Hi. I'm Diego Navarro, from the Stein Monogastric Nutrition Laboratory of the University of Illinois, and today I will be talking about the amino acid digestibility in six sources of meat and bone meal fed to growing pigs.

For this presentation, I will start by giving a brief introduction on the rendering industry here in the United States, and then discuss what meat and bone meal is. And then I will move to the materials and methods, and then dive into the results and the discussion of this experiment, before drawing conclusions and then giving a take home message.

In the US, approximately 25 million tons of animal byproduct is collected and processed annually by the rendering industry. There are about 50 firms that operate 200 rendering facilities here in North America, more than 180 of them in the United States and about 20 in Canada. Now, looking at this table, these four species raised in animal production, about 50% of the live weight of cattle is rendered, 44% of pigs, 37% of broilers, and almost 60% of the live weight of fish is rendered.

Rendering results in several animal products that include meat and bone meal, meat meal, blood meal, poultry byproduct meal, feather meal, fish meal, and animal fats such as tallow, lard, and choice white grease. These ingredients are commonly used in diets fed to livestock, aquaculture, and pets. For the purposes of this presentation, we will focus on meat and bone meal.

This diagram shows an overview of the key steps in the rendering process. The main goal of this process is the removal of water and fat through a series of steps that will eventually result in the final animal protein product. The starting raw material used will vary between rendering plants but an overall approximation of the composition would be 60% water, 20% crude protein and ash, and 20% fat.

The raw materials will go through several heating steps to remove water and to render the material safe from pathogenic microorganisms and to a certain degree increase the availability of amino acids by denaturation of protein matrices. However, heating also gives the possibility of heat damaging the product and decreasing the availability of amino acids.

The material then goes through a screw press to separate the fat, which results in your animal fat sources such as lard and tallow, and separates this from the protein and ash content, which then undergoes grinding and eventually result in the final product, meat and bone meal.

Based on the Association of American Feed Control Officials or AAFCO, an animal byproduct is considered meat and bone meal if it contains at least 4% phosphorus, but a calcium concentration of not more than 2.2 times the concentration of phosphorus. Samples that contain less than 4% phosphorus are then considered as meat meal. Meat and bone meal consists of parts of the animal that are not suitable for human consumption such as carcass trimmings, offals, bones, condemned whole body carcasses, and some organs, but excludes added blood, hair, horns, and hooves. The majority of the meat and bone meal produced in the US is produced from a mixture of materials from cattle, swine, and poultry.

Meat and bone meal is a good source of crude protein and amino acids and it is comparable to soybean meal. And since bones are included in the production of meat and bone meal, it becomes a good source of calcium and phosphorus, allowing it to replace inorganic phosphates in swine diets.

There are two possible sources of variation between sources of meat and bone meal. First is the raw material that is used, which entails the species or mixture of species used, as well as the ratio between soft tissue to bone in the material. For example, greater amounts of bones are contained in rendered material from cattle compared with those coming from swine or poultry, and so products with greater proportion of cattle tissue would result in greater concentrations of ash. The second source of variation is the conditions of the rendering process used to make these products. These two sources of variation may vary between rendering plants. Because of this, the composition and digestibility of amino acids and other nutrients may vary between sources of meat and bone meal.

So the objective of this experiment was to determine the standardized ileal digestibility, or SID, of amino acids in six sources of meat and bone meal.

Eighteen growing barrows of initial body weight of around 70kg were used. The experimental design was set up as a replicated 4 x 9 incomplete Latin square design with 4 periods and 9 diets for a total of 8 replicates per treatment.

The experimental diets consisted of one diet that includes soybean meal as a sole source of amino acids. Six diets included one of six sources of meat and bone meal partially replacing soybean meal. There was also a diet containing a source of blood meal, but was not included in the analysis of data. The last diet was a nitrogen-free diet that was used to measure basal endogenous losses of amino acids. 

Apparent and standardized ileal digestibility were calculated by difference. And data were analyzed using the Mixed procedure of SAS, with diet as the fixed effect and pig and period as the random effect.

Moving on to the results...

Looking at the concentration of crude protein of the ingredients on an as fed basis, we have the six sources of meat and bone meal on the x axis, and percentage units on the y axis. The crude protein ranged from 49.1% in the fifth source of meat and bone meal to 55.9% in the third source of meat and bone meal.

And now, looking at the concentration of lysine in the ingredients, concentration of lysine ranged from 2.63% in the fifth source of meat and bone meal to 3.21% in the third source of meat and bone meal. And for the sake of time I will only show lysine, but there were also differences in the concentration of amino acids between sources of meat and bone meal.

Now, looking at the concentration of ash, the differences in the crude protein content of the ingredients may in part be explained by the differences in their ash content. The ash ranged from 20.6% in the third source of meat and bone meal to 33.2% in the fifth source of meat and bone meal.

Now we'll look at the calcium and phosphorus levels of the ingredients. This table shows the calcium and phosphorus levels of the six sources of meat and bone meal. On the second row, we have the source of meat and bone meal, and on the first column we have either phosphorus or calcium.

The second and third sources of meat and bone meal have phosphorus levels of less than 4%. So according to the definition by AAFCO, these two sources should be considered as meat meal.

However, when we look at the calcium levels in these ingredients, it ranged from 5.09% in the third source of meat and bone meal to 11.03% in the fifth source of meat and bone meal.

And so, we now calculate the calcium:phosphorus ratio, and that ranged from 1.95 in the second source of meat and bone meal to 2.14 in the fourth source of meat and bone meal. Since all ingredients have a calcium:phosphorus ratio of less than 2.2, by definition these are all considered meat and bone meal.

Now, we look at the standardized ileal digestibility of lysine on a percentage basis. The SID of lysine in the fourth source of meat and bone meal was greater than in the second source, the third source, and the sixth source of meat and bone meal, but was not different from the first and the fifth sources of meat and bone meal.

Looking at the SID of methionine, the SID of methionine in the fourth source of meat and bone meal was greater than in the third and the sixth sources of meat and bone meal, but was not different from the first, the second, and the fifth sources of meat and bone meal.

Now looking at threonine, the SID of threonine in the first source of meat and bone meal was greater than in the second, the third, and the sixth sources of meat and bone meal, but was not different from the fourth and the fifth sources of meat and bone meal.

Similarly for tryptophan, the SID of tryptophan in the fifth source of meat and bone meal was greater than in the second, the third, the fourth and the sixth sources of meat and bone meal, but was not different from the first source of meat and bone meal.

In conclusion, the nutrient composition varies between sources of meat and bone meal in terms of crude protein and amino acids as well as calcium and phosphorus levels. And the SID of amino acids was different among sources of meat and bone meal. The differences in the SID of amino acids among the sources of meat and bone meal may have been caused by differences in the raw materials used, or heat damage during the processing of these products.

The take home message of this presentation is that the nutrient composition and digestibility of amino acids varies between sources of meat and bone meal. And this may be because of the variation in raw material used or the rendering processes used to produce this feed ingredient.

Thank you for your attention, and if you would like to know more about this topic, or want to learn more about nutrition, you can visit our web site at nutrition.ansci.illinois.edu.