Corn Prices and Methane Emissions

Corn grain usually makes up 30 to 35% of the total ration dry matter of a typical Midwestern lactating cow diet. Therefore, changes in corn price can have a significant impact on total feed costs. Since 2006 corn prices have doubled from nearly $3 to $6 in 2011. This price increase translates into the cost to feed a dairy cow by almost $1.00/cow/day. This is assuming an average corn crop but, in the event of a drought or any natural disaster, prices will drastically change and not for the better. The USDA has suggested it expects the corn reserves in 2011 to drop to a 20-day supply for next year short from the 30 days considered safe. Corn has been the main energy feed fed to lactating dairy cows for decades. Its high starch content allows for the formulation of energy-dense rations required by cows with high genetic merit for milk production. 

The milk-feed price ratio represents the pounds of 16% protein mixed dairy feed equal in value to produce 1 pound of whole milk. Whenever the ratio meets or exceeds 3.0, it is considered profitable to increase feed costs by feeding more feed to produce more milk. The feed price is calculated using the following formula, and average corn, soybean, and hay prices:

Milk price $ per hundred weight

(Corn $ per bu. /56)*50 +
(Soybeans $ per bu. /60)*8 +
(Alfalfa hay $ per ton/2000)*41

Although all three feedstuffs used in the calculation do not constitute an entire lactating cow ration, they are among the most common feedstuffs used to provide energy, protein, and forage. As of the end of 2006, a producer could buy 2.42 Lbs. of feed per pound of milk sold. Prices used for this calculation by the USDA were corn at $3.01/bu., soybeans at $6.14/bu., alfalfa hay at $112/ton, and milk at $14.20/ hundredweight.

Milk prices at around $20 during November 2011 were around 40% higher than in 2006. This seems like good news for most producers, but they were not. The milk-feed price ratio was 1.80. The prices used by USDA for this calculation were corn @ $6 per bushel; soybeans @ $11.50 per bushel, and alfalfa hay @ $198 per ton. The hay price was more than likely underestimated, since producers in the area are paying more than that for dairy quality alfalfa hay. 

In this difficult economic environment it is logical to attempt to reduce feed costs as they represent the largest component of the cost to produce milk (i.e. 50 to 60%). With high grain prices, producers and nutritionists, will try to maximize the inclusion of less expensive forages in the ration of dairy cow diets to replace corn grain. This substitution scenario has the potential to reduce the energy intake of the cow however the dairy cow must still meet her energy requirements for milk production. Thus, the dairy cow compensates either by increasing dry matter intake (up to where rumen fill allows – if possible), and/ or mobilizing body stores (loss of body condition). For example: a cow that eats 45 pounds dry matter of a total mixed ration balanced to supply .77 mega calories (Mcal) of net energy of lactation (NE_L) per pound ingests 35 Mcal NE_L daily. If the diet is reformulated and the energy density reduced to .69 Mcal NE_L per pound the cow must now eat 50 pounds and to still satisfy the 35 Mcal NE_L required. One issue to consider though is that feed intake is positively and strongly correlated (R² = 0.65) with methane production as described by the following equation.

Using this model the methane produced by the cow that eats 45 or 50 Lbs. of dry matter would be 19.8 and 21.6 MJ of methane daily. Ten cows fed at 50 pounds of dry matter produce as much methane as 11 cows fed at 45 pounds. Thus, if dairy cows can produce the same or more milk on less feed will result in reducing total methane and methane emissions per unit of milk.

These figures make even more sense in the context of a world demanding more food production. In that case one should address greenhouse gas emissions per pound of product being produced. Research by South Dakota State University and the University of Minnesota reported that the average dairy cow in the U.S. produced 0.33 MJ of methane per pound of milk (Garcia and Linn. 2008). In the example diet above there's enough energy (35 Mcal NE_L /day) supplied per day to sustain 77 pounds of milk both at 45 and 50 Lbs. dry matter per head. If we calculate the methane produced per cow it would be 0.26 and 0.28 MJ of methane produced per pound of feed for the 45 and 50 Lbs. intake, respectively, almost an 8% increase. 

The definition of feed efficiency is the unit of milk produced per unit of dry matter intake. Casper and Mertens (2007) reported that feed efficiency can range from less than 1.0 (very inefficient) to over 2.0 (very efficient) if cows are mobilizing body condition. The biggest factor affecting feed efficiency on the dairy farm is forage quality. Casper (2010, unpublished) reported that the average amount of carbon released as methane Carbon (C) was 11g/kg milk, but ranged from 1.8 to 41.7 g/kg milk. Cows that have higher feed efficiencies have lower methane emissions per unit of milk. Total Green House Gas (GHG) (carbon dioxide C plus methane C) average 0.156 kg C per kg milk, but ranged from 0.065 to .57 kg C/kg milk. Again, higher feed efficiencies resulted in lower GHG gas emissions per unit of milk. Cows can actually sequester C in milk, so cows are green.

Casper and Mertens (2007) reported that feed efficiency is directly related to the energy density of the ration (NE_L, Mcal/ kg). Thus, higher energy diets result in higher feed efficiencies. It is known that the biggest factor affecting energy content of the ration is the digestibility of the ingredients in the ration as measured by the digestibility of Dry Matter (DMD) and neutral detergent fiber (NDFd). Thus, feed and management factors like poorly digestible forages, (hay, haylage, corn silage, etc.), acidosis, sorting, inconsistent TMR mix, etc. all reduce ration digestibility, which in turn reduces ration energy density (NE_L, Mcal/kg) and ultimately reduces feed efficiency.

Within individual feed ingredients, grains (corn, etc.) can vary in nutrient content, but usually are much more consistent than quality of forages observed on the dairy operation. For example, Table 1 contains a breakdown of corn silage quality by DMD that was recently published in Hoards Dairyman for approximately 30,000 corn silage samples (Jones, et. al. 2011). The range in forage quality as measured by DMD ranges from the poor (low digestibility) to excellent (high digestibility) for corn silage is quite large. In addition, the starch content (amount of corn in corn silage) ranges from low to very high across these ranges of quality. Thus, the biggest factor controlling FE on the dairy is forage quality and can be managed either through purchasing or producing forages with the highest digestibility. Certainly seed hybrid selection for forage, soil fertility, fertilization, environmental conditions, and crop management all play a role in producing highly digestible corn silage.

Table 1. Range in corn silage quality from approximately 30,000 corn silage samples.

The inclusion of poorly digestible forages in substitution for highly priced corn grain in the ration will increase livestock methane emissions. This is of course something we don't want to happen when corn prices are high and nearly half of the corn crop goes for ethanol production to reduce greenhouse gas emissions. Whereas, in the face of this paradigm the only solution available is feeding highly digestible forges that will reduce methane emissions, as well as, reduce the need for purchased grain and increase ration forage concentrations. Improving the forage quality, as measured by DMD and NDF digestibility, offers the greatest opportunity to increase the amount of forage in the ration (50 to 60 to 70%), reduce the dependence on high price corn, improve feed efficiency, and subsequently reduce methane and GHG emissions by dairy cows, all the while, maximizing income over feed costs (IOFC). So, forage quality cannot be too good. 

Casper, D. P. and D. R. Mertens. 2007. Feed efficiency of lactating dairy cows is related to dietary energy density. J. Dairy Sci. (Suppl. 1) 90:407. (Abstr.).

Casper, D. P. and D. R. Mertens. 2010. Carbon dioxide, a green house gas, is sequestered by dairy cows. J. Dairy Sci. (E-Suppl. 1) 93:843. (Abstr.).

Jones, D. F., D. P. Casper, D. Schauff, D. Kleinschmit, G. Gengelbach, and K. E. Lanka. 2011. How does your forage measure up? Hoard's Dairyman, Dec. 10, page 796.

Ellis, J. L., E. Kebreab, N. E. Odongo, B. W. McBride, E. K. Okine, and J. France. 2007. Prediction of methane production from dairy and beef cattle. J. Dairy Sci. 90:3456–3467.

Garcia, A. D. and J. G. Linn. 2008. Dairy cows and the environment: Were we better off 83 years ago? J. Anim. Sci. Vol. 86, E-Suppl. 2/J. Dairy Sci. Vol. 91, E-Suppl. 1