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 2 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% 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
2 h after calving and the second 8 to 35 h 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 6 cases (0.6% of calvings) of clinical milk fever
occurred during the trial, and only 14% of cows tested
were hypocalcemic (Ca2+ less than 1.0 mmol/L) at 8
to 35 h after calving. Mean Ca2+ concentrations were
not different between the control and oral Ca bolussupplemented
groups. Blood samples from the cows
given oral Ca boluses were collected an average of 20.6
h 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 30 d 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%
of herd rank) and supplemented with oral Ca boluses
produced 2.9 kg 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.
Key words: oral calcium chloride , oral calcium bolus ,
hypocalcemia , dairy cow