Changes In Voluntary Food Intake Research Articles

Macronutrient-induced differences in food intake relate with hepatic oxidative metabolism and hypothalamic regulatory neuropeptides in rainbow trout (Oncorhynchus mykiss)

This study examines how dietary macronutrient-induced changes in voluntary food intake (FI) relate to changes in markers of hepatic oxidative metabolism and in the expression of FI regulatory neuropeptides in a teleost model, the rainbow trout. Rainbow trout were fed for 6weeks with one of four iso-energetic diets (2×2 factorial design), containing either a high (HP, ~500g·kg−1DM) or a low (LP, ~250g·kg−1DM) protein level (PL) with, at each PL, fat (diets HP-F and LP-F) being substituted by an iso-energetic amount of gelatinized corn starch (diets HP-St and LP-St) as non-protein energy source (ES). Irrespective of the dietary PL, FI (g·kg−0.8·d−1) and digestible energy intake (DEI, kJ·kg−0.8·d−1) were significantly (P<0.05) reduced by the iso-energetic replacement of fat by starch as non-protein ES. Interestingly, trout fed these St-diets had higher gene expression of markers of hepatic oxidative phosphorylation (OxPhos), i.e. ubiquinol-cytochrome c reductase subunit 2 (UCR2) and cytochrome oxidase subunit 4 (COX4) and of aerobic oxidative capacity (CS, citrate synthase), which paralleled glucokinase (GK) transcription. This positive relation suggests that glucose phosphorylation and markers of mitochondrial OxPhos are linked at the hepatic level and possibly triggered the observed reduction in FI. Moreover, trout displaying the reduced FI had higher cocaine amphetamine regulator transcript (CART) mRNA in hypothalamus, whereas neuropeptide Y (NPY) mRNA did not follow the macronutrient-induced changes in FI. Further studies are needed to unravel the mechanisms by which diet-induced changes in hepatic metabolism inform central feeding centers involved in the regulation of FI in fish.

Influence of birth weight, sex, age and adiposity on central leptin and insulin sensitivity in young growing sheep, as indicated by changes in voluntary food intake

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Influence of photoperiod and gonadal status on food intake, adiposity, and gene expression of hypothalamic appetite regulators in a seasonal mammal

We studied the effects of photoperiod on metabolic profiles, adiposity, and gene expression of hypothalamic appetite-regulating peptides in gonad-intact and castrated Soay rams. Groups of five to six animals were studied 6, 18, or 30 wk after switching from long photoperiod (LP: 16 h of light) to short photoperiod (SP: 8 h of light). Reproductive and metabolic indexes were measured in blood plasma. Expression of neuropeptide Y (NPY), proopiomelanocortin (POMC), and leptin receptor (ObRb) in the arcuate nucleus was measured using in situ hybridization. Testosterone levels of intact animals were low under LP, increased to a peak at 16 wk under SP, and then declined. Voluntary food intake (VFI) was high under LP in both intact and castrated animals, decreased to a nadir at 12-16 wk under SP, and then recovered, but only in intact rams as the reproductive axis became photorefractory to SP. NPY gene expression varied positively and POMC expression varied negatively with the cycle in VFI, with differences between intact and castrate rams in the refractory phase. ObRb expression decreased under SP, unrelated to changes in VFI. Visceral fat weight also varied between the intact and castrated animals across the cycle. We conclude that 1) photoperiodic changes in VFI reflect changes in NPY and POMC gene expression, 2) changes in ObRb gene expression are not necessarily determinants of changes in VFI, 3) gonadal status affects the pattern of VFI that changes with photoperiod, and 4) in the absence of gonadal factors, animals can eat less but gain adiposity.

Links between the appetite regulating systems and the neuroendocrine hypothalamus: lessons from the sheep.

The hypothalamus is integral to the regulation of energy homeostasis and the secretion of hormones from the pituitary gland. Consequently, hypothalamic systems may have a dual purpose in regulating both neuroendocrine function and appetite. To date, most studies investigating the interface between appetite and hormone secretion have been performed in rats or mice that have been acutely fasted or baring a genetic abnormality causing either obesity or aphagia. By contrast, various physiological models, including chronic food-restriction or photoperiodically driven changes in voluntary food intake, add further perspective to the issue. In this regard, sheep provide an innovative model whereby long-term changes in body weight or extended feeding rhythms can be investigated. This review compares and contrasts data obtained in different species with regard to the neuroendocrinology of appetite, and discusses the benefits and knowledge gained from using various nonrodent models with a particular emphasis on a ruminant species.

Photoperiodic entrainment of seasonal changes in the appetite, feeding behaviour, growth rate and pelage of pony colts

AbstractRelationships among photoperiod and changes in voluntary food intake, feeding behaviour, growth and pelage were determined in seven, 2-year-old pony colts (182·4 (s.e. 5·4) kg). Individually housed colts were provided with ad libitum access to a complete pelleted diet (gross energy = 16·7 MJ/kg dry matter). Voluntary food intake (VFI, kg/ day) was calculated daily and body weights were recorded weekly throughout the 36-week study. Feeding behaviour was evaluated at approximately 4-week intervals by continuous observation (24 h), and the hair weight density (HWD, mg/cm2) of shoulder pelage was determined fortnightly. Day length was artificially manipulated to mimic the prevailing mid-summer photoperiod (16 h light: 8 h dark, 16L: 8D). After 1 week of the study (and the preceding fortnight), day length was abruptly decreased and thereafter animals were exposed to alternating 14-week periods of short (SD, 8L: 16D) and long days (LD, 16L: 8D). The mean daily VFI of individual ponies was calculated weekly and normalized for digestible energy (DE) content and metabolic body weight (DEI, MJ/kg M0·75). The average daily gain (ADG, kg/day) in body weight of each individual was calculated weekly. The apparent digestibility of dietary energy (digestibility) was determined over 72 h (no. = 6) on two occasions (days 92 to 95 and 190 to 193) during the study. Digestibility was similar in both periods (0·48, s.e. 0·01). DEI, ADG and HWD changed in a cyclic manner throughout the study. The period of the appetite cycle (24·4 (s.e. 1·3) weeks) did not differ from that of the 28-week photoperiodic regime. DEI decreased from a maximum of 1·4 (s.e. 0·03) MJ/kg M0.75 per day (day 21), to a nadir of 0·75 (s.e. 0·02) MJ/kg M0.75 per day (day 154, P &lt; 0·001) and had increased (P &lt; 0·001) to attain a second zenith (0·93 (s.e. 0·01) MJ/kg M0.75 per day) before the end of the study. Ponies ate discrete meals of similar duration, but meal frequency was associated with changes in VFI (r = 0·77) as was proportion of time spent feeding (r = 0·79). Changes in ADG reflected those of DEI. Body weight was stable for 4 weeks at the nadir of the appetite cycle. Maximal HWD was coincident with the nadir of the appetite and growth cycles. Regression of individual values for DEI on ADG described a linear relationship (R2 = 0·80) which could be used to predict the energy requirements of growing ponies maintained under similar conditions:DEI total (MJ/kg M0·75 per day) = 0·654ADG (kg/day) + 0·789 (1).The duration of the photoperiod, appetite, growth and pelage cycles were similar, suggesting a causal relationship. Physiological responses to photoperiodic change were not immediate and exhibited a delay of 5 to 8 weeks.

Sex and season are major determinants of voluntary food intake in sheep.

Seasonal changes in voluntary food intake (VFI) are seen in various species, including sheep. This paper reviews recent work in this area, especially in relation to alterations in the expression of appetite-regulating peptides in the brain of the sheep. Work in the hamster is also reviewed because this is another species in which VFI is regulated by photoperiod. In normally grazing sheep, appetite is maximal in the late summer/early autumn and minimal in spring. This appears to be owing to increased expression of the orexigenic peptide, neuropeptide Y. Similar results are obtained in sheep that are subjected to controlled photoperiod. The same does not appear to be true for hamsters. Further work in sheep has shown that there is a seasonal pattern of responsiveness to leptin that is more pronounced in females than in males. In particular, the effect of leptin to reduce food intake is maximal in female sheep in the spring; reasons for the sex difference are discussed.

Photoperiodic entrainment of seasonal changes in appetite and growth in pony colts

During winter, voluntary food intake (VFI) and growth decreased in light horse weanlings given ad libitum access to a forage/concentrate diet (Cymbaluk et al, 1989). These changes were attributed to decreased ambient temperatures. However, photoperiodically entrained seasonal changes in VFI and growth are documented in other Northern ungulates (Moen, 1978) and may comprise an adaptation to changes in forage availability. Throughout their evolution, horses experienced similar environmental pressures and may demonstrate similar photoperiodic adaptations. This study characterised changes in VFI and growth in pony colts maintained under an artificial photoperiodic regime.Seven, 2 year-old pony colts of Welsh Mountain type (182.4 ± 5.4 kg), were obtained from pasture (53°N). Animals were individually housed in loose-boxes, within a light-proof building. Measured quantities of a complete pelleted diet (gross energy = 16.7 MJ.kgDM-1), calculated to exceed appetite by at least 1 kg, were offered daily.

Photoperiodic entrainment of seasonal changes in appetite and growth in pony colts

During winter, voluntary food intake (VFI) and growth decreased in light horse weanlings given ad libitum access to a forage/concentrate diet (Cymbaluk et al, 1989). These changes were attributed to decreased ambient temperatures. However, photoperiodically entrained seasonal changes in VFI and growth are documented in other Northern ungulates (Moen, 1978) and may comprise an adaptation to changes in forage availability. Throughout their evolution, horses experienced similar environmental pressures and may demonstrate similar photoperiodic adaptations. This study characterised changes in VFI and growth in pony colts maintained under an artificial photoperiodic regime.Seven, 2 year-old pony colts of Welsh Mountain type (182.4 ± 5.4 kg), were obtained from pasture (53°N). Animals were individually housed in loose-boxes, within a light-proof building. Measured quantities of a complete pelleted diet (gross energy = 16.7 MJ.kgDM-1), calculated to exceed appetite by at least 1 kg, were offered daily.

Physical characteristics of the alimentary tract in relation to seasonal changes in voluntary food intake by the red deer (Cervus elaphus)

SUMMARYVoluntary intakes of a medium-quality grass hay were measured in winter (early January) and in spring (late April) near Edinburgh for two separate groups of six red deer, together with digestibility and mean retention times of the particulate-phase marker, 103Ru-phenanthroline. The deer were then slaughtered and the weights of digesta and the dimensions of the alimentary tract were measured. Voluntary intakes of dry matter were significantly higher in spring than in winter, but there was no difference in digestibility or mean retention time of 103Ru-phenanthroline. There were no significant differences in any of the organ weights or the dimensions of the intestines between the groups slaughtered in winter and spring. Dry matter proportions of digesta in the rumen, abomasum, small intestine and caecum, the wet and dry weights of rumen digesta and the water-filled capacity of the rumen were significantly greater in spring.

Effects of chronic long-acting bromocriptine treatment on liveweight, voluntary food intake, coat growth and breeding season in non-pregnant red deer hinds.

Seventeen red deer hinds were housed in individual pens and from 28 February until 11 November were injected each week with vehicle (group A; n = 6) or 5 (group B; n = 6) or 12.5 mg (group C; n = 5) of a long-acting formulation of bromocriptine. Liveweight and voluntary food intake (VFI) were recorded for each hind, and blood was collected for determination of progesterone, prolactin, tri-iodothyronine (T3) and cortisol concentrations by radioimmunoassay. Treatment with the high dose of bromocriptine was associated with a significant (P less than 0.05) reduction in VFI, with the effect being greatest between March and July. There was no treatment effect on liveweight, but there was a significant (P less than 0.01) interaction between time and treatment due to the faster rate of weight gain in control animals at the beginning of the experiment. Changes in liveweight could be explained by changes in VFI rather than by changes in the efficiency of utilization of intake. Termination of the breeding season was significantly (P less than 0.01) delayed by 54 days in group C hinds. Growth of the summer coat and subsequent winter coats was delayed by 1 and 3 months respectively in group C hinds, and in groups B and C the duration that animals were in summer coat was increased by about 1 month. The seasonal increase in prolactin concentrations was seen in all groups, but levels were significantly (P less than 0.05) lower in group C hinds. Concentrations of T3 and cortisol were not affected by bromocriptine.

The Effect of Amino Acid Excess on Utilization by the Rat of the Limiting Amino Acid—Lysine and Threonine at Equalized Food Intakes

The effect of excess amino acids on utilization of the most limiting amino acid was investigated via restricted feeding. Lysine- and threonine-deficient amino acid mixtures were incorporated into diets for young growing rats to provide 75 or 85% of the NRC requirement of the limiting amino acid in combination with zero or 50% of relative excess of the nonlimiting amino acids. The amount of food offered was equalized within treatment groups and increased according to the intake of the group with the lowest rate of consumption. Because of differences in the amount of diet refused, total food intakes were not identical. At equal percentage of the NRC requirement, threonine- and lysine-deficient amino acid mixtures supported equal body weight, dry matter, lipid and ash gains. However, crude protein retention was greater when the threonine-deficient amino acid mixture was fed. The maximum depression in performance due to 50% of amino acid excess with restricted feeding was much less than the maximum decrease previously observed in the ad libitum feeding situation. This supports the conclusion that changes in voluntary food intake are the major effectors of depressed growth due to excess amino acids. These results raise serious concern over the usefulness of amino acid requirements and the applicability of the current system of chemical scores to evaluate protein quality.