Influence of hypo- or hyperthyroidism on ovarian function in Brahman cows

From ultrasound to microscopy: Actualities in thyroid investigation in cattle

Thyroid ultrasonography examination is widely used in human and small animal medicine. However, it has rarely been applied in cattle. The aim of this study was to determine whether the measurements of the thyroid gland by ultrasound examination correlate to those taken during post-mortem examination. A sample of 22 cows and 23 calves was selected for thyroid gland evaluation. An ultrasound scan was performed ante-mortem, followed by euthanasia (for medical reasons) or slaughtered in the food chain and the dissection of the thyroid gland was therefore performed. Post-mortem, the gland was weighed and its dimensions and volume measured. The volume and weight measurements were compared with the predicted ones on US using the formulas available in the literature. Finally, histological examination was performed on thyroid glands. The dimensions of the thyroid gland measured by ultrasonography were significantly different (p<0.05) from those observed post-mortem, except for lobe lengths in calves (p>0.1). However, in calves, there was no systematic bias between the ultrasound and post-mortem examination of the thyroid gland, which were concordant (with an average error of 18%). Cystic lesions were observed on ultrasound in 9/22 cows and could be found on histological examination in 7 of these. Other lesions, such as follicular hypoplasia and hyperplasia, were seen on histological examination but not on ultrasound. Although the ultrasound measurements did not significantly correlate with those taken post-mortem, this examination may allow to differentiate non-standard thyroids in the case of hyperplastic goiter, as demonstrated in other species. This study also describes and illustrates interesting lesions of the thyroid gland in cattle. These findings are innovative in the description of the use of thyroid ultrasound in cattle, although further studies are needed to allow deeper conclusions.

Adaptive Responses of Thyroid Hormones, Insulin, and Glucose during Pregnancy and Lactation in Dairy Cows

The study examined the effects of different stages of pregnancy and lactation on thyroid, insulin, and glucose responses in dairy cows. In the present study, 30 dairy cows (10 Holstein, 10 Simmental, and 10 Brown) at 30 ± 20 d of lactation were randomly selected and blood samples were collected once every 60 d for one year to measure circulating thyroid stimulating hormone (TSH), total and free triiodothyronines (T3, fT3) and thyroxines (T4, fT4), insulin, and glucose. Pregnant cows showed higher T4 (p = 0.010) and insulin (p = 0.046) concentrations at >180 d than at >60−120 d of pregnancy and in nonpregnant cows. Along the lactation phase, circulating T4 concentrations showed a biphasic trend, decreasing from 0−60 d to >60−120 d phase, which showed the lowest values, and then increasing until the end of lactation (>300 d) (p = 0.016). Glucose showed the highest concentrations at the start of lactation (0−120 days) and the lowest values at the end (p = 0.008). The monitoring of thyroid hormones, insulin, and glucose changes represents an important tool to evaluate the anabolic and/or catabolic adaptation in response to functional periods in dairy cows, which can potentially predispose the cows to an excessive negative energy balance and related metabolic issues.

Thyroid hormones and female reproduction

Thyroid hormones are vital for the proper functioning of the female reproductive system, since they modulate the metabolism and development of ovarian, uterine, and placental tissues. Therefore, hypo- and hyperthyroidism may result in subfertility or infertility in both women and animals. Other well-documented sequelae of maternal thyroid dysfunctions include menstrual/estral irregularity, anovulation, abortion, preterm delivery, preeclampsia, intrauterine growth restriction, postpartum thyroiditis, and mental retardation in children. Several studies have been carried out involving prospective and retrospective studies of women with thyroid dysfunction, as well as in vivo and in vitro assays of hypo- and hyperthyroidism using experimental animal models and/or ovarian, uterine, and placental cell culture. These studies have sought to elucidate the mechanisms by which thyroid hormones influence reproduction to better understand the physiology of the reproductive system and to provide better therapeutic tools for reproductive dysfunctions that originate from thyroid dysfunctions. Therefore, this review aims to summarize and update the available information related to the role of thyroid hormones in the morphophysiology of the ovary, uterus, and placenta in women and animals and the effects of hypo- and hyperthyroidism on the female reproductive system.

Cystic ovarian follicles and thyroid activity in the dairy cow

Thyroid activity affects the functionality of the reproductive axis and thyroid dysfunction has been associated with ovarian hyperstimulation syndrome and polycystic ovarian syndrome, in human medicine. This study investigates serum17-<beta> estradiol, progesterone, thyrotropic and thyroid hormone levels, in cyclic dairy cows on heat (Group H) and in dairy cows with ovarian follicular cysts (Group FC). Both 17-<beta> estradiol and progesterone serum concentrations were statistically higher in cystic than in cyclic cows (estradiol: 8.51±1.91 vs 6.32±1pg/mL) (progesterone: 0.49±0.17 vs 0.13±0.03ng/mL), whereas TSH and fT4 serum concentrations were statistically lower in cows with cystic ovarian follicles (COF), compared to cyclic ones (TSH: 2.48±1.31 vs 3.56±1.03ng/mL) (fT4: 5.86±1.69 vs 8.63±1.08). fT3 serum levels were similar, in both cystic and cyclic subjects (2.94±0.65 vs 3.02±0.9, respectively). Based on these results it was decided to examine the function of the thyrothropic axis of dairy cows in a similar manner to that conducted on humans. If severe hypothyroidism should be found, a hormone replacement therapy could be attempted in cystic cows refractory to "ordinary" therapies.

Plasma progesterone, metabolic hormones and beta-hydroxybutyrate in Holstein-Friesian cows after superovulation

Metabolic hormones [insulin, leptin, insulin-like growth factor-I (IGF-I), thyroxine (T4) and triiodothyronine (T3)], progesterone (P4) and beta-hydroxybutyrate (BHB) serum concentrations were evaluated and their effect on the superovulation results of donor cows was investigated in a semi-arid environment. Body weight, body condition score (BCS) and lactation stage were also included in the analysis. Twenty-three Holstein-Friesian cows were superovulated with 600 IU FSHp following the routine procedure and flushed on day 7 in a Multiple Ovulation and Embryo Transfer Centre in the semi-arid area of Brazil. The corpora lutea (CL) were counted and blood samples were collected for assays. All of the hormones investigated and BHB serum concentrations were within the physiological ranges. There was a positive correlation between hormones, except between BHB and all the others. The leptin level was influenced by feeding status, as indicated by the BCS. Insulin, T4, T3 and BHB levels were affected by milking status. Dry cows had higher levels of all hormones except BHB. An optimum level of leptin resulted in the highest number of CL, while the linear increase of P4, T4 and IGF significantly increased the number of CL.

Glutamate supply positively affects serum release of triiodothyronine and insulin across time without increases of glucose during the onset of puberty in female goats

The current study evaluated the effect of glutamate supply on the onset of puberty and possible links to changes in serum concentrations of insulin [INS], glucose [GLU] and triiodothyronine [T(3)]. The study was conducted from June to November in prepuberal female goats (n=18; 3 mo. old, 7/8 Saanen-Alpine, 1/8 Criollo, 26° north) randomly assigned to two experimental groups: (i) excitatory amino acids group (group AA, n=10; 16.52±1.04 kg LW, 3.4±0.12 body condition score [BCS], receiving an intravenous infusion of 7 mg kg(-1) live weight [LW] of l-glutamate, twice a week, and (ii) control group (group CC, n=8; 16.1±1.04 kg LW, 3.1±0.12 BCS) receiving saline. Blood samples were obtained twice a week, for assessing progesterone [P(4)], as well as in a monthly basis to evaluate INS and T(3) by RIA. Mean final LW and BCS were 23.2±0.72 kg, 3.53±0.10 units, without differences between groups. The AA group depicted an earlier onset of puberty (6.9±0.3 compared to 7.5±0.4 mo.; P<0.05) and an increased ovarian activity (70±0.28% compared to 25±0.26%; P<0.05). Neither serum INS concentrations nor serum glucose concentrations differed between treatments (1.2±0.06 ng mL(-1) and 89.6±1.8 mg 100 mL(-1); P>0.05, respectively). Serum T(3) concentrations, however, were greater in AA goats (1.55±0.03 compared to 1.39±0.04 ng mL(-1)). In addition, a treatment x time interaction occurred (P<0.05) across the experimental period for both T(3) and INS, with increases by the last third of the experimental period, time at which the onset of puberty occurred in both experimental groups. No differences (P>0.05) for glucose concentrations across time occurred between treatments. Results indicate that, in prepuberal goats, glutamate acts as a cue for sexual maturation in a glucose-independent pathway, while both T(3) and INS seem to act as metabolic modulators for the establishment of puberty in goats. Actions of INS and T(3) are mediated directly on hypothalamic centers regulating the pulsatile release of GnRH or indirectly by peripheral cues reflecting INS-T(3) actions on somatic development remains to be determined.

Influence of exogenous triiodothyronine (T3) on fecal shedding of Escherichia coli O157 in cattle

Fecal prevalence of Escherichia coli O157 in ruminants is highest in the summer months and decreases to low or undetectable levels in the winter. We hypothesize that the seasonal variation of this pathogen is a result of physiological responses within the host animal to changing day length. The thyroid is an endocrine gland known to respond to changing day length. Two experiments were conducted to determine if a hyperthyroid status would initiate fecal shedding of E. coli O157 in cattle during the winter when shedding is virtually nonexistent (winter experiment) or influence cattle actively shedding E. coli O157 (summer experiment). Yearling cattle were group-penned under dry-lot conditions, adjusted to a high concentrate ration, and randomly assigned to treatment: control (1 mL corn oil injected s.c. daily) or triiodothyronine (T(3); 1.5 mg suspended in corn oil injected s.c daily). Cattle were individually processed daily for collection of fecal and blood samples. Treatment with exogenous T(3) produced a significant change in serum thyroid hormone concentrations indicative of a hyperthyroid status in both experiments. No differences (P>0.10) were observed in fecal shedding of E. coli O157 in the winter experiment. In the summer experiment, fecal shedding of E. coli O157 was decreased (P=0.05) by administration of T(3) during the treatment period (days 1-10), tended to be lower (P=0.08) during the following 7-day period of no treatment, and was lower (P=0.01) when examined across the entire experimental period. Results of this research indicate that the thyroid or its hormones may be involved in the seasonal shedding patterns of E. coli O157 in cattle.

Serum thyroid hormones and performance of offspring in ewes receiving propylthiouracil with or without melatonin

Two experiments were conducted during mid-gestation to examine effects in ewes of propylthiouracil (PTU) treatment alone or with melatonin on serum thyroid hormones, postpartum reproduction, and lamb performance. In the first experiment, beginning on day 0 (first day of treatment when all animals were 72.2+/-0.9 days of gestation), ewes received daily treatments (gavage) consisting of either 0mg (n=6) or 40 mg (n=6) PTU/kg body weight/day for 15 days. After 15 days, the 40 mg dosage was decreased to 20mg/kg body weight for an additional 20 days (35 days of PTU). Serum thyroxine (T4) did not differ (P>0.10) between groups through day 4; but on day 5, control females had a serum value of 67 ng/ml compared with 46 (+/-5)ng/ml for PTU-treated ewes (P=0.02). On the last day that 40 mg of PTU was administered, serum T4 averaged 67 and 7 (+/-5)ng/ml (P<0.001) in the two respective groups. Serum T4 remained low and was 80 and 1 ng/ml (P<0.001) in control and treated ewes on day 34. Serum T4 rose gradually after PTU but remained different from that observed in control ewes through day 48. Lambs from control and treated ewes had similar (P=0.46) T4 values at birth but lambs from PTU-treated ewes had lower (P=0.03) birth weights than did those from control ewes. Serum progesterone (P4) after parturition indicated a lack of cyclicity in all ewes. In the second experiment, beginning on day 0 (76.8+/-4.7 days of gestation), ewes received PTU as in Experiment 1. In addition, after 15 days of PTU, melatonin was given (i.m. injections at 5mg/day) for 30 days. Propylthiouracil decreased (P<or=0.05) serum T4 on days 25 through 41 of the treatment period. Serum T3 was lower (P<0.05) in PTU-treated ewes from day 8 through the end of PTU administration. Postpartum P4 was below 1 ng/ml on all days indicating acyclicity. Lamb body weight and serum IGF-I were similar (P>0.60) for lambs born to control and treated ewes. Female offspring of PTU+melatonin-treated dams reached puberty, became anestrus, and returned to cyclicity at similar (P>0.10) times to contemporary ewe lambs. Results indicate that 40/20mg PTU alone or with melatonin does not induce cyclicity after lambing in spring lambing ewes and has little effect on offspring performance.

Effect of the thyroid on faecal shedding of E. coli O157:H7 and Escherichia coli in naturally infected yearling beef cattle

AIMS

To determine if thyroid function affects faecal shedding of Escherichia coli O157:H7.

METHODS AND RESULTS

Eight yearling cattle (n = 4 per treatment group), previously identified as shedding E. coli O157:H7, received either 0 or 10 mg 6-N-propyl-2-thiouracil (PTU) kg(-1) BW day(-1) for 14 days to reduce serum concentrations of the thyroid hormones, T(3) and T(4). Animals were monitored daily for changes in faecal shedding of E. coli O157:H7 and E. coli (EC) for the 14-day treatment period and an additional 7 days post-treatment. Body weight was measured weekly and serum concentrations of T(3) and T(4) were determined every 3 days. No differences in faecal shedding of E. coli O157:H7 were observed during the 14-day treatment period. However, compared with control animals, a greater percentage of PTU-treated cattle ejected E. coli O157:H7 on day 16 (100 vs 25%) and 18 (75 vs 0%) of the post-treatment period. Serum T(3) was lower in PTU-treated cattle during the 14-day treatment period and greater on day 18 of the post-treatment period.

CONCLUSION

Cattle with chemically altered thyroid hormones had similar shedding patterns of faecal E. coli O157:H7 and EC during the 14-day treatment period. However, faecal shedding of E. coli O157:H7 tended to be greater, and serum concentrations of T(3), were greater for PTU-treated cattle immediately following the termination of PTU treatment.

SIGNIFICANCE AND IMPACT OF THE STUDY

Short-term chemical inhibition of thyroid hormones had minimal effects on faecal shedding of E. coli O157:H7 in naturally infected cattle. However, a hyperthyroid state as observed postdosing might play a role in the seasonal shedding of E. coli O157:H7 in cattle.

Colocalization of GH, TSH and prolactin, but not ACTH, with betaLH-immunoreactivity: evidence for pluripotential cells in the ovine pituitary

Increasing evidence suggests that multihormonal cells in the pituitary gland may be more commonplace than previously thought. This has forced us to reconsider our classical view of cell populations in the pituitary gland. Studies so far have focused almost exclusively on the rat, and there is a dearth of information on other species. Our first objective was to determine whether a subpopulation of gonadotropes also express somatotropin in the ewe, as reported in the rat. In addition, we sought to determine whether gonadotropes express any of the other known pituitary hormones. Finally, we investigated whether the stage of the estrous cycle influenced the occurrence of these pluripotential gonadotropes. We found that a small population of betaLH-immunoreactive cells also expresses immunoreactive GH, prolactin and TSH. No gonadotropes colocalized with ACTH. Significantly (P<0.001) more gonadotropes expressed GH during the luteal (10.7+/-0.4%) than the late follicular (5.4+/-0.3%) phase but there was no difference between the luteal and follicular phases in the proportion of gonadotropes expressing prolactin (follicular: 5.7+/-0.7%; luteal: 5.5+/-0.6%) or TSH (follicular: 3.1+/-0.7%; luteal: 4.2+/-0.5%). Similarly, there was a significant (P<0.05) difference in the proportion of GH-immunoreactive cells expressing betaLH immunoreactivity in the luteal (5.9+/-0.3%) and follicular (3.4+/-0.5%) phases but no difference in the proportion of prolactin- (follicular: 2.2+/-0.7%; luteal: 2.0+/-0.8%) or TSH-immunoreactive cells (follicular: 9.6+/-3.7%; luteal: 10.8+/-2.9%) expressing betaLH. The specific function of these multihormonal gonadotropes in sheep remains to be determined.

A study on perchlorate exposure and absorption in beef cattle

Perchlorate exposure and potential effects were evaluated in large mammals by monitoring heifer calves placed on a site with access to streamwater fed by a perchlorate-contaminated groundwater spring ( approximately 25 ng/mL). Blood was collected from the two calves on the site (and two control calves from an uncontaminated site) approximately every 2 weeks for analysis of perchlorate residues and thyroid hormones. During the 14 week study, perchlorate was detected (detection limit = 13.7 ng/mL) in blood plasma twice (15 ng/mL and 22 ng/mL) in one of the heifer calves drinking perchlorate-contaminated water on consecutive sampling periods 4 and 6 weeks after the beginning of perchlorate exposure. Constant exposure to 25 ppb perchlorate in drinking water had no effect on circulating thyroid hormones (T(3) and T(4)) in the heifer calves.

Influence of body condition at calving and postpartum nutrition on endocrine function and reproductive performance of primiparous beef cows1,2

The influences of body condition score (BCS) at calving and postpartum nutrition on endocrine and ovarian functions, and reproductive performance, were determined by randomly allocating thin (mean BCS = 4.4 +/- 0.1) or moderate condition (mean BCS = 5.1 +/- 0.1) Angus x Hereford primiparous cows to receive one of two nutritional treatments after calving. Cows were fed to gain either 0.45 kg/d (M, n = 17) or 0.90 kg/d (H, n = 17) for the first 71 +/- 3 d postpartum. All cows were then fed the M diet until 21 d after the first estrus. A replication (yr 2; M, n = 25; H, n = 23) was also used to evaluate reproductive characteristics. Concentrations of IGF-I, leptin, insulin, glucose, NEFA, and thyroxine were quantified in plasma samples collected weekly during treatment and during 7 wk before the first estrus. Estrous behavior was detected by radiotelemetry, and luteal activity was determined based on concentrations of progesterone in plasma. All cows were bred by AI between 14 and 20 h after onset of estrus, and pregnancy was assessed at 35 to 55 d after AI by ultrasonography. Cows that calved with a BCS of 4 or 5 had similar endocrine function and reproductive performance at the first estrus. During treatment, H cows gained BW and increased BCS (P < 0.01), and had greater (P < 0.05) concentrations of IGF-I, leptin, insulin, glucose, and thyroxine in plasma than M cows. However, during the 7 wk before the first estrus, plasma concentrations of IGF-I, leptin, insulin, glucose, NEFA, and thyroxine were not affected by time. Cows previously on the H treatment had a shorter (P < 0.01) interval to first postpartum estrus and ovulation, and a larger dominant follicle (P < 0.01) at first estrus, than M cows, but duration of estrus and the number of mounts received were not influenced by nutrient intake. Pregnancy rate at the first estrus was greater (P < 0.03) for H (76%, n = 38) than for M (58%, n = 33) cows. Increased nutrient intake after calving stimulated secretion of anabolic hormones, promoted fat deposition, shortened the postpartum interval to estrus, and increased pregnancy rate at the first estrus. Concentrations of IGF-I and leptin in plasma were constant during 7 wk before the first estrus, indicating that acute changes in these hormones are not associated with the resumption of ovarian function in primiparous beef cows.

Effects of ammonium perchlorate on the reproductive performance and thyroid follicle histology of zebrafish

Adult zebrafish were reared up to eight weeks in control water or in water containing ammonium perchlorate (AP) at measured perchlorate concentrations of 18 (environmentally relevant, high) and 677 ppm. Groups of eight females were paired with four males on a weekly basis to assess AP effects on spawned egg volume, an index of reproductive performance. All treatments were applied to four to five spawning replicates. At 677 ppm, spawn volume was reduced within one week and became negligible after four weeks. At 18 ppm, spawn volume was unaffected even after eight weeks. Also, perchlorate at 18 ppm did not affect percentage egg fertilization. Fish were collected at the end of the exposures (677 ppm, four weeks; control and 18 ppm, eight weeks) for whole-body perchlorate content and thyroid histopathological analysis. Fish perchlorate levels were about one-hundredth of those of treatment water levels, indicating that waterborne perchlorate does not accumulate in whole fish. At 677 ppm for four weeks, perchlorate caused thyroid follicle cell (nuclear) hypertrophy and angiogenesis, whereas at 18 ppm for eight weeks, its effects were more pronounced and included hypertrophy, angiogenesis, hyperplasia, and colloid depletion. In conclusion, an eight-week exposure of adult zebrafish to 18 ppm perchlorate (high environmentally relevant concentrations) affected the histological condition of their thyroid follicles but not their reproductive performance. The effect of 677 ppm perchlorate on reproduction may be due to extrathyroidal toxicity. Further research is needed to determine if AP at lower environmentally relevant concentrations also affects the thyroid follicles of zebrafish.

Ovarian cyclicity in thyroid-suppressed ewes treated with propylthiouracil immediately before onset of seasonal anestrus

Two experiments were conducted to determine if propylthiouracil (PTU)-induced thyroid suppression immediately before onset of anestrus would extend the breeding season in mature ewes. In Exp. 1, twice-weekly serum concentrations of progesterone indicated that all ewes were cyclic before initiation of treatment. Beginning on d 0 (January 17), ewes received 0 (n = 4), 20 (n = 5), or 40 (n = 5) mg of PTU x kg(-1) of body weight (BW) x (-1) for 35 d. Blood samples were collected regularly throughout the trial and serum thyroxine and progesterone were quantified. Ewe BW were similar (P > 0.90) among treatments before the experiment began (mean = 78.2 +/- 4.5 kg). Likewise, serum concentrations of thyroxine averaged 86.5 +/- 8.0 ng/mL on d 0. After 11 d of PTU treatment, serum thyroxine was 90.2,75.2, and 44.2 +/- 14.0 ng/mL in ewes receiving 0, 20, and 40 mg of PTU/kg BW, respectively (linear effect, P = 0.04). On d 20, thyroxine values in the three respective groups were 73.0, 51.1, and 16.1 +/- 12.9 ng/mL (linear effect, P < 0.01). Fourteen days after PTU treatment ended, serum thyroxine did not differ (P = 0.53) among the three respective groups (71.4,73.3, and 57.5 +/- 11.8 ng/mL). Ewes receiving PTU tended to weigh less on d 42 (84.2, 78.2, and 71.8 +/- 5.1 kg for ewes treated with 0, 20, and 40 mg PTU/kg, respectively; linear effect, P = 0.10). Day of onset of anestrus was designated as the day on which serum progesterone decreased and remained below 1 ng/mL. Ewes treated with 0, 20, or 40 mg of PTU/kg BW became anestrous on d 16,40, and 81 (+/- 12) of the experiment, respectively (linear effect, P < 0.01). At the time the 35-d treatment period ended, 25, 60, and 100% of ewes receiving 0, 20, or 40 mg of PTU/kg exhibited normal estrous cycles. In Exp. 2, ewes received 0, 20, or 40 mg of PTU/kg BW for 14 d. The dose was then decreased to 0, 10, and 20 mg of PTU/kg BW for the remaining 21 d. Serum thyroxine decreased to concentrations below 20 ng/mL by d 9 after initiation of PTU treatment. Ewe weights did not differ throughout the trial and no BW loss was observed. The average day that each group entered anestrus was similar to those in Exp 1. Large doses of PTU dramatically lower serum thyroxine and this effect appears to inhibit onset of anestrus in ewes.