Effect of abraded intramammary device on outcome in lactating cows after challenge exposure with Streptococcus uberis

Intramammary devices (IMD) were abraded with medium-grade emery cloth or were left smooth. One IMD of each type was inserted into a mammary quarter of each of 5 lactating cows. The remaining 2 quarters served as controls. Quarter foremilk, bucket milk, and stripping milk samples were collected for 3 consecutive days at 2 weeks after IMD insertion, and milk somatic cell counts (SCC) were determined. Milk samples also were collected immediately after and 0.5, 1, 2, 4, 6, 8, and 11 hours after milking. All quarters were challenge exposed with 250 colony-forming units of Streptococcus uberis at 2 months after IMD insertion. Foremilk and stripping milk samples were collected for bacteriologic culture and SCC at the next 10 milkings. Mean foremilk, bucket milk, and stripping milk SCC (X 10(6) cells/ml) were 0.18, 0.07, and 0.91, respectively, for quarters with abraded IMD; 0.06, 0.05, and 0.43, respectively, for quarters with smooth IMD; and 0.03, 0.03, and 0.15, respectively, for control quarters. Mean SCC after milking (X 10(6) cells/ml) for the various intervals were 0.70, 1.29, 0.70, 0.97, 1.15, 1.17, 0.77, and 0.85 for quarters with abraded IMD; 0.43, 0.62, 0.61, 0.45, 0.64, 0.60, 0.31, and 0.26 for quarters with smooth IMD; and 0.15, 0.24, 0.15, 0.19, 0.15, 0.15, 0.14 and 0.06 for control quarters. After challenge exposure, 2 of 5 of the quarters with abraded IMD, 4 of 5 of the quarters with smooth IMD, and 8 of 9 control quarters became infected. Results indicated that abraded IMD increased SCC in stripping milk to concentrations that provided 60% protection against challenge exposure with S uberis.     

Effect of intramammary devices on the outcome of induced Escherichia coli infection of bovine mammary quarters

Eighteen Holstein cows, free of intramammary infection, were fitted with smooth (n = 9) or abraded (n = 9) intramammary devices (IMD) in 2 diagonally opposed quarters within 4 weeks after calving. The 2 other quarters of each cow were used as controls. Three to 6 weeks after IMD insertion, depending on when milk somatic cell counts returned to a base-line value of less than 4 X 10(5)/ml, all cows were subjected to bacterial challenge exposure in the front or rear quarters by intracisternal injection of about 30 colony-forming units of Escherichia coli/quarter. Challenge exposure was done immediately after milking. Three weeks after the initial bacterial exposure, the other quarter pairs were similarly challenge exposed. Quarter bacteriologic status, concentration of milk somatic cells, and clinical observations (rectal temperature, milk appearance, udder palpation, and general condition of the cow) were monitored. Infection developed in 14 of 16 (88%) quarters with smooth IMD vs 16 of 16 (100%) control quarters and in 7 of 17 (41%) quarters with abraded IMD vs 17 of 17 (100%) control quarters. The difference in infection frequency between quarters with smooth IMD and quarters with abraded IMD was significant (P less than 0.05). Protection against establishment of infection was associated with somatic cell counts greater than 8.0 X 10(5)/ml in milk collected immediately after milking (7 of 12 quarters) or 4 hours later (11 of 12 quarters). In 10 quarters (59%) of cows fitted with abraded IMD, secretory abnormalities appeared before bacterial challenge inoculation. Abnormal milk or visible blood was observed over periods varying from 2 weeks after insertion through the entire lactation.     

The use of polyethylene intramammary device in protection of the lactating bovine udder against experimental infection with Staphylococcus aureus or Streptococcus agalactiae.

The susceptibility of lactating bovine udder quarters fitted with a polyethylene intramammary device to infection was investigated. Following experimental challenge with Streptococcus agalactiae or Staphylococcus aureus, the incidence of infection was significantly (p less than 0.05) lower in intramammary device-fitted quarters compared to control quarters. In general, total foremilk and strippings milk somatic cell counts for intramammary device-fitted and control quarters were not significantly (p less than 0.05) different. Differential foremilk and strippings milk somatic cell counts were significantly (p less than 0.05) higher in samples from intramammary device-fitted quarters compared to control quarters.     

Effect of the intramammary device on milk infection status, yield, and somatic cell count and on the morphological features of the lactiferous sinus of the bovine udder

Twenty primiparous heifers were fitted intramammarily with polyethylene coils in both quarters of one random right or left udder half at 5 days after parturition. Foremilk samples were collected and udder-half milk yields were measured at the afternoon milking on days - 1, 3, 7, and 14 and on every 14th day for 8 months after the device was inserted. Three weeks after the heifers were fitted with the intramammary device, 6 were euthanatized for gross observation of devices and tissues and cytologic evaluation of the gland cistern epithelium. There were significantly fewer bacterial isolations (P less than 0.01) and less clinical mastitis (P less than 0.05) in treated quarters than in the control quarters. Coagulase-negative staphylococci were isolated at frequencies of 0 and 15.2% for treated and control quarters. The reduction in isolation frequency for treated, compared with control, quarters was less marked with other organisms. Intramammary devices in no way interfered with the milking process. Milk yields per milking were 4.2 kg for treated udder halves compared with 4.4 kg for control halves; however, this 0.2 kg difference was not significant. Mean milk somatic cell counts, as determined by electronic counter, were 34 X 10(3) and 81 X 10(3) cells/ml for control and treated quarters (P less than 0.05). Mean bovine serum albumin values were 0.160 and 0.175 mg/ml for control and treated udder halves (P less than 0.05), indicating an increased capillary permeability due to the device. Quantitative morphologic analysis of gland cisterns showed a significant (P less than 0.05) change toward a single layer of epithelial cells in treated quarters compared with a double layer in control quarters.(ABSTRACT TRUNCATED AT 250 WORDS)     

Physiological and morphological changes in bovine mammary glands following intramammary infusion of recombinant interferon-gamma.

Eleven lactating dairy cows were used to evaluate the response of bovine mammary glands to increasing doses of recombinant bovine interferon (rBoIFN)-gamma. Right front and rear quarters were intramammarily infused with eight different doses (10(2) U to 2 x 10(8) U/quarter) of rBoIFN-gamma; each dose was tested in at least two quarters. Left udder halves served as within animal controls in which quarters were injected with a saline placebo or were not infused at all. Milk secretion samples for compositional analysis were collected from each quarter prior to infusion and at 6, 24, 36 and 48 h following infusion. Animals were slaughtered immediately following the 48 h sampling period and mammary tissue was obtained for morphometric analyses. Milk composition was similar between control quarters and those quarters infused with up to 10(5) U of rBo-IFN-gamma during the entire sampling period. Quarters infused with 10(6) U and 10(7) U of rBoIFN-gamma had higher milk somatic cell counts (SCC) following treatment compared with preinfusion values. Changes in the composition of mammary secretion were most dramatic in quarters infused with greater than or equal to 10(8) U of rBoIFN-gamma as indicated by the significant increase in SCC and milk pH with a concomitant decrease in lactose concentration when compared with pre-infusion values or with control quarters. Morphometric analysis of tissue demonstrated an increase in stroma, a decrease in luminal area, and a marked increase in the number of infiltrating leukocytes in those quarters infused with the higher doses of rBoIFN-gamma.(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in the bovine udder quarters naturally infected by Corynebacterium bovis

Of 272 bovine udder quarters studied for mastitis, 19 of them naturally infected with Corynebacterium bovis alone, were compared with 16 others infected by C. bovis together with other bacteria and another 36 non-infected quarters. While there was no significant difference in milk somatic cell counts between the quarters infected by C. bovis alone and those affected by C. bovis together with other bacteria (33.37 +/- 20.28 X 10(3) and 33.86 +/- 23.18 X 10(3)/ml of milk, respectively), there was a significant difference between these and the non-infected quarters (5.60 +/- 3.23 X 10(3)/ml of milk). Microscopically, quarters infected by either C. bovis alone or C. bovis in combination with other bacteria had inflammatory changes in the teat cisterns, Furstenberg's rosettes and/or mammary parenchyma. The non-infected quarters had no changes. In all 82 quarters no pathological changes could be seen in the teat canals.     

Antibiotic therapy for subclinical mastitis in early lactation; effects on infection, somatic cell count and milk production

Cows with consistently high somatic cell counts (SCC) and bacterial infection, but no clinical signs of mastitis, were identified early in lactation. Some of these quarters were treated with Cloxacillin, while other similar quarters were left untreated. Prior to treatment, 74% of infected quarters had SCC higher than 300,000 cells/ml while 85% of uninfected quarters has SCC lower than 300,000 cells/ml. Infection was eliminated by treatment in five out of the eight quarters treated with Cloxacillin, and in these quarters SCC decreased from 4,200,000 cells/ml before treatment to 160,000 cells/ml after treatment. Milk production and composition were not affected significantly although production was about 14% higher in treated quarters than untreated quarters. The possible role of antibiotic therapy for subclinically infected quarters early in lactation was discussed in relation to a reduced rate of new infection in a herd.     

Experimental colonization of the bovine teat duct with Corynebacterium bovis and the effect on milk somatic cell counts.

Colonization with Corynebacterium bovis was established in 59 of 64 (92%), 58 of 59 (98%) and 19 of 34 (56%) of uninfected bovine mammary quarters following inoculation of 83.3 X 10(4) colony-forming units (CFU) of the organism into the teat cistern, 4.7 X 10(3) CFU 5 mm into the teat duct or by exposure of the teat orifice to a milk culture containing 1.6 X 10(7) CFU/mL respectively. Mean somatic cell counts for foremilk samples from 122 quarters were significantly higher after colonization with C. bovis (145,900/mL) compared to before exposure (130,900/mL).     

Sequential response of milk leukocytes, albumin, immunoglobulins, monovalent ions, citrate, and lactose in cows given infusions of Escherichia coli endotoxin into the mammary gland

Changes in concentrations of both the cellular and the humoral components of milk are known to occur during mastitis. This study was conducted to determine temporal changes in the concentrations of leukocytes, albumin, immunoglobulins (Ig), monovalent ions, lactose, and citrate in milk during the initial phases of simulated mastitis. Ten cows whose udders were pathogen free and had milk leukocyte counts of less than 0.5 X 10(6)/ml were used. Two dosages of Escherichia coli endotoxin were administered to simulate various degrees of mastitis. Two quarters in each cow were infused with the endotoxin and the other 2 served as controls. Quarter milk samples were collected frequently before and after infusion. Within 2 hours after infusion of a 100-micrograms dose of endotoxin, clinical mastitis was observed in most of the infused quarters. Leukocytes, albumin, IgG1, and conductivity showed significant increases. Values before infusion and at postinfusion (PI) hour 2 were as follows: leukocytes, 0.33 and 3.65 X 10(6)/ml, respectively; albumin, 0.38 and 4.49 mg/ml; IgG1, 0.34 and 0.79 mg/ml; and conductivity, 6.0 and 6.9 mmho. Average of the peak values and their average relative time of appearance after infusion were as follows: leukocytes, 28.82 X 10(6)/ml at 16 hours; albumin, 9.37 mg/ml at 4 hours; IgG1, 1.35 mg/ml at 4 hours; and conductivity, 95.5 mmho at 10 hours. The IgG1 values tended to remain high in the presence of rapidly declining albumin concentrations, indicating the possibility of an active, rather than a passive, transfer of IgG1 from the circulation. The response to the 10-micrograms dose of endotoxin ranged from subclinical to clinically mild mastitis with lesser cellular and humoral responses.     

Effects of intracisternal bead devices on lacteal secretion components, plaque formation, and bacterial infection during the nonlactating period

Effects of placing intracisternal bead devices (ICB) into teat cisterns of 6 dairy cows, from the end of lactation through parturition, were studied. Lacteal secretion samples were collected weekly from each mammary quarter during the nonlactating period to monitor composition changes in ICB-fitted and nonfitted quarters. In quarters remaining uninfected (n = 15), there were significantly higher mean somatic cell counts (P less than 0.05), percentage of neutrophils (P less than 0.019), and cell viability (P less than 0.038), but significantly lower percentage of macrophages (P less than 0.013) in ICB-fitted quarters compared with those in nonfitted quarters. The ICB had no significant effect on mean weekly values for percentage of lymphocytes, pH, lactoferrin, citrate, citrate/lactoferrin molar ratio, serum albumin, alpha-lactalbumin, and N-acetyl-beta-D-glucosaminidase. In infected quarters (n = 9), pH of mammary secretions was significantly (P less than 0.004) higher in ICB-fitted quarters, but concentrations of lactoferrin (P less than 0.004), alpha-lactalbumin (P less than 0.013), and N-acetyl-beta-D-glucosaminidase (P less than 0.028) were significantly lower, compared with those in nonfitted quarters. Coagulase-negative staphylococci comprised approximately 90% of all infections. Over the nonlactating period, 16.4 and 41.5% of samples from nonfitted and ICB-fitted quarters, respectively, contained coagulase-negative staphylococci. Microscopic examination of ICB from uninfected quarters revealed a thin coating of plaque with adhering neutrophils, macrophages, and multinucleated giant cells. Microscopic examination of plaque on devices from ICB-fitted quarters harboring coagulase-negative staphylococci revealed numerous adherent cocci and neutrophils.     

Bacterial cure and somatic cell count response of dairy cows with a positive California Mastitis Test at calving to therapy with cephapirin sodium

Cows without signs of clinical mastitis were evaluated by the California Mastitis Test at calving (Day 0). Milk samples from 117 of 184 quarters (64 cows) were positive by this test for mastitis and were submitted for bacterial culture and determination of somatic cell counts. Cows with infected quarters were randomly allocated to treatment with cephapirin sodium by intramammary infusion or to be untreated as controls. Two and 4 weeks following calving, milk was again sampled from the infected quarters and tested. By the 4-week evaluation, the quarters treated with cephapirin sodium had significantly (P < or = .05) fewer positive bacterial cultures and somatic cell counts were significantly (P < or =.05) reduced compared with untreated control quarters.     

A comparative field trial of cephalonium and cloxacillin for dry cow therapy for mastitis in Australian dairy cows

OBJECTIVE: To investigate and compare the therapeutic efficacy of dry cow agents containing either cephalonium or cloxacillin within Australian dairy herds. DESIGN: A treatment-control trial. METHODS: Milk from infected quarters of cows with high somatic cell counts in milk on eight Australian dairy farms was cultured to identify bacterial pathogens. Cows were randomly assigned to treatment groups and one group was treated with cephalonium at drying off and the other group was treated with cloxacillin at drying off. Milk samples from infected quarters were collected immediately after calving and were cultured for pathogens. The effect of treatment on bacteriological cure was examined and somatic cell counts from infected cows from the first two herd tests after calving were examined for a treatment effect. On four farms, milk samples were collected for culture from all cases of clinical mastitis identified within the first 7 days after calving. The effect of treatment upon incidence of clinical mastitis after calving was examined. RESULTS: There was no significant difference between treatments on quarter cure rates for new infections, for chronic infections and for infections with Staphylococcus aureus, Streptococcus agalactiae and Streptococcus uberis. Infected quarters treated with cephalonium had a significantly higher cure rate than quarters treated with cloxacillin when Corynebacterium bovis and Staphylococcus epidermids were included as pathogens combined (80.3% versus 70.7%). There was no significant difference between the treatments on somatic cell counts of infected cows at the first two herd tests after calving. There was no difference between treatments on the incidence of clinical mastitis in the first 7 days after calving.     

Pathological changes following implantation of intramammary devices (IMD) and immunological mediator release by cells on recovered IMDs

Implantation of abraded polyethylene intramammary devices (IMD) for six months in the mammary glands of cows resulted in macroscopic and microscopic pathological changes in udder tissue. These changes were characterised by hyperplasia and metaplasia of the epithelial cells and hypertrophy of the subepithelial connective tissue examined by light and electron microscopy (EM). Quarters containing IMDs also had increased numbers of neutrophils and macrophages in the subepithelial stroma compared with control quarters. IMDs recovered six months after implantation were shown by transmission and scanning EM to be covered with plaque and cells. These cells were mainly macrophages, although other leucocytes were also present. In vitro culture of recovered IMDs in the presence of lipopolysaccharide resulted in the release of neutrophil chemotactic factor, or factors, and interleukin-1. Some quarters with IMDs also had concurrent infections at the time of slaughter. In these cases both the pathological changes seen in the tissues and the release of soluble mediators following in vitro culture of the IMDs were significantly increased compared with sterile quarters containing IMD.     

N-acetyl-beta-D-glucosaminidase activities, milk somatic cell counts, and blood leukocyte and erythrocyte counts in cows after heat-induced stress or after intravenous administration of adrenocorticotropic hormone

Six midlactation, nonpregnant cows were subjected to heat-induced stress or to repeated injections of adrenocorticotropic hormone (ACTH). The heat stress (experiment 1) consisted of subjecting the cows to 7 days of fluctuating temperatures (21 C during the day, 32 C during the night). The ACTH-induced stress (experiment 2) was accomplished by giving each of the cows 100 IU of ACTH twice daily for 4 consecutive days. The cows' milk somatic cell counts (MSCC), milk N-acetyl-beta-D-glucosaminidase (NAGase) activity, quarter milk production (ie, milk production per mammary quarter), blood leukocyte counts, and plasma concentrations of NAGase were monitored in both experiments. Although heat stress did not result in significant differences in NAGase, heat stress did significantly (P less than 0.05) decrease milk production. The ACTH administrations resulted in increased milk NAGase activity, MSCC, and blood leukocyte counts, and in decreased plasma NAGase activity and quarter milk production. Therefore, milk NAGase activity and MSCC were not affected by short-term heat stress, but were increased by ACTH-induced stress. Blood erythrocyte concentrations were not affected by heat stress or by ACTH-induced stress.     

Role of leukotriene B4 in the pathogenesis of Klebsiella pneumoniae-induced bovine mastitis

Mastitis was induced in 4 lactating cows by inoculation of Klebsiella pneumoniae (10(7) organisms/ml) via the teat canal. Sterile isotonic saline solution (1 ml) was instilled into designated control quarters via the teat canal. Changes in milk leukotriene B4 and C4 (LTB4, LTC4) concentrations, milk somatic cell counts, and milk bovine serum albumin concentration were monitored over a 24-hour postinoculation period. Milk LTB4 concentration before inoculation in control quarters and quarters later to be infected was 376 +/- 45 and 326 +/- 56 pg/ml of milk, respectively. A significant (P less than 0.05) increase in milk LTB4 concentration in the infected quarters was first observed at postinoculation hour 6, and milk LTB4 concentration in infected quarters generally remained significantly high through postinoculation hour 14. Thereafter, milk LTB4 concentration in infected quarters was not significantly different from the concentration in control quarters. Measurable amounts of LTC4 were not detected in the milk of either control or infected quarters. Milk bovine serum albumin concentration in the infected quarters generally was high throughout the study, as were milk somatic cell counts. The results of this study suggested that LTB4 contributes to the pathogenesis of bovine mastitis.     

Somatic cells count in cow's bulk tank milk

The objective of this study was therefore to present factors affecting somatic cell counts in bovine bulk milk as a result of intramammary infections as well as non-infectious factors. The paper presents also the impact of on-farm management practices on the level of bulk milk somatic cell counts and presents quality indicators in bulk tank milk. At the farm level bulk milk bacterial infection takes place through three main sources: bacterial contamination from the external surface of the udder and teats, from the surface of the milking equipment, and from mastitis microorganisms within the udder. The threshold of 200,000 cells/ml identifies bacteriological negative quarters of the udder. The counts of mammary pathogens in bulk tank milk are relatively low, on average not exceeding 1,000 cfu/ml. Environmental pathogens predominate in bulk tank milk samples with somatic cells count <300 × 10(3) ml.     

Induction of Escherichia coli mastitis in cows fed selenium-deficient or selenium-supplemented diets

Ten Holstein heifers were fed a selenium-deficient (SeD) diet (0.04 mg of Se/kg on a total ration dry-matter basis) 3 months before calving and throughout their first lactation. A selenium-supplemented (SeS) diet (2 mg of Se/head/d) was fed to a group of 10 heifers. In about the 14th week of lactation, the cows were challenge-exposed to Escherichia coli by administering 15 to 40 colony-forming units (CFU) into 1 mammary gland. Selenium concentration (microgram/ml) in blood around the time of challenge exposure was 0.033 +/- 0.002 (mean +/- SEM) in SeD and 0.132 +/- 0.006 in SeS cows. Infections were established in all challenge-exposed quarters. The frequency of quarter atrophy and agalactia, and reduction in whole-udder milk yield in the first 4 days after challenge exposure, were greater (P less than 0.05) in the SeD cows. Log10 peak bacterial concentrations in milk were higher (P less than 0.05) in SeD (7.63 +/- 0.34 CFU/ml) than in SeS cows (5.57 +/- 0.66 CFU/ml). Mean log bacterial concentration was significantly higher (P less than 0.05) from 12 to 20 hours after challenge exposure in SeD than in SeS cows. Duration of infection was significantly greater (P less than 0.05) in SeD (162.0 +/- 12.0) than in SeS cows (114.4 +/- 18.0 hours). Milk somatic cell counts increased significantly more slowly (P less than 0.05) in SeD than in SeS cows from 8 to 16 hours after challenge exposure. Ratios of milk somatic cells to bacteria in milk were significantly lower (P less than 0.05) in SeD than in SeS cows at 12 and 16 hours after challenge exposure.     

Concentrations of triiodothyronine (T3), tumour necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) in milk from healthy and naturally infected quarters of cows

The effect of naturally acquired bacterial infection of the bovine udder on the activity of 5'-thyroxine monodeiodinase (5'-MD), and on the concentrations of the pro-inflammatory cytokines interleukin (IL)-6 and tumour necrosis factor (TNF)-alpha in milk, from healthy (control) and inflamed quarters, was determined. The diagnostic procedure included history and clinical examination of the udder, macroscopic evaluation of secretions, the Californian Mastitis Test, determination of somatic cell counts and bacteriological examination of milk. It has been found that the milk triiodothyronine (T3) content and the 5'-MD activity from inflamed quarters were decreased when compared with controls. The decrease in the milk T3 from subclinical mastitic quarters was manifested when somatic cell counts were > 10(6) ml(-1). TNF-alpha was on average 2-fold higher in infected milk, and the concentration of IL-6 was unchanged. These results suggest that the decreased T3 content in mammary secretions during naturally occurring mastitis is associated with the severity of inflammation, increased TNF-alpha concentration and impaired enzymatic activity of 5'-MD.     

Anti-inflammatory therapy in acute endotoxin-induced bovine mastitis

Acute mastitis was induced in lactating cows by intramammary challenge with 10 g of Escherichia coli lipopolysaccharide. The cows were monitored clinically prior to and for 96 hours after challenge. Milk production, complete blood counts, serum enzyme activities and milk indicators of inflammation were evaluated.Endotoxin challenge was in 7 groups of 3 cows each. Within the groups, cows were randomly assigned to 3 intravenous treatments: saline controls, steroid (one dose of dexamethasone at 0.44 mg/kg) and non-steroidal agent (two doses of flunixin meglumine at 1.1 mg/kg, 8 h apart).Anti-inflammatory therapy reduced rectal and mammary gland surface temperatures. Milk production was significantly reduced (p<0.05) in cows treated with dexamethasone. Although dexamethasone treatment produced significant increases (p<0.05) in blood leukocytes and segmented neutrophils, milk somatic cell concentrations were not significantly altered. Flunixin meglumine did not alter milk production or blood or milk leukocytes.     

Effects of intramammary infection and parity on calf weaning weight and milk quality in beef cows

The objectives of this study were to determine 1) the effect of intramammary infection on calf weaning weight, milk somatic cell count, and milk composition, and 2) the effect of parity on percentages of infected cows, infected quarters, and blind quarters. The number of infected quarters, milk somatic cell counts, milk components, and intramammary infection were studied at weaning in 164 beef cows. The percentage of infected cows ranged from 61.9% at first parity to 66.7% at fifth to ninth parities. Cows with three or four infected quarters had higher (P < .01) milk somatic cell counts than cows with zero, one, or two infected quarters. Among bacterial isolates, Staphylococcus aureus-infected quarters had the highest (P < .01) milk somatic cell count. Percentages of butterfat and lactose were lower (P < .01) in milk from infected quarters than from uninfected quarters. Infections by S. aureus and coagulase-negative staphylococci were the most common and accounted for 67 to 78% of the infections. Percentages of infected quarters and infections caused by S. aureus increased with parity (P < .01). Intramammary infections did not affect (P > .10) calf weaning weight. In conclusion, intramammary infection had no effect on calf weaning weight but increased milk somatic cell count and decreased the percentage of protein, lactose, solids-not-fat, and butterfat. The number of infected and blind mammary quarters increased with parity.