Recently, in Wisconsin, dairy producers have been feeding their lactating cows a higher proportion of corn silage relative to alfalfa than was common in the past. Some of the factors in favor of corn silage that are partially responsible for this trend include:

• Tons DM and energy per acre
• Problems with winter-kill of alfalfa
• High degradability of alfalfa protein
• Improved corn silage hybrids
• More consistent forage quality
• Rapid filling of horizontal silos
• Manure nutrient management.

Dairy producers are asking the following questions:

• What is the optimum mixture of corn silage and alfalfa?
• What is the upper limit on corn silage feeding?
• How do I balance and feed corn silage based rations?

Good quality corn silage and alfalfa compliment each other well in dairy rations. Their nutritional characteristics are presented in Table 1. Combining corn silage and alfalfa in dairy rations at moderate rates helps minimize deficiencies or excesses that may result from feeding either forage at a very high rate or as the sole forage.

Table 1. Nutritional characteristics of good quality corn silage vs. alfalfa.
 

Content or trait	Corn Silage	Alfalfa Silage	Alfalfa Hay
Moisture	High	Moderate to High	Low
Acidity	High	Moderate	Low
Buffering Capacity	Low to Moderate	High	Moderate to High
Bunk Stability	Low	Moderate to High	High
Starch	Moderate to High	Low	Low
Energy	High	Moderate to High	Moderate to High
Protein	Low	High	High
DIP1	Low	High	Moderate to High
Macro-mineral	Low	High	High
ADF	Low	Moderate	Moderate
NDF	Moderate	Moderate	Moderate
Effective Fiber	Low to Moderate	Moderate to High	High

¹Degraded intake protein as a % of DM.

Researchers at the U. S. Dairy Forage Research Center (Dhiman and Satter, 1997) assessed lactation performance of dairy cows fed different proportions of alfalfa silage and corn silage. Forty-five mature and 29 first-lactation Holstein cows were used in a full-lactation trial. Cows were fed diets with a 50:50 forage to concentrate ratio. The forage DM in the diet contained either all alfalfa silage (AS), 2/3^rd alfalfa silage:1/3^rd corn silage (1/3 CS), or 1/3^rd alfalfa silage:2/3^rd corn silage (2/3^rd CS). The silages used in the trial were of good quality averaging 40% DM-19.5% CP-40% NDF and 36% DM-8% CP-45% NDF for the alfalfa silage and corn silage, respectively. Diets were formulated to equal concentrations of UIP (% of DM) and energy (Mcal NEl per lb. DM) by varying the proportions of high-moisture corn, soybean meal, roasted soybeans, and tallow. Trial results are presented in Table 2.

Table 2. Lactation performance of dairy cows fed different proportions of alfalfa and corn silage.
 

Item	AS	1/3rd CS	2/3rd CS	(P<)
DMI, lb/d	46	47	46	NS
DMI, % BW	3.51	3.75	3.57	.05
Milk, lb/d	68	71	69	NS
FCM, lb/d	68	72	70	.15
Fat, %	3.53	3.67	3.65	NS
CP, %	3.08	3.15	3.19	.08
305-d Milk, lb
Mature	21,105	22,374	22,053	NS
1st-Lactation	17,873	18,506	17,970	NS

 

Lactation performance was good for all diets, but there was a slight advantage for the 1/3^rd corn silage diet. There appears to be reasonable flexibility between 1/3^rd and 2/3^rd of the forage DM as corn silage for animal performance. Forage inventory, crop rotation, risk management, and feed cost considerations largely determine what proportion of corn silage to feed within this range. An upper feeding limit of 2/3^rd -3/4^th of the forage DM as corn silage is recommended, because of its high moisture, acidity, starch, and energy content and low effective fiber content (Refer to Table 1). Manure nutrient management, risk management, and feed cost considerations also factor into this recommendation.

Suggested ration changes when switching from a low to a high proportion of forage DM as good quality corn silage are as follows:

• More protein supplement needed to meet requirements
• Protein supplement can contain less UIP
• Less corn supplemented to meet energy and fiber requirements
• Byproduct fiber sources may be needed to control ration starch levels
• Target 35% vs. 40% NFC to maintain good rumen pH and fiber digestion
• Less fat supplement may be needed to meet energy requirements and for conditioning
• More of the fat may need to be in rumen-inert form to minimize milk fat test problems
• Hay may be needed to provide adequate effective fiber, particularly for transition cows
• More cow groups may be needed to prevent over-conditioning of late lactation cows
• More supplemental Ca, Mg, K, and S will be needed to meet requirements
• More dietary buffer may be needed to maintain good rumen pH and fiber digestion.

Dhiman, T. R., and L. D. Satter. 1997. Yield responses of dairy cows fed different proportions of alfalfa silage and corn silage. J. Dairy Sci. 80:2069-2082.