A link between diet and avian intestinal anatomy is generally assumed. We collated the length of intestinal sections and body mass of 390 bird species and tested relationships with diet, climate and locomotion. There was a strong phylogenetic signal in all datasets. The total and small intestine scaled more-than-geometrically (95%CI of the scaling exponent > 0.33). The traditional dietary classification (faunivore, omnivore and herbivore) had no significant effect on total intestine (TI) length. Significant dietary proxies included %folivory, %frugi-nectarivory and categories (frugi-nectarivory, granivory, folivory, omnivory, insectivory and vertivory). Individual intestinal sections were affected by different dietary proxies. The best model indicates that higher consumption of fruit and nectar, drier habitats, and a high degree of flightedness are linked to shorter TI length. Notably, the length of the avian intestine depends on other biological factors as much as on diet. Given the weak dietary signal in our datasets, the diet intestinal length relationships lend themselves to narratives of flexibility (morphology is not destiny) rather than of distinct adaptations that facilitate using one character (intestine length) as proxy for another (diet). Birds have TIs of about 85% that of similar-sized mammals, corroborating systematic differences in intestinal macroanatomy between vertebrate clades.

Although relationships between intestinal morphology between trophic groups in reptiles are widely assumed and represent a cornerstone of ecomorphological narratives, few comparative approaches actually tested this hypothesis on a larger scale. We collected data on lengths of intestinal sections of 205 reptile species for which either body mass (BM), snout-vent-length (SVL) or carapax length (CL) was recorded, transforming SVL or CL into BM if the latter was not given, and analyzed scaling patterns with BM and SVL, accounting for phylogeny, comparing three trophic guilds (faunivores, omnivores, herbivores), and comparing with a mammal dataset. Length-BM relationships in reptiles were stronger for the small than the large intestine, suggesting that for the latter, additional factors might be relevant. Adding trophic level did not consistently improve model fit; only when controlling for phylogeny, models indicated a longer large intestine in herbivores, due to a corresponding pattern in lizards. Trophic level effects were highly susceptible to sample sizes, and not considered strong. Models that linked BM to intestine length had better support than models using SVL, due to the deviating body shape of snakes. At comparable BM, reptiles had shorter intestines than mammals. While the latter finding corresponds to findings of lower tissue masses for the digestive tract and other organs in reptiles as well as our understanding of differences in energetic requirements between the classes, they raise the hitherto unanswered question what it is that reptiles of similar BM have more than mammals. A lesser effect of trophic level on intestine lengths in reptiles compared to mammals may stem from lesser selective pressures on differentiation between trophic guilds, related to the generally lower food intake and different movement patterns of reptiles, which may not similarly escalate evolutionary arms races tuned to optimal agility as between mammalian predators and prey.

Our study objective was to determine the apparent metabolizable energy (AME) and apparent ileal amino acid digestibility (AIAAD) of spirulina fed to broiler chickens and laying hens using the difference method. In both experiments, birds were either fed corn-soybean meal basal diets, containing no spirulina and formulated to provide the nutrient requirements of either broilers or layers, or fed test diets consisting of 25% spirulina and 75% of the appropriate basal diet. Titanium dioxide was added to all diets as an indigestible marker. The diets were fed to 10 replicate cages/treatment of broilers and 15 replicate cages/treatment of laying hens. The AME of spirulina for broilers was significantly lower (p < 0.05) (2368 ± 104 kcal/kg, as fed) than for laying hens (3144 ± 173 kcal/kg, as fed), suggesting bird type and age may influence energy utilization. The AIAAD of spirulina fed to broiler chickens did not differ from that of laying hens (p > 0.05), except for valine, alanine, and glycine, which were all significantly higher in laying hens (p < 0.05). Overall, the AIAAD for nonessential amino acids averaged 81.1%, with no significant difference between essential and nonessential amino acids. Differences in spirulina nutrient content cited in the literature support further research to determine the optimal inclusion of this alternative ingredient in broiler and layer diets.

Microquantity laboratory procedures (<5 mL) are often used to analyze milk from non-bovid or less common species due to limited available samples and small sample sizes, unlike the large quantities of milk needed for macroquantity (~20 mL) assays standard in the commercial dairy industry. To better understand microquantity milk laboratory analyses, quarter horse (Equus caballus) milk from North Carolina State University (females = 4, n = 43) and California Polytechnic State University (females = 4, n = 42) equine centers was compared to investigate differences in macronutrient composition from 4 to 130 days after parturition. All mares were healthy, but consumed different diets. Major milk macronutrients were measured at the Smithsonian National Zoo and Conservation Biology Institute using a microquantity analysis of ash, crude protein (CP), dry matter (DM), crude fat, sugar, and gross energy. Of the six measured nutrients, only CP and crude fat differed (p < 0.05) by location, while sugar and crude fat had differences among individual mares. Californian mares had greater fat concentration means on a dry matter basis (DMB) than the North Carolinian mares (ANCOVA, p = 0.003). North Carolinian mares had greater CP concentration means than Californian mares. These findings indicate that dietary differences and/or environmental factors may play a role in CP and crude fat milk macronutrient composition within horse breeds. However, despite the differences noted, the microquantity analyses for nutritional means for all eight mares were within macroquantity horses ranges available in the previous literature. The results indicate that micro versus macroassays are comparable and supports clinical and scientific research on milk from species where large sample quantities are difficult to obtain.

The egg industry continues to search for alternative feed ingredients that support production efficiency, enhance egg quality, and add nutritional value. Microalgae are rich in protein, pigments, and long-chain polyunsaturated fatty acids, making them promising candidates for poultry diets. This study evaluated the effects of dietary inclusion (1 and 2%) of four microalgae species, Arthrospira platensis (Spirulina), Hydrodictyon sp., Uronema sp., and Vaucheria sp., on laying hen performance, egg quality, yolk fatty acid composition, and bone strength. Seventy-six Lohmann LSL-Lite hens (92 weeks of age) were randomly assigned to nine treatments (control diet or one of eight microalgae diets). Feed intake, egg production, egg mass, feed conversion ratio, eggshell traits, yolk color, yolk fatty acids, and tibial breaking strength were measured. Inclusion of microalgae did not negatively affect hen performance, egg quality, nor bone strength. Spirulina significantly improved egg production and egg mass (p < 0.05). Increasing levels of Spirulina, Hydrodictyon sp., and Uronema sp. enhanced yolk color (all p < 0.05), while Vaucheria sp. showed no effect (p > 0.05). Yolk fatty acid profiles were only modestly altered, with increased docosahexaenoic acid observed in hens fed Hydrodictyon and Uronema (p < 0.05). In conclusion, low-level dietary inclusion of these microalgae species appears safe for laying hens and may provide added value through improved yolk pigmentation and modest omega-3 enrichment.