Dairy Calves. Seen some cases of neurological signs with deaths? Could be related to the following, read on.
This season we have seen deaths in preweaned calves due to marked ruminal acidosis as a consequence of milk entering the rumen (so-called rumen drinkers) due to failure of the oesophageal groove to close.
Presenting signs vary with chronic rumen drinkers showing poor growth/illthrift to acute cases showing colic, neurological signs and death.
Milk entering the rumen is rapidly fermented, causing overgrowth of carbohydrate metabolising bacteria (mainly Streptococcus bovis) with production of volatile fatty acids and lactic acid. The ruminal fall in pH kills lactate-using microbes and increases growth of lactobacilli. Lactic acid is highly corrosive to the ruminal epithelium, causing rosions and ulcerations, leading the way for secondary infection by fungi and yeasts which can also tolerate the low rumen pH. In addition, lactic acid and VFAs increase the rumen osmolarity, causing decreased absorption of these acids and further build-up in the rumen exacerbating epithelial disruption and systemic dehydration.
Both D and L forms of Lactic acid are produced in the rumen and absorbed into the circulation. The L form is readily metabolised but the D form is not and accumulates in the circulation. Acute D-lactic acidosis has systemic and neurological effects ranging from depression, anorexia, ataxia, head-pressing, opisthotonus to coma and death.
The oesophageal groove fails to close with:
Irregular feeding times
Low quality milk replacer
Milk/milk replacer fed at too low a temperature
Open bucket feeding (gulping larger volumes)
Stressors (transport etc)