Management of beef and dairy herd replacement
Résumé
Cattle herd replacement management should be revisited because of the combined evolutions of animal type, size, and level of production, and of the evolutions of the economic and environmental context. This presentation will deal with both dairy and beef productions. In these two cases, the strategy of herd replacement has to be considered not only at the animal scale (rearing strategies and optimal lifespan duration), but also at the herd and farm levels according to the various objectives assigned to sustainable livestock systems. During this presentation, an update of the main effects of heifers rearing strategies on subsequent performances will be given, with focuses on the effects of feeding strategies on puberty attainment, fertility of heifers, production and reproduction performances when adults, calving difficulties, longevity of the animals and carcass characteristics at slaughter. Interactions with breed maturity will be highlighted. In the second part, considerations on the sustainability of the different ways of production will be developed, taking into account the various dimensions of sustainability. A special grazer role is generally assigned to heifers, which are used to make the most of the least productive pastures. Consequently they have a positive environmental impacts which could vary with breed and age. Short- and/or long-time perspectives will be included. This presentation will mainly focus on some common production systems, such as intensive Holstein dairy production or Charolais beef herd production. However, attention will be paid on some alternative production systems (i.e. organic farming for example) or on some other systems that are greatly influenced by the characteristics of their land (mountains or Mediterranean herds for example).