The Influence of Forage Type on the Production Response of Lactating Dairy Cows Supplemented with Different Types of Dietary Fat

Research has demonstrated a difference in fat utilization by lactating dairy cows with different dietary forage types. Responses appear to be greatest on alfalfa-based diets and poorest on all corn silage-based diets. The addition of extruded soybeans to dairy cow diets containing corn silage and alfalfa hay increased fat-corrected milk (FCM) production by an average of 2.4% compared to 10% for all alfalfa silage-based diets. In 11 experiments, the addition of whole cottonseed (WCS) to corn silage-based diets decreased FCM production by an average of 4% whereas the addition of WCS to alfalfa hay-based diets increased average milk fat percent and FCM production by 11 and 6%, respectively. When WCS was included in diets with corn silage as the primary forage and alfalfa hay or bermudagrass hay as a secondary forage, the fatinduced milk fat depression found on corn silagebased diets appeared to be alleviated. Alfalfa diets supplemented with yellow grease increased average milk production by 6.6% with milk fat percentage unchanged. Results supported the inclusion of tallow at 500 g/cow/day in diets based on ryegrass silage whereas the inclusion of tallow or blended animal-vegetable fats on corn silage- or cottonseed hull-based diets was not supported by summarized experiments. Supplementing corn silage/alfalfa silage-based diets with prilled fat increased FCM production by an average of 6.2% whereas the inclusion of prilled fat in alfalfa silage or corn silage based diets had inconsistent effects on production responses. The supplementation of different forage-based diets with Ca-salts of fatty acids resulted in an average FCM production increase of approximately 5%.