Organic zinc sources in broiler production at high altitude under on-top supplementation or total or partial replacement: 2. Effects on tibia and blood characteristics

The use of organic Zn sources has been claimed to reduce the environmental impact of poultry production and improve broiler performance and the quality of products. This study investigated the effects of three organic Zn supplementation strategies (i.e., TRE, total replacement; PRE, partial replacement; OTS, on-top supplementation) on tibia and blood biochemistry characteristics of broilers at high altitudes. Male Cobb 500 chicks were distributed in 54 floor pens (22 birds each) and assigned to nine experimental treatments. Birds were fed mash diets under three feeding phases until 42 days and following the standard Ecuadorian high-altitude production standard practices. The treatments were a basal diet supplemented with three inclusion rates of ZnSO₄ and the same diets including or not Zn from one of two organic Zn sources (i.e., ZPR, Zn proteinate; ZAC, Zn amino acid complex). Basal diets were analyzed for Zn concentration. Tibia ash and Zn concentrations and serum biochemistry variables were determined at 21 and 42 days. The strategies to supplement organic Zn were compared with the reference treatment containing 100 ppm Zn as ZnSO₄ (the standard practice; STD) using mixed models, being the block (i.e., the replication) as a random factor. The interaction of the strategy with the organic Zn source was assessed with the ANOVA and multiple comparisons. The organic Zn sources were compared considering the feed intake a random factor, and their interaction with the dietary Zn level was assessed using multiple regression. No overall effect of the Zn supplementation strategy was observed other than the reduced Zn concentration at 21 days in TRE birds. At 21 days, PRE and TRE increased the serum protein and phosphorus concentrations, respectively. At that age, TRE also increased insulin concentration, but only in the ZAC-fed birds. However, TRE produced the opposite effect on serum protein at 42 days. At the same age, ZAC-fed birds showed lower serum phosphorus concentration than ZPR-fed ones regardless of the dietary Zn supplementation level or the Zn intake. Also, ZAC under TRE produced no effect on tibia Zn concentration compared to STD, but ZPR increased it. The ZPR increased the tibia Zn concentration when fed under PRE or TRE, but not under OTS. In conclusion, the results showed no adverse effect of PRE or TRE strategies on tibia characteristics. The data indicate likely different effects of PRE and TRE on protein metabolism and a possible negative interaction of the organic Zn with a high Zn content as ZnSO₄.