Ruminal metabolic development in conventionally or early weaned Ruminal metabolic development in conventionally or early weaned calves calves

Accelerating the weaning age of


Introduction
A relationship between dry feed consumption and rumen developmen t of newborn calves has been well established.Although the rumen has an innate ability to develop, feeding only liquid or low amounts of dry feed will greatly decrease ~he rate of ruminal developmen t.An early weaning program has been shown to ~creas~fe~d consumption of calves and thereby allow weaning by 4 wk of ag~.
he obJectlYe of this investigation was to monitor changes in the metabolIc prOducts in the rumen of early-weaned or conventionally weaned calves from birth t to 3 mo of age.

Procedures d
Eight bull calves were removed from their dams within 24 hours postpartum ~placed in calf hutches.The calves were fed colostrum until 3 days of age, and ~n fed whole milk, at 8% body weight, until weaned.At 3 days of age, the ca ves Were ruminally cannulated and placed into one of two groups.Calves in one group Were placed on the early weaning program and weaned at 4 wk of age.The ~cond group comprised the conventionally weaned calves.They were fed a calf s arter ad libitum and weaned at 6 wk of age.o 1 At 1,4, 8 and 12 wk of age, ruminal fluid was collected from all calves at v' I ,.2, 3, 4, 6, 8 and 12 h postfeeding.The samples were analyzed for pH, and a atlle fatty acid (VF A), lactic acid, and ammonia concentrations.

Results and Discussion
12-h Calves in both groups exhibited similar trends for ruminal pH during the th Our sampling periods, with the pH decreasing for 1-3 hours postfeeding, and ca~n gradua!ly increasing to prefeeding levels by 12 hours.However, early-weaned (T a~es consIstently had lower ruminal pH than the conven tionally weaned group C Ie 1).This indicated a higher metabolic activity in the early-weaned calves.thoncurrently, the total VF A concentration peaked at 1-3 hours postfeeding and co~~decre.ased.Again, e~r1y-weaned c~1 ves consistently had higher total VF A ~entratI0ns than calves 1n the conventIonally weaned group (Table 2),

1IIn _
Milk was the major portion of the cal ves I diet at 1 wk of age, and this resulted in a high proportion of acetate in the rumen.As dry feed consumption of the calves gradually increased and milk consumption stopped, the overall proportion of acetate deminished and the proportion of propionic acid increased.
No significant difference in the proportions of acetic acid or propionic acid was found between the two groups.On the other hand, the proportion of butyric acid was significantly higher in early-weaned calves than in the control group.Low pH stimulates the production of butyric: acid, thus, the lower pH of the early-weaned calves may be associated with their higher percentage of butyric acid.Lactic acid concentrations were highest at 4 wk of age for both groups and then decreasE'd by the 8th week of age.Although no signific:ant difference between the two groups was found, there was a trend toward higher lactic acid concentrations in the early-weaned cal ves (T able 3).
Ruminal ammonia concentration decreased as the calves aged.This is indicative of increased bacterial utilization and ruminal absorption of ammonia.Although no significant difference in ammonia concentration was found between the two groups, milk intake has been shown to increase ruminal ammonia concentrations, and unweaned calves generally have higher ruminal ammonia than weaned calves.

Table 1 .
Ruminal pH I