79 Effect of source and dietary concentration of trace minerals on serum mineral status, ruminal pH, and ruminal volatile fatty acids in lactating Holstein dairy cows

Abstract

Abstract Inorganic sources of trace minerals are commonly supplemented in dairy cow diets; however, there has been an increase in the supplementation of minerals complexed with organic compounds. These organic trace minerals are thought to have greater bioavailability which may enhance rumen fermentation and absorption. The objective of this study was to assess the effects of dietary concentration and source of supplemental trace minerals on serum trace mineral status and rumen fermentation. Six lactating Holstein cows were used in a 6 x 6 Latin square design with a 23-day adaptation and 5-day experimental period. Cows were fed the same basal diet daily except for the difference in source [organic (ORG) versus inorganic (INO)] and concentration (50%, 100%, and 200% based on NRC recommendations) of trace mineral supplemented. During the experimental period feed intake and blood were collected daily. Rumen fluid was collected on the final two days of the experimental period. Data was analyzed with PROC MIXED in SAS 9.4. Dry matter intake (18.1 ± 0.70 kg), serum mineral concentrations (Cu, Mn, Se, and Zn), and rumen pH (6.5 ± 0.64) did not differ among the treatments. However, serum concentration of Co was higher in 200% ORG compared to 50% and 100% INO and 50% ORG. Ruminal concentration of acetate was higher in 50% and 100% ORG compared to 200% ORG. Butyrate ruminal concentration was higher at 50% ORG compared to 200% ORG. Ruminal propionate concentration was higher in 50% INO and 50% ORG compared to 100% INO and 200% ORG. These findings demonstrate serum trace mineral status and ruminal pH are not tightly controlled by the source of trace minerals when supplemented at 50%, 100% and 200% of the NRC recommendations, however rumen fermentation may be affected by the dietary concentration of trace minerals in the diet.