Risk Of Mastitis Research Articles

The use of Markov chain Monte Carlo for analysis of correlated binary data: patterns of somatic cells in milk and the risk of clinical mastitis in dairy cows

Two analytical approaches were used to investigate the relationship between somatic cell concentrations in monthly quarter milk samples and subsequent, naturally occurring clinical mastitis in three dairy herds. Firstly, cows with clinical mastitis were selected and a conventional matched analysis was used to compare affected and unaffected quarters of the same cow. The second analysis included all cows, and in order to overcome potential bias associated with the correlation structure, a hierarchical Bayesian generalised linear mixed model was specified. A Markov chain Monte Carlo (MCMC) approach, that is Gibbs sampling, was used to estimate parameters. The results of both the matched analysis and the hierarchical modelling suggested that quarters with a somatic cell count (SCC) in the range 41,000–100,000 cells/ml had a lower risk of clinical mastitis during the next month than quarters <41,000 cell/ml. Quarters with an SCC >200,000 cells/ml were at the greatest risk of clinical mastitis in the next month. There was a reduced risk of clinical mastitis between 1 and 2 months later in quarters with an SCC of 81,000–150,000 cells/ml compared with quarters below this level. The hierarchical modelling analysis identified a further reduced risk of clinical mastitis between 2 and 3 months later in quarters with an SCC 61,000–150,000 cells/ml, compared to other quarters. We conclude that low concentrations of somatic cells in milk are associated with increased risk of clinical mastitis, and that high concentrations are indicative of pre-existing immunological mobilisation against infection. The variation in risk between quarters of affected cows suggests that local quarter immunological events, rather than solely whole cow factors, have an important influence on the risk of clinical mastitis. MCMC proved a useful tool for estimating parameters in a hierarchical Bernoulli model. Model construction and an approach to assessing goodness of model fit are described.

Risk factors for dairy cow mastitis in the central highlands of Ethiopia.

This study, with the objective of assessing the effect of risk factors on dairy cow mastitis in the central highlands of Ethiopia, was undertaken between February and September 2001 in the urban and peri-urban areas of Addis Ababa, Ethiopia. A prevalence study and questionnaire survey were carried out simultaneously. Clinical examination of lactating udders and California mastitis test (CMT) determined clinical and subclinical mastitis, respectively. Risk factors for subclinical and clinical mastitis were identified from data on animals and farm management by chi-square analysis and subsequent logistic regression. Cows aged at least 8 years, with poor body condition, with at least 8 parities and in at least the eighth month of lactation had a significantly higher risk for subclinical mastitis (p < 0.05). The risk was reduced for cows up to their third parity in good body condition and for cows receiving dry cow therapy. Cows aged at least 4 years, or with at least 8 parities, cows in at least the fourth month of lactation, cows with poor body condition, leaking milk or previous udder infections had a significantly higher risk of clinical mastitis (p <0.05). The risk was reduced by the use of separate towels for udder cleaning and by drying off at the end of lactation. Most of the risk factors were in agreement with previous reports. However, stage of lactation and drying-off style were in contrast to others. Further research is needed to identify the interrelationship between production level, specific pathogens and management risk factors.

Peripartum serum vitamin E, retinol, and beta-carotene in dairy cattle and their associations with disease.

Peripartum decreases in serum concentrations of vitamins A and E may contribute to impaired immune function in dairy cows. The objectives of this study were to describe peripartum serum concentrations of alpha-tocopherol, beta-carotene, and retinol and their associations with disease risk. On 20 farms over 1 yr, blood samples were collected weekly from 1057 cows from 1 wk before expected calving until 1 wk postpartum. Serum concentrations of alpha-tocopherol, beta-carotene, and retinol, as well as several biochemical variables were measured. Their associations with the risk of retained placenta or clinical mastitis were modeled separately with logistic regression, and the factors associated with the concentration of each vitamin were modelled with mixed linear regression. Differences in vitamin concentrations between 2 batches of sera analyzed 6 mo apart required stratification of statistical analyses. Accounting for the effects of parity, season, and twins, an increase in alpha-tocopherol of 1 microg/mL in the last week prepartum reduced the risk of retained placenta by 20%, whereas serum nonesterified fatty acid concentration > or = 0.5 mEq/L tended to increase risk of retained placenta by 80%. In the last week prepartum, a 100 ng/mL increase in serum retinol was associated with a 60% decrease in the risk of early lactation clinical mastitis. There were significant positive associations of peripartum serum concentrations among each of alpha-tocopherol, beta-carotene, and retinol.

Growth of Seeded Escherichia coli in Rewetted Cattle Waste Compost of Different Stages

Compost is used mainly as an organic fertilizer, but it is also used as bedding material for cattle. Dairy cattle have been identified as a main reservoir of pathogenic Escherichia coli O157:H7. Further, E. coli is regarded as an environmental pathogen that causes bovine clinical mastitis. Hence, its growth in compost spread or compost bedding should be avoided. Physical and chemical conditions, available nutrients and microflora in compost change greatly during the composting process. Since pathogen growth in compost seems to be related to these changes, we assessed the possibility of E. coli growth in compost samples collected at 0, 7, 13, 22, 41, 190 and 360 d. Cattle waste composts with and without added tofu residue were collected from static piles and immediately air- dried. Compost samples were inoculated with a pure culture of E. coli, the moisture content was adjusted to 50%, and the samples were incubated for 5 d at 30°C. The numbers of E. coli in compost before and after incubation were determined by direct plating on Chromocult coliform agar. Almost all compost samples supported E. coli growth. Samples collected during or immediately after the thermophilic phase (day 7) showed the highest growth. Growth in samples more than 13 d old were not significantly different from those of aged compost samples. The addition of tofu residue gave a higher growth than its absence in younger samples collected prior to 13 d. To minimize the risk of environmental mastitis, the use of compost in the initial stage of the process is better avoided. (Asian-Aust. J. Anim. Sci. 2004. Vol 17, No. 2 : 278-282)

Milk Leakage—An Increased Risk in Automatic Milking Systems

Milk leakage (ML), or milk observed dripping or flowing from one or more teats between milkings, has been associated with increased risk of udder infections and mastitis in dairy cows. Preliminary observations indicate that ML might occur more often in automatic milking systems (AMS) than in conventional milking systems (CMS), but comparative data on the incidence of ML in AMS or in CMS are not available. Therefore, the occurrence of ML at various observation periods was studied in one AMS with cows housed in a free-stall barn in comparison to CMS with cows housed either in a free-stall barn or a tie-stall barn and milked at regular intervals in a herringbone milking parlor. Relationships between ML and other cow and management factors were also examined. In each of 2 yr, all cows (n=230 total; 46 cows present both years) were observed at 2-h intervals during six 24-h periods. At least one ML occurred in 39.0 (AMS) vs. 11.2% (CMS) of individual cows and in 16.2 (AMS) vs. 2.9% (CMS) of 24-h cow days studied. Milk leakage was not related to milk production, parity, stage of lactation, or estrous status. However, in the AMS, 62% of primiparous and 28% of multiparous cows leaked milk at least once. Milk leakage occurred more often in rear than in forequarters. Cows were usually lying down when ML was observed, but intervals from previous milking varied, especially in AMS. In AMS, about one-fifth of the ML observations occurred ≤4h after milking, and half of those were associated with disturbances at the previous milking. Milk flow rate was higher in quarters leaking milk than in other quarters. Strategies to reduce milk leakage in AMS may be important to minimize potential risks of udder disease.

Statistical modelling for clinical mastitis in the dairy cow: problems and solutions.

Modelling case occurrence and risk factors for clinical mastitis, as a key multifactorial disease in the dairy cow, requires statistical models. The type of model used depends on the choice of perception or the study level: herd, lactation, animal, udder and quarter. The validity of the tests that are performed through these models is especially ensured when hypotheses of independence between statistical units are respected, and when the model adjustments do not involve overdispersion faced with the observed data. In the article, the main sources of overdispersion are identified according to the different levels of perception of mastitis risk. Then, the proposed solutions to control for overdispersion at each study level are discussed and the difficulty to compare the study results is highlighted through a variety of methodological choices of the authors. Two main categories of models are used for modelling clinical mastitis, i.e. generalist exploratory models and explanatory designed models. The contribution of the explanatory models to improve modelling accuracy and relevance is documented through the two main published methodological approaches, the first one being based on a states model, and the second on a survival model. The integration and optimisation of such explanatory modelling methods should be possible in the future in order to develop a more global explanatory model including herd risk factors, which could pertinently predict udder infections (both clinical and subclinical) at the cow, lactation, or even udder and quarter levels.

Effects of lambing season and stage of lactation on ewe milk quality

A total of 240 bulk milk samples were collected and examined from January to July of 2000. The milk samples were obtained from 5 intensively managed flocks of Comisana ewes located in southern Italy. Milk sampling was performed separately on the ewes which had lambed in the autumn (October and November) of 1999 (ALB, autumn lambing) and in the winter (January and February) of 2000 (WLB, winter lambing). For each lambing season, 6 sampling cycles were carried out during early-, mid- and late-lactation (less than 60 days from 100 to 130 days and from 150 to 180 days in lactation, respectively), using the bulk milk of four consecutive milkings. In all the farms, the ewes received hay and concentrates during the winter season, while during the spring and summer season ewes grazed and were supplemented with hay and concentrates. The milk yielded by the WLB ewes recorded lower fat and protein contents compared to that of the ALB ewes (6.71 vs. 6.93% and 5.15 vs. 5.39%, respectively), as well as deteriorating renneting and hygienic characteristics. Irrespective of the lambing season, a higher SCC was recorded in late, compared to early- and mid-lactation milk (6.16 vs. 5.93 and 5.87log10somatic cells/ml) as well as a marked worsening in coagulating behavior. Reduced cheese-making efficiency was associated with a reduction in the casein and fat content of milk from the ALB ewes, and decreased calcium and phosphorus content in the WLB ewe milk. For both lambing seasons increased plasmin activity was recorded in the milk. Results suggest that ovine milk quality is strongly affected by the combined effects of seasonal changes in climate and herbage availability and variations in ewe metabolic status with the advancement of lactation. Proper housing sanitation, flock management and milking procedures play a major role in optimizing the quality of ewe milk during the late-lactation when several factors concur to increase the risk for mastitis, such as the involution of the mammary epithelium, rises in ambient temperatures, and worsening in air and surface hygiene. During the summer season, strategies to reduce the impact of high temperatures on lactating ewes and an appropriate administration of mineral elements with the feed diets are necessary to sustain the yield and quality of milk and cheese in ewes.

The association between quarter somatic-cell counts and clinical mastitis in three British dairy herds

The association between quarter somatic-cell counts (QSCCs) of milk and the risk of clinical mastitis (CM) was investigated in a 1-year study on three dairy herds in Somerset, UK. The three herds had 95–130 milking cows and an annual mean bulk milk somatic-cell count (BMSCC) of <150×10 3 cells/ml. The farms were visited every 4–6 weeks at morning milking when quarter-milk samples were collected. The farmers recorded all cases of CM and were trained to collect sterile milk samples from affected quarters, before treatment for bacteriology. The three herds had CM incidence rates of 25.4, 55.2, and 67.6 quarter-cases per 100 cow-years. Escherichia coli and Streptococcus uberis were cultured from approximately 50% of cases. QSCC was categorised and the risk of CM occurring in the month after the QSCC was examined using multilevel models to account for the correlated nature of the dependent data. Three models were developed: one for all cases of CM, one for those caused by coliforms and one for those caused by S. uberis. When all cases of CM were considered, quarters with somatic-cell count (SCC) 21–100×10 3 cells/ml had reduced odds (OR=0.60, P=0.06) and quarters with SCC >200×10 3 cells/ml has over three time the odds (OR=3.7, P<0.01) of CM compared with QSCC 1–20×10 3 cells/ml. When only coliform CM were investigated, quarters with SCC 6–200×10 3 cells/ml had reduced odds of coliform CM (OR=0.47, P=0.04) compared with QSCC 1–5×10 3 cells/ml, and SCC >200×10 3 cells/ml were not significantly different from the baseline. Finally, when S. uberis CM were investigated, quarters with SCC >200×10 3 cells/ml had more than three times the odds of S. uberis CM compared with QSCC 1–20×10 3 cells/ml (OR=3.73, P<0.01). QSCC <21×10 3 and >200×10 3 cells/ml are associated with increased odds of CM in the following 4–6 weeks; this association may be pathogen specific.

Immunity and mastitis. Some new ideas for an old disease.

The biggest challenge for host immune defense against mastitis-causing bacteria in dairy cows is to quickly recruit large enough numbers of opsonizing molecules and mature neutrophils into milk such that intramammary pathogens are cleared before they multiply significantly and the inflammatory response gets out of control. Currently, this challenge is best facilitated when established mastitis control procedures are practiced on the farm, including proper hygiene, milking procedures, and regular administration of approved mastitis vaccines. However, mastitis is still a significant problem. New animal functional genomics research is beginning to allow scientists to solve the puzzle of mastitis susceptibility. Results of this type of research offer the hope of giant leaps toward a clear identification of molecular genetic variation and potential gene targets for therapies and immune manipulations that could significantly reduce the risk of clinical mastitis in traditionally susceptible cows.

Influence of Dry Period Bacterial Intramammary Infection on Clinical Mastitis in Dairy Cows

Milk samples were taken from 1920 quarters (480 cows, six herds) on four occasions to examine the relationship between quarter level intramammary infection (IMI) during the dry period and clinical mastitis in the next lactation. All quarters were sampled at drying off and within 1 wk of calving, and two quarters from each cow were sampled both 0 to 7 and 8 to 14 d before calving. Milk samples were collected from all cases of clinical mastitis during the following lactation. Logistic regression models were developed to investigate the associations between IMI present during the sampling period and clinical mastitis. The probability of a quarter succumbing to clinical mastitis increased when Streptococcus dysgalactiae, Streptococcus faecalis, Escherichia coli, or Enterobacter spp. were cultured at drying off and when Escherichia coli, coagulase-positive staphylococcus, Serratia spp., or Streptococcus faecalis were cultured in two out of three late dry and post-calving samples. Quarters from which Corynebacterium spp. were isolated at drying off were at an increased risk of clinical mastitis, whereas the presence of Corynebacterium spp. in the late dry and post-calving samples was associated with a reduction in the risk of clinical mastitis. The risk of mastitis for specific pathogens increased if the same species of bacteria that had caused mastitis was isolated at least twice in the late dry and post-calving samples. Kaplan-Meier survival plots indicated that clinical mastitis associated with dry period infections was more likely to occur earlier in lactation than clinical mastitis not associated with dry period infections. There was evidence of quarter susceptibility to IMI or the possibility that infection with one organism led to clinical mastitis with another.

Investigations of Milk Quality from Teats with Milk Flow Disorders

The objective of this study was to investigate the quality of milk from teats with milk flow disorders. Somatic cell count, pathogens, and signs of mastitis (>100,000 cells/ml and pathogens detected) were determined in the milk from all teats of the udder before treatment of the affected teat, as well as 1 and 6 mo later. Teats with milk flow disorders were compared to all of the other teats from the same udder. Before treatment, the SCC from affected teats was 4.3million higher, the odds of detecting pathogens 6 times higher, and the odds of mastitis 11 times higher than in control teats (when adjusted for other significant explanatory variables). SCC and the risk of mastitis decreased after surgical treatment of the affected teats, whereas the chance of detecting pathogens was not affected. Six months after treatment, the SCC was 1.3million higher, and the odds of mastitis 6.5 times higher than in control teats. Throughout the study period neither SCC, the odds of detecting pathogens, nor mastitis changed significantly in control teats. It may be concluded from this study that milk quality from teats with milk flow disorders is decreased before treatment and does not reach the milk quality from unaffected teats within 6 mo after treatment.

Study of clinical mastitis in British dairy herds with bulk milk somatic cell counts less than 150,000 cells/ml

A 12-month prospective study of clinical mastitis was conducted in 482 British dairy herds with a bulk milk somatic cell count (BMSCC) of less than 150,000 cells/ml. The mean proportion...

Lactation mastitis: occurrence and medical management among 946 breastfeeding women in the United States.

In 1994-1998, the authors followed 946 breastfeeding women from Michigan and Nebraska for the first 3 months postpartum or until they stopped breastfeeding to describe mastitis incidence, mastitis treatment, and any associations between mastitis occurrence and hypothesized host characteristics and behaviors. Participants were interviewed by telephone at 3, 6, 9, and 12 weeks postpartum or until they ceased breastfeeding. A total of 9.5% reported provider-diagnosed lactation mastitis at least once during the 12-week period, with 64% diagnosed via telephone. After adjustment in a logistic regression model, history of mastitis with a previous child (odds ratio (OR) = 4.0, 95% confidence interval (CI): 2.64, 6.11), cracks and nipple sores in the same week as mastitis (OR = 3.4, 95% CI: 2.04, 5.51), using an antifungal nipple cream (presumably for nipple thrush) in the same 3-week interval as mastitis (OR = 3.4, 95% CI: 1.37, 8.54), and (for women with no prior mastitis history) using a manual breast pump (OR = 3.3, 95% CI: 1.92, 5.62) strongly predicted mastitis. Feeding fewer than 10 times per day was protective regardless of whether or not feeding frequency in the same week or the week before mastitis was included in the model (for the same week: 7-9 times: OR = 0.6, 95% CI: 0.41, 1.01; < or =6 times: OR = 0.4, 95% CI: 0.19, 0.82). Duration of feeding was not associated with mastitis risk.

Risk of clinical mastitis in dairy herds with a high proportion of low individual milk somatic-cell counts

The relationships between the herd-somatic-cell count (SCC) pattern on a test day and the incidence of clinical mastitis in the subsequent period were studied by collecting health data and monthly records from 2 years (1995–1997) from 121 farms located in the west of France. A total of 980 herd-periods (from one test day to the following one) were analyzed. The outcome variable was the incidence density of clinical mastitis (ICM) within the herd-period. The herd-SCC pattern on a test day was described by cross-combining the proportions of cows with low SCC (<50 000 cells/ml) or with high SCC (>250 000 cells/ml). The relationship between herd-SCC pattern and subsequent ICM was assessed using a generalized linear mixed model. A sensitivity analysis evaluated the effect of different proportions of cows with low SCC on significance and magnitude of the relationship. Risk of clinical mastitis was expressed as a risk ratio (RR) in comparison to a moderate herd-SCC level (with low proportions of cows with low or high SCC). Median ICM was 0.38 cases per 365 cow-days at risk (first and third quartiles: 0 and 0.88). In the situations where few cows (<15%) had SCC>250 000 cells/ml, ICM was higher (RR>1.31) when the proportion of cows with low SCC exceeded 50% than in the reference situation. Risk ratios increased as the proportion of cows with low SCC increased from 40 to 60%. In the situations where the proportion of cows with SCC>250 000 cells/ml exceeded 15%, ICM was higher compared to the reference situation (whatever the proportion of low SCC). Risk ratios were also higher when the proportion of cows with low SCC were >40–60%, compared to the pattern with the proportion of cows with low SCC below 40%. Herd situations with a high proportion of cows with low SCC appeared to be at increased risk of clinical mastitis.

Effects of different suckling systems on milk production, udder health, reproduction, calf growth and some behavioural aspects in high producing dairy cows — a review

This article discusses the consequences of different suckling systems in the industrial countries for the milk production, udder health, reproduction and behaviour of high producing dairy cows and the effects on the gain, health and behaviour of the calves. The suckling systems are divided into three different categories depending on the purpose and duration of the suckling period. Long-term suckling with or without additional milking covering the period where the calf has a nutritional need for milk, and short-term suckling, where cow and calf are kept together in the colostrum period only. Long-term suckling without additional milking in early lactation can in some situations stimulate the subsequent milk production to a greater extent than milking alone. No clear or significant differences can be found between restricted and free suckling systems. Most experiments show that suckling decreases the risk of mastitis in the suckling period and in some cases even for some time after the suckling has been terminated. Suckling and milking during the same period is not advantageous in production turns because of a very poor ejection of milk. Long-term suckling can increase the post-partum interval until first heat, in some cases until the end of the suckling period. However, as the cows appear to be more fertile, the net effect on reproduction is small. The suckled calves are usually healthy with a high daily gain. Short-term suckling have more advantages than disadvantages on production, health and behaviour of both the cow and the calf compared to an immediate separation after birth.

Risk factors for mastitis in breastfeeding women: results of a prospective cohort study.

To identify potential risk factors for the development of mastitis in breastfeeding women. A prospective cohort study with questionnaire and telephone follow-up was conducted. Women were recruited after delivery at either the teaching hospital or the only private hospital with an obstetric service during May to December 1994 in Newcastle, New South Wales and were followed up at home for six months. 1,075 breastfeeding women were recruited and were sent follow-up questionnaires at three, eight and 26 weeks post-delivery. Mastitis occurred in 20% (95% CI 18-22%) of women during the first six months. Factors that were statistically significantly and independently related to mastitis were: past history of mastitis (adjusted Hazard Ratio=1.74, 1.07-2.81), university or college education (HR=1.93, 1.18-3.16), blocked duct (HR=2.43, 1.68-3.49), cracked nipples (HR=1.44, 1.00-2.07), use of creams on nipples (HR=1.83, 1.22-2.73), particularly papaya cream (Relative Risk = 1.83, 1.36-2.47), and always starting with the alternate breast on consecutive feeds (HR=2.28, 1.50-3.44). Women with a past history of mastitis had an increased risk of developing mastitis. Blocked ducts and cracked nipples serve as warning signs for mastitis. Use of some creams may increase the risk of mastitis and their value should be tested in clinical trials. We have identified several pre-natal and post-natal markers for increased risk of mastitis that may assist in its early identification and treatment. The use of creams on nipples may introduce pathogens that cause mastitis and should be avoided.

Case-Control Study of Risk Factors for Clinical Mastitis in Postpartum Dairy Heifers

A case-control study was carried out to evaluate risk factors for clinical mastitis occurring in dairy heifers between 1 and 14 d postpartum. Case and control heifers were matched on herd; the control was the heifer that calved closest in time, before or after, the particular case. Data were analyzed by conditional logistic regression. The final multivariate model included 339 case-control pairs. Blood in the milk, udder edema, teat edema, and milk leakage, all recorded at the time of parturition, were significant risk factors. Purchased heifers and heifers with skin lesions between udder and thigh were not at increased risk of clinical mastitis. Separate analysis of a subgroup of case-control pairs identified teat edema, blood in the milk, and milk leakage at calving as risk factors for clinical mastitis caused by Staphylococcus aureus.

Cubicle Refusal and Rearing Accommodation as Possible Mastitis Risk Factors in Cubicle-Housed Dairy Heifers

Fifty-nine of the 65 dairy farms with cubicle sheds in the Norwegian county of Oppland in 1990 were included in a study of rearing accommodation, cubicle refusal and mastitis incidence. The farmers recorded the favoured resting location of the individual cows and heifers throughout the final week of pregnancy as well as during calving. The observations were matched with individual records of mastitis cases during the first 30 days after calving. Mastitis incidence in the heifers was analysed by logistic regression using rearing accommodation and cubicle refusal as independent variables, controlling for herd as a clustering factor. Cubicle refusal was found in 29% of the heifers, but in only 3% of older cows. The results of the analysis indicated a tendency for cubicle refusal to be associated with an increased mastitis incidence among the heifers (OR = 2.2, c.i.95%OR = 0.9–5.4, P = 0.08). Cubicle refusal accounted for 21% (0–32%) of the mastitis cases in the study population (PAF = 0.21).

Presence of glutamine at position 74 of pocket 4 in the BoLA-DR antigen binding groove is associated with occurrence of clinical mastitis caused by Staphylococcus species

Potential relationships between amino acid motifs in the antigen binding groove of various alleles of the bovine major histocompatibility complex DR (BoLA-DR) molecule and occurrence of clinical mastitis caused by Staphylococcus species (non- Staphylococcus aureus) were investigated in a case-control study. A significant association ( P≤0.05) was detected between the presence of glutamic acid at position β74 and occurrence of mastitis caused by Staphylococcus spp. with a relative risk of 11. This motif is present in BoLA- DRB3.2 ∗ 22, ∗ 23 and ∗ 24 alleles. Presence of a positively charged residue (arginine or lysine) at position 13 also showed a tendency ( P≤0.1) towards an association with a higher risk of clinical mastitis caused by the same bacteria. This motif is present in BoLA- DRB3.2 ∗ 23 and ∗ 8 alleles. Similarly, presence of arginine at position β71 (present in alleles ∗ 23 and ∗ 22) was associated with occurrence of this disease. These positions (β13, β71 and β74) form pocket 4 of the antigen binding groove, which plays an instrumental role in antigen binding and recognition by T-lymphocytes. Thus, it can be concluded that pocket 4 of the BoLA-DR molecule is involved in conferring susceptibility to clinical mastitis caused by Staphylococcus spp.

Relationship between milk somatic-cell counts in the first lactation and clinical mastitis occurrence in the second lactation of French Holstein cows

The relationship between 10 cell-level descriptors in the first lactation and the risk of clinical mastitis in the second lactation was studied in 10 205 Holstein cows from 1254 commercial herds using logistic regression. These 10 cell descriptors were based on the mean cell level over the whole first lactation, on the cell level at the beginning or at the end of the first lactation or on the proportion of cell counts below or above given thresholds. Separate analyses were also performed for subsets of herds defined according to their clinical mastitis incidence risk and their lactation mean somatic-cell count (SCC). Odds of clinical mastitis in second lactation was highest (lowest) for high- (low-) yielding cows. All cell descriptors provided consistent results. Lower (higher) mean cell level, higher (lower) proportion of low SCC values, and lower (higher) proportion of high SCC values in the first lactation were associated with a lower (higher) risk of clinical mastitis in the second lactation. The same trends were observed in all subgroups of herds. Cows with the lowest mean SCC in the first lactation had the lowest risk for clinical mastitis in the second lactation. This suggests that selection for decreased SCC may effectively reduce clinical mastitis incidence and that the breeding goal should favor cows with the lowest observed SCC.