Pilot implementation of a newly developed bovine leukemia virus control program on 11 Alberta dairy farms

We developed a custom bovine leukemia virus (BLV) control program for the Alberta dairy industry, consisting of a risk assessment and a comprehensive list of best management practices (BMP) aimed at prevention of BLV transmission between cattle. This control program was implemented on 11 farms for approximately 1 yr. Blood samples were collected from all cattle ≥12 mo old, and serum was tested with a commercial ELISA. Risk assessments were performed on each farm, risk-connected on-farm management was identified, and management changes expected to prevent transmission of BLV between cattle were suggested by the first author and agreed upon with each farmer. Throughout the following year, all participating farmers were visited multiple times to identify and overcome barriers to implementation and to monitor progress. After approximately 1 yr of implementing BLV control, all cattle ≥12 mo old on farm with a negative or no previous test result were sampled, and the within-herd prevalence was determined. The median number of cattle on farm that were ≥12 mo was 195 (range 110–524). The initial prevalence averaged 39% (13–66%). On average, 5 BMP (3–7) were suggested to each farmer. On average, 4 BMP (1–7) were implemented. At the second sampling, the average within-herd prevalence of all animals that tested positive (including the previous sampling) was 36% (12–62%). Eight farms reduced their within-herd BLV prevalence, within-herd prevalence stayed constant on 1 farm, and it increased on 1 farm. The remaining farm terminated their participation before the second sampling. The number of seroconversions per farm ranged from 3 to 109, highlighting the success of some producers to minimize new infections. The risk assessment was proven to be a valuable tool to identify flaws in on-farm management, although risk assessment score was unrelated to the within-herd BLV prevalence. Finally, it appeared that implementation of BMP aimed at prevention of BLV transmission between cattle could reduce within-herd BLV prevalence when farmers committed to their implementation.     

Economic losses associated with mastitis due to bovine leukemia virus infection

Bovine leukemia virus (BLV), which causes enzootic bovine leukosis and immunosuppression, is widely prevalent on Japanese dairy farms. However, in the absence of a national eradication scheme with compensation programs, it is important to estimate BLV-associated economic losses to raise farmers' awareness. Mastitis (includes both clinical and subclinical) is a common disease in the dairy industry and the most common reason for culling. We hypothesized that immunosuppression due to BLV predisposes subclinical mastitis. A retrospective cohort study was conducted to trace Holstein cows at 9 commercial dairy farms in the Nemuro and Kushiro regions of Hokkaido Prefecture, Japan, where monitoring of BLV proviral load is routine. Information regarding Dairy Herd Improvement data, parity number, and delivery day was collected at each farm. Cows with no confirmed infection with BLV during lactation were defined as non-infected. Low-proviral-load and high-proviral-load (H-PVL) cows were defined as those in which proviral load was below and over 2,465 copies/50 ng of DNA, respectively, or 56,765 copies/10⁵ cells, respectively, throughout the lactation period. Survival analysis was performed using the frailty model to estimate the hazard ratio of subclinical mastitis for BLV infection status using data from 1,034 dairy cows after adjusting for parity number and delivery season as confounding factors. Kaplan–Meier survivor curves demonstrated that half of the H-PVL cows developed subclinical mastitis within 52 d after calving. The hazard ratio of subclinical mastitis for H-PVL cows was 2.61 times higher than that of non-infected cows. In 2017, there were 264,443 clinical mastitis cases in Hokkaido. Using field and published data, annual economic losses were estimated using Monte Carlo simulation. The economic loss due to mastitis associated with BLV infection per H-PVL cow was $418.59 (¥43,952), with the annual economic loss in Hokkaido Prefecture due to mastitis caused by BLV infection estimated at $6,097,225 (¥640,208,633). In summary, H-PVL cows were more susceptible to subclinical mastitis than non-infected and low-proviral-load cows, and mastitis due to BLV infection was projected to cause significant economic losses.     

Short communication: Genotyping and single nucleotide polymorphism analysis of bovine leukemia virus in Chinese dairy cattle

Bovine leukemia virus (BLV) causes enzootic leucosis in cattle and is classified into 10 genotypes with a worldwide distribution, except for several European countries, Australia, and New Zealand. Although BLV is widespread in Chinese cows with the positive rate of 49.1% at the individual level, very little is known about the BLV genotype in dairy cattle in China. To determine BLV genetic variability in cows in China, 112 BLV-positive samples from 5 cities in China were used for BLV molecular characterization in this study. Phylogenetic analysis using the neighbor-joining method on partial env sequence encoding gp51 obtained from 5 Chinese cities and those available in GenBank (n = 53, representing BLV genotype 1–10) revealed the Chinese strains belonged to genotype 6. Seven unique SNP were identified among Yancheng, Shanghai, and Bengbu strains out of the total 12 SNP identified in Chinese strains. The genotyping coupled with SNP analysis of BLV can serve as a useful molecular epidemiological tool for tracing the source of pathogens. This study highlights the importance of genetic analysis of geographically diverse BLV strains to understand BLV global genetic diversity.     

Estimation of circulating bovine leukemia virus levels using conventional blood cell counts

Bovine leukemia virus (BLV) is widely prevalent in Japanese dairy farms. To control BLV infections in Japan, segregating or managing cows according to their proviral load (PVL) is a rational strategy. This study was conducted to establish a quantitative procedure for estimating blood PVL per microliter using a statistical model to offer a cost-effective alternative to the conventional quantitative real-time PCR method. In total, 250 Holstein cows infected with BLV were identified from 10 commercial dairy farms. Information on age was collected and blood samples were tested for white blood cell and lymphocyte counts and PVL using PCR. Generalized linear models with quasi-Poisson errors were used to estimate PVL by selecting age, logarithm of lymphocyte count, and their interaction term as explanatory variables. To evaluate the model, blood samples of 92 BLV-infected Holstein cows from 2 other commercial dairy farms were tested, and measured PVL values were compared with estimated PVL values by the model. The logPVL per microliter was modeled by positive associations with log lymphocyte count and age and a negative association with the interaction term. In the evaluation, measured PVL values had a strong correlation with estimated PVL values (Spearman's ρ = 0.87). In conclusion, our model provides a cost-effective and more rapid alternative to the conventional method to facilitate test and segregation or management of BLV-suspected cows.     

Short communication: Milk ELISA status for bovine leukosis virus infection is not associated with milk production in dairy cows

The objective of this study was to assess whether the milk ELISA status for antibodies against bovine leukemia virus was associated with 305-d milk production in Canadian dairy cattle. Test results and test-day production data from 19,785 dairy cows were available for analysis. A linear mixed model was used with the estimated 305-d milk production as the outcome and lactation number, somatic cell count, calving season, days in milk, and breed as fixed effects. Herd nested in province was included as random effect. In conclusion, bovine leukemia virus antibody milk ELISA status was not associated with milk production.     

Associations between bovine coronavirus and bovine respiratory syncytial virus infections and animal performance in Swedish dairy herds

To assess the economic impact of bovine coronavirus (BCV) and bovine respiratory syncytial virus (BRSV) infections, accurate estimates of their associated effects on animal performance are needed. This study aimed to quantify the variation in individual test-day milk yield and somatic cell count, risk of reproductive failure after first service of dairy cows, and risk of death of calves and heifers according to the BCV and BRSV status of the herd. Three types of status were defined for BCV and BRSV infections, based on 1) the dynamics over a 7-mo period of BCV- and BRSV-specific antibody levels in pooled milk of primiparous cows; 2) the possible occurrence of presumably BCV- and BRSV-related clinical outbreaks; and 3) the combination of both pieces of information. A total of 36,184 test days, 2,716 cows with a first service, and 4,104 calves and heifers in 65 Swedish herds were included in the analyses. Animal performance associated with BCV and BRSV infections was quantified using hierarchical mixed generalized and survival models, after adjustment for covariates known to influence the performance under study. A significant reduction in milk yield was observed for cows in presumably BRSV recently infected herds, as well as in herds having a presumably BRSV-related clinical outbreak (of 0.57 and 0.91 kg/d, respectively), compared with cows in presumably infection-free herds. There was also a significant increase in somatic cell count (of 12,000 cells/mL) for cows located in herds with a BRSV outbreak. The risk of failure after first service, as well as the risk of death in calf and heifer, was numerically higher in BRSV-infected herds, although this was not statistically significant. In contrast, BCV infection herd status, as defined in the present study, was not significantly associated with any production losses in animals from infected herds compared with those in infection-free herds.     

Economic effects of exposure to bovine viral diarrhea virus on dairy herds in New Zealand

The economic loss to dairy farmers associated with bovine viral diarrhea virus (BVDV) is believed to be high in New Zealand, but no estimates are yet available. The aim was therefore to estimate the economic loss associated with BVDV in dairy herds in New Zealand. Bulk tank milk (BTM) from a random sample of 590 herds from the Northland, Bay of Plenty, and Waikato regions was tested for antibody against BVDV. The inhibition percentage (sample to positive ratio), based on a threshold validated in an earlier study, was used to indicate herd-level infection. Herd reproductive indices, herd lactation-average somatic cell counts, and herd average production of milk solids were regressed on BTM inhibition percentage. Herd averages of the overall annual culling rate, the rate of culling because of failure to conceive, the proportion of physiological inter-service intervals, the first-service conception rate, the pregnancy rate at the end of mating, and somatic cell counts were not associated with BVDV antibody in BTM. Abortion rates, rates of calving induction, the time from calving to conception, and the number of services per conception increased, however, whereas milk production decreased with increasing BVDV antibody in BTM. The results indicated significant reproductive and production loss associated with the amount of BVDV antibody in BTM. Total loss attributable to infection with BVDV was similar to reports from other countries and estimated as NZ$87 per cow and year in affected herds, and NZ$44.5 million per year for the New Zealand dairy industry based on an estimated 14.6% affected herds. The loss estimate excludes added cost and negative consequences with respect to animal welfare attributable to increased induction rates, and a greater incidence of production disease because of BVD-induced immune suppression.     

Comparing microRNA in milk small extracellular vesicles among healthy cattle and cattle at high risk for bovine leukemia virus transmission

Enzootic bovine leukosis (EBL) is a B-cell lymphosarcoma caused by bovine leukemia virus (BLV) infection. In Japan, cattle diagnosed with EBL are not permitted for human consumption by the law, thereby causing serious economic losses to farmers. The prevalence of BLV is high in Japan (40.9% in dairy cattle and 28.7% in beef cattle, respectively), which makes it difficult to perform the test-and-slaughter of BLV-infected cattle. This necessitates preventing the spread of BLV infection in cattle by early detection, segregation, and the removal of BLV-infected cattle with high proviral load, which are considered high risk for BLV transmission. We aimed to identify cattle that were at high risk for BLV transmission by comparing microRNA (miRNA) profiles in milk small extracellular vesicles (sEV). At first, miRNA profiles in sEV were compared among 4 uninfected cattle and 4 BLV-infected cattle with high proviral load by using a microarray containing mixed probes for miRNA of cattle and humans. Significantly lower amounts of hsa-miR-557 and hsa-miR-19b-1-5p, and insignificantly but higher amounts of hsa-miR-424-5p were observed in milk sEV from BLV-infected cattle than those from uninfected cattle. Next, to evaluate the utility of the aforementioned miRNAs for the identification of cattle that were at high risk for BLV transmission, we performed quantitative real-time PCR using milk sEV newly collected from 5 uninfected cattle and 17 BLV-infected cattle with high proviral load. The cycle threshold value of hsa-miR-424-5p was significantly lower in milk sEV from BLV-infected cattle. The PCR detection was unavailable or a significant difference was not observed for hsa-miR-557 and hsa-miR-19b-1-5p, respectively. These results suggest that the amount of hsa-miR-424-5p was higher in milk sEV from BLV-infected cattle and increasing the hsa-miR-424-5p in milk sEV could be one of the characteristic trends in cattle that are high risk for BLV transmission. Moreover, assessing characteristic miRNA amounts in milk sEV, which can be recovered twice a day by milking, could be useful for the routine monitoring of cattle in dairy herds instead of blood collection.     

Genetic evaluation for bovine tuberculosis resistance in dairy cattle

Genetic evaluations for resistance to bovine tuberculosis (bTB) were calculated based on British national data including individual animal tuberculin skin test results, postmortem examination (presence of bTB lesions and bacteriological culture for Mycobacterium bovis), animal movement and location information, production history, and pedigree records. Holstein cows with identified sires in herds with bTB breakdowns (new herd incidents) occurring between the years 2000 and 2014 were considered. In the first instance, cows with a positive reaction to the skin test and a positive postmortem examination were defined as infected. Values of 0 and 1 were assigned to healthy and infected animal records, respectively. Data were analyzed with mixed models. Linear and logit function heritability estimates were 0.092 and 0.172, respectively. In subsequent analyses, breakdowns were split into 2-mo intervals to better model time of exposure and infection in the contemporary group. Intervals with at least one infected individual were retained and multiple intervals within the same breakdown were included. Healthy animal records were assigned values of 0, and infected records a value of 1 in the interval of infection and values reflecting a diminishing probability of infection in the preceding intervals. Heritability and repeatability estimates were 0.115 and 0.699, respectively. Reliabilities and across time stability of the genetic evaluation were improved with the interval model. Subsequently, 2 more definitions of “infected” were analyzed with the interval model: (1) all positive skin test reactors regardless of postmortem examination, and (2) all positive skin test reactors plus nonreactors with positive postmortem examination. Estimated heritability was 0.085 and 0.089, respectively; corresponding repeatability estimates were 0.701 and 0.697. Genetic evaluation reliabilities and across time stability did not change. Correlations of genetic evaluations for bTB with other traits in the current breeding goal were mostly not different from zero. Correlation with the UK Profitable Lifetime Index was moderate, significant, and favorable. Results demonstrated the feasibility of a national genetic evaluation for bTB resistance. Selection for enhanced resistance will have a positive effect on profitability and no antagonistic effects on current breeding goal traits. Official genetic evaluations are now based on the interval model and the last bTB trait definition.     

Controlling bovine leukemia virus in dairy herds by identifying and removing cows with the highest proviral load and lymphocyte counts

The objective of this field trial was to reduce bovine leukemia virus (BLV) transmission and prevalence in commercial dairy herds using proviral load (PVL) and lymphocyte count (LC) measurements as indicators of the most infectious animals for culling or segregation. Bovine leukemia virus causes lymphoma in <5% of infected cattle, and increased lymphocyte counts (lymphocytosis) in about one-third. Recent research has shown that dairy cows infected with BLV have altered immune function associated with decreases in milk production and lifespan. Recent findings show that a minority of infected cattle have PVL concentrations in blood and other body fluids of over 1,000 times that of other infected cattle. In combination with a high LC, these animals are thought to be responsible for most transmission of BLV in a herd. Milk or blood samples from adult cows in our 3 Midwestern dairy farm field trials were tested semiannually with ELISA for BLV antibodies, and ELISA-positive cattle were then retested using a blood LC and a quantitative PCR test for PVL to identify the animals presumed to be most infectious. Herd managers were encouraged to consider PVL and LC status when making cull decisions, and to segregate cows with the highest PVL and LC from their BLV ELISA-negative herd mates where possible. After 2 to 2.5 yr of this intervention, the incidence risk of new infections decreased in all 3 herds combined, from 13.8 to 2.2, and the overall herd prevalence decreased in all 3 herds combined from 62.0 to 20.7%, suggesting that this approach can efficiently reduce BLV transmission as well as prevalence. This is encouraging, because a very low prevalence of BLV infection would make it economically feasible to cull the remaining ELISA-positive cattle, as was achieved in national eradication programs in other countries decades ago.     

Economic analysis of reproductive management strategies on US commercial dairy farms

Reproductive management has received increased attention in recent years as new technologies and programs have been developed to aid dairy managers in efficiently breeding cows and heifers. Efficient breeding of cows and heifers has become increasingly difficult as fertility has decreased because of a correlated negative response with milk yield. Dairy farm survey results were used to parameterize the economic analyses of reproductive management programs. Reproductive management program costs and the levels of reproductive performance achieved with such programs varied significantly among farms and were especially sensitive to on-farm labor costs. For example, visual heat detection requires more hours of labor per cow than use of an estrus synchronization program. Therefore, visual heat detection programs were relatively more sensitive to labor costs than synchronization programs. In addition, past reproductive performance was found to affect the determination of which reproductive program was optimal. Farms that had attained high levels of labor efficiency for visual heat detection in the past had less incentive to adopt a synchronization program than farms with less efficient visual heat detection.     

Quantification of bovine leukemia virus proviral DNA using a low-cost real-time polymerase chain reaction

The detection of bovine leukemia virus (BLV) proviral DNA is an important tool to address whether an animal is infected with BLV. Compared with serological assays, real-time PCR accounts for greater sensitivity and can serve as a confirmatory test for the clarification of inconclusive or discordant serological test results. However, the high cost related to real-time PCR assays has limited their systematic inclusion in BLV surveillance and eradication programs. The aim of the present study was to validate a low-cost quantitative real-time PCR. Interestingly, by using SYBR Green detection dye, we were able to reduce the cost of a single reaction by a factor of 5 compared with most common assays based on the use of fluorogenic probes (i.e., TaqMan technology). This approach allowed a highly sensitive and specific detection and quantification of BLV proviral DNA from purified peripheral blood leukocytes and a milk matrix. Due to its simplicity and low cost, our in-house BLV SYBR quantitative real-time PCR might be used either as a screening or as a confirmatory test in BLV control programs.     

Production and feeding strategies for phosphorus management on dairy farms

Long-term accumulation of soil phosphorus (P) is becoming a concern on some watersheds heavily populated with animal feeding facilities, including dairy farms. Management changes in crop production and feeding may help reduce the accumulation of excess P, but farm profitability must be maintained or improved to assure adoption of such changes. Whole-farm simulation was used to evaluate the long-term effects of changes in feeding, cropping, and other production strategies on P loading and the economics of 100-cow and 800-cow dairy farms in southeastern New York. Simulated farms maintained a long-term P balance if the following occurred: 1) animals were fed to meet recommended minimum amounts of dietary P, 2) the cropping strategy and land base supplied all of the forage needed, 3) all animals were fed a high forage diet, and 4) replacement heifers were produced on the farm to utilize more forage. The most easily implemented change was to reduce the supplemental mineral P fed to that required to meet current NRC recommended amounts, and this provided an annual increase in farm profit of about $22/cow. Intensifying the use of grassland and improving grazing practices increased profit along with a small reduction in excess P. Conversion from dairy production to heifer raising or expansion from 100 cows to a 250-cow "state-of-the-art" confinement facility (with a 70% increase in land area) were also profitable options. These options provided a long-term P balance for the farm as long as the production and use of forage was maximized and minimum dietary P amounts were those recommended by the NRC. Thus, management changes can be made to prevent the long-term accumulation of soil P on dairy farms while improving farm profitability.     

The effect of bovine viral diarrhea virus introduction on milk production of Dutch dairy herds

Dairy cows are negatively affected by the introduction of bovine viral diarrhea virus (BVDV), and consequently, produce less milk. Existing literature on potential milk production losses is based on relatively outdated data and hardly evaluates milk production loss in relation to a new BVDV infection in a surveillance system. This study determined the annual and quarterly loss in milk production of BVDV introduction in 3,126 dairy herds participating in the Dutch BVDV-free program between 2007 and 2017. Among these herds, 640 were “breakdown-herds” that obtained and subsequently lost their BVDV-free status during the study period, and 2,486 herds obtained and retained their BVDV-free status during the study period. Milk yields before and after BVDV introduction were compared through annual and quarterly linear mixed models. The fixed variables for both models included herd type (breakdown-herd or free-herd), bovine viral diarrhea status (on an annual and quarterly basis), year, season, and a random herd effect. The dependent variable was the average daily milk yield on the test day. To define the possible BVDV-introduction dates, 4 scenarios were developed. In the default scenario, the date of breakdown (i.e., loss of the BVDV-free status) was assumed as the BVDV-introduction date. For the other 3 scenarios, the BVDV-introduction dates were set at 4, 6, and 9 mo before the date of breakdown, based on the estimated birth date of a persistently infected calf. In the default scenario, the loss in milk yield due to BVDV introduction occurred mainly in the first year after breakdown, with a reduction in yield of 0.08 kg/cow per day compared with the last year before breakdown. For the other 3 scenarios, the greatest yield reduction occurred in the second year after BVDV introduction, with a loss of 0.09, 0.09, and 0.1 kg/cow per day, respectively. For the first 4 quarters after BVDV introduction in the default scenario, milk yield loss was 0.14, 0.09, 0.02, and 0.08 kg/cow per day, respectively. These quarterly results indicated that milk yield loss was greatest in the first quarter after BVDV introduction. Overall, BVDV introduction had a negative, but on average a relatively small, effect on milk yield for herds participating in the BVDV-free program. This study will enable dairy farmers and policymakers to have a clearer understanding of the quantitative milk production effect of BVDV on dairy farms in a control program.     

Bovine leukemia virus alters growth properties and casein synthesis in mammary epithelial cells

Bovine leukemia virus (BLV) is widespread in US dairy herds, yet only about 1% of infected cattle develop bovine leukosis and are culled from the herd. A major concern is whether BLV infection of dairy cows alters milk yield. Although several studies have examined the effect of BLV on milk production in vivo, the results were inconclusive. No in vitro studies have been done. The discovery of BLV in mammary epithelial cells (MEC) of infected cows raises the possibility that the virus could affect these cells directly. The purpose of this study was to use an in vitro system to determine if BLV could alter milk yield by altering cell number and/or milk production per cell. A short-term cell line established from the MEC of a BLV-negative cow, and a proven casein-producer mouse cell line, Comma D, were stably transfected with a plasmid containing the entire BLV genome. Untransfected parental lines served as negative controls. The BLV-containing bovine MEC line has a reduced population-doubling time, higher saturation density, and increased longevity. The Comma D line is an already-transformed cell line, and growth properties did not change after transfection with BLV. Under appropriate differentiation conditions, both the bovine and mouse MEC transfected with BLV displayed decreased casein production and mRNA synthesis compared with control cell lines without BLV. Our results suggest that effects of BLV infection on milk production may not be related solely to overall animal health but may also be mediated directly at a cellular level.     

The economic value of organic dairy farms in Vermont and Minnesota

This study quantifies the overall economic values of organic dairy farms in Vermont and Minnesota and estimates the economic impacts of organic dairy farm sales relative to an equivalent level of sales from conventional dairy farms in those states. This question is of interest because the development of the organic dairy sector has allowed some farms that likely would not have remained in the conventional dairy business to continue being economically viable as organic dairy farms. Thus, these sales provide an economic impact in regions when this milk is exported to nonproducing regions. Organic and conventional dairy farm financial data in Vermont and Minnesota were collected and assembled to develop dairy farm production functions by region and dairy type. These production functions were then used in state-level input-output models to calculate economic impacts. The opportunity costs of organic dairy farm production were also estimated by comparing the relative statewide economic impacts of organic and conventional dairy farms if both experience a hypothetical 5-million-dollar increase in sales. Between 2008 and 2010, Vermont’s 180 organic dairy farms annually contributed $76.3 million in output (the value of an industry’s production within the state), 808 jobs, $34.1 million in gross state product, and $26.3 million in labor income to Vermont’s economy. Between 2009 and 2011, Minnesota’s 114 organic dairy farms annually contributed $77.7 million in output, 552 jobs, $32.1 million in gross state product, and $21 million in labor income to Minnesota’s economy. In Vermont, organic dairy farm sales revenue would result in greater state-wide impacts of 3% in output, 39% in labor income, 33% in gross state product, and 46% in employment relative to the impacts from an equivalent level of sales revenue to conventional dairy farms. In Minnesota, these economic impacts are 4, 9, 11, and 12% greater, respectively, for organic dairy farms relative to conventional dairy farms. This study concludes that organic dairy farms may contribute more to the local economy than average and similar-size conventional dairy farms in the Northeast and Upper Midwest and that organic dairy farm milk production supports economic development in rural communities.     

An economic evaluation of recombinant bovine somatotropin approval in Japan

A comprehensive econometric model was developed to evaluate potential impacts of recombinant bovine somatotropin (rbST) approval in Japan. Three novel features of the analyses include 1) investigation of impact of rbST on herd-size structure, 2) determination of economic feasibilities of rbST adoption by herd size, and 3) evaluation of policies to mitigate negative effects of rbST approval. Simulation analysis was conducted over a 10-yr projected period assuming rbST was approved in Japan in 2001. Nine hypothetical scenarios were simulated to examine sensitivity of simulation results. Simulation results indicate that rbST approval would accelerate structural change in Japan's dairy industry toward fewer, larger farms. Negative effects of rbST on farm income are projected to be more severe for smaller farms, because of higher costs, lower profit-earning ability, lower milk yields, and lower adoption rates of rbST. Larger farms benefit from rbST adoption if milk demand is maintained. However, if concerns about rbST induce significant milk demand decreases, even the largest farms' income and cow numbers will decrease. Thus, Japan's dairy industry could be caught in a double downward spiral of declining milk prices and production. Assuming rbST is approved, small farms would benefit by using the technology, but they fare best if rbST is not approved. Two policies could be effective in mitigating possible farm income losses. First, lost farm income can be offset if dairy cooperatives can exercise greater market power to control fluid milk marketings. Second, because generic milk advertising has positive effects on both milk demand and farm income, increasing check-off rates to fund more advertising could ease farm income losses.     

Cost structure and profitability of Assaf dairy sheep farms in Spain

Twenty dairy sheep farms of Assaf breed, located in the Spanish autonomous community of Castilla y León and included in a group receiving technical support, were used to study their production cost structure and to assess their economic profitability during 2009. On average, farms had 89.2 ± 38.0 ha (own, 38%), 592 ± 63 ewes, yielded 185.9 ± 21.1 × 10³ L/yr (i.e., 316 ± 15 L/ewe), and were attended by 2.3 ± 0.2 annual working units (family, 72%). Total annual income was €194.4 ± 23.0 × 10³/yr (€1.0 = $1.3) from milk (78.6%), lamb (13.2%), culled ewes (0.5%), and other sales (0.8%, wool and manure), and completed with the European Union sheep subsidy (6.9%). Total costs were €185.9 ± 19.0 × 10³/yr to attend to feeding (61.6%), labor (18.2%), equipment maintenance and depreciation (7.6%), finances (3.0%), animal health (2.5%), energy, water and milking supplies (2.2%), milk recording (0.5%), and other costs (4.4%; assurances, shearing, association fees, and so on). Mean dairy sheep farm profit was €8.5 ± 5.8 × 10³/yr (€7.4 ± 8.3/ewe) on average, and varied between –€40.6 and €81.1/ewe among farms. Only 60% of farms were able to pay all costs, the rest had negative balances. Nevertheless, net margin was €31.0 ± 6.5 × 10³/yr on average, varying between €0.6 and €108.4 × 10³/yr among farms. In this case, without including the opportunity costs, all farms had positive balances. Total annual cost (TAC; €/ewe) and total annual income (TAI; €/ewe) depended on milk yield (MY; L/ewe) and were TAC = 161.6 + 0.502 MY (R² = 0.50), and TAI = 78.13 + 0.790 MY (R² = 0.88), respectively, with the break-even point being 291 L/ewe. Conversely, farm TAC (€/yr) and farm TAI (€/yr) were also predicted as a function of the number of ewes (NOE) per flock, as TAC = 18,401 + 282.8 NOE (R² = 0.89) and TAI = 330.9 NOE (R² = 0.98), with the break-even point being 383 ewes/flock. Finally, according to the increasing trend expected for agricultural commodity prices, it was calculated that a 10% increase of concentrate price will require 5.2% milk price increase for constant profit. Similarly, a 10% increase of forage price will require 2.0% milk price increase to maintain profitability. Under these scenarios of increasing the commodity prices of key feedstuffs, a change of flock feeding should be expected to compensate the losses in farm profitability. Most Assaf dairy sheep farms studied were economically profitable, with flock size, milk yield, and feeding costs key for their profitability.     

Development of a clinical scoring system for bovine respiratory disease in weaned dairy calves

Clinical scoring systems for bovine respiratory disease (BRD) in weaned dairy calves have been developed in the past with calves experimentally infected with specific respiratory pathogens. In this prevalent case control study, a BRD clinical scoring system for weaned calves was developed using field data from 689 dairy calves housed in group pens on 5 dairies in California. Of the 689 calves in the study, 89 were selected because they appeared sick based on the display of lethargy, depression, or separation from the group, whereas the remaining 600 were randomly selected. Clinical signs were recorded for all calves, and BRD case status was determined by thoracic auscultation and ultrasound examinations, which were interpreted in parallel. Of the 689 calves, 238 were identified as BRD cases. Five survey-adjusted generalized linear mixed models with a logit link function, calf as the unit of analysis, and dairy as a random intercept were assessed using 3-fold cross-validation. The best model chosen based on performance and parsimony contained the variables cough (2 points), abnormal respiration (1 point), low body condition (5 points), sunken eyes (4 points), and a 24-h ambient temperature range >15°C (1 point) with a 2-point cutoff for a BRD suspect score. An alternative model did not contain a score for the covariate 24-h ambient temperature range and had a 1-point cutoff. The best model was tested on 174 observations not used for model training and resulted in 77.0% screening sensitivity, 100% diagnostic sensitivity, and 61.9% specificity. Adding rectal temperature ≥39.2°C (102.5°F) as a second-tier test increased specificity to 76.7% and lowered the screening sensitivity to 64.8% and diagnostic sensitivity to 76.9%. The alternative model had a screening sensitivity of 84.2%, diagnostic sensitivity of 100%, and specificity of 45.7%. Adding rectal temperature ≥39.2°C (102.5°F) as a second-tier test for score-positive animals improved specificity of the alternative model to 62.6% while lowering its screening sensitivity to 70.5% and diagnostic sensitivity to 76.9%. Use of a 2-tier California BRD postweaning scoring system may provide producers and veterinarians with a new tool to monitor BRD in group-housed dairy calves. Furthermore, the scoring system may aid in judicious medical intervention for BRD cases and reduce unnecessary treatments of animals with antimicrobials.