Fixed timed artificial insemination (FTAI) through the progesterone (CIDR) of 1^st, 2^nd, 3^rd and 4^th uses in bovine. I. Conception rate related to reproductive category, related to body condition scoring (BCS), related to calf withdrawal and use of eCG

W G Vale^*/***, P C H Melo^**, E Walter^**, H F L Ribeiro^**, S T Rolim-Filho^**, A N Reis^***, J S Sousa^*** and A O A Silva^***

* Instituto de Biodiversidade e Florestas, Universidade Federal do Oeste do Pará – UFOPA,
Rua Vera Paz, Campus I – Tapajós, CEP 68040-070, Santarém, Pará, BRAZIL,
wmvale@hotmail.com
** Universidade Federal Rural da Amazônia, Setor de Reprodução Animal,
Av. Presidente Tancredo Neves nº 2501, Montese, CEP 66.077-530 - Belém, Pará, BRAZIL
*** Central de Biotecnologia de Reprodução Animal – CEBRAN, Universidade Federal do Pará - UFPA,
Rua João Henrique de Carvalho, S/N, CEP 68.741-400 - Castanhal, Pará, Brasil,
http://www.ufpa.br/cebran

Abstract

This study had the purpose of verifying the efficiency of fixed timed artificial insemination (FTAI) through the progesterone releasing device (CIDR ® Pfizer 1.9g P₄) of 1^st, 2^nd, 3^rd and 4^th uses in n=18665 Zebu females (Bos taurus indicus) and n=409 crossed Zebu x European (Bos taurus indicus x Bos taurus taurus) breed in a total of n=19071 females.

Among n=19071 females subjected to FTAI, n=10797 became pregnant, representing an overall conception rate of 56.5%; the conception rate among nulliparous, primiparous lactating, milking cows and open, was 54.0%, 48.8%, 58.8% and 57.6% respectively, whereas the conception rate according to body condition scoring (BCS) in a scale of 1 to 5, showed that females with  BCS 2.5 and 4.0 had a conception rate of 55.8% and 61.0%, respectively, differing significantly (P = 0.0008); the conception rate after the calf withdrawal and use of eCG were 56.7% and 55.4%, respectively, whereas the conception rate related on amount of times of CIDR uses were 58.2%, 54.5%, 55.9%  and 56.3% for the first, second, third and four uses, respectively, with statistical significance  difference (P <0.0002) among the results. This study suggests that the adoption of FTAI and the re-uses progesterone (CIDR^® Pfizer 1.9g P₄) is a feasible and economic technology to be used to increase beef production system activity inside the  adaptations required among  the so-called development sustainable is achieved, actually one of the main challenges among the strategies  aiming to increase Brazilian cattle productivity.

Key words: Amazon, artificial insemination, CIDR, oestrous, ovulation, synchronization

Introduction

These are times when the world has witnessed the take-off of Brazilian beef industry towards the modernization process, which has been consolidating Brazil as a major producer and exporter of beef in the world. Actually, the Brazilian cattle herd consists of almost 200 million animals (IBGE 2010), being 80% zebu (Bos taurus indicus), due to the better adaptability to climatic conditions such as temperature and high humidity. However, for the Brazilian cattle industry to achieve high levels of productivity and quality, reproductive efficiency,  artificial insemination (AI) has been used  in the cattle population, making possible the multiplication of genetic material superior handling in adverse conditions and environment (Carvalho 2004). Recently, with technological advances in farming it have been developed oestrous synchronization protocols that allow inseminate a large number of females over a period of predetermined time. These treatments are known as protocols for fixed time artificial insemination (FTAI), Baruselli et al (2003). Synchronization is to shorten or lengthen the oestrous cycle by using hormones or hormonal associations that induce luteolysis and prolong the life of the corpus luteum so that a group of cows in oestrous or in anoestrous ovulate during a short period of time (Gonçalves et al 2001).

The conception rates in cows treated with progesterone (P₄) and estradiol benzoate (EB) are around 50-64% followed by FTAI (Baruselli et al 2003). Moreover, Sá Filho et al (2003), working with beef heifers, using protocols with an intra vaginal P₄ device (CIDR) associated with EB for FTAI, found conception rates ranging between 46.0 to 64.0%. Lucy et al (2001) working with beef cows in anoestrous and cyclic, pre-pubertal and pubertal heifers and milking cows had the following conception rates using CIDR/P₄  57.0%, 63.0%, 58.0%, 61.0 % and 54.0% respectively. Meanwhile, the PGF_2α can be used in combination with progesterone analogues, with the aim of promoting better synchronization of oestrous, especially if administered 24 and 48h before the withdrawal of progesterone source. Such treatment cause an increase in pulsatile LH secretion during the period between luteolysis induced by exogenous prostaglandin and removal of progesterone allows more uniform growth of the pre ovulatory follicle among the animals treated (Barros et al 2000). In beef and dairy breeds it has been  advocate the reuse of  P₄ intra vaginal device whereas the conception rates are similar to those obtained with devices used only once (Bartolomeu et al 2003; Macmillan 2002; Valentim 2004; Vilela 2004). The low reproductive rates are indicators of inadequate nutrition, health and genetic quality of livestock (Santos and Amstalden 1998). According to Sartori and Mollo (2007), the nutritional causes are of great importance because they affect the physiological functions of the animal organism and interfere with normal function of the reproductive tract. They are more frequent than for lack of excess nutrients. The body condition scoring (BCS) has been used to assess the nutritional status of cattle and, consequently, to estimate the reproductive performance (Pimentel et al 2005). Further, the BCS has a direct influence on fertility, since the nutrients are directed first to maintain the life of the cow and calf's foot, only then become available to the reproduction of the species. Therefore, heifers and cows to enter the program must submit a minimum body score of 2.5 (scale of 1 to 5) and be in positive energy balance (Barros 2007). 

On the other hand, FTAI has been established and disseminated as an important tool for reproductive management, contributing to a critical point observed in the traditional AI, which is the elimination of oestrus observation. Moreover, this technique has in its favour the fact shorten postpartum anoestrus, promoting the reduction of the calving interval contributing to it not exceeding 365 days (Baruselli et al 2003). That being so, then, an appropriate use of pharmacological substances on protocols, which provide a correct synchronization of oestrous, good fertility rates, rationalization of manpower, management within a coherent and obviously better financial return (Smith et al 1979). Thus the aim of this study was to evaluate the conception rate in cows submitted to artificial insemination in fixed time Farms located in southeaster Pará state, Brazil and the influence of factors such as conception rate; conception rate according to reproductive category; conception rate according to body condition score, conception rate after the calf withdrawal and use of eCG, conception rate related on amount of CIDR uses. 

Materials and methods

Location 

This study was conducted in partnership with 28 different commercial farms located in the municipalities of Paragominas, Ulianópolis, Aurora do Pará, Thailand and Tome-Açu, in northeaster Pará State, Brazil. The technical operations were performed such as selection of the females, synchronization, monitoring protocols, artificial inseminations and the final diagnosis in the period from July 2009 to March 2010. The average annual temperature was 26° C range (19-38^o C) where the dry period lasted from July to December and a rainy season from January to June, with annual rainfall of 2250-2750 mm and relative humidity around 85% (Portal Amazon 2007). 

Animals 

Zebu females (Bos taurus indicus) n=18662 and n=409 crossed Zebu x European (Bos taurus indicus x Bos taurus taurus) breed in a total of n=19071 female, raised in extensive management, belonging to different reproductive categories, namely n=2730 nulliparous females, n=2981 lactating primiparous, n=12907 lactating multiparous cows and 453 open cows. The postpartum females had at least 30 days calved. All animals were subjected to a gynaecological clinical examination and evaluated according to their body condition scoring (BCS), within a variation of 1.75 to 5.0 on a scale of 1.0 (very thin) to 5.0 (obese) at intervals of 0.25 points according to Freitas Junior et al (2008). All cattle were subjected to a routine health composed of vaccination against brucellosis, Foot and Mouth Diseases, rabies and dewormed twice a year.  

Hormonal treatments 

All animals were synchronized by the same protocol recommended by Pfizer Animal Health Program, which consisted of: day zero (D0) was held to consider the device to intra vaginal progesterone (CIDR® Pfizer 1.9g P4) which was the 1st, 2nd, 3rd or 4th use, randomly distributed among the animals. Then it was carried out applying 2 ml of estradiol benzoate (2.0 mg Estrogin Farmavet ®(EB) via intramuscle (IM). On day seven (D7) it was applied 2.5 ml tromethamine dinoprost (Lutalyse Pfizer® 5mg PGF2a) IM and day nine (D9) was held on removal of the intravaginal device (CIDR® Pfizer 1.9g P4) followed by an IM application of 0.3 ml of estradiol cypionate (ECP® 5mg Pfizer E2). Also in the D9, 15.351 animals (cows with calf at foot) were separated from their offspring, leaving the calves in a separate paddock for 24 hours and 3.748 females (nulliparous, open cows, and BCS below 2.0 received an application 2.5 ml IM 300 IU eCG (Intervet Folligon® 5000 IU eCG) without the need to remove the calf on day 11 (D11), AI was performed in all animals. The reuse the implants was performed with a wash with ethanol 70% for 5 minutes and subsequent washing with distilled water to remove excess alcohol following the drying at room temperature of  22o C (Pinto Neto et al 2009). 

Reproductive management 

The females were inseminated after hormonal protocol of 11 days duration and females presenting to the return-rate were subjected to a second conventional AI; however, the non-pregnant animals were further subjected to natural breeding. It was used frozen semen from n=20 selected sires randomly selected from a semen bank composed of n=81 sires, purchased from commercial artificial insemination stations. For purposes of statistical analysis only n=16623 females were considered (because some of them where not checked properly to pregnancy diagnosis).  On the whole the pregnancy diagnosis was performed by ultrasonography and rectal palpation between 30 and 45 days after FTAI. Further on the FTAIs were performed by 34 artificial insemination technicians with previous experience in AI and supervised by a Veterinarian; however, for statistical analysis only 14 technicians were evaluated (only AI technicians that have participated of the whole programme, that means start from the begin and went throughout the end). For the semen process thawing it was employed defroster electronics device, to facilitate and standardize the process. All animals were followed individually, and their data recorded in an Excel spread sheet.  

Statistical analysis 

The results were analysed using Statistical Analysis System program version 8.0 (SAS 1996). The original data were subjected to chi-square test, with significance level of 5%. Either it was compared conception rates between variables such as artificial insemination and sires semen used according to the different reproductive category (nulliparous, primiparous lactating, multiparous and lactating cow without calf), body condition score (BCS), number of uses of the intra vaginal device and use of eCG or calf removal in D9 protocol. 

Results and discussion

Conception rates  

Among n=19071 females subjected to FTAI, n=10769 became pregnant, representing an overall conception rate of 56.5%. This rate is higher than those found by Bo et al (2002) and Monteiro (2010), who reported rates of 52.3% and 49.4% respectively, but similar to the results obtained by Favacho (2009), 54.5%; however, it is lower  than the 64.0 % reported by Baruselli et al (2003). The conception rate related on amount of times of CIDR uses were 58.2%, 54.5%, 55.9%  and 56.3% for the first, second, third and four uses, respectively, with statistical significance  difference (P <0.0002) among the results.

On the other hand, regarding the number of inseminations performed in this study, it can be considered satisfactory, since according to Bo et al (2004), conception rates of around 50% by FTAI programs can be considered a good result. 

 Conception rate among each reproductive category  

The conception rates among nulliparous, primiparous lactating, milking and open cows, were 54.0%, 48.8%, 58.8% and 57.6% respectively. In the Table 1, it can be observed that there is a statistical significant difference among the results (P <0.0001).

There was a significant difference when compared the nulliparous and multiparous (P <0.0001), as well as  primiparous and multiparous (P <0.0001), with nulliparous  (P <0.0001) and primiparous (P = 0.0005). However, no statistical difference between open cows and multiparous (P = 0.6143),and open cows and nulliparous (P = 0.1557). Statistical difference was observed when compared categories showed differences in the number of animals or when they were compared with primiparous category which had lower conception rate (48.8%). The results of this research are similar to those reported by Vasconcelos et al (2000) when synchronized cows in lactation and found  conception rates between 32.4 to 50.0% as well as by Silveira et al (2009) which   synchronized 237 primiparous cows in lactation had conception rate of 48.1%, result similar results similar to those found in this study. On the other hand, Favacho (2009), achieved superior results, with 54.5% of primiparous cows in the southeast of Pará state. Indeed, the conception rates obtained in this study, 58.8% for the cows and 48.8% for primiparous lies within the range of 25.0% to 67.0%, respectively are in accordance to other reports in the literature for suckled beef cows using exclusively FTAI (Fernandes et al 2001; Baruselli et al 2003). Moreover the conception rate of 57.6% found in multiparous cows without calf at foot, or so-called open cow, is in accordance  with the report of Jaume et al (2000) which pointed the fact of these female had no calf suckling become pregnant sooner since they showed  a better BCS,  due not suffer the negative effect of suckling..

On the other hand the primiparous females had the lowest conception rate 48.8%, which was expected, as according to Soto Belloso et al (2002), for not having completed their growth phase and to provide energy for lactation, reproductive efficiency of this category is lower. In this way, based on the literature, the average conception rate found in this work was satisfactory, with exception for the primiparous females, a category which requires greater attention. 

Conception rate related to body condition score 

Animals that had BCS between 2.5 and 4.0 showed better conception rates, whereas conception rate in cows with BCS 2.5 and 4.0 showed 55.8% and  61.0%, respectively differing significantly (P = 0.0008) this sentence is not clear. It was also found that both animals with BCS too low or too high did not have good rates, as can be seen in Figure 1. This can be explained by the fact that the nutritional result in suppression of GnRH release and hence decrease in the frequency of LH pulses, failure of dominant follicle development and ovulation (Schillo 1992).

Further on in obese animals, the higher release of cortisol, endogenous opioids are also responsible for the suppression of the release of LH pulses (Stevenson et al 1994). Monteiro (2010), performed a FTAI program in bovine in southeast Pará state and found different results, with a high conception rate for cows with BCS 3.0 (56.9%) and 3.5 (52.1%). On the other hand animals with ECC 2.5 and 4.0 had a lower conception rate 42.9% and 43.1%, respectively, but the numerical representation of animals in this survey was quite lesser than when compared with the number of the present work which certainly had an influence in the final outcome.

Figure 1. Conception rates, according to body condition scoring (BCS) of 19.071 females submitted to FTAI in the northeast of Pará, in the period July 2009 to March 2010.

 The results here obtained are in line with those of Barros (2007) who stated the direct influence of BCS on fertility, since the nutrients are directed first to the life maintenance of the cow and calf's foot, only then become available for reproduction process. Therefore, one requisite for heifers and cows get in the program was in the time of selection present a minimum BCS of 2.5 (scale of 1 to 5) so in positive energy balance (Freitas Junior et al 2008). 

Effect of calf removal related to use of eCG on the conception rates 

The conception rate related to calf withdrawal and eCG group was 56.7% and  55.4%, respectively, Table 2, showing no statistical significant difference in the two managements used in D9 (P = 0.1434). 

 The results observed in this study are higher than the 29.8% conception rate reported by Vasconcelos et al (2009), who used the withdrawal of the calf associated with protocol-based GnRH-PGF_2α-EB. The calf removal for 48 hours increases the frequency of LH pulses (Williams et al 1983; Edwards 1985) by removing the stimulus of the calf through breastfeeding and stress the cow, blocking the release of endogenous opioids and consequently leading to oestrous behaviour (Vasconcelos et al 2009). either in this paper most of the animals had BCS between 2.5 and 4.0 which predict a good conception rate to the calf removal group (56.7%), aspect which agree with Kastelic et al (1999) and Baruselli et al (2003) which argue that it does not necessary the use of eCG in cyclic females with good BCS to enhance higher conception rates. With these results, it can be considered that calf withdraw at D9, are productively and economically viable.

Conclusions

• The adoption of FTAI and the re-uses progesterone releasing device (CIDR ® Pfizer 1.9g P₄) is a feasible and economic technology to be used to increase beef production system activity inside the  adaptations required among  the so-called  sustainable development with biodiversity protection, actually one of the main challenges among the strategies  aiming the increasing Brazilian cattle productivity.

  
  

• Based on these results, progesterone releasing device FTAI protocol and EB may improve reproductive performances in Bos taurus indicus cows grazing under range conditions.

  
  

• However for the incorporation of FTAI protocol it is necessary to overcome some management problems such nutritional and suckling origin. 

  
  

• Moreover, the use of eCG at the time of progesterone releasing device (CIDR) removal in a FTAI program improve the conception rates and these treatments may facilitate the application of genetic improvement programs more efficiently in Bos taurus indicus herds under Amazon tropical conditions.  

  
  

• The reuse of CIDR is an important measure for the cheapening of the cost of FTAI, being a feasible alternative to improve the cost benefit of this biotechnology 

References

Barros C M 2007 Técnica cada vez mais utilizada nos rebanhos brasileiros permite economia.

Rev nº 114 – agosto 2007. Disponível em: http://www.revistarural.com.br/Edições/2007/ Artigos /rev114 iatf.htm. Acesso em: 05 nov 2010.

Barros C M 2000 Controle farmacologico do ciclo estral e superovulacao em zebuinos de corte. In: Simpósio sobre controle farmacológico do ciclo estral em Ruminantes. São Paulo: Fundação da Faculdade de Medicina Veterinaria e Zootecnia, USP, p. 158-189

Bartolomeu C C, Del Rei, A J,  Oliveira, M A L, Lima P F, Silva, J E 2003 Inseminação artificial em tempo fixo de vacas leiteiras mestiças Holando-Zebu no pós-parto com emprego de CIDR reutilizado. Revista Brasileira de Reprodução Animal, 27(3):426-427.

Baruselli P S, Marques M O, Carvalho N A T, Madureira,E H and  Campos Filho E P 2003 Efeito de diferentes protocolos de inseminação artificial em tempo fixo na eficiência reprodutiva de vacas de corte lactantes. Revista Brasileira de Reprodução Animal 26(3):218-221.

Bo G A, Baruselli P S, Moreno D, Cutaia L, Caccia M,  Tríbulo R,  Tríbulo H and   Mapletoft R J 2002 The control of follicular wave development for self-appointed embryo transfer programs in cattle. Theriogenology (57):53-72.

Bo G A, Cutaia I and  Baruselli P S 2004 Programas de inseminacion artificial y transferencia de embriones a tiempo fijo. In: Simpósio Internacional de Reprodução Animal Aplicada. Londrina. Anais São Paulo: Faculdade de Medicina Veterinária e Zootecnia, Universidade de São Paulo, p. 56-8.

Carvalho J B P 2004 Sincronização da ovulação com dispositivo intravaginal de progesterona (CIDR®) em novilhas Bos indicus x Bos taurus e Bos taurus. Tese (Doutorado). Faculdade de Medicina Veterinária e Zootecnia, Universidade de São Paulo, São Paulo, 122p.

Edwards S 1985 The effect of short term calf removal on pulsatile LH secretion in the postpartum beef cow. Theriogenology (23):777-785.

Favacho H S 2009 Taxa de prenhez utilizando CIDR® de 1º, 2º e 3º uso em fêmeas nelore no sudeste paraense. Monografia (TCC em Reprodução Animal) – Coordenadoria do Curso de Medicina Veterinária, Instituto da Saúde e Produção Animal, Universidade Federal Rural da Amazônia, Pará, 66 p.

Fernandes P,  Teixeira, A B and Crocci A J 2001 Timed artificial insemination in beef cattle using GnRH agonist, PGF2 alpha and estradiol benzoate (EB). Theriogenology 55:1521-1532.

Freitas Júnior J E, Rocha Júnior V R, Rennó F P, Mello M T P, Carvalho A P, Caldeira L A 2008 Efeito da condição corporal ao parto sobre o desempenho produtivo de vacas mestiças Holandês × Zebu. Revista Brasileira Zootecnia 37(1):68-78. http://dx.doi.org/10.1590/S1516-35982008000100017 

Gonçalves P B D, Oliveira J F C, Silveira, R S and Ferreira R 2004 Anestro pós parto em vacas de corte. 1. Simpósio Internacional de Reprodução Animal Aplicada, Londrina. Anais, Faculdade de Medicina Veterinária e Zootecnia, Universidade de São Paulo, p.105-116.

IBGE 2010 http://www.ibge.gov.br/home/disseminacao/online/estatisticas/default.php

Jaume  C M,   Souza  C J H and Moraes  J C F 1999 Alternativas para aumentar a fertilidade póspartode bovinos de corte em sistemas extensivos de criação.  Bagé: Embrapa CPPSUL, 1999. 12p. (Embrapa CPPSUL. Comunicado Técnico, 22).

Kastelic J, Olson W O,  Martinez M, Cook R B and Mapletoft R J 1999 Synchronization of estrus in beef cattle with norgestomet and estradiol valerate. Canadian Veterinary Journal. 40:173-178.

Lucy M C,  Billings H J,  Butler W R, Ehnis L R,  Fields M J,  Kesler  D J, Kinder  J E, Mattos  R C,  Short  R E,  Thatcher, W W,  Wetteman  R P, Yelich  J V and  Hafs H D 2001 Efficacy of an intravaginal progesterone insert and injection of PGF2a for synchronizing estrus and shortening the interval to pregnancy in postpartum beef cows, peripubertal beef heifers and dairy heifers . Journal Animal Science. 79:982-995. http://jas.fass.org/content/79/4/982.full.pdf+html

MacMillan K L 2002 Advances in bovine theriogenology in New Zealand. Pregnancy, parturition and the post-partum period. New Zealand Veterinary Journal. 50:67-73 

Monteiro J P C 2010 Avaliação da Eficiência de Protocolo de Inseminação Artificial em Tempo Fixo em Vacas Nelore Puras de Origem (PO) na Fazenda Cedro em Marabá, Região Sudeste do Pará. Monografia (TCC em Reprodução Animal). Instituto da Saúde e Produção Animal, Universidade Federal Rural da Amazônia, . 57 p. 

Pimentel M A, Moraes J C F,  Jaume C M,  Lemes  J S and Bauner C C 2005 Produção de leite e desempenho pós-parto de vacas Hereford em distintas condições reprodutivas criadas extensivamente. Ciência Rural .35.1150-156.

Pinto Neto, A, Silva R Z, Mota M F and Alberton J 2009 Reutilização de implante intravaginal de progesterona para a sincronização de estro em bovinos. Arquivos CiênciasVeterinárias e Zoologia volume 12: : Retrieved May 10 2010 http://revistas. unipar.br/veterinária 

Portal Amazon 2007 http://www.portalamazonia.com.br/secao/noticias/para. 

Revista Rural 2007 http://www.revistarural.com.br/Edições/2007 /Artigos/rev 114_ iatf.htm.

SAS. Statistical Analysis System. 1996. User's guide: Stat, Version 6.11. SAS Institute, Cary.  

Sá Filho O G, Vasconcelos J L M , Santos  R M and Rossini  L C C 2003 Efeito do momento da aplicação de PGF₂α em protocolo de inseminação artificial com tempo fixo na taxa de concepção em novilhas de corte. Revista Brasileira Reprodução Animal 27:430-432.  

Santos  J E P and  Amstalden M 1998 Effects of nutrition on bovine reproduction. Arquivos da Faculdade Veterinária da UFRGS. 26(1):19-89. 

Sartori R and Mollo M R 2007 Influência da ingestão alimentar na fisiologia reprodutiva da fêmea bovina. Revista Brasileira de Reprodução Animal. volume 31: Retrieved May 9 2009, http://www.cbra.org.br/publicacoes/rbra.do 

Schillo K K 1992 Effects of dietary energy on control luteinizing secretion in cattle and sheep. Journal of Animal Science 70: 1271-1282. 

Silveira, P A S, Schineider A, Madeira E M., Hax  L T,  Lima  M E,  Antunes M M, Vieira  M B, Xavier E G., Bianchi  I and Corrêa  M N  2009  Efeito da reutilização do CIDR sobre a taxa de prenhez de vacas de corte primíparas de acordo com o escore de condição corporal. XXII Congresso Iniciação Científica, Universidade Federal de Pelotas,vol 1:1-6.  

Smith M F, Burrell W C,  Shipp,  L D,  Sprott, L R,  Songster, W N and Wiltblank L R 1979 Hormone treatments and use of calf removal in postpartum beef cows. Journal of Animal Science 48:1285-1294. 

Soto Belloso E, Martínez G P,  De Ondiz A, Rojas N and  Soto G C 2002 Improvement of reproductive performance in crossbred zebu anestrous primiparous cows by treatment with norgestomet implants or 96h calf removal. Theriogenology 57:203-207. 

Stevenson J S,  Knoppel E L and Minton J E 1994 Estrus, ovulation, luteinizing hormone, and suckling-induced hormones in mastectomized cows with and without unrestricted presence of the calf. Journal of Animal Science.72:.690-699.

Valenttim  R 2004 Concentrações plasmáticas de progesterona e eficiência reprodutiva de diferentes dispositivos de liberação lenta de progesterona usados em inseminação artificial em tempo fixo. Tese (Doutorado, Reprodução Animal). Universidade de São Paulo, Faculdade de Medicina Veterinária e Zootecnia. São Paulo, 106 p.

Vasconcelos J  L  M,  Vilela E R and Sá Filho O G 2009 Remoção temporária de bezerros em dois momentos do protocolo de sincronização da ovulação GnRH-PGF2α-BE em vacas Nelore pós-parto. Arquivo Brasileiro de Medicina Veterinária e Zootecnia, vol 6 Article #5 Retrieved November 2009 to http://www.scielo.br/cgi-bin/ wxis.exe /iah/? Isis Script =iah/iah.xis&base=article^dlibrary&format= iso.pft&lang=i&next Action=lnk&indexSearch= AU&exprSearch=VASCONCELOS,+J.L.M. 

Vasconcelos J L M, Santos R M and Perez G C 2000 Controle do estro e da ovulação visando a inseminação artificial em tempo fixo  em bovinos de leite a pasto ou confinados.  1. Simpósio Internacional de Reprodução Animal Aplicada, Londrina, Faculdade de Medicina Veterinária e Zootecnia, Universidade de São Paulo  p. 129-146 

Vilela E E 2004 Utilização de dispositivo de liberação intravaginal de progesterona no protocolo de sincronização (GnRH/PGF2α/ GnRH) associado à remoção temporária de bezerros em vacas Nelore paridas. Dissertação (Mestrado em Nutrição e Produção Animal). Programa de Pós-Graduação em Nutrição e Produção Animal, Faculdade de Veterinária e Zootecnia, Universidade Estadual Júlio de Mesquita Filho. 58 p

Williams G L, Talavera F and Petersen B J 1983 Coincident secretion of follicle-stimulating hormone and luteinizing hormone in early postpartum beef cows: effects of suckling and low-level increases of systemic progesterone. Biology of Reproduction .29:362-373.

Received 14 August 2011; Accepted 26 August 2011; Published 10 October 2011

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