Evaluation de la consommation d'un troupeau de chèvres laitières sur parcours forestier — Méthode d'observation directe des coups de dents — Méthode du marqueur oxyde de chrome

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Abstract
Two methods for estimating the DM intake of goats grazing on rangeland were studied. They were simultaneously applied to 5 Alpine Chamoisee dairy goats for 6 days. The animals grazed a white oak brushwood (Quercus pubescens) on the clacareous plateau near the Ardeche river (Southern France). During the study (July 25 to August 10, 1983) the flock took 82 p. 100 of its energy requirements on the rangeland. The first method of estimation was based on the observation of grazing behavior and the rate of biting. An evaluation of the "weight of bites" and that for each species consumed allowed to estimate the dry matter intake during the grazing period. In that study, evaluation of the weight of bites on the ligneous species (75 p. 100 of the diet: see table 1) used a particular method: distribution of branches and accurate weighing on the grazing site. The second method used chromic oxide (Cr2O3) as a marker incorporated to pelleted lucerne hay. The marker was ingested without losses or refusals. The method used to determine the Cr2O3 concentration was very rapid and precise: titration after an oxidation with a mixture of nitric and perchloric acids. A graph of the diurnal excretion cycle of chromic oxide by goats grazing a rangeland was established (fig. 2). Feed intake was 2.61 and 2.16 kg DM/animal/day, respectively for the direct biting observation and for the chromic oxide method. The results show that a large utilization of rangelands bound to a low nutritional value of the ligneous diet (0.59 MFU/kg DM) leads to a high daily feed intake (nearly 2.7 kg DM/day for an animal of 60 kg LW). The application of these methods shows the existence of gaps related to lack a knowledge about the treated topic (true digestibility of the diet, supplement of maintenance requirements due to grazing activity). Discussion of the problems encountered emphasizes the necessity of carrying out further research on this kind of pasture.