Performance and immune response of suckling calves fed organic selenium

The objective of this research was to explore whether supplementation of Se above the recommended levels or application directly to the abomasum is superior to rumen supplementation in terms of boosting the immune system and promoting the growth of suckling calves. Thirty newborn calves, 18 Jersey breed and 12 crossbred (Holstein × Jersey), during 75 days, were assigned in a randomized block design (sex and breed) with the following treatments C = control (no supplementation and selenium derived only from milk and concentrate); SeA = 0.80 mg of Se/animal per day to the abomasum (milk); and SeR = 0.80 mg of Se/animal per day to the rumen (oral). The blood concentration of Se was higher in the SeR- and SeA-treated animals than in the control animals (P = 0.001) at 30 days of age. The phagocytic activity of macrophages was higher in animals receiving Se supplementation compared to the control and in SeA animals compared to SeR (P = 0.007). No difference in the oxidative activity of neutrophils or hematocrit was observed among treatments regimes when the calves were 30 days old. Dry matter intake (P = 0.059) and HGG (P = 0.059) tended to be higher in SeR-treated animals than in SeA-treated animals at 30 days of age. Feed conversion tended to be more efficient in Se-supplemented animals compared to the control (P = 0.075). There were no significant differences in WG, HG or LG among treatment regimes at 30 days of age. At 75 days of age, Se-supplemented animals tended to present higher concentrations of Se in the blood (P = 0.079) and greater heart girth gain (P = 0.088). Supplementation of suckling calves with 0.80 mg of organic Se increased the serum levels of this trace mineral in the animals and boosted their immune systems at 30 days of age. A superior immune parameter response was observed in calves supplemented with Se to the abomasum. In addition, Se supplementation maintained the performance of animals that had a diagnosis of diarrhea. Selenium supplementation did not act as a growth promoter but did improve immune system function during this phase of compromised health.