Estrous synchronization using PMSG and GnRH in progesterone primed ewes.
Tropical sheep breed year round but lambing is concentrated during particular season due to nutritional variations caused by climatic differences. Diminishing pastures due to loss of natural grazing lands is leading to a shift in system of sheep rearing towards intensive farming. In such situations, the use of techniques like induction, synchronization and fixed time mating are useful to improve reproductive efficiency. Hormone based induction method brings more animals to heat and synchronization helps in planning for uniform management practices and market based production systems. The present paper reports incidence of estrum in response to intravaginal progesterone sponges used in conjunction with Pregnant Mare Serum Gonadotropin (PMSG) and Gonadotropin Releasing Hormone (GnRH) in non-cyclic Madras Red ewes.
Materials and Methods
Sixteen Madras Red ewes were used for the study. The animals were allotted at random to two treatment groups of eight each and the study was conducted during April when animals are not in breeding season. Intravaginal progesterone sponges were inserted for 12 days in all sixteen ewes. On day 11, luteolytic dose of [PGF.sub.2][alpha] (Lutalyse (a) @ 2.5 ml/ewe) was administered and progesterone sponges were removed on day 12.
The first treatment group received PMSG @ 200 IU per animal, while the second group received GnRH @ 10 [micro]g per animal at the time of sponge removal. Incidence of estrum was recorded by identifying animals in heat using teaser rams. Fertile apronised rams were used as teasers and teasing was done at 12 hours interval four times starting from 24 hours post sponge removal. Animals standing to mount were considered in heat.
Results and Discussion
All eight ewes in the PMSG group responded to treatment and stood to heat while only one ewe in GnRH group responded. Fischer's exact test indicated significant difference between the groups.
In present study, progesterone intravaginal sponges impregnated with Progesterone (b) 300 mg were inserted for a period of 12 days. Ewes usually exhibited estrus within 24-48 h after sponge removal when PMSG was used (Robinson, 1981; Wildeus, 2000). In the present study, 87.5 percent of animals exhibited heat after 36 hours while all animals exhibited heat within 48 hours in the PMSG group.
The levels of FSH and LH are usually less than 50 percent of normal levels during off season in non cyclic ewes. LH inducers have been commonly been used to bring seasonally anestrous ewes to heat and this in conjunction with progesterone pre-treatment has been more effective (Thimonier, 1981). Exogenous progesterone used mimics progesterone released from corpus luteum. Progesterone exposure is necessary to make hypothalamus responsive to estrogen and display of estrus. The most commonly used method for progesterone pre-treatment in ewes is the use of intravaginal devices impregnated with progesterone (FGA) or Medroxyl progesterone Acetate (MAP) (Fukui et al., 1999, Karaca et al., 2009). Among different LH inducers used, PMSG at the time of removal of sponge has been used extensively (Robinson, 1988; DeNicolo, 2007). A dose of 200 IU dose of pMsG is sufficient to stimulate ovulation and estrus without causing multiple ovulations (Ritar, 1993, Fonseca et al., 2005). The dosage of PMSG used in different synchronization programmes varied from 60 IU750 IU. A dose of 200 IU was used in this study to keep the cost at minimum and aim was not superovulation. In tropical sheep twinning is uncommon and singles are preferred to multiple births by farmers.
In GnRH group of this study, the only animal that exhibited heat was after 36 hours from sponge removal. Earlier study using GnRH (Husein and Kridli, 2003) indicates that progesterone pretreatment has a marked effect on ability of small doses of GnRH (250 ng) to induce ovulation and normal luteal function in seasonally anoestrous ewes.
In present study, response to estrus was very poor and probably the role of GnRH is more towards ovulation caused by LH surge and initial FSH concentration for sufficient follicular development was absent in this group. FSH is necessary for stimulating development of follicles and also release of oestrogen.
To conclude, for induction and synchronisation of anoestrous ewes, administration of PMSG at the time of sponge removal results in better response.
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R. Venkataramanan (1), C. Sreekumar, R. Abiraami, G. Manonnmani and H. Gopi
Postgraduate Research Institute in Animal Sciences Tamil Nadu Veterinary and Animal Sciences University (TANUVAS) Kattupakkam--603203 (Tamil Nadu)
(1.) Assistant Professor and Corresponding author. E-mail: email@example.com
(a)--Brand of Zoetis Animal Health, Mumbai
(b)--Research Product of CSWRI, Avikanagar
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|Title Annotation:||Research Article; pregnant mare serum gonadotropin and gonadotropin releasing hormone|
|Author:||Venkataramanan, R.; Sreekumar, C.; Abiraami, R.; Manonnmani, G.; Gopi, H.|
|Date:||Jan 1, 2015|
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