The objectives of this study were to investigate the effects of exogenous somatotropin on growth performance and carcass traits and on concentrations of somatotropin (ST), IGF-I, insulin, glucagon, free fatty acids (FFA), and glucose in plasma of finishing Simmental beef heifers. Three treatment groups, which included 12 heifers each, received a subcutaneous injection of a slowly released recombinant bovine somatotropin (rbST) at two doses (320 and 640 mg, respectively) or a placebo at 2-wk intervals. Treatments began at an average BW of 286 kg and continued until the animals were slaughtered at approximately 520 kg. Heifers had ad libitum access to corn silage and received 1.8 kg/d of concentrate. A before-feeding blood sample was collected from the jugular vein immediately before and 1 wk after each injection during treatment. Treatment tended to increase ADG and to reduce energy consumption per kilogram of gain, whereas feed and energy intake were not altered. Dressing percentage and conformation did not seem to be affected by treatment. Treatment led to a dose-dependent reduction of fat tissue in carcass as well as in kidney fat and to a simultaneous increase of lean tissue (P < .05). Furthermore, treatment caused moderate increases of ST in both treated groups, whereas IGF-I concentrations increased markedly soon after the beginning of the treatment. Insulin and FFA concentrations were elevated in treated groups compared with controls. Glucagon concentrations were not altered by treatment. Effects on growth performance and carcass characteristics are discussed in view of metabolic and endocrine changes.

bST, a milk production-enhancing compound not yet registered in the EG and the USA, has been evaluated as safe for the consumer. Nevertheless, actual discussions include a possible ban of applications; therefore, effective measures of control are demanded. The evaluation of bST plus IGF-I in blood only allows a monitoring of bST treatment. Under the condition of two blood samplings from each cow with a 7-day interval and the favorable experimental design (1. sampling rigorous on days 4 or 6 after injection of a bST depot preparation), an efficiency of 96% correct evaluations could be obtained; under field conditions, despite analytical efforts, about 20% false estimations must be taken into account. There is no means of monitoring milk and other products of cows treated with bST, hence analytical measures for the control of imports seems to be useless.

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Zusammenfassung 32 Fleckviehkühe wurden nach Milchmenge, Milchfettgehalt, Laktations‐ und Trächtigkeitsstadium sowie Zahl der Laktationen in 2 Gruppen eingeteilt. Bei Carotin‐ und Vitamin‐A‐armen Grundfutter (etwa 130 mg β‐Carotin/Tier und Tag) erhielt eine Gruppe pro Tier täglich 116 000 I. E. Vitamin A, die andere 340 mg β‐Carotin, jeweils über ein Mineralfutter verabreicht. Nach einer 4monatigen Hauptperiode wurden während einer 2monatigen Nachperiode ohne Supplementierung bei ausschließlich Weidegang weitere Werte gewonnen. Die zusätzliche β‐Carotinversorgung erhöhte die β‐Carotinkonzentration im Blutplasma signifikant. Bei Weidegang waren die β‐Carotinspiegel im Blut gegenüber der „Stallfütterung” auf das 4‐ bis 5fache erhöht. Die Vitamin‐A‐Gehalte im Blutplasma waren bei Vitamin‐A‐ und β‐Carotin‐Supplementierung gleich. Im Bereich niedriger β‐Carotinkonzentrationen im Blut besteht eine positive Korrelation zu den Vitamin‐A‐Blutspiegeln. Bei β‐Carotin‐Blutspiegeln über 120 μg / 100 ml steigt der Vitamin‐A‐Gehalt nicht mehr an. Etwa eine Woche vor dem Kalben fällt sowohl der Carotin‐ wie auch der Vitamin‐A‐Blutspiegel ab. Am Kalbetag beträgt er nur etwa zwei Drittel der Ausgangswerte. Die vollständige Normalisierung erfolgt erst nach einigen Wochen. Summary Studies on the supply of milk cows with ß‐carotene and vitamin A 1. Effect on blood levels Thirty‐two Fleckvieh cows were divided into two groups on the basis of milk yield, milk fat content and stage of lactation and pregnancy, as well as number of lactations. With a basal diet poor in carotene and vitamin A (about 130 mg. β‐carotene per animal per day), one group received daily 116,000 i. u. vitamin A, the other got 340 mg. β‐carotene, and both received a mineral supplement. After a 4 months main period there was a two months period at pasture with no supplementation. Adding β‐carotene raised significantly the β‐carotene level in the plasma. At pasture the β‐carotene level in blood, compared with stall feeding, was 4–5 times as high. The vitamin A level in plasma was the same with vitamin A as with β‐carotene supplementation. With lower β‐carotene levels in blood there was a positive correlation with the vitamin A blood picture. At β‐carotene blood levels over 120 μg / 100 ml. the vitamin A level showed no further rise. About a week before calving, both the carotene and vitamin A levels in blood fell. On the day of calving it was only about two‐thirds of the previous level. Complete return to normal took a few weeks. Résumé Recherches sur l'approvisionnement des vaches laitières en carotène ß et vitamine A Communication 1: Influence sur le taux sanguin 32 vaches tachetées ont été réparties en 2 groupes en fonction de la quantité de lait, du taux de graisse dans le lait, du stade de lactation et de gestation et du nombre de lactations. A un aliment de base pauvre en carotène et en vitamina A (environ 130 mg carotène β / animal / jour), on a ajouté en plus d'un aliment minéralisé, 116 000 U. I. de vitamine A / animal / jour pour un groupe et 340 mg carotèn...