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223Fixed-time AI in Bos indicus cattle
Corresponding author E-mail: gabrielbo@iracbiogen.com.ar
Technologies for fixed-time artificial insemination
and their influence on reproductive performance of
Bos indicus cattle
GA Bó1,2, L Cutaia1,3, LC Peres1,3, D Pincinato1,3, D Maraña1,3 and PS Baruselli4
1Instituto de Reproducción Animal Córdoba (IRAC), J.L. de Cabrera 106, X5000GVD, Córdoba,
Argentina, 2Universidad Católica de Córdoba, 3Universidad Nacional de Córdoba, 4Departamento de
Reprodução Animal, FMVZ-USP, Brazil.
The adaptation of Bos indicus cattle to tropical and subtropical
environments has led to their widespread distribution around the world.
Although artificial insemination (AI) is one of the best alternatives to
introduce new genetics into Bos indicus herds, the peculiarity of their
temperament and the tendency to show short oestrus (many of them
during the night) greatly affects the effectiveness of genetic improvement
programs. Therefore, the most useful alternative to increase the number
of females that are inseminated is the use of protocols that allow for AI
without the need for oestrus detection, usually called fixed-time AI (FTAI).
Besides, the development of protocols to advance the resumption of
cyclicity during the early postpartum period has a great impact on beef
production and will allow for the inclusion of a significantly larger
population of animals into genetic improvement programs. Fixed-time
AI protocols using progestin devices, oestradiol and eCG have resulted
in consistent pregnancy rates in suckled Bos indicus and Bos indicus x
Bos taurus cows. Furthermore, fertility in the successive cycles and the
overall pregnancy rates at the end of the breeding season, have been
shown to be improved by the use of progestin devices at the beginning
of the breeding season. In summary, exogenous control of luteal and
follicular development has facilitated the application of assisted
reproductive technologies in Bos indicus-influenced cattle, by offering
the possibility of planning programs without the necessity of oestrus
detection and may provide the opportunity to improve reproductive
performance of beef cattle in tropical climates.
Introduction
Most beef herds are located in tropical regions where Bos indicus breeds predominate. Data on
reproductive performance, such as calving rate, calf survival and weaning rate have indicated
both inferior and superior results for Bos indicus cattle (Chenoweth 1994). However, there is
little doubt that Bos indicus breeds, and their crosses, are superior to Bos taurus cattle when
they are both kept in tropical or subtropical environments, where stressors such as high tem-
224 G.A. Bó et al.
peratures and humidity, ectoparasites and low quality forages predominate. Artificial insemina-
tion is one of the best alternatives to introduce new genetics into Bos indicus herds (especially
from Bos taurus breeds); however, only a small percentage of beef animals are subjected to AI.
In Argentina for example, only 4.5% of the beef breeding females are artificially inseminated
and 80% of those are heifers (Marcantonio 2003). Among the main factors that affect the exten-
sive use of AI in the beef herd are those related to nutrition, management and inefficient
oestrus detection. The most useful alternative to significantly increase the number of animals
involved in AI programs is the use of protocols that allow for AI without the need for oestrus
detection, usually called fixed-time AI (FTAI) protocols. Also, the development of protocols for
suckled cows will allow for the inclusion of a significantly larger population of animals, and not
just limit the application of these technologies to heifers. The intention of this manuscript is to
present data from studies in which current methods of manipulation of follicular waves and
ovulation for FTAI have been successfully applied in Bos indicus and Bos indicus x Bos taurus
crossbred herds, and discuss how these protocols may impact the overall fertility of these herds,
paying particular attention to those currently applied in extensively managed Bos indicus or
Bos indicus x Bos taurus crossbred herds in South America.
Oestrous behaviour and reproductive physiology in Bos indicus cattle
The characteristics of the oestrous cycle and follicular dynamics in Bos indicus cattle have been
recently reviewed (Bó et al. 2003). Bos indicus cattle usually have a very particular tempera-
ment that makes oestrus detection a very difficult task. “Silent” or “missed” heats have been
reported, after a regular oestrus detection (Galina and Arthur 1990; Galina et al. 1996). Further-
more, duration of oestrus has been reported to be shorter in Bos indicus than in Bos taurus cattle
(Galina and Arthur 1990). The average duration of standing oestrus in Bos indicus cattle has
been shown to be about 10 h, with variations between 1.3 to 20 h (Galina and Arthur 1990;
Barros et al. 1995; Pinheiro et al. 1998). Other studies utilizing radiotelemetry have confirmed
that crossbred Bos indicus x Bos taurus females have a shorter duration of oestrus (approxi-
mately 10 h; Bertam Membrive 2000; Rocha 2000), and found more mounting activity during
the night (56.6%). These findings are in agreement with the results obtained by Pinheiro et al.
(1998), who reported 53.8% of the oestrous expression at night, with 30.7% of these beginning
and ending during the night. Mizuta (2003), using radiotelemetry, found that the mean dura-
tion of standing oestrus was 3.4 h shorter in Nelore (12.9 h) and Nelore x Angus crossbred (12.4
h) than in Angus (16.3 h) cows. However, the interval from the onset of oestrus to ovulation
was 27.1±3.3 h and 26.1±6.3 h in Nelore and Angus cows, respectively (Mizuta 2003). Thus,
the interval from the onset of oestrus to ovulation in Bos taurus and Bos indicus cows would not
appear to differ.
Several studies have also characterized follicular-wave dynamics in Bos indicus cattle (re-
viewed in Bó et al. 2003). Bos indicus cattle have two, three or four waves of follicular growth
during their oestrous cycle and have a smaller diameter of the dominant follicle and corpus
luteum (CL; Bó et al. 2003) and lower serum progesterone concentrations (Segerson et al. 1984)
relative to those of Bos taurus cattle.
In more recent studies, the diameter of the dominant follicle at the time of deviation has been
reported to be smaller in Nelore (6.0 to 6.3 mm, Sartorelli et al. 2005; Gimenes et al. 2005b) than
in Holstein (8.5 mm; Ginther et al. 1996) cattle. Futhermore, the diameter at which the dominant
follicle acquired the capacity to ovulate in response to a treatment with pLH (Lutropin-V, Bioniche
Animal Health, Canada) in Nelore heifers was found to be between 7 and 8.4 mm (Gimenes et al.
2005a); whereas, it was 10 mm in Holstein cows (Sartori et al. 2001).
225Fixed-time AI in Bos indicus cattle
Seasonality has also been shown to affect cyclicity in Bos indicus cattle. Randel (1984)
reported that Bos indicus cows had a decreased incidence of preovulatory LH-surges and their
luteal cells in vitro were less responsive to LH during the winter. Furthermore, conception rates
of Brahman cattle were higher in the summer (61%) than in the fall (36%; Randel 1994).
Stahringer et al. (1990) and McGowan (1999) also reported an increased occurrence of anoestrus
and anovulatory oestrus in Brahman females during the winter.
Physiology of the postpartum period
Following parturition, there is a dramatic increase in FSH that is followed by the emergence of
the first follicular wave (2 to 7 d postpartum; reviewed in Wiltbank et al. 2002). However,
ovulatory capacity of the dominant follicle only occurs when it is exposed to adequate LH-
pulse frequency (approximately 1 pulse/hour) to grow and increase oestradiol production, which
will result in an LH surge and ovulation (reviewed in Wiltbank et al. 2002). Gonadotrophin
secretion patterns in the postpartum period have been shown to differ between Bos taurus and
Bos indicus cattle. Thirty days after calving, Hereford x Shorthorn suckled cows had higher
plasma LH concentrations (0.7±0.1 ng/ml) than suckled Brahman cows (0.6±0.1 ng/ml) and
this difference appeared to increase over time (D’Occhio et al. 1990). In addition, a higher
proportion of Bos taurus cows had greater pulsatile LH secretion than Bos indicus cows (D’Occhio
et al. 1990). Futhermore, a greater proportion of Bos taurus cows became pregnant during
mating between 50 to 120 d after calving compared to Brahman cows. In this study, circulating
concentrations of LH were also affected by body condition and postpartum management
(D’Occhio et al. 1990), confirming the notion that nutrition is one of the major factors affecting
postpartum ovarian activity in cattle. In that regard, Ruiz-Cortez and Olivera-Angel (1999)
observed that Bos indicus suckled cows kept on natural pasture in Colombia re-established their
cyclicity from 217 to 278 d after calving. During the first 6 months after parturition, many of
these cows had only small follicles (<6 mm in diameter, exceptionally 8 mm). From 7 to 12
months postpartum, follicular waves were more regular and when cyclicity re-commenced at
217 to 278 d postpartum, oestrus preceded ovulation in 43% of the cases and cows had normal
(21.0±3.0 d), short (10.0±2.0 d) or long (50.0±4.0 d) first oestrous cycles. This condition may
not be uncommon in Bos indicus cattle and has to be taken into consideration when deciding to
begin an AI program. Cows in low body condition would rarely respond to oestrus synchroniza-
tion treatments (Wiltbank et al. 2002; Bó et al. 2002a; 2002b).
Synchronization of oestrus and ovulation
Prostaglandin F2α
Prostaglandin F2α (PGF) has been the most commonly used treatment for synchronization of
oestrus in cattle (Odde 1990). However, the variable interval from PGF treatment to expression
of oestrus and ovulation (Kastelic & Ginther 1991) makes oestrus detection essential to attain
high pregnancy rates in AI programs. In Bos indicus cattle, oestrus response was about 30% less
than that reported for Bos taurus cattle under the same conditions (reviewed in Galina and
Arthur 1990). In two other studies, although 80 to 100% of the cows treated with PGF had
luteal regression, only 29 to 60% were detected in oestrus (Moreno et al. 1986; Alonso et al.
1995) and 51% (29/57) ovulated (Alonso et al. 1995) within 5 d of treatment. The combination
of low and variable oestrus response and the high incidence of anoestrus common in animals
grazing tropical grasses explain the wide variability in oestrus response and pregnancy rates
226 G.A. Bó et al.
after PGF treatments (Galina and Arthur 1990; Moreno et al. 1986; Kerr et al. 1991; Alonso et
al. 1995; Pinheiro et al. 1998). These studies emphasize the need for treatments that control
follicular and luteal development to obtain high pregnancy rates to FTAI without the necessity
of oestrous detection. Furthermore, treatment protocols should be capable of inducing oestrus
and ovulation in anoestrus animals.
GnRH-based protocols
GnRH-based treatment protocols have been used extensively in recent years for FTAI in beef
and dairy cattle (Pursley et al. 1995; 1997; Geary et al. 2001). These treatment protocols consist
of an injection of GnRH followed by PGF 7 d later and a second injection of GnRH 48 h after
PGF treatment. In Co-Synch protocols cows are FTAI at the time of the second GnRH (Geary et
al. 2001), whereas in Ovsynch protocols, cows are FTAI 16 h after GnRH (Pursley et al. 1995).
The Ovsynch protocols have also been used in FTAI programs in Bos Indicus cattle (Barros et
al. 2000; Lemaster et al. 2001; Williams et al. 2002; Baruselli et al. 2004). However, overall
pregnancy rates have often been lower than those rates reported in Bos taurus cattle (Baruselli
et al. 2004; Saldarriaga et al. 2005), with low conception rates in anoestrus cows (Fernandes et
al. 2001; Baruselli et al. 2004). The addition of a progestin-releasing device increased preg-
nancy rates in anoestrus Bos taurus cows (Lamb et al. 2002); however, this approach has not
resulted in increased pregnancy rates in Bos indicus and Bos indicus x Bos taurus crossbred
cattle (Saldarriaga et al. 2005; Pincinato et al. 2006) and is probably related to a low ovulation
rate following the first GnRH treatment (Saldarriaga et al. 2005).
Treatments using progestins and oestradiol
Oestradiol and progestin treatments have been increasingly used over the past several years in
oestrus synchronization programs in cattle (Macmillan & Burke 1996; Bó & Baruselli 2002;
Yelich 2002; Bo et al. 2003). Treatments consist of insertion of a progestin-releasing device and
the administration of oestradiol on Day 0 (to synchronize follicular wave emergence), PGF at
the time of device removal on Days 7, 8 or 9 (to ensure luteolysis), and the subsequent appli-
cation of a lower dose of oestradiol 24 h later or GnRH/LH 48 to 54 h later to synchronize
ovulation (Bo et al. 2002a; 2002b; Martinez et al. 2002). The most commonly used treatment
for FTAI using progesterone-releasing devices in beef cattle in South America consists of the
administration of 2 mg of oestradiol benzoate (EB) im upon insertion of the device (Day 0); on
Day 7 or 8 the device is removed and PGF is administered im, and 24 h later, 1 mg of EB im is
given (Bó et al. 2002b); FTAI is done between 52 and 56 h after device removal. Data from
13,510 inseminations in Bos taurus and Bos indicus x Bos taurus crossbred cattle, performed
between December 2000 and December 2004, resulted in a mean pregnancy rate of 52.7%,
ranging from 27.8% to 75.0%. The factors that most affected pregnancy rates were body condi-
tion score (BCS) and cyclicity of the cows (Bó et al. 2005).
Progestin based treatments for FTAI in suckled cows
Under favourable conditions, a cow has the potential to produce one calf per year, with an
interval of 12 months between calvings. However, suckled beef cattle under grazing condi-
tions often have a high incidence of postpartum anoestrus, which extends the calving to con-
ception interval and, consequently, negatively affects their reproductive performance. The
insertion of subcutaneous norgestomet ear implants or intravaginal progesterone devices, com-
bined with the application of eCG at the time of device removal, has been extensively used in
Bos indicus herds with high incidence of postpartum anoestrus (reviewed in Baruselli et al.
227Fixed-time AI in Bos indicus cattle
2004). The use of 400 IU of eCG at the time of progestin device removal resulted in increased
pregnancy rates in cows without a CL at the time of insertion of the progestin device (Baruselli
et al. 2003; Cutaia et al. 2003a). In another study (Baruselli et al. 2004), eCG treatment in-
creased plasma progesterone concentrations and pregnancy rates in suckled cows treated during
postpartum anoestrus. Therefore, eCG treatment may be an important tool for increasing preg-
nancy rates at FTAI, to reduce the postpartum period, and to improve reproductive efficiency in
postpartum Bos indicus and Bos indicus x Bos taurus beef cows. Analysis of data collected from
9,668 FTAI done from December 2000 through December 2003 has shown that Bos taurus and
Bos indicus x Bos taurus crossbred animals treated with progestin-devices must have a BCS
higher than 2.5 (scale 1 to 5) and ideally ≥3 to achieve pregnancy rates of 50% or higher (Bó et
al. 2005). Conversely, the addition of eCG allowed for pregnancy rates close to 50% in cows
with a BCS of 2 (Bó et al. 2005). It is very important to note that these results have been
achieved only when cows were gaining body condition during the breeding season. If drought
conditions or lack of feed prevent cattle from improving BCS during the breeding season,
pregnancy rates will most probably be 35% or less, even after the administration of eCG
(Cutaia et al. 2003a; Bó et al. 2005; Maraña et al. 2006). Another analysis performed with 1,987
FTAI in Nelore cows confirmed that BCS is critical to achieve pregnancy rates and that the
beneficial effect of eCG treatments was significant in cows with a BCS ≤3 (Fig. 1; Baruselli et
al. 2005). Since BCS is usually associated with cyclicity (D’occhio et al. 1990), it is conceiv-
able that most cows in the lower BCS were anoestrus at the time that treatments were initiated.
When 485 Bos indicus x Bos taurus suckled cows were examined by real time ultrasonography
at the time of device insertion, pregnancy rates in cows that had a CL when treatments were
initiated did not differ between cows treated (56.3%) or not treated with eCG (56.5%; Bó et al.
2005). However, eCG treatments increased pregnancy rates (eCG: 49.5% vs no eCG: 40%;
P<0.05) in cows that only had follicles at the time of progestin device insertion. In yet another
retrospective analysis of 2,489 FTAI in suckling Nelore cows from two commercial farms in
Brazil, pregnancy rates were not different between cows that were 40 to >80 d postpartum at
the time of FTAI (40-49 d: 57/142, 52.8%; 50-59 d: 419/759, 55.2%; 60-69 d: 137/263, 52.1%,
70-79 d: 361/684, 56.3% and >80 d: 334/641, 52.1%; Marques et al. 2006).
0
10
20
30
40
50
60
70
80
2 2.5 3 3.5 4
Body Condition Score (BCS)
Pregnancy rates (%)
Without eCG With eCG
*
*
**
Fig. 1. Effect of body condition scores (1 to 5 scale) on pregnancy rates in Nelore cows
(n=1,984) treated with progestin-releasing devices with or without 400 IU eCG at device
removal (* P < 0.05; ** P<0.1). Adapted from Baruselli et al. 2005.
228 G.A. Bó et al.
Restricted suckling or calf removal associated with progestin devices has also been used for the
induction of cyclicity in Bos indicus cows (Williams 1990; Soto Belloso et al. 2002). We have
recently conducted two experiments to compare the effects of eCG treatment and temporary
weaning (TW) on ovulation and pregnancy rates in postpartum cows. In the first experiment, 39
lactating multiparous Bos indicus x Bos taurus crossbred cows, 60 to 80 d postpartum with a BCS
between 2.0 to 2.5 (scale 1 to 5) were randomly allocated to 1 of 4 treatment groups, in a 2 by
2 factorial design (Maraña et al. 2006). On Day 0, all cows received a DIB device (intravaginal
progesterone-releasing device with 1 g of progesterone, Syntex SA, Buenos Aires, Argentina)
and 2 mg EB im (Benzoato de Estradiol, Syntex SA). On Day 8, DIB devices were removed and
all cows received PGF and were randomly divided to receive 400 IU eCG im (Novormon,
Syntex SA) at the same time or no further treatment. In addition, half of the cows in each
treatment group had their calves weaned for 56 h from the time of DIB removal; the other half
remained with their calves. All cows received 1 mg EB im on Day 9 and were examined every
8 h by ultrasonography, from the time of DIB removal until ovulation. The interval to ovulation
(eCG, 72.0±1.4 h vs no eCG, 75.6±2.0 h and TW, 73.8±1.6 h vs no TW, 73.0±1.8 h) did not
differ among groups (P>0.05). However, TW increased (7/10, 70.0%; P<0.05) and eCG treat-
ment tended to increase (12/20, 60.0%; P<0.09) the proportion of cows ovulating compared to
control cows (no TW or eCG treatment: 2/9, 22.2%). Although there was no effect of eCG
treatment on the size of the preovulatory follicle (eCG, 11.1±0.4 mm vs no eCG, 10.1±0.6
mm), the growth rate of the ovulatory follicle was greater (P<0.02) in cows treated with eCG
(1.1±0.1 mm/d) than in those not treated with eCG (0.6±0.1 mm/d). Conversely, the ovula-
tory follicle was smaller in TW cows (9.9±0.4 mm), compared to those not TW (11.8±0.3 mm;
P<0.05).
The second experiment was conducted over 2 years; 769 Bos indicus x Bos taurus crossbred
suckled cows (year 2004, n=393 and year 2005, n=376) with a BCS of 2 to 2.5 were used
(Maraña et al. 2006). All animals were examined by palpation per rectum at the time of initiat-
ing the treatment to determine ovarian status. Cows were randomly assigned to 4 treatment
groups in a 2 by 2 factorial design (Control, eCG, TW and TW+eCG), so that cows with a CL
(22.5%), follicles > 8 mm (30.0%) or ovaries with small follicles (<8 mm; 47.5%) were
equally represented in each group. Temporarily weaned calves were separated from their dams
by approximately 1000 m, to prevent any kind of contact between cows and calves. All cows
were FTAI between 52 and 56 h after DIB removal. Data were analyzed by logistic regression.
There was no interactions between years and treatments or between treatments (P>0.7). The
overall pregnancy rate was lower in 2005 (109/376, 29.0%; P<0.01) than in 2004 (173/393,
44.0%), due to a drought during that breeding season; but in both years eCG treatment in-
creased pregnancy rates (eCG, 154/377, 40.8% vs no eCG, 128/392, 32.6%; P<0.01). Con-
versely, no differences were found between cows that were TW (141/379, 37.2%) and those
that were not (141/390, 36.1%; P>0.7). It was concluded that the use of eCG but not TW
improved pregnancy rates following FTAI in postpartum Bos indicus x Bos taurus crossbred
cows in moderate to low body condition. Results also suggest that the eCG-related increase in
pregnancy rates may be due to the final growth rate of the ovulatory follicle. On the other
hand, the absence or little effect of TW on pregnancy rates contrasts with data from another
study done with Nelore cows (Penteado et al. 2004), and those from other studies (reviewed in
Baruselli et al. 2004). In the experiment with Nelore cows (Penteado et al. 2004), 459 suckled
cows were treated with Crestar (Intervet, Sao Paulo, Brazil) for 9 d and were divided into 1 of
4 treatment groups to receive or not receive 400 IU eCG im (Folligon, Intervet), and have
calves TW for 56 h or not. In this case, both eCG and TW significantly increased (P<0.05)
pregnancy rates (eCG, 126/227, 55.5% vs no eCG, 98/232 42.2%; TW, 121/229, 52.8% vs no
TW, 103/230, 44.8%). Therefore, the beneficial effects of temporary weaning may differ, de-
229Fixed-time AI in Bos indicus cattle
pending on the management and body condition of the cows. Moreover, to set up a temporary
weaning program creates logistical problems in several farms and is probably the most resisted
management technique by beef producers, at least in Argentina and Brazil. Nevertheless, the
results from both studies confirmed those reported previously that eCG increased pregnancy
rates in suckled cows enrolled in a FTAI program utilizing progestin devices and oestradiol
(Cutaia et al. 2003a; Baruselli et al. 2004).
Impact of Fixed-time AI programs on the overall fertility of beef herds
One of the main advantages of implementing FTAI programs in a beef herd is that more cows
can be impregnated earlier in the breeding season to genetically improved bulls, resulting in
heavier weaning weights (Cutaia et al. 2003b). Fifty percent of the cows could potentially
become pregnant on the first day of the breeding season and result in a higher number of cows
calving at the beginning of the calving season. Therefore, their calves will be older and heavier
at weaning. Besides, the use of genetically superior bulls will also result in heavier calves at
weaning (Cutaia et al. 2003b). The impact of FTAI has proven to be equally efficient for differ-
ent beef operations in Argentina and Brazil (Bó & Baruselli. 2002; Baruselli et al. 2005; Bó et al.
2005) and examples will be shown in the following.
In 2002, the “Estancia El Mangrullo” (Lavalle, Santiago del Estero, Argentina) started imple-
menting FTAI programs. This operation is located in the semiarid region of Argentina, with
seasonal rainfalls of 600 mm per year from November-December to May-June (Summer and
Fall). Animals are all zebu-derived and a cross-breeding program with Bonsmara (Bos taurus
adapted breed) has been implemented with the use of semen and embryos. Table 1 shows the
evolution of the number of animals involved in FTAI programs and the pregnancy rates ob-
tained.
As shown in Table 1, a FTAI program was implemented in heifers and suckled cows which
resulted in pregnancy rates between 40 and 50%. It is important to highlight that the summer
of 2005 (i.e. the breeding season) was especially dry, with no rains between December and
March which, undoubtedly affected the pregnancy rates. However, it is apparent that an aggres-
sive FTAI program may still result in acceptable pregnancy rates, even in the presence of the
drought experienced that year. Probably, the main aspect of applying this system was its effect
on calving distribution as shown in Fig. 2. The progression of calvings throughout the calving
season was compared between years using Kaplan Meier’s Method for comparison of survival
curves. Survival curves across years were significantly different (P<0.01). In 2002/3 (no FTAI),
calvings were distributed over 6 months with a high number of cows calving from December to
March (late calvers). This was changed with the limited use of FTAI in 2003/04 (Table 1).
However, with a more aggressive FTAI program, calvings began earlier, with a high proportion
of heifers calving in September (i.e. 30 d prior to the cows) and a higher percentage of mature
cows calving earlier in the breeding season (October onwards) in 2004/05.
We also evaluated the impact of FTAI on weaning weights of the calves obtained through
natural service compared to that of calves obtained through FTAI in 2004 (Bó et al. 2005). Only
one group of animals in which all calving data could be collected was used. The cows from the
Natural Service Group were bred with Bonsmara bulls at a rate of 3% (i.e. 3 bulls per 100 cows)
for 90 d. Cows in the FTAI Group were inseminated at the beginning of the breeding season
and exposed to clean-up bulls at a rate of 1.5%. All cows were monitored during the calving
season and calves born were identified with ear tags and weighed. Table 2 shows the weaning
weights of calves produced through FTAI or natural service. Weight of the calves was adjusted
to 205 d to determine the proportion of the weight difference between groups that was due to
the age of the calves and the proportion that was due to a genetic improvement introduced with
230 G.A. Bó et al.
Table 1. Pregnancy rates following FTAI programs implemented in “Estancia El Mangrullo” in Lavalle,
northeast of the Province of Santiago del Estero, Argentina. Adapted from Bó et al. 2005.
Category Year 2002/03 Year 2003/04 Year 2004/05 Total
Heifers 148/292 341/619 564/1233 1053/2144
(50.7%) (55.1%) (45.7%) (49.1%)
Dry cows — 189/394 — 189/394
(47.9%) (47.9%)
Suckled cows 156/289 345/790 450/1199 951/2278
(54.0%) (43.7%) (37.5%) (41.7%)
0
20
40
60
80
100
120
A
US
E
O
C
NO DE
JA
FE
MR
2002-03
(n=2126)
2003-04
(n=2076)
2004-05
(n=2078)
Month
% cows without a calf
Fig. 2. Survival curves for calving distribution at “Estancia El Mangrullo” Santiago del Estero, Argentina
in three consecutive years. Curves differ significantly among the three years (P<0.01). Adapted from
Bó et al. 2005.
Table 2. Weaning weights (means ±SEM) of Zebu x Bonsmara calves produced through FTAI or Natural
Service. “Estancia El Mangrullo”, Santiago del Estero, Argentina, 2004. Adapted from Bó et al. 2005.
N Weaning weight (Kg) Adjusted 205 d-weight (Kg)
FTAI 138 178.1±1.9a184.2±1.6a
Natural service 181 149.4±1.5b173.8±1.4b
Difference 28.7 10.4
Means in the same column with different superscripts differ (ab P<0.01)
the bulls through FTAI. Calves from the FTAI Group were heavier at weaning than calves in the
Natural Service Group. Part of this difference (18.3 Kg) was attributed to age, because the
calves from the FTAI Group were born earlier than those in the Natural Service Group. There
was also a 10.4 Kg weight advantage for the FTAI calves due to genetic improvement. These
data confirm previous results in Angus cattle (Cutaia et al. 2003b) where differences in wean-
ing weights were 34.6 Kg for calves produced through FTAI compared to those produced through
natural service, and showed that it was possible to improve production in a beef herd with a
FTAI program at the beginning of the breeding season.
231Fixed-time AI in Bos indicus cattle
Another study was performed in Brazil using Nelore cows (Baruselli et al. 2005). In this
study, 594 suckled Nelore cows (55 to 70 d postpartum) were randomly allocated to 1 of 4
treatment groups. Cows in Group 1 were FTAI on Day 0 of the breeding season and were
exposed to bulls for a further 90 d. Cows in Group 2 were FTAI on Day 0, then AI based on
oestrus detection for 45 d and then exposed to bulls for the last 45 d of the breeding season.
Cows in Group 3 were AI based on twice daily oestrus detection for 45 d and then exposed to
clean-up bulls for another 45 d. Cows in Group 4 simply were exposed to bulls for 90 d. In order
to determine the progression of the pregnancies during the breeding season, cows were exam-
ined by ultrasonography on Days 30, 70 and 120 after the beginning of the breeding season.
Results are shown in Table 3 and survival curves for days open are shown in Fig. 3. The use of
FTAI improved fertility by having more cows pregnant at the beginning of the breeding season.
Survival curves in the FTAI + Bulls and FTAI + OED & AI + Bulls breeding schemes differed
from those in the OED & AI + Bulls breeding schemes and the cows that were bred by bulls for
the entire breeding season (P<0.01; Figure 3). Compared to the cows bred by bulls only, the
insertion of FTAI hastened the mean day of conception by about 17 d and increased the preg-
nancy rates after the first 45 d by 30% and at the end of the breeding season by about 9% (Table
3). Conversely, the application of a traditional scheme of oestrus detection and AI for 45 d was
the least efficient program; a reflection of the difficulty of oestrus detection in suckled Bos
indicus cows.
Table 3. Reproductive parameters in suckled Nelore cows managed under four different breeding programs
during a 90 d breeding season, Camapua, MS, Brazil. Adapted from Baruselli et al. 2005.
Breeding FTAI First 45 d of the breeding season Overall
strategy (90-d breeding season)
Pregnancy Oestrus Conception Pregnancy Pregnancy Mean interval
rate detection rate rate rate rate to conception (d)
FTAI1 76/150 - - 113/150 a 139/150 a 29.3±2.0 a
+ Bulls2(50.7%) (75.3%) (92.7%)
FTAI181/148 17/67 13/17 94/148 b 136/148 a 31.1±2.2 a
+OED & AI3(54.3%) (25.4%) (76.5%) (63.5%) (91.9%)
+Bulls2
OED & AI3- 59/150 35/66 35/150 d 125/147 b 57.3±2.3 b
+ Bulls2(39.3%) (53.0%) (23.3%) (85.0%)
Bulls2- - - 66/149 c124/149 b 46.5±1.9 c
(44.3%) (83.2%)
Means and percentages differ significantly (abcd, P<0.05).
1FTAI: fixed-time artificial insemination on Day 10 of the breeding season.
2Bulls: bulls until Day 90 of the breeding season.
3OED & AI: oestrus detection and AI until Day 45 of the breeding season.
Another example is the “Hofig Ramos Agricultura e Pecuaria”, located in Brasilandia, Brazil. In
this farm, an aggressive FTAI program was implemented in 5,579 suckled Nelore cows in 2005.
Cows were enrolled in a FTAI program early in the postpartum period (i.e. 35 to 45 d postpar-
tum) using Crestar ear implants and 400 IU eCG at the time of implant removal and 10 d later
were exposed to clean-up bulls for the remainder of the breeding season. Pregnancy rate to the
FTAI was 50.5% (2817/5579) and the overall pregnancy rate after two cycles of re-breeding
with bulls was 80.7% (4390/5579). As in the previous examples, comparison of survival curves
232 G.A. Bó et al.
0
20
40
60
80
100
120
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90
Day of the breeding season
% non pregnant cows
FTAI + Bulls (n=150) FTAI + OED & AI + Bulls (n=148)
OED & AI + Bulls (n=147) Bulls (n=149)
Fig. 3. Survival curves for days open in suckled Nelore cows managed under four different
breeding programs during a 90 d breeding season, Camapua, MS, Brazil. Survival curves
in the FTAI+Bulls and FTAI+OED&AI+Bulls breeding schemes differ from the
OED&AI+Bulls and the Bulls breeding schemes (P<0.01). Adapted from Baruselli et al.
2005.
for calving distributions in 2005 and the projected calvings for 2006 confirmed the notion that
the use of a progestin-based FTAI program at the beginning of the breeding season increased
the number of calvings early in the calving season (Fig. 4).
0
20
40
60
80
100
120
AU SE OC NO DE
Month
% cows without a calf
2005 (n=4883) 2006 (n=4541)
Fig. 4. Survival curves for calving distribution at “Hofig Ramos Agricultura e Pecuaria”,
located in Brasilandia, Brazil. Curves differ significantly between years (P<0.01). Marques
et al. 2006.
233Fixed-time AI in Bos indicus cattle
Another program worth mentioning is that applied at “Cabaña Ministaló”, in Río Ceballos,
Córdoba, Argentina. This operation is located in an area that is more temperate than the others,
with about 800 to 1000 mm of rain per year, in a seasonal fashion from October to June. This is
a mixed operation (soybean and corn crops and beef cattle) with purebred Brangus and Braford
cattle (3/8 Bos indicus and 5/8 Bos taurus). Fixed-time AI has been done in November and
December of the last 5 years in 22 to 26 month old heifers and suckled cows that were 45 to 70
d postpartum. In this herd, animals have always been in good BCS (2.5 to 3.5) at the beginning
of the breeding season; the FTAI treatment consisted of a progesterone-releasing device (Triu-
B, 1 g of progesterone, Biogénesis, Argentina; DIB, 1 g of progesterone, Syntex SA, Argentina
or CIDR-B, 1.9 g of progesterone, Pfizer Animal Health, Argentina), with 2 mg EB on Day 0,
device removal and PGF on Days 7 or 8, 1 mg EB 24 h later and FTAI from 52 to 56 h after
device removal. As the goal was to increase the number of offspring produced by AI, animals
were re-synchronized by re-insertion of the progesterone-releasing device on Day 13 after
FTAI. EB (1 mg im) was also given to cows (but not to heifers) on Day 13. In this case, oestrus
was detected for 5 d after device removal (Days 20 to 25 after the first FTAI) and all animals
were inseminated 8 to 12 h after the onset of oestrus. As is shown in Table 4, pregnancy rates
with FTAI were similar over the 5 years (P>0.88). Overall pregnancy rates with AI decreased
during 2004 (P<0.05), compared to the two previous years, due to failures in oestrus detection
after the re-synchronization protocol, which demonstrates the sensitivity of systems that de-
pend on oestrus detection in beef cattle. This was corrected in 2005 by the use of a re-synchro-
nization protocol that included a second FTAI. Briefly, the re-synchronization treatment con-
sisted of re-insertion of a once-used progesterone-releasing device from Day 16 to Day 21 and
GnRH was given on Day 21. On Day 28, all cows and heifers were examined by ultrasonogra-
phy and those that were open received PGF at that time, followed by 1 mg EB im 24 h later and
FTAI 30 h after EB. As is shown in Table 4, avoiding oestrus detection for the second AI
overcame the problem and approximately 70% of the cows were pregnant after two insemina-
tions.
Table 4. Pregnancy rates with FTAI, oestrus detection rate, conception and pregnancy rates following re-
synchronization and overall pregnancy rates on a purebred Brangus and Braford farm, “Cabaña Ministaló”,
Córdoba, Argentina. Adapted from Bó et al. 2005.
Year Pregnancy rate FTAI Re-synchronization Cumulative pregnancy rate
Oestrus detection Conception Pregnancy
rate rate rate
2001 107/189 44/82 ab 24/44 24/82 ab 131/189 ab
(56.6%) (53.7%) (54.5%) (29.3%) (69.3%)
2002 104/192 49/88 ab 35/49 35/88 b139/192 b
(51.2%) (55.7%) (71.4%) (39.7%) (72.4%)
2003 128/228 71/100 b36/71 36/100 b164/228 b
(56.1%) (71.0%) (50.7%) (36.0%) (71.9%)
2004 149/279 50/130 a25/50 25/130 a174/279 a
(53.4%) (38.4%) (50.0%) (19.2%) (62.4%)
20051164/309 — — 65/145 b 229/309 b
(53.1%) (44.8%) (74.1%)
Total 652/1197 214/400 120/214 185/544 837/1197
(54.5%) (53.5%) (56.1%) (34.0%) (69.9%)
ab Proportions in the same column with different superscripts differ (P<0.05).
1 In 2005 cows and heifers were not observed for oestrus and were re-inseminated based on a FTAI protocol.
234 G.A. Bó et al.
Conclusions
Currently, the world’s economic situation requires efficient management practices to increase
the profitability of beef cattle operations. Optimal reproductive efficiency is crucial to increase
net returns. The use of animal breeding technologies has become of great importance, particu-
larly in tropical and subtropical areas where AI is the only alternative to introduce Bos taurus
genetics into Zebu-based herds. However, variability in response to the traditional PGF-based
hormonal treatments and the time and effort required to perform oestrus detection, particularly
in Bos indicus influenced cattle, have limited the widespread application and success of these
technologies. The incorporation of techniques designed to control follicular wave dynamics
and ovulation in recent years has reduced problems associated with oestrus detection. Further-
more treatments with progestin-releasing devices, oestradiol and eCG have provided possibili-
ties for the application of FTAI in suckled cows and to advance the resumption of cyclicity in
cows that were in anoestrus. Furthermore, fertility in successive cycles and overall pregnancy
rates at the end of the breeding season have been shown to improve with the use of progestin-
releasing devices at the beginning of the breeding season in cows that were well managed and
on an increasing plane of nutrition. However, it is very important to recognize that the success
of the program will also depend on many management factors such as the nutritional and health
management, availability of qualified personnel, facilities and the objectives of the breeding
program.
Aknowledgments
Research was supported by FAPESP, Brazil (08363-0/2002), the Instituto de Reproducción Ani-
mal Córdoba (IRAC) and Estancia “El Mangrullo S.A.”, Argentina. We also thank Syntex S.A.,
Argentina; Biogenesis, Argentina; Pfizer Animal Health, Argentina and Brazil; Intervet, Brazil
and Tecnopec, Brazil for the hormones used in the studies. Special thanks to our colleagues of
IRAC, U. of São Paulo, GeraEmbryo and FIRMASA IATF for technical assistance. e-mail:
gabrielbo@iracbiogen.com.ar
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