Does closantel in therapeutic doses display thyroid hormone-like activity in sheep?

The aim of this study was to define the thyroid hormone-like activity of closantel in sheep by measuring some blood parameters that are known to be influenced by thyroid hormones triiodothyronine (T3) and thyroxine (T4). Our hypothesis was that, if closantel possesses thyroid hormone-like activity, its use under in vivo conditions will result in changes similar to those in hyperthyroidism. The study was conducted in 20 Jezersko-Solchava breed sheep. Blood sampling was performed before and 10 days after routine anthelmintic treatment with closantel. Complete blood count, plasma cholesterol, triglycerides, protein, and albumin levels, as well as those of serum T3 and T4, were compared before and 10 days after closantel administration. This routine anthelmintic treatment of sheep with closantel did not significantly influence hematological parameters, thyroid hormone levels, or most of the biochemical parameters. No evidence was found for thyroid hormone-like activity of closantel in sheep. However, significantly (P < 0.01) elevated levels of plasma triglycerides were present 10 days after closantel administration.

Fluctuations of serum cortisol, insulin and non-esterified fatty acid concentrations in growing ewes over the year

Background

The physiological levels of endocrine and metabolic parameters in Slovene autochthonous breeds of sheep are not yet well known, nor are the mechanisms of their adaptability and responses to climate and environmental factors.

Therefore, the aim of this study was to evaluate fluctuations of cortisol, insulin and non-esterified fatty acids (NEFA) in growing ewes over an one-year period. Blood samples were collected monthly from 10 yearling Jezersko-Solchava, 10 Bovec and 10 Istrian ewes. Serum cortisol, insulin and NEFA were measured with commercial kits.

Results

Mean monthly cortisol values fluctuated with low levels in summer and high levels in autumn. Significant peaked cortisol values of 25.69 ± 6.89, 14.67 ± 2.43 and 21.11 ± 7.25 μg/L in Jezersko-Solchava, Bovec and Istrian breed, respectively, were found in September (Bovec breed) and October (Jezersko-Solchava and Istrian breed). Mean monthly insulin values increased during the observation period. The highest levels of 14.60 ± 3.15, 16.03 ± 5.35 and 12.56 ± 2.52 μIU/mL in Jezersko-Solchava, Bovec and Istrian breed, respectively, were observed in the last sample collection in May. NEFA concentrations were found to be low except in some autumn and spring months. The peak values were observed in March for Jezersko-Solchava and Istrian breed (0.60 ± 0.05 and 0.66 ± 0.10 mmol/L), and in April for Bovec breed (0.71 ± 0.11 mmol/L).

Conclusions

Monthly fluctuations of cortisol, insulin and NEFA were measured in all observed sheep breeds, but between-breed differences in monthly values of examined parameters were insignificant. Significantly increased serum cortisol levels were found in autumn for all breeds and were probably associated with the onset of puberty and low environmental temperature. A gradual increase of insulin level in the examined ewes was in parallel with their growth. Significantly higher NEFA values in spring suggest qualitatively insufficient feed supply during that period.

Gonadectomy prior to puberty decreases normal parental behavior in adult mice

Sex steroid hormones secreted by gonads influence development and expression of many behaviors including parental behaviors. The capacity to display many behaviors develops under the influence of sex steroid hormones; it begins with gonadal differentiation and lasts through puberty. The timing of gonadectomy may have important and long lasting effects on the organization and activation of neural circuits regulating the expression of different behaviors. The present study investigated the importance of exposure to endogenous gonadal steroid hormones during pubertal period/adolescence on parental behavior in adult mice. Male and female WT mice were gonadectomized either before puberty (25 days of age) or after puberty (60 days of age) and tested for parental behavior with and without estradiol benzoate (EB) replacement in adulthood. Additional groups of mice were gonadectomized at P25 and supplemented with estradiol (females) or testosterone (males) during puberty. Female mice gonadectomized after puberty or gonadectomized before puberty and supplemented with estradiol during puberty, displayed better pup directed parental behaviors in comparison to mice gonadectomized at 25 days of age regardless of treatment with estradiol in adulthood. However, mice treated with EB in adulthood displayed better non-pup directed nest building behavior than when they were tested without EB treatment regardless of sex and time of gonadectomy. To examine whether the sensitivity to sex steroid hormones was altered due to differences in time without gonads prior to the testing, mice were also tested for female sex behavior and there were no differences between mice gonadectomized at P25 or P60, although this could not completely rule out the possibility that parental behavior is more sensitive to prolonged absence of steroid hormones than female sex behavior. These results suggest that the absence of gonads and thereby the absence of appropriate gonadal steroid hormones during puberty/adolescence may have a profound effect on pup directed parental behaviors in adult mice.

Retrospective study of bull semen quality - possible correlation with pesticide use?

Decline in semen quality in humans and increased incidence of male reproductive problems could be caused by different factors, including pesticides that could mimic or block the action of endogenous hormones. If the decline in semen quality is real, and environmental chemicals are at least partially responsible for this decline, similar changes should be observed in animals that live in close connection with humans and are exposed to similar levels of pollutants. In the present study, the semen quality of bulls in the last 30 years was examined with respect to the year of birth. Furthermore, semen quality results were correlated to the total pesticide use in a limited geographical area. The results indicate a notable decrease in both ejaculate volume and total number of spermatozoa in ejaculates of bulls born in the late 1970s, while after that (until 2006) there was no obvious downward or upward trend either in ejaculate volume or in the total number of sperm cells. The amount of pesticides released into the environment increased about twofold in the given period, and linear regression analysis revealed a strong and statistically significant correlation between the amount of pesticides used and the total number of spermatozoa in the ejaculate.

Higher thyroid hormone levels in neonatal life result in reduced testis volume in postpubertal bulls

Thyroid hormones appear to determine adult testis size in rodents by regulating the period of Sertoli cell proliferation in the neonatal period. In the present study, the correlation between neonatal thyroid hormone levels (T3 and thyroxin, T4) and postpubertal testis size in Simental bulls was examined. T3 and T4 levels were measured in blood plasma from 35 calves immediately after their arrival at the AI centre at age 3-6 months. Testis size (height and width) was measured at 12 months of age in the same live animals. A significant negative correlation (r = -0.55; p < or = 0.001) was found between T4 and calculated testicular volume using either the Pearson correlation test or linear regression analysis, while the levels of T3 and testis volume showed a negative correlation, although this did not reach statistical significance (r = -0.20, p < or = 0.05). The results of this study suggest, therefore, that neonatal thyroid hormone levels might have the same effect on testicular size in cattle as they do in rodents.