226 research outputs found
A short-term divergent selection for resistance to Teladorsagia circumcincta in Romanov sheep using natural or artificial challenge
This experiment was conducted to assess the efficiency
of selection on the basis of response to artificial challenges in order to
breed sheep resistant to natural infection. A short-term divergent selection
process was designed to estimate the genetic parameters of these two traits.
Two flocks, including 100 Romanov ram lambs each, were challenged in 1990 when they
were 6 months old. One flock received three artificial infections with 20 000
third-stage Teladorsagia circumcincta larvae, at intervals of 7 weeks. Faecal egg counts (FEC) were
performed on Days 22, 25 and 28 post infection (p.i.) and the animals were
drenched on Day 28Â p.i. The other flock was grazed for 5 months on a pasture
contaminated with the same species. Faecal samples were taken from the lambs
at similar ages.
About 5 rams with the lowest FEC and 5 with the highest
FEC were selected in each flock and mated with unselected ewes. Their
offspring (200Â animals) were challenged in 1992, half in the same way as
their sires, and the other half by the other method.
Because of a drought in
the summer of 1990, it was necessary to repeat part of the experiment, and
in 1992 the 5 and 8 rams with the lowest and highest FEC, respectively, were
selected from the offspring challenged on the pasture in 1992 and were mated
with unselected ewes. Their progeny (about 80Â animals) were challenged in
1994, half by natural infection, half by artificial infection.
The mean FEC
of the flock increased from the first to the third artificial
infection.
The
natural infection was highly variable in different years, reflecting the
difficulty of assessing resistance using this mode of challenge. Genetic
parameters were estimated using animal models and REML solutions. The
repeatabilities of the FEC following artificial and natural infection were 0.49
and 0.70 respectively within a period of one week, and 0.22 and 0.41
respectively for periods separated by intervals of 7 weeks; the
heritabilities of the single egg count were 0.22 and 0.38 respectively. The
genetic correlation was 0.87: the FEC recorded under natural or artificial
infection appear to depend on the same genetic potential
Quels animaux les agriculteurs ont-ils besoin de systèmes mixtes tropicaux dans les Caraïbes ?
In the Global South, improvement of agricultural outputs is eagerly awaited. While by 2050, its population will double areas devoted to agriculture will decrease exacerbating undernutrition of the poor. Unfortunately, the demand for fresh locally-produced meat products is not satisfied yet in the tropics. So, efficiency in animal productions is essential to allow coverage of protein nutritional needs of people, both in quality and quantity. In the Caribbean territories mixed farming systems are the most common farming systems (about 80%) and can constitute a solution to reach food sovereignty in such limited and isolated spaces. Lessons to be learned from these systems involve improving animal performance while respecting the natural balance with environment and maintaining the multi-functionality of plants and animals. Firstly, the natural (or selected) comfort zone of animal and plants must fit with the farm conditions, insuring thereby animal survival and welfare. Enhancement of adaptation to stresses (biotic, abiotic and socio- economic) in species or animal genotypes is a key element implying their equilibrium with the farm environment. This approach underpins for the farmer an integrated management of animal health, nutrition, genetics, reproduction, in close relationship with other compartments of the farming system. Secondly, animal adaptation may be completed by resilience ability within systems. Animals have to produce although facing stresses. Finally, the animal must be efficient that is to say must reconcile physiological functions of production, reproduction with adaptation functions. This optimization leads to decreased inputs and to overall efficiency of mixed farming systems at the end. The aim of the breeder is to choose the animal producing the best balance between output-reproduction-adaptation, at the individual or the flock scale combining genetic and physiological diversity. The underlying idea is to give to humans and animals their right place in the food chain taking into account the farmers? skills and wills. This idea is included in the agroecological approach and may give guidelines for food sovereignty worldwide
Agricultural co-conception in Guadeloupe for shared innovations
International audienc
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