Nutritional interactions with reproduction in birds

Circulating nutrient concentrations in free-ranging Humboldt penguins (Spheniscus humboldti) in Punta San Juan, Peru

Free-ranging Humboldt penguin (HP, Spheniscus humboldti) populations are under pressure from resource competition with industrial fisheries, habitat loss, and El Niño Southern Oscillation events. Foraging patterns for this top marine predator change during periods of aberrant oceanographic conditions and scarce fish stock numbers. These radical dietary fluctuations can lead to poor fertility, early embryonic death, poor hatchability, suppressed immune function, high chick mortality, and illness. To understand the variability of nutrient status in reproductive seasons, we measured select circulating nutrient concentrations (fat-soluble vitamins A, D, E, and carotenoids, fatty acids, amino acids, minerals, and electrolytes) of 105 HP at Punta San Juan, Peru during the first reproductive seasons of 2007 and 2008. We determined significant differences in nutrient status between sexes, years of sampling, and reproductive stages. Males (4.5 ± 0.38 kg) weighed more than females (4.0 ± 0.29 kg) and exhibited higher concentrations of vitamin A (0.71 ± 0.11 vs. 0.61 ± 0.12 µg/ml) and docosahexaenoic acid (6.70 ± 1.61 vs. 5.65 ± 1.59%). Males also displayed lower concentrations of β-carotene (0.01 ± 0.01 vs. 0.012 ± 0.001 µg/ml) and phosphorus (3.43 ± 0.83 vs. 4.40 ± 1.66 mg/dl). Comparison between the 2 years showed most circulating amino acid concentrations were higher in 2007. Significant differences in circulating amino acids and vitamins were also noted between different reproductive stages. These results demonstrate concentrations of nutrients can vary due to the physiological state of the animal, as well as the overall dynamics of their marine ecosystem habitat.

Chicken Is a Useful Model to Investigate the Role of Adipokines in Metabolic and Reproductive Diseases

Reproduction is a complex and essential physiological process required by all species to produce a new generation. This process involves strict hormonal regulation, depending on a connection between the hypothalamus-pituitary-gonadal axis and peripheral organs. Metabolic homeostasis influences the reproductive functions, and its alteration leads to disturbances in the reproductive functions of humans as well as animals. For a long time, adipose tissue has been recognised as an endocrine organ but its ability to secrete and release hormones called adipokines is now emerging. Adipokines have been found to play a major role in the regulation of metabolic and reproductive processes at both central and peripheral levels. Leptin was initially the first adipokine that has been described to be the most involved in the metabolism/reproduction interrelation in mammals. In avian species, the role of leptin is still under debate. Recently, three novel adipokines have been discovered: adiponectin (ADIPOQ, ACRP30), visfatin (NAMPT, PBEF), and chemerin (RARRES2, TIG2). However, their mode of action between mammalian and nonmammalian species is different due to the different reproductive and metabolic systems. Herein, we will provide an overview of the structure and function related to metabolic and reproductive mechanisms of the latter three adipokines with emphasis on avian species.

The insulin sensitiser metformin regulates chicken Sertoli and germ cell populations

Metformin, an insulin sensitiser from the biguanide family of molecules, is used for the treatment of insulin resistance in type 2 diabetes individuals. It increases peripheral glucose uptake and may reduce food intake. Based on the tight link between metabolism and fertility, we investigated the role of metformin on testicular function using in vitro culture of Sertoli cells and seminiferous tubules, complemented by in vivo data obtained following metformin administration to prepubertal chickens. In vitro, metformin treatment reduced Sertoli cell proliferation without inducing apoptosis and morphological changes. The metabolism of Sertoli cells was affected because lactate secretion by Sertoli cells increased approximately twofold and intracellular free ATP was negatively impacted. Two important pathways regulating proliferation and metabolism in Sertoli cells were assayed. Metformin exposure was not associated with an increased phosphorylation of AKT or ERK. There was a 90% reduction in the proportion of proliferating germ cells after a 96-h exposure of seminiferous tubule cultures to metformin. In vivo, 6-week-old chickens treated with metformin for 3 weeks exhibited reduced testicular weight and a 50% decrease in testosterone levels. The expression of a marker of undifferentiated germ cells was unchanged in contrast to the decrease in expression of ‘protamine’, a marker of differentiated germ cells. In conclusion, these results suggest that metformin affects the testicular energy content and the proliferative ability of Sertoli and germ cells.

Reproduction (2016) 151 527–538

Is There Peripheral or Ovarian Insulin Action Alteration in Broiler Breeder Hens Fed ad Libitum?

We investigated whether a change in peripheral glucose homeostasis, a local change in the insulin-related ovarian regulatory system, or both occurred in ad libitum-fed broiler breeder hens compared with feed-restricted counterparts. Feed-restricted (R, from 5 to 16 wk of age) and ad libitum-fed (A) hens from a standard commercial line (S) and an experimental dwarf genotype (E) were studied. Basal and stimulated plasma insulin and glucose concentrations were measured during the prebreeding and laying periods. In the basal state (after 16 h fasting) plasma glucose concentrations were significantly lower in SA chickens (-5% at 17 wk, -7.5% at 32 wk) compared with EA, SR, and ER chickens, with no difference in plasma insulin concentrations (n = 16). In 17-wk-old SA birds, 30 min after oral glucose loading, plasma glucose concentrations increased significantly compared with the basal state and were also significantly lower as compared with SR but did not differ significantly from EA and ER. Plasma insulin concentrations did not differ significantly between genotypes or regimens (n = 16). A potential modification of intracellular mediators involved in the regulation of cell growth and survival in small follicles that were overrecruited in SA compared with SR was also investigated in SA and SR hens at 32 wk. There was no effect of food restriction in phospho-Akt, Akt, phospho-ERK, and phospho-S6 in the small white ovarian follicles (n = 6) in the basal state and after 30 min of refeeding. In conclusion, the present study does not demonstrate any evidence of glucose intolerance during the prebreeding period, specific change in the ovarian small follicle insulin signalling pathway, or both, in laying broiler breeders fed ad libitum compared with feed-restricted hens.

Physiology of intermittent feeding: integrating responses of vertebrates to nutritional deficit and excess

Food intakes of wild animals may not match their requirements for nutrients and energy but may vary between periods of nutritional excess (hyperphagia) and nutritional deficit (hypophagia) at timescales that vary from days to months. We present a simple model of feeding patterns and requirements of vertebrates. Frequent fasts and high intakes are typical of endothermic predators and migratory birds, whereas slow cycles and long deficits typify feeding patterns of ectothermic predators and ungulates in seasonal environments. We propose that hyperphagia is constrained by the ability to increase processes of digestion, absorption, intermediary metabolism, net deposition in tissue, and excretion to match loads of digesta and metabolites. Hyperphagia on high-quality diets is limited by the clearance of metabolites, whereas digestive tract capacity and flow limit consumption of low-quality diets. Of all digestive strategies, small omnivores with simple digestive systems may be the most tolerant of frequent hyperphagia. Tolerance of hypophagia favors large endogenous stores or low mass-specific rates of metabolism and reproductive output. Large animals may be most able to sustain reproduction during prolonged deficits in seasonal environments. Responses to excessive and deficient intakes of food are constrained by the length of the feeding cycle. Animals adapted to short feeding cycles may be best suited to unpredictable food supplies but at the energetic cost of maintaining spare capacity for digestion and absorption. Predictions of the response to food disruption are best evaluated in the context of body size, nutritional physiology, and life history of the species and the time for internal response.

Effect of method and phase of nutrient restriction during rearing on productive performance of light hybrid pullets and hens

1. An experiment was conducted to study the effect of method (low-lysine or quantity of food) and phase (starter or grower) of restriction during rearing on growth and laying performance in Leghorn hybrids. 2. A reduction in body weight gain was achieved by feeding pullets a low-lysine diet in either the starter phase (0-6 weeks of age: 4.0 g/kg digestible lysine) or the grower phase (7-18 weeks of age: 3.0 g/kg digestible lysine). 3. In each phase, the lysine restriction was compared with a daily food restriction, in which pullets received a quantity of food sufficient to pair-gain with their lysine-restricted counterparts. 4. The delay in onset of production was greatest in the lysine-restricted birds, for both phases of restriction. 5. Hens restricted during the grower phase laid heavier eggs than those restricted during the starter phase, despite having similar body weights at end of rearing. This effect was not influenced by the restriction method. 6. Production traits varied between pullets reared on different feeding strategies up to similar body weights at 18 weeks and onwards. It is concluded that body weight is not the only factor determining laying performance.