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If we had asked this question to veterinarians, specialized technicians and swine producers a few years ago, the immense majority would almost certainly have answered that the best age for weaning is at three weeks. However, there are continuous changes in swine production and its evolution questions this old belief with respect to the weaning age. In this article I will try to explain why in many production systems the weaning age is being put back to 28 days in order to achieve the objective of producing a minimum of 200 kg of weaned weight per productive sow and year. To achieve this objective a herd that weans at an average of three weeks (18 – 23 days) with an acceptable weight of 6.5 kg LW must wean 30.76 piglets/sow/year while the same herd weaning at 28 days (25 – 30 days) with a weight of 7.5 kg needs to wean 26.66 piglets/sow/year. For 27 – 30 days (in the case of weaning on more than one day per week) with 8.0 kg it is necessary to wean 25 piglets/sow/year.
Weaning is an enormous change for the piglet and a great change for the sow. First we are going to analyze the changes that the piglets undergo, then the changes that correspond to the reproductive sows, and to finish we will make an economic analysis.
The piglet
Basically there are two main changes:
- Change of diet
- Weaning stress
Change of diet
Milk is the ideal alimentation for lactating piglets, it represents an important contribution of essential nutrients for the growth of the piglets, it gives the piglets a certain immunity and stimulates their physiological development. If we compare milk with feed we can observe the following:
- Milk production reaches its maximum at 21 days and it remains high up to nearly 5 weeks of lactation. Weaning at 25 – 30 days does not take place when the sow already produces less milk, but when the piglets are suckling when the production continues being very high (8 – 10 kg per day).
- The nutritive value of milk is superior to that of the feed that is supplied in this phase (better quality/quality of components and greater digestibility).
- When the sow has a normal/good production of milk, the piglet does not eat feed in the first 13 – 15 days of life. When weaning is at 3 weeks there is only one week for the piglet to adapt to the new feeds. Although feeds today have improved immensely in quality and digestibility, weaning at three weeks brings about an enormous nutritional stress since the majority of piglets have not adapted to the feeds and as a consequence their ingestion is dangerously low during the first days post-weaning. This fact involves a noticeable “catabolic state”, low growth, poor transformation rates and gastrointestinal problems (basically diarrhoeas). The consumption of feed when weaning is at four weeks represents 15% of the total ingestion in the days before weaning while it is equal or 5% lower than when weaning is at 3 weeks; in other words, between week 3 and week 4 the consumption of feed is tripled.
- Milk contains certain quantities of IgA which gives it better protective qualities tan feed. On the other hand, the active immunity in the piglet is much more efficient at 4 weeks than at 3 weeks. Faced with these precocious infections, the so-called “immunity gap” is inferior at 4 weeks.
- Enzymatic activity and intestinal development is superior at 4 weeks, this being an important factor to consider in the absorption and digestion of nutrients which affect growth and the transformation rate.
Weaning stress
The desciption of what the piglet goes through at weaning is a clear indication of the enormous stress involved. The following are changes that the piglet experiences:
- Loss of maternal protection.
- Change of living space and environment.
- Mixing with groups of larger sized piglets (normally from different litters)
- Change of diet and nutritional behavior:
- Change from warm liquid diet to normally solid and dry.
- There is a substantial change in the nutritive quality and composition (generally sudden contact with vegetal protein).
- There is no collective communication at feeding.
- The piglet stops suckling every 40 – 60 minutes.
- The piglet stops receiving the defences from the maternal milk.
In short: the piglet must learn to “look after itself”. The stress is an additional factor which makes it difficult for growth continuation and for the absorption of aliments during the first 3 – 5 days after weaning.
The separation from the sow is accompanied by characteristic and loud cries (grunts/calls) from the piglet that are produced immediately after weaning. The frequency and tone of these “calls” has been used as a method to evaluate the level of stress suffered by the piglet at weaning. The piglets that are colder and that feed more poorly cry more loudly and more frequently. The frequency of the cries is higher at the beginning of weaning, however, the piglets that wean at 3 weeks make more “calls” (3.6 c/m) than those weaned at 4 – 5 weeks (2.3 – 2.9 c/m).
All these arguments lead us to believe that with respect to the piglet it seems reasonable that weaning at an average of 28 days is better than at 21 days. First, the difference in weight in piglets weaned between 3 and 4 weeks is 0.5 – 0.9 kg per piglet in favour of those weaned at 28 days. The productive data of piglets weaned at 4 weeks are better for its future productive performance of posterior phases. This efficiency in the weaning phase (weaning – 20 kg LW) is expressed by an improved growth of 5 – 10%, improved transformation rate of 1 – 5%, and improved mortality rate of 20 – 60%. In the fattening period, in field tests of industrial production systems with many animals, we have seen that an improvement in weight at weaning of 0.5 kg leads to an improvement of 1.5 – 2.5 kg at the same age at the end of fattening when the slaughter weight is 100 kg LW. All this leads us to conclude that a suitable weaning weight for the optimum performance in the growing and fattening phases should be at an average minimum of 7.5 – 8.0 kg, with no more than 10% of the animals weighing less than 6 kg LW. This objective is achievable by weaning at 28 days and is very difficult if weaning is at 21 days.
Author’s note: I would like to express my gratitude to PigChamp Pro- Europa and to Servicio Técnico de Cefusa for supplying the field data without which it would be difficult to make the arguments expressed in this article.
