Applying the piglet’s senses to improve feed intake

By Sofie Tanghe (Swine Product Developer)

Good feed intake at a young age is essential for a smooth weaning process and excellent piglet health. Therefore, helping the piglet to cope with neophobia (the reluctance or avoidance to ingest new feed) during feed transitions will improve feed intake and result in better performance. Earlyfeed has launched an innovative feed intake solution to quickly familiarize the piglet with feed and help it cope with neophobia for smoother feed transitions.

Although not all of them are equally important—and importance differs between species—feed preference and feed intake is influenced by all five senses (Torrallardona and Solà-Oriol, 2009). As humans, we primarily judge food based on its color and appearance, using our sense of sight to determine if we will eat something or not. Pigs, like all mammals except for primates, have dichromatic vision. This means that pigs can see and discriminate colors but their color vision is not as rich as humans, who have trichromatic vision. Thus, pigs rely much less on their sight when it comes to making choices regarding feed preference (e.g. changing the color of the feed is not expected to influence feed intake).

As pigs can associate noises with the time of feeding, hearing is related to feeding behavior in pigs. This association starts at birth, as piglets are able to recognize the grunting sound of their mother at the time of nursing. In reaction to this grunting, piglets will assemble at the udder and start to massage the teat, which will lead to oxytocin release and milk let down (Špinka and Illmann, 2015). Research has shown that playing these grunting sounds after weaning can increase feeding and drinking behavior in newly weaned pigs (Petrie and Gonyou, 1988).

Well developed in pigs, the sense of touch allows pigs to differentiate between different feed temperatures or textures (e.g. wet vs. dry or pellet vs. mash). When it comes to feed intake, touch is important for a pig but the two most important senses are taste and smell (Roura and Tedó, 2009).

Taste is highly developed in pigs. Compared to humans, pigs have about 3–4 times more taste buds (Figure 1). The sensitivity to taste allows animals to identify both nutrients and anti-nutritional compounds. Generally, beneficial compounds will bind to receptors of pleasant tastes (sweet, umami, salty), whereas anti-nutritional compounds will bind to receptors of unpleasant tastes (sour and bitter). Therefore, taste provides valuable information on the quality of feed (Torrallardona and Solà-Oriol, 2009).

Finally, the sense of olfaction—or smell—is also highly developed in pigs. Pigs have the highest number of functional olfactory receptor genes, which means that they have a very sophisticated system to sense smell and are able to distinguish more diverse odors than other species, including humans (Nguyen et al., 2012; Table 1). Another way to understand a pig’s sensitive smell is by noting that a pig brain is much smaller than a human brain (0.05% vs. 2% of total body weight, respectively) but the olfactory system of the pig is 7% of the brain size vs. 0.01% in humans (Brunjes et al., 2016).

Throughout the pig’s life, dietary changes usually cause neophobic reactions. This is clearly observed at the time of weaning, when the piglet has to change from milk to solid feed, and later in life, when a dietary change can result in a temporary drop in feed intake. This is particularly true when less palatable ingredients are used. Some ingredients, like acids or tannins, are regularly added to a pig diet for their beneficial effect on animal health but they actually bind to acidic or bitter receptors and are therefore deemed unpleasant by the pig. Using the right feed intake solution that focuses on the pig’s most important senses (taste and smell) can help to overcome this neophobia right from the start. But how do we know what is the right feed intake solution? To answer this question, Earlyfeed, the young animal nutrition brand of the Royal Agrifirm Group, was inspired by newborn piglets.

The newborn piglet receives little assistance from the sow after birth and has to find the nipple to suckle from on its own. Therefore, the piglet relies on its senses. By hearing the sow’s vocalizations and specific grunting at the time of nursing, the piglet will be attracted to the udder. Touch also plays a role, as the orientation of the sow’s hair forms a particular pattern that assists the newborn piglet towards the nipples (McBride, 1963). Still, the most important sense the piglet uses to locate the nipple is its sense of smell.

Piglet olfaction plays a critical role in successful nipple attachment. To attract the piglet to the nipple, specific olfactory cues are secreted by the mammary gland of the sow. Research has shown that when the piglet’s sense of smell is blocked by flushing an anesthetic into their nose, their ability to locate a teat and begin to suckle is strongly impaired. Also, altering the smell of the sow’s udder by washing the abdomen with organic solvents has been demonstrated to hinder teat localization and suckling (Morrow-Tesch and McGlone, 1990).

Human infants also respond to olfactory cues coming from their mother’s nipple region. Soon after birth, maternal breast odors will guide the neonate to the nipple. Research has shown when breastfed babies are presented with a clean cotton pad on one side of their head and a cotton pad with the odor of their mother’s breast on the other side of their head, they will preferentially turn their face in the direction of the breast odor. This attraction is very natural and so strong that even bottle-fed babies have a higher preference for the breast odor of an unfamiliar lactating woman compared with their own familiar formula milk (Porter and Winberg, 1999). Doucet et al. (2009) also observed that babies showed more head and mouth movements when they are presented with the breast odor of an unfamiliar lactating woman compared to other odorants, such as human milk, formula milk, or water.

Odors coming from the breasts of lactating women thus function as general attractants for neonates, regardless of the babies’ feeding history and whether the source of the olfactory cues is the mother or an unfamiliar woman (Porter and Winberg, 1999). An interesting fact is that, to some extent, the chemical profile of breast secretions overlaps with that of amniotic fluid. This perinatal overlap shows that postnatal attraction to odors coming from the nipple may actually reflect prenatal exposure and familiarization in utero (Porter and Winberg, 1999; Schaal, 2010).

Earlyfeed has implemented this knowledge in their piglet feed and launched Piglet’s Flavorit. This innovative feed intake solution is based on how the olfactory cues secreted by the mammary gland create feelings of familiarity and recognition, triggering the piglet’s innate reflex to search for its mother. Through this maternal recognition, piglets can achieve smoother feed transitions to result in improved continuous feed intake, reduced stress levels, and increased overall welfare and performance.

References available upon request