Impact of breed, body score and animal category on the pregnancy rate of bovine females under

IATF management

Rosana Dias Campos1, Otaviano de Souza Pires Neto2, Carolina Magalhães Caires Carvalho3, Fernanda Santos

Silva Raidan4, Janderson Tolentino Silveira5, Igor Dias Soares6, Abel Martins Lafetá Lírio Brant7, Alice Ranielly

Chaves Santos8, Bruna Naiara Cardoso9

DOI: https://doi.org/10.35699/2447-6218.2023.45216

ABSTRACT:

This study evaluate the impact of the reuse of the intravaginal progesterone implant (DIP), the body condition score

and the racial composition on the pregnancy rate of Nelore and Angus heifers (F1) and Nelore cows of different

categories submitted to different protocols of TAI, from a database of 3,093 females submitted to the same hormonal

induction protocol and from the mating season of a commercial farm in the north of Minas Gerais. The racial com-

position influenced the pregnancy rate of heifers, with rates of 55.11% for Nellore heifers and 64.36% for ½ Angus,

showing that the ½ Angus breed has 1.55 times more chances of successful gestation compared to the breed Nellore.

There is no effect of the progesterone implant until the third use on the pregnancy rate of the heifers evaluated. The

increase of one unit in the body condition score on the scale of 1 to 5 implies 1.9109 or 91.09% times more success

in pregnancy. The category of calving cows did not significantly affect the pregnancy rate in the evaluated herd, with

pregnancy rates of 58.1%, 62.8%, 77.7% and 62.9% for primiparous, early primiparous, secondary and multiparous,

respectively. The introduction of ½ Angus heifers to explore the effects of heterosis and complementarity between

breeds is a viable alternative. Cows, when well managed in the postpartum period, obtain pregnancy rates higher

than that observed in the national average.

Key Words: Angus. Body score. Gestation rate. Nelore. Progesterone intravaginal device.

1Universidade Federal de Minas Gerais, Instituto de Ciências Agrárias. Pós Graduação em Produção Animal. Montes Claros, MG. Brasil.

https://orcid.org/0000-0001-7794-9212

2Faculdades Integradas do Norte de Minas. Curso de Medicina Veterinária. Montes Claros, MG. Brasil.

https://orcid.org/0000-0002-1159-4559

Universidade Federal de Minas Gerais, Instituto de Ciências Agrárias. . Montes Claros, MG. Brasil.

https://orcid.org/0000-0002-3145-0253

4Commonwealth Scientific and Industrial Research Organisation (CSIRO) - Brisbane - Austrália.

https://orcid.org/0000-0002-1919-295X

Universidade Federal de Minas Gerais, Instituto de Ciências Agrárias. . Montes Claros, MG. Brasil.

https://orcid.org/0000-0002-9497-8223

6Universidade Federal de Minas Gerais, Instituto de Ciências Agrárias, Zootecnista. Montes Claros, MG. Brasil.

https://orcid.org/0000-0002-1696-4424

7Faculdades Integradas do Norte de Minas-Funorte, Médico veterinário. Montes Claros - MG. Brasil.

https://orcid.org/0000-0002-5902-1370

8Universidade Federal de Minas Gerais, Instituto de Ciências Agrárias, Discente do curso de Zootecnia. Montes Claros, MG. Brasil.

https://orcid.org/0000-0003-2870-2517

9Universidade Federal de Minas Gerais, Instituto de Ciências Agrárias, Discente do curso de Zootecnia. Montes Claros, MG. Brasil.

https://orcid.org/0000-0002-9884-1566

*Autor para correspondência: rosanacampos8@yahoo.com.br

Recebido para publicação em 13 de março de 2023. Aceito para publicação 02 de junho de 2023. e-

ISSN: 2447-6218

Caderno de Ciências Agrárias está licenciado

com uma Licença Creative Commons

Atribuição - Não Comercial 4.0 Internacional

CADERNO DE CIÊNCIAS AGRÁRIAS

Agrarian Sciences Journal

Campos, R. D. et al.

Cad. Ciênc. Agrá., v. 15, p. 01–09, DOI: https://doi.org/10.35699/2447-6218.2023.45216

Impacto da raça, do escore corporal e da categoria animal na taxa de prenhez de fêmeas bovinas

em manejo de IATF

Resumo

Este estudo teve como objetivo estudar o impacto da reutilização do implante intravaginal de progesterona (DIP),

do escore de condição corporal e da composição racial na taxa de prenhez de novilhas Nelore e Angus (F1) e vacas

Nelore de diferentes categorias submetidas a protocolos de IATF, a partir de um banco de dados de 3.093 fêmeas

submetidas ao mesmo protocolo de indução hormonal e oriundos da estação de acasalamento de uma fazenda co-

mercial do Norte de Minas Gerais. A composição racial influenciou a taxa de prenhez das novilhas, com índices de

55,11% para novilhas Nelore e 64,36% para ½ Angus, mostrando que a raça ½ Angus tem 1,55 vezes mais chances

no sucesso da gestação comparado a raça Nelore. Não existe efeito do implante de progesterona até o terceiro uso

sobre a taxa de prenhez das novilhas avaliadas. O incremento de uma unidade no escore de condição corporal na

escala de 1 a 5 implica em 1,9109 ou 91,09% vezes mais de sucesso na gestação. A categoria de vacas paridas não

afetou significativamente a taxa de prenhez no rebanho avaliado, com taxas de prenhez de 58,1%, 62,8%, 77,7% e

62,9% para primíparas, primíparas precoces, secundíparas e multíparas, respectivamente. A introdução das novilhas

½ Angus visando explorar os efeitos da heterose e complementaridade entre raças é uma alternativa viável. Vacas

quando bem manejadas no pós-parto obtêm taxas de prenhez superiores ao observado na média nacional.

Palavras- Chaves: Angus. Dispositivo intravaginal de Progesterona. Escore corporal. Nelore. Taxa de gestação.

Introduction

It’s notable the distinction between nulliparous,

multiparous and primiparous with respect to reproductive

efficiency in beef cattle production systems. The hormonal

release responsible for raising stress levels in the pre and

postpartum associated with the presence of the calf, along

with the effect between growth and lactation, increases

the nutritional requirement and decreases reproductive

performance (Pilau; Lobato, 2009), especially for primi-

parous.

The Nelore breed, known for its adaptability and

robustness, is the most numerous racial group raised

in Brazilian herds. The crossbreeding between diffe-

rent breeds, such as Angus, allows to explore the effects

of heterosis and complementarity of the breeds, which

among other benefits can also increase the reproductive

efficiency of national cattle herds (Reggiori et al., 2016).

Some indices with marked differences between Bos in-

dicus and Bos taurus are age at puberty, environmental

adaptation, response to physiological stress and results

of estrus synchronization programs (Vasconcelos et al.,

2014).

Thus, to intensify the gain on the herds, it is

essential the efficient development, understanding, impro-

vement and use of technologies that contribute to optimize

the available labor and increase animal productivity (Ba-

ruselli et al., 2018). For example, the Fixed-Time Artificial

Insemination (TAI) can be a facilitating mechanism of

reproductive management that, when properly performed

paying attention to animal physiology, presents itself as

a positive artifice, ensuring a greater and more efficient

roof planning, births, weaning, and disposal of females

(Fontana et al., 2014).

Furthermore, fertility indices of females in the

herd can be improved through the use of estrous synchro-

nization protocol. For example, reduction in anestrous

period via hormonal stimulation, increase in the number

of calves and reduction in age at first covering and calving

by inducing puberty of replacement heifers (Santos et al.,

2018).

However, it’s important to note that, in any pro-

duction system, the applicability of this methodology is

available to help and optimize reproductive rates and

not exclusively to correct inefficient management in the

production process.

Given the above, the objective of this research was

to evaluate the pregnancy rate of different categories of

postpartum Nelore cows, Nelore and ½ Angus heifers, and

to study the impact of intravaginal progesterone implant

(IVP) reuse, body condition score and race composition

on the heifers’ pregnancy rate.

Material and Methods

The present study was conducted from the evalua-

tion of a database corresponding to the mating season of

the period 2018/2019, in a commercial beef cattle farm

located in the municipality of Jequitaí, Minas Gerais

(MG). The study implementation steps did not need to

go through the Ethics Committee on Animal Research,

given the character of the study in which there was no

effective manipulation of animals, but only the analysis

of data previously obtained by the property.

From the original database, the objective was to

evaluate the pregnancy rate of 3,093 females of reproduc-

tive age, subjected to TAI protocols and maintained under

Impact of breed, body score and animal category on the pregnancy rate of bovine females under IATF management

Cad. Ciênc. Agrá., v. 15, p. 01–09, DOI: https://doi.org/10.35699/2447-6218.2023.45216

the same conditions of feed management with Brachiaria

brizantha (cv. Marandu), mineral supplementation and

water ad libitum. As this is a retrospective analysis, only

animals with complete information that could be mani-

pulated were used.

It was considered as study material the animal

category (nulliparous, primiparous, early primiparous, se-

cundiparous and multiparous), racial composition (Nelore

vs Angus (F1)) and body condition score through visual

evaluation methodology (being classified on a scale of 1

to 5, where 1= very thin and 5= obese). As a criterion

for stratification of the animals to be evaluated, the body

condition score was used, including females with scores

from 2.25 to 4.

The animals were grouped according to the

categories studied: 2280 heifers (Nelore and Angus/

Nelore (F1) with average ages ranging between 36 and

24 months, respectively), and 813 calving and suckling

Nelore cows, divided into early primiparous, primiparous,

secundiparous and multiparous.

The estrous synchronization protocol started at a

random period of the reproductive cycle and a minimum

period of 45 days of uterine involution was respected

for the group of calving cows. All animals were sub-

jected to the same hormone induction protocol, with a

management model of 11 days. On Day zero (D0), 2mg

of Estradiol Benzoate was applied intramuscularly and

a 1.9g Progesterone intravaginal device of first, second

and third use was inserted. On Day 7 (D7), 500 mcg

of the luteolytic agent Prostaglandin PGF2α was also

applied intramuscularly. On Day 9 (D9), the intravaginal

device was removed and 0.5 mg of Estradiol Cypionate

and 500 mcg of Prostaglandin PGF2α was administered

intramuscularly. On day 11 (D11) insemination of all

animals was performed. As shown in Figure 1.

Figure 1 – Schematic representation of the hormone protocol.

Source: From the authors, 2020.

Inseminations were performed by trained and

experienced inseminators, using random semen from

Nelore and Angus bulls. After 35 days of artificial in-

seminations, gestational diagnosis was performed by

transrectal ultrasonography.

The variables considered were: female catego-

ries, number of progesterone device uses, body condition

score, and breed composition.

Pregnancy rates were grouped into tables and

evaluated by the non-parametric method of Chisquare

((χ2) with 5% probability of error.

The response variable of pregnancy diagnosis

was assumed for presenting a binomial distribution (P

= pregnant; V = empty), being analyzed based on the

logistic regression methodology. This analysis can verify

the significance of each variable to explain the variation

in pregnancy diagnosis, quantify the change in the chance

of pregnancy for each unit increase in the regressor varia-

bles and use these variables to predict the probability of

pregnancy. All analyses were performed using R Studio

software, version 3.5.1 (2020).

Results and Discussion

Pregnancy rates according to racial composition

are depicted in Figure 2, with rates of 55.11% for Nelore

heifers and 64.36% for Angus (F1). The pregnancy rates

obtained in this study are favorable at TAI and our results

corroborate those observed by Nonato et al. (2019) who

found pregnancy rates of 45% to 59% in pubertal and

pre-pubertal Nelore heifers. Pregnancy rates between 40%

Campos, R. D. et al.

Cad. Ciênc. Agrá., v. 15, p. 01–09, DOI: https://doi.org/10.35699/2447-6218.2023.45216

and 60% gestation rate are considered satisfactory when

compared to the national average in TAI rograms (Sales

al., 2014; Andrade et al., 2018). Heifers are represented

as the group of animals of primary importance in any

production system, because they will be the possible

replacements cows, so the earlier an animal contribute

te the breeding herd, greater the economic impact on the

productivity of the livestock sector, because heifers that

conceive early will produce more calves and have their

life cycle intensified.

Figure 2 – Pregnancy rate of artificially inseminated Angus/Nelore (F1) and Nelore heifers.

Prepared by the author himself (2020).

Table 1 shows an odds ratio of 1.56, indicating

that Angus (F1) breeds have 1.56 times more chance of

a positive pregnancy when compared to Nelore heifers,

probably due to the greater precocity observed in Bos

taurus cattle. And although zebu animals usually show

greater adaptability and rusticity to pasture production

systems in tropical regions, the effects of heterosis may

have favored sexual precocity in Angus heifers (F1) par-

tially explaining the superiority of the pregnancy rate for

the F1 animals evaluated in our study (Sartori et al., 2010;

Reggiori et al., 2016). In their experiment, Reggiori et al.

(2016) observed that the reproductive performance of ½

Angus x Nelore crossbred heifers were superior to Nelore

females due to the greater sexual precocity observed in

Bos taurus taurus.

Table 1 – Relationship between pregnancy probability and breed composition (½ Angus breed vs the Nelore breed).

Variable odds ration p value

Breed (1/2Angus x Nelore) 1.5587 (55.877%) p<0.01

Legend: *

Value (< 0.05). **

p Value (

< 0.01). ***

p Value (

< 0.001).

The successful pregnancy rate observed in this

experiment, greater than 55%, can be explained by the

fact that most heifers are already in puberty at the be-

ginning of the TAI rotocol (Batista et al., 2012) since the

inclusion of unproductive females is one of the causes of

low efficiency of the TAFI protocol (Gottschall, 2011).

Thus, gynecological evaluation prior to synchronization is

essential to ensure the success of the technique and avoid

losses in the production system. Nutrition also contributes

to the pregnancy rates obtained here, the animals were

kept on quality feed and with favorable body condition

scores when starting the mating season. On the other

hand, animals with compromised body condition scores

start their puberty later due to the demand of nutrients

for their basic functions, placing reproduction as the last

parameter to be attended.

Exposed to quality feed zebu heifers reach puberty

between 18 and 24 months of age, while taurines under

the same conditions begin their reproductive activity

between 11 and 15 months. In addition, taurines have

larger measures of follicular diameter, which demonstrates

their sexual precocity (Lunardelli et al., 2013; Nepomu-

ceno, 2013), and the corpus luteum of zebu females has

smaller dimensions due to the smaller follicular diameter

(Figueiredo et al., 1997).

There is no effect of intravaginal progesterone

implant of up to third use on the pregnancy rate of heifers

5 
Impact of breed, body score and animal category on the pregnancy rate of bovine females under IATF management 
Cad. Ciênc. Agrá., v. 15, p. 01–09, DOI: https://doi.org/10.35699/2447-6218.2023.45216 
 
 
evaluated (Table 2 and  3),  demonstrating  that  intrava- 
ginal progesterone(P4) devices can be reused, allowing 
the start of the synchronization of the cycle from lower 
concentrations  of  this  hormone,  without  reducing con- 
ception rates, being a viable and efficient way to perform 
the TAI Medalha et al., 2015). 
 
Table 2 – Correlation between pregnancy probability and reuse of intravaginal progesterone implantation in the Nelore 
breed. 
Variable  odds ratio  p value 
Implants up to 3 uses  1.1786 0.4828 
Legend: * 
= 
p 
Value (< 0.05). ** 
= 
p Value (
< 0.01). *** 
= 
p Value (
< 0.001).
 
 
Table 3 – Relationship between probability of pregnancy and reuse of the intravaginal progesterone implant in the ½ 
Angus breed. 
Variable  odds ratio  p value 
 
Implants up to 3 uses  0.9687 0.853 
Legend: * 
= 
p 
Value (< 0.05). ** 
= 
p Value (
< 0.01). *** 
= 
p Value (
< 0.001).
 
 
The results of this work corroborate those publi- 
shed in the literature on the reuse of heifer progesterone 
device  implants  up to  3  times  (Carvalho  et  al.,  2019; 
Santos et al., 2018; Medalha et al., 2015; Gottschall et al., 
2012). The use of fourth-use intravaginal  progesterone 
devices  is an  effective alternative for inducing puberty 
in heifers, thus, the authors reported  a pregnancy rate 
of 35.14% in this category (Coelho et al. (2021), and in 
the same In this sense, Figueredo et al., (2019) found a 
pregnancy rate of 48.18% also in beef heifers and under 
conditions similar to those observed in this study. 
The adequate concentration of P4 present in the 
CIDR of 1.9 g (Pereira et al., 2018) does not compromise 
the synchronization of a new follicular growth wave when 
the device is reused. The reuse of P4 implants is feasible 
as long as it has a concentration above 1ng/ml (Savio et 
al. 1993). In new devices, on the other hand, P4 values 
should remain above 2ng/ml until the device is removed 
in 7 or 9 days (Rathbone, 2012). 
 
According to  studies  by  Muth-Spurlock et al. 
(2016), the concentration of progesterone in the devices 
reused for up to two times was 1.5ng/ml, which did not 
influence the final pregnancy rate of heifers and Angus 
cows.
 
 
Follicles  become  more  responsive  to  Luteini- 
zing  Hormone  in  the presence  of high concentrations 
of  progesterone  which  consequently  improves  fertility 
and final conception rate (Giordano et al.,  2013). Thus, 
when thinking about  cost x benefit in TAI the reuse  of 
the  1.9g  progesterone  intravaginal  device  becomes  a 
viable procedure, since pregnancy rates are maintained 
independent of the use of new or reused progestogens. 
The reduction in production costs, without interference 
in production performance, means improvement in the 
efficiency of the system. 
Gottschall and Silva (2018) reported a pregnancy 
rate of 57.6% in beef heifers using third use progesterone 
devices, a result similar to that found in this study. Gotts- 
chall et al. (2009) observed pregnancy rates of 61.1% 
and  49.7%  in  Aberdeen  Angus cows  using  intravaginal 
progesterone devices, of 1st and 2nd use , respectively, 
showing that the reuse of the progesterone device in the 
protocol TAI is also effective in lactating cows with calf 
at foot.
 
 
The pregnancy rates and odds ratio obtained by 
heifers according to body condition score are summari- 
zed in Tables 4 and 5. The effect of body condition score 
on pregnancy  diagnosis  was evaluated through  logistic 
regression  (Table  5).  According  to  odds  ratio  and  cor- 
roborating the results shown in Table 4, the increase of 
one unit in the  body  condition score  of heifers implies 
in 1,9109 or 91,09% more success in pregnancy. 
 
Other authors reported the importance of body 
condition  on  the  conception rate  in  nulliparous,  primi- 
parous  and  multiparous  females  (Ferreira  et  al.,  2013; 
Costa et al., 2019; Hartmann; Machado, 2022). 
 
The results of this study are similar to the findings 
of  Alves  et  al.  (2022),  where  they  observed  pregnancy 
rates ranging from 50.78% and 39.68% in the first and 
second IATF in heifers with body score 3 (on a scale of 1 
to 5). Costa et al. (2019) also achieved a higher pregnancy 
rate in beef cattle with a score above 3 points, extensively 
bred in the North of Minas Gerais region. 
 
Therefore,  according  to Hartmann;  Machado 
(2022)  and  Martini et al.  (2022),  body  scores  equal  to 
or  greater  than  3.1  result  in  high  conception  rates  in 
systems that  adopt fixed-time artificial  insemination as 
a reproductive  method.  Demonstrating  that  nutrition 
is closely linked to the onset or return of clinical luteal 
activity in bovines. 

Campos, R. D. et al.

Cad. Ciênc. Agrá., v. 15, p. 01–09, DOI: https://doi.org/10.35699/2447-6218.2023.45216

Table 4 – Relationship between the probability of pregnancy and the evaluated body scores of Nelore and ½ Angus

heifers.

Score

Gestation Rate %.

Total inseminated

2.25 a 2.75

1009

1739

3.25 a 3.75

318

528

Table 5 – Correlation between ECC and pregnancy in artificially inseminated Nelore and ½ Angus heifers.

Variable

odds ratio

p value

ECC

1.9109 (91.09%)

0.00168

Legend: *

Value (< 0.05). **

p Value (

< 0.01). ***

p Value (

< 0.001).

Studies by Tarouco et al. (2020) indicate that the

probability of pregnancy increases when the animal has

a body condition score of at least 3 points on a scale of

1 to 5, and that increasing the body condition scale by

0.4 points increased the chances of pregnancy by 25%

in cows and heifers. Abreu et al. (2018) correlated body

condition score with pregnancy rate in Brangus and cross-

bred heifers, with scores that ranged from 2.5, 3.0 and

3.5 points on the 1 to 5 scale, and lead to the conclusion

that the pregnancy rate was considerably higher when

0.5 (half) unit was added to the body score of these ani-

mals, with a pregnancy percentage of 34.7%, 41.3% and

61.3%, respectively, Reinforcing the obtained results in

this study. Torres et al.(2015) and Vaz and Lobato (2010)

also observed a significant correlation between SCC and

probability of pregnancy.

The pregnancy rates of Nelore cows submitted to

the TAI protocol according to each category are simplified

in Table. 6.

Table 6 – Gestation rate of Nelore cows calved and divided according to animal category and inseminated by means

of IATF protocols.

Category

Inseminated Animals

Pregnant

Rate %

Primiparous

58.10

Early Primiparous

62.85

Secundiparous

77.77

Multiparous

686

432

62.97

Total

813

511

62.85

p=0.341 p=0.3417

Legend: *

Value (< 0.05). **

p Value (

< 0.01). ***

p Value (

< 0.001).

The animal category did not significantly affect

the pregnancy rate (p=0.3417) in the evaluated herd.

In the group of primiparous females, 58.1% or (43/74)

females became pregnant, while early primiparous females

obtained a pregnancy rate of 62.8% (22/35), while second

and multiparous females achieved a pregnancy rate of

77.7% (14/18) and 62.9% (432/686), respectively.

The results presented here corroborate those

reported by Silva et al., (2017) who found a pregnancy

rate of 61.88% and 61.49% among multiparous and

primiparous females, respectively. Usualty primiparous

females are less efficient when compared to multiparous

and secundiparous females, due to the higher nutritional

requirements of this category (Patterson et al., 1992;

Medalha et al., 2015). For this reason, the return to cyclic

luteal activity of these animals becomes compromised,

which increases the calving interval and service period

(Cunha et al., 2013).

Medalha et al. (2015) when synchronizing primi-

parous and multiparous cows, concluded that primiparous

cows had lower chances of conceiving compared to mul-

tiparous cows. However, Castilho et al., (2018) reported

a 55.2% gestation rate in primiparous Red Angus cows

calved and submitted to TAI protocols.

Similar results to those observed in this stu-

dy were reported by Resende et al. (2014), who found

that early primiparous well-nourished cows can achie-

ve pregnancy rates of 62.79% and that it is financially

viable to exploit their genetics to the maximum in rural

areas because the pregnancy rate is not lower than that

of multiparous or secondary cows. It is believed that

Impact of breed, body score and animal category on the pregnancy rate of bovine females under IATF management

Cad. Ciênc. Agrá., v. 15, p. 01–09, DOI: https://doi.org/10.35699/2447-6218.2023.45216

nutritionally well-managed primiparous cows may have

gestation results equivalent to those observed in older

and experienced cows and that the energy required for

their essential functions would be being supplied by the

good nutrition offered, not influencing the response to

estrous synchronization protocols (Silva et al., 2017)

which justifies the rates observed in our study.

The secundiparous achieved a high pregnan-

cy rate among the categories, demonstrating the good

potential of these animals, overcoming the conception

rate observed by Carvalho (2017) with pregnancy rates

close to 70%. The high pregnancy rate was due to the

feeding strategy implemented on the property for pre

and postpartum.

The postpartum period constitutes as the most

critical phase in the reproductive efficiency of an animal

and although there is follicular development during the

postpartum anestrus, no follicle matures sufficiently to

ensure an ovulation, and this occurs due to the interven-

tion in the release of LH due to the impairment in the

hypothalamic-pituitary-gonadal axis (Montiel; Ahuja,

2005). This intervention occurs mainly due to low food

intake, loss of SCC, lack of proper nutritional management

and the presence of the calf that together suppress the

release of hormones essential for follicular growth and

ovulation, compromising the results of the TAI (Bó et al.,

2016). However, these factors, do not seem to interfere

with the final gestation rate of the females due to the

nutritional management in a strategic way on the farm,

causing most of these animals not to lose body condition

during the transition period and to be able to perform

their genetics to the maximum. Animals that did not

conceive during the reproductive season were able to

return to cyclicity, increasing the probability of a new

conception.

Therefore, the satisfactory pregnancy rate ob-

served in this study was due to the strategic nutritional

management instituted in the property in the pre and

postpartum period, which caused most cows not to re-

main in reproductive anestrous due to low weight loss

and SCC and return as soon as possible to cyclic luteal

activity, with a total pregnancy rate of 62.8%. Similar

result to that obtained by Viana et al., (2015) in farms

in Northern Minas Gerais of 62% pregnancy rate.

The pregnancy rate found is above the national

average of 50% of pregnancies obtained in IATF programs

(Siqueira et al. 2008; Gottschall et al., 2009). According

to Borges (2008) the acceptable pregnancy rates to the

IATF can range from 25 to 70%, and according to Ereno

et al. (2007) are considered satisfactory pregnancy rates

above 50%, because the costs for implementation of the

technique, as well as specialized labor and purchase of

medicines would not justify the low percentages of preg-

nancy, however, the results obtained here can be seen as

appropriate in programs of IATF.

Conclusion

½ Angus heifers showed greater precocity com-

pared to Nelore heifers. Intravaginal progesterone devices

can be reused up to 3 times in pure and crossbred heifers

without affecting pregnancy rate at the end of the breeding

season. The body condition directly affects the cyclicity

and consequently the response to hormone treatment,

being observed a higher percentage of pregnancies in

nulliparous that were in better body condition. The in-

clusion of younger cows in the herd becomes feasible in

the production system, since the indexes are similar in

the different phases.

Acknowledgements

This study was financed in part by the Coordenação

de Aperfeiçoamento de Pessoal de Nível Superior

- Brazil (CAPES) - Finance Code 001 and UFMG- Pro-

-Reitoria de Pesquisas.

Authors

contribution

RDC, OSPN,CMCC, FSR - Conceptualization, Methodology,

Validation, Formal analysis, Investigation, Writing - Origi-

nal Draft; RDC, JTS, IDS, AMLLB - Investigation; ARCS,

BNC, Writing - Review & Editing.

References

Abreu, M. S.; Silva, L. S.; Gottschall, C. S. 2018. Resposta reprodutiva

e custo por prenhez em função do escore de condição corporal de

novilhas ao acasalamento. Revista de Iniciação Científica da ULBRA

16: 5–11. Available in: https://tinyurl.com/4c22buyp.

Alves, A. F. V.; Almeida, D. S.; Guimarães, A. L. S.; Brito, G. F. 2022.

Protocolo reprodutivo de indução à puberdade em novilhas da raça

Nelore: Relato de caso. XXII Jornada de Iniciação Científica ULBRA,

Palmas, TO, Brasil. Available in: https://tinyurl.com/ye2578pt.

Andrade,

S. et al. 2018. Aspectos uterinos, foliculares e seminais que

afetam a IATF em vacas de corte no período pós-parto. In: IX Congresso

Norte e Nordeste de Reprodução Animal. Anais…Revista Brasileira

de Reprodução Animal, Belém, PA, 42: 77–89. Available in: https://

tinyurl.com/yckryvef.

Baruselli, P. S.; Ferreira, R. M.; Sá Filho, M. F.; Bó, G. A. 2018. Review:

Using artificial insemination v. natural service in beef herds. Animal,

12: 45–52. Doi: https://doi.org/10.1017/S175173111800054X.

Batista, D. S. N.; Abreu, U. G. P.; Ferraz Filho, P. B.; Rosa, N. A. 2012.

Índices reprodutivos do rebanho Nelore da fazenda Nhumirim,

Pantanal da Nhecolândia. Acta Scientiarum, 34: 71–76. Doi: https://

doi.org/10.4025/actascianimsci.v34i1.12267.

8 
Campos, R. D. et al.
 
Cad. Ciênc. Agrá., v. 15, p. 01–09, DOI: https://doi.org/10.35699/2447-6218.2023.45216 
 
 
Bó, G. A.; La Mata, J. J.; Baruselli, P. S.; Menchaca, A. 2016. Alternative 
programs for synchronizing and resynchronizing ovulation in beef 
cattle.  Theriogenology,  86:  388–389.  Doi:  https://doi.org/10.1016/j. 
theriogenology.2016.04.053.
 
 
Borges, L. F. K. 2008. Sistema para inseminação artificial sem observação 
de estro em vacas de corte amamentando. Santa Maria: Universidade 
Federal de Santa Maria, 56f. Dissertação Mestrado. Available in: https:// 
tinyurl.com/5ap89znc.
 
 
Carvalho, 
J. 
S.;  Cavalcanti,  M.  O.;  Chaves,  M.  S.;  Rizzo,  H.  2019. 
Eficiência da inseminação artificial em tempo fixo em fêmeas zebuínas 
na mesorregião Sudeste do Pará, Brasil. Revista de Ciências Agrárias, 
62: 1–7. Doi: http://dx.doi.org/10.22491/rca.2019.2977.
 
 
Carvalho,  R.  S.  2017.  Influência  da  alteração  do  escore  de  condição 
corporal e de hormônios metabólicos pós-parto na eficiência reprodutiva 
de vacas Nelore inseminadas em tempo fixo. Botucatu: Faculdade de 
Medicina Veterinária e Zootecnia - UNESP, 80f. Dissertação Mestrado. 
Available in: https://tinyurl.com/2p95ewbs. 
 
Castilho,  E.  M.;  Vaz,  R.  Z.;  Fernandes,  T.  A.;  Conceição,  V.    G.    D.; 
Brum, O. B. 2018. Precocidade de parto na estação de parição sobre 
a eficiência produtiva de vacas primíparas aos 24 meses de idade. 
Ciência Animal Brasileira, 19: 1–9. Doi: https://doi.org/10.1590/1809- 
6891v19e-46667.
 
 
Coelho, M. R.; Correia, I. A.; Mota, D.A.; Júnior, A. R. L.; Alcebíades,
 
W. J.; Siqueira, J. B. 2021. Factors that influence the pregnancy rate in 
female nelore submetted to the FTAI. Brazilian Journal of Development, 
7
(
5): 46901–46915. Available in: https://tinyurl.com/4ac5r86t.
 
 
Costa, M. G.; Araújo, A. C. C.; Nonato, M. S.; Murta, D. C. R. X.; Murta,
 
D. V. F.; Rufino, C. A. 2019. Influência do Escore de Condição Corporal 
sobre a taxa de prenhez de vacas Nelore submetidas ao programa de 
IATF no norte de Minas Gerais. Brazilian Journal of Development, 11: 
24724–24728. Doi: https://doi.org/10.34117/bjdv5n11-151. 
 
Cunha, R. R.; Fernandes, C. A. C.; Garcia, J. A. D.; Gioso, M. M. 2013. 
Inseminação artificial em tempo fixo  em  primíparas nelore  lactantes 
acíclicas. Arquivo Brasileiro de Medicina Veterinária e Zootecnia, 65: 
1041–1048. Doi: https://doi.org/10.1590/S0102-09352013000400015. 
 
Ereno, R. L.; Barreiros, T. R. R.; Seneda, M. M.; Baruselli, P. S.; Pegorer, M. 
F.; Barros, C. M. 2007. Taxa de prenhez de vacas Nelore lactantes tratadas 
com P4 associada à remoção temporária de bezerros ou aplicação de 
gonadotrofina  coriônica  equina.  Revista  Brasileira  de  Zootecnia,  36: 
1288–1294. Doi: https://doi.org/10.1590/S1516-35982007000600010. 
 
Ferreira, M. C. N.; Miranda, R.; Figueiredo, M. A.; Costa, O. M.; Palhano,
 
H. B. 2013. Impacto da condição corporal sobre a taxa de prenhez de 
vacas da raça nelore sob regime de pasto em programa de inseminação 
artificial em tempo fixo (IATF). Semina: Ciências Agrárias, 34: 1861– 
1868. Available in: https://www.redalyc.org/pdf/4457/445744122032. 
pdf. 
 
Figueiredo, R. A.; Barros, C. M.; Pinheiro, O. L.; Soler, J. M. P. 1997. 
Ovarian  follicular  dynamics  in  Nelore  breed  (
Bos  indicus
)  cattle. 
Theriogenology, 47: 1489–1505. Doi: https://doi.org/10.1016/S0093- 
691X(97)00156-8.
 
 
Figueredo, V. C. S. 
et  al
.  2019.  Efeito  do  implante intravaginal de 
progesterona na taxa de prenhez de novilhas Nelore. Brazilian Journal 
of Development, 5: 24291–24295. Doi: https://doi.org/10.34117/ 
bjdv5n11-116.
 
 
Fontana, D. L.; Ulguim, R. R. 2014. Sistemas de inseminação artificial 
em tempo  fixo  (IATF). In:
. 
Produção  de suínos: teoria  e  prática  / 
Coordenação  editorial  Associação  Brasileira  de  Criadores  de  Suínos; 
Coordenação  Técnica  da  Integral  Soluções  em  Produção  Animal. 
Brasília,  DF.  908p  Available  in:  https://abcs.org.br/wp-content/ 
uploads/2020/06/01_Livro_producao_bloq_reduce.pdf.
 
Giordano, J. O.; Wiltbank, M. C.; Fricke, P. M.; Palisch, R.; Guenther,
 
J. N.; Nascimento, A. B. 2013. Effect of increasing GnRH and PGF2
α 
dose during Double- Ovsynch on ovulatory response, luteal regression, 
and fertility of lactating dairy cows. Theriogenology, 80: 773–783. Doi: 
https://doi.org/10.1016/j.theriogenology.2013.07.00.
 
 
Gottschall, C. S. 2011. Controle do ciclo estral e taxa de prenhez em 
matrizes de corte bovinas: Efeitos hormonais, genéticos e ambientais. 
Porto Alegre: Universidade Federal do Rio Grande do Sul, 190f. Tese 
Doutorado. Available in: http://hdl.handle.net/10183/36858.
 
 
Gottschall, C. S. et al. 2012. Avaliação do desempenho reprodutivo de 
vacas de corte lactantes submetidas a IATF a partir da aplicação do GnRH, 
da  manifestação  estral,  da  reutilização  de  dispositivos  intravaginais 
e  da  condição  corporal.  Acta  Scientiae  Veterinariae,  40:  1012–1022. 
Available in: https://www.ufrgs.br/actavet/40-1/PUB%201012.pdf. 
 
Gottschall,  C.  S.;  Costa,  R.  M.;  Bittencourt,  H.  R.;  Gregory,    R.    M. 
2009. Antecipação da aplicação de prostaglandina, em programa de 
inseminação artificial em tempo fixo em vacas de corte
. 
Revista Brasileira 
de  Saúde  e  Produção Animal,  10:  970–979.  Available  in:  https:// 
tinyurl.com/4vaw8mps.
 
 
Gottschall, C. S.; Silva, L. R. 2018. Taxa de prenhez de novilhas de corte 
submetidas à IATF com protocolo a base de Benzoato de Estradiol ou 
Ovsynch modificado. Pubvet, 12: 1–6. Doi: https://doi.org/10.31533/ 
pubvet.v12n9a177.1-6. 
 
Hartmann, W.; Machado, H.  A. S. 2022. Influência do  escore corporal 
sobre a taxa de prenhez de vacas Nelore no estado de Tocantins. Brazilian 
Journal  of  Animal  and  Environmental  Research,  5,  2–5.  Available  in: 
https://tinyurl.com/5dbj75x3. 
 
Lunardelli, P. A.; Gonzales, M. S.; Machado, Z. F.; Marinho, L. S. R.; 
Seneda, M. M.  2013.  Folículos  preantrales,  emergencia folicular  y 
aplicaciones. Spermova, 3, 130–133. Available in: http://spermova. 
pe/site/files/revista2013-vol3%20No.2/130-133okok.pdf.
 
 
Martini,  A.  P.;  Pessoa,  G.  A.;  Rubin,  M. I. B.  2022.  Conception  rate 
according to sire, body condition score and estrus occurrence of suckled 
Bos taurus beef cows submitted to timed artificial insemination. Arquivo 
Brasileiro  de  Medicina  Veterinária  e  Zootecnia,  74:  375–382.  Doi: 
https://doi.org/10.1590/1678-4162-12462. 
 
Medalha, A. G.; Souza, M. I. L.; Souza, A. S.; Sá Filho, O. G.; Queiroz, V.
 
L. D.; Costa Filho, L. C. C. 2015. Utilização do dispositivo intravaginal 
de progesterona, em até três usos, para inseminação artificial em tempo 
fixo  de  fêmeas  Bos  indicus.  Revista  Brasileira  de  Saúde  e  Produção 
Animal, 16, 458–469. Available in: https://tinyurl.com/2jcw64f8. 
 
Montiel, F.; Ahuja, C. 2005. Body condition and suckling as factors 
influencing the duration of postpartum anestrus in cattle: a review. 
Animal Reproduction Science, 85: 1–26. Doi: https://doi.org/10.1016/j. 
anireprosci.2003.11.001.
 
 
Muth-Spurlock, A. M.; Poole, D. H.; Whisnant, C. S. 2016. Comparison 
of pregnancy rates in beef cattle after a fixed-time AI with once- or 
twice-used controlled internal drug release devices. Theriogenology, 85: 
447–51. Doi: https://doi.org/10.1016/j.theriogenology.2015.09.019. 
 
Nepomuceno,  D. D. 2013.  Efeito  do  manejo  nutricional  sobre  a 
maturação do eixo reprodutivo somatotrófico no início da puberdade 
de novilhas Nelore. Piracicaba: Escola Superior de Agricultura Luiz de 
Queiroz, Universidade de  São Paulo, 138f. Tese Doutorado. Available 
in: https://tinyurl.com/yc3fp6tn. 
 
Nonato, M. S. et al. 2019. Programa de IATF em novilhas púberes e pré 
púberes. Brazilian Journal of Development, 5, 24707–24712. Available 
in: https://tinyurl.com/bde3kx58. 

9 
Impact of breed, body score and animal category on the pregnancy rate of bovine females under IATF management 
Cad. Ciênc. Agrá., v. 15, p. 01–09, DOI: https://doi.org/10.35699/2447-6218.2023.45216 
 
 
Patterson, D. J. 
et al
. 1992. Evaluation of reproductive traits in 
Bos 
taurus and Bos indicus crossbred heifers: relationship of age at puberty 
to length of the postpartum interval to estrus. Journal of Animal Science, 
70: 1994–1999. Doi: https://doi.org/10.2527/1991.6962349x.
 
 
Pereira, L. L.  et al. 2018. Effect  of body condition score and  reuse of 
progesterone-releasing intravaginal  devices on conception rate following 
timed artificial insemination in Nelore cows. Reproduction in Domestic 
Animals, 53: 624–628. Doi: https://doi.org/10.1111/rda.13150. 
 
Pilau,  A.;  Lobato 
J. 
F. P. 2009.  Desenvolvimento  e  desempenho 
reprodutivo de  vacas  primíparas  aos  22/24  meses  de  idade.  Revista 
Brasileira de Zootecnia, 38: 728–736. Available in: https://www.scielo. 
br/j/rbz/a/4G4yRzHZcFdwWZbLJ5QCnsN/?format=pdf&lang=pt.
 
 
Rathbone,  M. 
J. 
2012.  Delivering  drugs  to  farmed  animals  using 
controlled release science and technology. Journal of Thermal Science 
and Technology, 6: 118–128. Available in: https://iejsme.imu.edu.my/ 
wp-content/uploads/2021/09/16.Review_michael_s118-s128.pdf. 
 
Reggiori, M. R. et al. 2016. Precocidade sexual, eficiência reprodutiva e 
desempenho produtivo de matrizes jovens Nelore e cruzadas. Arquivo 
Brasileiro de Medicina Veterinária e Zootecnia, 68: 1563–1572. Available 
in: https://tinyurl.com/255wpup8. 
 
Resende,  A.  O.;  Campos,  C.  C.;  Oliveira,  M.;  Santos,  R. M. 2014. 
Eficiência reprodutiva de fêmeas primíparas da raça nelore. Archives 
of Veterinary Science, 19, 47–52. Available in: https://revistas.ufpr.br/ 
veterinary/article/view/34278/22982.
 
 
RStudio: Integrated Development for R. 2020. RStudio, PCB, Boston, 
MA. Available in: http://www.rstudio.com/.
 
 
Sales, L. H. B.; Rebello, R. V.; Soares, A. C. M.; Glória, J. R.; Oliveira, N.
 
J. 
F. 2014. Separação fenotípica e taxas de prenhez após inseminação 
Artificial em tempo fixo em bovinos de corte. Enciclopédia Biosfera, 10: 
2757–2766.  Available  in:  https://www.conhecer.org.br/enciclop/2014a/ 
AGRARIAS/separacao.pdf. 
 
Santos, M. H. et al. 2018. Decreasing from 9 to 7 days the permanence 
of  progesterone  inserts  make  possible  their  use  up  to  5  folds  in 
suckled Nellore cows. Theriogenology, 111: 56–61. Doi: https://doi. 
org/10.1016/j.theriogenology.2018.01.017.
 
 
Santos, R. et al. 2018. Protocolo com nove dias de progesterona para 
inseminação artificial em tempo fixo em vacas taurinas adaptadas ao 
clima tropical. Arquivo Brasileiro de Medicina Veterinária e Zootecnia, 
70: 1899–1906. Available in: https://tinyurl.com/2p9294f5. 
Sartori, R.; Bastos, M. R; Baruselli,  P.  S.; Gimenes,  L. U.;  Ereno, L. 
U.; Barros, C. N. 2010. Physiological differences and implications to 
reproductive management of 
Bos taurus 
and 
Bos indicus 
cattle in a 
tropical environment. Society of Reproduction and Fertility Supplement, 
67: 357–375. Available in: https://tinyurl.com/3vj72thh.
 
 
Savio, J. D.; Thatcher, W. W.; Morris, G. R.; Entwistle, K.; Drost, M.; 
Mattiacci, M. R. 1993. Effects of induction of low plasma progesterone 
concentrations  with  a  progesterone-releasing  intravaginal  device  on 
follicular turnover and fertility in cattle. Journal of reproduction and 
fertility, 98: 77–84. Doi: https://doi.org/10.1530/jrf.0.0980077.
 
 
Silva,  A. G. et al..  2017.  Performance,  endocrine,  metabolic,  and 
reproductive  responses  of  Nellore  heifers  submitted  to  different 
supplementation levels pre-and post-weaning. Tropical Animal Health 
And Production, 49: 707–715. Doi: https://doi.org/10.1007/s11250- 
017-1248-1.
 
 
Siqueira, L. C.; de Oliveira, C. 
J. 
F.; Loguércio, R. S.; Löf, H. K.; Gonçalves.
 
P. B. D. 2008. Sistemas de inseminação artificial em dois dias com 
observação de estro ou em tempo para vacas de corte amamentando. 
Ciência  Rural,  38:  411–415.  Doi:  https://doi.org/10.1590/S0103- 
84782008000200019.
 
 
Tarouco, A. K. 
et al
. 2020. Efeitos de fatores bioclimáticos no desempenho 
de  fêmeas  Brangus  e  Angus  submetidas  à  Inseminação  Artificial  em 
Tempo  Fixo  (IATF).  Pesquisa  Agropecuária  Gaúcha,  26:  68-81.  Doi: 
https://doi.org/10.36812/pag.202026168-81. 
 
Torres, H. A.  L.; Tineo, 
J. 
S. A.;  Raidan, F. S. S. 2015.  Influência do 
escore de condição corporal na probabilidade de prenhez em bovinos 
de corte. Archivo de Zootecnia, 64: 255–260. Available in: https:// 
tinyurl.com/yymvwsy8.
 
 
Vasconcelos, J. L. M,; Sá Filho, O. G.; Cooke, R. F. 2014. Impacts of 
Reproductive Technologies on Beef Production in South America. Current 
and Future Reproductive Technologies and World Food Production. 
752: 161–180.  Doi:  https://doi.org/10.1007/978-1-4614-8887-3_8. 
 
Vaz,  R.  Z.;  Lobato, 
J. 
F. P. 2010.  Efeito  da  idade  de  desmame  no 
desempenho reprodutivo de novilhas de corte expostas à reprodução 
aos 13/15 meses de idade. Revista Brasileira de Zootecnia, 39: 142–150. 
Doi: https://doi.org/10.1590/S1516-35982010000100019. 
 
Viana, W. A. et al. 2015. Taxa de prenhez de vacas zebuínas com uso 
da inseminação artificial em tempo fixo (IATF) em fazendas do norte 
de  Minas  Gerais.  Revista  Científica de  Medicina Veterinária,  24: 1–8. 
Available in: eyLdFyFTQfkRFCV_2015-4-9-15-10-56.pdf (revista.inf.br). 