The temporal pattern of feeding over the oestrous cycle of the mouse.

The detailed temporal pattern of feeding in female mice was measured by an automated method over the oestrous cycle whilst feeding on either of two foods differing in stimulus characteristics, but of similar calorific value. The total time spent feeding varied systematically over the cycle, being increased for sweet food and decreased for laboratory chow at the time of sexual receptivity. and increased for both foods towards the end of the cycle. The temporal pattern is analysed into a number of variables, which are seen to alter in different ways over the oestrous cycle. The pro-oestrus disturbance is due to alterations in meal size brought about solely by changes in mean bout length, themselves products of variations in the initial bouts of the meal. Inter-meal interval is unrelated to changes in meal size at this time, allowing the latter to affect food intake. The changes towards the end of the cycle are produced by alterations of meal frequency at constant meal size. It is argued that separable 'phasic' and 'tonic' effects of reproductive condition on feeding may therefore be identified, and that they might possibly have different functions.     

Rat hepatic prolactin receptor: pubertal exposure to sex steroids alters responsivity to testosterone

Administration of testosterone enanthate to adult female rats lowered the level of hepatic prolactin receptor. Pubertal exposure of intact female rats to testosterone enanthate at the dose used did not affect the level of hepatic prolactin receptor in adults. However, the responsivity of such treated rats to testosterone challenge in adulthood was enhanced. Prepubertal ovariectomy of female rats lowered the level of hepatic prolactin receptor in adulthood. Exposure of the ovariectomized rats during puberty to mestranol (ethynylestradiol 3-methyl ether) at the dose used did not restore the normal adult female rat's level of hepatic prolactin receptor. However, they did become more resistant to subsequent testosterone challenge in adulthood. Exposure of prepubescent ovariectomized rats to testosterone enanthate during puberty reduced the already diminished level of hepatic prolactin receptor further. In addition, these rats were rendered more responsive to testosterone challenge in adulthood.     

Plant secondary metabolites alter the feeding patterns of a mammalian herbivore (<Emphasis Type="Italic">Neotoma lepida</Emphasis>)

Mammalian herbivores are predicted to regulate concentrations of ingested plant secondary metabolites (PSMs) in the blood by modifying the size and frequency of feeding bouts. It is theorized that meal size is limited by a maximum tolerable concentration of PSMs in the blood, such that meal size is predicted to decrease as PSM concentration increases. We investigated the relationship between PSM concentration in the diet and feeding patterns in the herbivorous desert woodrat (Neotoma lepida) fed diets containing phenolic resin extracted from creosote bush (Larrea tridentata). Total daily intake, meal size and feeding frequency were quantified by observing the foraging behavior of woodrats on diets containing increasing concentrations of creosote resin. Desert woodrats reduced meal size as resin concentration in the diet increased, resulting in an overall reduction in daily intake and regulation of resin intake. Moreover, desert woodrats were able to detect resin concentrations in the diet and regulate the intake of resin very rapidly. We suggest that the immediate and sustained ability to detect and regulate the intake of resin concentrations during each foraging bout provides a behavioral mechanism to regulate blood concentrations of resin and allows desert woodrats to make “wise” foraging decisions.     

Influence of adult breeding experience on growth and provisioning of Wandering Albatross Diomedea exulans chicks at South Georgia

For most seabirds, reproductive performance improves with age; in albatrosses this is thought not to be so (experience being acquired before starting breeding) but only one study (of chick growth in a single season at one site) has specifically addressed this. We compared the provisioning performance and growth rates of chicks of Wandering Albatrosses Diomedea exulans breeding for the first (IN), second and third (LE) and fourth or more times (EE) on Bird Island, South Georgia in the austral winters of 1996 and 1997. Eggs from EE adults were significantly heavier than the other two categories and these chicks had a greater mass and longer wings up to 160 days of age and longer culmen and tarsus up to 115 days old. However chicks from all categories fledged at the same average mass, size and age. No significant differences between categories in feeding frequency or meal size were detected but experienced adults made shorter long foraging trips and spent more time at the nest than less experienced birds. Adults that remained at the nest gave chicks smaller meals than those that left immediately after feeding the chick. Although provision of smaller but more frequent meals by experienced adults promotes more rapid chick growth, the resulting differences do not persist into the late chick-rearing period. Our results were very similar to those from Iles Crozet in the Indian Ocean, supporting the hypothesis that when Wandering Albatrosses start to breed they are fully competent foragers but that it takes a while, during early chick-rearing, for birds breeding for the first time to adapt to the additional demands of provisioning a chick.     

Provisioning and growth in chicks of Wilson's storm-petrels (Oceanites oceanicus) on King George Island, South Shetland Islands

We present data on chick growth and chick feeding in Wilson's storm-petrel (Oceanites oceanicus) in a colony on King George Island, South Shetland Islands. Chicks were repeatedly weighed and the weight differences over 24 h were corrected for metabolic loss in order to obtain an estimation of meal sizes. Chicks were fed on 93% of the nights (n=688 nights). The average meal size for a single feeding was 8.5 g. Chicks received on average 1.2 feedings per night. These results are compared with data for this species from other locations. There was a trend for increased meal sizes from northern to southern populations, parallel to an increase in the adult mass, indicating that Wilson's storm-petrels carry optimal meal sizes according to their body size and may take advantage of increased food abundance by increasing feeding frequencies. We describe chick growth and discuss the influence of egg size, hatching date and feeding frequency on chick growth. The egg size had a positive influence on tarsus growth and body mass of chicks. Later-hatched chicks started wing growth and finished mass growth at a younger age and reached lower peak masses, indicating that late chicks may adapt to the restricted breeding season in their Antarctic breeding grounds by a more rapid development, but will fledge with a lower degree of development and less resources. Accepted: 22 May 2000     

Adolescent TBI‐induced hypopituitarism causes sexual dysfunction in adult male rats

Adolescents are at greatest risk for traumatic brain injury (TBI) and repeat TBI (RTBI). TBI‐induced hypopituitarism has been documented in both adults and juveniles and despite the necessity of pituitary function for normal physical and brain development, it is still unrecognized and untreated in adolescents following TBI. TBI induced hormonal dysfunction during a critical developmental window has the potential to cause long‐term cognitive and behavioral deficits and the topic currently remains unaddressed. The purpose of this study was to determine if four mild TBIs delivered to adolescent male rats disrupts testosterone production and adult behavioral outcomes. Plasma testosterone was quantified from 72 hrs preinjury to 3 months postinjury and pubertal onset, reproductive organ growth, erectile function and reproductive behaviors were assessed at 1 and 2 months postinjury. RTBI resulted in both acute and chronic decreases in testosterone production and delayed onset of puberty. Significant deficits were observed in reproductive organ growth, erectile function and reproductive behaviors in adult rats at both 1 and 2 months postinjury. These data suggest adolescent RTBI‐induced hypopituitarism underlies abnormal behavioral changes observed during adulthood. The impact of undiagnosed hypopituitarism following RTBI in adolescence has significance not only for growth and puberty, but also for brain development and neurobehavioral function as adults. © 2014 Wiley Periodicals, Inc. Develop Neurobiol 75: 193–202, 2015     

Cyclic estradiol treatment normalizes body weight and restores physiological patterns of spontaneous feeding and sexual receptivity in ovariectomized rats

Hypothalamic-pituitary-gonadal axis function strongly influences feeding and body weight in cycling females in many species. To test the sufficiency of cyclic variations in plasma estradiol to reproduce normal patterns of spontaneous feeding, food intake, and body weight, ovariectomized Long-Evans rats were subcutaneously injected every fourth day with 2 microg estradiol benzoate or with the oil vehicle alone. Cyclic estradiol treatment completely normalized the trajectory of body weight gain and total food intake through seven treatment cycles. The hyperphagia of ovariectomized rats was expressed as an increase in spontaneous meal size. Meal frequency decreased, but not enough to compensate for the increase in meal size. Estradiol treatment normalized both parameters. In addition, cyclic estradiol treatment produced a further phasic decrease in meal size (and increase in meal frequency) and a decrease in food intake during the second night after injection. This phasic change is similar to the feeding changes occurring during estrus in intact rats. Sexual receptivity was measured during the eighth estradiol treatment cycle, 4 h after injection of 0.5 mg progesterone. Lordosis scores at the time of the treatment cycle modeling estrus were maximal, and scores at the time modeling diestrus were slightly increased over those of rats that did not receive estradiol. Finally, plasma estradiol levels, measured during the ninth treatment cycle, revealed a near-normal cyclic pattern of plasma estradiol levels. These results provide the first demonstration that the induction of a cyclic, near-physiological pattern of plasma estradiol is sufficient to maintain normal levels of body weight, spontaneous feeding patterns, total food intake, and (together with progesterone) sexual receptivity in ovariectomized rats.     

Distinctive stress effects on learning during puberty

Puberty is a time of significant change in preparation for adulthood. Here, we examined how stressful experience affects cognitive and related hormonal responses in male and female rats prior to, during and after puberty. Groups were exposed to an acute stressor of brief periodic tailshocks and tested 24 h later in an associative memory task of trace eyeblink conditioning. Exposure to the stressor did not alter conditioning in males or females prior to puberty but enhanced conditioning in both males and females during puberty. The enhancement occurred in pubescent females irrespective of the estrous cycle. In adulthood, sex differences in trace conditioning and the response to stress emerged: females outperformed males under unstressed conditions, but after stressor exposure, trace conditioning in females was impaired whereas that in males was enhanced. These differences were not related to changes in gross motor activity or other nonspecific measures of performance. The effects of acute stress on corticosterone, estradiol, progesterone, and testosterone were also measured. Stressor exposure increased the concentration of corticosterone in all age groups, although sex differences were only evident in adults. All reproductive hormones except estradiol increased with age in a predictable and sex dependent fashion and none were affected by stressor exposure. Estradiol decreased in male rats across age, and remained stable for female rats. Together, these data indicate that males and female respond similarly to learning opportunities and stressful experience before and during puberty; it is in adulthood that sex differences and the opposite responses to stress arise.     

Increased short-term food satiation and sensitivity to cholecystokinin in neurotrophin-4 knock-in mice

Neurotrophin-4 (NT-4) knockout mice exhibited decreased innervation of the small intestine by vagal intraganglionic laminar endings (IGLEs) and reduced food satiation. Recent findings suggested this innervation was increased in NT-4 knock-in (NT-4KI) mice. Therefore, to further investigate the relationship between intestinal IGLEs and satiation, meal patterns were characterized using solid and liquid diets, and cholecystokinin (CCK) effects on 30-min solid diet intake were examined in NT-4KI and wild-type mice. NT-4KI mice consuming the solid diet exhibited reduced meal size, suggesting increased satiation. However, compensation occurred through increased meal frequency, maintaining daily food intake and body weight gain similar to controls. Mutants fed the liquid diet displayed a decrease in intake rate, again implying increased satiation, but meal duration increased, which led to an increase in meal size. This was compensated for by decreased meal frequency, resulting in similar daily food intake and weight gain as controls. Importantly, these alterations in NT-4KI mice were opposite, or different, from those of NT-4 knockout mice, further supporting the hypothesis that they are specific to vagal afferent signaling. CCK suppressed short-term intake in mutants and controls, but the mutants exhibited larger suppressions at lower doses, implying they were more sensitive to CCK. Moreover, devazepide prevented this suppression, indicating this increased sensitivity was mediated by CCK-1 receptors. These results suggest that the NT-4 gene knock-in, probably involving increased intestinal IGLE innervation, altered short-term feeding, in particular by enhancing satiation and sensitivity to CCK, whereas long-term control of daily intake and body weight was unaffected.     

Gastric emptying in Limanda limanda (L.) and the return of appetite

Limanda limanda (35–225 g) fed during daytime when trained to use demand feeders under natural photoperiods. Under continuous illumination different feeding rhythms developed which were detected by periodogram analysis. Interfeeding periods (P hours) varied with body weight (W grams) and temperature (T° C) over the range 6.5–15° C as: In P=4.4 – 0.167 (In W) – 0.05 T. Daily food intake (D grams increased with both temperature and size (In D = 0.099 T + 0.579 In W – 3.49). Relative daily intake (R as % body weight, b.w) increased with temperature but decreased with size (In R = 0.099T–0.41 In W + 1.05). These changes in daily intake are primarily caused by changes in feeding frequency; the amount eaten at a meal is relatively constant save at low temperatures (6.5° C) when appetite is suppressed. Dilution of the food with kaolin (from 4.8 to 2.2 kcal/g) did not cause a compensatory increase in meal size or frequency. Gastric emptying time (GET hours) measured by X-radiography changed with body weight, temperature and relative meal size (M % b.w.) as In GET = 0.68 In M + 0.39 In W – 0.035T + 1.46. With the exception of the lowest temperature (6.5° C) interfeeding periods closely followed GET (P = 1.09 GET – 2.6) supporting the proposal that stomach fullness is a major factor controlling appetite in the dab.     

Increasing sodium bicarbonate level in high-concentrate diets for heifers. II. Effects on chewing and feeding behaviors

Four Holstein heifers (264 ± 12 kg initial BW) were used in a 4 × 4 Latin square design with 21-day experimental periods to determine the effect of increasing levels of sodium bicarbonate (BICARB) (0%, 1.25%, 2.5% and 5%, of concentrate dry matter (DM) basis) on chewing and feed intake behavior when fed high-concentrate diets. Concentrate (13.41% CP, 13.35% NDF) and barley straw were fed once a day at 0830 h ad libitum. Feed bunks placed on scales and video recording were used to measure 24-h feed intake and chewing behavior, respectively. The patterns of feeding behavior (feed intake, meal size and length) and chewing behavior (eating, ruminating and total chewing) were studied by dividing the day into 12 intervals of 2-h each, beginning at feeding (interval 1 through 12). Number of meals per day and eating rate decreased linearly with increasing buffer level, but meal length increased linearly. No treatment effects were observed in sum of daily meal lengths or average meal size. The treatment × interval interaction was significant on meal size, length and feed intake. The size and length of those meals occurring during the 4 h post-feeding increased linearly. However, meal size tended to decrease in the evening between 8 and 12 h, whereas feed intake decreased linearly from 6 to 10 h and from 12 to 14 h post-feeding. Buffer concentration did not affect the percentage of time spent ruminating, eating or drinking per day but the buffer level × interval interaction was significant. Time spent eating expressed as min per kg of DM or organic matter (OM) intake increased linearly with buffer levels. Proportion of time spent eating increased linearly during the intervals between 0 and 4 h post-feeding. Time spent ruminating decreased linearly during the 2 h post-feeding, and also in the evening from 12 to 14 h, and at night from 18 to 22 h post-feeding, but the effect was quadratic between 8 and 10 h when intermediate buffer levels showed the greatest ruminating time. Time spent drinking decreased linearly from 6 to 8 h but increased during the 2 h following feeding and from 10 to 12 h post-feeding. Daily eating rate and meal frequency decreased linearly as the buffer level increased, but average meal size and daily chewing times were not affected. However, significant time of the day × buffer level interactions were observed for feed intake, meal size and length and chewing behavior.     

The effect of stomach fullness on food intake of whiting in the North Sea

The probability of a North Sea whiting Merlangius merlangus stomach containing fresh food was depressed when partially digested food was already present in the stomach. The lowered probability was detected even at levels where the fish was physiologically able to ingest an average meal. The feeding probability of c . 15% of the fish caught was predicted to be severely decreased at the level of partially digested food found in the stomachs. No effect of stomach fullness on meal size was found, indicating that the saturation is affecting search activity rather than prey or meal size selection. The diurnal pattern in food intake varied between the five sampling locations, presumably as a result of differences in prey availability.     

Hyperphagia and obesity in OLETF rats lacking CCK-1 receptors

The brain-gut peptide cholecystokinin (CCK) inhibits food intake following peripheral or site directed central administration. Peripheral exogenous CCK inhibits food intake by reducing the size and duration of a meal. Antagonist studies have demonstrated that the actions of the exogenous peptide mimic those of endogenous CCK. Antagonist administration results in increased meal size and meal duration. The feeding inhibitory actions of CCK are mediated through interactions with CCK-1 receptors. The recent identification of the Otsuka-Long-Evans-Tokushima Fatty (OLETF) rat as a spontaneous CCK-1 receptor knockout model has allowed a more comprehensive evaluation of the feeding actions of CCK. OLETF rats become obese and develop non-insulin dependent diabetes mellitus (NIDDM). Consistent with the absence of CCK-1 receptors, OLETF rats do not respond to exogenous CCK. OLETF rats are hyperphagic and their increased food intake is characterized by a large increase in meal size with a decrease in meal frequency that is not sufficient to compensate for the meal size increase. Deficits in meal size control are evident in OLETF rats as young as 2 days of age. OLETF obesity is secondary to the increased food intake. Pair feeding to amounts consumed by intact control rats normalizes body weight, body fat and elevated insulin and glucose levels. Hypothalamic arcuate nucleus peptide mRNA expression in OLETF rats is appropriate to their obesity and is normalized by pair feeding. In contrast, pair fed and young pre-obese OLETF rats have greatly elevated dorsomedial hypothalamic (DMH) neuropeptide Y (NPY) mRNA expression. Elevated DMH NPY in OLETF rats appears to be a consequence of the absence of CCK-1 receptors. In intact rats NPY and CCK-1 receptors colocalize to neurons within the compact subregion of the DMH and local CCK administration reduces food intake and decreases DMH NPY mRNA expression. We have proposed that the absence of DMH CCK-1 receptors significantly contributes to the OLETF's inability to compensate for their meal size control deficit leading to their overall hyperphagia. Access to a running wheel and the resulting exercise normalizes food intake and body weight in OLETF rats. When given access to running wheels for 6 weeks shortly after weaning, OLETF rats do not gain weight to the same degree as sedentary OLETF rats and do not develop NIDDM. Exercise also prevents elevated levels of DMH NPY mRNA expression, suggesting that exercise exerts an alternative, non-CCK mediated, control on DMH NPY. The OLETF rat is a valuable model for characterizing actions of CCK in energy balance and has provided novel insights into interactions between exercise and food intake.     

A study of seasonally delayed puberty in the male hare, Lepus Europaeus.

The brown hare, Lepus europaeus, has a mating season which extends from January to September. Adult males exhibit pronounced seasonal changes in the reproductive tract which are associated with changes in LH secretion. Maximum plasma levels of immunoreactive LH occur between March and June and minimal levels in the autumn non-mating period from September to December; this seasonal cycle in gonadotrophin output is reflected by the appropriate changes in the secretion of testosterone from the testes and in the activity of the accessory sex glands. Juvenile animals reach puberty only during the adult mating season, and the age of puberty thus varies with the date of birth. Males born before May reach puberty and become fertile at 3 months of age, while those born from May to July grow to a mature body size during the autumn non-mating season but puberty is delayed for several months. Since some animals experiencing delayed puberty were found to have elevated plasma levels of LH and testosterone, it is concluded that puberty is not completely suppresed by the environmental effects of the autumn, but that the developmental process is prolonged, resulting in the juveniles being synchronized with the adults in their reproductive activity.     

Relation between feeding behaviour and energy metabolism in pigs fed diets enriched in dietary fibre and wheat aleurone

Feed intake and its daily pattern are regulated both at a short and a long term by several control pathways, including energy balance regulation. This trial aimed to determine the effect of dietary fibre (DB) (mix of wheat, soy and sugar beet pulp fibres) and aleurone supplementation and their interaction on energy and nitrogen balances in growing pigs with ad libitum access to feed. Forty pigs (BW: 35 kg) were fed diets differing by fibre concentration (NDF concentration: 10% or 14% DM) and aleurone supplementation (0, 2 or 4 g/kg) during 3 weeks. Pigs were housed individually in a respiration chamber during the last week to record feeding behaviour and measure energy and nitrogen balances (n = 36). Glucose oxidation was studied on the 6th day with an injection of [U-¹³C] glucose and measurement of ¹³CO₂ production. There was no significant interaction between DB inclusion and aleurone supplementation on any variables characterizing feeding behaviour. Pigs had less but longer meals with high level of DB, with an increased interval between two meals without effect on daily feed intake. The meal frequency significantly decreased when aleurone supplementation increased. Total tract apparent digestibility coefficient of DM, organic matter, ash, nitrogen and gross energy decreased when pigs received high DB level. Dietary fibre level increased significantly faecal excreted nitrogen. Aleurone supplementation decreased nitrogen retention. Free access to the feed induced a great individual variability not only in feed intake level (from 784 to 2290 g/day) but also in feeding behaviour (from 5.5 to 21.5 meals per day). This variability can be linked with the importance of underlying feed intake regulation pathways and difference in energy balance and metabolism efficiency. Several profiles of metabolism efficiency can be discriminate, thanks to a clustering based on feeding behaviour and pre-prandial concentrations of metabolites and hormones. In conclusion, DB inclusion decreased meal frequency, increased average meal size, decreased total tract apparent faecal digestibility coefficient of nitrogen and gross energy. Supplementation of aleurone decreased average daily feed intake with a reduction of the meal number per day, without modification of average meal size. Aleurone supplementation decreased nitrogen retention and nutrient deposition. Independently of experimental diets, the high individual variability permitted discriminating different profiles with different metabolic strategies. Efficient pigs with a high energy retention as protein and lipid seem to be able to adapt their metabolism according to energy sources.     

Dairy goats adjust their meal patterns to the fibre content of the diet

Few studies have investigated how meal patterns of ruminants are affected by diet fibre content. Dairy goats (N = 32) in late lactation and early gestation were housed in eight groups of four goats, with all combinations of breed (Alpine and Saanen) and lactation number (1 and 2) represented in each group. Each goat had access to its own individual feed trough placed on a weigh scale with data logged automatically. All goats were fed the same total mixed ration (TMR; 30% concentrate and 44.6% NDF in DM) ad libitum for a control period of 22 days. Using the same feed ingredients, half of the groups were then offered a High fibre diet (20% concentrate; 47.3% NDF), and the other half a Low fibre diet (40% concentrate; 41.5% NDF) for a treatment period of 16 days. Daily meal patterns (meal frequency, duration and size, feeding rate, daily feed intake and daily feeding time) were computed for each animal using a meal criterion of 8 min. The last 10 days for each period (control and treatment) were used to calculate individual period means and individual differences between the two periods. During the control period, the goats ate on average 12.1 ± 0.49 meals/day, consuming 4.2 ± 0.10 kg fresh TMR daily. When the ration changed, all measures of feeding behaviour except meal size changed asymmetrically for the goats on the two diets. Goats fed the High fibre diet reduced their meal frequency by 10%, and the first meal after feed distribution lasted 11% longer, leading to a 9% reduction in feeding rate and no significant changes in daily feed intake and daily feeding time. Goats on the Low fibre diet did not significantly change their meal frequency or meal size, but the combined changes nevertheless led to a 9% increase in daily feed intake. On the Low fibre diet, goats were able to increase their feeding rate by a third, leading to a reduction in meal durations, thus reducing daily feeding time by 13%. Goats adapt their feeding behaviour to the fibre proportion of the offered diet, with more changes when fibre content is lowered, which needs to be taken into account when comparing phenotypes and adaptability of small ruminants to different diets.     

Measuring meals: structure of prandial food and water intake of rats

Attempts to understand ingestion have sought to understand the control of meals. The present study evaluated a meal definition that included prandial drinking (drinking-explicit meals). The spontaneous nocturnal intake of male Wistar rats was studied. The meal breakpoint was defined as the interval between feeding or drinking events providing the most stable estimate of meal structure. Alternative breakpoints derived from prevailing methodology, log-survivorship, or frequency histogram analysis of interfeeding intervals without respect to drinking were compared (drinking-naive meals). Threshold interfeeding intervals that accounted for drinking indirectly were evaluated as surrogate breakpoints (drinking-implicit meals). Definitions were compared by determining which criterion better conformed to predictions of satiety. Microstructural differences resulting from the definitions were also studied. Under the drinking-explicit definition, rats averaged nine or ten 13-min meals/night, during which they consumed food and water equally in duration (5-6 min) and quantity (2.3 g). Individual differences were observed in microstructure measures. Meals defined by drinking-informed, but not drinking-naive, methods were followed by the behavioral satiety sequence and by an initially low likelihood of resuming feeding that monotonically increased with time. The drinking-explicit definition uniquely revealed preprandial and postprandial correlations of similar magnitude. Under drinking-informed definitions, food restriction increased meal size, whereas drinking-naive definitions increased meal frequency. Drinking-implicit definitions provided workable approximations of meal frequency and size but inferior estimates of feeding duration, eating rate, and the preprandial correlation. Thus log-survivorship analysis is not appropriate for identifying meal breakpoints, and the consideration of drinking in meal definitions can provide a better estimate of meal structure.     

Blood meal as a source of protein for grower/finisher pigs

In the first of four experiments five dietary levels of ring-dried blood meal (0, 3.0, 5.9, 8.9 and 11.8%) were used for pigs of 21–70 kg live weight at two levels of feeding (restricted and ad libitum). Pigs receiving either 5.9 or 8.9% blood meal grew more efficiently than pigs receiving either 0 or 11.8%. The feed conversion ratio of pigs given 3.0% blood meal was of intermediate value. There were significant interactions; when feeding was ad libitum, a reduced intake at the higher levels of blood meal resulted in a slower growth rate at the 11.8% level of blood meal, but with restricted feeding, up to 11.8% blood meal could be included without adverse effects on feed intake or growth rate.In the second and third experiments grower pigs fed ad libitum, between 22 and 50 kg live weight, were used to investigate the effects of the addition of a feed flavour or of isoleucine to a diet containing 12% blood meal. Experiment 2 involved two levels of blood meal (0 and 12%) and two levels of a feed flavour (0 and 50 p.p.m.). The feed flavour failed to prevent the reduction in feed intake and growth caused by 12% blood meal. In the third experiment the addition of 0.1% isoleucine to the 12% blood meal diet significantly increased both intake and growth rate but not to the level of a diet containing no blood meal.In Experiment 4 the digestible energy (± SE) content of blood meal was determined to be 20.8 (± 2.15) MJ/kg dry matter.     

A mechanism underlying mature-onset obesity: evidence from the hyperphagic phenotype of brain-derived neurotrophic factor mutants

Mice deficient in brain-derived neurotrophic factor (BDNF) develop mature-onset obesity, primarily due to overeating. To gain insight into the mechanism of this hyperphagia, we characterized food intake, body weight, meal pattern, and meal microstructure in young and mature mice fed balanced or high-fat diets. Hyperphagia and obesity occurred in mature but not young BDNF mutants fed a balanced diet. This hyperphagia was mediated by increased meal number, which was associated with normal meal size, meal duration, and satiety ratio. In contrast, the high-fat diet induced premature development of hyperphagia and obesity in young BDNF mutants and a similar magnitude hyperphagia in mature mutants. This hyperphagia was supported by increased meal size and was accompanied by a reduced satiety ratio. Thus the mechanism underlying hyperphagia was present before significant weight gain, but whether it occurred, and whether meal frequency or meal size was altered to support it, was modulated by a process associated with aging and by diet properties. Meal pattern changes associated with the balanced diet suggested meal initiation, and the oropharyngeal positive feedback that drives feeding, were enhanced and might have contributed to overeating in BDNF mutants, whereas negative feedback was normal. Consistent with this hypothesis, meal microstructure revealed that all hyperphagic mutant groups exhibited increased intake rates at meal onset. Therefore, the central nervous system targets of BDNF actions may include orosensory brain stem neurons that process and transmit positive feedback or forebrain neurons that modulate its strength.     

Provisioning and growth rates of nestling Fulmars Fulmarus glacialis: stochastic variation or regulation?

The pattern of chick feeding in the Fulmar Fulmarus glacialis at St Kilda, Scotland, was examined by repeated weighing of chicks throughout 14 consecutive days during the first half of the chick-rearing period in 1994. After correcting for metabolic weight losses, the sizes of positive mass increments between weighings were used to assess meal sizes and feeding frequency for each chick. Individual meals fed to chicks averaged 80.8 g (s.d. ± 21.0 g), or approximately 10% of adult mass. Each chick received 0 to 4 meals per day, with an average of 1.9 meals per chick per day, giving an average interval of around 25 h between meals delivered by each parent. The distribution of time intervals between feeds for each chick (whether single or double meals) followed a negative exponential function with a maximum value of 80 h. These results are not compatible with the idea that the purpose of large fat deposits in procellariiform chicks is to guarantee survival over long intervals between feeds. Over 14 days, the chicks' mean daily food requirements for zero-growth increased from 98 g to 160 g. This corresponded with an increase in feeding frequency but not meal size. Chicks with lower scores for body condition after feeding by both parents received more meals during the subsequent 16 h and had shorter intervals to the next feed, indicating that adults regulated feeding frequency in accordance with chick condition at the previous feed. This does not agree with the hypothesis that lipid accumulation by nestling Procellariiformes is a response to stochastic variation in food delivery associated with an absence of regulation. In view of the diversity of growth and feeding patterns present among the Procellariiformes, it is possible that lipid accumulation in this group does not have a unitary explanation.