Download James G. Berardinelli - Reproductive Physiology

New insight into the biostimulatory effect of bulls on reproductive processes of
postpartum, anovular, suckled, beef cows
James G. Berardinelli
Professor, Animal Science; Department of Animal and Range Sciences,
Linfield Hall; Montana State University Bozeman, MT 59717
The purpose of this presentation is threefold: 1) to review the research from the Reproductive
Physiology Program at Montana State University (MSU)related to the biostimulatory effect of bulls to
accelerate resumption of ovulatory activity and improve pregnancy rates of primiparous, postpartum,
anovular, suckled, beef cows; 2) to present the latest data involving the biostimulatory effect of bulls on
postpartum cows; and 3) to present a model for the physiological mechanism whereby bulls exert this
effect. Extended postpartum anestrus/anovulation decreases reproductive efficiency in beef cattle herds.
The problem is exacerbated by substantially longer intervals to ovulation in primiparous, suckled, beef
cows. The goal of the research at MSU is to develop reproductive management strategies to overcome
extended postpartum anestrus and improve reproductive performance in primiparous, suckled cows
without increasing costs. The biostimulatory effect of bulls might be a means to satisfy this goal. There
are 27 peer-reviewed articles related to the biostimulatory effect of bulls on postpartum reproduction in
beef and dairy cattle. Of those, 11 (41%) have been from work developed at MSU. We have found that
exposing cows to bulls beginning 30 d after calving is more effective in reducing interval to ovulation
as exposing cows to bulls immediately after calving. In other words, there is a temporal aspect of the
biostimulatory effect of bulls in that it may not be effective within the first 2 to 3 weeks after calving.
In fact, we established that postpartum, suckled cows become more sensitive to the biostimulatory
effect of bulls as time after calving increases and that the biostimulatory effect of bulls causes an
increase in frequency of LH pulses of anovular cows that in turn stimulates the occurrence of
resumption of ovulatory activity in cows exposed to bulls compared to cows not exposed to bulls.
More importantly, in the course of these studies we found that there are a set of interacting effects that
modify the responsiveness of cows to bulls. These include duration of bull exposure (h/d), intensity of
bull exposure (distance from cows and bulls), and frequency of exposure (number of times per d that
cows are exposed to bulls). We then addressed questions related to the nature of this effect, i.e., what
causes the biostimulatory effect of bulls? We have found that this effect is primarily mediated by a
pheromone(s) produced by bulls or cows, under the influence of testosterone, and excreted in the
excretory products of bulls or estrual cows. Subsequently, we reported that an increase in cortisol
concentrations was associated with the biostimulatory effect of bulls. We hypothesized that cortisol
might be necessary to “re-enforce” the pheromonal signals in the olfactory-neuroendocrine pathway
involved with the effect of bulls. Indeed, we found that the presence of bulls decreased pulse
frequency of temporal patterns of cortisol concentrations which appeared to allow LH pulse frequency
to increase thereby accelerating occurrence of ovulatory activity in anovular cows. Ultimately, the
biostimulatory effect of bulls to accelerate ovulatory activity in anovular cows must change follicular
wave dynamics. We now have evidence to indicate that acceleration of occurrence of ovulatory activity
in anovular cows exposed to bulls is related to changes in developmental patterns of dominant follicles.
Maximum diameters of DFs increased more rapidly in cows exposed to bulls than in cows not exposed
to bulls. Whether this change is caused directly by altering LH and FSH concentrations induced by
bulls or related to some direct systemic action of a pheromone(s) is not known. The specific component
of bull excreta that “carries” the pheromone(s) is not known. We have evaluated continuous exposure
of anovular cows to bull urine using a CUDD and found that 24-h exposure to bull urine does not
accelerate ovulatory activity in anovular cows. An interesting outcome of this study was that AI
pregnancy rates for cows exposed to bull urine was 25% greater than that for cows exposed to steer
urine; indicating the possibility of a pheromone in bull urine that might improve conception/pregnancy
rates in female bovine. Currently, we are evaluating bull urine exposure presented to anovular cows in
a manner that would mimic natural cow-bull interactions. From this work I have developed a model for
the physiological mechanism of the biostimulatory effect of bull that includes interactions among: time
after calving, threshold duration changes, frequency and duration of pheromonal exposures, and the
role of cortisol to alter neuroendocrine mechanisms that influence temporal patterns LH concentrations
to accelerate ovulatory activity in postpartum, anovular, suckled cows.