BIOLOGY OF REPRODUCTION 65, 295–300 (2001)
Physiological Regulation of Maternal Behavior in Heifers: Roles of Genital
Stimulation, Intracerebral Oxytocin Release, and Ovarian Steroids1
G.L. Williams2,4,5O.S. Gazal,3,4L.S. Leshin,6R.L. Stanko,4and L.L. Anderson7
Animal Reproduction Laboratory,4Texas A&M University Agricultural Research Station, Beeville, Texas 78102
Center for Animal Biotechnology and Genomics,5Texas A&M University, College Station, Texas 77843
USDA/ARS Russell Agricultural Research Center,6Athens, Georgia 30613
Department of Animal Science,7Iowa State University, Ames, Iowa 50011
We tested the hypotheses that 1) epidural anesthesia at par-
turition would block both peripheral and central release of oxy-
tocin and eliminate the development of maternal behavior in
primiparous heifers and 2) estradiol priming, genital stimulation,
and appropriate neonatal stimuli would induce maternal behav-
ior in nulliparous heifers. In experiment 1, primiparous cross-
bred heifers (n ? 13) with cannulas in the third cerebroventricle
(IIIV) were assigned randomly to receive epidural treatments of
saline (SAL; n ? 6) or lidocaine HCl (EPI; n ? 7) at the onset
of labor induced between Days 270 and 280 of gestation. Epi-
dural anesthesia blocked (P ? 0.001) both central and periph-
eral release of oxytocin and markedly reduced (P ? 0.05) or
eliminated licking behaviors during a 3-h period following par-
turition as compared with SAL. Following approximately 1 wk
of controlled daily suckling, during which calves were permitted
access only to the inguinal region of their dams (three times
daily for 10 min each time), a second maternal behavior test
was performed. Although licking behavior remained markedly
reduced (P ? 0.001) in the EPI compared with the SAL groups,
all heifers accepted their calf at the udder. In experiments 2–4,
neither estradiol priming in ovariectomized heifers nor estradiol
plus progesterone in intact heifers resulted in an induction of
maternal behaviors following genital stimulation and presenta-
tion of a neonate wetted with amniotic fluid. Pelvic sensory def-
icits apparently block oxytocin release and disturb both short-
latency and long-term maternal behaviors but do not result ul-
timately in rejection of the calf. Combinations of hormonal, sen-
sory, olfactory, and visual cues observed previously to induce
maternal behavior in nulliparous ewes do not appear adequate
for induction of maternal behavior in nulliparous heifers.
central nervous system, oxytocin, posterior pituitary, reproductive
Pregnancy and parturition serve as physiological medi-
ators of a remarkable series of behavioral changes in female
ungulates. The typical disregard for neonates exhibited by
nulliparous females before and during early pregnancy is
transformed into an intense interest immediately before or
1Supported by USDA grant 94-37203-0924 and Texas Agricultural Exper-
iment Station Project H6881.
2Correspondence: G.L. Williams, Animal Reproduction Laboratory, Texas
A&M University Agricultural Research Station, 3507 Hwy 59E, Beeville,
TX 78102. FAX: 361 358 4930; e-mail: email@example.com
3Current address: Department of Biological Sciences, St. Cloud State Uni-
versity, St. Cloud, MN 56301-4498.
Received: 19 September 2000.
First decision: 10 November 2000.
Accepted: 6 March 2001.
? 2001 by the Society for the Study of Reproduction, Inc.
ISSN: 0006-3363. http://www.biolreprod.org
during fetal delivery. The onset of proceptive behaviors,
including sniffing, licking, and protection of the neonate,
and formation of a selective maternal bond follows [1–4].
This behavioral transformation often requires only a few
minutes to complete, and the sensitive period during which
the neural circuitry of the dam is capable of responding to
inductive stimuli lasts no more than a few hours [5–7]. In
those species studied, the induction of maternal behavior in
the primiparous female is the product of a cascade of sen-
sory and hormonal events, including exposure of the ma-
ternal brain to placental-derived estradiol, intense genito-
sensory stimulation, central release of oxytocin and opioid
peptides, and olfactory and visual cues from the neonate
Although at least one study has examined the relative
importance of olfaction and vision to the expression of ma-
ternal selectivity in cattle , the contributions of genital
stimulation and central oxytocin release at parturition to the
ontogeny of maternal behavior in this species are virtually
unknown. A better understanding of the endocrine and sen-
sory determinants involved in the induction of maternal
care and selectivity in cattle could assist in addressing be-
havioral anomalies and issues related to suckling-mediated
anovulation. In cattle, the maternal-offspring bond plays a
major role in the neuroendocrine regulation of this type of
anovulation . The objectives of studies reported here
were to determine the role of genital signaling at parturition
on brain oxytocin release and the onset of maternal behav-
ior in primiparous heifers and to evaluate the ability of
hormonal and sensory stimuli to induce maternal behavior
in nulliparous heifers.
MATERIALS AND METHODS
Our hypothesis was that epidural anesthesia at parturition inhibits or
delays central and peripheral oxytocin release and the establishment of
maternal behavior in primiparous heifers.
Preexperimental period. Thirteen crossbred (3/4 Bos taurus ? 1/4 Bos
indicus) pregnant primiparous heifers in excellent body condition (BC;
score of 6, where 1 ? emaciated and 9 ? obese) were brought in from
pasture during the third trimester of pregnancy. These heifers were tamed
previously for use in these studies and were accustomed to human contact.
Heifers were maintained in outdoor pens, fed according to National Re-
search Council (NRC) recommendations for late gestation , and ac-
climated to experimental conditions for 10–15 days. For acclimatization,
heifers were placed in stanchions for up to 2 h daily while haltered and
tied loosely to simulate experimental conditions. Between Days 267 and
270 of gestation, a third ventricle (IIIV) guide cannula was placed surgi-
cally in each heifer as described previously . Silicone elastomer tubing
(0.51 mm inside diameter [i.d.], 0.95 mm outside diameter [o.d.]; Silastic;
Konisberg Instruments, Pasadena, CA) or polyethylene tubing (0.58 mm
i.d., 0.965 mm o.d.; Intramedic and Clay Adams, Becton Dickson Co.,
Sparks, MD) was threaded through the IIIV guide cannula so that 5–15
WILLIAMS ET AL.
periment 4, maximal levels of estradiol were approximately
200 pg/ml, with a declining progesterone titer just before gen-
ital stimulation, similar to that observed just before parturition
[29, 30]. Again, these treatments combined with other factors
did not induce maternal behavior. However, approximately
50% of ewes at estrus can be induced to exhibit maternal
behavior . This finding suggests that gestational levels of
estradiol are not essential to sensitize the brain to oxytocin;
circulating concentrations of estradiol in sheep during estrus
are usually 10–15 pg/ml , at least 10-fold lower than con-
centrations observed during gestation or produced by the ex-
perimental protocols described herein.
The steroidal hormone milieu produced in experiments 3
and 4 resulted in basal concentrations and stimulated release
of plasma oxytocin that were similar to those present during
fetal delivery in pregnant heifers (experiment 1). Because pe-
ripheral and central release of oxytocin are highly correlated
after genital stimulation, it appears that factors other than cen-
tral oxytocin release were responsible for failure of these treat-
ments to induce maternal behavior. The effect of genital stim-
ulation on oxytocin release is potentiated by morphine in
sheep, and neither oxytocin infusion nor genital stimulation
produced maternal behavior of a quality equal to that ob-
served with normal parturition unless an opiate agonist was
given simultaneously . Conversely, opioid antagonists
tend to reduce the release of oxytocin in response to genital
stimulation in ewes, but because no increase in maternal be-
havior was observed after genital stimulation in our experi-
ments, the effects of an opioid antagonist could not be prop-
erly evaluated. All of the foregoing behavioral responses to
genital stimulation and central oxytocin are dependent upon
the influence of estradiol and its effects on the upregulation
of mRNA for oxytocin and oxytocin receptors . The spe-
cifics of these relationships, particularly in cattle, remain un-
clear. However, although the natural pattern of central oxy-
tocin release and the development of maternal behavior at
parturition in heifers are similar to those reported in the pri-
miparous ewe, combinations of genital and hormonal stimuli
shown previously to be effective for artificial induction of
proceptive behaviors in sheep were generally unrewarding in
the nulliparous heifer. Therefore, it can be assumed that the
conditions necessary for creating changes in chemical events
within the brain required for induction of maternal behavior
in this species were not met in these experiments.
The contributions of Guillermo Guzman Vega, Morgan Bednorz, Man-
uel Alvarado, and Clay Ball are gratefully acknowledged.
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