Thirty six lactating cows were used in a trial where low quality maize straw was used as a roughage source in complete diets. The effects of fineness of roughage and concentrate to roughage ratio on milk production and milk composition were studied. An increase in concentrate percentage (35 – 65 per cent) and a decrease in screen size (19 – 6 mm) increased milk production. Different quantities of milk were produced for each concentrate to roughage ratio and screen size combination. Butterfat production increased by 11 per cent when the concentrate in the diet was increased from 35 to 50 per cent. Screen size had no effect on butterfat production at the 35 per cent concentrate level. At 50 and 65 per cent concentrate, butterfat, production increased with a decrease in screen size from 19 to 13 mm. Milk DM and milk protein production were distinctly different for each specific treatment. The mean DM-, fat- and protein percentages of the milk were 12.3, 3.7 and 3.1, respectively. Treatment had little effect on milk DM and milk protein percentages.