Ketosis

Most affected cows show nothing obvious, and subclinical ketosis is found only by testing: elevated blood beta-hydroxybutyrate, commonly defined as at least 1.2 mmol/L in the United States or 1.4 mmol/L in Canada. In clinical cases, feed intake and milk yield fall. Some cows develop nervous signs: aimless wandering, an unsteady gait, bellowing and occasional aggression. Affected cows go on to have more displaced abomasum, metritis, retained fetal membranes, mastitis, lameness and poorer fertility; fatty liver accompanies the condition.

Ketosis is a metabolic disease of dairy cows in early lactation, not an infection. Around calving, feed intake falls while energy demand for milk rises, creating negative energy balance. The cow mobilises body fat, releasing non-esterified fatty acids into the blood; the liver oxidises them, but when gluconeogenic substrate runs short the resulting acetyl-CoA cannot enter the Krebs cycle and is diverted into ketone bodies: acetone, acetoacetate and beta-hydroxybutyrate. Fat also accumulates in the liver, producing hepatic steatosis. Abdominal fat in high-producing cows is especially quick to mobilise and pro-inflammatory, worsening ketone production and favouring endotoxaemia.

The disease affects dairy cattle in the transition period around calving. Subclinical ketosis is common: reported prevalence is 7.6-33.1% in US herds and 5.1-20.5% in Europe, and one review cites up to 40% at the start of lactation. New cases peak three to seven days after calving, and multiparous cows are affected more than first-calvers. Risk rises with high milk yield, over-conditioning in the dry period, loss of body condition before calving, longer dry periods, calving intervals longer than twelve months, first calving at 25 months or older, Jersey breed and genetic predisposition. In multiparous cows, dry matter intake can fall by about 31% over the last three weeks before calving.

Liver, adipose tissue (especially abdominal fat), blood, rumen and abomasum, mammary gland, central nervous system (nervous form), reproductive tract

Moderate body condition through the dry and transition periods with no loss before calving; balanced rations; gluconeogenic supplements (glycerol, calcium propionate, propylene glycol); monensin to raise rumen propionate; cow comfort.

Subclinical cases usually resolve with oral propylene glycol. Affected cows carry about 3.3 times the risk of displaced abomasum, 1.9 times the culling risk and lower first-service conception (35.1% vs 40%); a case costs US$77-289.