Maternal transfer in pigs is a strategy based on the inclusion of volatile compounds in diets, which after passing to the foetus or the newborn piglet, creates a “previous experience” or “familiarisation”. That familiarity can be later used to optimise feed intake, growth, feeding behaviour and reduction of post-weaning stress. This article gives an introduction to this fascinating topic, setting the basis for futher reading.
Introduction
When we talk about maternal transfer, we usually think about the nutrients, hormones and antibodies that are transferred via the placenta, or during lactation, via colostrum and milk (Glezen, 2003). However, to what extent diffusible substances, not naturally found in the body of the sow, can be transferred to the offspring, and produce effects on them?
A number of studies in different species have demonstrated that some compounds naturally found in feed ingredients, or added as a supplement in the maternal diet, can be detected in the amniotic fluid, colostrum and/or milk (Table 1). From Table 1 we can conclude that, for examples, terpenes can enter the amniotic fluid, colostrum and milk.
Table 1. Compounds appearing in amnions, colostrum and milk after administering them to the mothers in the feed. Data collected for humans, pigs and horses (√: detected; X: non-detected; –: Not tested).
Methods to detect compounds present in feed ingredients
There are different methods to detect these substances:
- liquid-liquid extractioncombined with gas chromatography-mass spectrometry (GC-MS)
- headspace solid-phase microextraction coupled to gas chromatography (HS-SPME)
- gas chromatography-olfactometry methodology (GC-O)
- nuclear magnetic resonance/mass spectrometry
Changes in the organoleptic composition
It has been observed that this type of maternal transfer (different from the immunological or nutritional transfer) can organoleptically and chemically modify the characteristics of the fluids, and even change its microbiome.
As we have observed previously (Table 1), some volatile compounds cross the placental barrier, enter the bloodstream and are directly transported to the foetus.
- They can reach the nasal capillaries and coming in contact with the olfactory receptors, which can be stimulated resulting in previous experience.
- These volatile compounds can also enter the amniotic fluid. When the foetus encounters these compounds through the oral and nasal cavities, the olfactory and/or taste receptors are stimulated (Hepper, 1988).
Maternal learning
Maternal learning is a phenomenon occurring when the exposure of the foetus to the volatile compounds creates a “previous experience” or “familiarity” with them. This can also positively modulate the post-natal recognition and acceptance of feed containing the same compounds before and after weaning (Mennella et al., 2001).
The learning can continue after birth, through the milk. The hedonic and post-ingestion effects of milk, in combination with the pleasure of suckling, could create an associative learning with volatile compounds found in the milk (Hepper and Wells, 2006; Figueroa et al., 2013).
The preference for volatile compounds found in the feed can increase when they are also present in the milk –Oostindjer et al., 2009–. Table 2 summarises the main effects of such compounds on pigs.
Maternal learning has positive effects on feed consumption, growth, feeding behaviour and reduction of post-weaning stress.
Changes in the chemical composition of colostrum and milk
Wang et al., (2008) added a mixture of essential oils, flavonoids, spicy substances, and mucilage to diets fed to pregnant and lactating sows. The authors observed an increase of immunoglobulin G (IgG) levels in the milk.
Zoidis et al. (2018) included α-pinene, limonene and β-caryophyllene in diets fed to goats during 18 days of lactation. They observed an increase in the levels of C 18:3 conjugated linoleic acid and monounsaturated fatty acids in milk, and a reduction in C 16:0.
In our research group, the addition of thymol and anethole in the diets of pregnant and lactating sows resulted in higher protein levels in colostrum and higher fat levels in milk (Figure 1) (Reyes-Camacho et al., unpublished data).
Figure 1. Composition of colostrum and milk in sows supplemented with anethol and thymol during pregnancy and lactation.
There are not many studies demonstrating changes in the chemical composition of milk. Most of those studies focused only on organoleptic changes related to maternal learning, without expecting changes in the chemical composition. However, according to recent studies carried out by our group, this effect associated with maternal transfer is promising. Further research is needed to understand its relevance to the development and early viability of piglets.
Changes in the microbial composition and milk bacteriostatic capacity
In our group, the inclusion of thymol + anethole during pregnancy and lactation resulted in bacteriostatic activity of the milk against Bacillus subtilis and Staphylococcus aureus (Reyes-Camacho et al., unpublished data). These results may represent improvements in the functionality and bioactive capacity of the mammary gland, contributing to preserving the health status and integrity of the sow and litter. For the piglet, this could mean the instauration of a healthy microbiota, improving the intestinal health after birth. This finding could also have effects on the enzymatic capacity of the milk.
Similar to what happens with the research on changes in milk chemical composition, there are few studies evaluating the changes in milk microbiota due to maternal transfer. Therefore, there is a need for further research in this area.
Conclusions
The addition of compounds to the maternal diet influences the organoleptic characteristics, as well as the chemical and microbiological composition, of amniotic fluid, colostrum, and milk. It also has an effect on the bacteriostatic capacity of milk.
Therefore, the maternal transfer is an indirect and modulable strategy (via feed manipulation) that goes beyond maternal learning. It gives us the possibility of regulating the levels of fat, protein, and/or the bacteriostatic activity of colostrum and milk.
This article was initially published in nutriNews Spain, under th title Oportunidades de la transferencia materna en porcino