High concentrate feed levels, with a consequent fall in the fibre content of the diet, are increasingly being offered to high genetic merit dairy cows. To improve fibre intake, small quantities of straw are often incorporated into the diet. This study was undertaken to examine the production response of dairy cows, offered a medium quality grass silage based diet together with relatively high levels of concentrate supplementation, to straw inclusion in the diet.

Forty high genetic merit dairy cows, 20 multiparious and 20 first lactation animals (PTA95 fat + protein = 41.4 and 39.7 kg respectively) were used in this study. The study consisted of four treatments, arranged in a two period (4 week duration), partially balanced change-over design trial, with first lactation and multiparious animals being blocked separately. The experimental treatments consisted of grass silage mixed with one of four levels of straw, and offered ad libitum in the form of a mixed diet.