Review: Piglets' (Re)Feeding Patterns, Mineral Metabolism, and Their Twisty Tail

The appearance rate of nutrients into systemic circulation affects hormones like insulin and through that efficiency of growth. This also affects mineral requirements critical for metabolism, notably phosphate (P), magnesium (Mg), and potassium (K). Fasting animals have a downregulated metabolism, upon which P, Mg, and K are exported from their cells into the blood and are subsequently excreted in their urine. Abrupt resumption of feed intake, especially of highly glycemic feeds, creates an acute need for these minerals, which can result in deficiency symptoms, particularly with P deficiency. In human medicine, this is called refeeding syndrome: a large meal after a period of fasting can prove fatal. Young animals seem to be especially sensitive, likely driven by their ability to grow rapidly and thus to drastically upregulate their metabolism in response to insulin. Symptoms of P deficiency are fairly a-specific and, consequently, not often recognized. They include edema, which makes it appear as if piglets are growing well, explaining the high gain/feed rate typically seen immediately after weaning, even when piglets are eating at or below the maintenance requirements. Phosphate deficiency can also result in hypoxia and hypercarbia, which may trigger ear necrosis, Streptococcus suis infections, or even death. Hypophosphatemia can also trigger rhabdomyolysis, which may contribute to tail-biting, but this requires further study. Arguably, when fasting cannot be avoided, diets for newly weaned piglets should be formulated to avoid these problems by lowering their glycemic load and by formulating diets according to the piglets' actual requirements inspired by their genuine intake and health and not simply by extrapolating from older animals.