Dietary Crude Protein and Phase Feeding

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We did not conduct any new nutritional trials for feedlot cattle because the most promising ones (i.e. reducing dietary crude protein, phase feeding) have been so comprehensively studied and validated in the literature and field trials that we did not need to "reinvent the wheel", so to speak. However, we do present information on the nutritional practices that are most successful as ammonia BMPs.

The easiest and most effective way of reducing ammonia volatilization from feedlot operations is with proper animal feeding and management. In this case, we are primarily addressing the feeding of crude protein, the primary nitrogen (N) source in cattle rations, as well as phase feeding.

The Problem
Background
The Solution

The Problem

Cattle producers can often times overfeed protein if cattle are not separated into groups of similar nutrient needs. A producer will feed the amount of protein needed to satisfy the animal with the greatest needs and assume the rest are covered. This practice often times leads to gross over feeding of protein which is excreted in the urine and subsequently volatilized as ammonia. This is important because, it has been shown that beef cattle can excrete up to 80 % of consumed CP nitrogen (19), the majority of which is excreted in the urine (14). Feeding a proper level of nitrogen (CP) in the diet will increase efficiency and performance, and less nitrogen will be excreted, reducing ammonia volatilization.

Background

Nutritionally, ammonia is produced from cattle when crude protein (CP) is degraded by proteolytic microbes in the rumen. In the presence of adequate amounts of fermentable carbohydrates, microbes capture the ammonia to synthesize protein (31), which is utilized by the animal for growth. Ammonia that is not utilized is absorbed through the rumen wall and into the blood plasma. It is subsequently converted into urea in the liver, which is then excreted in the urine, or recycled back to the rumen. Urea is the main N source in urine, comprising 50 to 90% of total urinary N (32). Fecal N is primarily organically bound with only a small amount (about 5 %) of the N in fresh feces in the form of ammonia or urea (9, 32).

Studies have shown that there is a direct link between the amount of crude protein in the diet and the amount of ammonia volatilized from pen surfaces; therefore, a reduction in crude protein in the diet leads to a reduction of ammonia volatilization (11, 14, 33). Feeding less crude protein not only reduces the amount of total nitrogen in the manure, but it also changes the partitioning of nitrogen between the urine and feces. Todd et al. (14) found that steers fed a reduced crude protein diet had 28% less nitrogen in the urine, and 44% less total ammonia loss from the manure. Since urinary nitrogen comprises 60 to 70% of the total nitrogen excreted (14, 19), and is the main component affecting ammonia volatilization, these results show that decreasing protein intake will decrease the amount of ammonia volatilized from the manure, partitioning more nitrogen in the feces. This can have beneficial effects later in the system when manure is applied to crops, as fecal N is found in more organic forms and will be less volatile. By practicing phase feeding in conjunction with reducing CP intake, N excretion and ammonia volatilization can be further reduced by up to 32% (33). Reducing the amount of protein fed will also decrease the cost of the ration, as protein is usually the most expensive part of an animal’s diet.

The Solution

The easiest way to reduce N output is to reduce N intake. By feeding the proper levels of crude protein to cattle you can reduce N excretion and subsequent ammonia volatilization. You will also save money by feeding less protein rich feedstuffs. Hiring a nutritionist to formulate rations based on stage of growth, sex, age, and breed (a.k.a. phase feeding) will help you pinpoint protein needs and feed the proper levels of protein rich feedstuffs. Having feedstuffs tested for crude protein content on a regular basis will assist in properly formulation rations for %CP.

Compared to other methods of ammonia reduction, reducing the amount of crude protein in an animal’s diet may provide the most cost effective and practical method of reducing ammonia emissions from livestock operations.

The industry standard for dietary crude protein for feedlot cattle is 13.5% CP, however this value will vary for individual animals and stage of growth. For guidelines on what is the optimal level of protein for you animals stage of growth or production contact your nutritionist, or view the guidelines set by the NRC (Nutrient Requirements of Beef Cattle, 2000).