Monitoring of dairy herds for Brucella abortus infection when prevalence is low

A total of 2,698 dairy herds were surveyed in 1981–1982 in New South Wales and north eastern Victoria in a review of the methods used to monitor them for the presence of Brucella abortus., The methods used to monitor dairy herds were testing of all breeding cows over 1 year of age using the rose bengal test (RBT) and complement fixation test (CFT), the bulk milk ring test (BMRT), and testing of blood samples collected at abattoirs using the RBT and CFT. The surveyed herds had at least one whole herd test, and BMRT was done at regular intervals in the period of the survey. Of the 99 (3.7%) herds that reacted to the BMRT, 91 (3.4%) herds had false positive reactions and 8 (0.3%) herds were declared infected on follow-up herd testing. False-positive reactions were obtained in 22 herds on more than one occasion. Common causes of false positive reactions to the BMRT were thought to be previous vaccination with Strain 19 and sampling in very early or late lactation. Of the 98 (3.63%) herds that reacted to the whole herd serological tests, 80 (2.96%) herds had false-positive reactions and 18 (0.67%) herds were declared infected. Strain 19 vaccination was thought to be an important cause of false-positive reactions. Fifty-three (2.0%) herds showed suspicious reactions on abattoir monitoring but none was declared infected on follow-up testing. Of the 18 herds with infected or equivocal status, the BMRT identified 8. In a further 6 herds, the infected cattle were not in the milking herd. Four other herds had milkers with high CFT titres which could not be confirmed as infected on culture. In no herds were culture positive RBT or CFT reactors from the milking herd detected without the BMRT being positive. The proportion of false-positive reactions to the BMRT was high but the BMRT proved very useful in identifying dairy herds infected with B. abortus, when the prevalence of brucellosis was very low. Aust Vet J, 64 : 97–100     

Disposal and disease rates in 340 British dairy herds

Data derived from 340 dairy herds, mainly in southern England, between April 1998 and March 1999, showed that the average total culling rate was 22.1 per cent, with 5.6 per cent for infertility, 3.6 per cent for mastitis, 1.7 per cent for lameness, 2.0 per cent for poor milk yield, 3.7 per cent for age and 5.5 per cent for miscellaneous reasons which included death. The average annual rate of assisted calvings was 8.7 per cent, of injury 0.9 per cent, digestive disease 1.3 per cent ketosis 0.4 per cent, hypomagnesaemia 0.7 per cent, hypocalcaemia 5.3 per cent, mastitis 36.6 per cent, and lameness 23.7 per cent. There was a significant association (P<0.001) between higher rates of mastitis in cows housed in straw yards as opposed to cubicles and also between higher rates of lameness in cows housed in cubicles as opposed to yards (P<0.015). However, there were farms with low rates of mastitis in cows kept in straw yards and low rates of lameness in cows kept in cubicles. Larger herds tended to have more problems with lameness and higher bulk milk somatic cell counts (BMSCC). There was a positive association between BMSCC and mastitis rate.     

Wastage and disease in Bay of Plenty dairy herds

Information on disease incidence and herd wastage was collected from 36 farms supplying the Rangitaiki Plains Dairy Company over a two-year period from June 1981 to May 1983. These herds contained 7050 milking cows and 1460 yearlings. Although 33.5% of calves horn were reared, only 21.7% entered the herd. The average wastage rate over the two seasons was 22.6%. This included a 2.5% death-rate. Main reasons for culling were infertility (6.3%), low production (3.7%) and mastitis (2.3%). Only 0.8% of cows died or were culled because of bloat and 0.4% from each of facial eczema and metabolic diseases. Treatments were administered by farmers or veterinarians to 18.8% of the cows for mastitis, to 3.9% for metabolic diseases and to 3.6% for lameness. In total, 34.6% of cows received treatment for disease. Wide differences were noted in the proportion of cases of different diseases for which veterinarians were consulted. These ranged from 83.6% for scours to 3.8% for mastitis. As well as confirming or quantifying the relative importance of various diseases and causes of wastage, the survey highlighted the problems in collecting reliable data from herd owners on the events in their herds.     

Mycoplasmal mastitis in dairy herds.

Mycoplasmal bovine mastitis is potentially a highly contagious disease that can cause severe economic problems in affected herds. The purchase of replacement heifers and cows are frequently the origin of mycoplasmal mastitis outbreaks in previously Mycoplasma-free herds. Purchased cows and heifers should be quarantined and tested for mycoplasmal mastitis before admission to the regular herd. Detection of Mycoplasma-infected cows by culture of milk is straightforward, although there are problems of sensitivity for its detection in milk samples that are inherent to the nature of the disease and laboratory procedures. After detection of infected cows, the best way to protect the herd is to culture all cows in the herd, cows with clinical mastitis, and all heifers and cows after calving and before entering the milking herd. Control of mycoplasmal mastitis requires test and culling from the herd of Mycoplasma-positive cows if possible. When a large number of cows are infected, strict segregation with adequate management is an option; however, animals in this group should never re-enter the Mycoplama-free herd. The functioning of the milking equipment and milking procedures should be evaluated carefully and any flaws corrected. There is no treatment for mycoplasmal mastitis, and vaccination has not proven to be efficacious to prevent, decrease the incidence, or ameliorate the clinical signs of mycoplasmal mastitis. Waste milk should not be fed to calves without pasteurization. M bovis may cause several other pathologies in animals of different ages on a farm, including pneumonia, arthritis, and ear infections. The survival of mycoplasmas in different farm microenvironments needs to be further investigated for its impact on the epidemiology of the disease.     

Use of metabolic profiles for the assessment of dietary adequacy in UK dairy herds

Between April 1999 and March 2004, metabolic profile analyses were performed on individual blood samples from 35,506 dairy cattle in the UK. Assessment of the cows' energy status by the analysis of plasma samples for beta-hydroxybutyrate, glucose and non-esterified fatty acids showed that 70.4 per cent of the cows in early lactation (10 to 20 days calved), 57.1 per cent of the cows in mid-lactation (51 to 120 days calved) and 57.7 per cent of the dry cows within 10 days of their predicted calving date had one or more energy metabolites outside the optimum range; in addition, 16 per cent of the cows in early lactation, 5.6 per cent of those in mid-lactation and 20.5 per cent of the dry cows within 10 days of their predicted calving date had a low plasma urea nitrogen concentration, indicating poor intakes of effective rumen-degradable protein. Abnormalities in the concentrations of magnesium, inorganic phosphate, copper, selenium and iodine were relatively uncommon. The transitional period, particularly in late pregnancy, was commonly identified as a constraint on productivity. Nutritional problems were most commonly associated with poor feed intakes and poor feed management, rather than with the formulation of the rations.     

A comparative study of metabolic profiles obtained in dairy herds in Romania

Data obtained for 15 blood constituents on 651 clinically-healthy dairy cows in 17 herds of varying types of nutrition, husbandry and breed were statistically analysed. Reference mean values and standard deviations were established, and compared between summer and winter and for three physiological groups: four weeks after calving, two to three months of pregnancy, and eight weeks before calving. The results are compared with the ‘Compton’ values obtained in the United Kingdom.     

Cubicle refusal in Norwegian dairy herds.

In order to survey the behaviour of choosing the alley area instead of a cubicle as a lying place (cubicle refusal), a questionnaire was sent to the 273 dairy farms in Norway known to keep cows in cubicle housing systems. Sixty-six percent of the farmers contacted were included in the study. The median herd size was 18 cows (range 7-118). More than 85% of the herds had sheds providing one or more cubicles per cow. The mean herd occurrence of cubicle refusal was 6%, but showed great variation (range 0-55%). Regression analysis showed a significant association between rearing heifers in slatted floor pens and an increased cubicle refusal occurrence (p = 0.02, R2 = 0.05), while herd size, use of litter, or cubicle-to-animal ratio were not found to be associated with cubicle refusal. The practice of rearing heifers in slatted floor pens accounted for about one half of the observed cubicle refusal (etiologic fraction = 0.51).     

Simulation model for evaluation of testing strategies for detection of paratuberculosis in midwestern US dairy herds

We developed a stochastic simulation model to compare the herd sensitivity (HSe) of five testing strategies for detection of Mycobacterium avium subsp. paratuberculosis (Map) in Midwestern US dairies. Testing strategies were ELISA serologic testing by two commercial assays (EA and EB), ELISA testing with follow-up of positive samples with individual fecal culture (EAIFC and EBIFC), individual fecal culture (IFC), pooled fecal culture (PFC), and culture of fecal slurry samples from the environment (ENV). We assumed that these dairies had no prior paratuberculosis-related testing and culling. We used cost-effectiveness (CE) analysis to compare the cost to HSe of testing strategies for different within-herd prevalences. HSe was strongly associated with within-herd prevalence, number of Map organisms shed in feces by infected cows, and number of samples tested. Among evaluated testing methods with 100% herd specificity (HSp), ENV was the most cost-effective method for herds with a low (5%), moderate (16%) or high (35%) Map prevalence. The PFC, IFC, EAIFC and EBIFC were increasingly more costly detection methods. Culture of six environmental samples per herd yielded >or=99% HSe in herds with >or=16% within-herd prevalence, but was not sufficient to achieve 95% HSe in low-prevalence herds (5%). Testing all cows using EAIFC or EBIFC, as is commonly done in paratuberculosis-screening programs, was less likely to achieve a HSe of 95% in low than in high prevalence herds. ELISA alone was a sensitive and low-cost testing method; however, without confirmatory fecal culture, testing 30 cows in non-infected herds yielded HSp of 21% and 91% for EA and EB, respectively.     

Use of every ten-day criteria for metabolic profile test after calving and dry off in dairy herds

The traditional metabolic profile test cannot be applied to peripartum dairy cows, because these cows are in a state of physiological abnormality making it difficult to interpret their blood components. This study aimed at establishing and evaluating the practicability of interpreting a metabolic profile test every 10 days (Ten-day criteria) during the dry and lactation periods in herds with high and no incidence of peripartum diseases. Data from 29,043 cows in 1,130 commercial dairy herds were used to establish standard values every 10 days, mean +/- 1.0 standard deviation for the metabolic profile test. The practicability of these criteria was evaluated in herds with peripartum diseases. In the ten-day criteria, the body condition score, albumin, blood urea nitrogen, glucose, total cholesterol, nonesterified fatty acids, gamma-glutamyl transpeptidase and aspartate aminotransferase, fluctuated during the dry and early lactation periods and there were very big changes in packed cell volume, blood urea nitrogen, total cholesterol and magnesium just after calving. The ten-day criteria were able to detect overconditioned cows, low levels of albumin, total cholesterol and magnesium, and high nonesterified fatty acids in herds with a high incidence of peripartum diseases. In conclusion, the ten-day criteria can be successfully applied to peripartum cows, and is recommended because it is able to detect metabolic abnormalities not only in the herd, but also in individual cows.     

Salmonella Give infection in 2 dairy herds.

Salmonella Give infection was investigated in 2 adjacent dairy herds because of the impact of milk contamination on public health. Once the status of the infection in a herd was established by fecal analyses, consecutive fecal testings, in conjunction with preventive measures, appeared to be consistent and cost-effective tools for the monitoring and control of salmonellosis in dairy herds.     

Optimizing replacement decisions for Finnish dairy herds

The purposes of the study were to determine how "an optimal herd" would be structured with respect to its calving pattern, average herdlife and calving interval, and to evaluate how sensitive the optimal solution was to changes in input prices, which reflected the situation in Finland in 1998. The study used Finnish input values in an optimization model developed for dairy cow insemination and replacement decisions. The objective of the optimization model was to maximize the expected net present value from present and replacement cows over a given decision horizon. In the optimal solution, the average net revenues per cow were highest in December and lowest in July, due to seasonal milk pricing. Based on the expected net present value of a replacement heifer over the decision horizon, calving in September was optimal. In the optimal solution, an average calving interval was 363 days and average herdlife after first calving was 48.2 months (i.e., approximately 4 complete lactations). However, there was a marked seasonal variation in the length of a calving interval (it being longest in spring and early summer) that can be explained by the goal of having more cows calving in the fall. This, in turn, was due to seasonal milk pricing and higher production in the fall. In the optimal solution, total replacement percentage was 26, with the highest frequency of voluntary culling occurring at the end of the year. Seasonal patterns in calving and replacement frequencies by calendar month and variation in calving interval length or herdlife did not change meaningfully (< 1%-2% change in the output variables) with changes in calf, carcass or feed prices. When the price of a replacement heifer decreased, average herdlife was shorter and replacement percentage increased. When the price increased, the effect was the opposite.     

Optimizing breeding decisions for Finnish dairy herds

The purpose of this study was to determine the effect of reproductive performance on profitability and optimal breeding decisions for Finnish dairy herds. We used a dynamic programming model to optimize dairy cow insemination and replacement decisions. This optimization model maximizes the expected net revenues from a given cow and her replacements over a decision horizon. Input values and prices reflecting the situation in 1998 in Finland were used in the study. Reproductive performance was reflected in the model by overall pregnancy rate, which was a function of heat detection and conception rate. Seasonality was included in conception rate. The base run had a pregnancy rate of 0.49 (both heat detection and conception rate of 0.7). Different scenarios were modeled by changing levels of conception rate, heat detection, and seasonality in fertility. Reproductive performance had a considerable impact on profitability of a herd; good heat detection and conception rates provided an opportunity for management control. When heat detection rate decreased from 0.7 to 0.5, and everything else was held constant, net revenues decreased approximately 2.6%. If the conception rate also decreased to 0.5 (resulting in a pregnancy rate of 0.25), net revenues were approximately 5% lower than with a pregnancy rate of 0.49. With lower fertility, replacement percentage was higher and the financial losses were mainly from higher replacement costs. Under Finnish conditions, it is not optimal to start breeding cows calving in spring and early summer immediately after the voluntary waiting period. Instead, it is preferable to allow the calving interval to lengthen for these cows so that their next calving is in the fall. However, cows calving in the fall should be bred immediately after the voluntary waiting period. Across all scenarios, optimal solutions predicted most calvings should occur in fall and the most profitable time to bring a replacement heifer into a herd was in the fall. It was economically justifiable to keep breeding high producing cows longer than low producing cows.     

Integrated disease control in dairy herds. A case study from the veterinarians' viewpoint

Integrated control of bovine virus diarrhoea virus, bovine herpesvirus-1, Leptospira interrogans serovar hardjo subtype hardjobovis, Mycobacterium avium subsp. paratuberculosis, and Salmonella dublin in dairy herds may provide economic benefits superior to those obtained by sequential disease control, because, among other things, it allows optimization of voluntary culling. However, in practice there are no adequate instruments to establish priorities in voluntary culling. Therefore, in this study the priorities in decision-making for voluntary culling of infected cattle, as indicated by more than 300 cattle veterinarians, were analysed. Based on our results and supplementary considerations, the priorities for voluntary culling in the Netherlands can be ranked as: 1st. cull S. dublin carriers, 2nd. cull persistently infected BVDV carriers, 3rd. cull paratuberculosis faecal culture positive cattle and their last offspring, 4th. cull, in paratuberculosis infected herds, paratuberculosis ELISA positive cattle and their last offspring and cull, in low prevalence herds, BHV1 gE-positive cattle, and 5th. cull leptospirosis seropositive cattle. Since this ranking was based on one case study only, other priorities may prevail in other herds.