Many of the graziers in the USA are located in the Northeastern and Midwestern part of the country, and typically have 6 to 7 months of grazing and 5 to 6 months with confinement feeding because of the winter climate. Many of these dairymen have the feeding equipment to feed a total mixed ration (TMR) during the winter feeding period.
Some dairymen are using this equipment to supplement pasture with a partial TMR (pTMR). This is called a pTMR because pasture is not physically part of the mixed ration. Feeding a pTMR to grazing cows offers more "control" over the entire feeding program compared to offering pasture and grain separately. An estimate of dry matter intake from pasture should be part of the ration formulation process by the nutritionist in order to develop a "balanced" ration.
As with all pasture supplementation strategies, there are advantages and disadvantages associated with feeding a pTMR that should be considered along with the goals of the dairy producer.
Advantages of feeding a pTMR include:
- Provides a more uniform ration with less chance for disruption of rumen function.
- Helps in monitoring dry matter intake (DMI) of pasture more easily.
- Forage is fed with the concentrate rather than separately, thus less chance for rumen digestive problems due to "slug" feeding of concentrate.
- Forage also provides fiber that may be needed with high quality pasture.
- Higher milk production per cow. Our recent research at Penn State University found grazing cows supplemented with a pTMR produced 8 lb more milk per day than grazing cows supplemented with just concentrate (70 vs. 62 lb milk/day), had a higher milk fat and milk protein content, and an improved body condition (see Table 1).
Table 1. Results of feeding a partial TMR to supplement pasture for high producing Holsteins.a
|aBargo, F. 2002. J. Dairy Sci. 85:2948-2963.|
|Item||Pasture + 19.1 lb concentrate||Pasture + pTMR||TMR (non grazing)|
|Pasture intake, lb DM||28.4||16.5||-.-|
|TMR intake, lb DM||-.-||38.9||58.7|
|Concentrate intake, lb DM||19.1||-.-||-.-|
|Total intake, lb DM||47.5||55.4||58.7|
|Total intake, % of BW||3.58||3.99||4.15|
|Milk yield, lb/day||62.7||70.4||83.8|
|Milk fat, %||3.13||3.35||3.30|
|Milk fat, lb/day||1.96||2.33||2.72|
|True milk protein, %||2.82||2.95||2.99|
|Milk protein, lb/day||1.74||2.05||2.48|
|Rumen NH3-N, mg/dl||20.9||10.8||9.7|
The disadvantages of feeding a "Partial" TMR include:
- Extra time and labor involved in feeding TMR.
- Feed costs may be slightly higher.
- Management of TMR in terms of changing formulations or amounts to feed.
- The need of a feeding area to feed the pTMR.
Using a "Partial" TMR
Because much of a TMR is stored forage, many similarities exist between supplementing grazing cows with TMR and with stored forages. The quality of the forage in the TMR will influence DMI and milk response, but substitution of pasture for TMR may differ from substitution with stored forage alone. Because the grain is included in the TMR, cows will replace less pasture with TMR supplementation than with supplementation of forage alone. Thus, the quality and amounts of stored forages in the TMR will affect the substitution rate, DMI, and milk production. The cows fed the pTMR in our Penn State study consumed about 8 lb more dry matter per day compared with pasture and concentrate.
The amount of pTMR to feed will depend on the cow requirements as well as the quantity and quality of available pasture. Time of feeding will also affect intake of both TMR and pasture. In general, feeding a pTMR before cows graze encourages more consumption of the pTMR and may decrease pasture intakes. Offering the pTMR after the initial period of grazing encourages less consumption of the pTMR. Generally, cows will adjust intake of pTMR based on how much pasture is available, but quality and palatability of forage species in the pasture will also affect how much TMR is left in the bunk. Many dairy managers and nutritionists adjust feeding practices and ration formulation based on two things - the amount of TMR left in the feed bunk and amount of milk going into the bulk tank. These need to be monitored closely and the amount of pTMR to feed adjusted.
Formulating a "Partial" TMR
Balancing a pTMR for cows is no different than balancing a TMR for non-grazing cows except for two things. It is much easier to estimate pasture DMI when supplementing with a TMR compared to feeding forage and concentrate separately. Using estimated DMI and forage analysis from pasture, it is possible to formulate a reasonably balanced ration to complement pasture. Having flexibility in the formulation is the key to maintaining optimal feed available for the cows. We suggest formulation of rations every 4 to 6 weeks during the grazing season. Planning ahead for changing pasture DMI from decreased availability can help to minimize problems that changes may cause. Important to the success of a pTMR with pasture based systems is the recording of bulk tank milk daily and monitoring TMR refusals.
Corn silage as part of the TMR can be an excellent supplemental forage to complement pasture because it adds needed rumen fermentable carbohydrates as a source of energy for the rumen microbes, "dilutes" out the high protein in pasture, and provides some needed fiber. Corn silage is a highly palatable feed, is an excellent carrier for the supplemental concentrate, and can allow for lower amounts of concentrate to be fed. Grazing herds in New York that supplemented with corn silage had $134 more net farm income/cow than non-supplemented herds. One management problem is that adequate amounts must be removed daily from a horizontal silo to maintain good quality silage.
The study with 45 high genetic Holstein cows at Penn State found that feeding a pTMR with pasture resulted in a higher milk yield, greater milk component yield, and less body condition loss compared with pasture plus concentrate. We calculated the net income per day to be $0.10/cow/day (US$) greater for the pTMR compared to pasture + concentrate. The pTMR fed was the same as was fed to the confinement herd. We could have formulated a specific pTMR for this study which cost less and would likely result in an even greater milk yield and profitability. The milk yields (70 lb) obtained in this study are comparable to what some of our graziers are achieving when supplementing with a pTMR.
Published as pages 43-45 in proceedings from "Nutrition of Dairy Cows on Pasture-Based Systems" held March 31, 2003 in Grantville, PA.