Effects of the Level, Type and Processing of Cereal Grains in Diets for Dairy Cows Feed Intake and Performance

Milk yield in dairy cows is directly dependent on their feed or energy intake. Due to genetic improvements, dairy cows have increased their potential for milk yield. This implies that the animal’s energy requirements are drastically increased. The presence of both physical and metabolic mechanisms for intake regulation and dynamic nature of lactating dairy cows has made ration formulation a challenging enterprise. Few strategies of ration formulation can be adapted to simultaneously address the issue of intake regulation and stimulate feed intake and milk yield in dairy cows. Strategies that may be useful in achieving these objectives include improving the grass silage quality and adjusting the rumen degradation of starch to match that of grass silage. Starch accounts for the bulk of the dry matter of cereal grains and has been shown to influence rumen functioning, fibre digestion and thereby animal performance. The overall aim of the studies presented in this thesis was to explore the scope for stimulating feed intake and milk yield in dairy cows through feeding management. Three feeding experiments and one laboratory study were conducted. Paper I evaluated the effects of increasing the proportion of wheat in diets containing maizeand grass-silages. Paper II evaluated the effects of interactions between grass silage digestibility (high vs. medium) and concentrate starch type (barley vs. maize) in the diets. Paper III evaluated the effects of increasing the proportion of NaOH-treated wheat in grass-silage based diets, and Paper IV estimated the ruminal digestion kinetics of different cereal starch using the in vitro gas production technique and compared the gas production data to in vivo starch digestibility data. The results obtained in Papers I-III indicated that the feed intake and milk yield were primarily affected by the level of concentrate and the digestibility of the grass silage in the diets. The results presented in Paper IV indicated that the differences between the digestion kinetics for starches of different origins are less than has been reported in literature, which is consistent with the results of feeding trials. Moreover, the predicted ruminal starch digestibility obtained using gas production data were in good agreement with the in vivo starch digestibility data.