Effects of reduced levels of organic trace minerals in proteinate forms and selenium-yeast in the mineral mix on lactation performance, milk fatty acid composition, nutrient digestibility and antioxidant status in dairy goats

The objective was to evaluate the effects of replacing inorganic trace minerals (ITM) with reduced levels of organic trace minerals (OTM) in proteinate forms and selenium yeast (Se-yeast) in the mineral premix of prepartal and lactating dairy goats on lactation performance, milk fatty acid (FA) composition, nutrient digestibility, and antioxidant status. Xinong Saanen dairy goats (n = 40) were blocked by parity and body weight, and randomly assigned to either ITM or OTM treatments from 4 wk prepartum to 8 mo of lactation. Both groups received the same basal diet except for the trace mineral supplement. The ITM supplement included Fe, Cu, Zn, and Mn as sulfates, and Se as selenite to meet the recommendations. The OTM supplement included Fe, Cu, Zn, and Mn as proteinates at 50% of ITM supplement levels, and Se as Se-yeast at 100% of ITM supplement level. Sampling and measurements were performed in the first, second, fourth, and eighth month of lactation. Data were summarized by month and treatment, and analyzed using the Mixed Model of SPSS with repeated measures. OTM group showed lower milk fat (P = 0.02) and higher milk Se (P = 0.03) with no compromised effects on milk yield and milk protein compared to ITM group. Furthermore, OTM decreased the content of C6:0, C8:0, and C10:0 (P < 0.05) and increased the content of odd- and branched-chain FAs in milk fat due to greater content of C15:0 (P = 0.01) and anteiso C15:0 (P = 0.07). OTM led to greater total tract digestibility of dry matter (P = 0.03), crude protein (P = 0.07), ether extract (P = 0.03), and acid detergent fiber (P = 0.05). OTM goats showed less fecal excretion of Fe (P = 0.01), Cu (P < 0.01), and Zn (P = 0.08) compared to ITM goats. There was a tendency for greater serum GSH-Px activity (P = 0.09) with OTM. Overall, the long-term substitution of reduced levels of OTM for ITM can change milk fat and FA composition while maintaining milk yield, digestibility, and antioxidant status.