Potential Impact of Nutritional Strategy on Noninvasive Measurements of Hormones in Birds

Abstract

The dietary preferences, gastrointestinal anatomy, digestive physiology, biochemical capabilities, and commensal microflora of a bird are collectively known as its nutritional strategy. Measurement of hormones in droppings requires an appreciation of an animal's nutritional strategy in order to optimize collection protocols, validate techniques, interpret results, and minimize variability and artifacts. Foods of animal origin, nectar, and seeds are highly digestible by relatively simple digestive tracts and result in low rates of feces production. Most frugivorous species also have simple digestive tracts, and they digest the fruit's simple sugars and proteins, but not the fiber in its pulp. Consequently, retention time of food in the digestive tract is short, and their droppings are voluminous. Herbivorous species possess enlarged ceca that house microorganisms that aid in the digestion of fibrous components of their food. Part of the digesta enters the ceca and is subjected to lengthy microbial fermentation. The rest is excluded and quickly passes through the rectum, and is quickly defecated. For measurement of hormones in droppings it appears prudent to collect only rectal feces and to avoid cecal feces. One-third of the avian families are omnivorous and consume a wide variety of foods. Their digestive strategies are highly variable and change with diet, as does the amount and composition of feces and the rate of passage.

Comparing plasma and faecal measures of steroid hormones in Adelie penguins Pygoscelis adeliae

“…This point is not as important for the measurement of baseline concentrations, but the pattern of excretion must be considered if using faecal samples to measure an acute stress response (see Scheiber et al, 2005). Additionally, the type of food consumed and the digestive physiology of the studied birds must be considered when comparing faecal hormone concentrations between species, or temporally within species in which diet may change (Klasing, 2005). In some bird species (which consume plant materials that are not easily digestible) part of the digesta is diverted into caeca for extended digestion, producing two types of faeces with differing retention times and thus hormonal concentrations (Klasing, 2005).…”

“…In some bird species (which consume plant materials that are not easily digestible) part of the digesta is diverted into caeca for extended digestion, producing two types of faeces with differing retention times and thus hormonal concentrations (Klasing, 2005). This does not apply to Adelie penguins, in which diet composition is relatively constant over time (during the summer Adelie penguins on Ross Island feed almost exclusively on two micronecktonic species, Euphausia crystallorophias and Pleuragramma antarcticum (Ainley, 2002)), and caecal digestion is absent due to their highly digestible animal prey (Klasing, 2005;Stevens & Hume, 2004). Faecal mass may also influence hormone measurement from faeces, with faecal hormone concentrations being more diluted in faecal events of larger mass relative to faecal events of smaller mass (Millspaugh & Washburn, 2004).…”

“…Additionally, the type of food consumed and the digestive physiology of the studied birds must be considered when comparing faecal hormone concentrations between species, or temporally within species in which diet may change (Klasing, 2005). In some bird species (which consume plant materials that are not easily digestible) part of the digesta is diverted into caeca for extended digestion, producing two types of faeces with differing retention times and thus hormonal concentrations (Klasing, 2005). This does not apply to Adelie penguins, in which diet composition is relatively constant over time (during the summer Adelie penguins on Ross Island feed almost exclusively on two micronecktonic species, Euphausia crystallorophias and Pleuragramma antarcticum (Ainley, 2002)), and caecal digestion is absent due to their highly digestible animal prey (Klasing, 2005;Stevens & Hume, 2004).…”

Excretion of Steroid Hormones in Rodents: An Overview on Species Differences for New Biomedical Animal Research Models

“…The use of a biological test or the so called "biologically relevant tests" (that expose an animal to a biological stressor to measure the glucocorticoids in samples) is also recommended; this ensures that the noninvasive monitoring will appropriately measure glucocorticoids in the field when animals are exposed to genuine stressors (Sheriff et al, 2011). Several reports may be useful to set up an experimental design for applying a noninvasive approach (Brown and Wildt, 1997;Wasser et al, 2000;Palme and Möstl, 2002;Buchanan and Goldsmith, 2004;Millspaugh and Washburn, 2004;Palme, 2005;Goymann, 2005;Klasing, 2005;Palme et al, 2005;Wielebnowski and Watters, 2007). Pharmacological and biological relevance tests are truly useful for validating non-invasive endocrine monitoring.…”

“…We consider that time peak excretion after radioinfusion or steroid hormone increase after gland has been stimulated is not a robust measure because there are too many sources of variation. Several variables, such as dietary preferences, gastrointestinal anatomy, digestive physiology, biochemical capabilities, and commensal microflora, called "nutritional strategy" by Klasing (2005) in birds, may affect retention time and consequently time course of excreted steroids among species and/or individuals of the same population. Besides, a different sample collection schedule also seriously affects interpretation of time course or hormonal profiles; collecting naturally all voided urine or feces is advisable, as it has been observed in many reports.…”