What goes in is what comes out: How a feeding program influences manure nutrient content

Matt Oryschak, Technical Services Division; Alberta Agriculture, Food and Rural Development

When looking at the risks posed to the environment by manure nutrients, there can be little dispute the greatest risks are posed by on-farm storage, handling and application procedures. In recognition of this fact, these aspects have traditionally been the primary focus of extension programming designed to mitigate environmental impacts of manure nutrient management.

In other parts of the world, however, particularly in regions where there is considerable environmental pressure due to intensive livestock production (e.g., the Netherlands), it has been recognized for some time that in order to facilitate environmentally responsible manure management, there must also be a focus on what happens at the front end of the animal.

Manure nutrient content is a direct result of dietary nutrient content, feed intake and the animal’s ability to extract and sequester these dietary nutrients in the form of useful products (i.e., offspring, growth, milk production, etc.). This relationship can be expressed conceptually as:

Livestock nutrient excretion = (dietary nutrient content) x (feed intake) x (nutrient digestibility) x (efficiency of nutrient utilization for productive functions)

Based on the relationship above, in order to alter the nutrient content of the manure we must alter one or more of the factors on the right side of the equation. The remainder of this article will focus on various strategies producers can use to minimize the nutrient content of their manure.

Diet formulation
Nutrients (in particular nitrogen (N) and phosphorus (P)) consumed at levels exceeding animal requirements are excreted in the urine and feces, creating a potential headache when it comes to managing the manure that results in an economical, yet environmentally responsible manner. One of the primary ways producers can address this situation is by paying careful attention to the recommended steps in developing rations for their animals, namely defining nutrient requirements.

Defining nutrient requirements
One of the key steps when developing feeding programs for animals is to define the nutrient requirements for the animals to be fed. A feeding program not based on scientifically derived nutrient requirements can potentially cost the producer money in two ways:

•unnecessarily inflating feed costs

•impacting animal performance

Feeding programs not designed to achieve a particular objective (i.e., meeting animal requirements) in an efficient manner can lead to excess nutrients being excreted by the animal, increasing the costs associated with handling nutrient-rich manure.
Animals require nutrients for:

•maintenance

•growth

•lactation

•reproduction

Of these four functions, maintenance is the only “non-productive function” which in a nutritional context can be considered as the overhead cost associated with keeping that animal. An animal not growing, lactating or reproducing (i.e., animal is at maintenance) is not retaining any significant portion of the nutrients it digests and is essentially in a net balance situation (i.e., what goes in equals what comes out). As such, special care should be taken not to feed animals at maintenance in excess of their nutrient requirements.

By ascertaining an animal’s nutrient requirements for a given level of production in a particular production environment, this provides the producer with a target to strive to meet when developing rations.

Producers who aim to meet these requirements without grossly exceeding them have taken the first step towards minimizing nutrient excretion (and minimizing feed costs) resulting from overfeeding their animals.

The National Research Council (NRC) has published several references on nutrient requirements for individual species and have also produced software models that allow the nutrient requirements for specific circumstances to be calculated. Requirements tables based on NRC estimates have also been published by several government agriculture departments and many take into consideration regional conditions.

Testing your feed ingredients
Nutritionists and extension personnel have been promoting the concept of feed testing for quite some time as a means for producers to collect another piece of information they need in order to help them make financially and environmentally responsible decisions for their feeding programs. There are several agencies that have published “book” values for average nutrient content of feedstuffs used in their area. While these values are certainly better than using nothing at all, they do not give the kind of precision required to develop a precise, operation-specific feeding program in a production climate where feed costs represent as much as 70 to 80 percent of production costs and every cent counts.

A feed test gives producers a second valuable piece of information: the nutritional value of the feeds they are dealing with on their specific operation. This is important because there can be tremendous variation in nutrient content between samples of a single ingredient grown in the same area in the same season. This variation is particularly important if a producer is buying feed for their operation since two batches of an ingredient may cost the same amount but may differ widely in nutrient content.

From a manure nutrient content standpoint, rations developed in the absence of feed tests are prone to both over- and undersupplying nutrients to the animal – both of which are situations that can lead to increased nutrient content in the manure. While the impact of oversupplying nutrients to the animal on manure nutrient content might seem obvious, undersupplying may not be as clear.

If an average (i.e., “book value”) nutrient content for a particular ingredient is used but the real nutrient content is actually lower, the nutrient in question may in fact be deficient. If this nutrient is one of the key limiting nutrients influencing an animal’s productivity (e.g., energy, protein, calcium, phosphorus) it may restrict the animal to a lower production level, resulting in the excretion of nutrients (amino acids or N, P) present in excess of the animal’s productive capabilities.

Many producers cite difficulties in interpreting and applying the results of a feed test to their feeding program as a major obstacle in the adoption of this practice as part of the routine. There are several ways producers can get help with this, such as consulting one of several online resources available to assist producers with this task.

Choosing digestible feed ingredients
Producers are relatively fortunate in that there are a variety of feedstuffs potentially accessible to livestock producers. It is important, however, producers take into consideration the fact that different feeds and ingredients will have different levels of digestible nutrients. For instance, a general rule that applies across all feeds and species is that the higher the fiber content of a feed, the less digestible the feed will be, and consequently fewer nutrients will be absorbed and more will be excreted.

To counter this, when considering different feed ingredients compare their digestible nutrient content, rather than their total nutrient content. (This information can also be found in the NRC nutrient requirement publications.) Ingredients that may have similar total crude protein or phosphorus content may differ considerably in their digestible crude protein (or amino acid) and digestible phosphorus content and consequently may result in very different manure nutrient concentrations.

Balancing your rations
In order to properly balance rations, we need three pieces of information:
1. Nutrient requirements for the animals. As previously mentioned, there are several sources for this information, but the standard in North America is the requirements published by the NRC. These requirements are usually expressed in terms of grams of a nutrient required per day or as a percentage of the diet.

2. Nutrient content of the ingredients available for inclusion in the ration. A feed test will provide this information, or in the absence of a feed test published averages may be used.

3. An estimate of animal feed intake. Producers may either use published feed intake estimates or they may use estimates based on personal experience under their specific production conditions.

Once this information has been collected, it is then possible to come up with a ration formula (i.e., relative proportions of ingredients) that will meet the animals’ nutrient requirements to achieve a certain level of performance at a particular feed intake level.
While some producers may like to work things out on paper (there are several methods of doing so), there are numerous software packages available to assist producers in balancing their rations.

Feeding program management
The real benefits of precise ration formulation are not realized unless coupled to the implementation of animal management practices designed to achieve maximum feed efficiency. Two key management practices producers can use to this end are phase or group feeding and managing feed wastage.

Phase or group feeding practices
Animal nutrient requirements are dynamic, in that an animal’s nutrient requirements are constantly changing during the production cycle. A cow in early lactation is not going to have the same nutrient requirements as a cow in late lactation. The key question then is how do producers deal with these fluctuations in a practical context. The answer is to group animals with like nutrient requirements and develop customized rations.
As growing animals increase in weight, the required concentration of nutrients in the diet decreases for two reasons:

1. their growth rate is gradually declining as they approach their mature weight

2. their average daily feed intake increases with age (i.e., gut capacity gradually increases)

In order to have nutrient supply closely approximate the animal’s requirement, producers can divide the growth period into phases and formulate specific rations for each phase.

Similarly, producers dealing with dairy animals can group animals based on the stage of their production cycle (e.g., early/late lactation, early/late gestation) or by age, where replacement animals are involved (e.g., heifers and first-calvers grouped together, mature cows fed separately).

Research with several species has demonstrated grouping and developing group-specific rations is an effective way to reduce nitrogen and phosphorus excretion and that there are potential cost savings to be realized, depending on local feed costs.

Managing feed wastage
In most typical confined feeding operations, feed wastage ends up with the manure and can be a significant contributor to the nutrient content of manure, particularly if feed wastage is a significant problem on the operation. A good rule of thumb is that if you can observe wasted feed accumulating around a feeder or feeding area, feed wastage is probably at least 15 percent. This has not only serious financial implications for the producer, but it also has environmental implications if the wasted feed becomes part of the manure.

For practical purposes, wastage is a combination of spillage and spoilage. Producers should strive to minimize feed wastage through appropriate management strategies for their operation. Using efficient feeder designs and making sure they are properly adjusted will reduce the opportunity for animals to waste feed while eating. Using a feed delivery system that minimizes feed spillage will reduce the amount of feed lost before the animal even has a chance to consume it. Making sure feed is stored in such a way that spoilage is inhibited (e.g., silage facilities and feed bins) will reduce feed refusal by animals and will also preserve the quality of the feed.

Advanced processing and feed additives
Producers already using precision feed formulation and who have implemented efficient management practices can consider looking at more advanced strategies to minimize manure nutrient content. These strategies are not only effective at reducing manure nutrient excretion but in certain cases can further reduce feed costs.

Some examples of advanced strategies include optimizing particle size of feed ingredients and using ionophores in ruminants.

Optimizing particle size
Perhaps the most common processing technique applied to feeds for animals is reducing particle size either through grinding, rolling or some other mechanical treatment. For producers who process their own feed ingredients on-site, it is very important they monitor the particle size that results from processing and that adjustments are made as necessary.

Ionophores
Ionophores (e.g., monensin, laidlomycin, lasolacid, narasin) are a commonly used feed additive in ruminant feeding and are sold commercially under trade names such as Rumensin® and Bovatec®. Ionophores are essentially antimicrobial compounds, many of which are derived from Streptomyces species.

Ionophores were originally promoted for their ability to improve feed efficiency in cattle, which occurs through a reduction in dry matter intake (DMI) with little impact on average daily gain. They accomplish this through targeting specific microbial populations in the rumen, causing a shift in the pattern of fermentation in the rumen that favors propionate production over acetate (the two major volatile fatty acids produced in the rumen that ruminants then use to meet their energy needs).

It has also been observed that the addition of ionophores suppresses methane production and degradation of dietary protein in the rumen, which allows more of the dietary protein to be absorbed by the animal.

The effect of ionophores on nutrient excretion are two-fold:

1. by increasing feed efficiency, the total volume of manure production is reduced

2. by increasing the amount of dietary protein (i.e., N) digested, absorbed and retained by the animal, which reduces the N content of the manure

As with using any feed additive, producers should carefully follow the manufacturer’s recommendations.

Conclusion
The previous sections show there are several things producers can do to alter the nutrient content of the manure produced by their animals. In reviewing these recommendations, there are two messages that become clear:

1. Anything a producer can do to optimize the efficiency of their feeding programs will ultimately have a positive impact on the volume and nutrient content of manure produced.

2. It is possible for producers to implement practices that enhance environmental quality and improve (or at least not adversely impact) their bottom line.

An important point that needs to be made is that not all practices designed to reduce manure production or manure nutrient content will be feasible on all operations. Producers and those working with producers to implement these and other environmentally focused beneficial management practices must carefully assess what is appropriate for a particular operation. PD

References omitted but are available upon request.

— Excerpts from Alberta Agriculture, Food and Rural Development website