A REVIEW OF THE IMPORTANCE AND PHYSIOLOGICAL-ROLE OF CURD FORMATION IN THE ABOMASUM OF YOUNG CALVES

The importance of abomasal protein clotting for optimal nutrient utili zation, health and growth of milk-fed calves remains a controversial i ssue. Clotting of casein in whole, waste and colostral milks was thoug ht to be responsible for improved digestibility, greater daily gains a nd improved calf health. Early milk replacers were formulated with cas ein containing protein sources. The milk replacer industry in the Unit ed States is currently using protein sources that are non-clotting, pr imarily whey and soy protein, in the formulations of replacers. In the past, milk replacers that exhibited no curd formation were characteri zed as inferior because of their association with poor growth rates an d high incidences of diarrhea. Research suggests that factors other th an clotting are directly responsible for this decreased performance. T he calf's immature digestive system during the first three weeks of li fe indicates a physiological need for clotting in the abomasum to full y utilize complex proteins. Thus whole milk proteins are suggested by some as the most suitable liquid diets for this age. Enzymatic secreti on is limited up to one month of age, restricting digestion of carbohy drate, fat and protein. After three weeks of age most calves can perfo rm comparably when fed non-clotting milk replacers. Inhibition of coag ulation with an oxalate-sodium buffer illustrated that clotting may on ly affect nutrient flow and not nutrient digestibility or performance of calves. Therefore, clotting may not be the fundamental element caus ing poor performance. Evidence suggests that the types of protein sour ces, the manufacturing methods and the inclusion of other less digesti ble sources of nutrients in the milk replacer may be the components hi ndering the growth and health of calves less than one month of age. Th e physical or chemical nature of milk substitutes as well as their dig estibility may influence the nutrient delivery from the abomasum to th e small intestine. The milk replacer industry in the US has been formu lating milk replaces based on calf performance rather than only analyz ed quality. (C) 1998 Elsevier Science B.V.