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Interpretive Summary: Relationship between energy intake and growth performance and body composition in pigs selected for low backfat thickness

By: Dr. Emily Taylor

The progression of genetic selection for reduced carcass backfat has increased over the past 20 years, causing an altered phenotypic relationship between energy intake and carcass backfat thickness. The current study aims to re-investigate this relationship. The authors hypothesized that carcass fatness measurements have become less responsive to energy intake in the genetics selected for low backfat. In contrast, protein deposition rate maintains a linear relationship with energy intake. 

Both intact male and female pigs (between 60 to 108 kg live weight) were fed wheat-based diets containing seven different amounts of amino acids at 14.3 MJ digestible energy (DE)/kg, which provided differing amounts of digestible energy intake. Body composition (protein, fat, and ash) was measured using the dual-energy X-ray absorptiometry (DXA) method when pigs reached 108kg. Following slaughter, carcass backfat measurements were also taken. Carcass backfat thickness increased by 0.125mm for every MJ increase in daily DE intake for male pigs. However, in female pigs, carcass backfat thickness was not responsive to DE intake. Male pigs' response to DE intake increases linearly or whole-body fat composition and fat deposition, while females responded quadratically. Protein deposition increased for male (3.8g) and female (2.5g) pigs with every MJ increase in DE intake. 

In conclusion, the current study supported the concept that restricting energy allowance to reduce fatness or backfat thickness of finisher pigs has decreased in the genetics selected for reduced backfat – this being more prominent in females. In addition, the protein deposition rate of both males and females maintained a linear relationship with energy intake. This mechanism is essential to avoid excessive fat deposition in response to high energy intake; however, male and female pigs seem to have developed different strategies for adapting to the selection pressure for low backfat over a prolonged period.

This article is available in the Journal of Animal Science.