Animal Reproduction (AR)
https://www.animal-reproduction.org/article/doi/10.1590/1984-3143-AR2023-0067
Animal Reproduction (AR)
Thematic Section: 36th Annual Meeting of the Brazilian Embryo Technology Society (SBTE)

Prohibition of hormones in animal reproduction: what to expect and what to do?

Gabriel Amilcar Bó; Alejo Menchaca

Downloads: 0
Views: 368

Abstract

Abstract: As our understanding of ovarian function in cattle has improved, our ability to control it has also increased. The development of Fixed-Time Artificial Insemination (FTAI) protocols at the end of the 20th century has increased exponentially the number of animals inseminated over the last 20 years. The main reasons for this growth were the possibility of obtaining acceptable pregnancy rates without heat detection and, above all, the induction of cyclicity in suckled cows in postpartum anestrus and prepubertal heifers at the beginning of the breeding season. Most FTAI treatments in South America have been based on the use of progesterone (P4) releasing devices and estradiol to synchronize both follicular wave emergence and ovulation, with pregnancy rates ranging from 40 to 60%. These protocols are implemented on a regular basis, allowing producers access to high-quality genetics, and increasing the overall pregnancy rates during the breeding season. In addition, it provided the professionals involved in these programs with a new source of income and the diversification of their practices into activities other than their usual clinical work. Many of these practices are now apparently at risk from restrictions on the use of estradiol by the European Union (EU) and other countries. However, the development of alternative protocols based on GnRH, with P4 devices and eCG and other new products that are not in the market yet will allow us to adapt to the new times that are coming. Logically, the challenge has already been raised and we must learn to use alternative protocols to try to continue increasing the use of this technology in beef and dairy herds. The objective of the present review is to describe the main aspects of banning estradiol in livestock production, the negative impacts on reproductive efficiency, and to present some alternative FTAI protocols for dairy and beef cattle.

Keywords

estradiol, fixed-time AI, GnRH, eCG

References

Abreu LA, Cutaia L, Wallace SP, Resende TS, Carreira ALM, Cunha BS, Sousa VG, Silva LA, Catussi BLC, Baruselli PS. Efficacy of equine chorionic gonadotrophin-like treatment on follicular dynamics and pregnancy rate in Nelore cows submitted to fixed-time AI. Reprod Fertil Dev. 2022;35(2):222. http://dx.doi.org/10.1071/RDv35n2Ab189.

Andersen CM, Bonacker RC, Smith EG, Spinka CM, Poock SE, Thomas JM. Evaluation of the 7 & 7 Synch and 7-day CO-Synch + CIDR treatment regimens for control of the estrous cycle among beef cows prior to fixed-time artificial insemination with conventional or sex-sorted semen. Anim Reprod Sci. 2021;235:106892. http://dx.doi.org/10.1016/j.anireprosci.2021.106892. PMid:34861592.

Argentina. Resolución 447/2004. Boletín Oficial de la República Argentina; Suipacha; 16 Apr 2004.

Baruselli PS, Ferreira RM, Colli MHA, Elliff FM, Sá MF Fo, Vieira L, Freitas BG. Timed artificial insemination: current challenges and recent advances in reproductive efficiency in beef and dairy herds in Brazil. Anim Reprod. 2017;14:558-71. http://dx.doi.org/10.21451/1984-3143-AR999.

Baruselli PS, Reis EL, Marques MO, Nasser LF, Bó GA. The use of hormonal treatments to improve reproductive performance of anestrous beef cattle in tropical climates. Anim Reprod Sci. 2004;82-83:479-86. http://dx.doi.org/10.1016/j.anireprosci.2004.04.025. PMid:15271474.

Baruselli PS, Sá MF Fo, Ferreira RM, Sales JNS, Gimenes LU, Vieira LM, Mendanha MF, Bó GA. Manipulation of follicle development to ensure optimal oocyte quality and conception rates in cattle. Reprod Domest Anim. 2012;47(Suppl 4):134-41. http://dx.doi.org/10.1111/j.1439-0531.2012.02067.x. PMid:22827362.

Batista EOS, Del Valle TA, Ortolan MDDV, Renno FP, Nogueira GP, Souza AH, Baruselli PS. The effect of circulating progesterone on magnitude of the GnRH induced LH surge: are there any differences between Bos indicus and Bos taurus heifers? Theriogenology. 2017;104:43-8. http://dx.doi.org/10.1016/j.theriogenology.2017.08.008. PMid:28810213.

Bó GA, Adams GP, Pierson RA, Mapletoft RJ. Exogenous control of follicular wave emergence in cattle. Theriogenology. 1995;43(1):31-40. http://dx.doi.org/10.1016/0093-691X(94)00010-R.

Bó GA, Adams GP, Pierson RA, Tribulo HE, Caccia M, Mapletoft RJ. Follicular wave dynamics after estradiol-17β treatment of heifers with or without a progestogen implant. Theriogenology. 1994;41(8):1555-69. http://dx.doi.org/10.1016/0093-691X(94)90821-Y.

Bó GA, Baruselli PS, Mapletoft RJ. Synchronization techniques to increase the utilization of artificial insemination in beef and dairy cattle. Anim Reprod. 2013;10:137-42.

Bó GA, Baruselli PS, Menchaca A, Mapletoft RJ. Evolution of synchronization protocols and use of fixed-time artificial insemination in beef cattle in South America. Clin Theriogenology. 2019;11:255-63.

Bó GA, Baruselli PS, Moreno D, Cutaia L, Caccia M, Tribulo R, Tribulo H, Mapletoft RJ. The control of follicular wave development for self-appointed embryo transfer programs in cattle. Theriogenology. 2002;57(1):53-72. http://dx.doi.org/10.1016/S0093-691X(01)00657-4. PMid:11775981.

Bó GA, De la Mata JJ, Baruselli PS, Menchaca A. Alternative programs for synchronizing and re-synchronizing ovulation in beef cattle. Theriogenology. 2016;86(1):388-96. http://dx.doi.org/10.1016/j.theriogenology.2016.04.053. PMid:27180326.

Bó GA, Huguenine E, de la Mata JJ, Núñez-Olivera R, Baruselli PS, Menchaca A. Programs for fixed-time artificial insemination in South American beef cattle. Anim Reprod. 2018;15(Suppl 1):952-62. http://dx.doi.org/10.21451/1984-3143-AR2018-0025. PMid:36249833.

Bó GA, Pierson RA, Mapletoft RJ. The effect of estradiol valerate on follicular dynamics and superovulatory response in cows with Syncro Mate B implants. Theriogenology. 1991;36(2):169-83. http://dx.doi.org/10.1016/0093-691X(91)90376-O. PMid:16726990.

Bó GA, Pinargote L, Bernal B, Mendoza B, Ocampo V, Cedeño AV. Follicular characteristics and pregnancy rates in suckling Bos indicus cows synchronised with oestradiol-based or gonadotrophin-releasing-hormone-based protocols with a lengthened proestrus. Reprod Fertil Dev. 2023;35:220.

Bonacker RC, Gray KR, Breiner CA, Anderson JM, Patterson DJ, Spinka CM, Thomas JM. Comparison of the 7 & 7 Synch protocol and the 7-day CO-Synch + CIDR protocol among recipient beef cows in an embryo transfer program. Theriogenology. 2020a;158:490-6. http://dx.doi.org/10.1016/j.theriogenology.2020.09.033. PMid:33080452.

Bonacker RC, Stoecklein KS, Locke JWC, Ketchum JN, Knickmeyer ER, Spinka CM, Poock SE, Thomas JM. Treatment with prostaglandin F2α and an intravaginal progesterone insert promotes follicular maturity in advance of gonadotropin-releasing hormone among postpartum beef cows. Theriogenology. 2020b;157:350-9. http://dx.doi.org/10.1016/j.theriogenology.2020.08.018. PMid:32858443.

Bosolasco D, Nuñez-Olivera R, Brun V, Meikle A, Menchaca A. Estradiol cypionate administered at the end of a progesterone-based protocol for FTAI induces ovulation and improves postovulatory luteal function and uterine environment in anestrous beef cows. Theriogenology. 2021;162:74-83. http://dx.doi.org/10.1016/j.theriogenology.2021.01.003. PMid:33450716.

Bridges GA, Ahola JK, Brauner C, Cruppe LH, Currin JC, Day ML, Gunn PJ, Jaeger JR, Lake SL, Lamb GC, Marquezini GHL, Peel RK, Radunz AE, Stevenson JS, Whittier WD. Determination of the appropriate delivery of prostaglandin F2α in the five-day CO-Synch + controlled intravaginal drug release protocol in suckled beef cows. J Anim Sci. 2012;90(13):4814-22. http://dx.doi.org/10.2527/jas.2011-4880. PMid:22871926.

Bridges GA, Helser LA, Grum DE, Mussard ML, Gasser CL, Day ML. Decreasing the interval between GnRH and PGF2A2α from 7 to 5 days and lengthening proestrus increases timed-AI pregnancy rates in beef cows. Theriogenology. 2008;69(7):843-51. http://dx.doi.org/10.1016/j.theriogenology.2007.12.011. PMid:18281085.

Bridges GA, Mussard ML, Helser LA, Day ML. Comparison of follicular dynamics and hormone concentrations between the 7-day and 5-day CO-Synch + CIDR program in primiparous beef cows. Theriogenology. 2014;81(4):632-8. http://dx.doi.org/10.1016/j.theriogenology.2013.11.020. PMid:24388673.

Codex Alimentarius Comission. Report of the second session of the Codex Committee on residues of veterinary drugs in foods [Internet]. Rome: Codex Alimentarius Comission; 1989 [cited 2023 Jul 18]. Available from: https://www.fao.org/input/download/report/207/al89_31e.pdf.

Codex Alimentarius Comission. Report of the twelfth session of the Codex Committee on residues of veterinary drugs in foods [Internet]. Rome: Codex Alimentarius Comission; 2001 [cited 2023 Jul 18]. Available from: https://www.fao.org/3/x7102e/x7102e00.htm#Contents.

Colazo MG, Ambrose DJ. Neither duration of progesterone insert nor initial GnRH treatment affected pregnancy per timed-insemination in dairy heifers subjected to a Co-synch protocol. Theriogenology. 2011;76(3):578-88. http://dx.doi.org/10.1016/j.theriogenology.2011.03.013. PMid:21529911.

Colazo MG, Kastelic JP, Mapletoft RJ. Effects of estradiol cypionate (ECP) on ovarian follicular dynamics, synchrony of ovulation, and fertility in CIDR-based, fixed-time AI programs in beef heifers. Theriogenology. 2003;60(5):855-65. http://dx.doi.org/10.1016/S0093-691X(03)00091-8. PMid:12935863.

Colazo MG, Kastelic JP, Martinez MF, Whittaker PR, Wilde R, Ambrose JD, Corbett R, Mapletoft RJ. Fertility following fixed-time AI in CIDR treated beef heifers given GnRH or estradiol Cypionate and fed diets supplemented with flax seed or sunflower seed. Theriogenology. 2004;61(6):1115-24. http://dx.doi.org/10.1016/j.theriogenology.2003.06.005. PMid:15036999.

Colazo MG, Martínez MF, Small JA, Kastelic JP, Burnley CA, Ward D, Mapletoft RJ. Effects of estradiol valerate on ovarian follicle dynamics and superovulatory response in progestin-treated cattle. Theriogenology. 2005;63(5):1454-68. http://dx.doi.org/10.1016/j.theriogenology.2004.07.004. PMid:15725451.

Colazo MG, Whittaker PR, Bignell DJ, Mapletoft RJ. Evaluation of a modified GnRH-based timed artificial insemination protocol associated with estrus detection in cyclic beef heifers inseminated with sexed-selected semen. Reprod Fertil Dev. 2017;29:112. http://dx.doi.org/10.1071/RDv29n1Ab9.

Consentini CEC, Wiltbank MC, Sartori R. Factors that optimize reproductive efficiency in dairy herds with an emphasis on timed artificial insemination programs. Animals. 2021;11(2):301. http://dx.doi.org/10.3390/ani11020301. PMid:33503935.

Council of the European Communities. Council directive of 31 July 1981 concerning the prohibition of certain substances having a hormonal action and of any substances having a thyrostatic action (81/602/EEC). Official Journal of the European Communities; Brussels; 7 Aug 1981.

Council of the European Union. Council directive 96/23/EC of 29 April 1996 on measures to monitor certain substances and residues thereof in live animals and animal products and repealing Directives 85/358/EEC and 86/469/EEC and Decisions 89/187/EEC and 91/664/EEC. Official Journal of the European Communities; Brussels; 23 May 1996.

Cruppe LH, Day ML, Abreu FM, Kruse S, Lake SL, Biehl MV, Cipriano RS, Mussard ML, Bridges GA. The requirement of GnRH at the beginning of the five-day CO-Synch + controlled internal drug release protocol in beef heifers. J Anim Sci. 2014;92(9):4198-203. http://dx.doi.org/10.2527/jas.2014-7772. PMid:25057035.

Day ML. State of the art of GnRH-based timed AI in beef cattle. Anim Reprod. 2015;12:473-8.

de la Mata JJ, Huguenine EE, Macagno A, Tschopp JC, Bó GA. Pregnancy rate in a fixed-time artificial insemination program comparing estradiol-based and no estradiol-based treatments in suckled beef cows with a moderate degree of anestrus. In: XXV Congreso Internacional ANEMBE de Medicina Bovina; 2023 May 24-26; Madrid, Spain. Asturias: ANEMBE; 2023a. p. 351 (abstract).

de la Mata JJ, Morone S, Beierbach R, Fraile S, Huguenine EE, Bó GA. Pregnancy rate in a fixed-time artificial insemination program comparing estradiol-based and no estradiol-based treatments in suckled beef cows with a high degree of anestrus. In: XXV Congreso Internacional ANEMBE de Medicina Bovina; 2023 May 24-26; Madrid, Spain. Asturias: ANEMBE; 2023b. p. 347 (abstract).

de la Mata JJ, Morone S, Macagno A, Tschopp JC, Huguenine E, Cedeño A, Bó GA. GnRH + P4-based treatment as an alternative for estradiol-based treatments for fixed-time artificial insemination in Bos Taurus beef cows. Taurus. 2022;93:39-53.

DEFRA [homepage on the Internet]. London: DEFRA; 2006. Hormones - EU hormones ban: new independent UK scientific assessment by the Veterinary Products Committee; 2006 Jul 5 [cited 2023 Jul 18]. Available from: https://www.reading.ac.uk/foodlaw/news/uk-06065.htm.

Dinusson WE, Andrews FN, Beeson WM. The effects of stilbestrol, testosterone, thyroid alteration and spaying on the growth and fattening of beef heifers. J Anim Sci. 1950;9(3):321-30. http://dx.doi.org/10.2527/jas1950.93321x. PMid:15436345.

European Parliament. Council of the European Union. Directive 2008/97/EC of the European Parliament and of the Council of 19 November 2008 amending Council Directive 96/22/EC concerning the prohibition on the use in stockfarming of certain substances having a hormonal or thyrostatic action and of beta-agonists. Official Journal of the European Union; Luxembourg; 28 Nov 2008.

FDA [homepage on the Internet]. Montgomery: FDA; 2023. Steroid hormone implants used for growth in food-producing animals; 2023 Jun 30 [cited 2023 Jul 18]. Available from: https://www.fda.gov/animal-veterinary/product-safety-information/steroid-hormone-implants-used-growth-food-producing-animals.

Ferraz MVC Jr, Pires AV, Biehl MV, Santos MH, Barroso JPR, Gonçalves JRS, Sartori R, Day ML. Comparison of two timed artificial insemination system schemes to synchronize estrus and ovulation in Nellore cattle. Theriogenology. 2016;86(8):1939-43. http://dx.doi.org/10.1016/j.theriogenology.2016.06.012. PMid:27474237.

Food Standards Australia & New Zealand [homepage on the Internet]. Kingston: Food Standards Australia & New Zealand; 2021. Hormonal growth promotants in beef; 2021 Mar [cited 2023 Jul 18]. Available from https://www.foodstandards.gov.au/consumer/generalissues/hormonalgrowth/Pages/default.aspx.

Garcia Pintos C, Cuadro F, Núñez-Olivera R, Brochado C, Fabini F, Abelenda C, Buero J, País V, Caffera C, Menchaca A. Protocolos a base de GnRH en ganado bovino de carne y leche: la experiencia de Uruguay. In: 14º Simposio Internacional de Reproducción Animal; 2022 Aug 23-25; Córdoba, Argentina. Córdoba: IRAC, 2022 p. 141-53.

Geary TW, Whittier WD, Hallford DM, MacNeil MD. Calf removal improves conception rates to the Ovsynch and Co-synch protocols. J Anim Sci. 2001;79(1):1-4. http://dx.doi.org/10.2527/2001.7911. PMid:11204688.

Geary WT, Downing ER, Bruemmer EJ, Whittier WD. Ovarian and estrous response of suckled beef cows to the select synch estrous synchronization protocol. Prof Anim Sci. 2000;16(1):1-5. http://dx.doi.org/10.15232/S1080-7446(15)31653-3.

Huguenine E, Peracchia S, Benitez R, Martini H, Cledou G, Bó GA, Callejas S. Effect of the utilization of 5-day CO-Synch protocols combined or not with eCG in suckled cows in postpartum anoestrus. In: X Symposium on Animal Reproduction; July 4-6, 2013; Córdoba, Argentina. Córdoba: IRAC, 2013. p. 313.

Joint FAO/WHO Expert Committee on Food Additives. Evaluation of certain veterinary drug residues in food. Rome: FAO/WHO; 1999 [cited 2023 Jul 18]. Available from: https://apps.who.int/iris/handle/10665/42251.

Kasimanickam R, Asay M, Firth P, Whittier WD, Hall JB. Artificial insemination at 56 h after intravaginal progesterone device removal improved AI pregnancy rate in beef heifers synchronized with five-day Co-Synch controlled internal drug release (CIDR) protocol. Theriogenology. 2012;77(8):1624-31. http://dx.doi.org/10.1016/j.theriogenology.2011.12.007. PMid:22289222.

Kasimanickam RK, Firth P, Schuenemann GM, Whitlock BK, Gay JM, Moore DA, Hall JB, Whittier WD. Effect of the first GnRH and two doses of PGF2α in a 5-day progesterone-based CO-Synch protocol on heifer pregnancy. Theriogenology. 2014;81(6):797-804. http://dx.doi.org/10.1016/j.theriogenology.2013.12.023. PMid:24485555.

Lamb GC, Stevenson JS, Kesler DJ, Garverick HA, Brown DR, Salfen BE. Inclusion of an intravaginal progesterone insert plus GnRH and prostaglandin F2α for ovulation control in postpartum suckled beef cows. J Anim Sci. 2001;79(9):2253-9. http://dx.doi.org/10.2527/2001.7992253x. PMid:11583411.

Levy L. The use of hormonally active substances in veterinary and zootechnical uses: the continuing scientific and regulatory challenges. In: Kay JF, editor. Analyses for hormonal substances in food-producing animals. Cambridge: Royal Society of Chemistry; 2010. p. 1-44.

Lima FS, Ribeiro ES, Bisinotto RS, Greco LF, Martinez N, Amstalden M, Thatcher WW, Santos JEP. Hormonal manipulations in the 5-day timed artificial insemination protocol to optimize estrous cycle synchrony and fertility in dairy heifers. J Dairy Sci. 2013;96(11):7054-65. http://dx.doi.org/10.3168/jds.2013-7093. PMid:24011941.

Macagno AJ, Tschopp JC, de la Mata J, Ezenga A, Bó GA. Ovulatory follicle size, time of ovulation, and pregnancy rates to AI in lactating dairy cows treated with a new gonadotrophin-releasing-hormone-based protocol with lengthened proestrus. Reprod Fertil Dev. 2022;35(2):219. http://dx.doi.org/10.1071/RDv35n2Ab183.

Madsen CA, Perry GA, Mogck CL, Daly RF, MacNeil MD, Geary TW. Effects of preovulatory estradiol on embryo survival and pregnancy establishment in beef cows. Anim Reprod Sci. 2015;158:96-103. http://dx.doi.org/10.1016/j.anireprosci.2015.05.006. PMid:26022231.

Mapletoft RJ, Bó GA, Baruselli PS, Menchaca A, Sartori R. Evolution of knowledge on ovarian physiology and its contribution to the widespread application of reproductive biotechnologies in South American cattle. Anim Reprod. 2018;15(Suppl 1):1003-14. http://dx.doi.org/10.21451/1984-3143-AR2018-0007. PMid:36249848.

Mapletoft RJ, Martinez MF, Colazo MG, Kastelic JP. The use of controlled internal drug release devices for the regulation of bovine reproduction. J Anim Sci. 2003;81(14, Suppl 2):E28-36.

Martinez MF, Adams GP, Kastelic JP, Bergfelt DR, Mapletoft RJ. Induction of follicular wave emergence for estrus synchronization and artificial insemination in heifers. Theriogenology. 2000;54(5):757-69. http://dx.doi.org/10.1016/S0093-691X(00)00388-5. PMid:11101036.

Martínez MF, Kastelic JP, Adams GP, Cook RB, Olson WO, Mapletoft RJ. The use of progestins in regimens for fixed-time artificial insemination in beef cattle. Theriogenology. 2002;57(3):1049-59. http://dx.doi.org/10.1016/S0093-691X(01)00682-3. PMid:12041899.

Martínez MF, Kastelic JP, Bó GA, Caccia M, Mapletoft RJ. Effects of oestradiol and some of its esters on gonadotrophin release and ovarian follicular dynamics in CIDR-treated beef cattle. Anim Reprod Sci. 2005;86(1-2):37-52. http://dx.doi.org/10.1016/j.anireprosci.2004.06.005. PMid:15721658.

Martínez MF, Kastelic JP, Colazo MG, Mapletoft RJ. Effects of estradiol on gonadotrophin release, estrus and ovulation in CIDR-treated beef cattle. Domest Anim Endocrinol. 2007;33(1):77-90. http://dx.doi.org/10.1016/j.domaniend.2006.04.009. PMid:16797154.

Ministry for Primary Industries. Animal Products Notice: Regulated Control Scheme for Hormonal Growth Promotants, New Zealand Government; Wellington; 22 Jun 2017 [cited 2023 Jul 18]. Available from: https://www.mpi.govt.nz/dmsdocument/4484-Animal-Products-Notice-Regulated-Control-Scheme-Hormonal-Growth-Promotants-2017.

Núñez-Olivera R, Castro T, García-Pintos C, Bó GA, Piaggio J, Menchaca A. Ovulatory response and luteal function after eCG administration at the end of a progesterone and estradiol-based treatment in postpartum anestrous beef cattle. Anim Reprod Sci. 2014;146(3-4):111-6. http://dx.doi.org/10.1016/j.anireprosci.2014.02.017. PMid:24646633.

Peterson C, Alkar A, Smith S, Kerr S, Hall JB, Moore D, Kasimanickam R. Effects of one versus two doses of prostaglandin F2alpha on AI pregnancy rates in a 5-day progesterone-based, CO-Synch protocol in crossbred beef heifers. Theriogenology. 2011;75(8):1536-42. http://dx.doi.org/10.1016/j.theriogenology.2010.12.017. PMid:21320721.

Pursley JR, Mee MO, Wiltbank MC. Synchronization of ovulation in dairy cows using PGF2A2α and GnRH. Theriogenology. 1995;44(7):915-23. http://dx.doi.org/10.1016/0093-691X(95)00279-H. PMid:16727787.

Rabaglino MB, Risco C, Thatcher MJ, Kim IH, Santos JE, Thatcher WW. Application of one injection of prostaglandin F2α in the five-day Co-Synch + CIDR protocol for estrous synchronization and resynchronization of dairy heifers. J Dairy Sci. 2010;93(3):1050-8. http://dx.doi.org/10.3168/jds.2009-2675. PMid:20172225.

Randi F, Kelly AK, Parr MH, Diskin MG, Lively F, Lonergan P, Kenny DA. Effect of ovulation synchronization program and season on pregnancy to timed artificial insemination in suckled beef cows. Theriogenology. 2021;172:223-9. http://dx.doi.org/10.1016/j.theriogenology.2021.06.021. PMid:34284217.

Richardson BN, Hill SL, Stevenson JS, Djira GD, Perry GA. Expression of estrus before fixed-time AI affects conception rates and factors that impact expression of estrus and the repeatability of expression of estrus in sequential breeding seasons. Anim Reprod Sci. 2016;166:133-40. http://dx.doi.org/10.1016/j.anireprosci.2016.01.013. PMid:26805603.

Sales JNS, Carvalho JBP, Crepaldi GA, Cipriano RS, Jacomini JO, Maio JRG, Souza JC, Nogueira GP, Baruselli PS. Effects of two estradiol esters (benzoate and cypionate) on the induction of synchronized ovulations in Bos indicus cows submitted to a timed artificial insemination protocol. Theriogenology. 2012;78(3):510-6. http://dx.doi.org/10.1016/j.theriogenology.2012.02.031. PMid:22503845.

Scheffler JM, Buskirk DD, Rust SR, Cowley JD, Doumit ME. Effect of repeated administration of combination trenbolone acetate and estradiol implants on growth, carcass traits, and beef quality of long-fed Holstein steers. J Anim Sci. 2003;81(10):2395-400. http://dx.doi.org/10.2527/2003.81102395x. PMid:14552364.

Silva LO, Motta JCL, Oliva AL, Silva MA, Silva TJB, Madureira G, Folchini NP, Alves RLOR, Consentini CEC, Galindez JPA, Wiltbank MC, Sartori R. Influence of the analogue and the dose of GnRH on the LH release and ovulatory response in Bosindicus heifers and cows with high circulating progesterone. Anim Reprod. 2020;17:38.

Small JA, Colazo MG, Kastelic JP, Mapletoft RJ. Effects of progesterone presynchronization and eCG on pregnancy rates to GnRH-based, timed-AI in beef cattle. Theriogenology. 2009;71(4):698-706. http://dx.doi.org/10.1016/j.theriogenology.2008.09.045. PMid:18977520.

Smith ZK, Johnson BJ. Mechanisms of steroidal implants to improve beef cattle growth: a review. J Appl Anim Res. 2020;48(1):133-41. http://dx.doi.org/10.1080/09712119.2020.1751642.

Souto LA, Maquivar M, Mussard ML, Bridges GA, Grum DE, Day ML. Fertility and luteal regression with 5-d CIDR synchronization programs in postpartum beef cows using differing luteolytic treatments. J Anim Sci. 2009;87(Suppl 2):372.

Uruguay. Decreto nº 915/988. Importaciones. Prohibición de medicamentos veterinarios hormonales. Registro Nacional de Leyes y Decretos; Montevidéo; December 28, 1988.

Villarraza CJ, Antuña S, Tardivo MB, Rodríguez MC, Mussio P, Cattaneo L, Fontana D, Díaz PU, Ortega HH, Tríbulo A, Macagno A, Bó GA, Ceaglio N, Prieto C. Development of a suitable manufacturing process for production of a bioactive recombinant equine chorionic gonadotropin (reCG) in CHO-K1 cells. Theriogenology. 2021;172:8-19. http://dx.doi.org/10.1016/j.theriogenology.2021.05.013. PMid:34082223.

Whittier WD, Currin JF, Schramm H, Holland S, Kasimanickam RK. Fertility in Angus cross beef cows following 5-day CO-Synch + CIDR or 7-day CO-Synch + CIDR estrus synchronization and timed artificial insemination. Theriogenology. 2013;80(9):963-9. http://dx.doi.org/10.1016/j.theriogenology.2013.07.019. PMid:24041825.

Wiltbank JN, Zimmerman DR, Ingalls JE, Rowden WW. Use of progestational compounds alone or in combination with estrogen for synchronization of estrus. J Anim Sci. 1965;24(4):990-4. http://dx.doi.org/10.2527/jas1965.244990x.
 


Submitted date:
05/15/2023

Accepted date:
07/18/2023

64f22989a953951a9477fdd5 animreprod Articles
Links & Downloads

Anim Reprod

Share this page
Page Sections