Effect of subclinical and clinical hypocalcemia and dietary cation-anion difference on rumination activity in periparturient dairy cows.

Rumination involves a complex series of muscle contractions that bring a bolus of ingesta to the mouth for further mastication before it is swallowed again. Healthy cows ruminate 8 to 9 h/d. Hypocalcemia is known to disrupt nerve and muscle function. Our hypothesis was that hypocalcemia in periparturient cows would reduce rumination activity. Twenty-six Holstein cows entering their third lactation or greater were fed a control diet [dietary cation-anion difference (DCAD) = +196 mEq/kg of dry matter (DM)] or a low DCAD diet supplemented with anions (DCAD = -9 mEq/kg of DM) prepartum. Periparturient plasma Ca concentration and rumination rate were determined. Four of 12 control cows developed clinical milk fever, necessitating intravenous Ca therapy. Rumination rate decreased in all cows around the time of calving. Rumination rate on the first and second day of lactation was highly correlated with the cow's plasma Ca concentration on the first day of lactation. In one of our statistical models, a normocalcemic cow was defined as a cow whose plasma Ca concentration remained above 2.00 mM. Cows were retrospectively classified as normocalcemic, subclinically hypocalcemic, or clinically hypocalcemic (milk fever). Only 4 cows were considered normocalcemic, and all had been fed the low DCAD diet. Normocalcemic cows spent more time ruminating on the first day after calving than subclinically hypocalcemic cows or cows with milk fever. Cows with milk fever had a lower rumination rate than normocalcemic cows through d 3 of lactation. Rumination activity in cows with milk fever was almost nondetectable in the hours before and after intravenous Ca treatment for an extended period, despite the return of muscle function that allowed the cows to stand and eructate following treatment. Other statistical models using different definitions of normocalcemia gave qualitatively similar results. Diet had a great effect on plasma Ca concentration and rumination rate. Even when cows with clinical milk fever were removed from the control cow data set, cows on the low DCAD diet had significantly greater plasma Ca concentrations in the first 36 h after calving and a higher rumination rate on d 1 of lactation (248 ± 26 min) than control cows (158 ± 32 min).

Effects of a Saccharomyces cerevisiae fermentation product on heat-stressed dairy cows.

The objective of this study was to evaluate the effects of supplementing a Saccharomyces cerevisiae fermentation product (SCFP) on body temperature indices, metabolism, acute phase protein response, and production variables during heat stress (HS). Twenty multiparous lactating Holstein cows (body weight = 675 ± 12 kg; days in milk = 144 ± 5; and parity = 2.3 ± 0.1) were used in an experiment conducted in 2 replicates (10 cows/replicate). Cows were randomly assigned to 1 of 2 dietary treatments: control diet (CON; n = 10) or the CON diet supplemented with 19 g/d of SCFP (n = 10; NutriTek, Diamond V, Cedar Rapids, IA). Cows were fed their respective diets for 21 d before initiation of the study. The experiment consisted of 2 periods: thermoneutral (period 1; P1) and heat stress (period 2; P2). During P1 (4 d), cows were fed ad libitum and housed in thermoneutral conditions for collecting baseline data. During P2 (7 d), HS was artificially induced using an electric heat blanket (EHB; Thermotex Therapy Systems Ltd., Calgary, AB, Canada). Cows were fitted with the EHB for the entirety of P2. Rectal temperature, respiration rate, and skin temperature were obtained twice daily (0600 and 1800 h) during both periods. Overall, HS increased rectal temperature, skin temperature, and respiration rate (1.4°C, 4.8°C, and 54 breaths/min, respectively) relative to P1, but no dietary treatment differences were detected. Compared with P1, HS decreased dry matter intake and milk yield (36 and 26%, respectively), and the reductions were similar between dietary treatments. Relative to P1, HS increased milk fat content and milk urea nitrogen (17 and 30%, respectively) and decreased milk protein and lactose contents (7 and 1.4%, respectively). Overall, HS increased (52%) plasma cortisol concentrations of CON, but circulating cortisol did not change in SCFP-fed cows. Heat stress increased circulating lipopolysaccharide binding protein and serum amyloid A (SAA; 2- and 4-fold, respectively), and SCFP supplementation tended to decrease peak SAA (∼33%) relative to CON cows. Overall, although HS did not influence circulating white blood cells and neutrophils, SCFP increased circulating white blood cells and neutrophils by 9 and 26%, respectively, over CON in P2. In conclusion, HS initiated an acute phase protein response and feeding SCFP blunted the cortisol and SAA concentrations and altered some key leukocyte dynamics during HS.

Validating a heat stress model: The effects of an electric heat blanket and nutritional plane on lactating dairy cows.

The efficacy of an electric heat blanket (EHB) has previously been confirmed as an alternative method to evaluate heat stress (HS). However, a pair-feeding design has not been used with the EHB model. Therefore, study objectives were to determine the contribution of the nutritional plane to altered metabolism and productivity during EHB-induced HS. Multiparous Holstein cows (n = 18; 140 ± 10 d in milk) were subjected to 2 experimental periods (P); during P1 (4 d), cows were in thermoneutral conditions with ad libitum feed intake. During P2 (4 d), cows were assigned to 1 of 2 treatments: (1) thermoneutral conditions and pair-fed (PF; n = 8) or (2) EHB-induced HS with ad libitum feed intake (n = 10). Overall, the EHB increased rectal temperature, vaginal temperature, skin temperature, and respiration rate (1.4°C, 1.3°C, 0.8°C, and 42 breaths/min, respectively) relative to PF cows. The EHB reduced dry matter intake (DMI; 47%) and, by design, PF cows had a similar pattern and extent of decreased DMI. Milk yield decreased in EHB and PF cows by 27.3% (12.1 kg) and 13.4% (5.4 kg), respectively, indicating that reduced DMI accounted for only ∼50% of decreased milk synthesis. Milk fat content tended to increase (19%) in the EHB group, whereas in the PF cows it remained similar relative to P1. During P2, milk protein and lactose contents tended to decrease or decreased (1.3 and 2.2%, respectively) in both EHB and PF groups. Milk urea nitrogen remained unchanged in PF controls but increased (34.2%) in EHB cows relative to P1. The EHB decreased blood partial pressure of CO2, total CO2, HCO3, and base excess levels (17, 16, 17, and 81%, respectively) compared with those in PF cows. During P2, the EHB and PF cows had similar decreases (4%) in plasma glucose content, but no differences in circulating insulin were detected. However, a group by day interaction was detected for plasma nonesterified fatty acids; levels progressively increased in PF controls but remained unaltered in the EHB cows. Blood urea nitrogen increased in the EHB cows (61%) compared with the PF controls. In summary, utilizing the EHB model indicated that reduced nutrient intake explains only about 50% of the decrease in milk yield during HS, and the postabsorptive changes in nutrient partitioning are similar to those obtained in climate-controlled chamber studies. Consequently, the EHB is a reasonable and economically feasible model to study environmental physiology of dairy cows.

Technical note: Developing a heat stress model in dairy cows using an electric heat blanket.

Precisely studying the biological consequences of heat stress (HS) in agriculturally relevant animals typically requires expensive climate-controlled facilities, infrastructure inaccessible to most researchers. Thus, study objectives were to explore the efficacy of an electric heat blanket (EHB) as an alternative method for evaluating HS and to determine whether EHB-induced hyperthermia affects production parameters similar to natural HS. Lactating Holstein cows (n = 8; 133 ± 3 d in milk; 709 ± 31 kg; 2.6 ± 0.3 parity) were housed in individual box stalls and allowed to acclimate for 3 d. After acclimation, the trial consisted of 2 experimental periods (P). During P1 (3 d), cows were housed in thermoneutral conditions for collecting baseline data. During P2 (7 d), cows were fitted with an EHB. During the entire experiment cows were fed ad libitum, and dry matter intake (DMI) was recorded daily. Cows were milked twice daily (0600 and 1800 h), and milk samples were collected on d 2 and 3 of P1 and d 3 and 7 of P2. Rectal temperature, respiration rate, heart rate, and skin temperature were obtained twice daily (0600 and 1800 h) during both P1 and P2. Overall, there was an increase in rectal temperature and respiration rate at 0600 h (1.0°C and 25 breaths/min, respectively) and 1800 h (1.2°C and 29 breaths/min, respectively) during P2. The EHB decreased DMI and milk yield (25 and 21%, respectively) by the end of P2. During P2, milk protein tended to decrease (4.4%) compared with P1. In contrast, milk urea nitrogen increased (33%) during P2 relative to P1. No other differences were observed in milk composition. In summary, our results indicate that employing an EHB affects physiological and production parameters similarly to natural HS (i.e., increased rectal temperature and respiration rate, decreased DMI and milk yield); thus, the EHB is an effective and inexpensive research tool for evaluating the biological consequences of HS in lactating dairy cows.

Short communication: The effect of novel antiseptic compounds on umbilical cord healing and incidence of infection in dairy calves.

The goal of dipping the umbilical cord after birth in calves is to promote healing of the umbilical stump, prevent infection, and encourage the umbilical tissue to detach from the body. Treatment applied to the umbilical area is an important management step for preventing morbidity and mortality in calves. The objective of this study was to compare the effect of 4 umbilical dips on the healing rate, incidence of infection, and age at umbilical cord detachment using newborn Holstein heifer calves (n = 73). Calves were alternately assigned by birth order to 4 treatment groups: 7% iodine, a dry dip formulated using an antibacterial peptide (nisin) mixed with talc (3.105 g of nisin per 100 g of talcum powder on a weight per weight basis), liquid nisin (64 µg/mL), and 4% chlorhexidine mixed with alcohol in a 50:50 solution. Umbilical cords were dipped 30 min after birth. Before initial dipping, umbilical cord diameter (as an indicator of the rate of cord drying and healing rate) was determined using a digital caliper. The caliper measurements were repeated at 24 ± 1, 48 ± 1, and 72 ± 1 h (±standard deviation) of age and were continued daily until the umbilical cord healed and detached from the animal's body. Diagnosed umbilical infections were documented by veterinary staff based on a combination of clinical symptoms (redness, swelling, purulent discharge, painful response (flinch or kicking) to palpation of the umbilical stump) in addition to a lack of appetite and fever. Data were analyzed using MIXED model procedures with fixed effect of umbilical treatment. No treatment differences were noted between dips on the umbilical cord drying rate or days for umbilical cord to detach. Treatment effects were observed on incidence of umbilical infection (incidence of infection for calves across all treatments was 9.0%).

Short communication: The effect of 4 antiseptic compounds on umbilical cord healing and infection rates in the first 24 hours in dairy calves from a commercial herd.

The objective of this study was to compare the effect of 4 antiseptic compounds on the healing rate and incidence of infection of umbilical cords in newborn calves (n=60). Late gestation Jersey cows were monitored at a commercial farm (Sioux Jersey, Salix, IA) and newborn purebred (n=30) and crossbred (n=30) calves were obtained within 30min after birth. Calves were alternately assigned by birth order to 4 treatment groups: 7% tincture of iodine, 0.1% chlorine created using a novel chlorine disinfectant technology, chlorohexidine gluconate 4.0% wt/vol, and 10% trisodium citrate. Prior to dipping (within 30min of birth), diameter of the umbilical cords (as an indicator of cord drying and healing) were determined using digital calipers. In addition, as an indicator of umbilical infections, surface temperature of the umbilical stump (along with a reference point at the midpoint of the sternum) was determined using a dual-laser infrared thermometer. These measurements were all repeated at 24±1 h of age. All data were analyzed using mixed model methods. All models included fixed effects of breed (Jersey or Jersey cross), sex (bull or heifer), and treatment. Fixed effect interactions were not included in the statistical model due to the relatively small sample size. No treatment differences were noted for healing rate of umbilical cords. Initially, mean umbilical cord diameter was 22.84±3.89mm and cords healed to a mean diameter of 7.64±4.12mm at 24 h of age. No umbilical infections were noted for calves on any treatment during the course of this study. Mean surface temperature of the umbilical stump was 33.1±2.2°C at birth (1.5±1.6°C higher than the sternal reference temperature), and at 24±1 h of age the mean temperature of the umbilical stump was 33.0±4.3°C (0.5±1.8°C lower than the sternal reference temperature). These data suggest that these antiseptic compounds are equally effective for preventing infections and permitting healing of the umbilical cord when used within 30min of birth.

Adherence and efficacy of an external teat sealant to prevent new intramammary infections in the dry period.

The efficacy and adherence of an external teat sealant applied at drying off was evaluated in 2 studies between 1997 and 1999. At drying off, 2 quarters were randomized to receive intramammary dry-cow antibiotic therapy, and the remaining 2 quarters were treated with either a single or double application of external teat sealant. Approximately 3 d before calving, all teats that had been dipped at drying off were redipped in a single coating of teat sealant. Adherence of the teat sealant was scored for the first 2 wk after drying off, and physical traits of the teat skin and teat ends were recorded. Quarter milk samples were collected 1 wk before drying off, at drying off, 0 to 7 d, and 14 to 21 d postcalving. Somatic cell counts were determined from quarter samples taken at d 7 and 14 to 21 d after calving. Data were analyzed from 172 dry periods of 162 cows. The mean time of sealant adherence following drying off application was 3 +/- 0.13 d. Double sealant application significantly increased the duration of adherence by 0.67 d. Teats that had teat sealant applied twice at drying off and that had up to 3 d of adherence had the lowest linear score (LS) at 14 to 21 d (1.89 +/- 0.31) of all quarters. The LS of quarters that received antibiotic therapy only was 2.27 +/- 0.19. The majority of intramammary infections identified at drying off were caused by the minor pathogens, coagulase-negative staphylococci and Corynebacterium bovis (51 and 23%, respectively). The results from this study indicate that duration of sealant adherence to the teat-end should be considered when evaluating the impact of teat sealant treatment at drying off on the level of infection after calving. Double sealant application, cooler seasons, and longer teat lengths were associated with a significant increase in the duration of sealant adherence to the teat-end.

Herd management factors that affect duration and variation of adherence of an external teat sealant.

During 1998 and 1999, a purposive sample of Ontario dairy herds was enrolled in a study to examine management factors associated with adherence of an external teat sealant. A total of 74 herds were recruited that had previously complied with a provincial Sentinel Herd mastitis study. All herds were sent a management survey and a commercially available external teat sealant product. The sealant was applied to all cows in first lactation or greater that were scheduled to go dry. Adherence of the teat sealant was scored on a scale of 1 to 5 (1 = sealant completely removed) for the first 12 d following dry off. Complete data were analyzed from 806 cows in 48 herds (mean of 17 cows/herd). Mean duration of adherence of the teat sealant was 4 d (range 1 to 7 d). Of the management factors recorded, only changing the feed to reduce milk production prior to drying off was significantly associated with 0.78-d prolonged adherence. No factors related to dry cow housing, bedding material, or floor surface were associated with the duration of adherence. The variance around the duration of adherence was examined. The median variance of adherence was 3.0 d(2), which was equivalent to a standard deviation of 2.6 d. Herds in which dry cows were housed in tie-stall barns, and the herds that used a penicillin and novobiocin combination dry cow antibiotic had the greatest variation. We concluded that modifying the ration to reduce milk production enhanced adherence of an external teat sealant. Teat-end preparation prior to application of the teat sealant is an important factor to consider when choosing to adopt this dry period mastitis prevention strategy. This study demonstrates that beyond cow- and quarter-level factors, herd management factors can influence the duration and variation of sealant adherence experienced among different herds.

Association of cow and quarter-level factors at drying-off with new intramammary infections during the dry period.

Our objective was to describe cow and quarter-level factors associated with drying-off, and to evaluate their impacts on new intramammary infections (IMI) during the dry period. Data from 300 cows in five research herds were collected starting 2 weeks prior to scheduled drying-off. Variables of interest included daily milk production, teat-end integrity, formation of the teat-canal keratin plug, and quarter-milk bacteriological culture results. Overall, 11% of quarters developed new IMI in the dry period; this varied by herd, parity and time of the study. Most new IMI were caused by environmental streptococci and coliform organisms (34 and 30%, respectively). Quarters that had a cracked teat-end had higher odds of developing new infections than those without cracks (15 and 10%, respectively). Quarters that formed a keratin plug early in the dry period had a lower odds than those that did not close (10 and 14%, respectively). After 6 dry weeks, 23% of quarters were still open. The hazard of quarters closing if milk production on the day prior to drying-off was >21 kg 1.8-times less.

Histologic features and results of virus isolation tests of tissues obtained from teat lesions that developed in dairy cattle during winter.

OBJECTIVE: To determine microscopic features and involvement of viruses in teat-end lesions (TEL) of dairy cows during winter. SAMPLE POPULATION: Teats with TEL on lactating Holstein cows and from udders of carcasses. PROCEDURE: Tissues obtained from TEL of 10 teats from 7 cows on 2 research farms during the winter of 1994 to 1995 and 13 teats with TEL excised from udders of carcasses at an abattoir during February 1995 were submitted for virus isolation. During the winter of 1995 to 1996, an increased prevalence of TEL was observed in a research herd. After a decrease in ambient temperature, TEL were identified, and a full-thickness section of epidermis was removed from skin surrounding teat orifices. Tissues were examined by use of light and electron transmission microscopy. RESULTS: Viruses were not isolated from TEL tissues. Lesions ranged from mild elevations of the epidermis to thickened oval regions that encircled the teat orifice. The most severe lesions were dark and had thick crusts. Histologically, TEL were composed of thickened regions of epidermis most notably caused by hyperplasia of cells within the stratum spinosum. Excess production of keratinocytes was also evident, and the keratinocyte layer often contained bacteria. Ultrastructurally, squamous cells contained large amounts of keratin, but virions were not detected. Evidence of a viral etiologic agent for TEL was not detected. CLINICAL IMPLICATIONS: Development of TEL may be associated with decreases in ambient temperature. Numerous bacteria were evident in the keratin of TEL. Lesions and associated bacteria may predispose cows to mastitis.

N-Acetyl-B-D-glucosaminidase activity and somatic cells in goat milk.

N-Acetyl-B-D-glucosaminidase activity, somatic cell count, and udder infection status were determined in milk of nine Saanen goats. Plasma enzyme activity was also measured. Individual half udder milk samples were taken for 12 d over a 3-wk period and animals were bled weekly. Three of the 18 udder halves were infected with coagulase-negative staphylococci over all 12 sampling d. The N-acetyl-B-D-glucosaminidase and somatic cells in milk were significantly elevated in samples where minor pathogens were isolated. Plasma enzyme was variable among goats but not within goats or across weeks. Greater daily variation was seen in somatic cell count as compared to milk enzyme activity. Correlation between milk N-acetyl-B-D-glucosaminidase and somatic cell count was .54.

N-Acetyl-B-D-glucosaminidase in milk and blood plasma during dry and early postpartum periods.

Milk and plasma N-acetyl-B-D-glucosaminidase activity was determined for cows during the dry and early postpartum periods. Milk samples were taken from individual quarters of 12 cows from 7 d preceding dry off until calving. Weigh jar milk samples were taken daily for 28 d postpartum from 9 of the 12 cows. Somatic cell concentration was also measured in the postpartum samples. N-Acetyl-B-D-glucosaminidase activity of mammary secretions was significantly elevated in the dry period. Activity in mammary secretions was significantly higher than blood plasma concentrations during the dry period, which suggests that the enzyme present in mammary secretions comes mainly from within the gland. Milk enzyme concentrations declined sharply by 4 d postpartum and gradually declined through 28 d postpartum. Activity was still slightly elevated at 28 d postpartum as compared with normal lactation. Greater daily variability was seen with somatic cells than with N-acetyl-B-D-glucosaminidase. However, somatic cells were more responsive to clinical infections postpartum, showing significant elevations in both clinical episodes. The enzyme was elevated in one clinical case, but relatively unchanged in the other. Plasma levels were constant throughout both trials.

Mastitis therapy for cows elevated somatic cell counts or clinical mastitis.

Intramammary treatment with a broad spectrum antibiotic was evaluated for cows treated after a single high monthly somatic cell count of for cows with clinical mastitis. Forty-three quarters of 36 cows were treated after a high somatic cell count, and 56 quarters of 48 cows were treated after clinical symptoms. There was no significant decrease of cell count in response to treatment in the high somatic cell group. Organisms were isolated from 70% of the pretreatment quarter samples, but only 13% of the isolates were major pathogens. Bacteriological cure rate for major and minor pathogens combined was 23.3%. Treatment costs (antibiotics and discarded milk) were $38.19 per animal treated. Organisms were isolated from 70% of the pretreatment quarter samples of the clinical group. Forty-nine percent of the isolates were major pathogens. Bucket and quarter somatic cell counts decreased following treatment. Production rose posttreatment almost back to normal. Bacteriological cure rate was 21.6% for major and minor pathogens combined with 37% of the cured quarters becoming reinfected with minor pathogens during the monitoring period. The predominant minor pathogens isolated micrococci and coagulase negative staphylococci. The predominant major pathogens were Streptococcus uberis and coliforms.

Estimates of variability for somatic cell count measurements in the Iowa dairy industry.

The SCC collected from 15 instruments in 12 laboratories were used to quantify accuracy, repeatability, and reproducibility in the Iowa dairy industry. For each of three trials, milk was sampled at the morning milking from 30 different Holsteins in the Iowa State University herd. Identified samples and unidentified duplicates were provided for each participating instrument. Mean SCC was 418,000 cells/ml, and mean SCC for duplicates ranged from 9000 to 3,966,000. Accuracy for a set of 30 duplicates was lowest for trial 1 (CV = 16.4%) and highest for trial 2 (CV = 7.6%). Intraclass correlations estimated repeatability and were .99 for all but one instrument. Coefficients of variation for repeatability (weighted mean = 11.4%) were similar to estimates for accuracy (weighted mean = 11.0%), but reproducibility was considerably lower (30.0%). Samples were classified by SCC as very low, < 125,000; low, 125,000 to 249,000; medium, 250,000 to 500,000; and high, > 500,000. Repeatability for high samples was higher than repeatability for very low SCC samples; coefficient of variation for high SCC samples was 6.8% but was > 25.0% for samples with < 500,000 cells. Repeatability was within standards set by the industry, but current procedures for quality control may not adequately address reproducibility.

Dynamics and significance of coagulase-negative staphylococcal intramammary infections.

Cows (n = 139) were sampled within 17 d postpartum and monthly thereafter to examine dynamics of mammary infections and relationships between infection status, milk yield, SCC, NAGase activity, and chloride concentration. Forty-eight and 67% of cows and 19.5 and 30.5% of quarters were infected at first test and lactation end, respectively, with 51% of all infections present at first test. Coagulase-negative staphylococci accounted for 67 and 65% of first test and total infections with 85% persisting to lactation end. Animals with coagulase-negative staphylococci infections had significantly elevated quarter SCC and NAGase activity and a decrease of 821 kg mature equivalent lactation milk production compared with uninfected animals. Clinical cases with no bacterial isolation or major pathogen infections were associated with significant elevations in bucket and quarter milk SCC, NAGase activity, chloride concentration in quarters, and a decrease of 1153 kg mature equivalent lactation milk production as compared with uninfected animals. Correlations between milk production and in SCC and ln NAGase and between ln SCC and ln NAGase were -.15, -.25, and .55 (-.23, -.28, and .41 for first lactation only).

Changes in bovine milk secretion following intramammary infusions of concanavalin A, oyster glycogen, or water.

Effects of sterile intramammary infusion of Concanavalin A on milk secretion were contrasted with infusion of oyster glycogen or water. Twenty-four cows were infused intramammary with 100 mg Concanavalin A, oyster glycogen in 20 ml water, or with 20 ml water alone. Concentrations of lactose, somatic cells, immunoglobulins G and A, serum albumin, and activity of N-acetyl-B-D-glucosaminidase were determined in milk. Blood N-acetyl-B-D-glucosaminidase activity and concentrations of blood immunoglobulins G and A and serum albumin were determined. Oyster glycogen and concanavalin A caused inflammation in treated quarters; peak elevations of milk somatic cell counts, serum albumin, immunoglobulin G concentrations, and N-acetyl-B-D-glucosaminidase activity were at 12 to 36 h following treatment. Milk production and lactose concentration were reduced by oyster glycogen and Concanavalin A. Selective indices of relative accumulation of milk immunoglobulins decreased following Concanavalin A and oyster glycogen, whereas the N-acetyl-B-D-glucosaminidase activity selective index generally remained unchanged. Inflammation reduced the selective accumulation of immunoglobulins, and absence of change in the N-acetyl-B-D-glucosaminidase selective index indicated that blood is not a major source of milk N-acetyl-B-D-glucosaminidase.

Preliminary report on BoLA polymorphism in Guernsey cattle.

A total of 95 registered Guernsey cows and heifers sired by 34 bulls were typed for class I antigens encoded by the bovine major histocompatibility complex (BoLA). A panel of alloantisera was used to detect 21 of the 33 internationally recognized BoLA specificities. Fourteen BoLA specificities were detected in the herd using a standard lymphocyte microcytotoxicity test. The most frequent BoLA specificity detected was w6; but in 85% of these animals, a subtype of w6, either w17 (13.7%) or UR6.2 (34.7%), could be assigned. The next most common BoLA specificities, by frequency, were w12, w15, UR1, and w21. Specificities not detected were w2, w3, w5, w7, w11, w16, w19, w20, and w24.

Detection of Mycoplasma bovis in preservative-treated field milk samples.

Control of mycoplasmal mastitis requires individual cow milk sampling for culture and identification of Mycoplasma bovis. This sampling is time-consuming and expensive. Currently, some herds sample cows monthly with the dairy herd improvement (DHI) program, but a preservative is added to this milk that kills M. bovis. In this paper, a nested polymerase chain reaction (PCR) procedure that allows for rapid testing of preservative-treated milk is validated. The specificity of the nested PCR assay was confirmed by testing isolated nucleic acids of other organisms phylogenetically related to M. bovis or common to milk. A comparison against blind-passage culture on 53 field milk samples determined its sensitivity. Exposure of seeded milk samples to the procedure resulted in a sensitivity of 5.1 cfu equivalents per milliliter. Analysis of these results proved that the nested PCR assay was as sensitive as traditional culture and can be used on preservative-treated milk.