Intramammary Infection Status Research Articles

Somatic Cell Count During and Between Milkings

The objectives of the study were to determine 1) how sampling time between milkings affects the sensitivity and specificity of somatic cell count (SCC) as an indicator for intramammary infection (IMI) status, and 2) which cells are responsible for the diurnal variation in SCC. Six Prince Edward Island, Canada, dairy herds were selected. Quarter samples for SCC were collected immediately before the a.m. milking (pre-a.m.), halfway through the a.m. milking, immediately after the a.m. milking, every 60min after detachment of the milking unit, and immediately before the p.m. milking (pre-p.m.). Compared with the geometric mean SCC at the pre-a.m. milking, SCC of quarters with no IMI between milkings was higher up to 7h after milking. The pre-p.m. SCC was significantly lower than the pre-a.m. SCC in quarters with no IMI. Specificity of SCC at a cutoff of 200,000 or 500,000 cells/mL as an indicator for IMI status declined substantially after the a.m. milking. In quarters with elevated SCC, the proportion of polymorphonuclear leukocytes was larger immediately after milking. For accurate interpretations of SCC tests—whether by a laboratory, portable SCC device, or the California Mastitis Test—veterinarians, researchers, and udder health advisors should take milk samples immediately before milking.

Influence of intramammary infection and non-infection factors on somatic cell counts in dairy goats.

A total of 1304 goat udder halves were sampled monthly during an entire lactation (6262 samples) with the aim of identifying factors affecting milk somatic cell count (SCC). Bacteriological analyses for identification of mastitis pathogens were carried out on all samples and SCC was also determined. All animals were examined for infection by caprine arthritis-encephalitis virus (CAEV) using a commercial ELISA test kit. Results obtained were arranged in two databases (whole-lactation average half-udder database and monthly half-udder database) and two mixed models were applied. Random effects of half udder nested into flock and fixed effects of flock, intramammary infection (IMI) status, number of kids born, length of lactation and interaction of parity with IMI status were significant for the first database. CAEV infection and its interaction with IMI status was not significant. Milk SCC was significantly increased for infected udder halves and milk from udder halves infected with minor pathogens had lower SCC than udder halves infected with major pathogens. For healthy udder halves, SCC was higher in older animals but this effect was not evident in halves with IMI. Multiple birth and short-duration lactation were factors associated with elevated milk SCC. The second mixed model considered repeated measures in time for consecutive samplings throughout lactation (stage of lactation) which was also a significant factor with increasing stage of lactation. The influence of all these factors should be taken into account in the establishment of more reliable diagnostic SCC thresholds for IMI.

Heritability of Intramammary Infections at First Parturition and Relationships with Sire Transmitting Abilities for Somatic Cell Score, Udder Type Traits, Productive Life, and Protein Yield

The objective of this study was to determine the relationships among daughter intramammary infections at first parturition and sire transmitting abilities for somatic cell score, udder type traits, productive life, and protein yield. Quarter milk samples from 958 daughters (in eight Pennsylvania herds and one Nebraska herd) of 182 Holstein sires were collected within a few days of first calving and cultured to determine intramammary infection status. A total of 446 cows had intramammary infections in 835 quarters at first parturition. Incidence of intramammary infections at first parturition and the proportion of quarters infected per cow were regressed on age at first calving, days in milk at sample collection, herd-season of calving (a classification variable), and sire transmitting abilities taken one at a time. Linear effects, non-linear effects, and odds ratios were estimated for sire transmitting abilities. Separate, preplanned analyses were conducted on data from one herd that gave all heifers an intramammary antibiotic infusion in each quarter 30 d prior to the expected calving date. Separate analyses were also conducted on dependent variables that considered intramammary infections at first parturition from: all organisms, coagulase-negative staphylococci, coliform species, streptococci other than Streptococcus agalactiae, and the most common environmental organisms (coliform species and streptococci other than Streptococcus agalactiae). Daughters of sires that transmit the lowest somatic cell score had the fewest intramammary infections at first parturition. Daughters of sires that transmit longer productive life, shorter teats, and closely spaced front teats had fewer intramammary infections at first parturition. Selection for lower somatic cell score, longer productive life, shorter teats, or closely spaced front teats may reduce the incidence of intramammary infections at first parturition.

Evaluation of the California Mastitis Test for Screening Dairy Cows for Intramammary Infection at Calving

Udder health management programs at dry-off and during the dry period are essential to control and prevention of mastitis in dairy cattle. Knowledge of the prevalence of subclinical intramammary infection status at calving, and the specific pathogens involved, allows producers to evaluate effectiveness of these udder health programs. However, milk sampling and culturing all cows at the time of calving can be expensive and time consuming, and has not been widely adopted by the industry. California mastitis test (CMT) has not been recommended for use in recently fresh cows. This study examined the use of the CMT for selecting quarters in fresh cows for further bacteriological examination to identify the presence of intramammary infection. Cut-points for defining a positive CMT test and length of time post-calving were evaluated.

Quarter-milk somatic cell count at calving and at the first six milkings after calving

Thirty cows were studied during the first six milkings after calving. Quarter foremilk samples were collected by the farmers at calving and at six subsequent milkings. Geometric-mean somatic cell count (SCC) decreased from 593 000 at calving to 126 000 cells/ml at the sixth milking after calving. In quarters infected with major pathogenic bacteria, geometric-mean SCC was 3 229 000 cells/ml at calving, and 1 257 000 cells/ml at the sixth milking after calving. In quarters infected with minor pathogenic bacteria, geometric-mean SCC was 1 000 000 cells/ml at calving, and 170 000 cells/ml at the sixth milking after calving. In culture-negative quarters, geometric-mean SCC decreased from 306 000 at calving to 42 000 cells/ml at the sixth milking after calving. Quarter SCC can be used early postpartum to give an indication of intra-mammary infection status.

Epidemiology of Heifer Mastitis

Until recently, it had been assumed that primigravid heifers were seldom affected by intramammary infections (IMI) at or near parturition. Recent research results now suggest that this assumption is false. A number of studies report a high rate of IMI in heifers at or near parturition.(1-3) Interestingly, the pathogens associated with these IMI's appear to have a regional distribution. A study in the southern United States found a high prevalence of IMI associated with Staphylococcus aureus.(2) Studies in the New England and Southeastern United States detected a high prevalence of IMI associated with coagulase negative staphylococci.(1,3) IMI's associated with Staphylococcus aureus are related to histopathologic lesions in the mammary gland which suggest that these infections may hamper the normal development of the lactating gland.(4) These findings have prompted research to investigate the use of antibiotic therapy to decrease the risk of IMI. This research has found that antibiotics administered prior to calving will decrease the prevalence of peripaturient IMI.(5,6) A question that has not been answered is: Do these infections in heifers, particularly IMI by the minor pathogens, warrant treatment? The objectives of this paper are to report preliminary data describing the incidence of IMI in heifers, the pathogens involved in the infections and the subsequent rates of clinical mastitis in first lactation heifers conditional on the IMI status at freshening.

Prevalence and Ultrastructural Characteristics of Bovine Mammary Corpora Amylacea During the Lactation Cycle

Morphologic and histochemical study of spherical, lamellated inclusion bodies in bovine mammary parenchyma established presence of corpora amylacea. The majority (90%) were in alveolar lumina, followed by stroma (7%) and epithelium (3%). Occurrence of corpora amylacea was unrelated to lactation age, intra-mammary infection status, milk somatic cell concentration, or milk production. Quantitative analysis demonstrated a progressive increase of prevalence of these structures from the early to later stages of lactation, followed by a return during the late dry period to concentrations at early lactation. Ultrastructural study revealed deeply basophilic, dense, lamellated deposits (70%) and less dense, fibrillar deposits (30%). Dense bodies stained partially or not at all for amyloid but stained for presence of calcium salts, whereas fibrillar bodies were amyloid positive and calcium negative. Corpora amylacea were most prevalent in fully differentiated parenchymal areas (47.1 bodies/unit tissue area of 2.4×106μm2), less numerous in intermediately differentiated areas (23.4), and sparse in nonsecretory areas (7.1). Morphologic relationships between deposits and parenchyma suggest that corpora amylacea suppress milk secretion and flow during late lactation in isolated areas by engorging luminal spaces and clogging small ducts, leading to milk stasis and involution.

Efficacy of an Iodine Backflush for Preventing New Intramammary Infections

Efficacy of an iodine backflush system for reducing new intramammary infection was tested in two 11-wk trials. Forty cows in each trial were paired by breed, age, stage of lactation, and intramammary infection status. Each pair was assigned randomly either to a group milked with clusters that were reverse flushed with water, 25ppm iodine, water and air or to a group milked with clusters receiving no backflush treatment between cows. Back-flushing clusters reduced infections caused by Corynebacterium bovis and coagulase-positive staphylococci in both trials. However, backflushing clusters produced no clear advantage for reducing new infections with coagulase-negative staphylococci, Gram-negative bacilli, or streptococci (species other than Streptococcus agalactiae). No differences in somatic cell counts between experimental groups were observed. Teat cup liners and teat ends were swabbed after 120 and 1200 milkings/liner. Total microbial counts were significantly greater for liners that were not backflushed than from backflushed liners at each swabbing. However, no differences were significant between groups for mean teat end microbial counts in either trial.