Differential effects of amount of feeding on cell proliferation and progesterone production in response to gonadotrophins and insulin-like growth factor I by ovarian granulosa cells of broiler breeder chickens selected for fatness or leanness.

Strain differences in reproductive performance were demonstrated between broiler breeder female chickens selected for growth (GL line) or for food conversion efficiency (FC line) and the improvement in reproductive performance due to feed restriction also differed significantly. Feed allowance effects on the maturation of ovarian follicles, the incidence of atresia and egg production differed between the two lines exposed to similar feeding protocols. Feed restriction reduced body weights significantly and to a similar extent in both GL and FC lines. The number of normal and atretic yellow follicles was significantly higher under ad libitum feeding and in GL line than it was in the FC line. In both lines, feed restriction decreased multiple ovulation and increased egg production. In culture, granulosa cells from the three largest follicles (F1, F2 and F3) increased progesterone production in response to LH, FSH and insulin-like growth factor I but responses were different between the GL and FC lines fed either ad libitum or restricted diets. Granulosa cells from the two or three largest follicles in GL and FC (ad libitum) lines produced similar amounts of progesterone in response to LH, FSH and insulin-like growth factor I whereas, in restricted birds, the progesterone production was of the rank order F1 > F2 > F3 in both lines. The responsiveness of the GL line fed ad libitum was higher for LH than for either FSH or insulin-like growth factor I but in the GL line fed a restricted diet, it was high for all the hormones. In the FC line, responses to LH, FSH or insulin-like growth factor I were high in ad libitum-fed birds, but low in birds fed a restricted diet for all hormones. Insulin-like growth factor I combined with LH or FSH significantly increased the progesterone production of granulosa cells from birds fed restricted diets of both lines and this effect increased with increasing follicular size. There was a lack of interaction between insulin-like growth factor I and LH or FSH in the regulation of progesterone production by birds of both lines fed ad libitum. Insulin-like growth factor alone or in combination with LH or FSH increased granulosa cell proliferation in birds fed ad libitum more than it did in birds fed restricted diets. The greater proliferation rate of granulosa cells of chickens fed ad libitum, in response to insulin-like growth factor I alone or in combination with gonadotrophins, leading to the simultaneous differentiation of two or three large follicles with high progesterone production in response to LH or insulin-like growth factor I, accelerates the rate of maturation of follicles. This may also be the major cause of erratic and multiple ovulations in broiler breeder female chickens fed ad libitum. In conclusion, insulin-like growth factor I, alone or in combination with LH or FSH, is an important component in the control mechanisms for follicular development in broiler breeder hens. It is this component that is targeted by feed allowance and inadvertently altered by selection for growth.     

Effect of nutritional repletion on pituitary and serum follicle-stimulating hormone isoform distribution in growth-retarded lambs.

Using nutritionally restricted ovariectomized lambs, we tested the hypothesis that nutritionally regulated endogenous increases in GnRH secretion (as assessed by LH pulsatility) not only alter the quantity of FSH present in the pituitary and serum, but also alter the pituitary and serum FSH isoform distribution. Eleven lambs were nutritionally restricted from weaning and ovariectomized at 12 wk of age. Beginning at 56 wk, 6 were fed ad libitum for 14 days, and the other 5 were continued on the restricted diet. Jugular blood samples were collected frequently (12-min interval) for 4 h prior to pituitary removal. Immunoreactive ovine LH (I-oLH) and immunoreactive ovine FSH (I-oFSH) concentrations were measured in sera and pituitary extracts. Bioactive (B) oFSH and I-oFSH isoform distribution patterns were determined in serum pools and pituitary extracts. Ad libitum feeding increased I-oLH pulsatility and mean concentrations of pituitary and serum I-oFSH and B-oFSH. The I-oFSH isoform distribution patterns in the pituitaries from the nutritionally restricted animals were not different from those of repleted lambs; in both, the predominant FSH peak eluted in the pH range of 3.5-5.6. A similar predominance of I-oFSH isoforms was also evident in the serum of ad libitum-fed animals. This predominance was not demonstrable in 3 of the restricted-fed animals due to low circulating concentrations of FSH (less than 2.5 ng/ml). Subsequent studies, utilizing serum from 4 additional restricted-fed lambs with circulating I-oFSH concentrations in the range of 4-14 ng/ml (but no detectable LH pulses) revealed similar predominance of oFSH isoforms in the pH 3.5-5.6 range.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of food restriction and restoration on gonadotropin and growth hormone secretion in immature male rats

This experiment concerned the changing patterns in secretion of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and growth hormone (GH) under conditions of food restriction and subsequent catch-up growth. Weanling male rats were given either restricted (4 g food/day) or unrestricted access to food until 60 days of age. At this age, food-restricted rats weighed only 25% as much as rats fed ad libitum. Food restriction resulted in a dramatic decrease in the frequency of LH and GH pulses, and in the amplitude of GH pulses. It also slightly but significantly decreased mean blood levels of FSH (which was not secreted in a pulsatile manner in 60-day-old controls fed ad libitum). When restricted rats were given unrestricted access to food, frequency of LH and GH pulses and mean levels of FSH increased significantly and simultaneously within 2 days in half of the animals. Only an additional 8-10% of their body weight decrement was recovered at this time. After 10 days of food restoration, when restricted rats still weighed 50% less than controls, their secretory patterns of all three hormones were not significantly different from those of controls. Thus, recovery of gonadotropin and GH secretion was relatively rapid. Except for the quantitatively lesser impact of food restriction on FSH secretion, there was no evidence of any priorities in the secretion of the three hormones. Under conditions of rapid catch-up growth, the secretory patterns of LH, FSH, and GH appeared to develop simultaneously.     

Effects of feeding time constraints on body mass regulation and energy expenditure in wintering dunlin (Calidris alpina)

We examined the effects of time-restricted feeding on regulationof body mass and activity energy expenditure in captive winteringdunlin (Calidris alpina) held in outdoor aviaries at TomalesBay, California. In the first of two experiments, we comparedbirds under 24 h : 24 h (fasting : ad libitum feeding) foodrestriction with controls under continuous ad libitum feeding. In the second experiment, we compared birds under 24 h : 6 h: 12 h : 6 h (fasting : ad libitum : fasting : ad libitum)food restriction with birds under 24 h : 24 h food restriction.We estimated total energy expended on activities from dailymass balance using an additive model based on measures of grossenergy intake, thermoregulation, basal metabolism, and a sensitivity analysis of gross utilization efficiency and energy densityof reserve body tissue. Dunlin under 24 h : 24 h food restrictionovercompensated for body mass lost while fasting, increasingtheir body mass relative to controls fed ad libitum. Dunlinunder 24 h : 6 h : 12 h : 6 h food restriction were unable to recover body mass lost during the first fasting day. Whenallowed to feed, food-restricted birds reduced the amount ofenergy spent on being active and increased food intake andenergy storage relative to controls, but when forced to fast,they increased their activity energy expenditure. These patterns suggest winter body mass regulation consistent with the behaviorsof free-living dunlin in winter.     

Effects of dietary zinc deficiency on gonadotrophin secretion and testicular growth in young male sheep.

The hypothesis that the secretion of gonadotrophins would be reduced by zinc deficiency was tested in five groups of four young Merino rams (initial liveweight 22 kg). Four groups were fed ad libitum with diets containing 4, 10, 17 or 27 micrograms Zn g-1. The effects of loss of appetite on the deficient diet was controlled by feeding a fifth group (pair-fed control) at a rate of 27 micrograms Zn g-1, but the amount of feed offered was restricted to that eaten voluntarily by the deficient (4 micrograms Zn g-1) group. Blood was sampled every 20 min for 32 h on two occasions before the treatments were imposed and 96 days later, at the end of the experiment. The rams were injected with gonadotrophin-releasing hormone (GnRH; 10 ng kg-1 i.v.) after each serial sampling, and with naloxone (1 mg kg-1 i.v.) 24 h after the end of the final GnRH test. In the group that were fed the diet with the lowest zinc content, the concentration of zinc in blood plasma was reduced to 18% of that in the pair-fed controls (P < 0.05) and was within the deficient range. The appetite of the deficient rams was half that of the controls fed 27 micrograms Zn g-1 ad libitum and there was no increase in liveweight or testicular diameter during pubertal development. Similar, but smaller, effects were observed in the pair-fed controls. There were no significant differences between pair-fed and deficient groups in the frequency of the luteinizing hormone (LH) pulses or in the concentration of follicle-stimulating hormone (FSH), but the secretion of gonadotrophins was markedly lower in both groups than in the control rams fed ad libitum. The response to GnRH was not affected by treatment, but the increase in LH pulse frequency evoked by naloxone was lower in the deficient animals than in other groups. The animals fed zinc at intermediate rates (10-17 micrograms g-1) showed similar responses to the controls fed ad libitum. It is concluded that the specific effects of zinc deficiency on testicular function were small. Most of the reduction in testicular growth in rams fed a deficient diet was not specifically related to the trace element, but was due to the fall in energy and protein intake caused by the loss of appetite. This leads to a reduction in the frequency of GnRH pulses secreted by the hypothalamus, and to low rates of gonadotrophin secretion by the pituitary gland.     

Effect of match or mismatch of maternal-offspring nutritional environment on the development of offspring in broiler chickens

In mammals, maternal food restriction around conception and during pregnancy results in low birth weight and an adjusted growth trajectory of offspring. If, subsequently, the offspring are born into a food-abundant environment, they are at increased risk of developing obesity, type 2 diabetes, hypertension and renal dysfunction. Here, we show similar effects of maternal undernutrition on hatch weight, growth and fat deposition in offspring of birds (domestic chicken). Both mothers and offspring were fed either ad libitum or restricted in a two-by-two factorial design, resulting in two matched and two mismatched maternal-offspring nutritional environments. Offspring of ad libitum mothers grew heavier than those of restricted mothers, possibly due to the larger muscle mass. Ad libitum-fed offspring, especially females, of restricted mothers were lighter at hatch, and were heavier and had more abdominal fat at 6 weeks of age than daughters of ad libitum-fed mothers. These results suggest a common mechanism in mammals and birds in response to a mismatch in the maternal-offspring nutritional environment. They also indicate that the common practice of restrictive feeding of the broiler breeders and subsequent ad libitum feeding of the broilers may result in reduced growth and increased abdominal fat as compared to broilers of less restricted broiler breeders.     

The effects of food restriction and hypophysectomy on numbers of primordial follicles and concentrations of hormones in rats

Three experiments were done to examine the effects of food restriction, beginning at 21 days of age, on loss of primordial follicles and on concentrations of gonadotropins and sex steroids in rats. In Experiment 1, food restriction (FR) from 21 to 51-55 days of age had no effect on number of primordial follicles, but increased the plasma concentration (p less than 0.05) of follicle stimulating hormone (FSH). (p less than 0.05). In Experiment 2, comparisons were made of groups of rats (1) fed ad libitum (AL) (2) hypophysectomized at 21 days of age and fed ad libitum (AL-HY), (3) food restriction from 21 to 52-58 days of age (FR), and (4) food restriction with twice-daily injections of follicular fluid (FR-FF). Hypophysectomy was the only treatment that decreased the loss of primordial follicles (p less than 0.001). Concentrations of FSH were decreased in AL-HY and increased in FR and FR-FF rats (144 +/- 13, 53 +/- 15, 275 +/- 30 and 359 +/- 56 ng/ml in AL, AL-HY, FR and FR-FF rats, respectively). Concentrations of luteinizing hormone (LH) were lower (p less than 0.05) in AL-HY, FR and FR-FF rats than in AL rats. In Experiment 3, AL and FR rats were unilaterally ovariectomized (ULO) at 30 days of age. Blood samples were taken 5 days prior to ULO, at ULO and at 12 h, 5 days, and 22-28 days after ULO.(ABSTRACT TRUNCATED AT 250 WORDS)     

Altered negative feedback response to ovariectomy and estrogen in prepubertal restricted-diet rats

Studies were conducted to explore the hypothesis that the delayed sexual maturation of female rats induced by reduced food intake (R) may result partially from an altered negative feedback response to estrogen. Animals were placed on 60% of normal food intake at 20 days of age. Controls (C) were fed ad libitum. Rats were used for three different experiments at 31-32 days of age. In Experiment I, rats were ovariectomized (OVX) and injected subcutaneously for 4 days with varying doses of estradiol benzoate (EB). They were killed the day after the last injection. In Experiment II, rats were ovariectomized and killed in groups at 4, 12, 24, 48, 72, and 120 h after OVX. In Experiment III, they were castrated and 1 wk later received a single injection of 0.5 microgram EB. Groups were killed at 1, 2, 4, 8, and 24 h after injection. Sera from all experiments were assayed for follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin. Results of Experiment I indicate that the efficacy of EB for suppressing LH, but not FSH, secretion is increased significantly in R rats. In Experiment II, OVX resulted in a delayed increase in serum LH, but not FSH, concentrations of R rats when compared to C animals. Results of Experiment III indicate a delayed, but more prolonged, suppression of LH secretion by EB in R rats when compared to C rats. Prolactin secretion, on the other hand, increased earlier in R rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of prior or concurrent food restriction on amylin-induced changes in body weight and body composition in high-fat-fed female rats

Amylin infusion reduces food intake and slows body weight gain in rodents. In obese male rats, amylin (but not pair feeding) caused a preferential reduction of fat mass with protein preservation despite equal body weight loss in amylin-treated (fed ad libitum) and pair-fed rats. In the present study, the effect of prior or concurrent food restriction on the ability of amylin to cause weight loss was evaluated. Retired female breeder rats were maintained on a high-fat diet (40% fat) for 9 wk. Prior to drug treatment, rats were either fed ad libitum or food restricted for 10 days to lose 5% of their starting body weight. They were then subdivided into treatment groups that received either vehicle or amylin (100 microgxkg(-1)xday(-1) via subcutaneous minipump) and placed under either a restricted or ad libitum feeding schedule (for a total of 8 treatment arms). Amylin 1) significantly reduced body weight compared with vehicle under all treatment conditions, except in always restricted animals, 2) significantly decreased percent body fat in all groups, and 3) preserved lean mass in all groups. These results indicate that amylin's anorexigenic and fat-specific weight loss properties can be extended to a variety of nutritive states in female rats.     

Gonadotropin-independent mechanisms participate in ovarian responses to realimentation in feed-restricted prepubertal gilts.

Short-term feed restriction in prepubertal gilts suppresses episodic LH secretion in the absence of changes in body weight or composition. To assess non-gonadotropin-mediated effects of realimentation at the ovarian level, 52 gilts were assigned to six treatments after 7 days (Days 1-7) of maintenance feeding (approximately 30% ad libitum). Groups R12 and R9 were maintenance-fed Days 8-12 or Days 8-9, respectively; A12 and A9 were fed to appetite Days 8-12 or Days 8-9, respectively. Groups R9P and A9P were fed as groups R9 and A9 were but received 750 IU eCG at 1500 h on Day 8. Groups R12 and A12 were ovariectomized at 1500 h on Day 12, and all other groups were ovariectomized at 1500 h on Day 9. All gilts received oral progestogen (15 mg allyl trenbolone) from Day 1 to ovariectomy, to antagonize the usual increases in endogenous gonadotropins that follow realimentation. Blood samples were obtained at 10-min intervals during selected windows during the experiment. Ovarian follicles were analyzed for development and steroidogenesis, and plasma samples were analyzed by RIA to determine concentrations of LH, FSH, insulin, and insulin-like growth factor-1 (IGF-1). Allyl trenbolone abolished pulsatile LH secretion, and realimentation did not stimulate LH or FSH secretion, with the exception of FSH secretion on Day 8 in A9 gilts. Postprandial insulin concentrations on Day 9 were greater after feeding to appetite (A9, A9P, and A12) than after feed restriction (R9, R9P, and R12). Pre- and postprandial IGF-1 concentrations were higher in re-fed gilts on Day 9 (A9 and A12) and Day 12 (A12) than in feed-restricted gilts. Follicular diameter, fluid volume, and basal granulosa cell estradiol synthesis per follicle were greater in A12 gilts than in R12 gilts, although there was no difference between A9 and R9 gilts. There was no effect of realimentation on follicular fluid concentrations of estradiol or testosterone, or on androgen-driven granulosa cell estradiol synthesis. Treatment with eCG increased follicular diameter, fluid volume, basal and androgen-driven estradiol synthesis, and fluid estradiol concentrations without interaction with feeding level. In conclusion, in the absence of LH elevations, realimentation over 5 days exerts effects at the ovary, increasing follicular growth and estradiol synthesis. These effects may be mediated by insulin, IGF-1, or unmeasured growth factors and would be expected to synergize with increases in endogenous gonadotropin that follow realimentation.     

Immunoreactive LHRH in chronic starved rats

The effects of chronic starvation (1/4 of ad libitum food intake) for 21 or 30 days were studied on the hypothalamic and serum concentrations of LHRH, the pituitary and serum concentrations of LH, and the weights of the anterior pituitary, ovary and uterus in adult female Wistar rats (chronic starved group, CSG). Control female rats were fed ad lib. for the same periods (control group, CG). On day 22 or 31, half of the rats of each group were weighed and sacrificed by decapitation. Since there were no difference on above parameters between the experiments on 22nd and 31st day, the results were combined for each parameters. At the time of sacrifice, the body weight of CSG was on the average 44% lower than that of CG rats, and also marked reduction in anterior pituitary (44%), ovarian (61%) and uterine weights (69%) was observed. Serum LH concentrations (mean +/- SE; 5.67 +/- 0.67 versus 33.30 +/- 6.00 ng/ml, P less than 0.001) and pituitary LH content (286.7 +/- 19.4 vs 451.0 +/- 32.8 micrograms, P less than 0.001) were significantly decreased in CSG than in CG rats. However, pituitary LH concentration was not reduced because of the proportional reduction to the pituitary weight of CSG rats. Hypothalamic immunoreactive LHRH (IR-LHRH) content in CSG showed a significant increase as compared to CG rats (5.77 +/- 0.52 vs 4.41 +/- 0.27 ng/hypothalamic extract, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Responses of luteinizing hormone (LH) and follicle-stimulating hormone levels to exogenous gonadotropin-releasing hormone during the estrogen-induced LH surge in the ovariectomized rhesus monkey

Experiments were performed to study the responsiveness of the pituitary to gonadotropin-releasing hormone (GnRH) during the dynamic changes in gonadotropin secretion associated with the estrogen-induced luteinizing hormone (LH) surge in the ovariectomized (OVX) rhesus monkey. Silastic capsules filled with estradiol-17-beta were implanted subcutaneously in ovariectomized rhesus monkeys, resulting in an initial lowering of circulating LH and follicle-stimulating hormone (FSH) concentrations followed by an LH-FSH surge. GnRH was injected intravenously just before estrogen implantation, during the negative feedback response and during the rising, the peak, and the declining phases of the LH surge. The LH and FSH responses during the negative feedback phase were as large as those before estrogen treatment (control responses). During the rising phase of the LH surge, the acute response to GnRH injection did not differ significantly from the control response, but the responses 60 and 120 min after injection were somewhat increased. During the declining phase of the LH surge, the pituitary was not responsive to exogenous GnRH, although LH probably continued to be secreted at this time since the LH surge decreased more slowly than predicted by the normal rate of disappearance of LH in the monkey. We conclude that an increased duration of response to GnRH may be an important part of the mechanism by which estrogen induces the LH surge, but we do not see evidence of increased sensitivity of the pituitary to GnRH as an acute releasing factor at that time.     

Proteome and radioimmunoassay analyses of pituitary hormones and proteins in response to feed restriction of dairy cows

The hypothalamic-pituitary system controls homeostasis during feed energy reduction. In order to examine which pituitary proteins and hormone variants are potentially associated with metabolic adaptation, pituitary glands from ad libitum and energy restrictively fed dairy cows were characterized using RIA and 2-DE followed by MALDI-TOF-MS. We found 64 different spots of regulatory hormones: growth hormone (44), preprolactin (16), luteinizing hormone (LH) (1), thyrotropin (1), proopiomelanocortin (1) and its cleavage product lipotropin (1), but none of these did significantly differ between feeding groups. Quantification of total pituitary LH and prolactin concentrations by RIA confirmed the results obtained by proteome analysis. Also, feed energy restriction provoked increasing non-esterified fatty acid, decreasing prolactin, but unaltered glucose, LH and growth hormone plasma concentrations. Energy restriction decreased the expression of glial fibrillary acidic protein, triosephosphate isomerase, purine-rich element-binding protein A and elongation factor Tu, whereas it increased expression of proline synthetase co-transcribed homolog, peroxiredoxin III, β-tubulin and annexin A5 which is involved in the hormone secretion process. Our results indicate that in response to feed energy restriction the pituitary reservoir of all posttranslationally modified hormone forms remains constant. Changing plasma hormone concentrations are likely attributed to a regulated releasing process from the gland into the blood.     

Triiodothyronine (T3) modulation of gonadotropin secretion in the female rat.

The effect of T3 upon gonadotropin secretion was examined in ovariectomized (Ovarx), Ovarx thyro-parathyroidectomized (Ovarx-TxPx), or proestrus rats. T3 (50 microgram/-100 gBW), administered late diestrus-2, abolished the LH surge during the critical period of proestrus in 7 out of 9 rats; the rise in sera FSH was not inhibited, although a distinct peak was absent. Administration of 5 or 50 microgram T3/100gBW 2.5h before the critical period resulted in either a suppression or an alteration of the timing of LH release. In the 5 microgram T3/100gBW treated animals the sera FSH peak was delayed in timing, whereas in the 50 microgram T3/100gBW treated rats sera FSH demonstrated two separate peaks during the critical period. Treatment with various dosages of T3 of Ovarx-TxPx rats resulted in significant suppressions (p less than 0.05) of sera LH and FSH. Despite depressed concentrations of sera LH and FSH in T3-treated rats pituitary sensitivity to a challenge of 3LHRH was enhanced. Hence, the pituitary was not the site of T3 inhibition of gonadotropin secretion. Additionally, T3 did not modify pituitary LH content or hypothalamic LH3 releasing activity (LHRH). Since T3 did not inhibit gonadotropin secretion at the pituitary level, a neural site of T3 action is suggested.     

Effect of ovariectomy at two periods of the year on LH and FSH basal concentrations and pituitary response to LHRH in the brown hare (Lepus europaeus)

In the brown hare, fertile mating takes place from the beginning of December to September. Seasonal variations of basal concentrations of LH and FSH, and pituitary response to a monthly i.v. injection of LHRH were studied in intact control females and in females ovariectomized during the seasonal anoestrus (OVX1) or during the breeding season (OVX2). In intact females, both basal and LHRH-stimulated LH levels showed an annual variation, with minimal values during anoestrus. During the breeding season, the LH response to LHRH exhibited a biphasic pattern. In contrast, there was no clear seasonal variation in basal and LHRH-stimulated FSH concentrations. After ovariectomy during anoestrus, basal LH remained low for 2 months and began to increase in December. After ovariectomy during the breeding season, LH basal concentrations increased within a few days after the operation. Thereafter, LH values remained high in both groups of females until September, and decreased significantly as in intact females. The pattern of LH release after LHRH remained monophasic in the two groups of ovariectomized females. In OVX1 females, the LH response increased as early as October, was maximum from December to April and decreased progressively until October. IN OVX2 females, the LH response decreased regularly after ovariectomy to a minimum in October. In the 2 groups of ovariectomized females, basal FSH concentrations and pituitary response to LHRH rose rapidly after ovariectomy and did not vary significantly thereafter. These results showed a direct central effect of season on the regulation of basal concentrations of LH, modulated by a negative feed-back of ovarian secretions during the breeding season. In intact hares, the enhanced LH response after LHRH during the breeding season was related to an acute positive effect of ovarian secretions. The regulation of FSH was less dependent on season and remained under a negative control of the ovary throughout the year.     

Use of the immature rat uterotrophic assay for specific measurements of chorionic gonadotropins and follicle-stimulating hormones in vivo bioactivities

The uterine weight growth stimulation by equine Chorionic Gonadotropin (eCG/PMSG) was found to occur at much lower eCG concentrations than ovarian growth. Human Chorionic Gonadotropin (hCG) which has only LH activity, was found to be as active as eCG in the uterotrophic assay whereas equine Luteinizing Hormone (eLH) which has dual LH+FSH activities like eCG, exhibited a much lower potency. In contrast to hCG, porcine and ovine LH as well as pFSH and oFSH exhibited no uterotrophic activity indicating that only gonadotropins with both LH activity and long half-lives are active alone in this assay. The FSH preparations were nevertheless found to trigger a dose-dependent response, but only in the presence of a subactive dose of hCG. The uterotrophic activity of hCG was found to be suppressed in ovariectomized immature rats and to be diminished after injection of GnRH antagonist suggesting an indirect pathway implicating the hypothalamo-pituitary complex.The data in this report together with the analysis of literature suggest that choriogonadotropins exert their stimulatory role on uterine growth by an indirect mechanism involving an increase in ovarian FSH receptors and FSH release by the pituitary. At the lowest concentrations of hCG, the increase in ovarian FSH receptors without endogenous FSH release is thought to be responsible for the sensitivity of the uterotrophic assay to exogenous FSHs. In conclusion, the immature rat uterotrophic assay is a sensitive and convenient assay for eCG and hCG as well as for FSHs in the presence of a sub-active dose of hCG.     

Circadian entrainment by feeding cycles in house sparrows,Passer domesticus

Summary We studied the potential zeitgeber qualities of periodic food availability on the circadian rhythms of locomotor and feeding activity of house sparrows. The birds were initially held in a LD-cycle of 12:12 h, with food restricted to the light phase. After transfer to constant dim light, the birds remained entrained by the restricted feeding schedule. Following an exposure to food ad libitum conditions, the rhythms could be re-synchronized by the feeding cycle. Shortening of the zeitgeber period to 23.5 h resulted in the loss of entrainment in most birds, whereas a longer zeitgeber period of 25 h re-entrained the rhythms of most birds. Although these results prove that periodic food availability can act as a zeitgeber for the circadian rhythms of house sparrows, several features of our data indicate that restricted feeding is only a weak zeitgeber. The pattern of feeding activity prior to the daily time of food access shown under some experimental conditions suggests that anticipation is due to a positive phase-angle difference of the birds' normal circadian system rather than being caused by a separate pacemaker.     

Measuring Motivation for Appetitive Behaviour: Food-Restricted Broiler Breeder Chickens Cross a Water Barrier to Forage in an Area of Wood Shavings without Food

Broiler breeders (parents of meat chickens) are selected for fast growth and become obese if fed ad libitum. To avoid this and maintain good health and reproductive ability, they are feed restricted to about 1/3 of what they would eat ad libitum. As a result, they experience chronic hunger and exhibit abnormal behaviour patterns that may indicate stress and frustration. One approach to measuring hunger is to observe how much birds will work, such as pecking a key, for access to more or different types of food. However, the sight, smell, and feedback from consumption of the feed reward changes the context and may artificially raise feeding motivation. To avoid this, we tested broiler breeders in an apparatus in which they could work for access to a wooden platform covered in wood shavings by crossing a water runway which increased in length and depth in 8 successive tests. In the wood shavings area, they could perform exploratory and foraging behaviour (the appetitive phase of feeding) but were never rewarded with feed. Sixty birds were divided into three feed quantity treatments: commercial restriction (R), and twice (2R) or three times (3R) this amount. Overall, birds fed R worked harder to reach the wood shavings area (reached it in a larger number of tests) than 2R and 3R birds (P<0.001). More restricted birds took less time to reach the area (P<0.001, R<2R<3R) and spent more time foraging while there (P<0.001, R>2R>3R). This indicates that restricted-fed birds were hungry and willing to work for the opportunity to forage even though food was never provided, suggesting that their motivation to perform the appetitive component of feeding behaviour (foraging/food searching) was sufficient to sustain their response. Thus food restriction in broiler breeders is a welfare concern. However these methods could be used to test alternative feeding regimes to attempt to find ways of alleviating hunger while still maintaining healthy growth and reproduction in these birds.     

Availability of water affects renewal of tissues in migratory blackcaps during stopover

Migrating blackcaps (Sylvia atricapilla) were used to test the predictions that (1) the rebuilding of the digestive tract, as reflected by mass-specific consumption of food on the first 2-3 days of a stopover, is faster in birds with access to drinking water than in birds without, and (2) that adipose tissue and pectoral muscles grow faster and to a greater extent in birds with unlimited access to water. We simulated migratory stopover in two experiments. In Experiment I, each of 31 birds was randomly assigned to one of three experimental groups for 6 days. Along with mealworms (～64% water) ad libitum, Group 1 received drinking water ad libitum; Group 2 had 0.5 h/day access to water; and Group 3 had no access to water. In Experiment II, 30 birds were offered a mixed diet for insectivorous birds (～33% water) ad libitum for 6 days, while randomly assigned to two groups: (1) Water ad libitum-control; and (2) 30 min access to water twice a day. We measured lean mass and fat mass using dual energy X-ray absorptiometry, as well as body mass (m(b)), pectoral muscle index (PMI), and daily intake of food and water. Mean daily water intake was significantly different among the groups in both experiments. However, the availability of drinking water positively affected the rates of gain of lean and fat mass only in birds fed with the mixed, relatively dry diet. Furthermore, mass-specific daily food intake was affected by the availability of drinking water only in the mixed diet experiment, in which birds with unlimited access to drinking water reached an asymptote, 1 day earlier than birds in the water-restricted group. We suggest that in birds consuming diets with low water content, the lack of sufficient drinking water may result in slower rebuilding of the digestive tract, or may influence biochemical processes in the gut that result in slower growth of tissue. Although blackcaps obtained sufficient water from preformed and metabolic water to renew lost tissues when eating mealworms, given access to water, the birds drank prodigiously. Our results also suggest that if drinking water is unavailable to migrating blackcaps, their choices are restricted to water-rich foods, which may constrain their rate of feeding and thus the rate at which they deposit fat. Consequently, drinking water may have an important influence on birds' migratory strategies with respect to habitat selection, use of energy, and the saving of time.