|Livestock Research for Rural Development 18 (4) 2006||Guidelines to authors||LRRD News||
Citation of this paper
A study was conducted at the Livestock Farm of the National Agricultural Research Institute, Mon Repos, East Coast Demerara, Guyana, between January 2000 and July 2003, to evaluate the production parameters of the Barbados Blackbelly and crossbred sheep in a controlled semi-intensive production system. The data were obtained from a comprehensive record keeping system used during the study.
The animals were separated into two groups as it relates to breed, the Barbados Blackbelly and the crossbred breeds of sheep. The dams were placed into groups based on their age 1-2 years, 2-3, 3-4, 4-5 and >5 years of age, to evaluate the birth weight of lambs born to dams within their age ranges. Young lambs were evaluated on their birth weight and weaning weight to yearlings. Other parameters evaluated were average daily gains, at the pre and post weaning stages of growth for the two breed types, birth types expressed as a percentage of total lambs born as well as pre and post weaned mortality.
There were no differences in live weight, (P<0.05) between the two breed types when comparisons were made separately for sex at the different intervals. These include birth weight, weaning weight at 90 days and weights at both 180 and 270 days. There were no differences in birth weights among sexes at the different age ranges. Female lambs, however, had lower birth weights in the 3-4 years and >5 years age range when compared to the 1-2 year, 2-3 and 4-5 year range. Based on the LSD test, no differences (P < 0.05) could be detected between the two breed types for males in relation to the average daily gains of the animals at pre and post-weaning stages. The percent single births were significantly higher for the crossbred sheep when compared to the Barbados Blackbelly; this trend was however reversed when comparisons were made for twin births.
Keywords: Average daily gains, Barbados Blackbelly, birth type, crossbred sheep, Guyana
Sheep were introduced in the Livestock Programme at the National Agricultural Research Institute (NARI) in November 1999. It was recognised that sheep production was one of the facets of the livestock sector that could have played a major role in the development of the agricultural production systems of the rural poor. These animals require little space and are efficient users of the abundant forage resources found in the rural areas of Guyana.
Sheep production at NARI was developed with the aim of assisting in the improvement of the overall welfare of low-income farm families. An innovative component of the NARI programme was the inclusion of the provision of breeding animals to the farming community, both to established and prospective farmers. In addition, one of the principal foci for the establishment of the sheep production unit was to acquire a flock of 150 breeding ewes so that breeding and multiplication work could be undertaken. Currently the farm has in excess of 300 animals and has supplied more than 150 breeding rams to the farming community across the country. The sale of these high quality animals is done to assist in the development of the production and marketing capabilities of these farmers.
The animals at the station are managed under a semi-intensive production system. They are exposed to improved pastures with a good grass-legume combination and are supplemented with commercial ration of beef and dairy types or molasses/poultry litter block. These supplemental diets are advocated at 0.25-0.50% of the animal's body weight based on the physiological status of the animals. Further, good animal husbandry and health care practices have been instituted within this unit from the inception of the project.
The sheep sub-sector in Guyana is of both national and regional significance, because of the sector's current and potential ability to contribute to national and regional food security and the impact it has for exports and consequently foreign exchange earnings.
In this regard, efforts were therefore made at the NARI Livestock Farm to ascertain and indeed improve on the production parameters of sheep reared in Guyana. Information is available on the performance of the Barbados Blackbelly and crossbred sheep throughout the Caribbean. In the case of Guyana, Nurse et al (1983) studied and reported on the performance of Barbados Blackbelly sheep and their crosses at the Ebini Research Station in the Intermediate Savannahs, Berbice River. A similar study was carried out by Cumberbatch et al (1998) in Region 5, (the Mahaica/West Berbice district), to acquire production data on hair sheep reared in extensive farmer-managed operations.
The studies/reviews were conducted in different ecozones under different production and management systems, hence the need for further evaluation. Thus, the objective of this study was to evaluate the production parameters of the Barbados Blackbelly and the crossbred breeds of sheep in a controlled semi-intensive system in Guyana.
This study was conducted at the National Agricultural Research Institute, Livestock Farm Mon Repos. This farm is located approximately 20 km from the capital Georgetown. The area has two wet and two dry seasons. Rainfall per annum ranges between 2,300-2600 mm, during the wet season, the duration of sunshine averages 5 hours per day, but during the dry season, it is about 7 hours or more per day. The daily temperature ranges between 22 and 320C and relative humidity is about 70-80%, usual wind movement is in a northeasterly direction at velocity of about 10-15 metres per second.
The sheep used in this review were the Barbados Blackbelly and the crossbred breeds of sheep. All data were obtained from the comprehensive record keeping systems used at the farm from the January 2000 to July 2003.
The animals were separated into two groups as it related to breed, the Barbados Blackbelly and the crossbred breeds of sheep. The dams were placed into groups based on their age 1-2 years, 2-3, 3-4, 4-5 and >5 years to evaluate the birth weights of lambs born to dams within these age ranges. Young lambs were evaluated on their birth weights and weaning weights to yearlings. The parameters evaluated were,
The data were analyzed using the ANOVA procedures and LSD to establish whether differences existed in animal performances based on breed and age.
Angwenyi (1990) indicated that management systems rather than flock structure played a more important role in the production efficiency of sheep and goat flocks located in an adaptive environment. In this study the focus was on the performance of the Barbados Blackbelly and the crossbred sheep, reared under a management system developed by NARI, and used at the Livestock Farm of NARI.
The animals are managed under the semi-intensive production system. They are housed at night and are released to pasture at 0700hrs and returned to the pens at 1700hrs. The management system developed also included the use of old dairy barns converted for use by sheep. The floor is concrete and paddy husk is used as a deep litter bedding material. The bedding material is changed every 14 days.
The animals are grazed on improve pastures which consists of Hemarthria altissima, Brachiaria arrecta, Brachiaria brizantha and Cynodon dactylon. In addition, there is a legume protein bank, which is a combination of Leucaena leucocephala and grass and is supplemented with a commercial beef and dairy ration or molasses/poultry litter block.
The flock is housed in separate pens and is managed differently. The lactating ewes and lambs are housed separately and are supplemented with dairy ration and the pregnant and dry ewes are fed beef ration. The weaned males and females are given the molasses/poultry litter block as a supplement. Weaning is done at 90 days of age. These supplemental diets are fed at 0.25-0.50 % of the animal's body weight based on the physiological status of the animals.
Good animal husbandry and health care practices are instituted within the unit. The animals are generally dewormed once per month and are treated for foot-rot as required. The weaned animals are weighed once per month until they are one year old.
The live weight of the two breed types, males and females at different intervals are shown in Table 1. There were no differences (P<0.05) between the two breed types when comparisons were made separately for sex at the different intervals. These include birth weight, weaning weight at 90 days and weights at both 180 and 270 days.
Live weight at birth, weaning (90 days), 180 days and 270 days are summarised in Table.1. The table show that the live weight of the animals on the farm compared favourably with those reported by Cumberbatch et al (1998), in a study that investigated the growth parameters of animals on the coastal plains. The live weights reported for crossbred sheep on the coast of Guyana were as follows, at birth-2.5 kg, 90 days - 11.4 kg, 180 days - 16.45 kg and 270 days - 17.81 kg. Although the study done by Cumberbatch et al (1998) did not specify performance by sex, comparison of the results showed that the two breed types of sheep at the NARI Livestock Farm had higher weight gains at the different stages of growth. The improved performances recorded at the NARI Livestock Farm, could be attributed to the improved husbandry and management practices instituted at the farm.
The age of animals giving birth in the study was between 1-5 years (Figure 1). There were no differences in birth weights among sexes at the different age ranges. Female lambs, however, had lower birth weights in the 3-4 years and >5 years age range.
|Figure 1. Birth weight of lamb born to dam of different age range|
Birth weight is an important factor of productivity, because, it is strongly correlated with growth rate and adult size, as well as lamb viability. Mean birth weight of lambs at NARI, (Figure 1), based on the ages of the dams showed a fluctuating trend. Lambs born to dams between 1-3 years old were however heavier than those between 3 -5 years old. The different age range comparisons among sexes for male and female lambs' mean birth weights were similar. In the case of dams older than 5 years, recorded mean birth weights were similar to those of dams 2-3 years old.
According to Combellas et al (1980), birth weight is affected by genetic, physiological and environmental factors. This notion suggested that genetic and environmental factors were most likely responsible for the varying trend in the birth weight of lambs observed at the NARI Livestock Farm.
The mean birth weight of lambs when compared by birth type (Figure 2), showed a general trend, where both the male and female lambs born of single births, recorded higher birth weights than lambs born as twins. No differences could however, be detected between the two breed types. Mannasmith et al (1991) reported a similar trend for hair sheep in relation to birth type and weight of lambs at birth for the Barbados Blackbelly. The mean birth weight for single lambs was 2.99 kg and the mean birth weight for twins was 2.75 kg. This suggested that the type of birth influences lamb birth weights, probably because the nutritional resources consumed by the dams would have to be shared for multiple foetuses, whereas the single foetus would enjoy the full benefits.
|Figure 2. Birth weights of lambs born to single and twin|
The Barbados Black Belly sheep is generally known for its prolificacy hence the incidence of twin births was relatively high (Figure 4). The birth weights of lambs did not differ significantly (P < 0.05) among sexes for single and twin births. Female lambs born in twin litters however, recorded lower birth weights than male and female lambs of single litter and males of twin litter.
Based on the LSD test, no differences (P < 0.05) could be detected between the two breed types for males in relation to the average daily gains of the animals at pre and post-weaning stages (Figure 3). The same trend was observed for the female lambs. When comparisons were however made between sexes, the males had higher weight gains than the females at both stages of growth. In addition, both the male and female crossbred animals had higher weight gains at the pre-weaning stage. The reverse was however observed in the post-weaning stage of growth.
|Figure 3. Pre and post-weaned average daily gains of Barbados Blackbelly
and crossbred males and females
Cumberbatch et al (1998) reported that the average daily gains of sheep on the coastal plains at 90 days were 88.0g, which were lower than the weights obtained in this study. Combellas (1980) documented average daily gains from a number of studies conducted. The average daily gains reported for Barbados Blackbelly and crossbred sheep were 154 g at 0-72 days. Riveron et al (1976) reported daily gains of 113 g/day for the Barbados Blackbelly breed while the Creole had gains of 107g/day from 0-90 days. Chacon et al (1970) reported that between 103-197 days, the average daily gains of Barbados Blackbelly sheep were 149 g.
Growth rate of animals is attributed to the genetic potential of the animals, the standard of animal management and the quality of feed (both pasture and supplemental feed), and most importantly the environmental conditions. During the duration of the study, the variation in seasonal conditions, which may be attributed to the El Nino phenomena (long dry season) which had a negative impact on pasture production over the past four years, may have contributed to the weight gains reported by the NARI Livestock Farm being lower than those cited by other researchers.
Birth types were different (P < 0.05) for single and twin births between the two breeds. The percentage single births were significantly higher for the crossbred sheep than the Barbados Blackbelly breed types. This trend was reversed when comparison was made for twin births as shown in Figure.4. The pure bred animals had a significantly higher percentage of twin births than the crossbred animals. Comparisons for triplets and quadruplets were similar between the two breed types.
|Figure 4. Birth types expressed as a percentage for the Barbados Blackbelly and crossbred sheep|
Mannasmith et al (1991) reported litter size by sheep breeds and they indicated that for the Barbados Blackbelly breed, the birth distributions for single were 30%, twins 49%, triplets 18% and quadruplets 2%. Patterson (1991), however, reported that the birth type distribution for the Barbados Blackbelly breed was singles 48.8%, twins 40.8%, triplets 8.8% and quadruplets 1.7%, while for the crossbred animals the birth distribution was single births 63%, twins 33.5%, triplets 3% and quadruplets 0.5%. The data obtained at the NARI Livestock Farm compared favourably with those obtained by the other researchers, indicating that the Barbados Blackbelly breed is more prolific than the crossbreed animals (Figure 4).
The percentage single births were higher for the dams between 1-3 years old, but decreased for the dams aged 3 to >5 years old. The frequency of twin births was higher in older dams 3 to >5 years old when compared to dams 1-3 years old. The frequency of triplets was negligible at the different age ranges as shown in Figure 5, but, increased as the animals became older. Quadruplets were only observed in dams older than 4 years.
|Figure 5. Percentage birth type for dams at different age range|
The older dams, those between 3 and 5 years of age, produced a higher percentage of twin and triple births than the younger dams. Therefore a fledging sheep production entity should seek to rapidly increase its flock for marketing purposes by using young dams for breeding after which the selection of older dams for the breeding flock would guarantee a higher lamb crop.
The percentages pre-wean (Birth - 90 Days) and post- wean (> 90 days) mortality at NARI Livestock Farm are shown in Figure 6. The pre-weaning mortality was significantly (P < 0.05) higher than post-weaning mortality.
|Figure 6. The pre and post- weaning mortality of sheep at NARI livestock farm|
Martinez (1983) and Nurse et al (1983) reported mortality percentages for Barbados Blackbelly of 19.1 and 43.0 at birth to 90 days and from birth to 120 days, respectively. These figures are higher than those reported in this study (Figure 6). This may indicate that the environment created for the animals at NARI Livestock Farm was more favourable than that reported by Martinez (1983) and Nurse et al (1983). Efforts would however have to be made to reduce the mortality of the lambs at the NARI Livestock Farm.
The causes of variation of sheep production parameters are numerous, and include breed differences, nutrition, litter size, crossbreeding and genotype-environment interaction.
The productive indices derived from this study give some insights into the production performances of the Barbados Blackbelly and the crossbred sheep at NARI Livestock Farm.
The production data obtained were superior to those of previous studies carried out in Guyana, and compare favourably with other studies conducted in the Americas and the Caribbean.
The authors wish to express our appreciation of the kindness of Mr C R L Paul (Biometrician) in analyzing our data from the investigation.
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Received 8 October 2005; Accepted 6 February 2006; Published 12 April 2006