Hello, my name is Maryane Oliveira. In this presentation I will discuss one of the our research conducted at the University of Illinois investigating the optimal Tryptophan (Trp) to Lysine (Lys) ratio for 25 to 40 kg body weight growing pigs fed diets containing 35% distillers dried with solubles (DDGS).

I will start by giving a brief background. Distillers dried grains with solubles is a by-product from corn resulted from ethanol production. Because there is a fermentation in the process, DDGS has higher concentration of crude protein and amino acids (AA) than in corn, which turns this by-product to be good and inexpensive feed alternative to include in pig diets.

However, if you take a look at this graph, the concentration of Trp is low in corn and corn by-products, whereas Leucine (Leu) is high in corn and becomes higher in the respective by-product. For this reason, if DDGS is included in growing pig diets, the Trp becomes the second limiting AA after Lys. As Lys, Trp has also an essential role in protein synthesis as well as immune responses.

In addition to protein synthesis and immune system, Trp also works in feed intake regulation, being the precursor of serotonin. As Trp shares the same brain transporters as Leu, excess Leu may reduce Trp transport to the brain for serotonin synthesis and affect feed intake. Thus, Trp requirement may be increased if large amount of DDGS are used.

Therefore, one experiment was conducted to test the hypothesis that Tryptophan: Lysine ratio may increase for pigs 25 to 40 kg body weight fed diets with excess Leucine from distillers dried grains with solubles.

Move on to the experimental diets. A basal diet was formulated based on corn, corn DDGS, soybean hulls and soybean meal, which contained 15% standardized ileal digestibility of Trp to Lys ratio. Four additional diets were formulated by adding crystalline Trp to the basal diet, in order to have 18, 20, 23 and 24 % SID of Trp to Lys ratio. Thus, there was a total of 5 diets. Now, looking at this graph, yellow line represents the percentage of AA that met the NRC requirement. For Trp which is in blue bars, the first diet was below of the requirement, whereas the subsequent diets were over of the NRC requirement. However Leu concentration was about 150% of requirement in all 5 diets.

Talking about experimental design, a total of one hundred twenty growing pigs with an average of initial body weight of 26 kg were allotted in a randomized complete block design with 5 diets and 8 pens per diet. There was 3 pigs in each pen. The experimental period was 21 days. Blood samples were collected at the end of the experiment to analyze for plasma urea nitrogen. Initial and final BW were recorded on day 1 and day 21, and the amount of feed consumption was recorded throughout the experimental period. Average daily feed intake, average daily gain, and gain to feed ratio was calculated as well.

For statistical model. Data were first analyzed using orthogonal contrasts to see the linear and quadratic effects of Trp in the diets. Then, the average daily gain and gain to feed ratio was submitted to linear broken line and quadratic broken line regressions analysis in order to calculate the optimum Trp to Lys ratio.

Now let’s move on to the results. First of all, I want to point out that for all graphs, the Y axis represents the response parameter and X axis represents the level of SID Trp to Lys ratio. The average daily feed intake increased linearly as the SID Trp to Lys ratio increased up 23 Trp to Lys ratio and had a plato after this level.

The same was observed for average daily gain which increased linearly as the level of SID Trp to Lys ratio increased up 23 percent, but had a plato after this level.

Likewise an increased gain to feed ratio was observed as Trp to Lys ratio increased up 20 percent and had a plato after this point.

Now, looking at final body weight, increasing levels of Trp increased the final body weight as well, but after 23 percent of Trp in the diet, there was also a plato. These results indicate that indeed Trp concentration in the diets affect the growth performance of growing pigs if they are fed with high concentration of Leu.

Now, talking about the plasma urea nitrogen. There was a reduction in plasma urea nitrogen as the level of Trp increased in the diets, indicating that protein synthesis has increased in the pigs.

Now, let’s take a look at the estimation of optimum Trp to Lys ratio. The blue lines represents the linear broken line and the orange line represents the quadratic broken line. Using the average daily gain as a response parameters. The estimation by the linear broken line was 20.9% whereas the estimation by the quadratic broken line was 23.4%.

Using the gain to feed ratio as a response parameter. The optimum Trp to Lys ratio estimated by the linear broken line was 18.7% whereas the estimation by quadratic broken line was 20.2%

Results from this experiment indicate that the optimum SID Trp: Lys ratio was 20.8% this value is a result of the 4 values found in the regression analyses. Diets with high Leu may reduce the feed intake by pigs if dietary Trp is not supplemented. Diets formulated with 35% of DDGS for growing pigs diets may need more dietary Trp. 

With this presentation, I want to make acknowledge for Evonik for the inputs financial support, and also to the whole team of Stein Monogastric Nutrition Laboratory thank you for your interest in this presentation and if you would like to know more about other research topics in nutrition you can always visit our website at nutrition.ansci.illinois.edu.