Comparison of Different Prostaglandin F2α Treatments in the GnRH ...

Comparison of Different Prostaglandin F 2α Treatments in the
GnRH + Prostaglandin F 2α Synchronization System in Cattle
of Bos indicus breeding 1,2
Eric Hiers
Christin Barthle
Mary Karen Dahms
Germán Portillo
Allen Bridges
Joel Yelich 3
Timed-AI pregnancy rates were
similar between three different PGF 2α
treatments including a single injection
of Lutalyse ® (36%), split injections of
Lutalyse ® (39%), or Estrumate ®
(41%) administered 7 d after a GnRH
injection in combination with
melengestrol acetate in non-lactating
crossbred cows of Bos indicus
breeding.
Summary
Non-lactating crossbred cows
(n=869) of Bos indicus breeding were
synchronized to determine the
effectiveness of different PGF 2α
treatments in combination with GnRH
and melengestrol acetate (MGA) for a
timed-AI protocol. On day 0 of the
experiment all cows received 2 cc of
GnRH and from days 1 to 7, cows were
fed a protein supplement containing MGA
(0.5 mg/cow/d). On day 7, cows were
equally distributed to one of three
treatments: 1) 5 cc injection of Lutalyse
Sterile Solution ® (n=297), 2) 2 cc
injection of Estrumate ® (n=297), or 3) 2.5
cc injections of Lutalyse Sterile Solution ®
(Split-Lutalyse ® ; n=275) on days 7 and 8.
On day 10, cows were timed-AI and
received 2 cc of GnRH. The timed-AI
pregnancy rates were similar between the
Lutalyse ® (36%), Split-Lutalyse ® (39%)
and Estrumate ® (41%). Across
treatments, 72.3% of the cows became
pregnant during the first 30-d of the
breeding season. In conclusion, type of
PGF 2α treatment administered 7 d after
GnRH did not statistically influence
timed-AI pregnancy rates in non-lactating
crossbred Bos indicus cows.
Introduction
One of the most common estrous
synchronization protocols used in beef
cattle is administration of gonadotropin
releasing hormone (GnRH) followed 7 d
later by an injection of PGF 2α. The GnRH
ovulates large follicles on the ovary,
thereby initiating a new wave of follicle
development on the ovaries. As a result,
most cows will have a similar sized
follicle ready for ovulation at PGF 2α
injection. The purpose of the PGF 2α is to
regress any corpus luteum (CL) present
on the ovaries, with most cattle showing
estrus within 2 to 5 d. Cattle can be
inseminated after a visual estrus or at a
predetermined time, known as timed-AI.
One problem with the GnRH +
PGF 2α synchronization systems is that
some cattle will show estrus 1 to 2 d
before the PGF 2α injection. To eliminate
the premature expression of estrus, the
orally active progestogen, melengestrol
acetate (MGA), can be administered to the
cattle during the period after GnRH
treatment, until the PGF 2α injection.
The effectiveness of the GnRH +
PGF 2α synchronization protocols appear to
be less successful in cattle of Bos indicus
breeding than in cattle of Bos taurus
breeding. The reason(s) for this are
unclear and have been the focus of much
of our research at the University of
Florida. It has been speculated that the
CL, the structure that secretes
progesterone and prevents the cow from
showing estrus, may be less responsive to
an injection of PGF 2α in cattle of Bos
indicus breeding compared to cattle of
Bos taurus breeding.
Previous work in Brahman cattle at
the University of Florida, showed that a
young CL (5 to 10 d old) was less
responsive to PGF 2α than a mature CL (10
to 15 d old). Subsequent research showed
that regression of the CL could be
increased by splitting the recommended
dose of PGF 2α (Lutalyse ® ) into two
consecutive smaller doses, delivered 24 h
apart. It is not known if a similar response
would be observed in cattle of Bos indicus
x Bos taurus breeding. An additional type
of PGF 2α that could also enhance CL
regression is a synthetic version called
cloprostenol sodium also known by the
brand name Estrumate ® . The cloprostenol
sodium is more potent and may not be
degraded as quickly in the cow’s blood
stream than the natural PGF 2α. Therefore,
the cloprostenol sodium may increase CL
regression rates compared to natural
PGF 2α .
Therefore, the objective of this
research was to determine the
effectiveness of a single dose of Lutalyse ®
compared against a split dose of
Lutalyse ® or Estrumate ® administered 7 d
after a GnRH treatment for improving
synchronized timed-AI pregnancy rates in
crossbred Bos indicus cattle.
Procedure
Non-lactating Bos indicus × Bos
taurus cows (n=869) at the Rollins Ranch,
Okeechobee, FL, and Deseret Cattle and
Citrus, Deer Park, FL, were synchronized
with a GnRH + PGF 2α protocol combined
with short-term administration of MGA
(Figure 1). For all replications, genotype
of cows was between one-fourth and onehalf
Bos indicus breeding with the
remainder being of Bos taurus breeding.
The start of the experiment was
designated as day 0 at which time cows
were assigned a body condition score
(BCS; 1=emaciated, 5=moderate,
9=extremely fat) and received 2 cc of
GnRH i.m. (Fertagyl ® ; Intervet, Inc. or
Factrel ® ; Fort Dodge Animal Health). At
both locations, cows received 0.5
mg/cow/d of MGA (Pharmacia Animal
Health) on day 1 to 7 of the experiment
(Figure 1). The MGA was administered in
a protein cube at a rate of 2 lb/cow/d and
cows were group fed the supplement on
2003 FLORIDA BEEF REPORT 77

the ground under pasture conditions. On
the last day of MGA feeding (day 7 of the
experiment), cows were randomly
assigned to one of three treatments within
each location to receive either 5 cc of
PGF 2α (Lutalyse Sterile Solution ® ), 2 cc
of cloprostenol sodium (Estrumate ® ), or
2.5 cc of PGF 2α (Split-Lutalyse Sterile
Solution ® ) on days 7 and 8. Cows were
timed-AI and received 2 cc of GnRH
approximately 72 to 80 h after the last
MGA feeding.
Cows were exposed to bulls
approximately 10 d following timed-AI
for a breeding season of approximately 60
d at all locations. Pregnancy status was
determined between 52 and 56 d after the
timed AI using a real-time B-mode
ultrasound. The data presented in this
paper includes timed-AI pregnancy
(number of animals pregnant to the timed-
AI divided by the number treated) and 30-
d pregnancy rates (number of cows
pregnant during the first 30 d of the
breeding season divided by the number
treated).
Results
There was no statistical difference in
the timed-AI pregnancy rates between
PGF 2α treatments (Figure 2). Although,
5% more Estrumate ® treated cows and 3%
more Split-Lutalyse ® cows became
pregnant compared to the single Lutalyse ®
treatment. For the Estrumate ® treatment,
this calculated to 15 extra pregnancies. A
greater number of calves born in the
subsequent calving season could certainly
have a positive economic benefit to a
producer. Furthermore, the Estrumate ®
treatment does not require the additional
cattle handling required by the Split-
Lutalyse ® treatment. Additional research
will need to be conducted with an
increased number of cattle and in
postpartum lactating cows of Bos indicus
breeding to determine if these results can
be replicated.
The importance of body condition on
reproductive function and breeding season
pregnancy rates has been well
documented by scientists and beef
producers. Body condition score can also
influence the effectiveness of
synchronization protocols. In the present
experiment, cows with a body condition
score ≥5 had a 6% increase in timed-AI
pregnancy rates (Figure 3) compared to
cows with a body condition score

Figure 2. Timed-AI pregnancy rates (number of cows pregnant to the timed-AI divided by the total treated) in non-lactating Bos
indicus × Bos taurus cows synchronized with GnRH + PGF 2α in combination with melengestrol acetate. Numbers in parenthesis
indicate the numbers of cows in each treatment.
45
Lutalyse
Percent pregnant
40
35
Split-Lutalyse
Estrumate
36
39
41
(297) (275) (297)
30
Treatments
Figure 3. Timed-AI pregnancy rates (number of cows pregnant to the timed-AI divided by the total treated) by body condition
score (BCS; 1=emaciated, 5=moderate, 9=extremely fat) in non-lactating Bos indicus × Bos taurus cows synchronized with
GnRH + PGF 2α in combination with melengestrol acetate. Numbers in parenthesis indicate the number of cows within each BCS
category.
45
41
Percent pregnant
40
35
35
30
(412) (457)
BCS < 5 BCS ≥ 5
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80 2003 FLORIDA BEEF REPORT