The influence of management routines on endocrine systems involved in the control of lactation in dairy cattle
1996
Samuelsson, B. (SLU, Uppsala (Sweden). Inst. foer Husdjurens Utfodring och Vaard)
The aim of this thesis was to investigate patterns in the release of certain lactational and metabolic hormones, with regard to their relations to production, when different milking and feeding routines were applied in cattle. A routine with simultaneous milking and feeding resulted in a higher milk production and higher milk flow compared with a routine where the cows were fed after the milking was completed, an effect that was most pronounced during the morning milking. Hormonal changes associated with simultaneous milking and feeding included a potentiated release of prolactin and somatostatin and a diminished release of gastrin. In lactating dairy cows feed deprivation resulted in severely reduced milk production and major changes in milk composition. These changes in production were accompanied by increased basal as well as milking related plasma levels of cortisol and growth hormone, reduced basal levels of prolactin, gastrin and CCK and reduced milking related levels of prolactin and somatostatin. These hormonal adaptations are proposed to be important for the survival of both mother and offspring in a situation with lack of nutrients. In dairy cows the calf's suckling was more efficient than the milking machine in stimulating the release of oxytocin. In calves oxytocin was released following feeding irrespective of whether the calves were suckling or ingesting the milk from a bucket, but the release was bigger in the suckling calves. The importance of the stimulated release of oxytocin for future milk production in suckling calves requires further investigation. A postitive relationship was found between the plasma somatostatin level and the milk fat content/ milk fat yield. The involvement of somatostatin in the regulation of milk fat synthesis is a subject for future studies.
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