Aggression is a feature on many pig farms, both in the rearing and breeding herd, and the cause of significant economic loss as well as great frustration on behalf of the producer. Potential causes worthy of mention include environment, health, stocking density and feeder space, before focusing on the more esoteric area of nutrition.
There are two types of hunger – physical and nutritional. Physical hunger is what we experience if deprived of food for a protracted period of time. From the pig’s perspective, it can also be a lack of feeder space and difficulty in getting the gut fill and comfort factor they’re looking for.
If an animal’s hungry and denied access to feed in front of it, its parasympathetic nervous system (PNS) has already ‘fired up’ the stomach to be ready for digestion. The first sight, smell and taste of feed stimulate the hypothalamus in the brain and delivers a message to the stomach via the vagus nerve to produce gastric juices.
If feed then enters the stomach, it becomes distended and more gastric juice, which is predominantly hydrochloric acid, is produced until such a point where the pH is too low. At this point juice secretion is reduced and the stomach has expanded to a degree where the vagus nerve tells the brain to stop eating. Denial of this process can lead to frustration, which can furthermore lead to behavioural vice. So access to feed or gut fill is essential.
Nutritional hunger is different and happens when the nutritional quality of the diet is insufficient to meet the pig’s physiological needs, even though the quantity of feed is sufficient to meet physical hunger. This could be caused by using low digestive value feed components to meet cost criteria. Feeding an unbalanced diet can cause the animal to search for the missing nutritional components of the diet within its immediate surroundings. When this can’t be reconciled, the levels of frustration and vice occur again.
So, the correct density diet combined with access to feed is essential in order to reduce stress that could lead to aggression.
To complicate matters more, there has been an increasing problem with gastric ulceration. This is where the mucosal lining of the stomach has been compromised and the impact of stomach acid on this region of tissue leads to pain and discomfort. If access to feed is denied and the preliminary stages of gastric juice secretion have taken place, the animal has little option but to vent its frustration.
There are products that can help manage acid secretion that are used widely in the cattle industry to control rumen pH – effectively antacids. There are other nutritional techniques that can be applied to control brain chemistry. But by far the best route is to ensure good access to the most nutritionally correct diet and then fine tune thereafter. This way the risk of stress and aggression caused by nutritional factors can be prevented.
> Born in Essex, schooled in Suffolk and a graduate of Reading University, Dr Phil Baynes has spent his career in pig welfare and nutrition. Now based in Cheshire, he runs Baynes Nutrition and is a consultant nutritionist to Provimi