Eimeria spp. in dairy calves in Uruguay. Identification, dynamics of oocyst excretion and association with the age of calves

Eimeria bovis, Eimeria zuernii, Eimeria ellipsoidalis, Eimeria auburnensis, Eimeria canadensis and Eimeria alabamensis were identified on different dairy farms in Uruguay. The most prevalent species were E. bovis and E. zuernii, which were mainly found in the feces of calves with diarrhea. The dynamics of oocyst excretion were evaluated via the weekly determination of oocysts per gram (OPG) values in fecal samples from 97 calves over seven months. Three groups of calves were formed according to their age in days: Group 1 (1-20 days old), Group 2 (21-40 days old) and Group 3 (41-65 days old). In Group 1, the median OPG was zero, and the maximum OPG was 1,680. In Group 2, the median OPG was between zero and 8,240, and the maximum OPG was 428,800. In Group 3, the median OPG was between zero and 220, and the maximum OPG was 16,000. For the evaluation of the relationship between OPG and age group, a proportional odds model was built. Two samples from 60 bovines evaluated in Group 2 and in Group 3 were selected. OPG was categorized as negative, moderate (lower than or equal to 4,000) or high (greater than 4,000). Calves of Group 2 (21-40 days old) were significantly (p < 0.001) more affected by eimeriosis than calves of Group 3 (41-65 days old). Considering that diarrhea in calves is a multifactorial disease, eimeriosis should be considered when evaluating the control measures for diarrhea syndrome, particularly in calves of 21-40 days of age.

Evaluation of losses in carcasses of cattle naturally infected with Fasciola hepatica: effects on weight by age range and on carcass quality parameters

Although fasciolosis is a relatively common disease, the productive and economic losses resulting from cattle with chronic fasciolosis are unclear. This paper aims to investigate the effect of fasciolosis on the parameters of carcass quality and discuss the hypothesis that the effects on weight differ among age ranges of cattle. For this, we analysed abattoir data of 30,151 bovines, from 928 farms, slaughtered in Uruguay in 2016, of which 33.9% (95% confidence interval (CI): 27.3-41.1%) had Fasciola hepatica (liver fluke). A mixed model was built to assess whether the effect of fasciolosis on weight differs depending on the age range, using the interaction term 'age*F. hepatica'. The effect on the carcass parameters was tested using a proportional logistic regression. The interaction of age and F. hepatica was statistically significant (P < 0.001). Differences in carcass weights between infected and non-infected animals were observed mostly at younger ages (up to 30 months), with the highest difference observed in the 23-30 months age range (estimated marginal mean difference of 6.34 kg). Overall, the presence of F. hepatica was positively associated with poor conformations and lower fat scores of carcasses (P < 0.001). The carcasses of cattle infected with F. hepatica had 0.16 times greater odds of having worse conformation scores than carcasses of cattle without F. hepatica (proportional odds ratio (POR) = 1.16; 95% CI: 1.07-1.26). Similarly, carcasses of cattle with F. hepatica had 0.30 times (POR = 1.30, 95% CI: 1.23-1.39) greater odds of having poorer fat scores than carcasses of cattle without F. hepatica. Therefore, infection with F. hepatica is associated with poorer carcass quality parameters and lower weights, and the effect on weight differs across age ranges.

Applicability of in vitro bioassays for the diagnosis of ivermectin resistance in Rhipicephalus microplus (Acari: Ixodidae)

The applicability of laboratory bioassays to diagnose ivermectin (IVM) resistance in Rhipicephalus microplus was evaluated. Adult immersion tests (AITs), larval immersion tests (LITs) and larval packet tests (LPTs) were performed to characterise the effects of ivermectin toxicity on adults and larvae of a susceptible reference strain. The AIT was determined to be a reasonable assay but requires a large number of individuals to attain interpretable results. The LIT and LPT were validated with an IVM resistant strain, revealing resistance ratios (RRs) of 6.73 and 1.49, respectively. In a field survey, nine different populations of cattle tick from the states of São Paulo and Mato Grosso do Sul, Brazil, were analysed with the LIT. Populations without previous exposure to ivermectin exhibited RRs between 0.87 and 1.01. Populations previously exposed to IVM showed RRs between 1.83 and 4.62. The LIT was more effective at discriminating between resistant and susceptible populations than the LPT. The use of the LIT is recommended for the diagnosis of ivermectin resistance in R. microplus.

In vitro tests to establish LC50 and discriminating concentrations for fipronil against Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) and their standardization

Laboratory test was carried out on larvae and adults of the cattle tick, Rhipicephalus (Boophilus) microplus, to determine fipronil toxicity. Adult immersion test (AIT, N=26), larval immersion test (LIT, N=71) and larval packet test (LPT, N=41) were standardized using susceptible strain (Mozo). Dose-response curves were compared with a fipronil resistant strain. Four variables were analyzed from AIT results: mortality, weight of eggs on day 7 and on day 14, index of fertility, and index of fecundity. For larval test, dose mortality curves were analyzed. In spite of the high LC(50) variability, all variables determined for AIT were appropriate to discriminate both strains. AIT and LIT had more sensitivity than LPT, with larger resistance factors. It was used two times LC(99.9) as discriminating doses (DCs) following FAO suggestion. For mortality by AIT, LIT and LPT the DCs were estimated: 4.98ppm, 7.64ppm and 2365.8ppm, respectively, for Mozo strain. DCs mortality values estimated for resistant strain by AIT, LIT and LPT were: 6.96x10(5)ppm, 343.26ppm and 5.7x10(3)ppm, respectively and their respective resistant factors were: 202.4, 5.36 and 1.52. Protocols for AIT, LIT and LPT have been presented in this paper.