Consider diet when selecting pigs for RFI

Consider diet when selecting pigs for RFI

THE largest cost component of pork production is feed, and increasing feed costs have motivated producers to look for better ways to improve feed efficiency as well as for alternative feedstuffs, according to researchers with the department of animal science at Iowa State University.

Residual feed intake (RFI) is a measure of feed efficiency that is defined as the difference between a pig's observed and expected feed intake based on its growth and back fat. Therefore, low-RFI (LRFI) pigs are more efficient than high-RFI (HRFI) pigs, Jennifer Young, John Patience, Nicholas Gabler and Jack Dekkers explained in a leaflet included in the 2013 "Iowa State University Animal Industry Report."

Young et al. said they conducted a study to determine if putting pigs selected for RFI on high-energy/low-fiber (HELF) diets would perform equally well and if LRFI pigs would maintain their advantage in feed intake and efficiency if they were reared on low-energy/high-fiber (LEHF) diets.

Materials and methods. Pigs in this study came from the Iowa State University RFI selection experiment. Using purebred Yorkshire pigs, a selection line for lower RFI (LRFI line) and a randomly selected control line were initiated in 2001. After five generations, the randomly selected control line was selected for higher RFI (HRFI line) to increase divergence between the lines, the researchers explained.

Using pigs from the second parity of the eighth generation of the RFI selection experiment, barrows and gilts (Table 1) from the LRFI and HRFI lines were placed on either the HELF or LEHF diet — 3.31 Mcal/kg of metabolizable energy (ME) and 9.5% neutral detergent fiber (NDF) or 2.91 Mcal ME/kg and 24.6% NDF, respectively — in pens that contained a single-space electronic feeder that allowed individual feed intake to be recorded, Young et al. noted.

Using data collected from the electronic feeders, average daily feed intake (ADFI) was calculated for each pig. All pigs were weighed every two weeks, and these data were used to estimate average daily gain (ADG) and calculate gain:feed.

Results. According to Young et al., pigs from the LRFI line ate less than pigs from the HRFI line when fed the HELF diet — 1.41 kg versus 1.62 kg per day (P < 0.01) — but not when fed the LEHF diet — 1.40 kg versus 1.47 kg per day (P = 0.23), as shown in Table 2.

They explained that diet did not affect ADFI of the LRFI pigs (P = 0.92), but HRFI pigs had lower ADFI when fed the LEHF diet compared to the HELF diet: 1.47 kg versus 1.62 kg per day (P = 0.14) , respectively.

ADG did not differ between the LRFI and HRFI lines no matter if the pigs were fed the HELF or LEHF diet — 637 g versus 645 g per day (P = 0.61) or 514 g versus 533 g (P = 0.20), respectively — Young et al. reported. Although there was no line effect on growth, pigs fed the LEHF diet grew significantly more slowly than pigs fed the HELF diet: 523 g versus 641 g per day (P < 0.0001).

Pigs from the LRFI line had a better gain:feed ratio than pigs from the HRFI line when fed the HELF diet — 0.46 versus 0.40 (P < 0.001) — but the researchers said this difference disappeared when feeding the LEHF diet — 0.35 versus 0.35 (P = 0.83). Both lines had improved feed efficiency when fed the HELF diet versus the LEHF diet: 0.46 versus 0.35 (P < 0.001) for LRFI and 0.40 versus 0.35 (P < 0.05) for HRFI.

Although diet did not affect line differences in ADG, differences in ADFI were reported, Young et al. said, adding that this resulted in a line-by-diet interaction effect on gain:feed.

Overall, rearing pigs on LEHF diets after being continually selected based on HELF diets results in pigs that do not differ in feed efficiency or feed intake, Young et al. said.

They concluded that as feed costs rise and swine producers look more toward alternative feedstuffs, selection may need to be based on the performance of pigs on such diets rather than a traditional corn/soybean meal diet.


1. Number of pigs on trial




















2. Performance data results









ADFI, kg/day





ADG, g/day










a,b,cValues within a row with different superscripts differ at P < 0.05.


More fiber

Eating a diet containing too many easily digestible carbohydrates and not enough fiber increases the risk of obesity and diabetes. The same is true for pigs, which are useful models for studying the effects of diet on metabolism in people.

Researchers at Aarhus University in Denmark have examined the dietary carbohydrate/fiber question by using the pig as a model.

The results showed that the types and quantities of fiber in bread affected metabolism to different degrees. Pigs were also found to be an effective model for this type of investigation, an announcement said.

"The diet in the western world is rich in easily digestible carbohydrates but generally contains too little dietary fiber. This leads to sharp fluctuations in blood sugar and insulin levels several times during a day. These fluctuations and a sedentary lifestyle are one of the main causes of the rise in lifestyle diseases like (being) overweight, obesity and diabetes," Aarhus doctoral student Kirstine Lykke Nielsen said.

In the first part of a project conducted by Nielsen, she investigated how different types and contents of dietary fiber affect metabolism by feeding pigs either dark rye bread with or without whole rye grain or white wheat bread to which either wheat fiber (arabinoxylan) or oat fiber (beta-glucan) had been added. An ordinary white wheaten loaf with a low fiber content was used as the control.

The results showed that dark rye bread and white wheat bread with arabinoxylan had the largest effects on metabolism by lowering the acute glucose and insulin response compared with normal white bread.

In the project, Nielsen also examined whether pigs and people are completely comparable when it comes to nutritional experiments.

"Pigs are often used as models for humans in experiments on nutrition, but the question is whether the two species react the same to a diet intervention and whether the effects found in pigs can be transferred to humans," she said.

To clarify this, a human test panel ate the same types of bread as the pigs and had blood samples taken at the same intervals as the pigs. The results were generally fully comparable between the pigs and the people, which supports the concept that the pig is a good model for predicting nutritional effects in humans.

In a third experiment, pigs were fed either ad libitum or a restricted diet corresponding to the white bread diet. The purpose of the ad libitum group — which was given free access to a low-fiber, high-calorie wheat diet over a longer period — was to examine whether the pigs would develop the same lifestyle diseases as people.

While the ordinary slaughter pigs did not develop those lifestyle diseases, the pigs fed the white bread restricted diet were healthier and leaner, according to the blood sample analyses.

"The results from the experiments give a closer insight into how the metabolism is affected by different carbohydrates. They show that both concentrated arabinoxylan and whole-grain bread can be used to prevent and treat lifestyle diseases and that it is good for health to reduce calorie intake," Nielsen said.


Sow eating

Heat stress can have a large effect on sow performance and longevity, and sows may feel heat stressed at temperatures lower than one might think.

As temperatures surpass 70 degrees F, depending upon humidity, sows can start to experience adverse effects from heat stress, such as reduced feed intake. Changes in the ration can help sows continue to consume the nutrients they need to maintain performance and body condition levels.

Sows are most comfortable between 45 degrees F and 70 degrees F, with 60-65 degrees F being optimal, according to Dr. Vern Pearson, swine nutritionist for Purina Animal Nutrition.

"The combination of hot temperatures and humidity results in a high heat stress index and can cause problems for the sow if we don't account for it," Pearson said, explaining that heat-stressed sows have a greater potential to experience seasonal infertility, smaller litter sizes, decreased embryo survival rates and death losses.

Heat stress can also affect boars, resulting in lower libido, lower sperm counts, abnormal sperm and smaller litters.

In addition to environmental controls, sow nutrition plays a role in sow productivity through the summer.

"There's a direct correlation between heat and reduced feed intake," Pearson said. "Heat-stressed sows will eat less because digestion gives off body heat and makes the sows even warmer.

"Lactating sows will first maintain their litters and then use nutrients from their feed for body condition; sows that are not eating can lose body condition quickly," he added. "An under-conditioned sow will be less likely to breed back, so we need to keep the sows eating and in good condition."

Volume:85 Issue:25

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