Decreasing the dose of equine chorionic gonadotropin does not affect ovarian or pregnancy responses of purebred taurine and crossbred beef heifers

Abreu, 2018, Role of progesterone concentrations during early follicular development in beef cattle: I. Characteristics of LH secretion and oocyte quality, Anim. Reprod. Sci., 196, 59, 10.1016/j.anireprosci.2018.06.020 Anderson, 1991, The use of reproductive tract scoring in beef heifers, AgriPractice, 12, 19 Ayres, 2009, Validation of body condition score as a predictor of subcutaneous fat in Nelore (Bos indicus) cows, Livest. Sci., 123, 175, 10.1016/j.livsci.2008.11.004 Baruselli, 2004, The use of hormonal treatments to improve reproductive performance of anestrous beef cattle in tropical climates, Anim. Reprod. Sci., 82–83, 479, 10.1016/j.anireprosci.2004.04.025 Batista, 2017, 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, 104, 43, 10.1016/j.theriogenology.2017.08.008 Bó, 2014, Synchronization of ovulation and fixed-time artificial insemination in beef cattle, Anim., 8, 144, 10.1017/S1751731114000822 Bó, 2012, Treatments for the synchronisation of bovine recipients for fixed-time embryo transfer and improvement of pregnancy rates, Reprod. Fertil. Dev., 272, 10.1071/RD11918 Bó, 2016, Alternative programs for synchronizing and resynchronizing ovulation in beef cattle, Theriogenology, 86, 388, 10.1016/j.theriogenology.2016.04.053 Butler, 2011, Pregnancy rates after fixed-time artificial insemination of Brahman heifers treated to synchronize ovulation with low-dose intravaginal progesterone releasing devices, with or without eCG, Theriogenology, 76, 1416, 10.1016/j.theriogenology.2011.06.010 Carvalho, 2008, Effect of early luteolysis in progesterone-based timed AI protocols in Bos indicus, Bos indicus x Bos taurus, and Bos taurus heifers, Theriogenology, 69, 167, 10.1016/j.theriogenology.2007.08.035 Cushman, 2013, Heifer calving date positively influences calf weaning weights through six parturitions, J. Anim. Sci., 91, 4486, 10.2527/jas.2013-6465 Cutaia, 2003, Effect of eCG treatment in postpartum beef cows synchronized with progesterone vaginal devices and estradiol benzoate and inseminated at a fixed-time, Theriogenology, 59, 216 de Sousa, 2016, Equine chorionic gonadotropin modulates the expression of genes related to the structure and function of the bovine Corpus luteum, PLoS One, 11, 10.1371/journal.pone.0164089 Dias, 2009, Progesterone concentrations, exogenous equine chorionic gonadotropin, and timing of prostaglandin F(2alpha) treatment affect fertility in postpuberal Nelore heifers, Theriogenology, 72, 378, 10.1016/j.theriogenology.2009.03.006 Dorneles Tortorella, 2013, The effect of equine chorionic gonadotropin on follicular size, luteal volume, circulating progesterone concentrations, and pregnancy rates in anestrous beef cows treated with a novel fixed-time artificial insemination protocol, Theriogenology, 79, 1204, 10.1016/j.theriogenology.2013.02.019 Doroteu, 2015, Avaliação de diferentes doses de eCG na ressincronização da ovulação em vacas nelore lactantes submetidas à IATF Evaluation of different eCG doses in resynchronization of ovulation in lactating nelore cows subjected to fixed-time insemination, Rev. Bras. Reprod. Anim., 16, 449 Echternkamp, 2009, Size of ovulatory follicles in cattle expressing multiple ovulations naturally and its influence on corpus luteum development and fertility, J. Anim. Sci., 87, 3556, 10.2527/jas.2009-2049 Fátima, 2013, Global gene expression in the bovine corpus luteum is altered after stimulatory and superovulatory treatments, Reprod. Fertil. Dev., 25, 998, 10.1071/RD12155 Gutierrez, 2014, Effect of reproductive tract scoring on reproductive efficiency in beef heifers bred by timed insemination and natural service versus only natural service, Theriogenology, 81, 918, 10.1016/j.theriogenology.2014.01.008 Holm, 2009, The value of reproductive tract scoring as a predictor of fertility and production outcomes in beef heifers 1, J. Anim. Sci., 1934, 10.2527/jas.2008-1579 Marquezini, 2013, Effects of equine chorionic gonadotropin on follicle development and pregnancy rates in suckled beef cows with or without calf removal, J. Anim. Sci., 91, 1216, 10.2527/jas.2012-5382 Meneghetti, 2009, Fixed-time artificial insemination with estradiol and progesterone for Bos indicus cows I: basis for development of protocols, Theriogenology, 72, 179, 10.1016/j.theriogenology.2009.02.010 Nett, 2002, Pituitary effects of steroid hormones on secretion of follicle-stimulating hormone and luteinizing hormone, Domest. Anim. Endocrinol., 23, 33, 10.1016/S0739-7240(02)00143-1 Peres, 2009, Strategies to improve fertility in Bos indicus postpubertal heifers and nonlactating cows submitted to fixed-time artificial insemination, Theriogenology, 72, 681, 10.1016/j.theriogenology.2009.04.026 Perry, 2012, Physiology and Endocrinology Symposium: harnessing basic knowledge of factors controlling puberty to improve synchronization of estrus and fertility in heifers, J. Anim. Sci., 90, 1172, 10.2527/jas.2011-4572 Perry, 2016, Factors affecting puberty in replacement beef heifers, Theriogenology, 86, 373, 10.1016/j.theriogenology.2016.04.051 Perry, 2007, Relationship between size of the ovulatory follicle and pregnancy success in beef heifers, J. Anim. Sci., 85, 684, 10.2527/jas.2006-519 Pessoa, 2016, Different doses of equine chorionic gonadotropin on ovarian follicular growth and pregnancy rate of suckled Bos taurus beef cows subjected to timed artificial insemination protocol, Theriogenology, 85, 792, 10.1016/j.theriogenology.2015.09.057 Rigoglio, 2013, Equine chorionic gonadotropin alters luteal cell morphologic features related to progesterone synthesis, Theriogenology, 79, 673, 10.1016/j.theriogenology.2012.11.023 Rodrigues, 2013, Progesterone-based strategies to induce ovulation in prepubertal Nellore heifers, Theriogenology, 79, 135, 10.1016/j.theriogenology.2012.09.018 Sá Filho, 2009, Fixed-time artificial insemination with estradiol and progesterone for Bos indicus cows II: strategies and factors affecting fertility, Theriogenology, 72, 210, 10.1016/j.theriogenology.2009.02.008 Sá Filho, 2010, Equine chorionic gonadotropin and gonadotropin-releasing hormone enhance fertility in a norgestomet-based, timed artificial insemination protocol in suckled Nelore (Bos indicus) cows, Theriogenology, 73, 651, 10.1016/j.theriogenology.2009.11.004 Sales, 2011, Fixed-time AI protocols replacing eCG with a single dose of FSH were less effective in stimulating follicular growth, ovulation, and fertility in suckled-anestrus Nelore beef cows, Anim. Reprod. Sci., 124, 12, 10.1016/j.anireprosci.2011.02.007 Sangsritavong, 2002, High feed intake increases liver blood flow and metabolism of progesterone and Estradiol-17 β in dairy cattle, J. Dairy Sci., 85, 2831, 10.3168/jds.S0022-0302(02)74370-1 Sartori, 2004, Comparison of ovarian function and circulating steroids in estrous cycles of Holstein heifers and lactating cows, J. Dairy Sci., 87, 905, 10.3168/jds.S0022-0302(04)73235-X Vasconcelos, 2001, Reduction in size of the ovulatory follicle reduces subsequent luteal size and pregnancy rate, Theriogenology, 56, 307, 10.1016/S0093-691X(01)00565-9 Wathes, 2014, Heifer fertility and carry over consequences for life time production in dairy and beef cattle, Anim., 8, 91, 10.1017/S1751731114000755