Evaluation of a refugia-based strategy for gastrointestinal nematodes on weight gain and fecal egg counts in naturally infected stocker calves administered combination anthelmintics.

Refugia-based strategies associated with a combination of anthelmintic drugs belonging to different drug classes are becoming more common management practices to mitigate anthelmintic resistance (AR) in gastrointestinal nematodes (GIN) in small ruminants. Though refugia-based strategies have been largely demonstrated in small ruminants, cattle veterinarians and producers are considering such management strategies in grazing cattle production systems. Implementing refugia-based strategies lowers the amount of anthelmintics used in the herd and therefore slows the progression of AR by allowing a proportion of worms to escape drug selection pressure. The objective of this study was to observe the effect of a refugia-based strategy on body weight (BW), average daily gain (ADG) and fecal egg counts (FEC) of trichostongyle-type nematodes in naturally infected beef calves over a 131-day grazing season when compared with a whole herd treatment strategy, using the same combination of drugs. Stocker calves (n = 160) were ranked by body weight within sex then allocated to 16 paddocks, which were randomly assigned to one of two treatment groups. All calves in Group 1 (n = 80) were administered treatment, while in Group 2 (n = 80) the steer with the highest FEC in eggs per gram (EPG) within the paddock was left untreated. Treated calves received an extended release injectable 5 % eprinomectin (LongRange®, Boehringer Ingelheim Animal Health USA Inc.; 1 mL/50 kg of BW) and a 22.5 % oxfendazole oral suspension (Synanthic®, Boehringer Ingelheim Animal Health USA Inc.; 1 mL/50 kg of BW). Fecal egg counts and BW were recorded on days (D) -35, 0, 21, 131, and 148 to calculate the average fecal egg count reduction (FECR) and ADG for both groups. Linear mixed models, with paddock as the experimental unit, were used for analyses. The EPG differed on D21 (p < 0.01) and D131 (p = 0.057) with Group 2 having a higher average FEC (15.2 EPG D21; 57 EPG D131) compared with Group 1 (0.4 EPG D21; 37.25 EPG D131). However, there was no significant difference in average BW or ADG between treatment groups throughout the study. Results suggest refugia-based strategies could be implemented without significant negative impacts on average BW and ADG across other calves in the herd.

Evaluation of effects of high incubation temperatures on results of protozoal culture and real-time PCR testing for Tritrichomonas foetus inoculated in a commercially available self-contained culture media system.

OBJECTIVE: To evaluate effects of high incubation temperatures on results of protozoal culture and real-time PCR testing for Tritrichomonas foetus inoculated in a commercially available self-contained culture media system. DESIGN: In vitro experimental study. SAMPLE: 2 strains of T foetus (1 field isolate from the University of California-Davis and 1 field isolate from the Texas Veterinary Medical Diagnostic Laboratory). PROCEDURES: 2 sets of 36 dual-chamber media pouches were inoculated with T foetus (36 sample pouches/strain) and incubated at temperatures of 37.0°C (98.6°F), 46.1°C (115.0°F), or 54.4°C (130.0°F) for 1, 3, 6, or 24 hours. Six uninoculated media samples in pouches stored at 37.0°C for the entire treatment period were used as negative controls. Pouches were removed from incubators and stored at 22.2°C (72.0°F) until all treatments were complete. Samples were submitted to a diagnostic laboratory for protozoal culture and real-time PCR testing. RESULTS: T foetus was detectable microscopically in inoculated pouches incubated at 37.0°C regardless of exposure time, whereas those incubated at 46.1°C yielded T foetus after 1 and 3 hours only, and those incubated at 54.4°C yielded T foetus after 1 hour only. Testing via real-time PCR assay yielded positive results for all inoculated media samples and negative results for all uninoculated control samples. CONCLUSIONS AND CLINICAL RELEVANCE: Samples collected into the self-contained culture media system for T foetus testing via culture alone should be protected from high temperatures. Realtime PCR amplification may be a more reliable method for identification of the organism if storage and transport temperatures cannot be controlled.