Détermination des principaux paramètres pour le contrôle de la reproduction chez la chèvre naine (Capra hircus) de la zone de forêt humide du Cameroun

Abstract

Studies have been carried out to improve knowledge and control of goat reproduction in traditional small ruminant (sheep and goat) breeding systems in the forest area of Cameroon (Central, Southern and Eastern regions). Indeed, the rational management of reproduction is non-existent and the constraints to production are numerous and poorly documented. Due to the ever-increasing national and sub-regional demand for dwarf goats, particular attention is being paid to efforts to improve the production and productivity of these livestock systems. In a first phase of the study, a survey was conducted among 400 livestock farmers in this forest area to characterize traditional livestock systems and identify the constraints that hinder efforts to improve the production and productivity of these farms. Experimental studies on reproductive parameters were then carried out in stations on several generations of goats in the Centre region. The determination of plasma progesterone levels (the main gestational hormone) in the jugular blood of goats collected at several stages of their reproductive life (at weaning at 3 months, in doe animals less than one year old, before and during breeding, during gestation, after farrowing, etc.) has made it possible to determine more precisely the main reproductive parameters of the dwarf goat. The main parameters determined are: age at puberty, characteristics of estrus, anoestrus, estrian cycles (normal and short), gestation (single and multiple), calving interval. Similarly, the local requirements for the natural induction and synchronization of estrus in dwarf goats have been determined. Finally, the effect of food availability on the seasonal variation in reproductive activity in goats was determined. These main parameters had not yet been the subject of any previous studies in dwarf goats. The survey results revealed that in traditional goat farming systems, there is a unique village herd consisting of groups of animals in which males and females of all ages are together. This herd builds up spontaneously and gradually every day and breaks up into small groups occasionally at the end of the day. No follow-up is observed in the herd that travels all day long (divagation). Without sanitary control, it is under permanent threat from seasonal epizootics of Small Ruminant Plague (PPR), snake bites, various predators and other environmental scourges. Without suitable habitat, it is exposed to frequent theft. The details and information on the production and reproduction parameters of this herd are approximate. The struggle is free riding and the prolificity is very high. Births gather around two peaks (March-June and October-January) during the year. Mortality is high, especially among children under one year of age (>30%) and abortion cases are frequent, especially in the dry season, due to the low availability of food and the toxicity of some foods consumed in the wild. In addition, the inbreeding problem does not arise due to frequent renewal. The major constraints in addition to PPR and parasitosis are poor husbandry and the lack of reproductive control (free riding). The results of experimental studies in the station made it possible to describe and characterize sexual cycles in the dwarf goat, to determine their duration (20 ± 1 days), the different phases and particularities, and to identify the specificities with regard to reproduction in sheep. Mean age and weight at female puberty were determined and the values specified (10 ± 1.4 months and 13.1 ± 0.6 kg, respectively).Hormonal profiles (plasma progesterone) at different physiological stages have been established. They made it possible to determine with more precision the characteristics of the estrus (average duration 2.57 ± 0.49 days), the postpartum anestrus (average duration ≥ 60 days), the average calving interval (≥ 7 months), the gestation period (145 ± 2 days on average). Some parameters that characterize twinning have been identified (plasma P4 level >13 ng/ml between the 20th and 140th days of gestation; any weight variation ≥1,5 kg over a period of 30 consecutive days during the first 2 months of gestation). A threshold weight (12 kg) has been defined for ovarian activity, regardless of age. The conditions required for induction, and synchronization of estrus by male effect have been specified (strict isolation of females from males, then reintroduction of males after a minimum period of three weeks, with a male/female ratio ≥ 5-10%). It has been shown that the improvement in food availability in a herd left free during the year allowed for three calving periods during the year (December-February, March-May and September-November) instead of the two observed in an uncontrolled traditional environment. Finally, practical advice on the rational management of livestock farms with a view to making them more competitive was provided. It is therefore recommended to develop well-secured habitats (sheepfold), to put the chevrette in reproduction only from 12 months of age, or when it has reached a minimum weight of 13 kg. Reproduction must also be carried out according to the food availability evaluated five months before the control. Weight monitoring and body condition score should be monthly, so that the type of gestation (single or multiple) can be determined and the dietary needs of the pregnant goat can be adjusted according to the type of gestation.