I have a site collection with the SharePoint Server Publishing Infrastructure feature enabled on the site collection and sites with the SharePoint Server Publishing site feature activated.

Go to Site Actions => Site Settings => Look and Feel => Navigation => Global Navigation.

LookandFeel.png


In the global navigation you could see the following options

GlobalNavigation.png

Programmatically Enable/Disable Global Navigation Settings


using (SPSite siteCollection = new SPSite("http://servername:1111/sites/sample"))
{
using (SPWeb web = siteCollection.RootWeb)
{
PublishingWeb publishingWeb = PublishingWeb.GetPublishingWeb(web);
// Global Navigation
//Show Subsites
publishingWeb.Navigation.GlobalIncludeSubSites = false;
//Show Pages
publishingWeb.Navigation.GlobalIncludePages = false;
// Maximum number of dynamic items to show within this level of navigation:
publishingWeb.Navigation.GlobalDynamicChildLimit = 60;

//Update the changes
publishingWeb.Update();

}
}