GDT Auction Improves Slightly October 20, 2016 12:00 am After falling by 3% at the beginning of the month, the overall GDT Price Index increased by 1.4% to $2,965 at the latest event. There were increases for WMP (2.9%), Butter (2.6%) and Anhydrous Milk Fat (1.1%). Both SMP and Cheddar fell by 0.3% and 3.7% respectively compared with the previous event. WMP made up nearly half of all the product traded.