Effect of diet and sex on feed efficiency and the fecal microbiome at slaughter weight

Introduction

Feed is a major cost of pig production. Therefore, feed efficiency (FE) is a critical trait for the swine industry. Availability in the market and cost of feed ingredients dictate changes in feed composition. As a result, fiber level and composition can vary between pig diets. Microbiota in the gastrointestinal tract play an important role in fiber digestion because they produce enzymes that break down fiber structures and deliver volatile fatty acids to the pig. These volatile fatty acids can be used as metabolic energy sources1. As such, microbial fermentation could influence FE in pigs. The aim of this study was to investigate the association between FE and fecal microbiome in commercial grower-finisher pigs. In addition, the effects of diet composition and sex on fecal microbiome composition were studied.

Materials and methods

A total of 154 three-way crossbred grower-finisher pigs (Synthetic boar x (Large White x Landrace)) were either fed a diet based on corn/soybean meal (CS) or a diet based on wheat/barley (WB). Littermates were split randomly over the two diets and sexes were housed in separate pens (10 animals per pen) equipped with individual feed intake registration feeders. Fecal samples were collected on the day before slaughter (mean body weight 122 kg) and DNA was extracted and sequenced for the V3V4 16S ribosomal DNA regions. Sequences were clustered according to operational taxonomic units (OTU) for each individual, forming a table of OTU abundancy. A discriminant analysis using principal components was applied to the dataset to test separation for diet, sex and FE extreme groups (10 high and 10 low FE animals for each diet by sex combination).

Results and discussion

Pigs on different diets had very distinct microbiome composition, needing only two OTUs to separate the diets (P=0.018). This finding is consistent with results reported in the literature, indicating that diet composition affects gut microbial composition2. In addition, males and females could be separated based on 18 OTUs (P=0.002). Previous studies in weaners did not detect a difference between sexes in fecal microbiome3, but in agreement with our study, did detect a difference at slaughter age4, which is most likely due to sex steroid hormones5. Results also show that microbiome composition significantly differed between sexes for pigs fed a (fiber-rich) WB diet, but not for pigs fed the CS diet.  In conclusion, our results show a diet and sex dependent relationship between fecal microbial composition and FE in pigs at slaughter weight. These results demonstrate the potential to modulate microbiome composition, and therefore feed efficiency, via changes in diet formulation.

This study is part of the Feed-a-Gene Project, funded from the European Union’s H2020 Program under grant agreement no 633531.