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Because of the natural adaptation of Mexican sheep, the aim of the present study was to identify the presence or absence of gastrointestinal parasitic nematodes (GIN) resistant to benzimidazole (BZ) in both Chiapas and Pelibuey sheep breeds on local farms. Both male and female GIN-infected grazing sheep of the two breeds were selected. Sheep faecal samples were collected to obtain infective larvae (L3). This evolving stage of the parasite was used for taxonomic identification of the genus, based on its morphological characteristics. BZ anthelmintic resistance was evaluated using a nematode-compound in vitro interaction bioassay and the allele-specific polymerase chain reaction technique to detect mutations of residues 198 and 200 on isotype 1 of the β-tubulin gene. Three BZ-based compounds (febendazole (FBZ), tiabendazole (TBZ) and albendazole (ABZ)) at concentrations of 1, 0.5, 0.25, 0.125, 0.062 and 0.03 mg/ml were used to estimate the anthelmintic efficacy and lethal dose (LD50, LD90 and LD99) of the drugs. Two parasitic nematodes, Haemonchus and Teladorsagia, were identified in both isolates. Also, the proportions of anthelmintic resistance identified in GIN of the two sheep breeds were 68% in isolates from the Chiapas breed and 71.8% in the Pelibuey breed. The specific lethal activity obtained with FBZ was higher than 90%. However, TBZ and ABZ showed a lethal activity lower than 50%. High variability in the discriminating dose values was found among the BZ drugs. For example, FBZ LD ranged from 0.01 to 1.20 mg/ml; on the other hand, TBZ and ABZ required a dose ranging from 0.178 to 759 mg/ml. In addition, amino acid changes of Phe (TTC) to Tyr (TAC) at codon 200 of the β-tubulin gene, showing resistance to BZ, and no changes at codon 198 Glu (GAA) to Ala (GCA) were observed for both isolates. These results confirmed the presence of a genetic mutation associated with BZ in both Chiapas and Pelibuey nematode isolates.

Objective: To evaluate the effect of different selenium (Se) doses on semen quality and fertility of rams. Design/Methodology/Approach: Se was administered subcutaneously each month to nine two-month-old rams (from April 2018 to February 2020). The treatments were: T1 = without Se, T2 = 0.1 mg Se kg-1, and T3 = 0.3 mg Se kg-1. Semen evaluations were carried out using an electroejaculator; a total of 180 ejaculations were analyzed. The rams with better semen quality (one per treatment) were subjected to a mating. The following variables were evaluated: volume (Vol), masal motility (MM), progressive motility (MP), sperm concentration per mL and ejaculation, acrosome integrity percentage, living spermatozoa, normal spermatozoa, and fertility percentage. The normal distribution variables were evaluated using an analysis of variance (ANOVA) and Tukey’s comparison test (Tukey, 0.05); the percentages were raised to the inverse sine in order to perform the appropriate ANOVA. Fertility was analyzed using a χ2 test. Results: There was no difference in semen quality and fertility percentage (p > 0.05). The ejaculation volume showed differences between treatments (p ≤ 0.05). Study Limitations/Implications: A study including a higher number of rams and a previous fieldwork practice should be carried out, in order to evaluate semen parameters. These evaluations would help to accurately estimate semen quality and fertility, as well as to corroborate the results. Findings/Conclusions: Se did not improve semen quality and fertility of rams