The relationship between mineral and nitrogen balances in growing pigs fed diets supplemented with zinc oxide

The present study was conducted to determine if there were effects of increasing levels of dietary zinc supplementation on the turnover of zinc and other minerals and trace elements in growing pigs. Thirty crossbred female pigs, with an initial body weight of approximately 25 kg, were randomly assigned to five diets with increasing levels of supplemented zinc (as zinc oxide); i.e. from the intrinsic level of 42 mg kg(-1) diet to 72, 105, 170, and 255 mg kg(-1), respectively. The animals were subjected to Mio 7-d balances in metabolic cages, separated by 15 d in pens. Balances consisted of controlled feed intake, i.e. approximately 10% below the expected ad libitum intake, and quantitative collection of feces and urine. Zinc supplementation did not affect nitrogen absorption, excretion, or retention (P > 0.05). The inclusion of zinc oxide did not affect (P > 0.05) weight gain of the animals throughout the 34 d experiment. Neither mineral nor trace element balances, except for zinc, were affected (P > 0.05) by zinc supplementation. Urinary excretion of zinc was not affected (P > 0.05), but zinc absorption and retention calculated in absolute amounts or in proportion to nitrogen retention (i.e. lean body accretion) increased several-fold when diets were supplemented with zinc oxide. Mineral and trace element absorption in proportion to nitrogen retention appeared remarkably constant throughout the experimental period, although feed intake and body size increased with time. Only calcium absorption and retention, determined in proportion to nitrogen retention and as fractions of ingested calcium increased (P < 0.001), 14 and 9%, respectively, with time. In general, mineral and trace element absorption and retention, expressed in proportion to nitrogen retention, appear to be a useful expression for comparisons between observations across time intervals.