Seasonal variation in body weight and mortality rate in Mecheri adult sheep

M R Purusothaman, A K Thiruvenkadan and K Karunanithi 

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

Abstract

Data on monthly body weights of Mecheri rams and non-pregnant ewes were collected from adult weighment register for a period of 11 years (1991-92 to 2001-02). Data are based on 489 rams and 1185 ewes to study the seasonal variation in body weight of Mecheri adult sheep. In addition mortality details were collected from 380 adult Mecheri sheep died from 1979 to 2002 to study the mortality pattern.

The overall least-squares means of adult Mecheri sheep at winter, summer, south-west and north-east monsoon seasons were 25.2 ± 0.13, 23.8 ± 0.20, 24.5 ± 0.21 and 25.4 ± 0.20kg respectively. The overall mortality pooled over the years and sex was 8.39 per cent and ranged between 0.00 to 24.3 per cent. The mortality rate observed in 1-2, >2-3, >3-4, >4-5, >5-6 and > 6 years was 14.5, 9.21, 16.1, 22.1, 13. and 24.5 per cent respectively.  The respiratory and gastero- intestinal disorders were the predominant causes of mortally in all the seasons. They accounted for 31.1 and 24.5 per cent respectively.

Since the mortality rate was more in above six years age groups, an effective culling policy has to be adopted for disposal of ewes at this age. Effective monitoring of ewes during lactation and summer season by providing proper feed and management will reduce the mortality due to debility/weakness. Identification of causative agents for pneumonia and lung abscess and proper treatment to the affected animals based on Antibiotic Sensitivity Test (ABST) is essential to control the disease and also to reduce the mortality percentage.

Key word: body weight, Mecheri sheep, mortality, season

Introduction

Season is one of the main non-genetic factors which influences the performance of sheep. Months to month changes in body weights of native sheep have been ascribed to reflect the pastoral conditions of arid areas (Taneja 1968, 1969) or temperate regions (Mahajan and Bohra 1971) of this country. Hence, study on body weight at different seasons will be useful for devising suitable management programmes at different seasons for effective utilization of the resources available at different periods to get better profit from sheep rearing. In addition, there may be year to year and season to season variations in the mortality pattern and also the causes of death. A study on year-wise and season-wise mortality will be useful for taking suitable precautionary measures to reduce the mortality during adverse climatic conditions.   The good body condition and high survivability are the two main requirements for a profitable sheep industry. This study was made to find out the magnitude of seasonal variation in body weight and mortality rate in Mecheri sheep under dry land farming conditions.

Materials and methods 

Data on monthly body weights of Mecheri rams and non-pregnant ewes were collected from adult weighment register for a period of 11 years (1991-92 to 2001-02). Data are based on 489 rams and 1185 ewes. Rams and ewes that were present in the subsequent years were considered as a separate observation. The Mecheri sheep were grazed from 8 am to 5 pm daily. They were given concentrate mixture at the rate of 200 g per day per animal. During lean grazing months (April to June) animals were given Cenchrus spp. and horse gram hay. Animals were given access to water twice daily. A free choice of mineral bricks was given to all animals. The body weights were recorded once a month and in the morning hours before the animals had access to food and water. To study the mortality rate in adult Mecheri sheep the death and cause of death of each animal were collected from the death and disposal register for a period of 24 years (1979 to 2002). A total of 380 adult sheep had died during this period, made up of 45 males and 335 females. For analysis, the year was divide into four seasons viz. winter (December to February), summer (March to May), south-west monsoon (June to August) and north-east monsoon (September to November). The body weight of the rams and ewes were analysed by the method of least-squares (Harvey 1990). For mortality analysis, the animals were grouped according to age groups as 1 to 2, >2 to 3, >3 to 4, >4 to 5, >5 to 6 and > 6 years. The various causes of death were divided into 5 classes according to the organs or systems affected. The annual mortality was computed as the number of animals died, as a proportion of those at risk during the year.

Results and discussion 

The overall least-squares mean body weight of Mecheri sheep at different seasons is presented in Table 1.

The body weight of Mecheri sheep was significantly (P<0.01) higher in north-east and winter seasons, when compared to summer seasons. The monthly mean maximum temperature ranged between 30.6 to 35.1^o C in cooler part as compared to 37.4 to 37.8^o C during hotter part of the year. The total rainfall during the year confined mainly to June to November months. The total rainfall received during winter, summer, south-west and north-east monsoon seasons were 50.12, 162.1, 282.12 and 476.6 mm respectively. The decline in body weight at summer was due to extreme harsh climatic conditions and availability of poor quality vegetation in the grazing fields. It is in accordance with the reports of Taneja (1969) and Kaushish and Sahni (1976). The sex of the animal had significant (P<0.01) effect on all seasons and the males were heavier than females. Year also played  significant effect (P<0.01) on body weight of Mecheri rams and ewes. Maximum adult body weight was observed during the year 1993 and the lowest body weight was observed during the year 1991. Study on analyze of variance revealed that the effects due to years, season within year and sex of the animal influenced the live weight significantly (P<0.01). It is in accordance with the reports of Singh et al (1980).

Study on analysis of body weight at different age groups revealed that the body weight of Mecheri ewes were increasing linearly from 16.4 kg at 12 months (1 year) to 21.7 kg at 36 months (3 years). Afterwards the body weight of the Mecheri sheep were ranged between 19.1 and 21.9 kg at different months and the maximum body weight was generally observed between September and October months. The body weights of ewes pooled over age groups ranged between 18.7 and 20.9 kg. The body weight of rams were increasing linearly from 20.0 kg at 12 months to 33.1 kg at 48 months and the body weight of the rams pooled over age groups ranged between 25.8 and 30.3 kg respectively. The study revealed that the rainfall and temperature played a major role in fluctuation in body weight at different months. Because of erratic nature of rainfall and grazing material, it was not certainly that the Mecheri ewes would perform satisfactorily at all times under semi-arid conditions but the system of management in vogue at this station had certainly helped in keeping the body weight loss within the physiological limit. Hence, the Mecheri sheep could be expected to thrive and multiply moderately if they were managed on the pattern followed in this study.

Mortality

Annual mortality

The annual mortality rate of adult Mecheri sheep from 1979 to 2002 is presented in Table 2.

The overall mortality pooled over the years and sex was 8.39 per cent and ranged between 0.00 to 24.32 per cent. The annual mortality rate was below the average mortality rate (8.39%) in 15 out of 24 years. Year-wise mortality did not exhibit any definite trend in this study. Variation in mortality over the years was due to fluctuations in climatic conditions, availability of fodder and management practices. It is in accordance with the report of Prasad et al (1992). However, Taneja et al (1991) and Reddy and Choudhuri (2000) reported higher mortality rates. The percentage of animals died during the month of January, February, March, April, May, June, July, August, September, October, November and December was 11.84, 10.79, 14.47, 12.63, 7.37, 2.89, 2.89, 4.74, 7.63, 7.11, 11.05 and 6.59 per cent respectively. The highest mortality rate was observed in the month of March and lowest in June and July months and they differed significantly (P<0.01).

Season-wise mortality

The mortality rate observed in winter, summer, south-west and north-east monsoon seasons were 29.21, 34.47, 10.53 and 25.79 per cent respectively. The highest mortality observed in summer season might be due to the availability of poor vegetation and extreme harsh climatic conditions. Reddy and Choudhuri (1999) and Narwade et al (1999) reported maximum mortality in summer season and minimum during the monsoon season. On the contrary, Palanivel and Gajendran (2006) reported highest mortality in rainy season in sheep of Tamil Nadu.

Mortality on the basis of age and sex

Mortality of Mecheri sheep on the basis of age and causes are presented in Table 3.

The mortality rate observed in 1-2, >2-3, >3-4, >4-5, >5-6 and > 6 years was 14.47, 9.21, 16.05, 22.11, 13.68 and 24.48 per cent respectively. The highest mortality rate observed in the age group of above six years might be due to that the animals in this age groups were aged and weak due to wearing and loss of one or more incisors. So, keeping animals above six years of age should be considered only on the exceptional breeding performance and mothering ability. In above 6 years age group, the percentage of death due to respiratory, gastero-intestinal and weakness/debility was 35.48, 23.66 and 23.66 per cent respectively.

Among the total mortality, the mortality of males and females was 11.8 and 88.2 per cent respectively. The low mortality rate observed in males was probably due to intensive culling practiced in the flock and fewer males were kept in the farm for breeding purpose for limited period of time.

Causes of mortality

The respiratory and gastero-intestinal disorders were the predominant causes of mortally in all the seasons and they accounted 31.05 and 24.47 per cent respectively. It is similar to the reports of Prasad et al (1992), Mandal et al (2005), Mandal et al (2007).  Percentage of animals died due to other causes such as weakness/debility, circulatory causes and miscellaneous were 21.05, 6.85 and 16.58 per cent respectively. The death due to respiratory (31.37 %) and gastero-intestinal (35.48 %) disorders was more in winter season and the death due to weakness/debility (36.25%) was high in summer season. Among the respiratory disorders, percentage of animals died due to pneumonia, lung abscess, hydrothorax, cyst in the lungs and pleurosis were 50.85, 36.44, 4.24, 5.93 and 2.54 per cent respectively. I Among the total death due to gastero-intestinal disorders, the death due to bloat and enteritis accounted 33.33 and 29.03 per cent respectively. The other causes accounted for 36.56 per cent, which includes ruminal impaction, stomatitis and foreign body in the gastero-intestinal tract. In general, among the total death, the death due to pneumonia was highest (15.79%) followed by lung abscess (11.31%), bloat (8.16%) and enteritis (7.37%).

Conclusions 

• Study on body weight changes at different seasons in Mecheri adult sheep revealed that the body weight was lower in summer and early part of south-west monsoon seasons.

  
  

• Hence it is suggested that supplementation of concentrate mixture and dry fodder’s is essential during these periods for maintaining the body weight of adult sheep at normal level.

  
  

• From the mortality results it was concluded that the pneumonia, lung abscess, bloat and enteritis were the probable causes of death and among the seasons, winter and summer seasons recorded the most occurrence of deaths.

  
  

• Effective monitoring of ewes during lactation and summer season by providing proper feed and management will reduce the mortality due to debility/weakness.

  
  

• Identification of causative agents for pneumonia and lung abscess and proper treatment to the affected animals based on Antibiotic Sensitivity Test (ABST) is essential to control the respiratory diseases (namely pneumonia and lung abscess) and also to reduce the mortality percentage.

References 

Harvey W R 1990 Mixed Model Least Squares and Maximum Likelihood Computer Program, PC-2 version. Ohio State University, Columbus, USA.

Kaushish S K and Sahni K L 1976 Monthly variation in body weights of Russian Merino sheep under semi-arid conditions. Indian Veterinary Journal 53:927-932

Mahajan J M and Bohra S D J 1971 Monthly variation in body weight in Gaddi hill ewes under farm conditions in Kullu Valley. Indian Veterinary Journal 48:1039

Mandal A, Barua S, Rout P K, Roy R, Prasad H, Sinha N K and Sharma N 2005 Factors affecting the prevalence of mortality associated with pneumonia in a flock of  Muzzaffarnagari sheep. Indian Journal of Animal Sciences 75:407-410

Mandal A, Prasad H, Kumar A, Roy R and Sharma N 2007 Factors associated with lamb mortalities in Muzzaffarnagari sheep. Small Ruminant Research 71:273-279

Narwade V E, Thorat B P, Deokar D K. and Bhoite U Y 1999 Effect of season on pre-weaning mortality in lambs of Deccani and its crosses. Indian Journal of Small Ruminants 5:31-34

Palanivel K M and Gajendran K 2006 Retrospective analysis of clinical diseases in sheep under farm condition. Indian Journal of Field Veterinarians 2:22-24

Prasad R D, Sreenivasalu D, Madhava Rao T, Charyulu E K and Munirathnam D 1992 An analysis of mortality in sheep. Indian Veterinary Journal 69:1115-1119

Reddy M P and Choudhuri P C 1999 Study on lamb mortality in organised sheep farms in Andhra Pradesh. Cheiron 28:200-204

Reddy M P and Choudhuri P C 2000 Epidemiological studies on lamb mortality inn certain sheep farms in Andhra Pradesh. Indian Veterinary Journal 77:542-543

Singh G, Singh V K and Mishra R K 1980 Seasonal variation in performance of ewes of Corridale, Coimbatore and their crosses (1/2 bred, 5/8^th and 3/4^th ). Cheiron 9:3

Taneja G C 1968 Variation in body weight of Marwari sheep. Indian Veterinary Journal 45:488

Taneja G C 1969 Variation in body temperature, respiratory rate, pulse rate, water intake and body weight of Marwari sheep during the year. Indian Veterinary Journal 46:47-56

Taneja A D, Yadav S B S and Pant K 1991 Morbidity and mortality rates in Magra sheep of arid region. Indian Journal of Animal sciences 61:1138-1139

Received 4 January 2008; Accepted 19 March 2008; Published 4 September 2008

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