Calves with Sam

My Ruminations about Rumen pH Among Weaned Calves

By using intensive data collection methods a research team was able to monitor rumen pH in  calves before, during and after weaning. Because of practical limitations (equipment, rumen canulas) the number of calves was limited to six.

"Pre-weaning the average daily pH was low (5.6 ) implying rumen acidosis. The pH reached its lowest levels during the week after weaning (wk 7) with a mean of 5.5 and did not increase before wk 11. Furthermore, ruminal pH was below 5.5 and 5.2 for approximately 745 and 220 minutes daily during wk 7 and 8, respectively. The pH increased significantly in wk 11 and 12 with a mean pH of 6.1."

Even when calves were not eating very much calf starter grain the pH levels were low. I did not expect that finding. In addition to 900g of milk replacer powder daily these calves had free-choice access to chopped straw - supposedly that ration should modify the rumen environment to achieve more favorable pH conditions. Among these few calves clearly the addition of straw did not improve pH conditions pre-weaning.

I noted that rumen pH dropped to 5.2 during weeks 7 and 8 for 220 minutes a day. Those prolonged low pH times suggest a depression of the favorable rumen microbial populations. The article did not mention whether or not  fresh concentrate was provided  before these periods of low pH. If calf "slug fed" on concentrate (usually due to not having a consistent supply 24/7) I would expect depressed pH conditions post feeding.

When feeding my own calves I thought that feeding a big handful of palatable alfalfa hay daily to my older calves would lead to more favorable rumen conditions - the fiber would form a stabilizing mat in the rumen, the calve would be encouraged to spend more time chewing a cud thus delivering more pH neutralizing fluid for the rumen. 

Now ,I wonder about feeding the hay. How well did this dietary rumen adaptation post-weaning work to manage rumen pH? My intent was to start building the appropriate rumen microbial population for fiber digestion (alfalfa hay). I didn't even think about rumen pH.

 I do know that I tried to be sure that after the calves had a milk step-down as part of weaning they always had access to plenty of clean water and palatable calf starter grain - never let either of those run out. At the time I thought that this was a best management practice. I wanted to prevent "slug" feeding (that is, eating an excessively large volume of grain at one time).

I recall that a few of my calves would cycle in their grain intake during weeks six and seven - up and down, up and down over a period of three to five days.  Maybe these were the ones where the rumen pH was very low for prolonged periods of time - perhaps they "went off-feed" because of this - then after recovering they dug into the grain, often eating six or more pounds of grain for the next several days. Then, off-feed again.

Perhaps the take-home message from this research is that we need to pay closer attention to the dietary transitions from weeks 5 through 12 to gradually ease the rumen into the most favorable pH conditions. 

Reference:

J.K. van Niekerk and Others, "Ruminal pH in Holstein dairy bull calves from pre-weaning to post-weaning." Journal of Dairy Science, 100:178 July 2017