Responses of thyroid activity to feed restriction in the goat

Urinary total T3 levels as a method to monitor metabolic changes in relation to variation in caloric intake in captive bonobos (Pan paniscus)

Monitoring metabolic activity in wild living animals has become of particular interest in the field of ecological research. Methods for the repeated non-invasive sampling of individuals are needed. Thyroid hormones (TH) are involved in the regulation of metabolic activity, and their measurement can be used as a proxy to monitor metabolic changes. During periods of low energy intake, serum TH levels are reduced, leading to a decrease in metabolic activity. Using urine samples collected during a food restriction experiment in captive bonobos we validated a total triiodthyronin (TT3) enzyme immunoassay (EIA) for the monitoring of metabolic changes. We found that the majority of immune reactivity of the assay in the urine samples could be explained through immunoreactivity to T3. Furthermore, urinary T3 was stable through repeated freeze-thaw cycles but prolonged exposure to room temperature lead to degradation. Most importantly, we found that for all animals urinary total T3 levels were higher when more digestible energy was consumed. We concluded that urinary total T3 measurements are a suitable method for monitoring metabolic changes in bonobos and potentially in a wide range of animal species.

Applications for non-invasive thyroid hormone measurements in mammalian ecology, growth, and maintenance

Thyroid hormones (THs) play a pivotal role in the regulation of metabolic activity throughout all life stages. Cross-talk with other hormone systems permits THs to coordinate metabolic changes as well as modifications in growth and maintenance in response to changing environmental conditions. The scope of this review is to explain the relevant basics of TH endocrinology, highlight pertinent topics that have been investigated so far, and offer guidance on measuring THs in non-invasively collected matrices. The first part of the review provides an overview of TH biochemistry, which is necessary to understand and interpret the findings of existing studies and to apply non-invasive TH monitoring. The second part focuses on the role of THs in mammalian ecology, and the third part highlights the role of THs in growth and maintenance. The fourth part deals with the advantages and difficulties of measuring THs in non-invasively collected samples. This review concludes with a summary that considers future directions in the study of THs.

Fecal thyroid hormones allow for the noninvasive monitoring of energy intake in capuchin monkeys

Measuring energetic condition of wild animals is of major importance in ecological research, as it is profoundly linked to fitness. However, noninvasive monitoring of energetic condition in wild-living animals is methodologically challenging. Measuring urinary C-peptide levels is a suitable method to noninvasively assess energy balance in wild-living animals. As collecting urine is not always feasible in the wild, it is essential to establish alternative biomarkers for other sample types to assess energy balance. Thyroid hormones (TH) are potential candidates as they are involved in the regulation of metabolic processes. During periods of low energy intake, serum TH levels are reduced, leading to a decrease in metabolic activity. To investigate whether fecal TH can serve as a biomarker for energy balance, we validated a total T3 ELISA to measure immunoreactive T3 (iT3) in fecal samples of yellow-breasted capuchins. We restricted caloric intake of seven males, assessed daily group caloric intake and determined daily individual fecal iT3 levels. Analytical validation of the assay showed that fecal iT3 levels can be reliably measured; however, proper storage conditions must be implemented and possible degradation to be accounted for. IT3 levels were significantly higher on days with high group caloric intake. However, individual iT3 levels varied substantially, resulting in an overlap across individuals between conditions. Our results indicate that fecal iT3 levels can serve as a useful biomarker to detect changes in energy intake of yellow-breasted capuchins. Overall, measuring fecal iT3 levels may present a suitable method for monitoring energy balance when urine collection is impossible.

The effect of plane of nutrition and shearing on the pattern of the moult in Scottish Cashmere goats

The effect of plane of nutrition on the timing of the moult in cashmere goats was investigated. Three groups of mature does were individually offered food to supply 0·8 (L, no. = 14), 1·2 (M, no. = 14) or 20 (H, no. = 13) times their estimated maintenance energy requirements from mid December until mid May. Two other groups of goats which were shorn in mid January, were offered 1·2 times maintenance requirements from mid December until mid March when food levels were increased to either 1·6 M (SL, no. = 6) or ad libitum (SAL, no. = 6). In mid May mean live weights for treatments L, M, H, SL and SAL were 36·0, 41·5, 46·9, 33·0 and 43·1 kg (average s.e.d. = 2·27, P < 0·001).

The pattern of moult was described by changes in a subjectively assessed moult score, the proportion of follicles with brushes and staple length. The loss of brushes, indicating the start of the moult, began from the primary follicles on days 143, 131, 76, 150 and 129 (average s.e.d. = 13·5, P < 0001), and from the secondary follicles on days 141, 128, 104, 144 and 125 (average s.e.d. = 14·1, P = 0·053) for treatments L, M, H, SL and SAL respectively. The loss of brushes from primary and secondary follicles was completed on average, by days 194 and 206 of the experiment respectively, and there were no differences between treatments. Moult score and staple length data confirmed the conclusion that lowering the plane of nutrition delayed the start of the moult. No additional effect of fleece removal in the shorn treatments was observed.

Changes in circulating levels of plasma prolactin, thyroxine, tri-iodothyronine, insulin, insulin-like growth factor-1 and growth hormone were related to seasonal changes in daylength and plane of nutrition. Their rôle in the control of the moult is discussed.

Manipulation of the nutrition of cashmere goats in early spring has the potential to delay and increase the synchrony of fibre moult and to improve the efficiency of cashmere harvesting.

The effect of Trypanosoma vivax infection on energy and nitrogen metabolism and serum metabolites and hormones in West African Dwarf goats on different food intake levels

Effects of Trypanosoma vivax infection on nitrogen and energy metabolism and serum hormones and metabolites were measured using 24 castrated West African Dwarf bucks. In order to discriminate between the effect of infection and the effect of food intake level on energy and nitrogen balance, food quantity restriction was applied for isonutritional comparison; a number of the animals were not infected and served as controls. Daily dry-matter (DM) intake was measured, and energy and nitrogen balance for a 7-day period in weeks 2, 4 and 6 after infection. Weekly blood sampling for analysis of hormones and metabolites was carried out.

Infected animals had a lower DM intake, compared with control animals, viz. 38·6 (s.e. 3·2) and 16·1 (s.e. 2·0) g/kg M0·75 per day, respectively (P < 0·001). Intake of gross energy and nitrogen followed the same pattern.

Metabolizability was not changed by infection and averaged 0·44. Heat production was increased by infection with an average of 33 kJ/kg M0·75 per day. Energy and nitrogen retention were negative for all groups; infection reduced energy retention and, during week 2 and 4 after infection, also nitrogen retention. The required metabolizable energy (ME) intake for maintenance was increased in infected animals (406 and 335 kJ/kg M0·75 per day for infected and control goats respectively), based on linear regression of energy retention on ME intake. The efficiency with which energy mobilization from body stores was substituted by dietary ME was estimated at 0·809 for both infected and control animals. The relationship between nitrogen retention and energy retention was not changed by infection. Therefore no indications were found for an increased catabolism of protein due to infection. Serum thyroxine and triiodothyronine were reduced by infection; serum metabolites and insulin levels reflected the negative energy balance in infected animals.

Seasonality of meal patterns and hormonal correlates in red deer

Two groups of six adult, castrated, male red deer were housed under natural daylength conditions and at ambient temperature at 57 degrees N and fed ad lib. (AL) or at a fixed rate of 50 g/kg0.75 initial liveweight per day throughout the study (restricted, R). Mean daily intakes of AL animals were higher during periods of long daylength than during short daylength (p < 0.001). The higher rates of food intake during periods of long daylength were a function of greater meal durations (p < 0.001), shorter inter-meal intervals (p < 0.001) and higher (p < 0.001) mean rates of ingestion (g/min). In both groups mean plasma concentrations of prolactin, T3, T4, and insulin-like growth factor 1 (IGF-1) were higher (p < 0.001) during long daylength than short daylength although changes in thyroid hormone profiles were much less marked in AL animals. Insulin and growth hormone (GH) profiles exhibited no consistent seasonal trend. Mean plasma concentrations of T3 were higher in AL than in R animals. Mean plasma IGF-1 concentrations during long days were consistently greater in the AL than R animals. It is concluded that the effects of seasonal changes in daylength on appetite and food intake are expressed through changes in both the duration of daylight periods per se and in underlying seasonal changes in physiology and associated meal patterns and eating rates. It is concluded that the roles of T3, IGF-1, and prolactin in the expression of seasonal changes in appetite should be investigated further and, particularly, their effects on other hormone profiles and liver and gut function.

Utilization rates of thyroid hormones in mammals

1. Thyroxine utilization rates (T4U: N = 37 species) and triiodothyronine utilization rates (T3U: N = 7 species) scale with body mass to the 0.81 and 0.74 power respectively. 2. T4U rates tend to be lower in summer relative to other seasons, vary unpredictably during pregnancy and lactation, increase with regular physical activity, and generally decrease with age. 3. Both T4U and T3U increase with cold exposure, decrease with heat exposure and during fasting, and increase/decrease with hyperthyroidism/hypothyroidism. 4. Since these T4U and T3U changes are qualitatively similar but quantitatively different, the T3U/T4U ratio varies, suggesting a variable deiodination rate from thyroxine to triiodothyronine.

Food deprivation suppresses stress-induced rise in catabolic hormones with a concomitant tendency to potentiate the increment of blood glucose

The organism of a food-deprived animal is directed toward minimizing energy expenditure and plasma levels of catabolic hormones and glucose are also reduced. Stress, on the other hand, is associated with enhancement of metabolic processes, elevated plasma catabolic hormones, and higher glucose levels. The question arises as to whether food deprivation may be able to attenuate the rise of plasma catabolic hormones seen in stress. For this purpose the variations in triiodothyronine (T3), thyroxine (T4), cortisol and glucose in blood plasma of sheep were monitored during 101 hr of food deprivation and 5 hr of stress. Stress was evoked by isolation of individual sheep from the flock. Blood was sampled by venipuncture once a day during 4 days preceding the isolation stress. On the day of isolation, blood was taken 4 times at 1.5- to 2-hr intervals. Food deprivation lowered the T3, T4 and glucose levels to 45.0, 59.5 and 78.0 percent of the basal level, respectively. Plasma cortisol level did not change over the fasting period in sheep not having visual contact with fed animals. Maintaining such a contact elevated cortisol level maximally by 139 percent over basal level. This indicates that the involvement of an emotional factor seems to be necessary for manifestation of stress. Isolation stress acting on fed and fasting sheep increased all measured hormones and glucose levels. However, in fed sheep, the maximal levels of T3, T4 and cortisol were 72.5, 48.4 and 50.0 percent higher than in corresponding isolated and food-deprived animals. Inversely, the maximal concentration of plasma glucose was about 16.6 percent higher in food-deprived than in fed animals.(ABSTRACT TRUNCATED AT 250 WORDS)

The Spitzbergen reindeer--a winter-dormant ungulate?

Seasonal changes in serum levels of growth hormone, cortisol and thyroxine in calves and adult Spitzbergen reindeer (Rangifer tarandus platyrynchus) were measured and compared to those previously found in Norwegian reindeer (R.t. tarandus). Cortisol did not differ significantly between summer and winter, or between the subspecies. Growth hormone and thyroxine exhibited highly significant seasonal changes and subspecific differences: winter levels of growth hormone were much higher than summer levels in the Spitzbergen reindeer, while Norwegian reindeer differed very little from season to season. Both Spitzbergen and Norwegian reindeer had markedly reduced thyroxine levels during winter, but the values from the former were much lower than those from the latter. In summer, however, the levels were equal. The high levels of growth hormone and low levels of thyroxine in the Spitzbergen reindeer during winter are indicative of high lipolytic activity and a reduced metabolic rate, respectively.