EFFECT OF DIETS ON GROWTH AND DEVELOPMENT OF EARLY WEANED HOLSTEIN-FRIESIAN CALVES
Three experiments were conducted with Holstein-Friesian calves to study the effects of diets and early weaning on body growth and development of rumen function. In the first experiment, calves fed restricted levels of milk replacer and a simple calf meal grew as fast to 120 days of age as calves fed high levels of milk replacer or a complex calf meal. When calves were fed a high-energy milk replacer and weaned at 3 weeks of age, feed consumption and growth rate to 120 days of age was comparable with that of calves fed a low-energy milk replacer and weaned at 4 weeks of age. There were no differences in digestibility of the simple and complex calf meals. Apparent coefficients of digestibility of dry matter, nitrogen and gross energy increased slightly between the 5th and 9th weeks; nitrogen retention increased from 14.9 to 29.9%. Concentrations of total volatile fatty acids (VFA) averaged 10.3 and 10.0 mmoles/100 ml rumen fluid at 5 and 9 weeks, respectively, and there were no significant changes in proportions of VFA.In the second experiment, there was no difference in feed consumption or growth rate when calves were fed the simple and complex calf meals in pelleted form.In the third experiment, concentrations of total VFA increased from 2.3 to 12.6 mmoles/100 ml rumen fluid between 6 and 37 days of age. The proportion of acetate decreased from 71.6% at 6 days to 42.9% at 37 days, while molar proportions of propionate and butyrate increased from 19.7 and 4.5% to 37.5 and 12.0%, respectively, for the same period of time. Rumen pH declined as the concentration of volatile fatty acids increased. Blood glucose levels increased from 6 to 55 days of age.