Mucin excretion status and its relation to digestibility and growth in Holstein suckling calves

Mucin, a filamentous glycoprotein, is responsible for lubrication and protection of the mucosal epithelia from damages caused by the digesta, digestive secretions, and microorganisms. Goblet cells have potential to secrete granules which is distributed in the intestinal epithelium. The secretory granules contain glycoproteins, including mucins, which are classified into two types, neutral and acidic. The latter can be further differentiated into sulphomucins or sialomucins. There is increased attention to the bovine mucosal immunity because it can aid in preventing colonization and eventually infection of mucosal epithelia. Moreover, mucus is also a selective barrier for absorption across the small intestine. Additionally, as the mucus constitutes the interface between the epithelium and the lumen, mucin could be used as a marker of interaction between the epithelium and dietary components. Measuring the flow of intestinal mucin is a challenge for better understanding the interactions between nutrient digestibility and the gastrointestinal mucosa. The ileal flow of mucin in pigs has been estimated indirectly by using hexosamines as markersThirty-two calves (16 males and 16 females) were randomly divided into two treatment groups and fed with starter diets based on corn or barley as the grain source. Starter feeding began on the third day of life, and high quality alfalfa hay and fresh cow milk were fed according to the farm schedule. The calves were weighed at birth and weekly thereafter until weaning. Nutrient digestibility was determined at 2, 6, and 8 weeks of age. Mucin was crudely separated from fecal samples, and correlation of mucin concentration with digestibility parameters and growth characteristics determined. Mucin excretion rate was negatively correlated with the nutrient digestibility; at 8 weeks of ages it has also negatively correlated with feed intake (r=-0.37, P=0.0406). Further research is required to determine the detailed metabolism of mucin in the gastrointestinal tract of calves and its effect on animal performance.