Manitoba Pork Marketing Co-op is suggesting producers lock in as much as half of their feed requirements for the 1st half of 2007.Director of Risk Management Tyler Fulton says downside potential looks limited due to the explosive demand for corn for ethanol production. He notes there could be some opportunities this year during breaks in the rally.  Fulton stresses volatility remains the operating phrase on the feedgrain markets as corn and soybean meal prices have dropped over 15% and then rallied 20% in just the last couple of months.