As animals grow, the environment that they are exposed to can often impact how they develop across their lifetime. Mammals are an especially interesting group in which to study this development, as they wean from milk and typically start to eat solid foods. This transition is important and thought to lay the foundation for how a mammal will chew food throughout its lifetime. Weaned human children sometimes need to return to a soft or liquid diet after weaning when they are unwell, but little is known about how this may affect their ability to eat solid foods later, or whether this could affect the development of their jaw shape. Pigs are often used to infer how treatments may affect humans, as we can easily control their diets. To understand how soft diets can impact the jaw and chewing in pigs, Stéphane Montuelle and Susan Williams from Ohio University College of Osteopathic Medicine, USA, investigated how diet impacts the shape of a young pig's jaw and how they chew.
The researchers compared two groups of juvenile pigs – one that was only fed regular pellet feed, which is relatively hard, after weaning and the other group that was only fed soft water-soaked pellets. The duo then implanted small metal beads at specific locations in the jaws, which would help them to analyse X-ray videos of the jaw movements while the piglets were eating and drinking. Then, after 6 weeks on the diet when the piglets were 16 weeks old, the duo fed them a meal of tough foods, such as apples and almonds, and recorded X-ray films of the animals while they were eating. Finally, they compared the shapes of the pigs’ jaws, how fast they chewed and swallowed and the movements of their jaws as they masticated after growing up on the different diets.
The pair discovered that the diets had no effect on the shape of the pigs’ jaws, suggesting that short periods of an exclusively soft diet are not likely to alter the physical characteristics of the jaw. However, the pigs did move their jaws and eat differently depending upon the food that they were raised on. The pigs that had eaten a soft diet didn't switch the side that they chewed on as often as the pigs raised on a normal diet. In addition, the pigs that had consumed soft pig pellets when young also spent less time chewing tough foods than the pigs that were raised on a normal, hard pellet, diet. The chewing cycle itself, as the pigs moved their jaws up and down, also had a shorter duration when the pigs raised on a soft diet were eating. This suggests that even when exposed to a soft diet for a short period (just 6 weeks) after weaning, pigs change how they chew, especially when consuming foods that are tougher or stiffer.
Learning how an animal's diet during important developmental periods can affect it long term can tell us a lot about short-term adaptations. Changes to an animal's diet may cause changes to some aspects of their lives, such as their movements, but other aspects, such as the shape of bones, may not be affected at all. This knowledge can help scientists to understand better why animals might be affected physically by experiences early in life. We may be able to translate this knowledge to understand the impact of different diets on humans too. Human children may need a liquid or soft diet for extended periods when they are sick. Through studies on animals, we might be able to predict how diet changes could affect these children.
