Why are the first days post-weaning so important?

For several decades now, the pig industry has been addressing the piglet's adaptation to a solid diet after weaning. The gastrointestinal consequences associated with weaning are well known and several nutritional and management strategies have been developed to improve this phase. However, there are certain limitations to which the industry is still adapting. For example, the weaning age, which, if around 28 days of age or more, improves adaptation and post-weaning intake.

An issue has been that poor post-weaning feed acceptance has been considered a general group tendency and individual variability, a key aspect, has been overlooked. The most illuminating scientific work on initial post-weaning intake is probably by Brunninx et al, dating back to 2001. They identified that on day three after weaning 10% of piglets had not yet consumed feed. However, we have reason to believe that this fact does not reflect the whole problem.

Assuming the piglet's ability to digest solid feed and based on maintenance requirements (179 kcal EN/ kg^0.6; Everts, 2015), for a 6-kg pig to not lose weight it needs 207 g of feed per day (2500 kcal/kg), which is generally achieved after the first week. However, the following questions arise:

• What about the pigs that consume less than maintenance?
• What about the minimum intake to help maintain intestinal integrity?
• Are these pigs well characterized and can we help them?

Without clear answers to these questions, we present the proportion of pigs consuming less than 10, 30, 60, and 100 g/day during the first 4 days after weaning in Table 1 (Swine Research Center, Boxmeer, The Netherlands). Considering these values, 30% of the pigs eat less than half of their maintenance requirements in the first days, which has lasting consequences.

Table 1. Proportion of pigs with poor onset of feed intake after weaning using electronic feeding stations and individual monitoring.

Recent studies show that:

• A high voluntary feed intake days 1 to 3 after weaning resulted in higher feed intake and growth towards the end of post-weaning (Fabà et al., 2024a, 2024b).
• A high initial feed intake was associated with a greater surface area and villi length in the jejunum and a lower histamine (proinflammatory) content and protein fermentation products in the small intestine (Fabà et al., 2024a).

Low initial intake leads to poorer gut health and inflammation. In addition, the recovery process is hindered by the presence of unabsorbed nutrients and the risk of dysbiosis.

Therefore, to influence these pathways we want to:

• Reduce stress
• Increase appetite
• Provide nutrients that are key to intestinal integrity
• Reduce inflammation
• Minimize the risk of dysbiosis and pathogens

One study opted for a simple evaluation and compared three strategies expected to modify initial feed intake and feed acceptance.

• Two groups were fed the same diet, which included a combination of highly palatable ingredients, fed only after weaning:
  • with prior access to creep feed before weaning (Control with creep feed) or
  • without prior access to creep feed before weaning (Control without creep feed).
• A third treatment was a diet formulated to be less palatable and was fed only after weaning without prior access to feed (low palatability without creep feed).

The treatment diets (d 0-14) were strictly formulated with the same nutritional value:

• Standardized ileal digestible lysine (SID Lys) = 11.3 and the same amino acid profile
• Crude protein (CP) = 17.4%.
• Neutral detergent fiber (NDF) = 110
• Acid detergent fiber (ADF) = 50
• Non-starch polysaccharides (NSPs) = 148
• Digestible phosphorus (DP) = 4.2
• Calcium (Ca) = 5.9
• Net energy (NE) = 2400 kcal/kg

All diets were offered ad libitum in pens of 12 pigs (12 pens) equipped with a single-opening electronic feeding station to monitor individual feed intake (N = 108). Saliva samples were collected for cortisol analysis to assess whether there was an effect on the stress level.

Daily feed intake after weaning was strongly affected in the group with a lowly palatable diet, with reduced feed intake (Figure 1). Likewise, an effect was observed in the proportion of piglets with low initial intake (piglets with a cumulative intake <80 g from days 1-3 post-weaning). This was 5.55% for control with creep feed, 11.1% for control without creep feed, and 38.9% for the lowly palatable diet without creep feed (Table 2). Although there was a compensatory effect between days 23-28 for the low palatability group without creep feed, the response was not enough to equalize the weights at the end of the nursery period.

The final weight of the pigs was higher in the control group (19.2 kg), followed by the control without creep feed (18.5 kg), and was lowest in the low palatability treatment (18.1 kg) at day 34 (see Table 2). In addition, the diet influenced the level of stress. The low palatability group presented higher cortisol levels in saliva than the control group with creep feed while it was intermediate in the control without creep feed.

To study the long-term consequences, we used the final body weight of the trial to model the costs/kg gained in finishing, using Watson^® modeling software. Based on previous literature (Pluske et al., 1997; Fabà et al., 2024a), we expected pigs with low initial feed intake at weaning to have poor gastrointestinal health with long-lasting, negative consequences on intake and growth. Therefore, we included the proportion of pigs that had low intake the first week post-weaning in our modeling (5.55%, 11.1%, and 38.9%, respectively).

The costs and the resulting technical results for the finishing phase are very enlightening. The animals in the control group with creep feed showed on average better average daily gain, a better feed conversion rate, and 1.9 kg more final weight than the control without creep feed, resulting in an improvement of the margin on the feed cost of approximately 5€. The low palatability diet without creep feed resulted in worse production parameters and a worse margin on feed cost (5.8€) than the control group without creep feed (Table 2).

Table 2. Zootechnical parameters between dietary treatments and modeling of growth and feeding costs

*Piglets with a cumulative intake below 80 g between days 1-3 post-weaning.
ADFI = average daily feed intake; ADG = average daily gain; FCR = feed conversion ratio; MOFC = Margin on feed cost.

We can thus conclude that a good start in early feed consumption plays a fundamental role in the highest percentage of piglets in the herd. Including a creep feed in the farrowing room and a highly palatable diet are keys to achieving better technical and economic results in the finishing phase.