A few features of suckler hardy breeds

Les bovins des races rustiques allaitantes ont des caractéristiques physiologiques qui leur permettent de s’adapter à des conditions difficiles et d’y maintenir assez bien leurs productions. Là où les ressources alimentaires sont limitées, ils maintiennent mieux leur développement squelettique au-delà du sevrage que ceux de race à viande à fort potentiel de croissance musculaire. De même, les femelles (au moins de certaines races rustiques) soutiennent mieux leur production laitière et leur reproduction lorsqu’elles font appel à leurs réserves corporelles dans les toutes premières années de vie productive. Cela pourrait être attribué à une maturité plus précoce, accompagnée d’une quantité plus importante de tissu adipeux aisément mobilisable et de besoins de croissance devenus moins élevés. L’aptitude à l’allaitement des vaches Aubrac et surtout des vaches Salers est élevée. Elles sont capables de vêler plus tôt au cours de l’hivernage que les vaches des races à viande, ont un intervalle entre le premier et second vêlage plus réduit (anoestrus plus court, durée de gestation plus faible). La capacité d’ingestion de fourrages grossiers est satisfaisante chez les bovins de races rustiques, mais inférieure à celle de types plus laitiers. Les races rustiques présentent aussi d’autre capacités d’adaptations physiologiques et comportementales à l’environnement (climat, pâturages), qu’il conviendrait de préciser.
The cattle of hardy breeds have special physiological characteristics that enable them to adapt to difficult environments and to maintain their productivity to some extent. Some results obtained more particularly at the INRA experimental farms located in the highlands of Auvergne prove these abilities. In areas with restricted food resources, hardy breeds seem able to maintain during the rearing period better growth, espacially of their skeleton (height of the withers), than beef breeds with high muscular potential. This could result from smaller adult size and/or earlier maturity. Like other types of cows, those of hardy breeds mobilize their body reserves during food shortage and then recover them during grazing. Their special feature seems to lie in their ability to maintain their milk yield and reproduction better than beef breeeds do, when they use their reserves in the first years of productive life. This could also be attributed to earlier maturity, going with a greater quantity of adipose tissue, which is easy to mobilize, and with reduced growth requirements. Most females of hardy breeds are sexually earlier maturing than beef breeds. They are also able to calve earlier in season, even in difficult food conditions. They maintain better a short interval between first and second calving, mainly because of a shorter post-calving anoestrus and also a shorter gestation period. It is also in these extreme conditions (Ranch ITEB-INRA, 1972-76) that Aubrac and Salers cows gave better overall reproductive performances than Charolais and Limousin ones, espacially during their two first years of production. The suckling ability of the Aubrac and above all of the Salers cows rank them among the best French suckling cows, mainly due to their dairy origin. It is fully expressed among young cows, and milk production of young Salers cows is less reduced in difficult food conditions than the one of French specialized beef cows. This production ensures their calves satisfactory live weight gain with limited complementary concentrate expenditure, in particular since it maintains well at the end of suckling period. The intake capacity of roughages is satisfactory among cattle of hardy breeds but remains lower than in specialized dairy breeds. Hardy breeds seem to have other assets, espacially in their behavioural adaptations to difficult pastures (travels, eating rate), which should be studied. The extreme limits of use of hardy breeds should also be studied, especially females’capacity to mobilize their body reserves, with regard to reproduction.