Associations of subclinical hypocalcemia at calving with milk yield, and feeding, drinking, and standing behaviors around parturition in Holstein cows.

The objectives of this study were to describe the associations of subclinical hypocalcemia with milk yield, and feeding, drinking, and resting behavior during the period around calving. Blood was sampled within 24h of calving and analyzed for serum total calcium. Fifteen Holstein dairy cows were classified as having subclinical hypocalcemia (serum calcium concentration ≤ 1.8 mmol/L, without clinical milk fever) and were matched with 15 control cows (serum calcium concentration >1.8 mmol/L) based on parity and presence of other diseases. Daily feeding and drinking behavior were monitored using an electronic feeding system (Insentec, BV, Marknesse, the Netherlands) and summarized by week relative to calving (wk -3, -2, -1, +1, +2, and +3). Standing behavior was monitored from 7 d before until 7 d after calving using dataloggers. Daily milk yields were obtained for all cows up to 280 d in milk (DIM). These data were summarized by week for the first 4 wk of lactation to assess short-term differences in milk yield, and were summarized into 4-wk periods to assess long-term (280 DIM) differences in milk yield between groups. Cows with subclinical hypocalcemia produced, on average, 5.7 kg/d more milk during wk 2, 3, and 4 compared with control cows; however, only subclinically hypocalcemic cows in their third lactation sustained greater milk yields throughout 280 DIM. Despite greater milk yield during the weeks following calving, cows with subclinical hypocalcemia did not consume more water after calving and tended to have greater dry matter intake only during wk 2. However, these animals made fewer visits to the water bins during the first 2 wk after calving and tended to make fewer visits to the feed bins during wk 1 and 3, suggesting that they used these resources more efficiently. Dry matter intake was, on average, 1.7 kg/d greater during wk -2 and -1 among cows subsequently diagnosed with subclinical hypocalcemia compared with control cows but neither group was lactating during this period. Cows with subclinical hypocalcemia stood for 2.6h longer during the 24-h period before parturition, which may suggest these animals experience increased discomfort at calving; these cows spent 2.7h less time standing during d +1. Although milk yield was greater among cows with subclinical hypocalcemia, this study controlled for the confounding effects of disease incidence; these results do not refute previous research that associates subclinical hypocalcemia with an increased risk for health disorders. The mechanisms by which subclinical hypocalcemia is associated with behavior and production require further investigation.