Humoral Immune Response in Beef Heifers Supplemented with Mineral Salt with or Without the Addition of Rumen-Protected Methionine

The aim of this study was to evaluate the humoral immune response in beef heifers supplemented with mineral supplementation with or without the addition of rumen-protected methionine. Forty-eight Brangus nulliparous heifers were distributed into four experimental groups with three replications each: control group without supplementation and without vaccination (CG01), control group without supplementation and with vaccination (CG02), treatment group with mineral supplementation and vaccination (TG01), and treatment group with mineral supplementation added with protected methionine and vaccination (TG02). The animals were maintained under native pasture with access to water ad libitum and the supplementation was available in high-consumption covered troughs. A supplementation period of 60 days prior to vaccinations was adopted until the first dose of a monovalent experimental vaccine inactivated for BoHV-5 was applied as a method of stimulating the immune response to evaluate the supplementation effects. After a 21-day interval, blood samples were collected to evaluate the humoral response and the second vaccine booster dose was applied following the 21-day interval for new blood samples in order to evaluate the immune response against the two-vaccination protocol. From the beginning of the experiment, the animals were weighed on the days ?60, ?10, 0, 21, and 42 in relation to the vaccine protocol. The experimental groups did not differ for body weight, mean daily weight gain, and body condition score after 102 days of supplementation regardless of the treatment. No animals belonging to CG01 seroconverted throughout the experiment, proving that there was no introduction of the agent (BoHV) in the studied area. When vaccinated animals were compared to the CG01 control group, statistically higher levels of neutralizing antibodies (P ? 0.0001) and IgG (P ? 0.0001) were verified 21 days after the second vaccine dose. Among the animals of the three vaccinated groups, there was no difference in seroconversion and IgG production. Therefore, no benefits of mineral supplementation or enriched with protected methionine were observed for the humoral immune response of the studied animals.