Jörn Hamann

Role of endotoxin and TNF-α in the pathogenesis of experimentally induced coliform mastitis in periparturient cows

Twelve cows were experimentally infected in two quarters with 1 x 10(4) cfu Escherichia coli per quarter and six cows were infused with 500 microg endotoxin into two quarters. Six cows infected intramammarily with Esch. coli were treated intravenously with a bactericidal antibiotic 10 h after infection and subcutaneously 20 h later. Blood and milk samples were collected from all cows at regular time intervals. Milk production decreased more rapidly, but was less pronounced, after endotoxin infusion than (during Esch. coli mastitis. The milk production losses in the noninflamed quarters were negligible in endotoxin mastitis, but were substantial during Esch. coli mastitis, probably due to more pronounced systemic effects. Reticulorumen motility was inhibited only during Esch. coli mastitis. Changes in plasma haptoglobin were more pronounced during Esch. coli mastitis, although they occurred sooner during endotoxin mastitis. No changes in plasma activities of enzymes such as lactate dehydrogenase, glutamic-oxaloacetic transaminase and gamma-glutamyl transpeptidase were observed. Concentrations of tumour necrosis factor-alpha increased in both types of mastitis. Absorption of these cytokines into the circulation was highest during Esch. coli mastitis, especially in the untreated control group. We found only minor differences between the treated and untreated Esch. coli groups, but there were larger differences between the Esch. coli groups and the endotoxin group. These differences were probably due to differences in kinetics, composition and amounts of different cytokines released in the mammary gland and subsequently absorption into the circulation. Endotoxin is probably not directly responsible for the systemic changes during coliform mastitis.

Machine-induced teat tissue reactions and infection risk in a dairy herd free from contagious mastitis pathogens

Machine-induced changes in teat thickness were measured in a randomly selected group of 22 cows from a commercial dairy herd consisting of 110 cows during an experiment lasting 1 year. Half the cows used were free from mastitis whereas the remainder had at least one quarter infected by environmental pathogens. Teats were classified according to a threshold change in teat end thickness of 5%. The relationships between quarter infection or teat duct colonization and teat end thickness changes induced by machine milking were investigated. Teats with greater than 5% change in thickness had significantly increased teat duct colonization and a slight, non-significant, increase in quarter infection. We conclude that machine-induced changes in teat end thickness are predisposing factors for teat duct colonization by environmental pathogens. This may provide an increased new infection risk, especially when hygiene is poor.

Compensatory milk production within the bovine udder: effects of short-term non-milking of single quarters

Daily quarter-milk yields of eight high-yielding cows (24-28 kg/d) and eight heifers (14-24 kg/d) were measured to examined to examined compensatory changes in milk production between quarters within an udder. Either one, two or three quarters per cow were left unmilked for 12 d, in early or late lactation, and then all quarters of all cows were milked normally for a further period of 12 d. Concentrate feeding levels were constant throughout the experiment. The mean daily yield per cow fell to 26, 59, and 75% during the period of milking either one, two or three quarters respectively. Twelve days after resumption of normal milking the total daily yield per cow was the same for cows continuously milked in two, three or all four quarters. Daily yield in cows with only one quarter milked continuously recovered to only 78% of the level of the pretreatment period. During the treatment period, the mean daily yield of the continuously milked quarters increased by almost 14% for cows milked in one quarter only, by more than 10% for two quarters milked, and by 4% per quarter if three quarters were milked. Milk yields of these quarters remained above their pretreatment levels when milking was resumed in the adjacent quarters. There was no difference in the compensatory effect between cows and heifers in early lactation, but the compensatory effects were lower in the lower in late lactation heifers.

Measurement of machine-induced changes in thickness of the bovine teat

Machine milking induced repeatable, short-term changes in thickness of the teat apex. These changes were measured with a spring-loaded caliper instrument under milking conditions that imposed differing forces on the teat apex. The mean percentage changes in teat end thickness (relative to the premilking values for individual teats) varied from 10% decrease up to 20% or more increase depending on the particular milking system used. The overall decrease in teat end thickness associated with cannula milking, milking at very low vacuum levels or milking with positive pressure pulsation may result from: (i) decrease in the intramammary pressure; and/or (ii) small changes in tone of teat musculature; and/or (iii) changes in the distribution of interstitial fluids in the teat apex. The overall increase in teat thickness caused by conventional or PKME milking systems results mainly from oedema (the extravascular accumulation of fluid). It is likely that milking equipment can, and should, be designed to minimize circulatory impairment resulting in oedema of the teat.

Responses of the bovine teat to machine milking: measurement of changes in thickness of the teat apex

Changes in the teat apex before and after different milking treatments were measured with a spring-loaded caliper device known as a cutimeter which could detect changes in thickness of the tissues of the teat end, presumably due to congestion and/or oedema, with a high degree of accuracy (± 2%) and repeatability ( r = 0·99). Teat end thickness increased with increasing vacuum level. The mean increase immediately after milking with a conventional cluster was 2% for 24 teats milked at 30 kPa, 8% at 50 kPa and 21% at 70 kPa. At these vacuum levels, the mean increases for the same teats milked with an unconventional (PKME) teatcup were 10, 18 and 25% respectively. Cyclic application of 35 kPa positive pressure to the pulsation chamber of a conventional teatcup operating at 50 kPa reduced teat end thickness by 8% compared with the mean premilking value. Although most teats returned to within ± 2% of their premilking thickness values by 1 h after milking, differences were apparent between different milking systems for up to 4 h postmilking.

Cell function in the bovine mammary gland: a preliminary study on interdependence of healthy and infected udder quarters

Udder defence mechanisms are not completely explained by current mastitis research. The anatomical construction of the udder implies that infection of one udder quarter does not influence the immune status of neighbouring quarters. To test this hypothesis, we compared the immune reactions of individual udder quarters in response to microbial attacks. In the course of immune reactions, polymorphonuclear leucocytes (PMN) release oxygen radicals, which can be determined by chemiluminescence (CL). Milk from 140 udder quarters of 36 cows was analysed for somatic cell count (SCC), differential cell count, viability and CL activity. Quarters with an SCC < 100,000 cells/ml and free of pathogens were defined as uninfected, all other quarters were categorized as infected. Three groups of cows were classified cytologically: group A (healthy, 11 animals, SCC limit < 100,000 cells/ml); group B (moderate mastitis, 8 cows, SCC > or = 100,000 and < 400,000 cells/ml in at least one quarter); and group C (severe mastitis, 17 cows, SCC > or = 400,000 cells/ml in at least one quarter). Infected and uninfected quarters in groups B and C were analysed separately. Viability of PMN leucocytes was significantly (P=0.0012) lower in group A (72.6%) than in healthy quarters of group C (84.0%). Lowering the SCC limit of healthy quarters to <50,000 cells/ml (group A: all quarters within the udder) revealed striking differences between samples of groups B and C: in addition to varying differential cell counts and viabilities, CL activity of group B<50 (2929 CL units/million PMN) was markedly lower than that of the other groups (5616 in group A<50 and 6445 CL units/million PMN in group C<50). These results allow the conclusion that the infection of one udder quarter influences the cell activity of neighbouring quarters. When the SCC threshold for healthy quarters was reduced to 50,000 cells/ml, greater differences in cell activities were detected between healthy udders and healthy quarters of infected udders.

Teat thickness changes may provide biological test for effective pulsation

Pulsation rates of 40, 60 and 80 cycles/min were combined with pulsator ratios of 50, 60, 70 or 80 percent in two experiments with different liners. Machine-induced, short-term changes in teat thickness of 14 cows were compared with milk flow rate characteristics and machine strip yields to evaluate the effectiveness of pulsation in relation to liner type. Post-milking teat thickness increased progressively as the b phase of the pulsation cycle was lengthened, and as the d phase was shortened, at all pulsator rates and with either liner. Teat thickness values increased significantly (P < 005) when the d phase was < 15%. For ratios of 50 and 60% , teat thickness decreased progressively as pulsation rate was increased. At the higher ratios, thickness values were lowest at 60 cycles/min. Pulsation settings that tended to increase teat thickness values also increased both peak milk flow rates and machine strip yields. The influence of liner type on teat thickness changes appeared to be at least as important as the influence of pulsator ratios and greater than the effect of pulsation rate. If so, then international standards for acceptable pulsation characteristics cannot be defined solely in terms of pulsator settings. A limit of +/- 5 percent for machine-induced changes in thickness of the teat apex would be an additional guideline for effectiveness of pulsation in relation to both liner type and vacuum level. This could provide a basis for a dynamic test applied to milking cows under field conditions.

Treatment of acute Escherichia coli mastitis in cows with enrofloxacin: effect on clinical signs and chemiluminescence of circulating neutrophils.

We have studied the effect of treatment with enrofloxacin on local and general clinical signs and chemiluminescence of circulating polymorphonuclear leucocytes during experimentally induced Escherichia coli mastitis in cows immediately afer parturition. Twelve cows were infected with 10(4) cfu Esch. coli P4:032 into both left quarters. Six cows received an intravenous injection of 5 mg enrofloxacin/kg at 10 h after infection and a second enrofloxacin treatment administered subcutaneously at 30 h post infection. The other six cows were controls that received no treatment. General clinical signs (fever, tachycardia, loss of appetite, reduced rumen motility and depression) were similar in both groups. Local clinical signs, such as swelling, pain and firmness of the inflamed mammary quarters, were less severe in the treated cows. We saw no difference in the appearance of the milk: flecks and watery or purulent milk were observed in both groups. The beneficial effects of treatment with enrofloxacin were mainly on milk production and composition. The decline in milk production and the changes in milk concentrations of lactose, Na+ and bovine serum albumin were less pronounced in the treated cows. Treatment with enrofloxacin accelerated the clearance of bacteria from the infected quarters, but had no effect on the chemiluminescence response of isolated polymorphonuclear leucocytes. The changes in the number of circulating leucocytes and the appearance of immature neutrophils in the circulation of the treated cows indicated possible beneficial effects on migration of neutrophils into the inflamed glands. Higher milk somatic cell counts in the treated cows supported this hypothesis. The results of this study indicated that treating cows that have been experimentally infected with Esch. coli mastitis after parturition with enrofloxacin reduced the severity of the disease, especially the decline in milk production and the changes in milk composition.

Relationship between numbers of α2- and β2-adrenoceptors on blood cells of bulls and milkability of their daughters

Milk yield and milking time mere measured on one occasion for several daughters (n = 6-44) from 16 bulls at morning milkings. Blood from the bulls was collected, and platelets and mononuclear leucocytes were isolated. The alpha(2)-adrenoceptors on platelet membranes were identified by binding of [H-3]rauwolscine, whereas for the determination of beta(2)-adrenoceptors on intact mononuclear leucocytes, [H-3]CGP-12177 was used. It was found that mean milk flow rate was highly correlated (P < 0.001) with the alpha(2)-adrenoceptor densities on blood platelets. No correlation was found with the beta(2)-adrenoceptors on mononuclear leucocytes. It is concluded that estimation of the alpha(2)-adrenoceptors on blood platelets from bulls could eventually be used to investigate milking characteristics of cows, and might be useful in the future as a marker in genetic studies.

Effects on milk yield, somatic cell count and milk conductivity of short-term non-milking of lactating quarters of cows

Compensatory changes in daily milk production between quarters within an udder were investigated, together with related changes in cell count and electrical conductivity of fore milk samples. Two quarters per cow were left unmilked for 2 d (Group 1, four cows) or for 4 d (Group 2, four cows), and then all quarters of all cows were milked twice daily for a further period of 16 d. The mean daily yield per cow fell 50% during the period of milking two quarters. Daily yield for cows in Group 1 decreased significantly only during the treatment period and the first post-treatment period of 4 d, whereas the daily yield for Group 2 was significantly reduced during the whole post-treatment period. The cell count for all continuously milked (control) quarters was stable during the experiment, but increased in the treated quarters during the first 4 d of the post-treatment period. Non-milking was accompanied by a significant increase in fore milk conductivity which persisted for an additional 4 d after the resumption of normal milking. Throughout the last 12 d of the post-treatment period milk from both control and treated quarters had significantly decreased conductivity levels compared with the pretreatment values.