Calf growth: the influence of odorants and taste buds

by Wiehan Visagie

Recently, animal nutritionists have been busy acquiring new information on farm animals’ senses of smell and taste. Whether it is chickens, pigs, goats, or cows, we know very little about the way in which their smell systems work.

Although numerous studies of olfaction indicate the importance of smell to the animal, we tend to neglect this matter when we formulate feed as our aim is always to achieve higher yields. The immediate effect of that aim is more readily measurable, but our time should rather be spent on the animals’ chemosensory systems.

For ruminants, taste and smell are separate senses with their own receptor organs. However, they are intimately entwined. Taste-provoking chemical molecules called tastants are detected by the animal’s taste buds, which consist of special sensory cells. When stimulated, these cells send signals to specific areas of the brain, which makes the animal conscious of the perception of taste. Similarly, specialised cells in the nose pick up odorants, which stimulate receptor proteins that initiate a neural response. Ultimately, messages about taste and smell converge, causing the animal to detect the flavours of food.

According to Professor Ivan Manzini, from the Institute of Animal Science at Germany’s Giessen University, olfactory receptors in mammals represent three percent of its entire genome – the largest family of g-protein coupled receptors in the genome. This indicates the importance of olfactory receptors in animals, particularly when considering the feeding of younger animals. Calves rely on their senses of smell and taste to evaluate the desirability of feed. Feed having an unpleasant taste or smell can result in lower levels of feed intake, which eventually affects the return on investment in the farm. The best way to improve the smell and taste of feed is to make use of feed flavours. Calf feed then becomes more palatable to them, its digestion is indirectly increased, and better feed efficiency is the result.

In dairy nutrition, the adding of feed flavours has been widely accepted for two reasons. Calves respond better to feed with feed flavours. Calves have approximately 25 000 taste buds situated on the dorsal surface of the tongue, in the pharynx, and in the larynx. Compare this to humans (9 000 taste buds) and chickens (24 taste buds) and it becomes clear that calves need special attention. Feed tends to stay longer in the mouths of calves than other species, which will certainly favour the inclusion of feed flavours. Better feed intake and performance will be achieved.

‘Promoting’ raw materials

When calves are fed on silage-based diets it might be essential to include flavours, as doing so will mask the effects of alcohols formed in the silage during the fermentation process. The palatability of these types of silage is heavily affected when they contain high levels of moisture and are not left to dry before being piled. Flavours will also play an important role when coarselychopped straw or grass is fed, as calves usually avoid these types of raw materials. Adding flavours will help to ‘promote’ feeds and a gradual increase in consumption will be observed.

Growth performance of calves

In a study published in the Journal of Dairy Science, calves fed flavoured feed consumed more than calves fed unflavoured feed. The researchers added flavours to milk and to a calf starter feed to determine if young calves could be encouraged to eat dry feed by association of the starter feed and the milk. Twenty-four calves received flavoured milk containing butterscotch, ethyl butyrate, and maple flavours. Twelve of the calves were fed a normal pelleted starter feed. The other twelve were fed the same starter feed, but with the addition of the same flavouring products added to the milk. After two weeks, the calves fed the flavoured starter feed began to consume more pellets than those consuming starter feed without any added flavours.

This resulted in significantly higher weight gains for the calves fed on the flavoured feed, compared to the calves fed on unflavoured feed. It is therefore essential to stimulate intake in dairy calves to achieve optimal growth. As indicated by the study above and the information in literature, it is clear that calf pellets should contain quality flavourants.

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