Hormonal strategy to reduce suckled beef cow handling for timed artificial insemination with sex-sorted semen
Introduction
Sex-sorted semen has been gradually used in reproductive programs of cow-calf operations due to its potential to increase the ratio of sex-desired calves [1,2]. From a practical viewpoint, it is possible stating that this recommendation does not meet the current reproductive management adopted by extensive beef farms that follow the timed artificial insemination protocol (TAI), although artificial insemination (AI) companies recommend the use of sex-sorted semen upon estrus detection due to its relatively adequate rate of pregnancy per AI (P/AI) [3]. (see Table 1)
Nowadays, TAI programs allow the use of sex-sorted [[4], [5], [6]] and non-sex-sorted semen [[7], [8], [9]]. Estradiol (E2) and progesterone (P4)-based protocols are the most common therapies applied in association with TAI to treat beef cattle in South America [9,10]. Estradiol benzoate (EB) administered 24 h after P4 device removal (EB-24h protocol) or estradiol cypionate (EC) administered simultaneously to P4 device removal (EC-0h protocol) are the most commonly used ovulation inducers in these protocols [[11], [12], [13]].
Despite the distinguished chemical structures of EC and EB, and their estradiol-17β releasing profiles [14], both protocols were equally capable of inducing preovulatory LH surge [12] and synchronic ovulation in beef cattle [[11], [12], [13]]. Moreover, the two estradiol esters led to similar interval among P4 device removal, ovulation and P/AI, when TAI was performed with non-sex-sorted semen [7,[10], [11], [12], [13]]. However, the EC-0h protocol was more advantageous than EB-24h, because it reduced the animal handling required to TAI (3 vs. 4 managements). Furthermore, although EC-0h has been successfully used to induce ovulation in large-scale TAI programs [15], assumingly, this protocol has not yet been properly tested with sexed semen. Thus, the present study was conducted to provide satisfactory scientific information about the applicability of sexed semen in large beef cattle herds.
Therefore, the aims of the present study were 1) to compare the time of ovulation and P/AI after TAI with sex-sorted semen based on ovulation synchronization protocols EC-0h vs. EB-24h (Experiment 1) and 2) to assess P/AI based on synchronization ovulation protocols EC-0h or EB-24h with non-sex-sorted or sex-sorted semen (Experiment. 2). Our hypothesis was that EC could be administered at progesterone (P4) device removal to reduce handling and to achieve satisfactory pregnancy rates in suckled beef cows after TAI with sex-sorted semen.
Section snippets
Animals and location
The experiment was conducted in three commercial beef farms located in Parnarama, Maranhão State, Brazil. All cows were maintained on a Brachiaria decumbens pasture and supplemented with mineralized salt; the cows had free access to water. Four-hundred ninety-one (491) Nelore (Bos indicus) cows (454 multiparous and 37 primiparous), from 60 to 90 postpartum days, participated in the study. Body condition score (BCS) was recorded on the first treatment day based on a 1–5 scale (1 = emaciated;
Statistical analysis
The statistical analyses were performed in the SAS for Windows software (SAS 9.3 Institute Inc., Cary, NC, USA 2003) in both experiments. The continuous variables were analyzed through ANOVA based on the GLIMMIX procedure, which was adjusted to normal distribution. Categorical data were analyzed through logistic regression based on models adjusted to binary distribution. The continuous variables were expressed as the mean ± standard error of the mean (mean ± SEM) and the occurrence frequency
Experiment 1: time of ovulation and P/AI after the EB-24h or EC-0h protocols were applied
There was no difference in the diameter of the dominant follicle at P4 device removal (EB-24h = 10.3 ± 0.5 mm vs. EC-0h = 10.2 ± 0.4 mm; P = 0.97) or in the maximum diameter of the dominant follicle (EB-24h = 11.8 ± 0.5 mm vs. EC-0h = 12.3 ± 0.3 mm; P = 0.74). Moreover, there was no difference in the time of ovulation associated with P4 device removal (EB-24h = 70.0 ± 2.9 h vs. EC-0h = 66.0 ± 2.8 h; P = 0.52) or in the ovulation rate (EB-24h = 92.3% vs. EC-0h = 92.3%; P = 0.61). Despite the
Discussion
The current study provided knowledge about the use of two different ovulation synchronization protocols applied to TAI with sex-sorted semen in suckled beef (Bos indicus) cows. The EC-0h protocol provided similar follicular growth and ovulation responses to that recorded for the EB-24h protocol, but greater P/AI. Furthermore, non-sex-sorted semen led to greater P/AI than the sex-sorted semen (Experiment 2). Such result, besides being expected, corroborated results in previous studies [[1], [2],
Acknowledgement
The authors would like to thank Santa Cristina, Olho D’Água, Águas de Março and São Benedito farms for providing animals and for making their facilities available for the experiments. We are grateful to Evanil Campos Filho of the Sexing Technologies Brazil and Gabriel Armond Crepaldi of CRV-Lagoa for the semen donation. Thanks to Danilo Pincinato and Lucas Peres of Clivar Reprodução Bovina and to Marcio W. de Castro of Aliança Assessoria Pecuária for their technical assistance in animal
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