No indications that zinc and protein source affect Zn bioavailability in sows during late gestation fed adequate dietary Zn concentrations

• Zinc source and protein source did not affect Zn bioavailability.
• Hydrolysed feather meal showed lower apparent nutrient digestibilities.
• Zinc source did not affect faecal Zn excretion.
• No indications of spontaneous chelation of Zn.

Previous in vitro research has shown the possibility of spontaneous chelation of Zn in the presence of easily digestible protein sources. The objective of this study was to investigate the possible interaction between zinc (Zn) source and protein source on the in vivo Zn bioavailability in sows during late gestation that were fed adequate dietary Zn concentrations. Fifty-six sows were randomly allocated to one of four dietary treatment groups during a 20-day experimental period: (1) organic Zn + soybean meal, (2) inorganic Zn + soybean meal, (3) organic Zn + hydrolysed feather meal, and (4) inorganic Zn + hydrolysed feather meal. Zinc was provided at adequate dietary Zn concentrations, in which organic Zn was added as a Zn amino acid complex and inorganic Zn as ZnO. Blood samples were collected at the start (day 1) and at the end (day 20A) of the experimental period before feeding and 3 h after feeding (day 20B) to determine plasma Zn and serum metallothionein (MT) concentration. Faecal samples were collected rectally, alternately in the morning (day 15, 17, and 19) and afternoon (day 16, 18, and 20) directly after feeding to calculate apparent nutrient digestibility and apparent Zn absorption. Neither Zn nor protein source affected Zn status (plasma Zn: P = 0.288 and P = 0.237, respectively, Serum MT: P = 0.161 and P = 0.193, respectively) or apparent Zn absorption (P = 0.360 and P = 0.527, respectively). Hydrolysed feather meal showed lower crude protein, crude fat, and crude ash digestibility compared to soybean meal (P < 0.001). Faecal Zn concentration was not affected by Zn source (P = 0.442). This study did not confirm the earlier observed in vitro effect of protein source on Zn bioavailability and shows that, at adequate levels commonly used in practice, the choice of Zn or protein source does not influence Zn status.