2010-11 Corn Silage and Grain: Milk Yield and Fat Content
In contrast to summer 2010 milk fat was low across the country, by late 2010 dairy producers and nutritionists in Michigan reported that with the new corn crop, milk fat percent was more normal and milk production was lower than expected. Much of the 2010 corn silage crop was harvested too dry and mature. Dry mature corn silage can result in lower fiber and starch digestibilities, which significantly affect milk production and milk fat test. Corn silage neutral detergent fiber (NDF) digestibility can vary by more than 20 percentage units. Each unit of forage NDF digestibility lost results in about 0.5 lb loss of 4% fat-corrected milk yield. Fiber digestibility cannot be compensated for by replacing it or supplementing other ingredients so it is important to select corn silage hybrids with high NDF digestibility and harvest at proper moisture content. Lower starch digestibility in corn silage can be compensated for by adding additional starch to the diet or generally by grinding available corn grain finer.
It was noted that corn crop harvested in fall 2010 may be beneficial for fresh cows and maintenance cows (to maintain BCS at target values given level of milk production). They do not need much highly fermentable dietary starch sources. When making nutritional changes to the milking herd ration with the goal of increasing milk components or milk yield do so gradually so that rumen microbes have time to adapt. Although reaching your target may take several weeks, movement in the right direction may be detectable within the first week of implementation.
click image to zoom The higher than usual milk fat concentration seen this past winter is in stark contrast to the issue of low butterfat test seen during most of 2010 across the country. The figure on the right illustrates the low milk fat test during 2010 that was observed not only in Michigan, but in the whole United States. From February through October 2010, monthly butterfat percentage averages in the Mideast Federal Milk Marketing Order ranged from 0.4 to 0.9 % below the 10-year average for those same months. Although the exact reason for the struggle has not been pinpointed, it probably has to do with poor forage growing conditions in 2009.
Iron in Drinking Water
Concerns about high iron concentrations in drinking water were raised in some Roundtables. Higher concentrations [such as 2 to 10 parts per million (ppm)] may be a problem by reducing water and feed intake, milk yield, immune function, reproductive performance, and absorption of copper and zinc. These problems can be magnified during stress associated with transition of fresh cows. Additionally, high iron is implicated in reduced water intake. When stumped by the reason for lower than expected milk yield and health problems, dairy nutritionists and producers are sampling and checking water to see if high iron might be a contributing factor.