Multiple tags on web pages
You can install multiple instances of the Analytics tag on your web pages to send data to multiple properties in your account.
Not all configurations are supported. You can, for example, install multiple instances of the Universal Analytics tag (analytics.js) on your web pages but only one instance of the Classic Analytics code (ga.js). Multiple instances of ga.js might result in inaccurate data collection, processing, or reporting. You can, however, install one or more instances of analytics.js on web pages that also have a single instance of ga.js.
Using multiple tags might be useful if users with access to different properties need to see data from the same web site, or if you have multiple versions of a web site. You might, for example, want to collect data from example.com using one instance of analytics.js, collect data from example.co.uk in another instance of analytics.js, and use a third instance of analytics.js on both websites to see the aggregate data.
Read Working with multiple tracking objects for information on implementing multiple instances of the tag with the analytics.js library.