Reproductive and economic efficiency in Nilagiri and Sandyno ewes treated with PMSG

R Anilkumar, C Chandrahasan*, M Iyue, M Selvaraju** and A Palanisamy***

Sheep Breeding Research Station, Sandynallah - 643 237 Tamilnadu Veterinary and Animal Sciences University, The Nilgiris district, Tamilnadu, India
ootyanil@yahoo.com
* Veterinary College and Research Institute, Namakkal 637001
** Department of Animal Reproduction, Gynaecology and Obstetrics, Veterinary College and Research Institute, Namakkal 637001
*** Department of Animal Biotechnology, Madras Veterinary College, Chennai - 600 007 Tamilnadu

Abstract

Sixty multiparous healthy Nilagiri (30 ewes) and Sandyno (30 ewes) ewes per breeding season were randomly subjected to PMSG administration (PM - Estrus synchronization and injection of 300IU PMSG) and control (CC) groups of 15 ewes each. Estrum in PM group was synchronized with progesterone impregnated intravaginal sponges. Duration of estrum and the economics of the treatment were calculated.

The tupping percentage during off breeding season (OBS) was significantly higher in PM ewes than CC ewes (93.3 vs 73.3 %). PM group of ewes had higher lambing percentage in both breeds of sheep and during different breeding seasons. Duration of estrum was significantly (P<0.01) higher in ewes treated with PMSG (34.4 ± 0.99 h vs 27.9 ± 1.08 h). The litter size and twinning percentage were significantly higher in PM group ewes (1.33 ± 0.07 and 31.2 %) than in CC group ewes (1.03 ± 0.07and 4.44 per cent). Twinning percentage in PM group was higher during MBS (36.7 %) than OBS (22.2 %). The litter weight at birth and weaning were higher in PM group of ewes. The survivability of lambs was similar for PM and CC. The twins had similar survivability as that of single lambs. The cost of producing an extra lamb was Rs 919 in PM group. It was less during MBS (Rs 728) than OBS (Rs 1247). PMSG can be administered during the MBS for increasing the litter size in ewes.

Keywords: birth, economics, litter size, litter weight, twinning percentage, weaning

Introduction

Ovulation rate and litter size have a major impact on the reproductive efficiency of sheep. Ovulation rate is influenced by the breeding season, nutritional status (Scaramuzzi et al 2006) and genotype (Bindon and Piper 1986). It can also be manipulated by the use of gonadotrophins (FSH and PMSG – Pregnant Mare Serum Gonadotrophin). The gonadotrophins improve follicular development, increased ovulation rate and multiple births in ewes (Kridli et al 2006).

Estrus synchronization rate ranging from 80 and 97 % has been obtained in experiments carried out during the breeding season involving Progestogen treatment with eCG in Dorset and Dorset x Rambouillet ewes (Cardwell et al 1998), Ethiopian Menz ewes (Mutiga and Mukasa-Mugerwa 1992), Chios and Berrichorn ewes (Boscos et al 2002) and in Dorper ewes ( Zeleke et al 2005). Higher estrus responses of 100 % have been reported by Greyling et al (1994) in Merino ewes and Anilkumar et al (2003) in Nilagiri ewes. Information regarding synchronization efficiency, fertility and litter size in Sandyno and Nilagiri ewes during different seasons of breeding is non existent. In addition the litter size at birth in Nilagiri and Sandyno ewes were low (Rajendran 2005) and hence the reproductive efficiency is also less in these breeds. Increasing the ovulation rate and litter size using PMSG will help in improving the reproductive efficiency in these breed. The use of PMSG and progesterone sponges increases the cost of production of lambs and no conclusive study on the economic effect of use of PMSG has been carried out. Thus this project was aimed at evaluating the effect of genotype, season of breeding on the efficiency of estrous synchronization, lambing percentage and litter size in Nilagiri and Sandyno ewes.

Materials and methods 

Selection of experimental animals

Sixty multiparous healthy Nilagiri (30 ewes) and Sandyno (30 ewes) ewes between 2 and 5 ½ years of age per breeding season were randomly selected. The selected ewes were randomly allotted to PMSG (PM) and control (CC) groups of 15 ewes each. The experiment was carried out in two breeding seasons viz., Main Breeding Season (MBS-September to October) and Off Breeding Season (OBS-March to April).

Synchronization of estrum, PMSG administration, estrus detection and duration of estrus

During the breeding seasons, the estrum in PM group of ewes were synchronized with progesterone impregnated intra vaginal sponges (45 mg Flurogestone acetate-FGA, Chronogest, Intervet, Holland) for 12 days. At the time of sponge removal, 300 IU of Pregnant Mare Serum Gonadotrophin (PMSG- Folligon, Intervet, Holland) was injected intramuscularly to all the ewes. The ewes were teased with apronized rams 24 h after sponge removal and the ewes in estrum were bred with suitable rams twice at 12 h interval. Ewes were teased with apronized rams at the ratio of 1:25 twice daily in the morning (6.30 am to 8.00 am) and evening (4.30 pm to 6.00 pm). The ewes found in estrum were brought to the breeding pen, weighed and were hand mated with selected rams twice at an interval of 12 h. Teasing of ewes in estrum after breeding was continued once in 4 h using apronized rams in both groups. Duration of estrum was calculated as the time interval between the first and last acceptance of the teaser ram by the ewe (Selvaraju 1994).

Ewes which were bred were grouped into single flock and maintained under standard managemental condition until lambing. The ewes were monitored closely during lambing and the lambs were marked with their dam immediately after birth. The lambs were ear tagged, weighed and were allowed to suckle the mother. The lambs were weaned from the dam at the age of 90 days.

Parameters studied

Date of breeding, weight at the time of breeding and date of lambing as well as number of lambs born, born alive, still born, number of lambs weaned and weight of lambs at birth and weaning were collected. Based on these data tupping percentage, lambing percentage, litter size, twinning percentage, weaning percentage, litter weight at birth and weaning were calculated. The economics of using PMSG was analyzed. The cost of drugs used per ewe was calculated based on the total cost of drugs utilized. The number of lambs produced over control ewes by ewes treated with PMSG was noted. The cost of producing an extra lamb and profit/loss of PMSG treatment were calculated The cost of feed and other managemental items (drugs, vaccines etc.) were not included for the study, since both the group of ewes were maintained under uniform management condition.

Statistical analysis

Least square procedure (Harvey 1990) was used to study the effects of treatment and other factors on various traits. All possible interactions with set of fixed effects were fitted initially and insignificant interaction effects were omitted. Linear statistical models were used for analysis of various traits. Chi square test was used to compare the difference in tupping (yes, no) and lambing (yes/no) percentage.

Results and discussion 

Tupping percentage and lambing percentage

The overall tupping percentage in PM group was 96.7% (Table 1).

Ewes from PM group showed a significantly higher tupping percentage than CC group of ewes and was more pronounced during OBS (93.3 vs 73.3%). Similarly the tupping percentage during MBS was significantly (P<0.01) higher (100%) than OBS (80%). The ewes available for breeding during the OBS were from severe winter months and are weighing less, hence a lower tupping percentage during this season in control ewes. The response in PMSG treated ewes was 100% in MBS and in Sandyno ewes it was 100% in both the seasons. Similar response for estrus synchronization was obtained by Greyling et al (1994) and Anilkumar et al (2003).

The PM group of ewes had higher lambing percentage in both the breeds of sheep and different breeding season. The ewes bred during MBS (98.3%) had significantly (P<0.01) higher lambing percentage than the ewes bred during the OBS (56.7%). During the OBS there was a reduction in lambing percentage both in PM and CC groups (60.0 and 53.3%). The reduction was more pronounced in Sandyno ewes treated with PMSG. The poor response might be due to the poor nutritional status of the animals during the winter and summer months. The lambing percentage observed in PM group was similar to the results obtained by Anilkumar et al (2003) and higher than those reported by Zaiem et al (1996) and Zeleke et al (2005).

Duration of estrum

The duration of estrum was significantly (P<0.01) higher (34.4 ± 0.99 h) in PM ewes than in control ewes (27.9 ± 1.08) (Table 2) and was similar to the observations of  Philipon and Driancourt (1987).

The long biological half life of PMSG leads to continuous recruitment of antral follicles, which results in large number of unovulated follicles (Armstrong et al 1983). The presence of large unruptured follicles leading to persistent estrogen level and the duration was more in these animals (Dhinsa et al 1971). However, Zeleke et al (2005) observed no significant effect on the duration of estrum between ewes treated with 300IU of PMSG and control ewes.

Litter size at birth and twinning percentage

The litter size at birth an easily measurable trait, determines the efficacy of any reproductive improvement experiment in small ruminants. Litter size at birth was significantly higher in PM group ewes (1.33 ± 0.07) than in CC group ewes (1.03 ± 0.07) (Table 2), which was in consonance with the findings of Boscos et al (2002), Galmessa and Prasad (2003), Anilkumar et al (2003) and Zeleke et al (2005). However Zafracas et al (1992) did not observe any effect on the number of lambs born in ewes injected with 330 IU of PMSG. Litter size at birth in Sandyno ewes treated with PMSG was higher than Nilagiri ewes. Rajendran (2005) in their study found that the litter size at birth in Nilagiri ewes (1.12 ± 0.01) was significantly higher than Sandyno (1.05 ± 0.01) ewes. Increase in litter size at birth in Nilagiri and Sandyno ewes was 0.25 and 0.32 respectively. This result showed that, Sandyno ewes responded better to PMSG treatment than Nilagiri ewes. The litter size was significantly higher in ewes bred during MBS (1.25 ± 0.06) in comparison to ewes bred during OBS (1.11 ± 0.08). The better response to PMSG during the MBS might be due to better body weight and condition of the animals during this season. Similarly, Crocker et al (1987) observed that the ewes joined in late December gave better litter size at birth than ewes joined in February. Twinning percentage in PM group was increased by 28.9%. Anilkumar et al (2003) recorded a similar increase (34.2%) in twinning percentage in Nilagiri ewes. Whereas, Galmessa and Prasad (2003) observed a higher (42%) twinning percentage than in the present study. The ovulation rate was correlated with the live weight of animal and the ewes during MBS were good in body weight correspondingly more number of ovum will be ovulated that leads to more twins. The reduced body weight in ewes bred during the OBS might be the reason for the moderate response for PMSG stimulation during OBS. Twinning percentage was significantly higher in PM group of ewes bred during MBS (36.7 %) than OBS (22.2 %). 

Litter weight at birth and weaning

The litter weight at birth was non significantly higher in PM group of ewes. The ewes treated with PMSG had more twins and their weights added up for the increase in litter weight in PM group. The Sandyno lambs had significantly (P<0.01) higher litter weight at birth and weaning than Nilagiri lambs. The litter weight at weaning was higher in PM group (12.2 ± 0.49 kg) than in CC groups of lambs (11.1 ± 0.53 kg). The lambs born during March had higher litter weight at weaning than September born lambs. Overall weaning percentage was 95.8 and it ranged from 91.3 to 100 %. The weaning percentage was higher in PM (96.5 %) than CC (91.3 %) groups. Survival rates of twins were often markedly lower than singles (Mutiga and Mukasa-Mugerwa 1992). However, in the present study the weaning percentage of twins were similar to singles. The better management of the lambs at birth and during the pre-weaning period in semi-intensive system of rearing might be the reason for higher survivability of twins in this study.

Cost of producing an extra lamb and net profit in ewes treated with PMSG

The cost of producing an extra lamb using PMSG was Rs 919. The response was higher during MBS (12 and 7 respectively) and hence the cost was less during this season (Rs 728) than OBS (Rs 1247). The cost was less in Nilagiri (Rs 794) ewes than Sandyno ewes (Rs 1091). However, during MBS the cost was less in Sandyno ewes (Rs 624) than in Nilagiri (873) ewes. Cost of intravaginal sponges and PMSG in ewes treated with PMSG had increased the cost of producing an extra lamb. The increase in the litter size at birth and litter weight at weaning does not compensate for cost of producing of an extra lamb using PMSG and results in a loss of Rs 95.9 /ewe.

Conclusions

• It was found that the use of PMSG in Nilagiri and Sandyno ewes has improved the tupping percentage during the OBS.

  
  

• The litter size at birth, twinning percentage, litter weight at birth and weaning were increased in PM treated group and is more pronounced during MBS. Hence PMSG can be administered during the MBS for increasing the litter size in Nilagiri and Sandyno ewes.

References

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Received 25 November 2009; Accepted 5 January 2010; Published 7 February 2010

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