Layer feed should not be started before 15 to 16 weeks, in order to prevent health problems.  Here is a link which discusses this extensively.  Scroll down near the bottom for this recommendation:
 
http://www.hyline.com/aspx/redbook/redbook.aspx?s=5&p=36
	
		
			
		
		
	
				
			http://www.hyline.com/aspx/redbook/redbook.aspx?s=5&p=36
 
	 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
	 
 
		 
	 
 
		 
 
		
 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		