Full text of DOI:10.3168/jds.S0022-0302(01)74597-3

J. Dairy Sci. 84:1627–1631
 American Dairy Science Association, 2001.
Effects of Naloxone on Calcium Turnover
in Cows Affected by Milk Fever
R. L. Sciorsci,* M. E. Dell’Aquila† and P. Minoia†
*Department of Veterinary and Agroalimentary Sciences
Faculty of Veterinary Medicine—University of Teramo—Italy
†Department of Animal Production—Section of Reproduction
Faculty of Veterinary Medicine—University of Bari—Italy
ABSTRACT
INTRODUCTION
Milk fever is a metabolic disorder of calcium homeo-
Milk fever, also known as periparturient paresis or
stasis that affects about 2 to 6% of postpartum cows. recumbent hypocalcemia syndrome, occurs in pluripar-
Current therapy is based on the administration of cal- ous dairy cows ages 4 to 10 yr (Goff et al., 1989; Goff
cium gluconate. On the basis of the clinical signs, and et al., 1991; Oetzel et al., 1988; White, 2001; Yamagishi
given that endorphins increase at parturition, we sup- et al., 1999). The pathology is characterized by progres-
posed that endogenous opioid peptides (EOP) could be sive symptoms and starts with the inability to remain
responsible for this pathology. In this study, cows with standing followed by, in the final stage, nervous disor-
milk fever were administered the opiate antagonist, ders, anorexia, digestive atonia and meteorism, sup-
Naloxone (Nx; experiment 1) or Nx with calcium salts pressed defecation, unconsciousness, cardiorespiratory
(experiment 2). In experiment 1, Nx induced the recov- difficulties, coma, tetany, and death (Gaines, 1997;
ery of affected cows. The effects of Nx therapy, ex- Noakes, 1996; White, 2001). This disease is related to
pressed in terms of proportion of recovered cows, of the metabolic turnover of calcium and affects the bovine
cows recovering in less than 30 min and cows requiring species, which has the highest calcium turnover per
repeated treatments, were not statistically different kilogram of BW during milk production (Minoia, 1978).
Current therapy is based on the i.v. administration of
calcium gluconate, thus replacing serum calcium until
the homeostatic mechanisms can maintain physiologi-
cal calcium levels.
than those obtained by means of calcium administra-
tion (17/17, 100%; 10/17, 59% and 7/17, 41% vs. 33/35,
94%; 22/35, 63% and 11/35, 31%, respectively; NS). In
experiment 2, a significantly higher ratio of cows recov-
ered in less than 30 min in the group of animals treated
with Nx in association with calcium salts, compared
with the group of cows treated with the calcium tradi-
tional therapy (106/118, 90% for calcium-Nx treated
cows vs. 34/62, 55% for calcium-treated cows). More-
over, in the group of cows treated with calcium-Nx,
the number of cows requiring repeated treatments was
significantly reduced and no unrecovered cows were
observed. The results support the idea that high EOP
levels interfere with inward movement of calcium
through the cell membrane and with calcium activity.
The association of calcium and Nx at low dosage is a
safe method to treat milk fever in cows and reduces
muscular complications.
In all mammals the highest concentrations of endoge-
nous circulating opioid peptides (EOP), namely met-
enkephalin, leu-enkephalin, β-endorphin, dynorphin,
endomorphin, etc., occur at parturition (Dobrinski et
al., 1991; Dondi et al., 1991; Terzic et al., 1995; Weiss-
berg et al., 1992). In human drug addicts, a high level
of these substances can influence behavior. Exogenous
drug poisoning (morphine, other opioid or related
drugs) in human overdose results in many symptoms
similar to the clinical signs reported in milk fever in
the cow, i.e., nervous disorders, respiratory difficulties,
tetany, coma, and death. The elective therapy in opioid
addicts is to administer the opioid antagonist, Naloxone
(Nx), which occupies the opioid receptors without affect-
ing behavior.
(Key words: cow, milk fever, hypocalcemia, Naloxone)
The opioid-dependent calcium L-channel block can
alter the intracellular calcium, both acutely and chroni-
cally, thus affecting changes in the calcium-mediated
signals that control metabolic activities. The voltage-
independent inhibition is effective on all calcium chan-
nel subtypes but predominates on L-type calcium chan-
nels (Albillos et al., 1995; Page et al., 1997; Sciorsci et
al., 2000).
Abbreviation key: EOP = endogenous opioid pep-
tides, Nx = Naloxone.
Received October 2, 2000.
Accepted February 21, 2001.
Corresponding author: P. Minoia; e-mail: p.minoia@veterinaria.
uniba.it.
1627

1628
SCIORSCI ET AL.
The aim of the present study was to evaluate the Nx
Experiment 1.Group 1: 35 cows were treated with
therapy, alone (experiment 1) or in association with the traditional therapy, consisting of 2 ml of 20% cal-
calcium salts (experiment 2), on cows with milk fever. cium pH (n = 29 cows) or calcium borogluconate (n = 6
cows) per kg of BW. Group 2: 17 cows were injected
intravenously with 0.01 mg of Nx hydrochloride per kg
of BW dissolved in 2 ml of physiological saline (0.9%
wt:vol NaCl).
MATERIALS AND METHODS
Drugs
Experiment 2. Group 1: 62 cows were treated with
the traditional therapy, consisting of 2 ml of 20% cal-
cium pH (n = 33 cows) or calcium borogluconate (n =
29 cows) per kg of BW. Group 2: 118 cows were injected
intravenously with 0.01 mg of Nx per kg of BW plus
0.2 ml per kg of BW of 20% calcium pH (n = 70 cows)
or calcium borogluconate (n = 48 cows).
Therapy outcome was recorded in terms of number
of recovered/treated cows, number of cows recovered in
less than 30 min/treated cows; and number of cows
requiring repeated treatments/treated cows. Treat-
ment was repeated if cows showed no signs of recovery
within 120 min.
Two commercial preparations of calcium were used:
calcium pH (446 mM calcium gluconate, 18 mM sodium
toldimfos, 16 mM magnesium chloride; Fatro, Ozzano
Emilia, Italy) and calcium borogluconate (446 mM cal-
cium gluconate, 15.4 mM magnesium cloride and 646.9
mM boric acid; Nuova ICC-UPJOHN S.p.A., Aprilia-
LT, Italy). Naloxone hydrochloride (Diosynth B.V.; 5340
BH OSS, The Netherlands) was used as the opiate an-
tagonist.
Animals
The research was conducted on 53 (experiment 1) and
180 (experiment 2) mixed breed cows affected by milk
fever, aging from 5 to 10 yr (mean SD = 7.8 1.6). Statistical Analysis
The animals came from several farms in Southern Italy.
The proportions of recovered cows, of cows recovered
The pathology was clinically evident from 2 to 20 h after
normal parturition. Many of these cows had developed
milk fever during previous parturitions and had been
successfully treated by means of calcium gluconate.
Milk fever diagnosis was based on clinical signs. The
cows admitted to the study were recumbent and de-
pressed; body temperature was normal to decreased;
respiration was shallow and irregular; heart rate was
irregular and rapid (about 90 pulses/min); rumen motil-
ity was decreased; extremities were cool to the touch.
Diagnosis was confirmed, in the laboratory, by serum
calcium values. Blood samples were collected from all
cows immediately before treatment. The results of the
serum calcium tests were not known until after treat-
ment. Calcium values were measured with a DU640
Beckman Spectrophotometer, by using a Boehringer-
Mannheim kit (n. 1553953, Boehringer-Mannheim,
Monza, Italy). Samples with calcium levels lower than
5.5 mg/dl were considered hypocalcemic (Goff et al.,
1989; Goff et al., 1991b; Oetzel et al., 1988). Milk from
treated cows was marketed 5 d following treatment,
even though Nx has a brief half-life of 15 to 20 min
(Panerai, 1998).
in less than 30 min, and of cows requiring repeated
treatments were compared between groups of treat-
ment by chi-square test with the Yates correction for
continuity. Fisher’s exact test was used when a value
of less than 5 was expected in any cell. Values with P
< 0.05 were considered significant.
RESULTS
Experiment 1
The results of calcium or Nx alone treatment are
compared in Table 1. There was no statistical difference
in response to calcium treatment due to calcium source
(calcium pH or calcium borogluconate), so data in the
table were pooled. Overall, calcium treatment resulted
in recovery of 33 out of the 35 cows (94.3%) (Table 1).
All six cows (100%) treated with calcium borogluconate,
recovered. Four of them (67%) recovered in less that 30
min, and 2 cows (33%) needed repeated treatments.
Twenty-seven of the calcium pH group (93%) recovered.
Eighteen of them (62%) recovered in less than 30 min,
and nine cows (31%) needed repeated treatments. In
seven of these nine cows, the serum calcium tests
showed severe hypocalcemia with levels lower than 5
mg/dl. Three cows of this group were treated 9, 13, and
14 h following recumbency. Two cows in this experimen-
tal group did not recover (6%) and were slaughtered
after 1 wk. There were no relationships between the
Experimental design
Except for the cases indicated in the Results, the cows
were treated as soon as possible and in less than 2
h from the onset of recumbency for progressive and
ingravescent hypocalcemia. They were randomly as- three cows treated late and the two cows that did not
signed to experimental groups as follows:
recover. One of the cows that did not recover was treated
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NALOXONE AND CALCIUM IN COWS WITH MILK FEVER
1629
Table 1. Effects of therapy with calcium or naloxone in cows affected by milk fever.
No. (%) of cows
Recovery
< 30 min
no. (%)
requiring
repeated
Total no.(%)
of recovered
cows
No. (%) of
unrecovered
cows
No. of
treated cows
Therapy
treatments
Calcium borogluconate
Calcium pH
Total calcium
Naloxone
6
29
35
17
4 (67)
18 (62)
22 (62.8)
10 (59)
2 (33)
9 (31)
11 (31.4)
7 (41)
6 (100)
27 (93)
33 (94.3)
17 (100)
0 (0)
2 (6)
2 (6)
0 (0)
less than 2 h after the recumbency, and the other was cows requiring repeated treatments was significantly
treated 13 h after recumbency.
reduced and no unrecovered cows were observed.
Naloxone treatment resulted in the recovery of all 17
treated cows (100%; Table 1). Ten of them recovered in
less than 30 min (58.8%); in fact, recovery appeared
complete within 20 min. In seven cows, it was necessary
to repeat the Nx treatment (41.2%). Two cows received
treatment after 10 and 15 h, respectively, and the re-
gression of clinical symptoms among these cows was
less rapid. In these cows, the serum calcium tests values
before treatment were lower than 5 mg/dl. The number
and the rate of recovery among cows and the number
of cows that needed repeated therapy did not differ
between treatments (P > 0.05). Thus, Nx appears to
be as effective as calcium therapy in the treatment of
milk fever.
DISCUSSION
In this study, the traditional therapy with calcium
gluconate was effective and observed results were simi-
lar to those previously described in the literature
(Gaines et al., 1997; Noakes, 1996). The administration
of Nx resulted in recovery from this syndrome. All ani-
mals recovered, except one that had been recumbent
for 5 d and that was not included in Table1. In this
cow, Nx chlorhydrate treatment was administered on
d 5, and it was preceded by traditional therapy with
calcium gluconate on d 1, 2, and 3 without positive
results. Intravenous Nx treatment on d 5 abruptly in-
duced standing, tetanic syndrome, and immediate
death. After this outcome, the treatment with Nx alone
was interrupted. Recovery was obtained in all the ani-
Experiment 2
The results of calcium or calcium-Nx treatments, in mals not presenting severe hypocalcemia (5.5 to 5.0
relation to two different calcium sources of Calcium pH mg/dl).
and Calcium borogluconate, are compared in Table 2.
The therapeutical efficacy of Nx indirectly demon-
No statistical difference in response to calcium treat- strates an involvement of EOP in calcium homeostasis,
ment due to calcium source was observed. A signifi- and, thus, it strongly supports the idea that the opioid-
cantly higher rate of cows recovered in less than 30 min ergic system is involved in the etiopathogenesis of this
was observed in the group of animals treated with Nx syndrome. The high and selective affinity of Nx for opi-
in association with calcium salts, compared with the oid receptors suggests that the results obtained here
group of cows treated with the calcium traditional ther- may have been mediated through an opioid displace-
apy (106/118, 90% for calcium-Nx treated cows vs. 34/ ment. Throughout the pregnancy, there is a progressive
62, 55% for calcium-treated cows). Moreover, in the increase of the opioidergic tone, i.e., a marked and pro-
group of cows treated with calcium-Nx the number of gressive increase of EOP plasma concentrations, with
Table 2. Effects of naloxone (Nx) and calcium therapy in cows affected by milk fever.
No. (%) of cows
Recovery
< 30 min
no. (%)
requiring
repeated
Total no. (%)
of recovered
cows
No. (%) of
unrecovered
cows
No. of
treated cows
Therapy
treatments
Calcium pH
Calcium borogluconate
Total calcium
Nx + calcium pH
Nx + calcium borogluconate
Total Nx + calcium
33
29
19 (58)
15 (52)
34 (55)a
63 90)
11 (33)
9 (31)
30 (91)
24 (83)
3 (9)
5 (17)
8 (13)
0 (0)
0 (0)
0 (0)
62
20 (32)a
7 (10)
54 (87)
70
48
118
70 (100)
48 (100)
118 (100)
42 (87)
6 (12)
106 (90)b
12 (10)b
a,bP < 0.001, within columns, numbers with different superscripts are significantly different.
Journal of Dairy Science Vol. 84, No. 7, 2001

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SCIORSCI ET AL.
a peak at parturition and the highest level of EOP genesis of milk fever. The hypothesized interaction be-
is dependent by placental and hypophyseal production tween opioids and calcium and the results of the treat-
(Genazzani et al., 1981; Nakai et al., 1978; Petraglia ment provided us with greater insight into the
et al., 1985). Moreover, it may be suggested that the periparturient hypocalcemia as the disease was re-
opioid increase at parturition, if not naturally regress solved in cows without severe hypocalcemia by adminis-
to normal levels, is responsible for milk fever.
tering only Nx. This experience presents new perspec-
One of the treated cows with milk fever that was tives for the management of diseases involving changes
severely hypocalcemic developed tetany after intrave- in tissue-linked opioid levels.
nous infusion of Nx and died soon after. Tetanic move-
Based on the data obtained, it can be suggested that
ments and death naturally occur in highly hypocalcemic many diseases controlled by calcium-related functions
cows (Goff et al., 1991). In our opinion, in this subject, may be influenced by altered levels of endogenous opi-
the Nx treatment may have induced a displacement oids. Our results demonstrate that endogenous opioids
of opioids from their receptor sites, calcium channels are related to a progressive disease that may culminate
opened and calcium moved according to its gradient. in death through an interaction with calcium homeosta-
In the presence of a severe hypocalcemia, cytoplasmic sis and calcium turnover. This agrees with the demon-
calcium levels may have been altered, thus inducing strated role of opioids on the disruption of calcium ho-
tetany. Tetany and death after Nx treatment was also meostasis in mouse astrocytes in vitro (Hauser et al.,
described in human stroke, but the tetanic symptom- 1998). We believe that endogenous opioids linked to the
atology was not identified and not ascribed to calcium tissues involved in parturition and in the postpartum,
deficiency (Andree, 1980; Smith and Pinnok, 1985).
such as muscles, particularly miocardium and nervous
Naloxone is commonly used, both in human and vet- system, influence the balance between extracellular
erinary medicine, to counteract anesthesia and opioid and intracellular calcium with a block of L-calcium
overdosage in humans. As previously reported, Nx gated channels.
shows a wide range of affinity to all opioids’ receptors:
In conclusion, Nx appears to interact with calcium
mu, delta, and kappa with respective decreasing affin- ions exchanges in milk fever cows and in association
ity. At the low doses we used, Nx probably reacts only with calcium salts is an effective and safe therapy.
with mu receptors, whereas at higher doses it interacts
with all other receptors resulting in the modulation of
different functions. All these need to be considered in
addition to normal pharmakokinetics (Sciorsci et al.,
2000).
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