Influence of subclinical infection by agents of tick fever in milking dairy cows / Influencia de la infección subclínica por agentes de la fiebre por garrapatas en vacas lecheras

ABSTRACT Objective. The objective of this study was to evaluate the effect of subclinical infection by agents of tick fever in dairy cattle on milk parameters, such as production, composition, and quality. Materials and methods. The study was conducted in a private farm with 75 free-stall-housed dairy cows, from which 37 were evaluated. Monthly, individual milk samples were collected for compositional (fat, lactose, protein, and total solids) and quality (somatic cell counts (SCC)) analyses. In addition, blood samples were collected in order to identify cows that were tick fever-negative and positive by PCR for one or more of the following etiological agents: Babesia bovis, Babesia bigemina and Anaplasma marginale. Results. The results showed increased SCC in positive animals for at least one of the agents when compared to non-infected cows (p<0.05). Milk production was significantly lower in A. marginale positive animals (p<0.05). An increase of about 40% in milk solids content was found in B. bovis positive cows. Also, an increment of approximately 23% in lactose was found on cows positives for B. bigemina. Conclusions. We may conclude that the presence of at least one of these parasites in dairy cattle affects composition or quality of their milk.

RESUMEN Objetivo. El objetivo de este estudio fue evaluar el efecto de la infección subclínica por agentes de la fiebre por garrapatas en el ganado lechero en producción de leche, la composición y calidad. Materiales y métodos. El estudio se realizó en una finca privada con 75 vacas lecheras alojadas-libre puesto, y de estas se evaluaron 37. Se recogieron muestras de leche individuales mensuales para determinar la composición (grasa, lactosa, proteína y sólidos totales) y la calidad (recuento de células somáticas (SCC)). Además, se recogieron muestras de sangre para identificar vacas que fueron negativas a fiebre de garrapatas y positivos por PCR para uno o más de los siguientes agentes etiológicos: Babesia bovis, Babesia bigemina y Anaplasma marginale. Resultados. Los resultados mostraron un aumento de SCC en los animales positivos, al menos para uno de los agentes cuando se comparó con vacas no infectadas (p<0.05). La producción de leche fue significativamente menor en A. marginale animales positivos (p<0.05). Un aumento de aproximadamente el 40% en el contenido de sólidos de la leche fue encontrado en vacas positivas a B. bovis. También, un incremento de aproximadamente el 23% de la lactosa se encontró en vacas positivas para B. bigemina. Conclusiones. Se puede concluir que la presencia de al menos uno de estos parásitos en el ganado lechero afecta composición o calidad de su leche.

Toxoplasma gondii infection in dairy ewes: Vertical transmission and influence on milk production and reproductive performance.

The present study aimed to evaluate the transmission of toxoplasmosis (vertical and venereal) and its influence on milk production and reproductive problems of Lacaune sheep seropositives for Toxoplasma gondii. Males and females were serologically selected using indirect immunofluorescence method in three steps of the study. Step 1: In order to evaluate the influence of toxoplasmosis on milk production, the volume of milk produced by 40 sheep (22 seronegatives and 18 seropositives for T. gondii) was weekly measured throughout the lactation period. There were no significant differences between these two groups; in other words, toxoplasmosis did not affect milk production. Step 2: In order to assess T. gondii venereal transmission, five samples of semen from seropositive rams (n = 5) were tested by endpoint and real time PCR with two days of interval; however, these semen samples were PCR negatives for T. gondii. Step 3: To evaluate reproductive problems, 12 seropositive animals out of a flock of 68 pregnant ewes showed signs of reproductive problems, such as abortion or fetal resorption. T. gondii transplacental transmission was evaluated on blood drawn from newborn lambs (n = 41), and their respective seropositive mothers (n = 30) after single, double or triple births. Serological tests showed that 65.8% of the lambs had antibodies against this protozoan, indicating a high transmission from ewe to fetus during pregnancy. Therefore, it is concluded that toxoplasmosis in sheep may impair reproduction with a high percentage of vertical transmission.

Relation between Neospora caninum and abortion in dairy cows: Risk factors and pathogenesis of disease.

Neosporosis is a parasitic disease cause by Neospora caninum, a parasite of great importance in livestock. This study aimed to evaluate the presence of antibody against N. caninum in dairy cattle with history of abortion, as well as to identify associated risk factors for neosporosis. Animals suspected of neosporosis (n = 130) after clinical examination were randomly selected. Sera samples from 29 farms were submitted to indirect immunofluorescence technique (IFA) in order to detect antibodies against N. caninum, and animals were considered positive if ≥ IFA 1:200. An epidemiological questionnaire was used to verify probable risk factors for neosporosis and their cause-effect relation. Serological results showed that 43.8% of the animals were seropositives for N. caninum. The univariate statistical analysis found a significant relation between neoporosis and age. The number of pregnancies and the number of years that the farms had been producing milk were found as associated risk factors for the disease either by univariate or by multivariate analyses. The cause-effect model found a possible relation between reproductive problems and positive serology for neosporosis (P = 0.06). Therefore, it was concluded that approximately 44% of dairy cows with history of abortion were seropositives for N. caninum and that age and the number of years that the farms had been producing milk are risk factors for parasite infection in dairy cattle.

Experimental infection by Trypanosoma evansi in sheep: Occurrence of transplacental transmission and mice infection by parasite present in the colostrum and milk of infected ewes.

The aims of this study were to evaluate vertical transmission of Trypanosoma evansi in sheep experimentally infected, in addition to the mammary transmission by colostrum or milk of these infected sheep to mice. Three pregnant sheep were used: one uninfected, four months pregnant (Sheep A); and two (Sheep B and C) infected intravenously by T. evansi trypomastigotes (4.6×10(6) per animal) on the third (Sheep C) and fourth (Sheep B) month of pregnancy. Both infected sheep developed low and oscillating parasitemia measured by blood smears. Hemogram was performed at seven day intervals, showing anemia, leukocytosis, and lymphocytosis on sheep B and C. Three sheep had twins, where sheep A delivered healthy lambs and both infected sheep had delivered at least one stillborn. Additionally, lambs from sheep B and C died 24 and 72 h post-partum, respectively. Before colostrum intake, four lambs from infected sheep were positives for T. evansi according to blood smear evaluation, serology (CATT/T. evansi), and PCR. Sheep colostrum and milk samples collected from the first four days post-partum were positives for T. evansi on PCR, and these samples were able to infect seven mice (out of 10) orally (n=4/5) and intraperitoneally (n=3/5). Therefore, we conclude that the vertical transmission of T. evansi occurs in pregnant sheep, in addition to a strong possibility of the transmission by colostrum and milk.

Trichostrongylus and Haemonchus anthelmintic resistance in naturally infected sheep from southern Brazil.

The anthelmintic resistance in small ruminants is a common problem and concern worldwide. The aim of this study was to verify anthelmintic treatment efficacy in naturally infected sheep. This study was conducted on nine herds that used the same anthelmintic management for over a year. In each farm, the animals were divided into two groups: untreated control group (n = 5) and treated (n = 10) according to the number of eggs per gram of feces (EPG). The treatment effect was checked based on EPG results and larval culture performed before treatment and 10 days after treatment. Significant differences were not observed (P > 0.05) on EPG results between untreated and treated groups. The coproculture showed that the animals were infected primarily by Haemonchus spp., Trichostrongylus spp., Teladorsagia spp., Cooperia spp. and Oesophagostomum spp. In all farms, anthelmintic resistance by genera Haemonchus and Trichostrongylus was found, but this resistance varied greatly between farms. Haemonchus spp. showed resistance to closantel, levamisole, and albendazole. Trichostrongylus spp. was shown to be resistant to closantel, levamisole, and albendazole. The drugs tested showed to be efficient against the genera Teladorsagia, Cooperia, and Oesophagostomum. Based on these results, we conclude that the anthelmintic resistance to the tested drugs is a problem present in the farms evaluated.