Facteurs influençant le profil métanologie des vaches laitières.

Forty Holstein dairy cows were used to determine the effects of forage feeding system, season and stage of lactation on some blood parameters. Blood urea nitrogen was higher for cows consuming higher levels of crude protein and particularly for the ones on pasture. Hemoglobin and packed cell volume values were correlated with the level of crude protein intake and stage of lactation. Lower values of these parameters were observed with lower crude protein intake and in early lactation. Serum levels of albumin, calcium, inorganic phosphorus, sodium and potassium were not affected either by forage system, season or stage of lactation. Serum magnesium level was lower for forage system containing corn silage. Blood glucose was lower for cows in early lactation but was not affected by feeding systems during winter. Cows on pasture had higher blood glucose levels. Lower total protein concentration in blood was observed between 90 and 180 days of lactation as a result of lower gammaglobulins. Blood parameters are good indicators of nitrogen and energy nutritional status of dairy cows. However, blood mineral concentrations are not related to the level of mineral intake of animals.