Capacity of high milk yielding goats for utilizing cultivated pasture
Résumé
Nine experiments with 120 Alpine goats lasting from 3 months to 3 years have been carried out at the experimental station of Le Pradel, South-eastern France on the management of grazing high yielding goats (1000–1100 kg milk/goat/year), the continuous or rotational grazing, the early or late turn-out, and the strategy of concentrate supply so as to get optimal milk production and composition. Goats grazed from March to November on cultivated pastures composed of 5.2 ha of hybrid or English rye-grass and orchard grass, 3.6 ha tall fescue and 6 ha alfalfa plots. During 3 years and 100 days, respectively, the 2 first experiments compared 2 goat managements: indoors exclusively and rotational grazing by giving complementary hay to grazing group when available grass was insufficient, particularly in winter and in summer or during rainy days. The supplies of dehydrated alfalfa and concentrate were identical in the 2 groups. Grazing covered more than 50% of dietary requirements of goats. The milk production of indoors and the grazing groups were similar but the milk fat percentage in the grazing group tended to be slightly higher. During 100 days in spring, a 3rd experiment compared a rotational grazing on 13 plots with a stocking rate varying from 140 to 260 goats/ha and a grazing duration of 1–4 days per plot, and a continuous grazing on a same pasture with a stocking rate of 35–60 goats, with a same daily quantity of concentrate per day in the 2 groups. No significant difference on milk production and composition has been observed on goats managed with these two grazing methods. During a 4th experiment, a better milk production was observed with an early turn-out (around 1st March) in comparison with a later turn-out frequently adopted in this region around 1st April. The early turn-out required a longer transition from winter diet to fresh grass based diet. It allowed a better utilization of grass at the start of grazing and a better grass re-growth. Four experiments compared various levels of concentrate supplies in grazing goats. The higher concentrate supply increased milk production in a limited way, particularly above 0.8 kg of concentrate/day/goat and with grass of high dietary value when milk composition was very little influenced. From the results of a 9th experiment and the 8 previous experiments where the concentrate composition varied, the nature of nitrogen sources (protein highly or little degradable in the rumen) influenced more strongly the goat milk production than the type of energy sources (starch vs. fiber + fat). A high proportion of little degradable protein in the concentrate raised the milk production without modifying milk composition. Increased fiber and fat in the concentrate raised milk fat percentage in comparison with a concentrate rich in starch. These experiments showed that an annual production of 1000–1100 kg of milk can be obtained with a feeding system based on cultivated grazing which covers more than 50% of dietary requirements, if this level of production is allowed by the genetic potential of the goats, if daily grazing duration is sufficient (more than 10 h/day), if the supplies of conserved fodders distributed at the trough are very limited or withdrawn, if concentrate supplies are limited to 0.8–1 kg/goat/day, and if animal grazing and pastures are managed by goat farmers by precise daily observations and controls on pastures.