By Jose Soto, Mike Tokach, Steve Dritz, Jason Woodworth, Joel DeRouchey and Robert Goodband, Kansas State University; Marcio Goncalves, PIC.
Multiple studies have investigated the impact of high fiber ingredients on swine growth and carcass performance. Reports have indicated that up to 30% distillers dried grains with solubles DDGS can be fed without compromising performance. However, research has also shown that carcass yield is reduced when feeding DDGS or other ingredients containing higher concentrations of dietary neutral detergent fiber (NDF). The high NDF levels increase the weight of intestinal contents at harvest. One successful strategy to ameliorate the negative effects on yield is withdrawing high NDF ingredients before harvest. Research had reported that pigs transitioned from a high NDF diet to a corn-soybean meal diet before harvest had similar carcass yield compared with pigs fed a corn-soybean meal diet during the whole finishing phases. Taking into consideration the financial implications of modifying carcass yield, the objective of this research project was to develop equations to accurately estimate carcass yield from dietary NDF and withdrawal strategies.
To develop prediction equations, a literature review was conducted to gather studies that examined the effects of high NDF ingredients and withdrawal strategies on carcass yield. In order to be included in the final database, experiments had to meet the following criteria: 1) pigs used in experiments had ad libitum access to feed and water; 2) the percentage of dietary ingredients fed throughout the experiment was adequately defined; 3) the experiments included control treatments and NDF withdrawal strategies, and 4) the experiments provided information including duration of the feeding period, initial body weight, final body weight, average daily gain, feed intake, feed efficiency, NDF from the last 2 dietary phases, withdrawal period, and carcass yield. The final database resulted in seven papers and eight different studies with a total of 43 treatment observations. Dietary treatments of each trial were reformulated using the NRC ingredient library (NRC, 2012) to obtain dietary nutrient content including percent NDF in the last two dietary phases. Regression equations were then developed using a selection procedure that determined which terms were meaningful to estimate carcass yield. Studies were weighted according to their standard errors for carcass yield, thus, giving more credit to larger, more heavily replicated studies.
The regression analysis showed that number of days in the withdrawal period (WP), neutral detergent fiber level in dietary phase prior to final phase (NDF1), neutral detergent fiber level in the last dietary phase (NDF2), and the interaction between NDF2 and WP (NDF2 × WP) were the most important variables in the dataset to explain carcass yield (Table 1). As expected, higher levels of NDF had a negative impact on carcass yield. Increasing the length of the withdrawal period improved carcass yield, however, the effect of withdrawal period was dependent on the level of NDF2, as indicated by the interaction term.
Table 1. Regression equation to predict carcass yield from dietary NDF and withdrawal period
An example with this equation is presented in figure 2. In our simulation, pigs were fed with moderate and high NDF1 diets (16 and 21% NDF; equivalent to 35 and 50% DDGS inclusion, respectively), and then transitioned to a diet with varying NDF levels (9 or 13%) during the last dietary phase (NDF2) and fed from 5 to 40 d. Predicted carcass yield when pigs are fed a corn-soybean meal (9% NDF) diet during both dietary phases is 75.0%. There is an estimated yield decrease of 0.84 and 1.44% when NDF is 16 and 21%, respectively, during the last two dietary phases. Partial carcass yield recovery is apparent when pigs are fed a 16 or 21% NDF diet and transitioned to a 9% NDF diet, depending on the length of the withdrawal period. However, the model predicts that yield is not continually improved when the diet in the last phase contains 13% NDF. In this situation, the entire benefit is found in the first five days of feeding the 13% NDF diet with no further improvement. In summary, fiber withdrawal strategies appear to recover carcass yield with the magnitude depending on the NDF level of the last two dietary phases as well as the fiber withdrawal length.