Brief refeeding restores reproductive readiness in food-restricted female musk shrews (Suncus murinus)

Food deprivation blocks sexual behavior and disrupts estrous cycles in mammals. We asked whether reduced copulatory behavior, produced by limited food intake, could be reversed by brief refeeding intervals in the female musk shrew. In Experiment 1, animals were food restricted to 60% of ad lib (FR), and an additional group of FR females were refed for 90 min prior to testing (RF). Refed and ad lib (AL) fed females were significantly more likely to mate than FR females. To test the hypothesis that food-induced restoration of copulatory behavior is not the result of changes in peripheral steroids, we repeated Experiment 1 using ovariectomized and testosterone-implanted females. The results from Experiment 2 were similar to those found in the first study. Next, a more severe refeeding schedule was employed; females were restricted to 50% of ad lib intake. Females in the RF and FR groups were significantly less likely than the AL animals to mate. In the last experiment, females were food restricted to 50% and longer refeeding intervals were employed. Four and one-half hours of food intake did not reinstate sexual behavior, but females refed for 12 h were as likely to mate as ad lib fed controls. We also did not detect any differences in plasma concentrations of testosterone and cortisol in AL, FR, and RF ovary-intact animals. These results define a nutritional threshold for copulatory behavior in the musk shrew. Since this species is highly sensitive to small alterations in food intake, it is a useful model for studies of interactions between metabolic fuels and behavior.     

Energy requirements of fat sand rats (Psammomys obesus) and their efficiency of utilization of the saltbush Atriplex halimus for maintenance

The fat sand rat (Psammomys obesus; Gerbillinae), a diurnal gerbillid rodent, is herbivorous and able to thrive while consuming only the saltbush Atriplex halimus (Chenopodiaceae), a plant relatively low in energy content and high in ash and water. We measured the basal metabolic rate offat sand rats, their energy requirements in captivity when they were offered only A. halimus, and their efficiency of utilization of this diet for maintenance.
Before consuming A. halimus leaves, the fat sand rats scraped off the surface layers with their teeth. This behavioural activity removed 6.4% to 8.5% of the dry matter of the leaf, but increased the gross energy and organic matter content of the leaf by only approximately 3.1%. Basal metabolic rate of the fat sand rats was 167.9 kJ.kg-O 7s d-', approximately 57% of that expected for an eutherian mammal of its body mass, and energy requirements for maintenance, or average daily metabolic rate, were 498.7 kJ.kg-0'7s d-', approximately 90% of that expected for a rodent of its body mass. Dry matter digestibility of the consumed A. halimus averaged 67% and apparent digestible energy and apparent metabolizable energy averaged 65.3% and 63.4% of the gross energy, respectively. The efficiency of utilization of A . halimus for maintenance energy (k,) by the fat sand rats was 0.32 and the heat increment of feeding (HIF) was 0.68. The k, of A. halimus appeared to be low compared to other feeds, and this characteristic plus its low energy value and high water content forced the fat sand rats to consume large quantities of forage for maintenance.
It was concluded that although A. halimus has a low energy and high ash content, there are several advantages for fat sand rats consuming mainly this diet. Among them are: (1) it provides a more stable diet throughout the year than do seeds; (2) fat sand rats have no competition for this food resource from other rodents; and (3) their burrows are at the base of the     

Effects of feed restriction on fertility in female rats

BACKGROUND: Feed restriction with its resultant body weight loss impacts the rodent estrous cycle; however, the manifestation of these changes in a regulatory study design has not been documented. This study reports the effects of feed restriction in the context of an FDA regulatory submission. METHODS: Adult female rats (n = 20/group; weighing approximately 200 g each) were provided rodent chow ad lib (control) or at 20, 15, 10, or 7.5 g/rat/day (g/day) during a 2-week pre-mating phase, throughout the mating phase, and up to gestation day (GD) 7. On GD 8, all animals were provided ad lib feed until necropsy on GD 14. Estrous cyclicity, mating, and fertility parameters were evaluated. RESULTS: Ad lib rats consumed approximately 20 and 28 g/day during the pre-mating and gestation phases, respectively. All measured fertility parameters in the 20 g/day group were similar to control values. In the 15 g/day group, body weight was reduced by 16% at 2 weeks, prolonged diestrus occurred, and fertility was compromised due to reductions in corpora lutea. Within 2 weeks, mean body weight in groups receiving < or = 10 g/day was reduced by > or = 29% compared to ad lib values, and overt changes in estrous cyclicity, mating, and fertility occurred. The 7.5 g/day group was not sustainable beyond the pre-mating phase. CONCLUSIONS: For this study type, feed intake at < or = 50% ad lib values (< or = 10 g/day) was inadequate due to the magnitude and rapidity of body weight effects. Estrous parameters appeared slightly more sensitive than functional measures, as body weight changes of approximately 16% appeared near the threshold of changing routinely calculated estrous cycle parameters and were later associated with reduced fertility. In general, body weight differences of 10-15% by themselves were not adverse to normal reproduction (20 g/day).     

Modified activity-stress paradigm in an animal model of the female athlete triad.

The exercising woman with nutritional deficits and related menstrual irregularities is at risk of compromising long-term bone health, i.e., the female athlete triad. There is no animal model of the female athlete triad. The purpose of this study was to examine long-term energy restriction in voluntary wheel-running female rats on estrous cycling, bone mineral content, and leptin levels. Twelve female Sprague-Dawley rats (age 34 days) were fed ad libitum and given access to running wheels during an initial 14-wk period, providing baseline and age-related data. Daily collection included dietary intake, body weight, estrous cycling, and voluntary running distance. At 4 mo, rats were randomized into two groups, six restrict-fed rats (70% of ad libitum intake) and six rats continuing as ad libitum-fed controls. Energy intake, energy expenditure, and energy availability (energy intake - energy expenditure) were calculated for each animal. Serum estradiol and leptin concentrations were measured by RIA. Femoral and tibial bone mineral density and bone mineral content (BMC) were determined by dual-energy X-ray absorptiometry. Restrict-fed rats exhibited a decrease in energy availability during Weight Loss and Anestrous phases (P = 0.002). Compared with controls after 12 wk, restrict-fed rats showed reduced concentrations of serum estradiol (P = 0.002) and leptin (P = 0.002), lower ovarian weight (P = 0.002), and decreased femoral (P = 0.041) and tibial (P = 0.05) BMC. Decreased energy availability resulted in anestrus and significant decreases in BMC, estrogen and leptin levels, and body weight. Finally, there is a critical level of energy availability to maintain estrous cycling.     

Randomised comparison of diets for maintaining obese subjects' weight after major weight loss: ad lib,low fat,high carbohydrate diet v fixed energy intake.

OBJECTIVES: To compare importance of rate of initial weight loss for long term outcome in obese patients and to compare efficacy of two different weight maintenance programmes. DESIGN: Subjects were randomised to either rapid or slow initial weight loss. Completing patients were re-randomised to one year weight maintenance programme of ad lib diet or fixed energy intake diet. Patients were followed up one year later. SETTING: University research department in Copenhagen, Denmark. SUBJECTS: 43 (41 women) obese adults (body mass index 27-40) who were otherwise healthy living in or around Copenhagen. INTERVENTIONS: 8 weeks of low energy diet (2 MJ/day) or 17 weeks of conventional diet (5 MJ/day), both supported by an anorectic compound (ephedrine 20 mg and caffeine 200 mg thrice daily); one year weight maintenance programme of ad lib, low fat, high carbohydrate diet or fixed energy intake diet (< or = 7.8 MJ/day), both with reinforcement sessions 2-3 times monthly. MAIN OUTCOME MEASURES: Mean initial weight loss and proportion of patients maintaining a weight loss of > 5 kg at follow up. RESULTS: Mean initial weight loss was 12.6 kg (95% confidence interval 10.9 to 14.3 kg) in rapid weight loss group and 12.6 (9.9 to 15.3) kg in conventional diet group. Rate of initial weight loss had no effect on weight maintenance after 6 or 12 months of weight maintenance or at follow up. After weight maintenance programme, the ad lib group had maintained 13.2 (8.1 to 18.3) kg of the initial weight loss of 13.5 (11.4 to 15.5) kg, and the fixed energy intake group had maintained 9.7 (6.1 to 13.3) kg of the initial 13.8 (11.8 to 15.7) kg weight loss (group difference 3.5 (-2.4 to 9.3) kg). Regained weight at follow up was greater in fixed energy intake group than in ad lib group (11.3 (7.1 to 15.5) kg v 5.4 (2.3 to 8.6) kg, group difference 5.9 (0.7 to 11.1) kg, P < 0.03). At follow up, 65% of ad lib group and 40% of fixed energy intake group had maintained a weight loss of > 5 kg (P < 0.07). CONCLUSION: Ad lib, low fat, high carbohydrate diet was superior to fixed energy intake for maintaining weight after a major weight loss. The rate of the initial weight loss did not influence long term outcome.     

Long-term obesity levels in female OLETF rats following time-specific post-weaning food restriction

Obesity and the metabolic syndrome represent serious health threats affecting increasing numbers of individuals, with females being more affected than males and with growing incidence among children and adolescents. In the present study, we used the OLETF rat model of early-onset obesity to examine the influence of different timing of food restriction on long-term obesity levels in females. Food restriction took place at different time windows: from weaning until postnatal day (PND) 45 (early); from weaning until PND90 (chronic); or from PND45 until PND70 (late). Follow-up continued until PND90. During and after the termination of the diet-restriction period, we focused on peripheral adiposity-related measures such as fat pad weight (brown, retroperitoneal and inguinal); inguinal adipocyte size and number; and leptin, oxytocin and glucose levels. We also examined body weight, feeding efficiency, spontaneous intake after release from diet-restriction, and plasma creatinine levels and estrous cycle characteristics as a result of the chronic diet. The results suggest that while food restriction produced significant weight and adiposity loss, OLETF females presented poor weight loss retention after the early and late short-term diets. The estrous cycle structure and time of first estrous of the OLETF rats were normalized by chronic food restriction. Females responded to early food restriction in a different manner than males did in previous studies, further emphasizing the importance of sex-appropriate approaches in the investigation and treatment of the pathologies related to obesity and the metabolic syndrome.     

Long-term obesity levels in female OLETF rats following time-specific post-weaning food restriction

Obesity and the metabolic syndrome represent serious health threats affecting increasing numbers of individuals, with females being more affected than males and with growing incidence among children and adolescents. In the present study, we used the OLETF rat model of early-onset obesity to examine the influence of different timing of food restriction on long-term obesity levels in females. Food restriction took place at different time windows: from weaning until postnatal day (PND) 45 (early); from weaning until PND90 (chronic); or from PND45 until PND70 (late). Follow-up continued until PND90. During and after the termination of the diet-restriction period, we focused on peripheral adiposity-related measures such as fat pad weight (brown, retroperitoneal and inguinal); inguinal adipocyte size and number; and leptin, oxytocin and glucose levels. We also examined body weight, feeding efficiency, spontaneous intake after release from diet-restriction, and plasma creatinine levels and estrous cycle characteristics as a result of the chronic diet. The results suggest that while food restriction produced significant weight and adiposity loss, OLETF females presented poor weight loss retention after the early and late short-term diets. The estrous cycle structure and time of first estrous of the OLETF rats were normalized by chronic food restriction. Females responded to early food restriction in a different manner than males did in previous studies, further emphasizing the importance of sex-appropriate approaches in the investigation and treatment of the pathologies related to obesity and the metabolic syndrome.     

The effect of food restriction on morphological and metabolic development in two lines of growing Japanese quail chicks

To investigate whether there is a relationship between the inherent maximum growth rate of a chick and its degree of developmental plasticity, we studied the effects of food restriction on morphological and physiological development in P-line (selected for high growth rates) and C-line (nonselected) chicks of the Japanese quail between 2 and 64 d of age. In each line, three groups were created; one group in which the chicks were fed ad lib. and two other groups in which the chicks received 70% and 40% of the line-specific ad lib. feeding levels, respectively. In all three groups, chick survival rates were very high, and no relationship was detected between feeding level and chick mortality. The experimental feeding levels strongly affected the chicks' attainment of body mass at all ages. In addition, at most ages the growth of the structural components (wing, tarsus, and head) were also significantly affected by the feeding experiment but to a much smaller extent than the body mass. The feeding levels also affected the achievement of female sexual maturity such that, at the end of the experiment, most of the ad lib.-fed females and none of the females that received 40% of the ad lib. feeding level were laying eggs. In chicks of both lines that were fed ad lib., homeothermy was achieved at 7 d of age, but in chicks that received 40% of the line-specific ad lib. levels, homeothermy was achieved after 15-22 d of age. Poikilothermic chicks (P- and C-line) that were relatively heavy for their age exhibited relatively high resting metabolic rates (RMRs) and peak metabolic rates (PMRs) for their age. In addition, a positive relationship was found between the chicks' relative mass and RMR (based on mass-based predictive equations). No relationship was detected between the chicks' relative body mass and their relative PMR (relative to mass-based predictive equations). With respect to the metabolic scope (i.e., PMR-RMR), Japanese quail chicks exhibited remarkable developmental plasticity: chicks with body masses that were 50% lower than the normal growing chicks did exhibit a normal capacity of thermogenic heat production for their mass. Because no differences were found with respect to the level of plasticity of morphological and physiological development between the two strains, we conclude that the selection for high postnatal growth rates in P-strain chicks has not resulted in a in a higher vulnerability of these chicks to food restrictions.     

Effects of photoperiod and food availability on growth, leptin, sexual maturation and maintenance in the Mongolian gerbils (Meriones unguiculatus)

Reproductive activity of Mongolian gerbils is regulated by photoperiod nevertheless body weight regulation is controlled without ambient photoperiod. Food intake is a major factor affecting rodent reproductive efficiency. Leptin is a hormone secreted by adipose tissue and modulates food intake, energy expenditure and body fat stores. In this study we studied the interaction of photoperiod and food availability on growth, sexual maturation and leptin concentration in the male and female gerbils. Gerbils were gestated and reared in either 14L:10D or 2L:22D. At weaning, gerbils were housed individually and divided into three groups: fed ad libitum, fed 80% of ad libitum or fed 60% of ad libitum. Body weights were recorded at weaning and every week thereafter. After twelve weeks of treatment, animals were sacrificed and testes and uterine weights were determined and blood was collected for leptin measurement. Food restriction reduced body weight and inhibited reproductive development. Absolute paired testis weights were similar in ad lib and 80% of ad lib groups but significantly different compared with the 60% of ad lib group in both photoperiods. Body weights were also directly dependent upon the level of food restriction. Uterine mass was only affected in the 60% of ad lib group in 14L but both food restriction levels significantly affected the uterine weights in 2L. Significant variations were found in leptin profiles. Leptin concentration was highest in ad lib and 80% of ad lib groups and lowest in 60% of ad lib groups. These results suggest that the reproductive activity of Mongolian gerbils is sensitive to food intake and multiple potential environmental cues (e.g., food availability, temperature) can be utilized.     

Milk composition and growth in wild and captive Tasmanian bettongs,<Emphasis Type="Italic"> Bettongia gaimardi</Emphasis> (Marsupialia)

Changes in milk composition (total solids, carbohydrate, protein, lipid and calculated gross energy content) during lactation in three groups of Tasmanian bettongs ( Bettongia gaimardi): free-living animals (wild group), captive animals offered a diet of dry dog food and apples ad libitum (ad lib group), and captive animals fed restricted amounts of the same diet (maintenance group) were related to growth rates (measured as body mass and head length) of their young. There were no significant differences in the concentration of milk solids among the three groups, but the wild group had higher lipid concentrations and the maintenance group had higher carbohydrate but lower protein concentrations. For all three groups, milk total solids increased through lactation from ca. 25% to ca. 45% and carbohydrate concentrations decreased from ca. 18% to about 3%. Protein concentrations increased from ca. 5% to ca. 10% in the wild and ad lib groups, but only from 4% to 8% in the maintenance group. Lipid concentrations increased in the wild and ad lib groups from ca. 4% to ca. 18%, but in the maintenance group only to ca. 7%. Calculated gross energy content of milk increased through lactation in the wild and ad lib groups (from ca. 500 kJ.100 ml(-1) to ca. 1,000 kJ.100 ml(-1)), but there was no significant increase in the maintenance group. The volume of milk produced increased to a peak just prior to permanent pouch vacation by the young, when the gross energy output in milk was 120-150 kJ.3 h(-1) in the wild and ad lib groups. On a daily basis this is equivalent to the milk energy output of larger wallabies, and helps to explain the relatively high growth rates of young Tasmanian bettongs. There were significant differences in growth rates among the groups, with the heaviest young always in the ad lib group. Thus differences in milk composition resulting from different planes of nutrition can lead to differences in growth rates of marsupial young.     

Water, electrolyte and nitrogen balances of fat sand rats (Psammomys obesus) when consuming the saltbush Atriplex halimus

The fat sand rat (Psammomys obesus), a diurnal gerbillid rodent, is able to thrive while consuming only the saltbush Atriplex halimus. This plant has a high ash, nitrogen and water content but low energy yield. We measured the electrolyte, nitrogen (N) and water balances of fat sand rats in captivity when they were offered only A. halimus.
The fat sand rats scraped the outer layers of A. halimus leaves before consuming them. This removed 14.3% to 19.6% of the ash content of the leaves, and thus substantially reduced the electrolyte intake of the fat sand rats. Total urine osmolality ranged between 2739 and 3098 mOsm/kg, with Na+, K+ and CI - comprising 74.3% to 82.5% of the total osmolytes, percentages much higher than those usually found in desert rodents. Water intake was relatively high compared to other rodents because of the high water content of A. halimus. Evaporative water loss averaged approximately 50% of the total water output. Nitrogen requirements were easily fulfilled, even when the fat sand rats did not meet their energy requirements because of the high N content of the plant. Metabolic faecal nitrogen was 70.5 mg-kg-' 75.d-', endogenous urinary nitrogen was 171.9 mg. kg-0'75 d-' and minimal N requirements were 242.3 mg.k g-75d -1 . Minimal N requirements for the fat sand rats were approximately 98% of that expected for a eutherian mammal of its body mass.
It was concluded that fat sand rats can maintain water, electrolyte and nitrogen balances when consuming only A. halimus without producing highly concentrated urine. This is due, in part, to their ability to remove much of the electrolytes before consuming the plant and by producing urine of which Na+, K+ and C1- comprise a large percentage of the total osmolytes.     

Energetic challenges unmask the role of ovarian hormones in orchestrating ingestive and sex behaviors

Effects of ovarian hormones on sex and ingestive behavior are well studied, and yet, their role in diverting attention from food to sex has not been examined directly, possibly because these functions are masked under conditions of excessive food abundance typical of the laboratory. Female Syrian hamsters were either fed ad libitum or food-restricted to 75% of their ad libitum intake for 8 days and then tested every day of the estrous cycle for their preference for males versus food, food hoarding and food intake in an apparatus designed to mimic aspects of their natural habitat. The food-restricted, but not the fed females, varied significantly over the estrous cycle in appetitive behaviors, which included their preference for males versus food and in the amount of food hoarded, with low food hoarding and high male preference on the night of ovulation. In contrast, there were no significant differences between restricted and ad libitum-fed females in the consummatory behaviors, namely, food intake or lordosis duration. In ovariectomized females, estradiol plus progesterone treatment delayed food restriction-stimulated hoarding and hastened feeding-inhibited hoarding without affecting food intake or lordosis duration. In summary, energy restriction and the presence of males unmasked an effect that was obscured in the normal laboratory conditions characterized by isolation and an over abundance of readily available food. These results are consistent with the idea that ovarian hormones orchestrate appetites for food and sex to optimize reproductive success under fluctuating energetic conditions.     

Dietary protein content alters energy expenditure and composition of the mass gain in grizzly bears (Ursus arctos horribilis)

Many fruits contain high levels of available energy but very low levels of protein and other nutrients. The discrepancy between available energy and protein creates a physiological paradox for many animals consuming high-fruit diets, as they will be protein deficient if they eat to meet their minimum energy requirement. We fed young grizzly bears both high-energy pelleted and fruit diets containing from 1.6% to 15.4% protein to examine the role of diet-induced thermogenesis and fat synthesis in dealing with high-energy-low-protein diets. Digestible energy intake at mass maintenance increased 2.1 times, and composition of the gain changed from primarily lean mass to entirely fat when the protein content of the diet decreased from 15.4% to 1.6%. Daily fat gain was up to three times higher in bears fed low-protein diets ad lib., compared with bears consuming the higher-protein diet and gaining mass at the same rate. Thus, bears eating fruit can either consume other foods to increase dietary protein content and reduce energy expenditure, intake, and potentially foraging time or overeat high-fruit diets and use diet-induced thermogenesis and fat synthesis to deal with their skewed energy-to-protein ratio. These are not discrete options but a continuum that creates numerous solutions for balancing energy expenditure, intake, foraging time, fat accumulation, and ultimately fitness, depending on food availability, foraging efficiency, bear size, and body condition.     

Nutrition and energetics of the canary (Serinus canarius)

Canaries appear to be primarily seed-eaters, although there are no reports of their feeding ecology in the wild. In captivity, they are offered seed-based diets, preferring to consume seeds such as canary, rapeseed and millet. The mean daily dry-matter intake ranges from 3 to 4 g, which corresponds to a mean gross energy intake of approximately 70 kJ per bird per day. The efficiency of dietary metabolism is high (0.85), which equates to individual metabolizable energy intakes of 45-75 kJ per bird per day. For a canary of average body weight (22 g) the data can be fitted to a regression equation to predict a requirement of 62 kJ ME per day. This corresponds to published information on the energy requirements of other passerine species, but deviates from the predictive equation for poultry. The digestibility values for protein, fat and carbohydrate are similar to those obtained for the budgerigar, although it is likely that the digestibility coefficient is dependent upon the seed type and alimentary tract lipase and amylase activities. Nutrient requirements of canary chicks have not yet been determined, although recent studies have provided data on the nutrient intakes of developing chicks. The newly-hatched canary chick has a rapid growth rate, achieving 90% of its asymptotic body mass by 11 days of age. Gross energy intake is approximately 3 kJ per day following hatching and by day 10 is equivalent to that of an adult canary. It appears that the protein intake should lie between 16.5 and 21.9% of the diet (as is), with peak intake occurring between 8 and 10 days of age.     

Selective Leptin Insensitivity and Alterations in Female-Reproductive Patterns Linked to Hyperleptinemia during Infancy

The dramatic increase in the prevalence of childhood obesity worldwide makes the investigation of its early developmental stages and effective prevention strategies an urgent issue. CCK₁ deficient OLETF rats are a model of obesity previously used to study the early phases of this disorder. Here, we exposed wild type (LETO) females to an early obesogenic environment and genetically obese OLETF females to a lean postnatal environment, to assess long term alterations in leptin sensitivity, predisposition to diet induced obesity and adult female health. We found that genetically lean females reared by obese mothers presented early postnatal hyperleptemia, selectively reduced response to leptin and sensitivity to diet induced obesity when exposed to a high palatable diet as adults. The estrous cycle structure and intake profile were permanently disrupted, despite presenting normal adiposity/body weight/food intake. Genetically obese females reared by lean dams showed normalized early levels of leptin and reduced body weight, food intake and body fat at adulthood; normalized estrous cycle structure and food intake across the cycle, improved hormonal profile and peripheral leptin sensitivity and a remarkable progress in self-control when exposed to a high fat/palatable diet. Altogether, it appears that the early postnatal environment plays a critical role in determining later life coping with metabolic challenges and has an additive effect on the genetic predisposition that makes OLETF females morbidly obese as adults. This work also links, for the first time, alterations in the leptin system during early development to later life abnormalities related to female reproduction and health.     

Food restriction and refeeding in growing rats.

1. The interrelationship between food intake, body weight and oxygen consumption was analysed at 25 degrees C in growing rats. 3. The experiment was divided into two phases lasting four weeks each. During the first phase the animals were subjected to energy restriction and during the second phase they were allowed ad lib energy intake. Four groups of rats were studied: Control with ad lib food intake and three restricted groups R4, R5, and R6 which received during the first phase 4, 5, and 6 g per day of stock diet in a single meal. 3. The results showed a decrease in body weight and oxygen consumption during the restriction period and a recovering of the latter during the refeeding period, without body weight recovering. 4. It is concluded that an energy conservation mechanism is present during food restriction and for some time after refeeding.     

Peripheral oxytocin in female baboons relates to estrous state and maintenance of sexual consortships

The neuro-hypophysial hormone oxytocin (OT) has been implicated in female reproductive and maternal behaviors and in the formation of pair bonds in monogamous species. Here we measure variation in urinary OT concentrations in relation to reproductive biology and socio-sexual behavior in a promiscuously breeding species, the chacma baboon (Papio hamadryas ursinus). Subjects were members of a habituated group of baboons in the Okavango Delta, Botswana. We collected behavioral data and urine samples from n = 13 cycling females across their estrous cycles and during and outside short-term, exclusive sexual consortships. Samples were analyzed via enzyme immunoassay (EIA) and we used linear mixed models (LMM) to explore the relationship between peripheral OT and a female's estrous stage and consortship status, her previous reproductive experience and fertility. We also used a Pearson's correlation to examine the relationship between OT concentrations of consorting females and their extent of behavioral coordination with their consort partners. The results of the LMM indicate that only estrous stage had a significant influence on OT levels. Females had higher OT levels during their periovulatory period than during other stages of their estrous cycle. There were no differences in the OT levels between consorting and non-consorting periovulatory females. However, among consorting females, there was a significant positive relationship between urinary OT levels and the maintenance of close proximity between consort partners. Our results suggest that physiological and behavioral changes associated with the initiation and maintenance of short-term inter-sexual relationships in baboons correspond with changes in peripheral OT.     

The responses of rats to various combinations of energy and protein. II. Diets made from natural ingredients

Natural diets with metabolizable energy levels of 8.5, 10.0, 11.5 or 13.0 MJ/kg and protein:energy ratios of 1:1, 1.33:1, 1.67:1 or 2:1 %:MJ/kg were fed ad libitum for 28 days to male and female weanling rats. Records of food intake and bodyweight were maintained weekly, and at post mortem examination body length, abdominal fat, liver and kidney weights were measured. Food intake was reduced when dietary energy level increased but this reduction was not sufficient to prevent energy intake increasing, especially in males. Female rats showed only small increases in energy intakes as dietary energy levels rose. The increase in energy intake at higher dietary energy levels increased food conversion efficiency, weight gain and abdominal fat deposition. The responses of male rats were greater than females. Protein intake had a smaller and less consistent effect than energy intake. Increased protein:energy ratio resulted in higher absolute and relative liver and kidney weights and greater body length. This reflected the increase of bodyweight gain at higher protein:energy ratios.     

15N-Harnstoffumsatz bei Schafen nach Verabreichung in gelöster Form

Two slaughter experiments were carried out to determine whether the protein content of the diet has an influence upon the efficiency of utilization of ME in fast growing chickens. A normal‐protein diet (NPD, 204 g CP/kg DM; 14.7 MJ ME/kg DM) based on soybean meal as the sole source of protein was given at four different levels of intake (ad libitum or restricted at about 90, 65 and 40% ad lib) to 10‐d‐old animals for 2 weeks. In a parallel experiment the chickens were fed ad libitum a low protein diet (LPD, 66 g CP/kg DM; 15.0 MJ ME/kg DM) based on soybean meal. The intake of metabolizable energy ranged from 1675 to 777 and 1770 to 832 kJ/kgW^0.75 per day for NPD and LPD treatments, respectively. Mean values of energy retention, gross efficiency of energy utilization and energy retained as protein were significantly (P<. 05) lower and heat production (expressed as both kJ/kgW^0.75 per day and kJ/kg body protein content^0.75 per day) was significantly higher (P < .05) for the chickens fed on LPD. These findings support the concept of dietary‐induced thermogenesis in response to reductions in dietary protein concentration. It is concluded that the increased heat production found in the birds fed on the low‐protein diet can be explained by both an increase in energy requirements for maintenance (ME_m) and a sharp decrease in the efficiency of utilization of ME for growth (k₈).     

Effect of salinity on hatching, survival and infectivity of Anguillicola crassus (Nematoda: Dracunculoidea) larvae

The effect of salinity on hatching, larval survival and infectivity of Anguillicola crassus was studied under experimental conditions using eggs obtained from naturally infected eels. Egg hatching rate, second-stage larval survival and larval infectivity were maximal in fresh water and declined with increase in salinity. Larvae survived up to 100 d in fresh water, 70 d in 50 % sea water and 40 d in 100% sea water. Infectivity experiments demonstrated that salinity influenced transmission success throughout the life cycle by decreasing total infectivity of the larval population in utero within female A. crassus and when larvae were free-living in the aquatic environment. Infectivity was age-dependent in relation to salinity. Larvae were infective to intermediate and paratenic hosts for up to 80 d in fresh water, 21 d in 50% sea water and up to 8 d in 100% sea water. The data confirm field observations that infection levels decrease with an increase in salinity. The study contributes to experimental verification of the colonization abilities of A. crassus and supports the hypothesis that A. crassus can be disseminated and transmitted in brackish water. The importance of regular monitoring and stringent hygiene practices in the transportation of eels is emphasized.