California Dairy Cattle Research Articles

Feeding high amounts of almond hulls to lactating cows

California is the leading state for the production of almonds, with more than 400,000 bearing hectares of orchards that produced approximately 1 billion kilograms of shelled nuts in 2017. Almond hulls (AH) are a regional by-product feedstuff fed predominantly to dairy cattle in California. A 2012 study surveyed 40 dairy farms in California and found that 39 out of 104 total mixed rations contained AH, with a mean daily feeding rate of 1.45 kg/cow. In 2017, approximately 2 billion kilograms of AH was produced. At a feeding rate of 1.45 kg/cow daily, even if all 1.7 million lactating cows in California are consuming AH, there will be a surplus of AH on the market as the approximately 130,000 nonbearing hectares come into nut production. Therefore, the potential of feeding varying amounts of AH to lactating dairy cows was investigated using 12 Holstein cows with 4 primiparous and 8 multiparous cows. The dietary treatments were 4 total mixed rations containing 0, 7, 13, or 20% AH. The AH used contained 12.8% crude fiber (as-is basis), which was below the 15% legal limit set by state feed regulations. Diets were formulated so that as the inclusion rate of AH increased, the amount of steam-flaked corn and soyhull pellets decreased and soybean meal inclusion increased. Experimental design was a replicated 4 × 4 Latin square. Diet had a cubic effect on actual milk yield, energy-corrected milk yield, and dry matter intake, with the 7% AH diet having the highest values and the 13% AH diet having the lowest. The percent and yield of total solids and the yields of lactose and fat did not differ with diet, but percent and yield of protein declined linearly with increased AH inclusion, and fat percent increased linearly. Apparent total-tract digestibilities of dry matter and organic matter were higher with the inclusion of AH in the diet. Total percentage of the day spent ruminating increased linearly with higher amounts of AH. Overall, this work demonstrated that AH can be fed at varying amounts, up to 20% of the diet, to lactating dairy cows to support high levels of milk production and that increasing amounts of AH (up to 20%) in the diet could lead to improved digestibility and milk fat percentage but decreased milk protein production.

Net reductions in greenhouse gas emissions from feed additive use in California dairy cattle.

The livestock industry is one of the main contributors to greenhouse gas emissions and there is an increasing demand for the industry to reduce its carbon footprint. Several studies have shown that feed additives 3-nitroxypropanol and nitrate to be effective in reducing enteric methane emissions. The objective of this study was to estimate the net mitigating effect of using 3-nitroxypropanol and nitrate on total greenhouse gas emissions in California dairy industry. A life cycle assessment approach was used to conduct a cradle-to-farm gate environmental impact analysis based on dairy production system in California. Emissions associated with crop production, feed additive production, enteric methane, farm management, and manure storage were calculated and expressed as kg CO2 equivalents (CO2e) per kg of energy corrected milk. The total greenhouse gas emissions from baseline, 3-nitroxypropanol and nitrate offered during lactation were 1.12, 0.993, and 1.08 kg CO2e/kg energy corrected milk, respectively. The average net reduction rates for 3-nitroxypropanol and nitrate were 11.7% and 3.95%, respectively. In both cases, using the feed additives on the whole herd slightly improved overall carbon footprint reduction compared to limiting its use during lactation phase. Although both 3-nitroxypropanol and nitrate had effects on decreasing the total greenhouse gas emission, the former was much more effective with no known safety issues in reducing the carbon footprint of dairy production in California.

Fecal Microbial Communities in a Large Representative Cohort of California Dairy Cows.

Improved sequencing and analytical techniques allow for better resolution of microbial communities; however, the agriculture field lacks an updated analysis surveying the fecal microbial populations of dairy cattle in California. This study is a large-scale survey to determine the composition of the bacterial community present in the feces of lactating dairy cattle on commercial dairy operations. For the study, 10 dairy farms across northern and central California representing a variety of feeding and management systems were enrolled. The farms represented three typical housing types including five freestall, two drylot and three pasture-based management systems. Fresh feces were collected from 15 randomly selected cows on each farm and analyzed using 16S rRNA gene amplicon sequencing. This study found that housing type, individual farm, and dietary components significantly affected the alpha diversity of the fecal microbiota. While only one Operational Taxonomic Unit (OTU) was common among all the sampled individuals, 15 bacterial families and 27 genera were shared among 95% of samples. The ratio of the families Coriobacteriaceae to Bifidobacteriaceae was significantly different between housing types and farms with pasture fed animals having a higher relative abundance of Coriobacteriaceae. A majority of samples were positive for at least one OTU assigned to Enterobacteriaceae and 31% of samples contained OTUs assigned to Campylobacter. However, the relative abundance of both taxa was <0.1%. The microbial composition displays individual farm specific signatures, but housing type plays a role. These data provide insights into the composition of the core fecal microbiota of commercial dairy cows in California and will further generate hypotheses for strategies to manipulate the microbiome of cattle.

Antimicrobial resistance trends in fecal Salmonella isolates from northern California dairy cattle admitted to a veterinary teaching hospital, 2002-2016.

Nontyphoidal Salmonella infections contribute to approximately 1.2 million annual illnesses in the United States. Historical and recent outbreaks have been associated with dairy products, ground beef, and direct contact with cattle. Salmonella antimicrobial resistance (AMR) is a serious concern that can reduce successful treatment of infections, increasing recovery time, medical costs, and mortality rates in humans and animals. This highlights the need to track AMR in Salmonella isolated from cattle to improve treatment plans, manage trends in AMR, and prevent future AMR development. A total of 242 Salmonella isolates were retrieved from 9,162 cattle fecal samples submitted to the University of California, Davis Veterinary Medical Teaching Hospital from 2002 to 2016. These isolates were tested for antimicrobial susceptibility using a standardized broth dilution panel. Multidrug resistance (MDR) to three or more classes of antimicrobials was observed in 50.8% of isolates, and the most common MDR pattern was amoxicillin-ampicillin-cefoxitin-ceftiofur-ceftriaxone-chloramphenicol-streptomycin-tetracycline (23.2%). There were significantly greater odds for antimicrobial resistance to aminoglycosides (OR: 2.03, 95% CI: 1.1–3.7), penicillins (OR: 1.87, 95% CI: 1.007–3.5), and tetracyclines (OR: 1.87, 95% CI: 1.017–3.4) for the 2002–2009 period when compared to the 2010–2016 period. The most prevalent MDR serotypes were Newport (100% MDR, n = 52), Typhimurium (100%, n = 20), and Dublin (71% MDR, n = 46). Risk factors associated with higher odds for isolating MDR Salmonella included isolates from calves when compared to adult cattle (OR: 22.0; 95% C.I.: 3.9–125.7), and isolates obtained from cattle suspect of having salmonellosis versus from the infectious disease control surveillance program (OR:13.7; 95%C.I.: 2.8–66.8). Despite a temporal trend for reduced AMR to most antimicrobial drug classes, a lack of this observed in the 2002–2009 period when compared to the 2010–2016 period for important drug classes such as cephalosporins (OR: 1.6, 95% CI: 0.87–3.1), and a trend for temporal increase in resistant to quinolones drugs (P value 0.004) highlight the relevance of AMR surveillance in cattle with Salmonella infections with the aim of targeting future prophylactic interventions.

A Deterministic Model to Quantify Risk and Guide Mitigation Strategies to Reduce Bluetongue Virus Transmission in California Dairy Cattle.

The global distribution of bluetongue virus (BTV) has been changing recently, perhaps as a result of climate change. To evaluate the risk of BTV infection and transmission in a BTV-endemic region of California, sentinel dairy cows were evaluated for BTV infection, and populations of Culicoides vectors were collected at different sites using carbon dioxide. A deterministic model was developed to quantify risk and guide future mitigation strategies to reduce BTV infection in California dairy cattle. The greatest risk of BTV transmission was predicted within the warm Central Valley of California that contains the highest density of dairy cattle in the United States. Temperature and parameters associated with Culicoides vectors (transmission probabilities, carrying capacity, and survivorship) had the greatest effect on BTV’s basic reproduction number, R0. Based on these analyses, optimal control strategies for reducing BTV infection risk in dairy cattle will be highly reliant upon early efforts to reduce vector abundance during the months prior to peak transmission.

Anthropogenic and meteorological factors influence vector abundance and prevalence of bluetongue virus infection of dairy cattle in California

Bluetongue is an economically important arboviral disease of ruminants that is transmitted by hematophagous Culicoides midges. In light of dramatic recent changes in the global distribution of bluetongue virus (BTV), the goals of this study were to re-evaluate the prevalence of BTV infection of cattle and abundance of Culicoides midges on individual dairy farms in California. A serosurvey of adult dairy cattle confirmed that BTV infection is prevalent throughout much of the state, although the coastal northwestern region remains free of infection and prevalence varies markedly among farms in the remainder of the state. Intensive sampling for one year of 4 farms in the northern Central Valley of California showed that the abundance of Culicoides midges was markedly different and coincided with the prevalence of BTV infection of sentinel cattle on each farm. Mean maximum and minimum temperatures and other meteorological parameters were similar on all 4 farms, thus we speculate that particular management practices were responsible for both the increased midge abundance and prevalence of BTV infection of cattle at individual farms. Specifically, it is concluded that variation in vector abundance at individual farms most likely is the result of waste-water lagoon and irrigation management practices, leading to higher BTV infection rates among livestock held on farms with more waste-water lagoons and greater acreage of land for waste-water irrigation.

Amino acid needs of lactating dairy cows: Predicting limiting amino acids in contemporary rations fed to high producing dairy cattle in California using metabolic models

The objectives were to predict amino acid (AA) profiles of intestinally delivered protein in California high group ( i.e., lactating but not yet confirmed to be in calf) dairy cattle fed contemporary rations using three metabolic models of dairy cows. This was done in order to predict limiting AA in dairy rations to determine if there was enough consistency in the nutrient profiles of these rations to support a common ruminally protected (RP) AA package to supplement similar rations. Nutrient profiles of 16 commercial high group dairy cow rations were evaluated, and limiting AA predicted by the metabolic models ‘Amino Cow’, ‘CPM Dairy’ and ‘Shield’. Higher inclusion levels of corn products in rations increased the contribution of corn CP to the total CP content of the total mixed ration (TMR), from 0.20 to 0.40. Even though the lysine to methionine ratio decreased as more corn CP was included in the TMR, it did not have a major impact on the final predicted AA profile of metabolizable protein (MP), but MP delivery (g/d) to the duodenum was predicted to decrease with increased corn CP levels. None of the models predicted any affect of increased corn CP levels on milk components but, according to Shield, it did have an effect on milk yield which increased when the ratio of lysine to methionine in MP decreased. The sequence of AA limitation among rations was the same within model, but differed substantially among models. Methionine, isoleucine and lysine were predicted to be most limiting according to Amino Cow, CPM Dairy and Shield, respectively. There appears to be sufficient consistency in nutrient profiles among rations to support a ruminally protected AA complex to balance the model predicted AA profile in order to increase animal productivity and efficiency of utilization of nutrients. There is no absolute way to decide which model predictions are most correct. However because Shield predictions suggested a higher correlation between Lys and Met in MP and production, as well as predicted AA ratios to milk responses related to these ratios, use of the Shield predicted AA package is supported.

Precipitation and Temperature Effects on Mortality and Lactation Parameters of Dairy Cattle in California

Data from 3 commercial rendering companies located in different regions of California were analyzed from September 2003 through August 2005 to examine the relationship of dairy calf and cow mortality to monthly average daily temperature and total monthly precipitation respectively. Yearly average mortality varied between rendering regions from 2.1 to 8.1% for mature cows. The relationship between cow and calf monthly mortality and monthly average daily temperature was U-shaped. Overall, months with average daily temperatures less than 14 and greater than 24°C showed substantial increases in both calf and cow mortality with calf mortality being more sensitive to changes in these temperature ranges than cow mortality. Temperature changes were reflected in a 2-fold difference between the minimum and maximum mortality in cows and calves. Precipitation showed a weak effect with calf mortality and no effect with cow mortality. Data from Dairy Herd Improvement Association were used from 112 California herds tested over a 24-mo period to examine the relationship of milk production and quality with monthly average daily temperature and monthly precipitation. Somatic cell count and percent milk fat were either weakly or not associated with monthly average daily temperature and total monthly precipitation. However, total monthly precipitation was negatively associated with test day milk per milking cow regardless of the dairy's geographical location. Housing-specific associations for test day milk per milking cow were greater for total monthly precipitation than monthly average daily temperature, with the strongest negative association seen for dairies that do not provide shelter for cows. This suggests that providing suitable housing for lactating dairy cattle may ameliorate the precipitation-associated decrease in test day milk per milking cow.

Direct measurements of the ozone formation potential from dairy cattle emissions using a transportable smog chamber

Tropospheric ozone continues to be an air pollution problem in the United States, particularly in California, Texas, and across the eastern seaboard. The obvious sources of ozone precursors have been largely controlled over the past several decades, leading to the critical examination of secondary sources. In particular, California has new air quality rules addressing agricultural sources of ozone precursors, including dairy farms. Some recent estimates predict that dairy cattle are second only to on-road vehicles as a leading source of ozone precursor emissions in California's San Joaquin Valley. The objective of this work was to directly measure the ozone formation potential from dairy housing. A transportable “smog” chamber was constructed and validated using organic gases known to be present in dairy emissions. The ozone formation potential of emissions from eight non-lactating dairy cows and their fresh waste was then directly evaluated in the field at a completely enclosed cow corral on the campus of the University of California, Davis. The results demonstrate that the majority of the ozone formation is explained by ethanol (EtOH) in the emissions from the dairy cows, not by acetone as previously thought. Ozone formation potential is generally small, with <20 ppb of ozone produced under typical conditions when EtOH concentrations were ∼200 ppb and NO x concentrations were ∼50 ppb. The results match our current understanding of atmospheric ozone formation potential, ruling out the possibility of unknown organic compounds in dairy emissions with significant ozone formation potential. Simulations carried out with a modified form of the Caltech Atmospheric Chemistry Mechanism verify that actual ozone formation from dairy emissions is much lower than what would be predicted using the current regulatory profiles. Based on these results, the ozone formation potential of emissions from dairy cattle in California seems to be lower than previously estimated.

Seroprevalence of Johne’s-disease infection in dairy cattle in California, USA

A total of 1950 serum samples from dairy cattle in California, USA were tested for the presence of antibodies to Mycobacterium avium subspecies paratuberculosis (MAP) using a commercial enzyme-linked immunosorbent assay (ELISA) kit. The sampled animals came from 65 herds and were sampled to reflect the relative numbers and distribution of dairy herds within three geographic regions in the state. Using the manufacturers suggested cut-off for a positive test, 89 animals (4.6%) were positive. The seroprevalence was 6.9% in the northern region of the state, 3.7% in the central region and 5.2% in the southern region. Using the sensitivity and specificity claimed by the manufacturer of the ELISA kit, the true prevalence in California dairy cattle overall was calculated as 9.4% (99% CI, 7.7%, 11.1%) and the true prevalences for the northern, central and southern regions were 14.1% (99% CI, 9.6%, 18.65%), 7.5% (99% CI, 5.6%, 9.4%), and 10.6% (99% CI, 5.9%, 15.6%), respectively.

Characterization of Treponema phagedenis-like spirochetes isolated from papillomatous digital dermatitis lesions in dairy cattle.

Four spirochete strains were isolated from papillomatous digital dermatitis (PDD) lesions in Iowa dairy cattle and compared with two previously described spirochete strains isolated from dairy cattle in California. These six strains shared an identical 16S ribosomal DNA sequence that was 98% similar to Treponema phagedenis and 99% similar to the uncultivated PDD spirochete sequence DDLK-4. The whole-cell protein profiles resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of these six strains were similar. However, these strains showed differences in the antigenic diversity of lipopolysaccharide (LPS). Genetic diversity was also detected by pulsed-field gel electrophoresis of genomic DNA digests, revealing differences among five of the six strains. Serum immunoglobulin G antibodies from dairy cattle with active PDD lesions reacted with the LPS of all but one PDD spirochete strain. Likewise, peripheral blood mononuclear cells from cattle with active PDD lesions produced blastogenic responses to one of the two California isolates. Both antibody and lymphocyte blastogenic responses were reduced in convalescent dairy cattle, suggesting the immune response to these spirochetes has short duration. These results demonstrate genetic and antigenic diversity among T. phagedenis-like treponemes and provide further evidence for the involvement of these spirochetes in the pathogenesis of PDD.

Evaluation of the Field Performance of the First Commercial Neospora Vaccine in Dairy Cattle

Neospora caninum, the causative agent of neosporosis, was recognized in 1991 as a major cause of abortion in dairy cattle in California. The first isolation of Neospora caninum from bovine aborted fetuses and experimental reproduction of neosporosis in cattle was reported in 1993. Today, neosporosis is described more commonly in dairy cattle, but also has been identified in beef breeds. Infections with Neospora, which can be acquired by cattle via congenital or horizontal transmission, have been associated with a 3-fold increase of abortion for herds with endemic abortions. For herds with epidemic abortion, the increased abortion risk can be as high as 40-fold, indicating a significant economic impact of neosporosis in affected herds. A research project was initiated to evaluate feasible control measures aimed at reduction or elimination of abortions caused by Neospora caninum.

Spatial and temporal clustering of Salmonella serotypes isolated from adult diarrheic dairy cattle in California.

Electronic records from the California Animal Health and Food Safety Laboratory System between January 1, 1991, and June 30, 1998, were reviewed, and data on 593 Salmonella serotypes isolated from feces or intestinal contents of adult dairy cattle with diarrhea were analyzed to determine spatial and temporal clustering. A statistically significant clustering in space was detected with 10 (Typhimurium, Montevideo, Muenster, Anatum, Give, Menhaden, Kentucky, Agona, Derby, and Newport) of the 13 serotypes examined. Significant temporal clustering was also detected with 10 serotypes (Typhimurium, Montevideo, Muenster, Anatum, Give, Newbrunswick, Menhaden, Kentucky, Derby, and Newport). Six serotypes (Anatum, Menhaden, Montevideo, Muenster, Newbrunswick, and Newport) were significantly spatially and temporally clustered. A difference in temporal and spatial distribution patterns of some serotypes associated with diarrhea in adult dairy in California was found. Knowledge of the specific type of clustering, if present, should improve our understanding of the transmission and control of salmonellosis in the field.

Sweet clover poisoning in dairy cattle in California

Sweet clover poisoning in dairy cattle in California

Papillomatous digital dermatitis (footwarts) in California dairy cattle: clinical and gross pathologic findings.

Clinical, gross pathologic, and therapeutic studies were performed on a contagious, painful, wart-like digital disease of unknown etiology in California dairy cattle. The disease was called papillomatous digital dermatitis (PDD). Survey indicated that the disease spread geographically throughout southern California over the past few years. In 1991, 31% of herds had papillomatous digital dermatitis, whereas in 1994, 89% were affected. Increased incidence occurred during late spring and summer, 1-3 months after the rainy season. Within-herd morbidity ranged from 0.5% to 12% per month. Study of 93 cows in 10 drylot dairies revealed that 91% had characteristic circumscribed, erosive to papillomatous, intensely painful lesions often surrounded by a ridge of hyperkeratotic skin bearing hypertrophied hairs. Lesions were 2-6 cm across (88%), circular to oval (78%), and raised (59%) and had surfaces that were uniformly erosive and granular (31%), uniformly papillary (28%), or composites of both appearances (41%). Lesions were most frequently seen in lactating heifers (31%) and 3-year-old cows (43%). Clinical signs were characterized by lameness, with walking on toes and clubbing of hooves. Lesions exclusively involved the hind limbs in 82% of cows and the plantar/palmar regions in 84% of cows. Lesions had high (89%) prediliction for plantar/palmar skin bordering the interdigital space. Lesions exclusively involved either the medial or lateral digit in 10% and 28% of cows, respectively. In 50% of cows, both medial and lateral digits of individual limbs were involved; in most cows (31%), lesions apposed each other across the plantar interdigital space, whereas in others (19%), lesions confluently involved the entire plantar/palmar commissural skin folds. In another 12% of cows, lesions were axial. High proportions of lesions showed complete therapeutic responses to antibiotics: parenteral penicillin (9/9) and ceftiofur (41/44), and topical oxytetracycline (4/4). Recurrence or new lesion development occurred in 48% of cows reexamined 7-12 weeks after complete therapeutic response was observed. Overall, the findings indicated that PDD is a distinct disease entity of economic importance in which bacteria may play an important pathogenic role.

Salmonella dublin Infections in Cattle in California

Salmonellosis is a commonly encountered disease of cattle. Of the many serotypes of Salmonella known to exist, Salmonella typhimurium and S. dublin are the two most frequently isolated from cattle. Salmonella dublin is isolated commonly from cattle in states west of the Rocky Mountains. Reports of isolations of S. dublin from states east of the Rockies are increasing.2,4 Salmonella dublin is also isolated commonly in Europe and South Africa. Unlike S. typhimurium, which shows no special affinity for a particular host, S. dublin is host-adapted for cattle. While other animal species can be infected with S. dublin, cattle account for approximately 96% of the isolations from animals. This host-adaptation for cattle has special implications regarding epidemiology and control measures. The purpose of this presentation is to give an overview of the current spectrum of S. dublin infections in dairy cattle in California.

Neospora-like protozoan infection as a cause of abortion in dairy cattle.

In 1989,29 of 240 drylot Holstein cows from a New Mexico dairy aborted over a 5-month period. Seven of the 9 fetuses examined had multifocal necrotizing encephalitis and multifocal myocarditis. Neospora-like protozoa were found in tissues from 3 of the fetuses. More recently, a protozoan that reacted positively with anti-N. caninum serum was identified as the most common cause of abortion in California dairy cattle. 1,2 Many of these abortions were epizootic, with multiple abortions over a 1 or 2-month period. 1 Abortions and congenital infections in calves infected by a Neosporalike protozoan have been reported in the United States, but these were isolated cases involving only a single calf in each herd. This protozoan has never been isolated, so its exact identity remains unknown. Recent studies indicate that the organism is closely related to N. caninum, but some ultrastructural and antigenic differences exist between the bovine parasite and N. caninum isolated from dogs. Except for a single case of abortion in a beef cow from Maryland, the cases of fetal and congenital neosporosis previously reported from the United States are from the western states of New Mexico, 11 Califomia and Washington. Nineteen additional cases of bovine abortion associated with Neosporalike infection that were submitted to the South Dakota Animal Disease Research and Diagnostic Laboratory (SDADRDL) are herein reported. Specimens from cases of bovine abortions that are submitted to the SDADRDL undergo a routine protocol of testing to determine the cause of the abortion. Entire animals are necropsied and samples of brain, heart, lung, liver, kidney, placenta, tissues with gross lesions, and, since February 1991, skeletal muscle are fixed for histopathologic examination. Abomasal fluid is cultured for aerobic and microaerophilic bacteria and fungi. Scrapings of placenta are digested with potassium hydroxide and examined for fungal hyphae by a direct, nonspecific fluorescent antibody (FA) technique. If hyphae are found, the placenta is cultured for fungi. Impression smears of kidney are examined by a direct FA technique for 6 serovars of Leptospira. Direct FA tests are performed on frozen sections of kidney and spleen for infectious bovine rhinotracheitis (IBR) virus and bovine viral diarrhea (BVD) virus. Pools of brain, lung, liver, kidney, and spleen are homogenized and inoculated onto primary cultures of fetal bovine lung and turbinate cells for virus isolation. When received, a homogenate of placenta is inoculated by itself onto the same cell lines. Formalin-fixed paraffin-embedded

Milk Protein Polymorphisms in California Dairy Cattle

Milk samples from 1454 first lactation heifers were collected from five breeds of cattle in a representative sampling of the California dairy cattle population. Samples were phenotyped for αs1-casein, β-casein, κ-casein, and β-lactoglobulin using PAGE. Lactation yields for milk, fat, and protein were available on 1166 heifers. Genetic linkage of the casein loci and the relationship between milk protein genotypes and production parameters (milk, fat and protein yield, fat and protein percentage) was investigated. Gene frequencies were similar to those found in other studies of the American dairy cattle population. Linkage was found between β-casein and κ-casein in four of the five breeds and between β-casein and αs1-casein in the Jersey breed. Casein haplotypes BBB and CA3A (αs1-, β-, κ-casein respectively) occurred in the Holstein population more often than would be expected from a random combination of the alleles. Least squares analysis of the production data indicated that the only significant effect was that of κ-casein genotype on protein yield; the highest yields were obtained for the BB genotype.

Neospora-like protozoan infection as a major cause of abortion in California dairy cattle

Summary Ninety-five aborted bovine fetuses received from California dairies over a 4.5-year period had histologic lesions of focal encephalitis. Protozoa that reacted with Neospora caninum antiserum were detected in the brain of 88 of these fetuses and in the heart of 1 fetus. Sarcocystis spp schizonts were seen in the vascular endothelium of 1 fetus. It was concluded that a Neospora-like cyst-forming coccidian may be a major cause of abortion in California dairy cattle.

The use of the enzyme-linked immunosorbent assay (ELISA) in serological diagnosis of Mycoplasma bovis in dairy cattle

Between December 1985 and March 1987 an enzyme-linked immunosorbent assay (ELISA) was used with 3774 sera to estimate the prevalence of antibodies to Mycoplasma bovis in sera from three age groups of cattle in four dairies in California and to test for possible associations between the presence of M. bovis antibodies and the age or breed of the cattle and the farm. Unadjusted and adjusted associations were evaluated using the chi-square test for associations and multiple logistic regression analysis, respectively. There was a tendency for the proportion of cattle seropositive for M. bovis to increase steadily and approximately linearly with age (p less than 0.05). There was also a statistically significant relationship between a M. bovis seropositive test and being from Farm IV (p less than 0.05). Farm IV was the largest of the four dairies and this association may be due to the effect of herd size. These findings confirm the ubiquitous distribution of antibodies to M. bovis in dairy cattle in California and also support previous reports of herd size as an important factor in mycoplasmal mastitis.