Effect of non-genetic factors on birth weight of Mecheri sheep of India

A K Thiruvenkadan, K Chinnamani, J Muralidharan and K Karunanithi

Mecheri Sheep Research Station, Pottaneri- 636 453,Tamil Nadu, India
drthirusiva@yahoo.com

Abstract

Data on birth weight of 2365 Mecheri lambs born between 1978 and 2005 recorded at Mecheri Sheep Research Station, Pottaneri, Tami Nadu were analysed to identify the factors affecting birth weight of Mecheri lambs.

The lambing occurred throughout the year, however majority of the Mecheri sheep (76.2 per cent) lambed between September and February months. The overall least-squares means for birth weight of males and females pooled over parity and type of birth were 2.30 ± 0.02 and 2.18 ± 0.02 kg respectively. Study on non-genetic factors revealed that the birth weight was highly significantly (P<0.01) affected by period of birth, season of birth, sex of the lamb and parity. Hence, efforts should be made for better management of pregnant ewes when the climatic conditions are not conducive to them.

Keywords: Heritability, lambs, meat, parity, sex ratio

Introduction

Sheep occupies a special place in the rural economy of Tamil Nadu. Mecheri sheep are one among the eight recognised breeds of Tamil Nadu, India and distributed in Salem, Erode, Namakkal, Karur and parts of Dharmapuri districts.  They are reared mainly for meat and the primary by-product is skin. Birth weight is the first observed trait in life of an animal on which growth, production and reproduction traits are dependent. So the present investigation was carried out to study the various non-genetic factors affecting birth weight of Mecheri lambs born under organized farm conditions.

Materials and methods 

The data on birth weight of 2365 Mecheri lambs born during 1978 to 2005 recorded at Mecheri Sheep Research Station, Pottaneri were utilized for this study. The Mecheri sheep were reared under semi-intensive system of management. The animals were grazed from 8.00 to 17.00 hours. In addition ewes were maintained with 100 to 250 g of concentrate mixture. The data were analysed by least-squares technique (Harvey 1990) adapting linear model after adjusting the fixed effects of period and season of birth, sex of the lamb and parity, since these being considered as the potential sources of variation. The period of birth has been divided into seven periods and the season of birth was classified as season 1 (September to February) and season 2 (March to August). The parity has been grouped as first, second, third, fourth, fifth and sixth and above. The data were subjected to standard statistical analysis as per Snedecor and Cochran (1986). The fixed effects model used for the analysis estimating the least-squares means to find out the non-genetic factors affecting birth weight in the Mecheri sheep was as follows:

Y_ijlklm = m + P_i +S_j+  T_k + O_l+ e_ijklm,

Where

m = overall mean when equal subclass frequencies exist,
P_i  =effect of i^th period (_i= 1to 5),
S_j  =effect of j^th  season (_j =1 to 4),
T_k =effect of k^th sex of lamb _(k= 1 and 2), 
O_l =Effect of l^th parity  (_l = 1 to 6) and
E_ijklm=Residual error.

The heritability for birth weight was estimated by paternal half-sib method by including the sires in the model after adjusting the data for significant non-genetic factors.

Results and discussion 

Sex ratio

Among the total lambs born, the male to female sex ratio was 1:0.97 (i.e., 50.78 per cent males and 49.22 per cent females). The chi-square test (of goodness of fit) revealed no significant difference between two sexes. Kale and Raman (1994) reported a sex ratio of 52.93% males for Madras Red and 50% for Mandya sheep.  

Lambing pattern

The lambing pattern revealed that the lambing occurred throughout the year. However most of the lambing was observed between September and February months with maximum in the month of September. The percentage of Mecheri sheep lambing in the month of January, February, March, April, May, June, July, August, September, October, November and December was 15.6, 10.9, 6.7, 1.8, 1.4, 4.7, 1.5, 8.0, 20.3, 7.1, 10.9 and 11.4 per cent respectively. The season wise analysis revealed that the percentage of animals lambing in winter, summer, south-west and north-east monsoon seasons was 37.9, 9.9, 14.2 and 38.3 per cent respectively. It is in accordance with the report of Pattanayak et al (2003) for Ganjam sheep. Patro et al (2006) also reported that the indigenous sheep of Kendraprada district of Orissa were bred throughout the Year. However on the contrary they reported that the majority of the ewes (67 per cent) came to heat in April to June months.

Effect of non-genetic factors

The least-squares means of birth weight of Mecheri sheep is presented in Table 1.

Period of birth

It was observed from the results that the period of birth had highly significant (P<0.01) effect on birth weight (Table 1). Further it has been noted that the lambs born in period 1 and 2 (1978-1981 and 1982-1985) had higher birth weight and lambs during the period 7 (2002-2005) had lowest birth weight. The present findings of highly significant effect of period is in agreement with the observations made by Bobhate et al (2003), Nehra and Singh (2006) and Jadav et al (2007). The birth weight observed in 7^th period (2004-2007) was highly significantly (P<0.01) different from period 1 (1978-1981), period 2 (1982-1985), period 4 (1990-1993) and period 6 (1998-2001). The significant differences in birth weight among lambs born in different period may be attributed to difference in management, selection of rams and environmental conditions.

Season of birth

The season had highly significant (P<0.01) effect on  birth weight of lambs. It is in accordance with the report of Sivakumar et al (2006). The lambs born during season 1 (September to February) were having higher birth weight than those born during season 2 (March to August). The ewes those conceived during September to November months had lambing during January and February, favourable environmental conditions with good availability of the fodder during the gestation period, which might have been contributed to higher body weight at birth.

Parity

Parity has highly significant effect (P<0.01) on birth weight of the lambs. The birth weight of the lambs was lowest in the first parity and it increased as the parity advanced with maximum in the fifth parity. It is in accordance with the report of Karunanithi et al (1994) for the same breed and Mandal et al (2003) for Muzaffarnagari sheep.

Sex of the lamb

The average birth weight of  different sexes revealed that the male lambs had higher birth weight than females. The sex of the lambs had highly significant (P<0.01) effect on birth weight. High birth weight of ram lambs and significant  effect of sex was also reported by several authors (Karunanithi et al 1994, Sivakumar et al 2006;  Ravimurugan et al 2007). Higher growth in prenatal stage under the influence of male sex hormones with anabolic effect (Hafez 1962) might be the reason for higher birth weight of male lambs.

Genetic parameters

The estimate of heritability for birth weight observed in this study was 0.061 ± 0.071. It is similar to the report of Nehra and Singh (2006). Jadhav et al (2007) reported a heritability value of 0.14 ± 0.02 for crossbred sheep. The relatively low estimate of heritability with high standard errors indicated that a greater portion of variation in growth traits was due to non-genetic factors.

Conclusions 

• The study revealed that the birth weight of Mecheri lambs was influenced by various non-genetic factors viz., period of birth, season of birth, sex of the lamb and parity.

  
  

• Efforts should be made for better management of  pregnant ewes when the climatic conditions are not conducive to them. 

  
  

• Since the birth weight is the first observational trait on which growth, production and reproduction traits are dependent, efforts have to be made for improvement of the same through better nutrition and  management.

References 

Bobhate S D, Barbind R P and Hanmante A A 2003 Factors causing variation in birth weight of goats. Indian Journal of Small Ruminants 9:173-175

Hafez E S E 1962 Reproduction In Farm Animals. (2^nd edition). Lea and Febizer, Philadelphia

Harvey W R 1990 User’s Guide for LSMLMW and MIXMDL PC-2 Version. Mixed model least-squares and maximum likelihood computer program. Ohio State University, Columbus, Ohio, U.S.A.

Jadhav S, Qureshi M I, Ashok Singh and Nanavati  S 2007 Study of birth weight in crossbred sheep. Indian Journal of Field Veterinarians 2:71-72

Kale D G and Raman K S 1994 Sex ratio, twinning, still births and abortions in Madras Red and Mandya breeds of sheep. Indian Veterinary Journal 71: 1195-1197

Karunanithi K, Natarajan N and Thangaraju P 1994 Genetic and non-genetic variation in birth, placental weight and number of cotyledons in Mecheri and its Dorset cross sheep. Cheiron 6:255-260

Mandal A, Pant K P,  Nandy D K, Rout P K and Roy R 2003 Genetic analysis of growth traits in Muzaffarnagari sheep. Tropical Animal Health and Production 35:271-284

Nehra K S and Singh V K 2006 Genetic evaluation of Marwari sheep in arid zone :Growth. Indian Journal of Small Ruminants 12:91-94

Patro B N, Mallick C R,  Rao P K and Panda P 2006 Production performance of indigenous meat type sheep in Kendrapada Distirct of coastal Orissa. Indian Journal of Small Ruminants 12: 42-47

Pattanayak G R, Patro B N, Das S K and Nayak S 2003 Survey and performance evaluation of Ganjam sheep. Indian Journal of Small Ruminants 9:47-49

Ravimurugan T, Thanaseelaan V, Piramanayagam S and Balachandran S 2007 Effect of non-genetic factors on birth weight and body measurements of Vembur lambs,  Indian Journal of Small Ruminants 13:100-102

Sivakumar T,  Soundararajan C, Palanidorai R, Ganeshkumar K, Mahendran M and Malathi G 2006 Factors affecting birth weight in Madras Red lambs. Indian Journal of Small Ruminants 12:115-116

Snedecor G W and Cochran W G 1989 Statistical Methods. 8^th edition. Iowa State University Press, Ames, Iowa. pp. xx + 503

Received 4 January 2008; Accepted 19 March 2008; Published 10 June 2008

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