Effects of Age and Diet on Rumen and Blood Components of the Young Calf

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Abstract
Changes in ruminal organic acids, ruminal ammonia and blood lactic acid were observed in early-weaned calves fed starter (G) or starter and alfalfa hay (HG) diets. Rumen samples and venous blood were obtained at weekly intervals 3 hr post-feeding from 3-8 wk of age. At 9 and 13 wk of age blood and rumen fluid were taken at 0, 1, 1.5, 2, 3 and 5 hr after feeding. Molar proportions of acetic, propionic and butyric acids were similar for both groups of calves through 7 wk of age. As the HG calves became older and began to consume more hay, the proportion of acetic acid increased whereas the proportion of propionic acid decreased. Little change in volatile fatty acids was observed in rumen fluid of G calves. Rumen lactic acid levels varied from 0-95 mg/100 ml with peak production occurring at 1-2 hr post-feeding. No differences in either blood or rumen lactic acid were observed between groups. Ammonia concentrations in rumen fluid were highest at 3-5 wk in both groups. As age increased there appeared to be greater utilization of ruminal ammonia. Concentrations of ammonia at 9 and 13 wk tended to remain relatively constant throughout the sampling period with little difference due to diet.