Open Journal of Veterinary Medicine, 2012, 2, 151-157
http://dx.doi.org/10.4236/ojvm.2012.23024 Published Online September 2012 (http://www.SciRP.org/journal/ojvm)
Pharmacological Control of Estrus in Tropical Cattle, an
Economical Assessment of Different Synchronization
Protocols
——Economics of Estrus Control in Tropical Cows
Juan J. Molina1, Iván Molina2, Alejandro Jiménez3, Carlos S. Galina3, Juan J. Romero4,5*
1Asesor Laboratorios Intervet Schering Plough, Bogotá, Colombia
2Director Técnico Agropecuaria Las Tinajas S. A., Bogotá, Colombia
3Departamento de Reproducción, Facultad de Medicina Veterinaria y Zootecnia, Universidad Nacional Autónoma de México,
Mexico City, México
4Programa de Investigación en Medicina Poblacional, Escuela de Medicina Veterinaria, Universidad Nacional, Heredia, Costa Rica
5Campus Benjamín Núñez, Heredia, Costa Rica
Received July 12, 2012; revised August 3, 2012; accepted August 9, 2012
ABSTRACT
To compare the fertility results and to assess the cost-effectiveness of several synchronization protocols applied under
the conditions of beef cattle enterprises in Colombia, 1658 multiparous zebu crossbred cows mostly Brahman and
Nelore ranging between 2 - 6 parities were used. Five protocols of pharmacological treatments varying in hormones
used, dosage and the time of application were tested. All cows were inseminated at 52 h by appointment. Pregnancy
diagnosis was undertaken over 45 d after insemination by rectal palpation. The total cost per cow and the total cost per
gestation, for each protocol, were calculated. Taking a herd of one-hundred cows as baseline for calculations, it was
estimated the cost of the total amount of pregnancies possibly obtained in each protocol; then, the excess between the
costs of a pregnant cow and the cost of a treated cow was estimated. Additionally, the costs due to cows empty after
four services were calculated. A total of 874 pregnancies were registered (52.7%), with pregnancies per protocol vary-
ing between 46.9% and 66 .2% (p < 005). The cost per treated cow, varied betw een $64.08 and $97.47 and the co st per
gestation from $126.01 to $177.26, without association between the cost of the treatment and the pregnancy rate. Pro-
tocol A was the best cost-effective with the lowest additional costs, the lowest amount of open days (2107.7 to 2231.7 d)
and IA straws (average = 134), with an additional costs of $6940.00. Synchronization of estrus using pharmacological
products seems to have a place in the management of cattle; however, caution should be called upon a careful assess-
ment both from the part of the farm and the professional in charge of the enterprise to avoid using the technique indis-
criminatively thus propitiating the use of a method that might not be cost efficient.
Keywords: Tropics; Bos Indicus; Cost-Benefit; Estru; Synchronization
1. Introduction
The use of Artificial Insemination in the trop ics has been
hampered by the difficulties in accurate detection of
signs of estrus in Zebu type cattle, the most popular
crossbred animal in the beef industry of the area. One
possible solution to implement the technique is to ma-
nipulate pharmacologically the estrous cycle and cou-
pling this procedure with fixed-time artificial insemina-
tion (F-TAI) regardless the signs of estrus, so called in-
semination by appointment. In relation to animals kept at
pasture under tropical conditions, the rate for detecting
animals in estrus does not go beyond 40% [1,2]. The
reasons for this low detection rate is multifactorial
mainly related to social behavior in the herd [3], age,
breed of the animals and the presence of the male [4,5].
Because of these limitations, the number of protocols to
synchronize estrus is abundant [5,6], the same can be
noted as to the hour(s) where F-TAI is app lied following
removal of the treatment [7,8]. However, few studies are
published whilst comparing protocols under the same
conditions and with the same clinicians applying the
procedure, particularly under beef cattle enterprises in the
tropics.
*Corresponding author. Interventions in the beef cattle in dustry have to be cost
C
opyright © 2012 SciRes. OJVM

J. J. MOLINA ET AL.
152
effective and render economic dividends to the producer
otherwise they will become an academic exercise. For
example Tenhagen et al. [9] showed that synchronization
of estrus in dairy cows in the USA was more cost-effec-
tive than inseminating animals displaying overt signs of
estrus and this was mainly due to more cows that were
culled and more open days among cows not culled.
However, Hoff-Sousa and Ferrugem-Moraes [10] in beef
cattle raised in southern Brazil, showed that whilst the
total cost for a pregnancy using natural mating was 5
dollars, this cost increased to 20 dollars if AI was to be
applied and 24 if AI was accompanied with an estrous
synchronization protocol. Oltenacu et al. [11] in the USA
working with dairy cows undertook an economic evalua-
tion of several factors that affect pregnancy. Accurate
estrus detection was among the most profitable manage-
rial decisions. Thus, economic calculations will certainly
differ according to the type of enterprise and production
item to be evaluated .
The objective of the present study is to compare the
fertility results and to assess the cost-effectiveness of
several protocols applied under the conditions of beef
cattle enterprises in Colombia.
2. Material and Methods
2.1. Animals
A total of 1658 multiparous zebu cros sbred cows, mostly
Brahman and Nelore, were chosen from 4 farms located
in the Department of Antioquia-Medellin, Puerto Berrío,
Colombia. The site is located at 125 m above sea level, at
06˚29'40" latitude north and 74˚24'24" longitude west.
Average temperature is around 29˚C and pluvial precipi-
tation around 2300 mm. Animals ranged from 4 to 12
years old, with 2 to 6 parities. The selection was done by
the same two practitioners ba sed on: 1 ) having at least 40
days since calving when the synchronization procedure
was implemented; 2) the body condition score of the
cows, including only those with a minimum of 2.5 in a
scale 1 to 5; and 3) presence of a corpus luteum, or traces
of follicular activity, detected by rectal palpation.
2.2. Treatments
Five protocols of pharmacological treatments were ob-
served on field conditions. All used a synthetic pro-
gestagen (Crestar, Intervet Schering Plough Animal
Health) as base at day 0, with several variations between
them like the hormones used, dosage and the time of ap-
plication (Table 1). Not all protocols were used in each
farm because that depended of the willingness of the
farmers; however, all of them were applied under the
supervision of the same two veterinarians. Moreover, in
order to distribute similarly the experimental error, all
cows were inseminated by the same veterinarians fol-
lowing the FTAI at 52 h. In farms where two or more
protocols were applied, cows were randomly allocated in
each treatment.
No experimentation was performed during this study,
this was an observational study of the estrus synchroni-
zation on field conditions. The approval of the Animal
Welfare and Bioethics Committee of the Veterinary
School of the National University in Costa Rica was ob-
tained.
2.2.1. Pregnancy Di agnosis
In all protocols the pregnancy diagnosis was done over
45 d after insemination by rectal palpation by the same
veterinarians that selected and treated the cows. They
have at least ten years of experience in this kind of re-
productive procedures.
2.2.2. Cost Analyses
To assess the monetary cost of each protocol, it was cal-
culated the cost of the pharmaceutical treatments, ad-
ding the costs for the professional labor of the veter-
inarians. The rate of each hormone was estimated using
the current price in Mexico quoted in US dollars as cur-
rency. So, the price for each dose of drug was the fol-
lowing: Norgestomet (Crestar® implant) + estradiol va-
lerate (Crestar® injection), $15.87; equine chorionic go-
nadotropin (Folligon®), $16.27; estradiol benzoate (Me-
salin®), $4.65; gonadorelin (Fertagyl®), $18.30; clopros-
tenol (Estrumate®), $14.48; estradiol ciprionate, $9.58.
All these products are manufactured by Intervet Schering
Plough Animal Health. Additionally, the cost for the
professional labor of the veterinarian was estimated in a
total of $20.00 per cow for the whole treatment. At last,
the mean price fo r the semen was fit o n $10.00. The total
cost for veterinary services during the complete protocol,
including all the visits, was estimated on $20.00 per cow.
With these data, the total cost per cow (TCPC) for
each protocol (TCPP), was calculated. Once the preg-
nancy rate (PR) of each protocol was obtained, a calcula-
tion of the cost of each gestation (TCG) was done as fol-
lows: . TCG TCPCPR

Taking a herd of one-hundred cows as baseline for
calculations, it was estimated the co st of the total amo u n t
of pregnancies possibly obtained in each protocol (CTPP)
using the formula: CTPP = (100*PR)*TCG. Finally, in
order to have a relative estimation of the cost of a ges-
tation per protocol, the excess between the cost of a preg-
nant cow in relation to the cost a treated cow (EPP) was
calculated using the formulae EPP = (TCG/TCPC)*100.
The estimation of both costs for a treated cow and for
a pregnant animal, at 95% of confidence was carried out
using @RISK 5.7 software (Palisade), using the mod-

J. J. MOLINA ET AL.
153
Table 1. Description of protocols used for heat synchronization in zebu cows on field conditions in the humid tropic of Co-
lombia. The name of the product in bolds indicates the hormone that makes the treatment different.
Day Protocol A
Estradiol Benzoate Protocol B Gonadorelin Protocol C Equine Chorionic Gonado t ropin
With Without With Without With Without
0 Crestar® implant
Crestar® injection Crestar® implant Crestar® injection Crestar® implant Crestar® injection Crestar® implant Crestar® injection Crestar® implant Crestar® injection Crestar® implant Crestar® injection
9 Remove Implant
Folligon® 400 UI Remove Implant Folligon® 400 UI Remove Implant Folligon® 400 UI Remove Implant Folligon® 400 UI Remove Implant Folligon® 400 UI Remove Implant Folligon® 400 UI
11 FTAI 52 h. FTAI 52 h. FTAI 52 h.
Fertagyl 1ml FTAI 52 h. FTAI 52 h. FTAI 52 h.
24 Crstar® Reimpla nt
Mesalin 1 mg Crestar® Reimplant Crestar® Reimplant Crestar® Reimplant
30 Remove Implant
Folligon® 150 UI Remove Implant
31 - 33 FTAI 52 h. FTAI 52 h.
32 Remove Implant Remove Implant
33 - 35 FTAI 52 h. FTAI 52 h.
40 - 45 Pregnancy
diagnosis Pregnancy diagnosis Pregnancy diagnosis Pregnancy diagnosis Pregnancy diagnosis Pregnancy diagnosis
Day Protocolo D
Crestar new/used Protocolo E
Estradiol Ciprionate (ECP)
New Used With Without
0 Crestar® implant Crestar® implantEstradiol
Benzoate 2.5 mg Crestar® implant Crestar® implant
8
Remove Implant Estrumate®
2 ml Folligon® 330 UI
9 Remove Implant
Folligon® 400 UI Remove Implant
Folligon® 400 UI ECP
0.5 ml (1 mg)
Remove Implant
Folligon® 400 UI
11 FTAI 52 h. FTAI 52 h. IATF 52 h. IATF 52 h.
22
31 - 33 Heat detection Heat detection
36
36 - 47
40 - 45 Pregnancy diagnos is Pregnancy diagnosis Pregnancy diagnosis Pregnancy diagnosis
FTAI 52 h = Fixed time artificial insemination, Crestar: Implant (Norgestomet 3 mg) + Injection (Norgestomet 3 mg, Estradiol Valerate 5 mg), Folligon:
eCG (equine Chorionic Gonadotropin), Fertagyl: GnRH(Gonadotropin R elease Hormone), Mesalin: Estradiol beanzoate.
cost estimation assuming a variation of 10% from the
base price for each component of the treatment. The
variation from demean was obtained after a run with
10,000 iterations. Additionally, an approach of the costs
for the owner due to cows empty after four services, for
each protocol was estimated by means of a deterministic
model carried out in Microsoft Excel. For this purpose, it
was assumed a constant pregnancy rate (the observed one
in the protocol i.e. fertility at first insemination) for each
time of AI and a heat interval of 21 d. This calculation
included the total amount of days empty, AI straws pro-
jected to use and their associated costs assuming a cost of
$3.00 US dollars per day empty and a cost of $10.00 US
dollars per AI straw.
The costs for the remaining days empty and AI straws
after four services were not estimated. Cost for manage-
ment, feed, and others related to the maintenance of the
herds was not taken into consideration due to the vari-

J. J. MOLINA ET AL.
154
ability in the sample.
3. Results
3.1. Reproductive Efficacy of the Protocols
A total of 874 pregnancies were registered from the 1658
cows studied (52.7%). The general percentage of preg-
nancies per protocol varied between 66.2% (protocol A)
and 46.9% (protocol D). There were not differences be-
tween protocols B, C, D and E, but all of them were dif-
ferent to protocol A (Table 2).When segregating the re-
sults per treatment within each protocol, these percent-
ages vary to 66.9% for protocol A with estradiol benzo-
ate, and 43.7% for protocol D with the re-used implant of
Norgestomet (p < 0.05) (Table 2).
3.2. Costs per Treated Cow (Gross Cost)
Regarding the cost per treated cow, in average, protocol
D was the cheaper whilst protocol C was the most ex-
pensive. Even within each protocol, the total cost varied
between 64.08 US dollars for protocols B and D; spe-
cifically without Gonadorelin and with the new Crestar,
respectively, while it was $97.47 for protocol C when
using eCG (Table 3).
3.3. Costs per Pregnant Cow (Net Cost per
Pregnancy)
When the pregnancy rate was taken into account, the cost
for each gestation varied from $126.01 in protocol A
without estradiol benzoate, to $177.26 in protocol C with
eCG (P < 0.05). No statistical differences were found in
the net cost per pregnancy within each protocol; however,
the absolute difference in some protocols was quite im-
portant. For instance, in protocol B, there was an abso-
lute difference of $29.97 while in protocol D it was
$26.57 (Table 3). So, at the end, although protocol B
without Gonadorelin was the cheaper regarding th e gross
cost of treatment ($64.08), it was, the second one with
the higher excess cost between treated and pregnant cows
($121.27). Besides, the protocol D had excess costs of
$99.10 and $128.86 when using new and re-used Cre-
star (Table 3). These results indicate that there is not a
direct association between the cost of the treatmen t and its
efficacy measured as pregnancy rate.
Table 2. Percentage of gestations, by protocols used for heat synchronization, in zebu cows on field conditions in the humid
tropic of Colombia.
95% CI Diff.*
Protocol Treatment Total Gestations%
IL SL
A Total 394 261 66.2 61.6 70.9 a
Estradiol benzonate With 305 204 66.9 61.6 72.2
Without 89 57 64.0 54.1 74.0 0.70
B Total 280 131 46.8 40.9 52.6 b
Gonadorelin With 145 70 48.3 40.1 56.4
Without 135 61 45.2 36.8 53.6 0.63
C Total 82 44 53.7 43.9 64.5 a,b
Equine chorionic gonadotr opin With 40 22 55.0 39.6 70.4
Without 42 22 52.4 37.3 67.5 0.82
D Total 601 282 46.9 42.9 50.9 b
Implant of norgestomet New 301 151 50.2 44.5 55.8
(new/used) Used 300 131 43.7 38.1 49.3 0.12
E Total 301 156 51.8 46.2 57.5 b
Estradiol ciprionate With 198 104 52.5 45.6 59.5
Without 103 52 50.5 40.8 60.1 0.81
*Different letters indicate difference in the global percentage of gestations between protocols. The numbers indicate the exact P-value of the
comparison within each protocol; both calculations at 95% of confidence.

J. J. MOLINA ET AL. 155
Table 3. Costs analyses for each protocol of synchronization used for heat synchr onization in zebu cows on field conditions in
the humid tropic of Colombia.
Protocol A Protocol B Protocol C Protocol D Protocol E
Estradiol benzoate Gonadorelin eCG Norgestomet new/used ECP
Parameter
With Without With WithoutWith WithoutNew Used With Without
% of gestation 66.9 64.0 48.3 45.2 55 52.4 50.2 43.7 52.5 50.5
Total cost per treated cow* 85.33 80.59 82.70 64.08 97.47 80.62 64.12 67.39 73.94 64.21
Cost per gestation

127.66 126.01 171.76 141.79 177.26 153.63 127.66 154.23 140.78 127.00
Excess cost pregnant/treated
cow (%) 49.61 56.36 107.69 121.27 81.86 90.56 99.10 128.86 90.40 97.79
Cows pregnant after 4
services** 83 82 73 72 77 75 74 71 75 74
Total of AI straws until 4
services** 133 135 151 154 144 147 149 156 147 149
Total of days empty until 4
services*** 2107.7 2231.7 3223.6 3409.6 2789.6 2975.6 3099.6 3533.5 2975.6 3099.6
Total cost due to days empty 6155.8 6695.1 9615 10191.58368.9 8852. 5 9261.6 10470.4 8833.9 9205.8
Additional costs due to IA +
days empty**** 6648.3 7230.8 10384.311006.99038.5 9560.7 10002.6 11308.2 9540.7 9942.4
*In US Dollars. Based on a stochastic model using the cost estimation module in @Risk. **On a base of 100 cows treated per protocol. ***This does not include
the days before treatment. ****This is the sum of the cost due to days open + the extra cost due to AI straws used, assuming a cost of $10.00 US Dollars per
straw.
3.4. Estimated Economic Losses Associated to
Reproductive Failure per Protocol
The failure of getting the cows pregnant at first service
adds to the costs for days open and additional AI straws
used until the pregnancy of the cows in a hypothetical
fourth service. Protocol A was the best cost-effective
because its additional costs were the lowest among all
protocols and had the lowest amount of open days
(2107.7 to 2231.7 d) and IA stra ws ( aver age = 134), then,
the additiona l costs reached almost $6940.00 on average.
Protocols B and D were less efficient, with more than
3200 d of additional open days due to reproductive fail-
ure, reaching, on average, more than $10500.00 in addi-
tional costs after four simulated rounds of AI keeping
constant the pregnancy rate observed in each protocol.
On the other hand, the protocols C and E occupied an
intermediate position; however, both had estimated addi-
tional costs over $9300.00 (Tab le 3 ). The sensitivity an a l y -
sis indicated that the most important source of variation
in the model assessing the eco nomic losses was the preg-
nancy rate of the protoco l s.
4. Discussion
The use of pharmacological agents to promote estrous
expression is a technique to ascertain a massive use of
Artificial Insemination in cattle raised under tropical
conditions. The value of this procedure has to be meas-
ured by the number of animals pregnant after an inter-
vention. It is however, a rather difficult task to compare
fertility results between different experiments for the
variability that exists in each field trial. The protocols
tested in the present study afforded an overall fertility of
52% which is rather similar to many of the studies re-
viewed; in effect, conception rates after treatment with
hormonal combinations in different studies vary between
40% and 70% [12-17]. Reviews of several studies have
been published by Bo et al. [5] and Barusselli et al. [18]
and earlier by Galina and Arthur [19]. The ranking of all
these studies established an average of around 40%
ranging from 20% to 60% after first insemination.
Nonetheless, the remaining non-pregnant animals had the
inherent cost of being inseminated, especially if fixed
time insemination is used, with negative results resulting
in lengthier periods of days open. Most of the studies
report the number of animals pregnant following an in-
tervention but hard ly any information if the no n-pregnant
animals were actually at the risk of becoming pregnant.
Diaz et al. [20] in a survey where cows were sampled for
progesterone following a protocol of synchronization
observed that 30% of the animals did not form a CL.
Moreover, in an old study Landivar et al. [21] compared
fertility in different herds, either following spontaneous
or synchronized estrus and using either natural mating or
artificial insemination, reported no differences in fertility
if AI or natural mating were used being the variation the

J. J. MOLINA ET AL.
156
animals utilized in the study rather than the technique to
make them pregnant. So, the relationship of cost-benefit
of synchronizing zebu cows with the goal of pregnancy
should be an exercise that practitioners should undertake
before embarking in costly protocols which are not cost-
effective. Two of the main challenges of zebu cattle un-
der tropical conditions are the long postpartum anestrus
and the low estrus detection rate [5,19]; so the protocols
for synchronization of ovulation can have large positive
impacts on the reproductive efficiency in the herds raised
under tropical conditions if adequately used [6].
Several protocols have been tested for estrus synchro-
nization, since the early days of utilizing only pros-
taglandins, to those more elaborate using progestins, es-
trogens and GnRH [12,13,17,22-25]. Diverse studies hav e
documented the success of several protocols applied in
diverse climatic conditions, different breeds, time post-
partum where the intervention was undertaken and feed-
ing strategies. However, studies comparing the results of
protocols used on the same field conditions applied rou-
tinely by practitioners in different management condi-
tions are less frequent. Besides, several progesterone or
progestins have been investigated for estrus synchroniza-
tion in zebu cows in controlled conditions, varying con-
siderably the success in synchronization and gestation
rates [12,13,17,18,24].
Whilst rates of gestation of the protocols tested in the
present report are similar to others, we are aware that the
absence of the characteristics for each cow included in
the study, did not allow us to carry out a mixed model
including fixed and random effects, which could assess
the effect of variables such as breed, number of parities,
body condition score and time postpartum among others
taking into consideration the random effect of the herd,
on the synchronization and pregnancy rates. What we can
assume is that there aren’t differences between the body
condition score, number of parities and time postpartum,
as well as the breeds between protocols. In this scenario
we can take for granted a global similarity of the groups
treated. A favorable argument is that all cows of the
study were selected by only two veterinarians who were
the same that applied the treatments and undertook the
pregnancy diagnosis hence the sources of error were
equally distributed in all protocols.
Some studies report the costs of hormonal treatments
for synchronization in beef cattle, most of them in Bos
taurus; however, the calculations are based on the costs
of hormonal treatment, without taking into consideration
fixed cost such as labor and the possibility of applying
various treatments in the case of cows having to be rein-
seminated. Also, fewer studies used mathematical mod-
els to simulate the effect of measures of management on
the net income of a beef farm [26] the modeling of the
cost-benefit of different protocols taking into account
other aspects such as the cost of the IA straws, the added
value of labor as well as the cost of the days open, are
exercises that should be taken to understand the economic
merit of hor monal treatments. Bolivar and M al do na do [ 27 ]
and Alarcón et al. [28] have attempted to analyze the
cost-benefit of using embryo transfer in cattle; their re-
sults indicate that the technique might be overvalued for
the average farmer for it has its place in stud farming.
In conclusion, synchronization of estrus using phar-
macological products seems to have a place in the ma-
nagement of cattle and its popularity h as expanded in the
last decade. However, caution should be called upon a
careful assessment both from the part of the farm and the
professional in charge of the enterprise to avoid using the
technique indiscrimin atively thus propitiating the use of a
method that might not be cost-efficient.
REFERENCES
[1] P. I. Rekwot, E. O. Oyedipe, E. Mukasa-Mugerwa, V. O.
Sekoni, O. P. Akinpelumi and A. A. Anyam, “Fertility in
Zebu Cattle (Bos indicus) after Prostaglandin Administra-
tion and Artificial Insemination,” Veterinary Journal, Vol.
158, No. 1, 1999, pp. 53-58. doi:10.1053/tvjl.1998.0313
[2] M. G. Diskin and J. M. Sreenan, “Expression and Detec-
tion of Oestrus in Cattle,” Reproduction and Nutrition
Development, Vol. 40, No. 5, 2000, pp. 481-491.
doi:10.1051/rnd:2000112
[3] C. S. Galina and A. Orihuela, “The Detection of the Es-
trus in Cattle Raised under Tropical Conditions: What We
Know and What We Need to Know,” Hormones and Be-
havior, Vol. 52, No. 1, 2007, pp. 32-38.
doi:10.1016/j.yhbeh.2007.03.025
[4] A. Orihuela, “Some Factors Affecting the Behavioural
Manifestation of Oestrus in Cattle: A Review,” Applied
Animal Behavior, Science, Vol. 70, No. 1, 2000, pp. 1-16.
doi:10.1016/S0168-1591(00)00139-8
[5] G. A. Bo, P. S. Baruselli and M. F. Martínez, “Pattern and
Manipulation of Follicular Development in Bos indicus
Cattle,” Animal Reproduction Science, Vol. 78, No. 3-4,
2003, pp. 307-326. doi:10.1016/S0378-4320(03)00097-6
[6] O. Gomes-de Sá Filho and J. L. Moraes-Vasconcelos,
“Treatments to Optimize the Use of Artificial Insemina-
tion and Reproductive Efficiency in Beef Cattle under
Tropical Environments,” Veterinary Medicine Interna-
tional, Vol. 2011, No. 2011, 2011, Article ID 923053.
[7] G. A. Bo, L. Cutaia, L. C. Peres, D. Pincinato, D. Maraña
and P. S. Baruselli, “Technologies for Fixed-Time Artifi-
cial Insemination and Their Influence on Reproductive
Performance of Bos indicus Cattle,” Society of Reproduc-
tion and Fertility Supplement, Vol. 64, 2007, pp. 223-236.
http://www.ncbi.nlm.nih.gov/pubmed/17491150
[8] K. L. Macmillan, “Recent Advances in the Synchroniza-
tion of Estrus and Ovulation in Dairy Cows,” Journal of
Reproduction Development, Vol. 56, 2010, pp. S42-S47.
[9] B. A. Tenhagen, M. Drillich, R. Surholt and W. Heuwie-
ser, “Comparison of Timed AI after Synchronized Ovula-

J. J. MOLINA ET AL.
157
tion to AI at Estrus: Reproductive and Economic Consi-
derations,” Journal of Dairy Science, Vol. 87, No. 1,
2004, pp. 85-94.
doi:10.3168/jds.S0022-0302(04)73145-8
[10] C. J. H. de Sousa and J. C. Ferrugem-Moraes, “Manual de
Sincronização de Cios em Ovinos e Bovinos,” Embrapa
Pecuária Sul, Rio Grande do Sul, Brasil, 1998.
[11] P. A. Oltenacu, J. D. Ferguson and A. J. Lednor, “Eco-
nomic Evaluation of Pregnancy Diagnosis in Dairy Cattle:
A Decision Analysis Approach,” Journal of Dairy Sci-
ence, Vol. 73, No. 10, 1990, pp. 2826-2831.
doi:10.3168/jds.S0022-0302(90)78970-9
[12] J. R. Pursley, M. C. Wiltbank, J. S. Stevenson, J. S. Otto-
bre, H. A. Garverick and L. L. Anderson, “Pregnancy
Rates per Artificial Insemination for Cows and Heifers
Inseminated at a Synchronized Ovulation or Synchro-
nized Estrus,” Journal of Dairy Science, Vol. 80, No. 2,
1997, pp. 295-300.
doi:10.3168/jds.S0022-0302(97)75937-X
[13] U. Singh, N. K. Khurana and Inderjeet, “Plasma Proges-
terone Profiles and Fertility Status of Anestrus Zebu Cat-
tle Treated with Norgestomet-Estradiol-eCG Regimen,”
Theriogenology, Vol. 50, No. 8, 1998, pp. 1191-1199.
doi:10.1016/S0093-691X(98)00219-2
[14] R. Cortes, J. A. Orihuela and C. S. Galina, “Effect of
Sexual Partners on the Oestrus Behaviour Response in
Zebu Cattle (Bos indicus) Following Synchronisation
with a Progestagen (Synchromate B),” Asian-Australa-
sian Journal of Animal Science, Vol. 12, No. 4, 1999, pp.
515-519.
[15] M. C. Cordoba and P. M. Fricke, “Evaluation of Two
Hormonal Protocols for Synchronization of Ovulation
and Timed Artificial Insemination in Dairy Cows Ma-
naged in Grazing-Based Dairies,” Journal of Dairy Sci-
ence, Vol. 84, No. 12, 2001, pp. 2700-2708.
doi:10.3168/jds.S0022-0302(01)74724-8
[16] M. G. Maquivar, C. S. Galina, J. R. Galindo, S. Estrada,
R. Molina and G. D. Mendoza, “Effect of Protein Sup-
plementation on Reproductive and Productive Perform-
ance in Bos indicus × Bos taurus Heifers Raised in the
Humid Tropics of Costa Rica,” Tropical Animal Health
and Production, Vol. 42, No. 4, 2010, pp. 555-560.
doi:10.1007/s11250-009-9470-0
[17] S. A. Buttler, P. C. Atkinson, G. B. Boe-Hansen, B. M.
Burns, K. Dawson, G. A. Bo and M. R. McGowan, “ Pre g-
nancy Rates after Fixed-Time Artificial Insemination of
Brahman Heifers Treated to Synchronize Ovulation with
Low-Dose Intravaginal Progesterone Releasing Devices,
with or without eCG,” Theriogenology, Vol. 76, No. 8,
2011, pp. 1416-1423.
doi:10.1016/j.theriogenology.2011.06.010
[18] P. S. Baruselli, E. L. Reis, M. O. Marques, L. F. Nasser
and G. A. Bó, “The Use of Hormonal Treatments to Im-
prove Reproductive Performance of Anestrous Beef Cat-
tle in Tropical Climates,” Animal Reproduction Science,
Vol. 82, 2004, pp. 479-486.
doi:10.1016/j.anireprosci.2004.04.025
[19] C. S. Galina and G. H. Arthur, “Review of Cattle Repro-
duction in Tropics,” Animal Breeding Abstracts, Vol. 59,
No. 9, 1990, pp. 805-813.
[20] G. S. Díaz, C. S. Galina, C. H. Basurto and G. P. Ochoa,
“Efecto de la Progesterona Natural con o sin la Adición
de Benzoato de Estradiol Sobre la PresentaciÓN de Celo,
OvulaciÓN y GestaciÓN en Animales Tipo Bos Indicus
en el TrÓPico M e xicano,” Archivos de Med icina Veterinaria,
Vol. 34, No. 2, 2002, pp. 235-244.
[21] C. Landivar, C. S. Galina, A. Duchateau and P. Na-
varro-Fierro, “Fertility Trial in Zebu Cattle after a Natural
or Controlled Oestrus with Prostaglandin F2
 Compar-
ing Natural Mating with Artificial Insemination,” The-
riogenology, Vol. 23, No. 3, 1985, pp. 421-429.
doi:10.1016/0093-691X(85)90014-7
[22] G. A. Bo, G. P. Adams, R. A. Pierson, H. E. Tribulo, M.
Caccia and R. J. Mapletoft, “Follicular Wave Dynamics
after Estradiol-17B Treatment of Heifers with or without
a Progestogen Implant,” Theriogenology, Vol. 41, No. 8,
1994, pp. 1555-1569.
doi:10.1016/0093-691X(94)90821-Y
[23] J. E. Jefrisch and C. J. Ó Neill, “Calving Rates in a Tropi-
cal Beef Herd after Treatment with a Synthetic Pro-
gestagen, Norgestomet, or a Protaglandin Analogue, Clo-
prostenol,” Australian Veterinarian Journal, Vol. 73, No.
3, 1996, pp. 98-102.
[24] J. R. Baca, E. Pérez and C. S. Galina, “Comportamiento
Reproductivo de Vacas Bos Taurus × Bos Indicus Bajo
Programas de Inseminación Artificial a Estro Sincroni-
zado y Natural en Condiciones del Trópico Seco de Costa
Rica,” Veterinaria México, Vol. 29, No. 1, 1998, pp. 67-
73.
[25] J. N. Sales, J. B. Carvalho, G. A. Crepaldi, R. S. Cipriano,
J. O. Jacomini, J. R. Maio, J. C. Souza, G. P. Nogueira
and P. S. Baruselli, “Effects of Two Estradiol Esters
(Benzoate and Cyprionate) on the Induction of Syn-
chronized Ovulations in Bos indicus Cows Submitted to a
Timed Artif icial Insemination Protocol,” Theriogenology,
Vol. 78, No. 3, 2012, pp. 510-516.
doi:10.1016/j.theriogenology.2012.02.031
[26] L. A. Werth, S. M. Azzam, M. K. Nielsen and J. E.
Kinder, “Use of a Simulation Model to Evaluate the In-
fluence of Reproductive Performance and Management
Decisions on Net Income in Beef Production,” Journal of
Animal Science, Vol. 69, No. 12, 1991, pp. 4710-4721.
[27] P. A. Bolivar and J. G. Maldonado, “Análisis de Costos
de Esquemas de Trasnferencia de Embriones Bovinos
Utilizados en Colombia,” Revista Colombiana de Cien-
cias Pecuarias, Vol. 21, No. 3, 2008, pp. 351-364.
[28] M. A. Alarcón, C. S. Galina, M. D. Corro and M. A.
Asprón, “Embryo Transfer, a Useful Technique to Be
Applied in Small Community Farms?” Tropical Animal
Health and Production, Vol. 42, No. 6, 2010, pp. 1135-
1141. doi:10.1007/s11250-010-9536-z