How to Specify MDC Field Type with SLF4J MDC With Logback?

I'am using SLF4J MDC (using logback as logging framework) like below:

MDC.put("numericField", Long.valueOf(500).toString());
log.info("Testing MDC");
MDC.clear();

But when I send these logs to elasticsearch via filebeat (without using logstash), I get this field as text. How can I have numeric fields in Kibana for some specific fields with using logback MDC? If it is possible with configuration change (in logback or filebeat configuration) it will also solve the problem.