What would it take for your pigs to consistently achieve average daily gain of 2 pounds?

KansasStateUniversity swine nutrition researchers, including Steve Dritz, Mike Tokach, Bob Goodband, Joel DeRouchey and Jim Nelssen, have dug into this question.

Steve Dritz, DVM, cites the following three main nutrition drivers that affect average daily gain:

1.   Feed intake — dietary energy intake.

2.   Protein and amino acids.

3.   Macro and micro nutrients.

Feed intake

Dietary energy intake has the greatest influence on growth rate.  “Variability in feed intake explains 65 percent to 80 percent of the pig-to-pig growth rate variability,” Dritz emphasizes.  “The complex interplay of the environmental, health and genetic factors are mediated through feed intake.”

Environmental factors, especially, play a key role in eliminating the feed intake limitation. This is shown through an analysis of university and commercial field conditions in 26 KansasState research trials. (See the accompanying graph.) “The trials were all performed with a similar genotype,” Dritz says.  “The big differences were fewer pigs per pen and very high health status in the university pigs.”

 Another important aspect of feed intake is the impact that dietary energy density has on growth rate. For pigs up to about 150 pounds, feed intake does not change over a wide range of dietary energy density. This is termed the energy-dependant growth phase. “Thus, pigs consuming the same amount of an increased-energy-density diet consume more total calories that are available for growth,” Dritz says.

Research shows there is no impact on feed intake in increasing energy density of a corn/soybean meal-based diet by adding fat from 0 percent to 6 percent.  However, there was a linear improvement in growth rate through the highest added-fat level.

“So,  if the production goal is to maximize ADG, the diet’s energy density for this phase would be constrained by the amount of added fat that could be provided in the diet without causing feed flowability problems,” he says.

This contrasts to pigs in later growth stages. “When you increase energy density for these pigs, it results in lower feed intake as well as the number of calories consumed per day,” Dritz says.  There is no impact on growth rate across a range of energy densities, he explains.

Other research suggests that at a certain point, the pig is unable to alter its feed intake enough to make up for the lower energy density. Thus, a lower number of calories are consumed and growth rate declines.

The transition from the energy-dependent to the non-energy-dependant growth phase depends on environmental constraints placed on feed intake.

This is demonstrated by the 26 KansasState trials that show feed intake declines as much as 30 percent in the field situations, compared with university trials. In the field setting, feed intake peaks at about 200 pounds, while continuing to increase in the university trials.

“In the university trials, as pigs grow larger, they transition to a less energy-dependant growth phase at a lighter weight than those in the field,” Dritz explains. “Therefore, in the university data, growth-rate improvements related to increased dietary energy from adding fat declines with increasing body weight.  However, in the field data, where feed intake does not increase as rapidly with body weight gain, this decline in response is lower.”

In terms of practical implications for farms with high feed intake, the value of increasing ADG with dietary energy density is less and the transition away from the energy-dependant growth phase will occur at a lighter body weight, according to Dritz.

Protein and amino acids

After determining the optimum dietary energy density needed to achieve 2-pounds-per-day ADG, the next driver is the appropriate dietary lysine concentration. 

Due to variability in dietary energy density, Dritz says, you should set the appropriate lysine concentration as a ratio to dietary energy.  “After the target lysine-to-energy ratios are established, target levels for other amino acids and phosphorus can easily be estimated.”

The lysine requirement is expressed as a lysine-to-calorie ratio to ensure the right lysine amount is provided in diets that vary in energy density.  “As the diet’s energy density increases, either feed intake decreases or growth rate increases.  Therefore, when feed intake declines with more energy-dense diets, a higher dietary lysine percentage is required to maintain similar lysine intake,” he explains. “If energy density results in increased growth rate while feed intake remains constant, more lysine is required.  Both scenarios require higher dietary lysine percentages, but the amount of lysine needed per calorie of energy remains relatively constant.”

Here are four different approaches that you can use to determine a farm specific lysine-to-calorie ratio:

1. Conduct full-scale nutrition experiments where pigs are fed different diets and the animal response is closely monitored.  This requires a major commitment and accurate data collection.

2. Establish lean-tissue growth and feed-intake curves based on weighing and scanning representative groups of pigs with real-time ultrasound at regular intervals.  This approach is critical in multiple-phase feeding programs to establish the optimum diet composition for various growth stages.  It requires expertise in taking and interpreting real-time ultrasound measurements and creating lean-tissue growth curves and feed-intake curves.

3. Use a standardized version of the second approach by deriving average lean-tissue growth rates over the entire grow/finish period and use some standard lean-tissue growth curves to estimate farm-specific curves.

4. Use a developed regression equation that predicts lysine-to-calorie ratio based on body weight.  This equation is then scaled, based on a judgment of the pigs’ genetic potential and the potential influence of other factors. You can then use regression equations or constants to determine minimum ratios in relation to the lysine requirement.

Macro and micro nutrients

Phosphorus is an important nutrient for lean growth and skeletal development. Traditionally, phosphorus has been provided beyond nutrient requirements because it makes up a low percentage of total diet costs, Dritz says.

As producers have moved toward diets that minimize nutrient excretion, it is important to use less phosphorous in swine diets.  However, you don’t want to use too little phosphorous because “if phosphorous margins are too low, processing plants report problems of vertebral breakage from weakened bones,” he notes.

Other considerations that drive pig growth are the ratio of calcium to phosphorus.  “Elevated calcium-to-phosphorus ratios reduce feed intake, leading to lower growth rates,” he says.

Other macro minerals, vitamins and trace minerals can be important nutrients for growth but are usually included in more than adequate amounts in diets. Deficiencies are typically caused by feed manufacturing errors.

While there are some systems that achieve 2 pounds ADG on an individual group basis, there aren’t many that can hit it system wide, Dritz says. Some production systems consistently achieve 1.85 pounds, he says.  “It’s very common to see 1.7 to 1.75 pounds ADG.”

Dritz believes that 2 pounds ADG is a reasonable industry goal. “It’s reasonable that we should be striving for it, especially on a larger production system basis.”