Project Number: 3640-12210-001-02
Project Type: Specific Cooperative Agreement

Start Date: Jul 22, 2008
End Date: Jul 31, 2009

Objective:
The escalating price of corn and other feed grains has caused dairy producers to consider increasing the proportion of forage crops in dairy cow diets in order to reduce costs. However, the current high price of milk is a disincentive to such a cost-saving change if milk production drops too quickly as the forage proportion in the diet increases. Unfortunately, because starch in grain is more digestible than cell wall material in forages, milk production is expected to drop as forages replace grain. But the steepness of this decline and the economic tradeoff is not well defined. The objective of this study is to quantify the ability of high-quality alfalfa and orchardgrass hays to support milk production as forage replaces increasing amounts of grain. In addition to measuring cow performance traits, such as feed intake and digestibility, and milk yield and composition, an economic analysis of milk income over feed costs will be conducted.

Approach:
A response curve design will be used to compare high-quality alfalfa and orchardgrass hays for their ability to support milk production as these hays replace grain in the diet of dairy cows. Based on the actual measured quality of the two procured hays and the available corn silage, a series of 10 treatment diets will be formulated. All diets will contain a constant amount of corn silage (35 to 40% on a dry matter basis). Hays will be included at 5, 10, 15, 20, and 25% of diet dry matter, resulting in diets ranging from approximately 40 to 65% forage. The grain mix will decline over this series of forage inclusion rates from roughly 60 to 35% of the diet. Based on the composition of the hays and corn silage, the grain mixture will be formulated to meet protein, mineral, and vitamin requirements of the cows. The trial will include 60 dairy cows assigned to treatment by blocking for sire breed of the cows and calving date, and subsequently randomly assigned to treatments (6 cows/treatment). Average milk production on a standard diet during the 14 d preceding the experiment will be used for co-variate adjustment of the data. Cows will be fed their respective treatment diets for 56 d. Feed intake and milk production will be recorded daily (2x milking), and samples for milk composition analysis will be taken every 14 d. Fecal grab samples will be collected during wk 4 and 8 of the experiment. Feed composite samples (alfalfa and orchardgrass hays, corn silage, and diets) will be collected weekly. Cows will be weighed on two consecutive days at the beginning and end of the experiment. Feed samples will be analyzed for protein, detergent fiber and cell wall composition, and in vitro digestibility. Fecal samples will also be analyzed for composition and used to calculate in vivo digestibility of diets, using acid insoluble ash as an internal marker. Current feed and milk prices will be used to determine income over feed costs for the various treatments.