Milk Fever (Parturient Paresis)

Stage I: the cow still stands but is abnormal, with hypersensitivity, excitement, fine muscle tremors, ear twitching, head shaking, teeth grinding, reduced appetite and an unsteady gait. Stage II: she goes down on her sternum, depressed, with cold extremities, a fast heart rate, weak rumen contractions and low body temperature. Stage III: lateral recumbency, flaccid paralysis, reduced consciousness or coma, and death if untreated; bloat may develop from rumen stasis. Subclinical hypocalcaemia has no distinctive signs, only reduced rumination, feed intake and activity.

Parturient paresis (milk fever) is clinical hypocalcaemia around calving, a metabolic rather than infectious disorder. Colostrum and milk production suddenly pull calcium out of the blood faster than the cow can replace it from the diet, bone and kidney retention. Normally parathyroid hormone, renal activation of vitamin D to calcitriol, intestinal absorption and skeletal mobilisation hold blood calcium above about 2.0 mmol/L; when these responses are too slow, it can fall below 1.4 mmol/L. Magnesium deficiency blunts parathyroid hormone secretion and action, and a high dietary cation-anion difference, often from high potassium, causes metabolic alkalosis that reduces tissue responsiveness. Because calcium is needed for nerve and muscle function, skeletal muscle fails and the cow cannot rise; smooth muscle weakness slows the rumen and abomasum and impairs teat closure. Inflammation also suppresses parathyroid hormone and worsens the fall.

Milk fever is a disease of dairy cows and usually occurs within the first 24 hours after calving. Risk rises with parity: first-lactation cows were unaffected in one large study, while cows in third or later lactations, high yielders, Jersey and crossbred cows, cows with a previous episode, cows in abnormal body condition and cows fed high-potassium or poorly balanced close-up rations are most at risk. In cows of third or later parity or with a previous case, a frequency of 20-50% may be expected, and a specific control programme is advised once incidence exceeds 10% in such cows. On a large Holstein farm in Abu Dhabi, United Arab Emirates, the monthly cumulative incidence over 2019-2022 was 2.2%, higher in winter and spring, climbing from 0% in first lactation to about 12.6% in sixth lactation, and associated with subclinical ketosis.

Blood calcium regulation (parathyroid glands, kidneys, bone, intestine), skeletal muscle, nervous system, rumen and abomasum, teat sphincter, heart

Negative dietary cation-anion difference (anionic salt) rations or low-calcium rations in late pregnancy, adequate magnesium, avoiding over-fat dry cows, and oral calcium around calving for high-risk cows.

Intravenous calcium cures most cases, but relapse can occur and oral calcium helps prevent it; untreated cows die. Affected cows face more mastitis, retained membranes, displaced abomasum and ketosis, lower yield, and shorter productive life.