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La conduite de la plupart des troupeaux de vaches allaitantes, basée sur l’utilisation de l’herbe pâturée ou conservée, est déjà extensive. Modifier la date de vêlage permet d’adapter la conduite du troupeau aux ressources fourragères. Lorsque la production d’herbe est suffisante pour satisfaire les besoins alimentaires du couple vache-veau, faire vêler les vaches au début de la période de végétation accroît la part de l’herbe pâturée dans l’alimentation du troupeau et limite ainsi les besoins en fourrages récoltés. Inversement, si la production des prairies est insuffisante, les vaches peuvent vêler pendant l’hivernage et être taries au pâturage. Leurs performances de reproduction sont alors préservées. Dans ces conditions plus difficiles, la durée de lactation peut être raccourcie, ce qui dissocie les besoins de la mère et du jeune. Les troupeaux de bovins allaitants peuvent contribuer à l’entretien des espaces herbagers avec des ajustements de la conduite du pâturage, par exemple en allongeant la durée de pâturage au-delà de la période de végétation active. Une augmentation du chargement à certaines périodes clés limite l’extension de végétations indésirables. Les races adaptées aux conditions extensives se caractérisent par leurs bonnes aptitudes maternelles et leur aptitude à mobiliser puis reconstituer leurs réserves corporelles et à ingérer des fourrages grossiers., Suckler herd management, based on the maximal use of grazed or harvested grass, is already extensive in most situations. Appropriate change of calving date fits herd management to seasonal variations in food supply, When grass production is sufficient, spring calving increases the proportion of grazed grass in the annual feed and reduces the need for harvested forages. If good forages are available for only a short time, the lactation period can also be shortened, which splits up the requirements of the dam and the calf. On the other hand, when grass production is low and/for grassland of poor quality, cows can calve in early wintering and be dried off when turned out at pasture. Their reproductive performance is thus maintained at an acceptable level. Suckler herds can contribute to the control and the maintenance of vegetation, for example by lengthening the grazing season far beyond the period of active vegetation growth. An increase in stocking rate at certain key periods can be used to control undesirable species efficiently. The genotypes adapted to extensive management conditions are characterized by their good maternal abilities, their relatively high intake capacity on roughages and low quality grass, and their ability to mobilise then recover body reserves.

We developed a grazing index that objectively defines livestock operations based on the proportion of grass in the annual diet of the dairy cow herds. Data were collected from 102 cattle farms, and the results show that, in general, levels of grazing were higher in less intensive farming systems. Simultaneously, higher levels of grazing were associated with a decrease in the number of veterinary visits (notably to treat digestive and metabolic issues), the overall consumption of medications (notably those involved in curative treatments), and the frequency of severe hoof-related lameness. Animal lifespan and perinatal mortality were, respectively, positively and negatively correlated with higher levels of grazing. Some of the limits to interpreting these data are discussed.

Crop residues are important for livestock feed and nutrient cycling among many other functions on smallholder farming systems of sub-Saharan Africa. The objective of this study was to assess differences in resource endowment, crop productivity and crop residue management in selected sites in southern Africa. Three sites were selected along a gradient of intensification of crop production; Murehwa, Zimbabwe and Ruaca and Gorongosa, central Mozambique. Murehwa and Ruaca have mixed crop-livestock systems with more intensive crop production in Murehwa. Gorongosa is predominantly crop based with small livestock that do not impact on crop production. A combination of land size and cattle ownership was the major attribute that defined wealth status among farmers in mixed crop-livestock systems whereas land size and labor availability were important under crop-based extensification systems. Farm systems were more diverse where livestock was more important. The wealthiest farmers (resource group-RG1) in Murehwa produced an average of 2.2 t ha-1 maize crop residues, and productivity decreased with decrease in resource ownership with the poorest (RG4) achieving only 0.8 t ha-1. In Ruaca 1.3 and 0.5 t ha-1 was produced by RG1 and RG4 respectively, whereas in Gorongosa 0.4 and 0.2 t ha-1 was produced by RG1 and RG4. These crop residues are insufficient to achieve the minimum threshold of soil cover (30%) required for the practice of conservation agriculture. However, they can provide sufficient feed to sustain livestock of RG1 farmers in Murehwa for 63 days and 54 days for RG2 farmers. In Ruaca, they can feed cattle for 37 days for RG1 and 17 days for RG2 farmers. The product of livestock × population density determined the extent and manner in which crop residues are used. The population density limited the extent of the grazing area, increased grazing frequency and reduced the grazing quality leading to the need to supplement animal feed with crop residues. Farmers preferentially allocate crop residues to livestock where labor is available. The crop residues fed to animals allow farmers to increase manure quantity and quality which explains the major differences in crop productivity between the different resource groups. In the absence of cattle, crop residues are burned before the cropping season to facilitate land clearance. In conclusion, land size, cattle ownership and labor availability largely define the intensity of crop production and the fate of crop residues on smallholder farms in southern Africa.

International audience; Question: How do functional types respond to contrasting levels of herbage use in temperate and fertile grasslands? Location: Central France (3 degrees 1' E, 45 degrees 43' N), 870 m a.s.l. Methods: Community structure and the traits of dominant plant species were evaluated after 12 years of contrasted grazing and mowing regimes in a grazing trial, comparing three levels of herbage use (high, medium and low). Results and Conclusions: Of 22 measured traits (including leaf traits, shoot morphology and composition, phenology), seven were significantly affected by the herbage use treatment. A decline in herbage use reduced individual leaf mass, specific leaf area and shoot digestibility, but increased leaf C and dry matter contents. Plants were taller, produced larger seeds and flowered later under low than high herbage use. Nine plant functional response types were identified by multivariate optimization analysis; they were based on four optimal traits: leaf dry matter content, individual leaf area, mature plant height and time of flowering. In the high-use plots, two short and early flowering types were co-dominant, one competitive. grazing-tolerant and moderately grazing-avoiding, and one grazing-avoiding but not -tolerant. Low-use plots were dominated by one type, neither hardly grazing-avoiding C 0 nor grazing-tolerant, but strongly competitive for light.