when the developing disease was predicted by changes in the electrical conductivity of quarter foremilk and was treated aggressively by administering an intramammary antibiotic at each milking for 3 d. Treatment of 20 IU of oxytocin at six successive milkings of cows that were predicted to develop disease eliminated 25% of the infections, but 75% of the cows developed clinical mastitis. Those cases were resolved by sustained daily treatment using the same intramammary antibiotic. Elimination (100% clinical and bacteriological cure) of all infections caused by Strep. uberis was possible with early and aggressive or sustained use of the intramammary antibiotic. The early intervention using an intramammary antibiotic, when infection was first indicated by changes in the electrical conductivity of milk, was the most efficient method to achieve cure and led to quicker recovery of milk quality to a saleable standard.
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Detection of antimicrobial substances in individual cow and quarter milk samples using Delvotest microbial inhibitor tests.
The use of antibiotic therapy to treat and prevent udder infections of cows during the dry period is a key component of mastitis control in many countries. At the same time, the general public is becoming increasingly aware of potential hazards from antibiotic residues in foods. Consequently, Delvotest Cow Test (Royal Gist-brocades NV, Delft, The Netherlands), an on-farm version of Delvotest P, a microbial inhibitor test for antimicrobials, is being increasingly used by farmers to assess that milk from individual cows is fit for consignment to the bulk tank. Occasional reports of unexplained positive test results have led to suggestions of possible false-positive reactions in milk from individual cows. To investigate the potential causes of such positive test results, three separate investigations were undertaken. In a field survey of unexplained positive reports from farmers, 14 milk samples from six farms that tested positive were all found to contain antibiotic residues. In more formal investigations of individual quarter milk samples from an experimental herd, none of 134 milk samples from midlactation cows yielded positive reactions; for cows that had just calved, 16 of 144 milk samples were positive, and, of those, 13 had somatic cell counts > 4,000,000/ml. Natural inhibitors were responsible for 1 positive reaction, 8 positive reactions were related to incomplete milking, and 7 samples contained beta-lactam antibiotics. Positive reactions caused by antibiotic persisted in individual quarter samples for up to 7 d postcalving compared with 4 d for milk samples from the whole udder. Delvotest was sensitive to cephalonium, the active ingredient of Cepravin Dry Cow (Mallinckrodt Veterinary Ltd., Uxbridge, United Kingdom), which is the market-leading product in the United Kingdom. Test results yielded a partial purple color reaction in the presence of 8 micrograms/kg of cephalonium and a completely purple reaction at 16 micrograms/kg. These results confirm the validity of Delvotest when used to examine composite milk samples from individual cows supplying the United Kingdom dairy industry and suggest that, with proper attention to milk withdrawal periods and complete milking, there is no obvious risk of antibiotic contamination of milk.
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Bovine spongiform encephalopathy: current status and possible impacts.
Bovine spongiform encephalopathy is an apparently new disease; first recognized in 1985, its pathological distinction was first reported in 1986. Bovine spongiform encephalopathy is a member of a group of transmissible encephalopathies that includes scrapie in sheep and Creutzfeldt-Jakob Disease in humans. Early indications of its epidemiology suggested that the disease was transmitted via cattle feed containing meat and bone meals from previously infected animals. The tissues most likely to contain infectious agents were considered to be nervous tissues and offal, and their inclusion in ruminant feed was banned in the United Kingdom in 1989; regulations were tightened in 1992. Subsequent diagnosis has indicated that this ban has been effective and that confirmed cases are predicted to decline from a peak in the United Kingdom of 37,490 in 1992, to 7417 actual cases in 1996, and then to virtual extinction in 2001. Subsequent culling of all nonproductive cattle more than 30 mo of age and culling of cohort animals of confirmed cases is likely to reduce the predicted numbers and times significantly. Current interest is in the means of transmission of bovine spongiform encephalopathy within species and possibly to humans. A new variant of Creutzfeldt-Jakob Disease, with 28 cases confirmed, is virtually certain to be bovine spongiform encephalopathy in humans. The outbreak of bovine spongiform encephalopathy has had major impacts on the United Kingdom dairy industry, including the loss of beef from dairy markets, the culling of more than 900,000 dairy bull calves, the removal of all cattle more than 30 mo of age from the human food chain, and now slaughter of cohort animals. Impacts on dairy marketing have yet to be properly assessed. Information and statistics for bovine spongiform encephalopathy can be found on the worldwide web at http:@www.maff.gov.uk/maffhome.html.
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The effects of early antibiotic treatment following diagnosis of mastitis detected by a change in the electrical conductivity of milk.
Mastitis was induced experimentally by infusion of Streptococcus uberis or Staphylococcus aureus into the mammary glands of lactating dairy cows. Clinical mastitis was identified when clots appeared in foremilk (conventional diagnosis) or was predicted by changes in the electrical conductivity of foremilk (early diagnosis). The responses to intramammary antibiotic treatment that was initiated after early diagnosis of mastitis and after conventional diagnosis were compared. Early treatment significantly limited the severity of the disease and, in many cases, prevented the appearance of any visible signs of infection. Milk yield was less depressed, and the somatic cell count (SCC) was lower, when treatment was initiated earlier. The SCC of the quarter at the time mastitis was predicted was approximately 2 x 10(6) cells/ml for both pathogens, which was significantly less than when clots appeared at conventional diagnosis, approximately 4 x 10(6) and 12 x 10(6) cells/ml for Staph. aureus and Strep. uberis, respectively. The time required for SCC to recover to < 4 x 10(5) cells/ml was significantly less, approximately half, for both pathogens following early detection and early initiation of treatment. When treatment was administered in response to early detection, the bacteriological and clinical cure was almost complete, and the amount of antibiotic used was < or = 50% less. Obvious benefits for milk yield and quality and the health of the cow would result when changes in the electrical conductivity of milk are used to predict clinical mastitis and when treatment is initiated early.
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Transmission dynamics and epidemiology of BSE in British cattle.
A comprehensive analysis of the bovine spongiform encephalopathy (BSE) epidemic in cattle in Great Britain assesses past, present and future patterns in the incidence of infection and disease, and allows a critical appraisal of different culling policies for eradication of the disease.
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Influence of pulsationless milking on teat canal keratin growth and turnover.
In two separate experiments, the effects of pulsationless milking and milking vacuum on the rate of keratin removal from the teat canal were determined. Sixteen cows were milked with or without pulsation for either a single milking or for eight milkings. Milking without pulsation removed 10% of keratin present before milking, significantly less than milking with pulsation, which removed 32%. After eight milkings (4 d) without pulsation, up to 20% more keratin had accumulated within the teat canal but the rate of keratin regeneration reduced significantly upon return to pulsation milking. In a second experiment, ten cows were milked at 45 or 55 kPa and without pulsation. Only the absence of pulsation significantly reduced keratin loss during milking. Keratin loss during milking appears to be controlled by liner compression rather than by the rate of milk flowing through the teat canal. Pulsationless milking may increase penetrability of the teat canal to bacteria by reducing the natural rate of keratin removal during milking and reducing the rate of keratin regeneration.
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Hyperkeratosis of the teat duct orifice in the dairy cow.
Teat orifice hyperkeratosis, a commonly observed condition in dairy cows, has been considered a consequence of machine milking and the degree of hyperkeratosis may be increased by a poor milking system. A fully illustrated technique is described which uses a scoring system from 0 for a perfect orifice to 5 for an orifice significantly enlarged with extensively protruding fronds of teat duct keratin. A range of scores found in 25 commercial dairy herds is presented. The scores have been averaged for each cow and the markedly skewed distribution corrected by a square root transformation. This scoring procedure allows comparative measures of hyperkeratosis within and between herds. An 8-fold difference (0.17-1.31) in herd average score was found. Within all herds the score increased with lactational age of the animals and peaked, for any lactation, some 3-4 months post partum, declining as the animals dried off. There was no significant relationship between mean somatic cell count and degree of hyperkeratosis at the herd level. This implies that such chronic pathological changes are unlikely to be related to the level of intramammary infection. It appeared that some hyperkeratosis is an obvious and probably natural response to milking and occurs in a significant proportion of animals in all herds although often only to a slight degree. Much more hyperkeratosis may be a measure of the performance and management of the herd. The genetic influence is unknown. Higher yielding cows will score higher as they milk for longer, but generally high scores may reflect consistent and possibly considerable overmilking. Hyperkeratosis may be an indicator of the quality of management and show the level of attention being paid to the welfare of the herd.
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Detection of clinical mastitis by changes in electrical conductivity of foremilk before visible changes in milk.
Mastitis was induced by the direct infusion of Staphylococcus aureus or Streptococcus uberis into the mammary gland of lactating cows. Changes in electrical conductivity of foremilk indicated the establishment of bacteria, increased SCC, increased clotting of milk, and, hence, disease, in advance of visible changes in the milk that could be diagnosed by a herdsperson. Clinical mastitis was detectable by changes in electrical conductivity of foremilk, 90% of cases were detectable when clots first appeared in foremilk, and 55% of cases were detectable up to 2 milkings prior to the appearance of clots. All subclinical infections from Staph. aureus were detected, but subclinical infections from Strep. uberis were not detected. The results suggested that clinical mastitis caused by these two major pathogens could be detected earlier by measuring changes in electrical conductivity of milk than by waiting for a herdsperson to detect visible changes in milk. Earlier detection would permit earlier treatment. However, the handheld sensor used in this experiment is impractical for commercial application, and reliable automated sensors and decision-making algorithms are required.
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