Nutritional Strategies to Reduce Nutrient Output in Sheep Manure
Table of Contents
There are a number of environmental consequences associated with improper management of phosphorus (P) and nitrogen (N). As a result, public concerns are pushing the livestock industry to show that they are managing these nutrients appropriately.
One way to improve nutrient management is to look at the feed rations being used. Many producers feed P and N above recommended levels. However, over-supplementing nutrients as a safety factor is simply adding cost to your feed bill and causing potential harm to the environment. The extra nutrients are ending up in the manure and, if continuously and excessively applied on soils, could contaminate surface and ground water.
By better balancing P and N in the ration, many livestock producers have been able to reduce feed costs, as well as minimize land requirements and improve efficiency of manure application by reducing the amount of nutrients that need handling.
Nutrients are brought on the farm as either fertilizer, commercial feed (such as grain), or dietary mineral supplement and leave the farm as livestock (lamb, milk, cull ewes, replacement females, and manure) and cash crops. With the exception of cash crops, most nutrients remain on the farm.
The objective is to achieve nutrient balance on the farm and in order to do so, the following should be considered (Powell et al., 2001):
The following table, adapted from data provided by Stratford Agri Analysis and Agri-Food Labs between June 2002 and August 2003, illustrates the average P content in common Ontario feed ingredients.
Using the above data as a guide of the nutrient content in feed ingredients, the following tables were constructed to illustrate how much P a producer may be overfeeding above the National Research Council's (NRC) 1985 recommendations.
Sheep Type: Mature Ewe
GH = Grass Hay (14.7% CP); GH1 = Grass Hay (11.0% CP); MG = Mixed Grain; SBM = Soybean Meal; CP = crude protein
Sheep Type: Ewe Lamb
The estimated savings for a sheep ration are between $2 and $4 per tonne of concentrate, if no additional P is included in the ration.
The following table, adapted from data provided by Stratford Agri Analysis and Agri-Food Labs between June 2002 and August 2003, illustrates the average CP content in common Ontario feed ingredients.
Using the above data as a guide of the nutrient content in feed ingredients, the following tables were constructed to illustrate how much CP a producer may be overfeeding above the National Research Council's (NRC) 1985 recommendations.
Sheep Type: Mature Ewe
Sheep Type: Ewe Lamb
Based on these numbers, a typical farm could be overfeeding as much as 16% for P and 4% for CP. This is why feed and ration evaluation is so important. Analyzing feed ingredients as well as rations routinely allows you and/or your nutritionist to determine the nutrient content of your feed and allows you to adjust the ration, if needed, to assure that it is being fed to meet rather than exceed nutrient requirements. For a list of labs equipped for feed testing, refer to the Fact Sheet titled Nutrient Testing, Order No. 03-007. Consequently, feeding to meet requirements will lower your feed costs and may also give you some additional opportunities to meet the requirements of the Nutrient Management Act.
Urea nitrogen has been an extremely useful tool in monitoring protein utilization in dairy cattle. Testing urea nitrogen concentration used to require some invasiveness, as a blood sample was needed. However, it is now possible to measure urea nitrogen concentration in the milk. The procedure is very simple, non-invasive, and merely requires a sample of milk.
Currently, 18% of Ontario dairy cattle producers use DHI services to monitor milk urea nitrogen (MUN) regularly. Knowledge of herd MUN levels have assisted some dairy cattle producers in detecting nutritional problems, making more efficient use of dietary protein, reducing feed costs, and preventing unnecessary loss of nitrogen.
However, this is an area where more research is needed, as there are no target MUN concentrations available for sheep. Monitoring urea nitrogen levels in your flock may be something to think about. Perhaps with more interest it would be possible to establish baseline concentrations for a flock to determine the practicality of monitoring MUN on sheep farms.
Under the Nutrient Management Act, some farms may have difficulty finding enough acreage to spread manure. Reducing P and N content in feed rations may help with this problem. The Ontario Ministry of Agriculture and Food's Nutrient Management Program, June 30 2003 R1 version, was used to determine the effects of manure P reduction on land base requirement for spreading. The software program was developed to assist farmers interested in preparing a nutrient management strategy and plan (NMS/P). Preparing and following a NMS/P is a requirement for those farms regulated by Ontario's Nutrient Management Act.
Table 1 shows the nutrient content available in the manure, the amount of nutrients to be used by the crop and the land required for spreading manure.
Because P concentration is lower when less dietary P is fed, you can apply more total tonnes of manure on the same land. Subsequently, reducing P output in manure minimizes the land required for spreading and can improve efficiency of application.
Most grains and forages fed to sheep contain more P and CP than NRC (1985) recommends for the entire ration. But producers are still insisting on feeding nutrients above recommendations, as a safeguard. The excess nutrients are simply ending up in manure, which means higher than necessary feed bills, possible additional landbase requirement and an increased risk of environmental pollution.
Nutrition is the simplest and most effective approach in reducing P losses from livestock operations. By feeding less P and N, nutrient output in manure can be reduced. Consequently, less acreage will be needed to spread manure at a higher application rate. This is a solid benefit for those farms regulated by Ontario's Nutrient Management Act and who are having difficulty managing their nutrients.
National Research Council. 1985. Nutrient Requirements of Sheep, Sixth Revised Edition. National Academy Press, Washington, D.C.
Powell, J. M., Wu, Z., and L. D. Satter. 2001. Dairy diet effects on phosphorus cycles of cropland. Journal of Soil and Water Conservation. 56(1):22-26.
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