Effect of food or water deprivation on circulating levels of pituitary, thyroid and adrenal hormones and on glucose and electrolyte concentrations in domestic ducks (Anas platyrhynchos)

Long-term fasting induced basal thermogenesis flexibility in female Japanese quails

Male Japanese quails (Coturnix japonica) have been found to exhibit a three-phase metabolic change when subjected to prolonged fasting, during which basal thermogenesis is significantly reduced. A study had shown that there is a significant difference in the body temperature between male and female Japanese quails. However, whether female Japanese quails also show the same characteristic three-phase metabolic change during prolonged fasting and the underlying thermogenesis mechanisms associated with such changes are still unclear. In this study, female Japanese quails were subjected to prolonged starvation, and the body mass, basal metabolic rate (BMR), body temperature, mass of tissues and organs, body fat content, the state-4 respiration (S4R) and cytochrome c oxidase (CCO) activity in the muscle and liver of these birds were measured to determine the status of metabolic changes triggered by the starvation. In addition, the levels of glucose, triglyceride (TG) and uric acid, and thyroid hormones (T3 and T4) in the serum and the mRNA levels of myostatin (MSTN) and avian uncoupling protein (av-UCP) in the muscle were also measured. The results revealed the existence of a three-phase stage similar to that found in male Japanese quails undergoing prolonged starvation. Fasting resulted in significantly lower body mass, BMR, body temperature, tissues masses and most organs masses, as well as S4R and CCO activity in the muscle and liver. The mRNA level of av-UCP decreased during fasting, while that of MSTN increased but only during Phase I and II and decreased significantly during Phase III. Fasting also significantly lowered the T3 level and the ratio of T3/T4 in the serum. These results indicated that female Japanese quails showed an adaptive response in basal thermogenesis at multiple hierarchical levels, from organismal to biochemical, enzyme and cellular level, gene and endocrine levels and this integrated adjustment could be a part of the adaptation used by female quails to survive long-term fasting.

REFERENCE VALUES AND COMPARISON OF BLOOD CHEMISTRY AND PLASMA PROTEIN VALUES BETWEEN GOLD STANDARD ANALYZERS AND FOUR POINT-OF-CARE DEVICES IN FREE-RANGING CANVASBACKS (AYTHYA VALISINERIA)

Accurate, timely, and cost-effective blood chemistry analysis is an essential tool for directing emergency treatment, monitoring the health status of captive and free-ranging individuals and flocks, and improving the efficacy of conservation actions. Blood samples were obtained from 52 canvasbacks (Aythya valisineria) that were captured on San Francisco Bay, California, during December 2017 as part of a long-term study. Reference values and clinical agreement were determined for blood chemistry and plasma protein parameters among four commonly used point-of-care devices (VetScan^® VS2, i-STAT^®, AlphaTRAK^®2 glucometer, refractometer) and two gold standard laboratory analyzers (Roche cobas^® c501, Helena SPIFE 3000 system). Canvasback reference values were generally within expected ranges for Anatidae species with the exception of higher upper limits for sodium and chloride. Creatine kinase and aspartate transaminase values exceeded a published threshold for diagnosis of capture myopathy even though study birds were captured using low-stress techniques and successfully released. With the exception of higher alkaline phosphatase in hatch-year canvasbacks, no age or sex differences were observed for any analyte in this population that was captured during a nonbreeding period. Analysis of analyzer agreement found raw VetScan aspartate transaminase, calcium, glucose, and uric acid values; corrected VetScan albumin, potassium, sodium, and total protein values; raw i-STAT glucose and potassium values; and corrected i-STAT sodium and chloride values were clinically interchangeable with Roche cobas values. Raw VetScan and i-STAT glucose values were also interchangeable. However, none of the Roche or point-of-care analyzer plasma protein values were in clinical agreement with gold standard electrophoresis values. The findings of this study highlight the need for analyzer- or technique-specific reference values and provide biologists and veterinarians quantitative reference values using currently available analyzers to better assess and respond to the health of individuals and populations.

Daily and fasting variation in blood parameters and H/L ratio in house sparrows (Passer domesticus)

Fluctuations in food supply are frequent in nature during seasons, in different stages of annual cycle of animals and lately, climate change is a strong driving force that could affect food supply. An animal's capacity to resist fasting is, therefore, determined by its ability to store energy and control its allocation during periods of food restriction. Daily variations of metabolic substrates and their fluctuation during fasting are relevant to understand the acclimation to fasting. Since fasting is an ecological stressor, we investigated the daily variation of corticosterone levels in feeding and fasting in Passer domesticus Linnaeus, 1758 and its short-term effect on some biochemical parameters. We found daily variations in body mass, glucose, triglycerides, plasma total protein, uric acid and corticosterone. However, we did not find diurnal variations of hematocrit and the Heterophil:Lymphocyte ratio (H/L ratio). Moreover, we did not find sex-related differences in any parameter. Throughout fasting we found variations of glucose, triglycerides, total protein, uric acid, H/L ratio and corticosterone. During the photophase, biochemical and physiological responses to food deprivation contribute to the efficient use of resources in this small bird. In the course of fasting period corticosterone could be responsible of alterations of some blood parameters such as glucose.

Changes in plasma hormone levels correlate with fledging in nestling Leach's storm-petrels

Leach's storm-petrels accumulate large amounts of body mass throughout the nestling period. Approximately 4days before fledging, nestlings weigh 50-100% more than adults. In order to shed this excess mass, nestlings engage in behavioral anorexia, and leave the burrow when they are light enough to fly. During this prefledging period, we measured several plasma hormones (corticosterone, thyroxine, and testosterone) to determine whether the behavioral changes associated with fledging are correlated with endocrine changes. In several species, including petrels, corticosterone levels are known to increase near fledging. Reduced food consumption has been shown to elevate corticosterone levels and decrease thyroxine levels in nestling birds. In nestling storm-petrels, levels of both corticosterone and thyroxine increased. Storm-petrels were found to secrete measurable levels of testosterone, but levels did not change during the prefledging period. Increased corticosterone levels might be part of an endocrine signal that initiates changes in feeding behavior, or may result from reduced food intake. Elevated thyroxine levels may be related to metabolic changes involved in mass loss. Future experimental work is needed to ascertain whether the described endocrine changes are responsible for, or result from, prefledging changes in petrel feeding behavior.

Osmotic stress induced alteration in the expression of arginine vasotocin receptor VT2 in the pituitary gland and adrenal function of domestic fowl

The role of arginine vasotocin in the regulation of the pituitary-adrenal axis of domestic fowl was analyzed by studying the expression of its recently cloned pituitary receptor VT2 and adrenal activity following osmotic stress. Four days of water deprivation induced an increase in plasma osmolality-a known stimulator of AVT synthesis and release from hypothalamic magnocellular neurons. Water deprivation also decreased pituitary mRNA levels for both the VT2 receptor and for pro-opiomelanocortin (POMC). Despite a decrease in the expression of VT2 mRNA, immunoreactive-VT2 receptor levels in the pituitary increased, suggesting a possible role for post-transcriptional mechanisms in the regulation of this receptor. Further, adrenal activity (as judged by adrenal weight, cholesterol content, 3beta hydroxysteroid dehydrogenase, cortical cord width and cortico-medullary ratio) showed stimulation in water-deprived chicken as compared to control. On the basis of present findings, it is concluded that water deprivation down regulates the mRNA expression of AVT receptor VT2 as well as POMC but stimulates adrenal function. It is also suggested that in addition to the release of magnocellular AVT into the neurohypophysis to act as antidiuretic hormone following water deprivation, AVT may also modulate HPA axis to cope with the osmotic stress.

Plasma thyroid hormone concentrations in a wintering passerine bird: their relationship to geographic variation, environmental factors, metabolic rate, and body fat

Winter acclimatization among passerine birds involves metabolic adjustments that allow for high rates of thermogenesis. In previous studies, we observed geographic variation in the basal metabolic rate (BMR) of overwintering cardinals along a latitudinal gradient at two different longitudinal transects. Because thyroid hormones (THs) are important for metabolic adjustments in endotherms, we determined whether geographic variation in BMR can be explained by variation in thyroid status. We measured total plasma TH (thyroxine [T(4)] and 3,5,3'-triiodothyronine [T(3)]) concentrations by radioimmunoassay in birds from two latitudinal transects extending from approximately 31 degrees to 42 degrees. Birds from both transects had higher plasma THs in the late afternoon than in the early morning. Plasma T(3) increased with latitude, while plasma T(4) varied such that the southernmost birds and the northernmost birds had higher hormone concentrations than birds at the intermediate latitude. There was no correlation between plasma TH concentrations and BMR. To test whether thyroid status influences metabolic parameters in winter-acclimatized captive cardinals, we fed cardinals diets supplemented with T(4) (5 microg T(4) g(-1) food), the goitrogen methimazole (1 mg g(-1) food), or both. Plasma T(4) concentrations were altered by most of the treatments, but we observed no significant effects on any metabolic parameter. We conclude, therefore, that there is latitudinal variation in metabolic parameters in cardinals but that this variation is not explained by variation in plasma TH concentrations.

The influence of fasting on blood and plasma composition of herring gulls (Larus argentatus)

Populations of scavenging seabird species in the North Sea may fluctuate with an artificial food source: the availability of fishery waste. To document this impact, it is necessary to assess the birds' nutritional status during periods with decreased fishing activity. Reference data for this purpose was collected from 22 herring gulls investigated during laboratory fasting. After 6 d of food deprivation and body mass losses exceeding 15%, the first birds entered starvation phase 3. Comparatively, this is a rather weak fasting capacity. Plasma levels of total protein and thyroid hormones decreased and beta-hydroxybutyrate increased with fasting duration. The leucocyte proportions were shifted from lymphocytes to heterophils. After 3 d of refeeding, most of the fasting changes were reversed. Plasma enzyme activities increased and hematocrit, hemoglobin, and erythrocyte numbers decreased in both fasting and control birds, most likely as a result of experimental stress and repeated blood sampling. Glucose, cholesterol, monocytes, basophils, and glycosylated hemoglobin remained fairly constant. Triglycerides, free fatty acids, uric acid, and urea varied significantly, but changes were not as clearly a result of fasting. Therefore, total protein, beta-hydroxybutyrate, triiodothyronine, thyroxine, and lymphocyte and heterophil percentages may be the most reliable indicators of the nutritional status and the condition of free-living herring gulls.

The acute effects of alteration in the dietary concentrations of carbohydrate, protein, and lipid on plasma T4, T3, and glucose levels in rainbow trout, Oncorhynchus mykiss

The acute (4 hr) postprandial effects of a single isocaloric meal varying in the proportions of either carbohydrate (C)/lipid (L), C/protein (P), or L/P on plasma levels of glucose, T4 (L-thyroxine) and T3 (3,5,3'-triiodo-L-thyronine) were examined in rainbow trout starved for 3 days. Relative to starved controls, plasma T3 was generally uninfluenced by feeding but was increased by diets containing the highest C/L and P/L ratios. Plasma T4 was elevated only in instances where there was sufficient available dietary C to raise plasma glucose to at least 126 mg/100 ml. High dietary P or L levels in combination with low C levels and a postprandial plasma glucose level below 126 mg/100 ml did not elevate plasma T4. For fish fed an acaloric alpha-cellulose diet, plasma T4 was unchanged indicating that gastric filling alone does not contribute significantly to the T4 surge. It is concluded that the previously demonstrated postprandial elevation in plasma T4 is determined mainly by the level of dietary C and the available glucose, and not by P, L, total caloric content, or bulk properties of the ingesta.

The effect of severe starvation and captivity stress on plasma thyroxine and triiodothyronine concentrations in an antarctic bird (emperor penguin)

The effect of confinement and severe starvation on the plasma thyroxine (T4) and triiodothyronine (T3) concentrations was determined in emperor penguins (Aptenodytes forsteri). During their annual cycle, emperor penguins fast freely for periods of up to 4 months and may thus represent a unique subject to study endocrine adaptations to fasting. Plasma T4 concentrations progressively decreased following capture and confinement of naturally fasting penguins, and within 15-20 days stabilized at levels three times lower than in free-living penguins. A transient fourfold increase in plasma T3 concentration developed within the day following confinement in parallel with a rise in daily body mass loss. Both plasma T3 concentration and mass loss subsided to normal levels within 15 days. The decrease in plasma T4 concentration is in accordance with the well-known inhibitory effect of stress on thyroid function in birds and mammals, whereas the transient increase in plasma T3 concentration seems related to enhancement of energy expenditure as a consequence of restlessness. Starvation severe enough to exhaust fat stores and to activate protein catabolism induced a 6- and 5 to 10-fold fall in plasma T4 and T3, respectively. This is in marked contrast with maintenance of plasma thyroid levels during long-term natural fasting associated with protein sparing (R. Groscolas and J. Leloup (1986) Gen. Comp. Endocrinol. 63, 264-274). Surprisingly, there was a final reincrease in plasma T4 concentration in very lean penguins. These results suggest that the effect of starvation on plasma thyroid hormones seems to depend on how much protein catabolism is activated and demonstrate the acute sensitivity of thyroid hormone balance to stress in penguins.

Growth-associated traits in parental and F1 populations of chickens under different feeding programs. 4. Growth and thyroid hormones

Plasma levels of growth hormone (GH), triiodotyronine (T3), and thyroxine (T4) were compared at 25 and 61 days of age in parental lines and F1 crosses between parental lines under ad libitum and alternate day feeding. Parental lines included White Rocks selected for high and low body weight and a White Leghorn population. Differences among populations for hormone levels were more pronounced at 61 than at 25 d of age. Growth hormone decreased and T4 increased with age in all populations except the line selected for low body weight, whereas the pattern for T3 varied with genetic stock. On days when chicks were not fed, plasma GH and T4 increased and T3 decreased. On days of feeding, GH and T4 returned to the level of chicks fed ad libitum while T3 was either identical to or higher than that for the ad libitum chicks. Population by feeding regimen interactions were not significant at either age for any of the hormones measured showing that responses to the feeding regimens were similar for all populations.

Flight stimulates adrenocortical activity in pigeons (Columba livia)

The influence of long-distance flight on corticosterone secretion has been examined in trained racing pigeons. Flights of 315-561 min from release sites 115-557 km from the home loft greatly increased the circulating corticosterone concentration in comparison with the levels in nonexercised controls sampled before release or bled in the loft at the times of release or arrival. The increase in corticosterone concentration was unrelated to the distance flown or duration of flight. Flights of less than 1 min duration (from release sites 100 m from the loft) increased the corticosterone concentration, in comparison with that in the loft controls, but to levels much lower (P less than 0.001) than those following long-distance flights and to concentrations similar to those in birds that were returned to the loft by hand.

The effects of ACTH and dexamethasone upon plasma thyroid hormone levels and heat production in the domestic fowl

Treatment with long acting ACTH (20 IU kg-1) produces a large and sustained elevation of plasma corticosterone in the domestic fowl. Both ACTH treatment and administration of dexamethasone produce significant reductions in plasma concentrations of T4 and T3, and these changes are accompanied by a sustained hyperglycaemia. Despite the changes in circulating thyroid hormones only a small reduction in heat production (-14%) was induced by either treatment and mainly during the dark period. Whilst there may be some causal relationship between increased corticosterone secretion, decreased plasma thyroid hormone levels and reduced metabolic heat production it is unlikely that these responses alone account for the adjustments in energy expenditure observed in short term food deprivation.

The effects of glucagon and insulin on plasma thyroid hormone levels in fed and fasted domestic fowls

Glucagon injection (50 micrograms kg-1) produced a biphasic response in plasma thyroxine (T4) level in both fed and fasted chickens. An initial inhibition was followed by an increase to levels above control value. Glucagon reduced plasma triidothyronine (T3) possibly as a consequence of inhibition of peripheral monodeiodination. This inhibition persisted in fasted animals despite a glucagon induced hyperglycaemia. Insulin injection (4 IU kg-1) decreased plasma T4 concomitant with a profound hypoglycaemia. These effects were more pronounced in fasted birds. Insulin induced hypoglycaemia was associated with decreased plasma T3 probably as a consequence of reduced thyroidal T4 secretion and reduced peripheral monodeiodination. Glucagon and insulin may play direct or indirect roles in the regulation of thyroid hormone secretion and metabolism in the domestic fowl.

Efficiency of food utilization during fat deposition in the long-distance migratory garden warbler, Sylvia borin

1 Intake of food, fat, protein and carbohydrates and their fecal output were recorded during the annual body weight cycle of the garden warbler, and old-world longdistance migratory bird species, and the efficiencies of food and nutrient utilization, defined as the ratio (intake-fecal output)/intake, were calculated. 2. Gross food intake and food and nutrient utilization differed significantly between different phases of the birds' body weight cycle. 3. During premigratory fattening, both in "autumn" and "spring", food intake and utilization of fat, protein and carbohydrates were significantly higher than during the low body weight prefattening periods. 4. The increase in efficiency of nutrient utilization accounted for about 1/3 and the increase in gross food intake about 2/3 of all surplus energy for hyperlipogenesis in the premigratory periods of the garden warbler. 5. The seasonal changes in efficiency of food and nutrient utilization seem to be driven by a circannual timing mechanism.

The effect of exposure to 40 degrees on the heat production and the serum concentrations of triiodothyronine, thyroxine, and corticosterone in immature domestic fowl

Four-week-old fowl were exposed to 40 degrees for 35 days and the effects on the serum concentrations of triiodothyronine (T3), thyroxine (T4), and corticosterone were investigated. Changes in resting heat production, food intake, body temperature, body weight gain, and growth (both in terms of skeletal growth and weight of selected organs) were also measured. Body temperature was increased at 40 degrees, and body weight gain and skeletal growth were both reduced. The serum concentrations of T3 and T4 were reduced at 40 degrees. The decrease in serum T3 was more strongly correlated with the reduction in food intake than was the reduction in T4. Resting heat production was decreased by exposure to 40 degrees; the reduction in heat production was correlated with serum T3 and serum T4 concentrations. Exposure to 40 degrees had no effect on adrenal weight or on serum corticosterone concentration but weights of the bursa, spleen, and thymus glands were decreased. These results suggest that (a) T3 is the principle metabolically active thyroid hormone in the chicken and that the reduction in heat production at 40 degrees is related to the decline in T3; (b) the reduction in T3 is a consequence of the reduction in food intake; and (c) the response to a stressor need not involve increased adrenocortical activity.

Adrenocortical responses to novel stressors in acutely or repeatedly starved chickens

The effect of starvation on the corticosterone responses of immature cockerels to acute, novel stress has been determined. The marked corticosterone responses of fed birds to either horizontal treadmill exercise (0.04 km/hr) or intravenous adrenocorticotrophic hormone (ACTH) administration (P less than 0.001 in both cases) were reduced by starvation (P less than 0.01 and P less than 0.001, respectively). This reduction did not appear to be due to either feedback inhibition of corticosterone on the hypothalamus or pituitary, or to reduced adrenal responsiveness to endogenous ACTH. Starvation significantly elevated the basal level of circulating corticosterone (P less than 0.001), but the magnitude of this elevation and the level of corticosterone attained were less (P less than 0.05) in birds that were accustomed to starvation. This habituation of adrenocortical activity may be due to reduced pituitary ACTH secretion, and was specific in that the corticosterone responses to novel stressors were unaffected.

Endocrine changes associated with fat deposition and mobilization in svalbard ptarmigan (Lagopus mutus hyperboreus)

Plasma concentrations of Triiodothyronine (T3), thyroxine (T4) and growth hormone (GH) have been measured in blood samples taken from Svalbard ptarmigans (Lagopus mutus hyperboreus), shot throughout 1 whole year at Svalbard (79 degrees N). Plasma T3 levels varied in a monophasic pattern with low levels in winter and a peak in August, whereas plasma T4 levels remained constant throughout the year. High plasma T3 levels coincide with molt and a large food intake while low plasma levels of T3 coincide with molt arrest and a low food intake. Plasma GH levels were highest in winter and lowest in May and September. The low plasma GH levels in early autumn coincide with elevated liver weights and maximum rate of fat deposition. High GH levels in midwinter coincide with low liver weights and the mobilization of fat stores. A possible relationship between molt, food intake, fat deposition/mobilization, and plasma levels of T3 and GH is discussed.

Effects of chronic changes in dietary electrolytes and acute stress on plasma levels of corticosterone and aldosterone in the duck (Anas platyrhynchos)

Plasma levels of corticosterone and aldosterone were determined by radioimmunoassay in ducks consuming diets containing different concentrations of sodium and potassium. Compared with control diet birds, maintenance on a high-Na+ diet for 5 days caused a 2-fold increase in the basal plasma corticosterone concentration, while adaptation for 8 days to a low-Na+ diet resulted in a 2.6-fold increase in the basal plasma concentration of aldosterone. Both corticosterone and aldosterone basal plasma levels were greatly elevated in birds denied access to drinking water for 4 days. Adaptation to a high-Na+ diet or deprivation of water resulted in hyperosmolality and hypernatremia, while the high-K+, low-Na+/low-K+, and low-Na+ diets did not significantly alter the plasma sodium or potassium levels from the control levels. In addition, birds were stressed by semi-immobilization to determine the effects of acute stress-induced ACTH secretion on the adrenocortical response following changes in dietary sodium and potassium intake. In ducks adapted to low-Na+/low-K+, high-Na+, and low-Na+ diets, stress-induced adrenocorticotrophic hormone (ACTH) increased the aldosterone, but not the corticosterone, response to a level significantly greater than in the controls. These results demonstrate that in the duck secretion of corticosterone and aldosterone can be independently regulated. Furthermore, the endocrine changes that are induced by altered sodium and potassium intake are reflected in the adrenocortical responses to acute stress.

Thyroid and adrenal responses of ducks (Anas platyrhynchos) during saline adaptation

Fresh water-reared Aylesbury ducklings were given 0.1 or 0.2 M NaCl drinking water and variations in the plasma concentrations of thyroxine (T4), triiodothyronine (T3), corticosterone, and aldosterone were determined. Within 24 hr of being transferred to 0.2 M NaCl the corticosterone concentration was increased, whereas the levels of plasma T3 and aldosterone were reduced. The increase in corticosterone secretion persisted for at least 7 days, but the T3 and aldosterone concentrations had returned to control levels within 5 days. The concentrations of plasma aldosterone and T3 were similarly affected in birds transferred to 0.1 M NaCl, although corticosterone levels increased only after the birds were maintained on 0.1 M NaCl for 7 days. Plasma concentrations of T4 were increased in 1- to 2-week-old (but not 7-week-old) birds 7 days after their transfer to 0.1 and 0.2 M NaCl. In birds maintained on saline for 6 weeks the basal concentration of each hormone was not significantly different from that in fresh water-reared controls. When saline-reared birds were returned to freshwater conditions the plasma aldosterone and T3 concentrations were increased over a 5-day period. Transfer to saline consistently reduced body weight and food intake, whereas the transfer of saline-reared birds to fresh water stimulated body weight gain. Consequently, although these endocrine responses during saltwater adaptation might be expected to minimise the loss of body reserves and to facilitate the extra renal excretion of sodium, these alterations in endocrine function may be partly due to salt water-induced changes in food intake.

Effect of intermittent feeding on blood plasma growth hormone and prolactin in chickens of a heavy breed

1. Variations in plasma growth hormone (GH) and prolactin concentrations were determined during growth (at 20, 33, 56 and 83 d of age) in ad libitum (control) and intermittently (alternate days) fed chicks. 2. In each group of birds the concentration of plasma GH was inversely related to age. The mean prolactin concentration was highest in the youngest (20-d-old) birds. 3. The concentration of plasma GH in the intermittently-fed birds deprived of food for 24 h (depleted birds) was significantly higher than that in the controls at 33, 56 and 83 d of age. The mean GH concentration in the intermittently-fed birds 24 h after refeeding (repleted birds) was less than that in the depleted ones. 4. The overall mean concentration of plasma prolactin in the depleted birds was significantly less than that in the control and repleted birds. 5. These results are consistent with the effects of fasting on GH and prolactin secretion and demonstrate that growth retardation in the intermittently-fed birds was not due to impaired GH secretion.

Influence of ingested petroleum on the reproductive performance and pituitary-gonadal axis of domestic ducks (Anas platyrhynchols)

1. The chronic ingestion of a sublethal dose (5%) of dietary North Sea crude oil delayed the onset of lay in adult Khaki Campbell ducks transferred from a short (8L:16D) to long day (16L:8D) photoperiod and greatly reduced the rate of oviposition and quality (weight and shell thickness) of the eggs subsequently laid. 2. Refeeding the oil-fed birds with the uncontaminated control diet stimulated the rate of egg production and improved egg quality, but in both cases not to the level in the controls. 3. Food intake and the plasma calcium level in the petroleum-fed birds were reduced, but these effects are unlikely to be causally responsible for the adverse effects of petroleum on avian reproduction. 4. Gonadotrophic (luteinizing hormone, LH) hormone secretion in the oil fed birds was not suppressed and the impairment of reproductive performance was not due to low plasma LH levels. 5. The reduced rate of lay in the oil-fed birds was accompanied by low gonadal steroid (progesterone) levels. The detrimental effects of oil and reproduction may be due to direct or indirect effects on the ovary or shell gland.