The objective of this study was to evaluate the effect of supplementation with oral Ca boluses after calving on early-lactation health and milk yield.

Cows in their second lactation or greater (n=927) from two large dairies in Wisconsin were enrolled during the summer of 2010. Both herds were fed supplemental anions during the prefresh period and less than 1 percent of fresh cows were treated for clinical milk fever. Cows were scored before calving for lameness and body condition, and then randomly assigned to either a control group or an oral Ca bolus-supplemented group. Control cows received no oral Ca boluses around calving. Cows in the oral Ca bolus group received 2 oral Ca boluses (Bovikalc, Boehringer Ingelheim, St. Joseph, Mo.), one bolus 0 to 2h after calving and the second 8 to 35hours after calving. The oral Ca bolus administration schedule allowed fresh cows to be restrained in headlocks only once daily. Whole-blood samples were collected immediately before the second oral Ca bolus was given and were analyzed for ionized Ca (Ca2+) concentration.

Early-lactation health events were recorded and summed for each cow. Only sixcases (0.6 percent of calvings) of clinical milk fever occurred during the trial, and only 14 percent of cows tested were hypocalcemic (Ca2+ less than 1.0mmol/L) at 8 to 35h after calving. Mean Ca2+ concentrations were not different between the control and oral Ca bolus-supplemented groups. Blood samples from the cows given oral Ca boluses were collected an average of 20.6hours after administration of the first bolus.

Subpopulations of cows with significant responses to oral Ca bolus supplementation were identified based on significant interactions between oral Ca bolus supplementation and covariates in mixed multiple regression models. Lame cows supplemented with oral Ca boluses averaged 0.34 fewer health events in the first 30days in milk compared with lame cows that were not supplemented with oral Ca boluses. Cows with a higher previous lactation mature-equivalent milk production (greater than 105 percent of herd rank) and supplemented with oral Ca boluses produced 2.9kg more milk at their first test after calving compared with cows with higher previous lactation milk yields that were not supplemented. Results of this study indicate that lame cows and higher producing cows responded favorably to supplementation with oral Ca boluses.

Supplementing targeted subpopulations of cows with oral Ca boluses was beneficial even for dairies with a very low incidence of hypocalcemia.

Source: Journal of Dairy Science/G.R. Oetzel, B.E. Miller