I think Kay Carslaw recommended 9 inches / cow, and my 1980's ICI booklet I just dug out recommends at least 6 inches as long as there is 24 hr access.
Depending whether you have use for a lot of bedding muck , a set of kennels would be a cheaper and easier run than a straw yard I would think.
looking back at when we started milking here in the 70's our new 100 cow kennels made from second hand timber and tin sheeting ,cost us very little.
Dug a hole in front of the pit and kennels and scrape straight in , over the edge.
Depending whether you have use for a lot of bedding muck , a set of kennels would be a cheaper and easier run than a straw yard I would think.
looking back at when we started milking here in the 70's our new 100 cow kennels made from second hand timber and tin sheeting ,cost us very little.
Dug a hole in front of the pit and kennels and scrape straight in , over the edge.