Effect of postweaning feed intake on performance, intestinal morphology, and the probability of diarrhea in piglets

Commented article

Engelsmann MN, Nielsen TS, Hedemann MS, Krogh U, Nørgaard JV. Effect of postweaning feed intake on performance, intestinal morphology, and the probability of diarrhoea in piglets. Animal. 2023; 17: 100891. https://doi.org/10.1016/j.animal.2023.100891

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Academic commentary, by Josep Gasa

At weaning, piglets usually suffer changes in the intestinal structure, a high incidence of diarrhea, and reduced feed intake, although a clear direct relationship has not been established between feed intake during the first days after weaning and the appearance of diarrhea. In this study, a total of 120 piglets weaned at 28 days (7.20 ± 0.26 kg) were used, which were housed individually and distributed into five nutritional treatments:

• two diets varied in crude protein content
• three diets varied in threonine and tryptophan levels

The possible effect of the feed composition is not analyzed and is included in another article by the same authors.

After receiving feed for four days after weaning, the following were selected:

• The 30 piglets that consumed the most feed (181 ± 5.75 g/day, HIGH-intake)
• The 30 piglets that consumed the least feed (35.7 ± 5.9 g/day, LOW-intake)

The remaining 60 piglets were discarded. In addition to the performance results, fecal consistency was monitored, blood samples were taken at 4, 14, 21, and 28 days post-weaning, and on day 28 the piglets were sacrificed and samples of intestinal and colon mucosa were taken.

The results at 28 days post-weaning show that, compared to LOW-intake piglets, HIGH-intake piglets significantly:

• Consumed more feed, weighed more, and grew more.
• Had a 55% higher probability of having diarrhea.
• Received more antibiotic treatments.

Regarding the metabolic and intestinal parameters measured, the HIGH-intake piglets showed:

• A higher concentration of acute phase proteins in the blood
• An increased number of mucus-producing cells in the intestine
• No differences in the mucosa structure or the permeability in the small intestine or colon.

The authors indicate that the higher incidence of diarrhea in the HIGH-intake group would be of mechanical, non-infectious origin and does not necessarily require intervention with antibiotics. They suggest that the higher concentration of acute phase proteins is associated with an inflammatory process derived from anti-nutritive factors provided with the diet and the greater production of intestinal mucus is interpreted as the piglets' intestinal defense mechanisms. The authors conclude that HIGH-intake piglets had better performance and that the higher incidence of diarrhea does not necessarily require treatment with antibiotics.

The research is very interesting but leaves some loose ends that would be interesting to clarify before applying the conclusions in practice:

1. It is unknown to what extent the individual housing of the piglets influenced the results.
2. It is important to delve into how feed intake occurs during the first four days post-weaning: for the same feed intake, a longer or shorter duration of the fasting period can condition subsequent digestive events. This is a very interesting factor as it is the basis for classifying piglets into HIGH- and LOW-intake groups.
3. By not administering one single diet, the possible effect that the diets could have is also unclear, especially the difference in protein level.
4. Although diarrhea in HIGH-intake piglets occurs mainly due to mechanical causes, the fact that all the animals that had diarrhea were treated prevents us from knowing how they would have evolved in the absence of antibiotic treatment.

On-farm commentary, by Josep Casanovas

The authors clearly and concisely describe that at the time of weaning, piglets face a series of physiological, environmental, social, and nutritional changes that create a stressful situation. This situation, they again rightly comment, is usually accompanied by a decrease in feed intake.

Despite knowing how critical the situation is, they decided to house the animals individually, which can only make the situation more stressful. Just like how for humans the worst punishment that can be given to a prisoner in a penitentiary is to house him in a punishment cell in solitary confinement, for a gregarious animal such as the pig, solitude creates a particularly stressful situation of abandonment and helplessness.

This lonely situation is particularly aggravated by the decision to house the animals at 23°C on day 0 and to gradually decrease to 21°C at the end of the experimental period. Pigs housed in groups can better defend themselves against low temperatures by increasing the contact between them at rest times.

Another surprise that the authors have in store for us is that to simulate the conditions of commercial farms, they worsened the hygienic conditions by "painting" the walls of the pens with fresh feces diluted in water. This situation does not at all reflect the reality of the production that I know.

Of course, a pig stops eating after weaning, but as it adapts to the new situation it starts to eat and drink. The goal is to work to make this fasting period as short as possible. Animals housed in groups adapt earlier, as pigs are animals capable of learning by observing what others do.

Once the fasting time is over, the pigs are hungry, they have built up an appetite. When they are nursing, they tend to suckle once an hour, 24 times a day on average, so the hunger sensation is quickly extinguished while they are with their mother and siblings.

One of the things that most influences the consistency of feces is the speed of intestinal transit. This parameter depends directly on the intake.

• In animals that eat little, transit is slow, so the digestive process is much more meticulous and the feces have a solid consistency. Farmers usually associate the presence of hard feces with the presence of fever. When animals get sick, they stop eating and as a consequence they usually present constipation.
• In animals that eat a lot, transit is fast, so the digestive process is not completely efficient and the feces have a softer consistency than usual; presenting softness or even diarrhea.

The fact that after weaning the piglets go through a period of fasting, immediately followed by a period of eager consumption, means that the presence of diarrhea is common between 3 and 5 days after weaning. This is mechanical diarrhea as the authors of the article note. In this situation, it is not necessary to be too hasty, since after this phase of high consumption, the animals usually regulate themselves. They exercise this ability much better when they are housed in groups.

Cold conditions increase consumption, so the situation may last longer than expected.

Antibiotic treatment, due to its harmful effect on the microbiota and the risk of causing resistance, is not recommended in cases of mechanical diarrhea.

One way to differentiate mechanical diarrhea from that caused by different infectious agents is by the clinical picture and by the color. When diarrhea is mechanical there are no clinical symptoms and the color is the same as the rest of the feces. In cases of diarrhea caused by pathological agents, there are symptoms, even deaths, and the color of the diarrhea is usually different from the rest of the feces.

The authors present us with a study with too many limitations to be of much benefit from the farmers' point of view. It is clear that if I were a test pig, this experimental design would not be my favorite.