Growth hormone stimulates the in vitro development and establishment of Haemonchus contortus in sheep.

The physiologic increase in some sex hormones has been associated with an increase in the parasite load caused by Haemonchus contortus in ewes, especially prolactin. In lambs that are especially susceptible to hemonchosis, the levels of sex hormones are low; in contrast, the levels of another pituitary hormone, growth hormone (GH), which is structurally very similar to prolactin, are high. In this study, the in vitro and in vivo effects of GH on H. contortus larvae development and establishment were evaluated. The addition of 20 ng/mL GH for 5 and 10 days to cultures of H. contortus larvae induced an enlargement (p<0.01) and an L3/L4 molting rate (p<0.03) greater than that of untreated larvae or those treated with other concentrations of the hormone. Flow cytometry showed that 3.8% of the largest and most complex cells of newly obtained larvae of H. contortus were positive for the GH receptor, and by immunofluorescence with confocal microscopy, it was observed that these receptors are located in the intestinal region larvae. In the in vivo assay, the administration of recombinant GH to gonadectomized lambs produced an increase in FEC (p<0.03), the number of female adult worms in the abomasum (p<0.05) and the levels of specific antibodies (p<0.04) in relation to the control lambs; however, it did not affect the fertility of H. contortus females. Although many factors affect the development and implantation of H. contortus in the abomasum of sheep, the results of this study strongly suggest that GH participates in the development and establishment of the parasite in sheep, mainly in young sheep.

Subclinical experimental infection with Taenia hydatigena in sheep is associated with production losses.

The effect of experimental infection by Taenia hydatigena metacestodes on different productive parameters in sheep was evaluated. Seventeen male Columbia lambs distributed in three groups were used. The lambs of the first group (n = 5) were orally inoculated with 1000 T. hydatigena eggs (low dose). The lambs of the second group (n = 5) were inoculated orally with all the eggs of the last proglottid of an adult cestode (high dose). The lambs of the third group (n = 7) only received a placebo and were used as a control group. All lambs were humanely euthanized at week 13 postinfection, and carcass yield and conformation were evaluated. The infection rates of the lambs from the high-dose infected group and the low-dose infected group were 100% and 40%, respectively, with a mean of 2.4 ± 0.6 and 1 ± 0.7 metacestodes of T. hydatigena in the abdominal cavity, respectively. In a first multivariate study (MANOVA) considering the under the curve (AUC) values of body condition, weight gain, and feed consumption, as well as the final feed conversion values, showed a highly significant (p < 0.0001) group effect (high dose/low dose/uninfected). In a second multivariate study (MANOVA) considering the AUC values of eosinophils blood count, packed cell volume and alkaline phosphatase showed a highly significant (p < 0.0001) group effect (high dose/low dose/uninfected). The increase in serum ALP is a consequence of liver damage that had a strong negative correlation (r = -0.63, p < 0.007) with the body condition of the lambs. Despite these findings, we did not observe obvious clinical manifestations in any of the infected lambs. In general, no differences (p > 0.1) were observed between the lambs of the control group and the lambs of the low-dose infected group in the parameters evaluated. The results of this study show that the infection of T. hydatigena metacestodes subclinically produces a decrease in productive efficiency, alterations of some hematological and biochemical values, and a slight deterioration in the general appearance of the infected lambs. The above aspects are rarely detected by most farmers, but they have a negative impact on the productivity of infected lambs.