Summary

Background: fixed-time artificial insemination programs (FTAI) in Bos indicus heifers have low pregnancy rates. Objective: the aim of this study was to evaluate the effect of cyclicity and equine chorionic gonadotropin (eCG) treatment in fixed-time artificial insemination (FTAI) programs in Bos indicus cattle. Methods: a total of 100 heifers were assigned to four treatments using a completely randomized design with a 2 x 2 factorial arrangement, where one of the factors was ovarian status (cyclic or acyclic) and the other was eCG use (with and without eCG). Follicular growth, ovulation, and pregnancy rates were evaluated using analysis of variance or X² test. Results: no effect (p>0.05) of cyclicity on follicular diameter was observed while eCG showed a significant effect (p<0.05). Cyclicity status and eCG use had no significant effect (p>0.05) on ovulation or pregnancy rates. Conclusions: the eCG application at the time of intravaginal device (IVD) withdrawal increased the size of the ovulatory follicle on insemination day. However, the ovarian state and the use of eCG did not affect ovulation and pregnancy rates of the heifers.

Key words: follicular growth, heifers, ovulation, pregnancy.

Resumen

Palabras clave: crecimiento folicular, novillas, ovulación, preñez.

Resumo

Antecedentes: os programas de inseminação artificial em tempo fixo feitos em novilhas Bos indicus apresentam baixa taxa de prenhez. Objetivo: o objetivo desta pesquisa foi avaliar o efeito da ciclicidade e da gonadotrofina coriônica equina (eCG) em programas de inseminação artificial em tempo fixo (IATF) em gado Bos indicus . Métodos: utilizaram-se 100 novilhas divididas em quatro tratamentos utilizando um delineamento inteiramente casualizado com arranjo fatorial 2 x 2 com duas categorias de acordo como o status ovariano (cíclico e acíclico) e o uso de eCG (com e sem eCG). O crescimento folicular, a taxa de ovulação e a taxa de prenhez analizaram-se usando análise de variância. Resultados: não houve efeito significativo (p>0,05) da ciclicidade sobre o diâmetro folicular, en quanto que a eCG apresentou efeito significativo (p <0,05). A ciclicidade e a aplicação de eCG não tiveram efeito significativo (p> 0,05) sobre a taxas de ovulação e prenhez. Conclusões: a aplicação de eCG no momento da remoção do dispositivo intravaginal (DIV), aumentou o tamanho do folículo ovulatório no dia da inseminação, embora, o status do ovário e o uso de eCG não afetaram as taxas de ovulação e prenhez nas novilhas avaliadas nesta pesquisa.

Palavras chave: crescimento folicular, novilhas, ovulação, prenhez.

Introduction

There are two main methods used to synchronize estrogen levels in bovines: by shortening the luteal phase through the use of luteolytic agents such as PGF2α, or artificially expanding the corpus luteum life through progestagen (Richardson et al., 2002). Besides changing the sensibility to progesterone and estrogen in the central nervous system, recent research suggests that manipulating and synchronizing the follicular growth wave is also required (Garcia et al., 2004). Therefore, the use of equine chorionic gonadotropin (eCG) at the end of the treatment is a proposed alternative to synchronize ovulation (Baruselli et al., 2004). The eCG is a glycoprotein characterized by a long halflife. It has a similar effect to FSH and can be used to stimulate follicular growth in cattle (Murphy and Martinuk, 1991; Yavas and Walton, 2000).

Regarding the use of eCG in Bos indicus heifers, significant differences have been reported in favor of using eCG, which is probably associated with the presence of prepubertal animals (Williams et al., 2002). Following the above, the aim of this study was to evaluate the effect of cyclicity and eCG on follicular dynamic, ovulation, and pregnancy rate of Bos indicus heifers under fixed-time artificial insemination (FTAI) programs.

Materials and Methods

Location

This study was conducted in La Macarena Farm (Tierra Alta municipality, Córdoba province, Colombia), located at 8°18' N and 76°04' W, at 52 m above sea level, with an annual average temperature of 28 °C, and 1680 mm annual precipitation.

Animals

A total of 150 Brahman heifers were evaluated. From these animals, 100 were selected with a 3.5 corporal condition score (1 to 5 scale). These animals weighed more than 350 kg and were clinically healthy with a normal reproductive tract and proper development of uterine horns.

The presence of a corpus luteum or a follicle greater than 10 mm was used to classify the ovarian status. Ovaries were evaluated by two 12-day interval tests using a 7.5 MHz ALOKA SSD 500 ultrasound and lineal transducer (Hitachi Aloka Medical, Ltd, Tokyo, Japan). Animals with a corpus luteum and follicle smaller than 10 mm or absence thereof were classified as acyclic and those diagnosed with corpus luteum and follicle greater than 10 mm were considered as cyclic.

Treatments

A completely randomized design in a 2 x 2 factorial arrangement was used in which one factor was ovarian state (cyclic or acyclic) and the other was the use or non-use of eCG. Twenty five heifers were included in each treatment (T), which were randomly assigned to groups according to the following combinations: T1 (Cyclic heifer with eCG); T2 (Cyclic heifer without eCG); T3 (Acyclic heifer with eCG); T4 (Acyclic heifer without eCG).

FTAI Protocol

Data collection

Follicular size was assessed for the presence of corpus luteum by reproductive ultrasonography on day 8 after removing the IVD, and 3 days after artificial insemination. The pregnancy rate was evaluated 45 days post-insemination.

Statistical analysis

Data were analyzed with InfoStat Sotfware (2008) using the following statistic model:

Y_ijk= u + T_j + B_j + (TB)_ij + E_ijk

Where:

Y_ijk: k-th observed value in the j-th level of cyclicity and i-th level of eCG.

μ: overall average.

T_i: effect of i-th level of eCG.

(TB)_ij: interaction of i-th level of eCG with the j-th level of cyclicity.

E_ij: random error associated with each observation.

Results

Effect of cyclicity and eCG on the follicular dynamic in Brahman heifers

Statistical analysis showed no significant effect (p>0.05) for the interaction of the factors under study. For this reason, the factors were analyzed separately. The cyclicity effect was not significant (p>0.05) for follicular growth on the day of the FTAI, while application of 400 UI of eCG on the FTAI day had a significant effect over follicular growth in the heifers (p<0.05) (Table 1).

The ovarian function (cycling and not cycling) at the start of treatment showed that this had no significant effect (p>0.05) on follicular growth rate at the day of FTAI. On the contrary, the use of 400 IU eCG on IVD withdrawal day was significant (p<0.05). Heifers receiving eCG had higher follicular growth rate than those not receiving eCG (Figure 1).

Cyclicity and eCG application had no significant effect (p>0.05) on the ovulation rate across treatments (Figure 2).

Effect of cyclicity and eCG on pregnancy rate in Brahman heifers

Cyclicity and eCG application had no significant effect (p>0.05) on pregnancy rate on the day of FTAI (Figure 3).

Discussion

Effect of cyclicity and eCG on follicular dynamic in Brahman heifers

The ovarian state of the heifers at the start of the treatment did not affect the pre-ovulatory follicle diameter on the day of FTAI. Similar results were reported by Sá Filho et al. (2005, 2010), who found no significant differences in follicular growth with respect to cyclicity in Bos indicus heifers synchronized with Crestar.

Effect of cyclicity and eCG on ovulation rate in Brahman heifers

This study found no significant effect (p>0.05) of ovarian status and eCG on ovulation. This is in agreement with Figueira et al. (2011). However, there were high ovulation rates ranging from 85 to 94%, which could be attributed to the dominant follicle diameter in the different treatments (approximately 10 mm). This could be supported by the results published by Gimenes et al. (2008), who found ovulatory capacity greater than 80% in Bos indicus heifers when the dominant follicle had a diameter greater than 8.5 mm.

The results of this study differ with Baruselli et al. (2004) and Sá Filho et al. (2010), who used IVD in FTAI protocols in Nellore heifers. They found that eCG application at the moment of IVD removal has a significant effect (p<0.05) on the ovulation rate. Although 400 IU eCG application had no effect on ovulation and pregnancy rates in this study, there was a trend of higher rates with this treatment.

Effect of cyclicity and eCG on pregnancy rate in Brahman heifers

Cyclicity and eCG use yielded pregnancy rates between 32% to 48%. However, no significant effect was found for the factors evaluated on the pregnancy rate (p>0.05). These results were similar to those of Márques et al. (2005), Butler et al. (2011), and Figueira et al. (2011), who found no significant effect (p>0.05) of ovarian status and eCG on pregnancy rate in Nellore heifers. On the contrary, Sá Filho et al. (2005) reported that in addition to cyclicity, eCG also has a significant effect on pregnancy rate (p<0.05) in Bos indicus heifers.

In this study, no significant statistical differences could be attributed to homogeneity of the groups of heifers used in reference to weight, age, uterine development, corporal condition (≥ 3.5; in a scale of 1 a 5), so that these females would not need the extra stimulation that eCG offers for follicular growth because they were in good nutritional status (Baruselli et al., 2004).

In conclusion, eCG application increased dominant follicle growth rate from the time of bovine IVD removal (day 8) to the FTAI (day 10). However, ovulation and pregnancy rates were achieved with equal efficiency with or without eCG application. Additional research is required on the use of this hormone as a tool in FTAI protocols in Bos indicus heifers.

^¤ To cite this article: Salgado RD, Maza LA, Vergara OD. Effect of cyclicity and Equine Chorionic Gonadotropin (eCG) in fixed-time artificial insemination programs in Bos indicus cattle. Rev Colomb Cienc Pecu 2013; 26:9-14.

Acknowledgments

We are grateful to the Tropical Animal Reproduction Biotechnology Laboratory of University of Cordoba (Colombia) for providing the materials required for this study. We also thank Macarena Farm managers for allowing the use of their facilities, and to veterinarians Daime Garcés and Fabián Jaramillo for their contribution to this research.

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