On the composition of gastroliths from broiler breeders
Although aforementioned gastroliths are most commonly found in ground‐living birds, they can also be found many reptiles and a few mammals (e.g., seals and whales), and fossil records confirm their presence in extinct animals such as plant‐eating dinosaurs and marine reptiles like plesiosaurs.
The composition of gizzard stones in birds remains a problem, and its resolution has been delayed as a consequence of the approach chosen in the literature, in which the composition of the gastroliths (or other liths) from different species, for alleged analogy, has been extrapolated without direct investigation. Consequently, the expected constituents of the advocated composition would have been chitosan, glycosaminoglycans, calcite, whewellite, apatite or carbonate apatite. The presence of glycosaminoglycans and chitosan has been postulated on the basis of findings of crustaceans (Luquet et al., 2012); calcite/vaterite and apatite have been suggested due to their usual involvement in biomineralisation processes (Luquet et al., 2012; Müller, 2011; Sigel, Sigel, & Sigel, 2008) and because they are components—together with bilirubinate—of gallbladder stones (San Miguel Hernández et al., 2014); and, in the case of whewellite, because it is the most frequent component of urinary tract stones (Martín‐Gil & Represa, 1982). Nonetheless, if the location of the gizzard in the upper digestive tract is considered, a closer correspondence of the gizzard stones’ composition with the polysaccharides of the outermost layers of bezoars found in herbivorous mammals (Allred‐Crouch & Young, 1985; Martín‐Gil, Blanco‐Álvárez, Barrio‐Arredondo, Ramos‐Sánchez, & Martín‐Gil, 1995) would be expected. Unfortunately, this later model has not been contemplated.
In the study presented herein, we report the vibrational and structural analyses (by ATR‐FTIR and X‐ray powder diffraction respectively) of gizzard stones from broiler breeders.