Effect of hCG application on day 12 post-mating on the reproductive efficiency and plasmatic concentrations of progesterone in hair ewes

Efecto de la aplicación de hCG en el día 12 post-servicio sobre la eficiencia reproductiva y las concentraciones plasmáticas de progesterona en ovejas de pelo

J. Quintero,^I H. Olguín,^I A. Quezada,^I H. Janacua,^I R. Rivas,^I U. Macías,^II

^IUniversidad Autónoma de Ciudad Juárez. C.P. 32310. Anillo Envolvente del Pronaf S/N. Departamento de Ciencias Veterinarias.
^IIICA, Universidad Autónoma de Baja California. C.P. 21705. Mexicali, Baja California, México.

ABSTRACT

The application of human chorionic gonadotropin on day 12 post-mating on the reproductive efficiency and plasmatic concentrations of progesterone in hair ewes submitted to an estrus synchronization program was assessed.  Twenty four hair ewes were treated with vaginal sponges for 12 d and one application of 200 IU of PMSG at sponge removal.  On day 12 post-estrus, ewes were injected with a saline solution (control group) or 300 IU of hCG (hCG group).  Hormonal concentrations were determined in each female group.  Blood samples were collected 2 h before and 0, 2, 4, 6, 8, 24 and 48 h after the beginning of the hCG application for the P4 analysis.  The pregnancy diagnostic was realized 30 d post-mating.  The pregnancy rate, lambing and fertility rates were analyzed through X² and an analysis of variance was used for prolificacy.  Treatment effects on plasmatic concentrations of P4 were determined by the analysis of repeated measurements using the SAS (2004) program.  The hCG increased pregnancy rate compared to the control group (81.8 vs. 63.6 %; P < 0.001) and in the same way fertility was favored with hCG application (81.8 vs. 54.6 %; P < 0.001). There was significant difference (P < 0.001) in P4 plasmatic concentrations between treatments, being higher in ewes treated with hCG.  Considering the results conclusions can be drawn that hCG administered on day 12 post-mating increases pregnancy rate, besides increasing the fertility of the treated ewes.  The hCG also provokes significant increases in the progesterone plasmatic concentrations (P4) of female sheep.

Key words: hCG; ewes, progesterone, fertility.

RESUMEN

Se evaluó la aplicación de (Gonadotropina cariónica humana) en el día 12 post-servicio en la eficiencia reproductiva y concentraciones plasmáticas de progesterona en ovejas de pelo sometidas a un programa de sincronización de estros. Se utilizaron 24 ovejas de pelo, tratadas con esponjas vaginales durante 12 d y una aplicación de 200 UI de PMSG al momento del retiro de la esponja. En el día 12 post-estro, las ovejas fueron inyectadas con una solución salina (grupo testigo) o300 UI de hCG (grupo hCG). Las concentraciones hormonales fueron determinadas en cada grupo de hembras. Las muestras sanguíneas fueron colectadas 2 horas antes y 0, 2, 4, 6, 8, 24 y 48 horas después del inicio de la aplicación de hCG para el análisis de P4. El diagnóstico de gestación se realizó 30 d después del servicio. La tasa de gestación, tasa de partos y fertilidad se analizaron con X² y para la prolificidad se utilizó un análisis de varianza. Los efectos de los tratamientos en las concentraciones plasmáticas de la P4 se determinaron por el análisis de medidas repetidas utilizando el programa SAS (2004). La hCG incrementó la tasa de gestación en comparación al grupo control (81.8 vs 63.6%; P˂0.001) y de igual manera la fertilidad se vio favorecida con la aplicación de hCG (81.8 vs 54.6%; P˂0.001). Hubo diferencia significativa (P˂0.001) en las concentraciones plasmáticas de P4 entre los tratamientos, siendo altas en las ovejas tratadas con hCG. En consideración a los resultados se puede concluir que la administración de hCG en el día 12 post-servicio incrementa la tasa de gestación, además de aumentar la fertilidad de las ovejas tratadas. La hCG además provoca  aumentos significativos en las concentraciones plasmáticas de progesterona (P4) en hembras ovinas.

Palabras clave: hCG, ovejas, progesterona, fertilidad.

High temperatures affect negatively sheep fertility, provoking failures in the hormonal system, and consequently a deficient embryonic development. In this regard, some studies have found deficiencies in the luteal function and low progesterone concentrations during the first pregnancy stages (Khan et al. 2009) provoking early embryonic deaths.  Some of these research studies have been focused to decreasing the incidence of embryonic deaths in ewes, through progesterone and gonadotropin supplementation during early pregnancy. Recently, human chorionic gonadotropin is used (hCG; Khan et al. 2009 and Lashari and Tasawar 2010) for improving the luteal function and favoring luteinization of development follicles for the formation of accessory luteal bodies that would increase the progesterone plasmatic concentrations (necessary for the maintenance of gestation), which will help stimulate the growth of the conceptus in the uterus, assuring with the best placentation and consequently an increase in the conception rate. Hormonal treatments with hCG are utilized for increasing progesterone production on day 12 post-mating for preventing luteolysis in the luteal body and prostaglandin F2α (PGF2α) secretions. In view of the above mentioned, the purpose of this study was to study the effect of the treatment with hCG in hair ewes on day 12 post-mating on reproductive efficiency and embryonic and fetal development.

MATERIALS AND METHODS

The experiment was carried out at the Ranch of the Autonomous University of Juárez City, located in Juárez Valley, Praxedis G. Guerrero, Chihuahua.  Twenty four adult hair ewes were randomly separated in two groups (12 ewes/group).  Estrus was synchronized in all ewes using vaginal sponges impregnated with progestogens (Chronogest®Intervet®) for 12 d. At sponge removal each ewe was injected with a dosage of 200 IU of PMSG (Folligón®Intervet®). To the synchronized estrus, ewes were served 48 h after sponge removal through the system of direct natural mating.  On day 12 post-estrus, ewes were injected intramuscularly with a saline solution (control group) or 300 IU of hCG (Chorulón®Intervet®; hCG group).  Two hours before and at 0, 2, 4, 6, 8, 24 and 48 hours after the application of hCG, blood samples were taken by jugular puncture.  After collection, the blood samples were centrifuged for separating the plasma which was stored at -20º C until its later hormonal analysis. Sheep P4 determination was carried out using the technique defined by Law et al. (1992). Pregnancy diagnostic was made 30 d after service with ultrasonography equipment. The effect of the hCG (300 IU) application on the reproductive efficiency (pregnancy rate and lambing, fertility and prolificacy rates) and on the plasmatic concentrations of progesterone were evaluated.  Pregnancy rates and lambing and fertility rates were analyzed through the procedure PROC FREQ. and prolificacy was by PROX MIXED of the SAS (2004) package. Mean comparison for prolificacy was made using Tukey test for α = 0.05. Treatment effects on plasmatic P4 concentrations were determined by the analysis of repeated measurements using SAS (2004) program.

RESULTS AND DISCUSSION

The percentage of pregnant ewes, lambed ewes, fertility and prolificacy for the hCG groups (day 12 post-mating) and the control are shown in table 1.  Results of this study confirm the hypothesis that the gonadotropin supplementation on the 12 d of pregnancy in the ewe improves the fertility through conceptus and placentation assurance. When hCG was applied there was a significant effect on the variables pregnancy and fertility rates, coinciding with Cam and Kuran (2004) who report an increase in the pregnancy rate in ewes treated with hCG (84.1 %) regarding the control group (62.2 %) the same as prolificacy which was improved with hCG application (1.5 vs. 1.12 litters). In the same way, Khan et al. (2009) obtained a higher lambing percentage in ewes treated with hCG regarding the untreated (57 vs. 50 %), the same as prolificacy (2.0 vs. 1.8 litters). All these results indicate that hCG administered before the maternal pregnancy examination improves the gestation rate, lambing percentage and prolificacy.   The effect is attributed to hCG, which increases progesterone production and uterine secretions which are of embryotrophic origin.

Mean progesterone concentrations in plasma were significantly (P < 0.001) high in the group of ewes treated with hCG compared to the control group (figure 1).  It was observed that 2 hours after hCG application the plasmatic P4 concentrations increased until reaching its maximum concentration between 24 and 48 h after its application regarding the control group.  The increase in the progesterone concentration in ewes treated with hCG noticed in this study is similar to that obtained by Khan et al. (2007), who estimate that these high concentrations of progesterone as a consequence of hCG administration are considered as responsible of the rapid growth of the blastocyst resulting in a greater interferon IFN-r secretion and thus an increase in embryonic survival, bringing about increase in the number of pregnant females and ultimately improvement in ewe fertility.

Results of this study demonstrate that luteal function during the beginning of pregnancy is significantly high in ewes treated with hCG, which stimulates conceptus growth, due to the considerable increase of the plasmatic concentrations of progesterone.  The hCG application on the day 12 post-mating improves the reproductive efficiency by increasing pregnancy rate and fertility in hair ewes.

REFERENCES

Cam, M. A. & Kuran, M. 2004. “Effects of a single injection of hCG or GnRH agonist on day 12 post mating on fetal growth and reproductive performance of sheep”. Animal reproduction science, 80 (1): 81–90.

Khan, T. H., Beck, N. F. G. & Khalid, M. 2007. “The effects of GnRH analogue (buserelin) or hCG (Chorulon) on Day 12 of pregnancy on ovarian function, plasma hormone concentrations, conceptus growth and placentation in ewes and ewe lambs”. Animal reproduction science, 102 (3): 247–257.

Khan, T. H., Beck, N. F. G. & Khalid, M. 2009. “The effect of hCG treatment on Day 12 post-mating on ovarian function and reproductive performance of ewes and ewe lambs”. Animal reproduction science, 116 (1): 162–168.

Lashari, M. H. & Tasawar, Z. 2010. “The effect of hCG given on day 12 post-mating on ovarian function and embryo survival in Beetal goats in southern Punjab, Pakistan”. Turkish Journal of Veterinary and Animal Sciences, 34 (6): 513–517.

Law, A. S., Baxter, G., Logue, D. N., O’shea, T. & Webb, R. 1992. “Evidence for the action of bovine follicular fluid factor (s) other than inhibin in suppressing follicular development and delaying oestrus in heifers”. Journal of Reproduction and Fertility, 96 (2): 603–616.

SAS 2004. SAS/STAT, users guide software released. version 9.12, Cary, NC: SAS Institute Inc.

Received: November 25, 2015
Accepted: January 25, 2016

J. Quintero, Universidad Autónoma de Ciudad Juárez. C.P. 32310. Anillo Envolvente del Pronaf S/N. Departamento de Ciencias Veterinarias. Email: juan.quintero@uacj.mx