Analysis of antimicrobial sales data of the main distributor in Quebec from 2016 to 2019: An estimate of usage in dairy cattle, horses, and small animals.

Because antimicrobial usage (AMU) data are crucial in understanding and dealing with the threat that antimicrobial resistance (AMR) poses to global health, data of the sale of antimicrobials from 2016 to 2019 of CDMV Inc. - a major distributor of veterinary products in Canada - were collected and analyzed for the province of Quebec. The primary objective was to describe the evolution of AMU sales data for dairy cattle, small animals, and horses; a secondary objective was to determine effects of a new provincial regulation on antimicrobials of very high importance (in Quebec) on sales for dairy cattle. Results are described in milligrams of antimicrobials per kilogram of animal biomass (mg/PCU) for dairy cattle, small animals, and horses; intramammary products were analyzed for number of treatments per 100 cow-years; and results for dairy cattle were compared in Canadian-defined course doses for cattle (DCDbovCA) per 100 cow-years to a recent study for this species in Quebec. Between 2016 and 2019, there were decreased sales of Category 1 antimicrobials for all species included in the study (Category 1-VI for small animals). This reduction was even more apparent for dairy cattle, for which a 76% decrease occurred from 2018 to 2019 (1.7 to 0.4 mg/PCU). This marked reduction was attributed to the new regulation implemented in February 2019. Since a farm- and clinic-level AMU monitoring system has not yet been implemented in Quebec, analysis of CDMV Inc. sales enabled observations of temporal trends in AMU for dairy cattle, horses, and small animals. These temporal trends based on CDMV Inc. sales will be useful for making comparisons and validating trends derived from farm- and clinic-level data generated by a monitoring system.

Analyse des données de ventes d'antibiotiques du principal distributeur de médicaments au Québec de 2016 à 2019 : une estimation de l'utilisation des antibiotiques chez les bovins laitiers, les chevaux et les animaux de compagnie. Étant donné que les données sur l'utilisation des antimicrobiens (UAM) sont cruciales pour comprendre et faire face à la menace que la résistance aux antimicrobiens (RAM) fait peser sur la santé mondiale, les données sur les ventes d'antibiotiques de 2016 à 2019 de CDMV Inc. ­ un important distributeur de produits vétérinaires au Canada ­ ont été recueillies et analysées pour la province de Québec. L'objectif principal du projet était de décrire l'évolution des données de ventes d'antibiotiques pour les bovins laitiers, les animaux de compagnie et les chevaux; un objectif secondaire était de déterminer les effets d'une nouvelle réglementation provinciale relative à l'usage des antimicrobiens de catégorie 1 ­ très haute importance ­ (au Québec) sur les ventes d'antibiotiques pour les bovins laitiers. Les résultats sont décrits en milligrammes d'antibiotiques par kilogramme de biomasse animale (mg/PCU) pour les bovins laitiers, les animaux de compagnie et les chevaux. Les produits intramammaires sont analysés selon le nombre de traitements par 100 vaches-années. Les résultats pour les bovins laitiers ont aussi été comparés à une étude récente réalisée au Québec pour cette espèce en « traitement type pour les bovins au Canada ¼ (DCDbovCA) par 100 vaches-années. Entre 2016 et 2019, les ventes d'antimicrobiens de catégorie 1 ont diminué pour toutes les espèces de l'étude (catégorie 1-VI pour les animaux de compagnie). Cette réduction a été encore plus apparente pour les bovins laitiers, pour lesquels une diminution de 76 % s'est produite de 2018 à 2019 (1,7 à 0,4 mg/PCU). Cette baisse marquée a été attribuée à la nouvelle réglementation mise en place en février 2019. Puisqu'un système de surveillance sur l'utilisation des antibiotiques à l'échelle des fermes et des cliniques vétérinaires n'a pas encore été mis en place au Québec, l'analyse des ventes de CDMV Inc. a permis d'observer les tendances temporelles de l'UAM pour les bovins laitiers, les chevaux et les animaux de compagnie. Ces tendances temporelles, basées sur les ventes de CDMV Inc., seront utiles pour effectuer des comparaisons et valider les tendances dérivées des données au niveau des fermes et des cliniques vétérinaires générées par un futur système de surveillance sur l'utilisation des antibiotiques.(Traduit par les auteurs).

Whole Genome Sequencing of a Canadian Bovine Gammaherpesvirus 4 Strain and the Possible Link between the Viral Infection and Respiratory and Reproductive Clinical Manifestations in Dairy Cattle.

Bovine gammaherpesvirus 4 (BoHV-4) is a herpesvirus widespread in cattle populations, and with no clear disease association. Its genome contains a long unique coding region (LUR) flanked by polyrepetitive DNA and 79 open reading frames (ORFs), with unique 17 ORFs, named Bo1 to Bo17. In 2009, a BoHV-4 strain was isolated (FMV09-1180503: BoHV-4-FMV) from cattle with respiratory disease from Quebec, Canada, and its LUR was sequenced. Despite the overall high similarity, BoHV-4-FMV had the most divergent LUR sequence compared to the two known BoHV-4 reference strain genomes; most of the divergences were in the Bo genes and in the repeat regions. Our phylogenetic analysis based on DNA polymerase and thymidine kinase genes revealed that virus isolate was BoHV-4 gammaherpesvirus and clustered it together with European BoHV-4 strains. Because BoHV-4-FMV was isolated from animals presenting respiratory signs, we have updated the BoHV-4 Canadian cattle seroprevalence data and tried to find out whether there is a link between clinical manifestation and BoHV-4 seropositivity. An indirect immunofluorescence assay (IFA) was performed with nearly 200 randomized sera of dairy cattle from two Canadian provinces, Quebec (n = 100) and Ontario (n = 91). An additional set of sera obtained from Quebec, from the healthy (n = 48) cows or from the animals experiencing respiratory or reproductive problems (n = 75), was also analyzed by IFA. BoHV-4 seroprevalence in Canadian dairy cattle was 7.9% (Quebec: 6% and Ontario: 9.9%). Among animals from the Quebec-based farms, diseased animals showed higher BoHV-4 seropositivity than healthy animals (P < 0.05), with a significant 2.494 odds ratio of being seropositive in sick compared to healthy animals. Although there is no established direct link between BoHV-4 and specific diseases, these seroprevalence data suggest the possible involvement of BoHV-4 in dairy cattle diseases.

Efficacy of extended intramammary ceftiofur therapy against mild to moderate clinical mastitis in Holstein dairy cows: a randomized clinical trial.

Few studies have investigated the efficacy of extended ceftiofur therapy and none have focused on extended therapy for naturally occurring clinical mastitis. The objective of this study was to compare the efficacy of extended intramammary ceftiofur therapy of 8 d duration with a standard 2-day regimen for the treatment of naturally occurring mild to moderate clinical mastitis in lactating dairy cows. Holstein cows from 22 dairy herds (n = 241) were randomly allocated to the 2 treatment groups. For each case of mastitis, 125 mg of ceftiofur hydrochloride was administered intramammary once a day for 2 or 8 d. Clinical cure, 21 d after the last treatment, was 89% (98/110) in each group. Bacteriological cure 21 d after the last treatment for the 2- and 8-day regimens were 32% (15/47) and 61% (25/41), respectively, for all bacteria (P = 0.007), 64% (9/14) and 82% (9/11), respectively, for streptococci (P = 0.50), and 0% (0/20) and 47% (9/19), respectively, for Staphylococcus aureus (P = 0.0004). There were no statistical differences between groups for new intramammary infections. Overall, ceftiofur extended therapy increased cure when compared to a 2-day regimen for the treatment of naturally occurring mild to moderate clinical mastitis in lactating dairy cows.

Peu d'études ont investigué l'efficacité d'une thérapie prolongée avec du ceftiofur et aucune n'a examiné attentivement une thérapie prolongée dans le cas de mammite clinique se produisant naturellement. L'objectif de la présente étude était de comparer l'efficacité d'une thérapie intra-mammaire prolongée d'une durée de 8 jours avec du ceftiofur à la thérapie standard de 2 jours pour le traitement de mammite clinique légère à modérée survenant naturellement chez des vaches laitières en lactation. Des vaches de race Holstein provenant de 22 troupeaux laitiers (n = 241) ont été réparties de manière aléatoire dans les 2 groupes de traitement. Pour chaque cas de mammite, 125 mg d'hydrochlorure de ceftiofur furent administrés par voie intra-mammaire une fois par jour pour 2 ou 8 jours. La guérison clinique, 21 jours après le dernier traitement, était de 89 % (98/110) dans chaque groupe. La guérison bactériologique 21 jours après le dernier traitement pour les groupes 2 et 8 jours était respectivement 32 % (15/47) et 61 % (25/41) pour toutes les bactéries (P = 0,007), 64 % (9/14) et 82 % (9/11), respectivement, pour les streptocoques (P = 0,50) et 0 % (0/20) et 47 % (9/19), respectivement pour Staphylococcus aureus (P = 0,0004). Il n'y avait aucune différence statistiquement significative entre les groupes pour les nouvelles infections intra-mammaires. Globalement, une thérapie prolongée au ceftiofur augmenta la guérison lorsque comparée à une thérapie de 2 jours pour le traitement de mammite clinique légère à modérée survenant naturellement chez les vaches laitières en lactation.(Traduit par Docteur Serge Messier).

Repeated pericardiocentesis as palliative treatment for tamponade associated with cardiac lymphoma in a Holstein cow.

Maintaining a good quality of life for cows with cardiac manifestation of lymphoma may be valuable, especially in high-producing cows. This report describes the medical management of cardiac lymphoma in a cow by means of repeated pericardiocentesis. The cow survived for 34 days and was productive.

Comparison of results for commercially available microbiological media plates with results for standard bacteriologic testing of bovine milk.

OBJECTIVE: To compare results for 3 commercially available microbiological media plates with those for standard bacteriologic testing of bovine milk. SAMPLE: Milk samples from postpartum cows and cows with a high somatic cell count (SCC) or clinical mastitis (CM). PROCEDURES: Sample-ready Staphylococcus culture medium (SRSC) plates were used to detect Staphylococcus aureus in milk samples obtained from postpartum cows and cows with a high SCC or CM. Rapid coliform count (RCC) plates were used to detect coliforms in milk samples obtained from cows with CM. Aerobic count (AC) plates were used to detect streptococci in CM samples. Fresh mastitic milk samples were frozen and then thawed to evaluate the effects of freezing for the SRSC and RCC plates. The effects of dilution (1:10) of samples were determined. Agreement of results between the commercially available plates and standard bacteriologic testing was evaluated. RESULTS: The ability of SRSC plates to detect S aureus in milk samples was highest with diluted samples from postpartum cows and cows with a high SCC or CM. Sensitivity of the RCC plate for detection of coliforms was highest with diluted mastitic milk samples. The AC plates had a poor positive predictive value for detection of streptococci in mastitic milk samples. Freezing increased S aureus detection. CONCLUSIONS AND CLINICAL RELEVANCE: Overall, the SRSC and RCC plates were accurate, were easy to use, and yielded results comparable to those of standard bacteriologic testing for the detection of S aureus and coliforms in bovine milk.

A field study on the effects of dietary monensin on milk production and milk composition in dairy cows.

The objectives of this study were to quantify the effect of 16 ppm of dietary monensin on milk production and composition of dairy cows, and to investigate factors having a potential impact on this effect. Data were generated from a total of 3577 Holstein dairy cows (47 herds) in Quebec enrolled in a herd-level, randomized clinical trial investigating the effects of monensin supplementation. Milk production and composition data were collected from monthly dairy herd improvement (DHI) testing. Monensin increased milk production by 0.9 kg/cow/d in cows under 150 days in milk (DIM) (P < 0.05). Monensin decreased milk fat percentage by 0.18 percentage points during the whole lactation (P < 0.05). This decreasing effect was larger for component-fed cows (P < 0.05) and for cows being fed low levels of dietary physically effective particles (P < 0.05) when compared respectively to cows fed total mixed ration and cows fed high levels of dietary physically effective particles. The results of this study suggest that monensin influences milk production and milk composition of dairy cows, and that diet composition and feeding system influence those effects.

Development and validation of a bilingual questionnaire for measuring udder health related management practices on dairy farms.

Questionnaires are frequently used instruments to collect data in epidemiological studies. In countries where more than one language is spoken, the development of a questionnaire in more than one language is needed. The objective of this study was to develop and test the repeatability and validity of English and French versions of a personal interview-format questionnaire designed to capture udder health related management practices used on dairy farms. A standardized protocol was used to develop and translate the research instrument. Equivalence of the English and French questionnaires was assessed using a cross-over study design with 24 bilingual dairy producers completing both versions on three different occasions in a randomly assigned sequence. Repeatability of the questionnaire was evaluated using the test-retest method with the same questions being asked on two different occasions to 88 dairy producers participating in the National Cohort of Dairy Farms of the Canadian Bovine Mastitis Research Network. Validity of the questions related to milking procedures and general housing was assessed using on-farm observations as a gold standard. Measures of agreement were calculated using kappa, quadratic-weighted Kappa and concordance correlation coefficients for categorical, ordinal and continuous variables, respectively. Sensitivity and specificity estimates were computed for the validity analysis. The overall equivalence of the English and French versions of the questionnaire was adequate; agreement measures when administered twice in the same language were not significantly higher than when administered in each language. Similarly, questionnaire overall repeatability was good. When accounting for prevalence bias, Kappa and CCC estimates ranged from 0.40 to 0.92 for 27 of the 29 items evaluated in the questionnaire, with 18 items yielding agreement estimates greater than 0.60. Finally, milking procedures and general housing questions validity was excellent with mean sensitivity and specificity of 86% and 92%, respectively. Although the overall evaluation of the instrument was satisfactory, specific doubtful items were identified. This illustrates the need to address questionnaire reliability as even rigorously designed and pre-tested questions can have poor repeatability or validity. Our results indicate that the developed English and French questionnaires can be used simultaneously to accurately measure the udder health related management practices used on Canadian dairy farms. This questionnaire is adaptable for use in other developed dairy industry populations. The questionnaire is freely available online at www.mastitisnetwork.org under the "Publications/others" section.

Ultrasonography of the bovine female genital tract.

The objective of this article is to help interested readers learn to use ultrasound for female bovine reproductive tract examinations. The first section discusses practical issues for using ultrasound in the field, such as animal restraint and preparation, type of ultrasound units available, and scanning technique. The second section reviews ultrasound diagnosis of various ovarian structures. The third section explores uterine changes during the estrous cycle, in addition to uterine pathologic conditions. The fourth section covers early pregnancy, twinning, embryonic and fetal viability, and fetal anomalies. The final section considers the use of ultrasound with advanced techniques, such as embryo transfer, in vitro fertilization, and color Doppler technology, and as a complement tool in reproduction synchronization protocols for dairy cattle.

[The use of monensin premix in dairy cows: simple and essential steps for ensuring its proper use]. / L'utilisation du prémélange de monensin chez les vaches laitières: un suivi simple et essentiel pour s'assurer d'une utilisation adéquate.

The use of monensin premix in dairy cows: Simple and essential steps for ensuring its proper use. Dietary monensin, containing monensin sodium as active ingredient, is frequently used on dairy farms in Canada. Although the use of monensin is safe, some overdose situations have been reported following consumption of higher than recommended doses. A regular monitoring of bulk tank milk fat percentage should be performed to ensure quick detection of a potential overdose situation. Diarrhea and sudden drop in dry matter intake are other potential clinical signs of monensin overdose. Quick detection of such cases will allow rapid correction of the situation.(Translated by the authors).

Evaluation of the California Mastitis Test as a precalving treatment selection tool for Holstein heifers.

The objective of this study was to evaluate the California Mastitis Test (CMT) and a portable electrical conductivity meter for diagnosing precalving intramammary infection (IMI) in Holstein heifers. A total of 428 dairy heifers from 23 dairy herds were enrolled between 6 and 12 days before the expected calving date from June 2002 to June 2003. Mammary secretions were tested by both diagnostic methods and by bacterial culture for evidence of IMI. California Mastitis Test was considered negative if the score was negative, trace or 1 and was considered positive otherwise. Two cut-off points were evaluated for milk electrical conductivity (>5 and >6.5 mS/cm). From this study, an overall proportion of 69% of heifers had precalving IMI and the overall heifer prevalence of major pathogen IMI was 16.8%. At the quarter level, sensitivity and specificity of CMT (68.9% and 68.4%, respectively) and milk conductivity >5 mS/cm (41.0% and 65.2%, respectively) or >6.5 mS/cm (25.2% and 83.3%, respectively) to identify all IMI were low. However, the heifer level sensitivity and specificity of CMT for major pathogens were 91.0% (81.5-96.6) and 27.5% (22.8-32.6), respectively. Using a cut-off point of 5 mS/cm, the heifer level sensitivity and specificity for major pathogens was 68.7% (56.2-79.4) and 44.1% (38.7-49.6), respectively. A conductivity cut-off value of 6.5 mS/cm decreased the sensitivity and increased the specificity to 53.7% (41.1-66.0) and 59.5% (54.0-64.8), respectively. California Mastitis Test and milk electrical conductivity are not good predictors of major pathogen IMI in heifers during the last 2 weeks before calving. However, the negative predictive values at quarter or heifer level were high and the heifer false negative rate was 6-14% using CMT or conductivity, respectively. Therefore, these measures could be useful for screening out heifers or quarters that are unlikely to have a major pathogen IMI.

Efficacy of a 5-day extended therapy program during lactation with cephapirin sodium in dairy cows chronically infected with Staphylococcus aureus.

This study determined the efficacy of a 5-day extended therapy with cephapirin sodium in dairy cows chronically infected with Staphylococcus aureus. Chronically infected cows selected from 14 dairy herds in the St-Hyacinthe region, Québec were randomly allocated to a group of 31 cows treated for 5 consecutive days with 200 mg of cephapirin per quarter BID or a group of 30 untreated control cows. Bacteriological cure was determined by 3 negative bacterial cultures at 10, 24, and 31 days after treatment. The cow cure rates were 25.8% (8/31) in the treated cows and 3.3% (1/30) in the control group (P = 0.013). The quarter cure rates at first sampling post-treatment were 77.6% (38/49) and 18% (9/50) in the treated and the control groups, respectively (P < 0.0001). A 5-day extended therapy with cephapirin is effective in treating cows chronically infected with S. aureus.

A study of 55 field cases of uterine torsion in dairy cattle.

Two-hundred and seventy-three animals were enrolled in a case-case comparison of uterine torsions and other dystocias. The purpose of the study was to describe field cases of uterine torsion and their clinical management, compare them with other types of dystocia attended by field veterinarians, and evaluate the effect of season and housing on the incidence of torsions. Fifty-five cases of uterine torsions representing 20% of the dystocias were diagnosed. Most cases of uterine torsion were successfully corrected and followed by the vaginal delivery of a live calf. When compared with other types of dystocia, cows were at greater risk for uterine torsion than were heifers (OR = 5.2; P < 0.0001), while animals suffering from fetopelvic disproportion or carrying twins were at a lesser risk (OR = 0.05; P < 0.0001 and OR = 0.09; P = 0.007, respectively). Heifers had a lower risk when calving alone in a pen versus a tie-stall (OR = 0.2, P = 0.04). There was no significant effect of season on the risk of uterine torsion.

Effect of precalving intramammary treatment with pirlimycin in nulliparous Holstein heifers.

A clinical trial was conducted to determine whether prepartum intramammary pirlimycin reduces the proportion of nulliparous heifers with intramammary infection (IMI) during early lactation and improves milk production. Quarter milk samples were collected from 428 heifers, systematically allocated to treatment and control groups, 6 to 12 d before the expected calving date and 2 to 8 d after calving. At the prepartum visit, heifers in the treatment group (n = 219) received an infusion of pirlimycin hydrochloride in all 4 quarters; the control heifers (n = 209) received no infusions. Intramammary infection was detected in 69% of the heifers and 33% of the quarters before calving. After calving, the proportion of treated heifers with IMI was significantly lower than the proportion of control heifers (31% versus 45%). Staphylococcus aureus was isolated from 10% of the heifers and 3% of the quarters before calving. After calving, the proportion of IMIs due to S. aureus was significantly lower in the treated heifers than in the control heifers (5.6% versus 10%). Antibiotic treatment increased the percentage of cures and prevented new IMIs caused by gram-positive bacteria after calving. The incidence of new IMIs caused by gram-negative bacteria and yeast was higher among treated heifers than among control heifers. There was no overall effect of treatment on milk production, but there was a significant interaction effect of treatment and the interval between treatment and calving. An increase of 302 kg of milk was observed when antibiotic treatment was applied more than 1 wk before calving. Treatment did not affect the milk somatic cell count on the 1st 3 test days after calving.

Efficacy of using an internal teat sealer to prevent new intramammary infections in nonlactating dairy cattle.

OBJECTIVE: To determine whether insertion of an internal teat sealer (ITS) at the end of lactation would prevent development of new intramammary infections (IMIs) during the nonlactating period. DESIGN: Controlled clinical trial. ANIMALS: 939 Holstein-Friesian dairy cows from 16 herds. PROCEDURES: Results of bacteriologic culture of milk samples collected 14 days prior to the end of lactation were used to assign cows to groups (group 1 = negative results for all quarters; group 2 = positive results for > or = 1 quarter). Quarters of cows in group 1 were treated with an ITS or a single intramammary dose of cloxacillin; quarters of cows in group 2 were treated with cloxacillin in conjunction with an ITS or with cloxacillin alone. Milk samples were collected at the end of lactation and within 8 days after calving. RESULTS: Regardless of whether the outcome of interest was new IMIs caused by any pathogens, major pathogens, environmental pathogens, or streptococci other than Streptococcus agalactiae, quarters in group 2 treated with both cloxacillin and an ITS were less likely to develop a new IMI than were quarters treated with cloxacillin alone. For cows in group 1, no significant difference in risk of new IMIs was found between treatments. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that for dairy cattle with an IMI late in the lactation period, intramammary administration of cloxacillin at the end of lactation followed by insertion of an ITS enhanced protection against development of new IMIs, compared with use of cloxacillin alone.

A meta-analysis of the milk-production response after anthelmintic treatment in naturally infected adult dairy cows.

Meta-analysis was used to estimate the effects of anthelmintic treatment on milk production in dairy cows. The literature search included peer-reviewed journals (both full articles and abstracts), conference proceedings and theses and included documents written in English, Spanish, French, Portuguese or Italian. The study outcome was defined as the difference in milk production (kg/cow per day) between treated and untreated cows. Random effect meta-analyses were performed on 75 trials published between 1972 and 2002. The combined estimate after controlling for publication bias and/or small-study effect was of 0.35 kg/cow per day. Significant variation among studies was detected and although several variables were associated with the study outcome, they did not significantly reduce the unexplained variability among trials. Trials reporting the use of endectocides had higher milk-production response compared with trials using older anthelmintics. Similarly, whole-herd treatment trials or trials which applied the treatment in mid-lactation or strategically throughout the year had higher response compared with calving or dry-period treatment trials. Trials reporting the results as total 305-day milk production had lower response compared with trials which measured production as daily milk weight. Primiparous cows trials had lower responses compared with multiparous cows trials.

Comparison of humoral immune responses in dairy heifers vaccinated with 3 different commercial vaccines against bovine viral diarrhea virus and bovine herpesvirus-1.

A randomized clinical trial was conducted to compare the humoral immune response to 3 different commercial vaccines in dairy heifers housed in 3 different dairy farms in Quebec. All heifers were seronegative to type 1 bovine viral diarrhea virus (BVDV) (Singer strain), type 2 BVDV (NVSL 125c strain), and bovine herpesvirus-1 (BHV-1) at the beginning of the trial. In addition, control heifers in group 1 remained seronegative to the 2 viruses till the end of the trial. Significant differences in humoral immune responses occurred among the 3 commercial vaccines at 4 weeks and 6 months following vaccination. The vaccine in group 2 elicited higher mean antibody titers and seroconversion rates to both type 1 and type 2 BVDV than that in groups 3 or 4. Vaccines in groups 2 and 3 induced higher mean antibody titers to BHV-1 than did the vaccine in group 4.

A longitudinal study of gastrointestinal parasites in Canadian dairy farms. The value of an indirect Ostertagia ostertagi ELISA as a monitoring tool.

The general objective of this study was to evaluate a crude Ostertagia ostertagi antigen enzyme-linked immunosorbent assay (ELISA) for monitoring gastrointestinal parasites in lactating dairy cattle. A longitudinal study of gastrointestinal parasites in lactating dairy cows was carried out in 38 herds in four provinces of Canada (Prince Edward Island, Quebec, Ontario and Saskatchewan) from September 1999 to October 2000. Bulk tank milk, cow milk, serum and fecal samples were collected monthly or quarterly from all these farms. Information on herd management factors was collected by a standard questionnaire and individual cow production data were obtained from an electronic database. The overall mean optical density ratio (ODR) was 0.30 and ranged from -0.05 to 1.55. Although a clear seasonal pattern was not observed, the ODR values tended to decrease during the housing period and start increasing in the spring before the cows went out to pasture. The second and third or greater lactation cows had significantly higher ODR values compared with first lactation animals. The individual cow ODR had a very low correlation with individual squared root fecal egg counts but showed a reasonably high correlation when herd averages values were computed (r=0.73). A moderate correlation (r approximately 0.50) between the bulk tank and herd average ODR was observed. Milk yield was negatively associated with individual cow milk ODR and a quadratic effect on ODR was observed for days in milk. Twenty-eight of the herds participated in a clinical trial of eprinomectin (Ivomec Eprinex) treatment at calving. The cow level ODR values determined late in the previous lactation had a marginally significant effect (P=0.07) on treatment response, suggesting that high OD cows responded better to the anthelmintic treatment. However, because of the small sample size available in this model, more research is needed to better understand this relationship. In conclusion, the indirect ELISA using an O. ostertagi crude antigen appears useful as a technique for monitoring gastrointestinal parasite burdens in adult dairy cows and holds promise as a potential predictor of response to anthelmintic treatment.

Increase in milk yield following eprinomectin treatment at calving in pastured dairy cattle.

Gastrointestinal nematodes rarely cause signs of clinical disease in adult cattle. However, they have been shown to exert a negative impact on production in lactating animals, as seen by improved production following elimination of the worms using anthelmintics. A double blind, randomized clinical trial was performed in 28 dairy herds in Canada. The objective of the study was to evaluate the effect of treatment with eprinomectin pour-on solution (IVOMEC EPRINEX) at calving on production, in cattle that have had some exposure to pasture. Cows were randomly allocated to treatment or placebo in blocks of 10, based on calving date, and treated with eprinomectin or placebo on the day of calving. Information on milk production was obtained from all animals, as well as recorded cases of selected diseases. Milk production results from the Canadian dairy herd management system database were analysed using a mixed model with herd as a random effect and test within-cow as a repeated measurement. Test day milk yields from the first six tests after treatment were included in the model, representing a period of between 180 and 200 days in milk (dim). Treated cows produced an additional 0.94 kg of milk per day when compared to the controls over this period. The production effect was independent of calving season, age of the animal and geographical location. No effect of treatment was seen on milk composition, somatic cell count (scc) or on the selected health parameters that were recorded for all included animals. Monthly fecal egg counts (FEC) were performed for eight randomly selected animals in each herd. The observed FEC were low in this study, with a range from 0 to 419 trichostrongyle type eggs per 5g (ep5g) of feces in animals not yet treated with the anthelmintic. The average count was 9.8 and the median was 1.0. FECs dropped immediately after calving and stayed lower for at least 100 days in treated animals when compared to controls. In conclusion, gastrointestinal nematodes appear to have an effect on milk production in Canadian dairy cows that have had some degree of pasture exposure. Eliminating the present subclinical parasite burdens produced a consistent increase in milk production that can yield economic benefits for the dairy producer.