Better Pork - June 2007

Research

Compensatory growth: not all pigs have equal response

Research at the University of Guelph suggests that CG following amino acid intake restriction occurs only in some pigs – those with high lean tissue growth potential

by KATHY ZURBRIGG

Compensatory growth (CG) is the faster growth rate seen in pigs following a period of reduced growth.

Reduced growth rates can occur for a number of reasons, including feed restriction (or a pig not eating), key nutrients in the feed being restricted, or stress. Essentially, once the reason for the growth restriction is removed, the animal’s body plays “catch-up” as compared to other herd-mates who did not face growth restrictions.

Researchers have begun purposely restricting feed or protein intake in the grower phase to study the effects of CG on carcass quality, average daily gain (ADG) and average daily feed intake (ADFI) during the finisher phase. The benefits of this strategy may include increased ADG and ADFI and leaner carcasses in finishing hogs, with a reduced cost of feeding these pigs.

There are conflicting reports from researchers about the extent of CG in pigs. Different researchers vary the extent of feed or protein intake restriction during the grower phase, which produces various ranges of CG in finishing pigs. And the actual mechanics of how the body undertakes CG is not completely understood. University of Guelph graduate student Hector Martinez and Dr. Kees de Lange are striving to understand these mechanics and have discovered that not all pigs have equal CG responses.

In two separate experiments, Martinez and de Lange studied growing barrows and intact males. Within each group, half of the pigs were fed a diet with amino acid (protein) levels below the pigs’ requirements during the grower phase and the other half were fed an adequate diet. During the finishing phase, all pigs were fed adequate diets and monitored for at least 30 days for weight gain and body composition.

The barrows on the amino acid limiting grower feed were not able to “catch up” to the barrows fed the adequate grower diet. However, the intact males on the amino acid limiting diet did display complete CG and had equal ADG and carcass quality traits to the intact males fed adequate diets all along. 

The hormones produced by intact males, such as testosterone, direct the body to increase lean tissue growth and reduce body fat stores, when compared to barrows. Pigs with high lean tissue growth potentials, such as intact male pigs, generally don’t express their full potential, simply because they don’t have the capacity to consume sufficient energy. 

When fed protein limited grower diets, intact males will have larger body fat stores at the end of the grower phase. As a consequence, these pigs do not need to gain more body fat during the finisher phase and can use more of the feed energy for lean muscle growth. This results in compensatory growth during the finisher phase. Since barrows have lower lean tissue growth potentials, they don’t show CG during the finisher phase.

The combined results from Martinez and de Lange’s two experiments suggest that CG following amino acid intake restriction occurs only in some pigs – those with high lean tissue growth potential.

Taking advantage of compensatory growth can reduce feed costs by reducing the amount of expensive protein fed to growing pigs. It may even enhance gut health in growing pigs and meat quality in market weight pigs. However, says de Lange, producers shouldn’t be too hasty to restrict amino acid intake in the grower barn. When genetics alone determines the lean tissue growth potential of a pig and not energy intake, the diet should always exceed the nutritional requirements in order to maximize growth performance and carcass quality.

Kathy Zurbrigg is animal health and welfare specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs, based in Fergus.