Strategies dealing with problems in relation to weaning need to consider many issues. This is further complicated, however, due to the fact, that some strategies counteract each other. What are the most important things to be mindful of to support further growth in pig herds?
Weaning represents a number of challenges that the piglet has to overcome. At this stage, the digestive tract of the piglet has to adapt from mainly absorbing nutrients from milk, to digest feed components, mainly of vegetable origin, which means developing the ability to secret enzymes, suitable for this purpose. Low feed intake after weaning is a well-known issue, that traditionally has been handled through increasing the nutrient density of the feed.
As it is known, piglets are more or less sterile at birth, the microbiome is established and is very variable within the first weeks of life, hence is susceptible to change by factors such as infections, changes in feed substrate, and especially by use of antibiotics. Normally, the microbiome is not stable until 4-5 weeks of age. Over recent years we have gained more and more knowledge regarding the importance of a healthy microbiome in the development of the gut function – both in absorbing nutrients, but also when it comes to the gut as an immune organ.
Besides this, weaning is a quite stressful procedure, since the piglets will most likely be introduced to a new environment and pen-mates, which in addition also enhances the risk of obtaining novel infections. In most modern pig productions, this occurs at the exact time where the passive immunity, acquired from colostrum, is fading and the active immune system is not yet fully developed.
One of the most challenging issues is to avoid anorexia after weaning. For many years, supplementing a creep feed has been common practice in a lot of farms, either as a simple diet, mainly to stimulate digestive enzyme secretion, or as a diet with high nutrient density, based on components with high protein digestibility and palatability. Dutch research has shown that even if creep feed is offered, not all piglets will eat it, and that non-eaters can be fasting up to 48 hours after weaning. Fasting this long leads to an empty stomach and intestine, which is known to cause tissue damage.
To avoid intestinal damage and prevent dysbiosis, it is essential for gut health that the piglets keep eating throughout the weaning period. To achieve this, a palatable and attractive feed should be offered pre-weaning and presented in a way, that as many piglets as possible have eaten it before they are weaned. This is easily done by offering sow milk replacer to teach the piglets to eat out of a trough. The milk replacer can then be changed into an actual creep feed, possibly in a liquid form, which is also offered a few days after weaning. Furthermore, to prevent infections, mixing litters at weaning should be kept at a minimum, and only enter piglets into pens that have been thoroughly cleaned and disinfected, including drying. This also goes for feeders and any other equipment that comes into contact with the piglets.
Post-weaning diarrhoea (PWD) often occurs as a consequence of the intestinal tract not yet being adapted to the feed offered. Adding high/pharmacological levels of zinc oxide (2,500-3,000 ppm Zn) to the diets to counteract PWD is very cost-effective. This has been carried out for several years, even though the actual mode of action is not fully understood. One of the theories is that the piglets simply experience a zinc-deficit after weaning. This could be due to zinc from sow milk having a much higher availability than the inorganic zinc, which is normally used in feed. A recent study investigated the correlation between zinc source and weaning on plasma and serum concentrations of zinc, and found that zinc levels in piglets actually drop after weaning, no matter if the piglet is eating or not. Only pigs receiving pharmacological zinc in the prestarter showed a zinc level similar to unweaned piglets. Unfortunately, the pharmacological use of zinc has a downside too. There is some evidence, that this use of zinc oxide could stimulate the development of antibiotic resistance of E. coli, and since the absorption of zinc is quite low, the high levels lead to a significant excretion to the environment. Based on these facts, this use of zinc oxide will need to be replaced by other alternatives in the coming years.
The very nutrient dense feeds piglets are fed after weaning, in order to obtain a large nutrient intake while feed intake is low, means that highly digestible nutrients, if not absorbed in the small intestine, pass on to the large intestine, where it can act as a substrate for bacterial growth. Some research points out that undigested protein could act as a substrate for pathogenic bacteria, stimulating the development of dysbiosis. Changing into less digestible nutrient bearing components is not a suitable solution, as the digestive capacity of the newly weaned piglet is limited. Instead, highly digestible components should be used in combination with inert fibre, that dilutes the diet, without working as an alternative substrate for bacteria.
Another well-known feed additive is organic acids in the feed or drinking water. Organic acids have an antibacterial effect, through lowering gastric pH, but also in the intestinal tract. Additionally, lowering the pH also optimises the environment for enzymatic digestion in the stomach.
Finally, dealing with stress factors is not only a matter of minimising stress. Under stressful conditions, the need for vitamins and trace minerals increases, partly due to the increased need for antioxidants. Increasing the micronutrients provides a reserve, making sure that the body is able to function optimally, adding to the well-being of the pig. While a stressed pig both physiologically and psychologically experiences a loss of appetite and an increased need for essential nutrients, oversupplying these nutrients during the critical period of weaning, prevents deficiency, and thereby helps maintaining high performance, even though lower levels of vitamins, under experimental conditions, have been shown to be sufficient.