|Breed Characterisation, including on-farm surveys||| Print ||
Characterisation means the distillation of all knowledge which contributes to the reliable prediction of genetic performance of an animal genetic resource in a defined environment and provides a basis for distinguishing between different AnGR and for assessing available diversity. Characterisation thus includes a clear definition of the genetic attributes of an animal genetic resource and the environments to which it is adapted or known to be partially or not adapted to at all. It should include the population size of the animal genetic resource, its physical description, adaptations, uses, prevalent breeding systems, population trends, predominant production systems, description of environment in which it is predominantly found, indications of performance levels (milk, meat, growth, reproduction, egg, fibre, traction etc.), genetic parameters of the performance traits and information on genetic distinctiveness of the animal genetic resource and its evolutionary relationship with other genetic resources in the species [Oromiya ILRI and FAO/ILRI Zimbabwe Report]; [Yak-ILRI].
Sources of phenotypic data include: published and unpublished or grey literature; short-term on-farm (rapid) surveys; short- to long-term on-farm studies; and on-station studies, including laboratory analyses of samples collected on-farm or on-station. The on-farm or on-station samples may include use of biochemical or molecular (e.g. DNA) techniques to quantify genetic diversity, determine distinctiveness of breeds and/or measure genetic distances among populations (see Section 3, of this module) [CS 1.10 by Okomo]; [CS 1.11 by Gwakisa]; [CS 1.38 by Ofelia]. It must be noted that molecular characterisation on its own is not adequate. Characterisation must therefore be presented and undertaken in a broader context of utilisation.
A thorough review of, and synthesis of data from, the (conventional and grey) literature should be a first step in any breed characterisation work. Not only does this provide an indication of performance under specific environmental conditions, but it also can be a useful source of anecdotal information and is invaluable for the formulation of hypotheses that can be tested in subsequent more detailed characterisation studies. It is also possible to identify, from the literature, multiple trials which have the same basic design and experimental protocol and which therefore qualify for meta-analysis. This is particularly useful in breed characterisation: it provides opportunity to include characterisation data which may not have been published simply because they did not meet the expectations of the researcher (e.g. they were 'not significant').
In the developed world, livestock recording schemes provide a continuous source of data for monitoring trends in the industry, including improved understanding of breeds and the production system. Unfortunately, such structures are not available in most developing countries. Here, designed, rapid, on-farm surveys can be useful for collecting basic (macro-level) information on production systems, population statistics of breeds, physical (or descriptive) characteristics and performance levels-milk production, fertility, mortality, longevity, growth, meat production etc. [Oromiya ILRI]. While rapid surveys can provide indicative figures (see Module 4, Section 7), reliable compilation of data on production systems and particularly on phenotypic chara cteristics of a breed can only be obtained from more detailed on-farm studies. Such studies may involve whole flock or village as basic experimental units and require collection of data over relatively long periods of time, i.e. monitoring. On-farm studies can be used to collect such information as lactation length, parturition interval, growth rates, off takes or, if done over sufficiently long periods, estimates of herd/flock structures and population trends essential for assessing rates of decline and identifying causes of such declines [Indian case - National Bureau of Animal Genetic Resources-NBAGR].
Physical description of a breed should focus on characters which, in the view of keepers of the breed and local experts, facilitate identification of animals as being members of the breed or strain. These should include coat colour (common and/or special colours and colour combinations); horn shape and size; and presence or absence of hair/wool, hump (including relative size), tail type, dewlap and other specific visible characteristics Physical or morphological characteristics can be particularly useful in the classification of populations/strains/breeds within a species (see photos of Indian cattle breeds). FARM-Africa (1996) reported work in which various measurements-both qualitative (e.g. presence or absence of beard, wattles, ruff; and ear form, horn orientation, coat colour etc.) and quantitative (e.g. height, body length, chest girth, body weight, ear length etc.)-were subjected to multivariate analyses to classify heterogeneous, previously unclassified indigenous Ethiopian goat populations into taxonomically distinct, relatively similar entities or groups. This approach is recommended as a first step in the classification of heterogeneous previously uncharacterised populations. [FARM-Africa-ILRI Goat Survey].
As part of surveys, farmers should be interviewed to determine the extent of 'indigenous' knowledge (see Section 5, this module) on common diseases, whether or not the breed is thought to be tolerant of/resistant to some diseases and what evidence (indicators) farmers have to support such claims [Ndama]. Farmers should also be asked to indicate whether they believe the breed has any other adaptive characteristics (e.g. tolerance of excessive heat, humidity etc.). In addition, farmers should be asked to rank current uses of the breed (e.g. traction, meat, milk, fibre etc.) and to indicate any outstanding characteristics of the breed (e.g. exceptional prolificacy, growth rate etc.)
It is also possible to design on-farm studies to estimate genetic parameters (see Section 3, this module) of certain traits and to provide an indication of specific adaptive attributes, e.g. heat tolerance or disease resistance. Compared to on-station characterisation, on-farm studies are less precise. However, they have the advantage of providing accurate indications of performance levels as measured under farm conditions in which the animals (are expected to) live and produce.
The advantage of on-station breed characterisation (and evaluation) is that the controlled experimental conditions ensure a high precision. Special adaptive attributes, which are difficult to measure at field level, are also generally best studied on-station. As has been stated, the high precision to which on-station studies can be undertaken make them appealing for breed evaluation despite the fact that they are less accurate as indicators of performance in farmers' flocks/herds. Indeed, in the presence of genotype × environment interaction, conclusions drawn from on-station characterisation could be misleading.
The objective of obtaining population estimates is to assess current population size for planning and to determine population trends to establish whether or not populations of certain breeds are declining. When declining trends are detected, investigations into possible reasons for decline can be initiated to identify appropriate corrective actions.
Current sources of livestock population statistics in developing countries include periodic national livestock censuses; occasional estimates by relevant government ministries; estimates by national scientists; and estimates by such agencies as FAO, NGOs etc. It is also possible to obtain indicative population figures and relative distribution of different livestock species from aerial photographs with or without application of GIS (geographic information systems). The major shortcoming of most of these methods is that they tend to provide only species level statistics and not breed/strain level information. Thus, the general situation is that available statistics are on numbers of cattle, sheep, goats, pigs, poultry etc. in a country but hardly any information on the composition of these species. Even where such statistics are broken down into breeds, their accuracy is doubtful as the data are usually collected and compiled by people who might not be experts in breed identification, hence may not accurately differentiate between the different breeds. Such data are not useful for monitoring the status of within-species diversity.
To obtain breed level statistics, it is not practical to count animals over a whole country or region. A sampling scheme can be developed whereby total counts are obtained on randomly chosen sample areas [ILRI-SDP]. However, on the basis of known distributions of animals in the particular area of a country, sampling can be stratified according to breed and animal density. Similarly, the size and number of blocks, quadrants or strip transects to be used can be determined by several factors, including the heterogeneity of the area in terms of breeds/types [FAO/ILRI Zimbabwe Report]. The purpose of these surveys is to quantify the proportionate composition of animal populations by breeds and species and thus to estimate total population size of each breed. Where national animal population statistics are available for species, such as cattle, sheep and goats, estimated proportionate compositions (by region within country) can be used to partition the national or regional figures into breeds/types. Key statistics to be obtained during such a survey are number of herds/flocks in the sample area, their sizes and breed composition by species. In some countries, species level animal statistics at (administrative) regional level may already be accurate enough so that the main task is to partition these into breeds/strains.
Physical counts necessitating visits to localities in which these breeds are found can be combined with collection of data on factors which characterise the production systems. Longitudinal surveys can be undertaken to provide a time series of population figures over years [Oromiya and FAO/ILRI Zimbabwe Report].
Data on the physical environment can be obtained from local government stations, where available. These include climatic data (rainfall amount and distribution, monthly temperature figures, humidity etc.), vegetation and incidences of diseases. Where these are not already available, collection of such data can be in-built into the characterisation protocol. Indeed, even where facilities already exist for collection of these data, additional steps should be taken to ensure that an acceptable level of reliability is achieved. Participatory exercises such as focus group discussions, farmer workshops and phenotypic rankings by farmers are quite illuminating and therefore should be undertaken, in addition to the conventional questionnaire-based surveys (Wurzinger et al. 2005).
Detailed description of the production system should include a statement on the management system (sedentary, transhumant, nomadic etc.), housing, feeding practices and nutritive value of feeds by seasons.
|Last Updated on Wednesday, 02 November 2011 13:26|