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.

Zusammenfassung Einfluß von Geschlecht und Gewicht auf die Plasmakonzentrationen von Wachstumshormon (GH), Insulin‐like growth factor I (IGF‐I) und Insulin bei Mastrindern der Rasse Deutsches Fleckvieh Bei wachsenden Bullen, Ochsen und Färsen (Deutsches Fleckvieh) wurden die Blutplasma‐Konzentrationen von Wachstumshormon (GH), Insulin‐like‐growth‐factor I (IGF‐I) und Insulin bestimmt. Der Versuch bestand aus drei Versuchsdurchgängen und begann bei einem durchschnittlichen Alter von 3 Monaten beziehungsweise einem Lebendgewicht von 110 kg. Das Mastendgewicht betrug 510 kg (Färsen) und 660 kg (Bullen, Ochsen). Während der Mast wurden in jedem Versuchsdurchgang jeweils drei Tiere bei Mastgewichten von 200 kg, 360 kg und 425 kg (Färsen) bzw. 200 kg, 360 kg, 510 kg und 585 kg (Bullen, Ochsen) geschlachtet. Die Blutproben wurden durch Punktion in 14‐tägigem Abstand gewonnen. Die GH‐, IGF‐I‐ und Insulin‐Konzentrationen waren durch das Geschlecht signifikant beeinflußt (p<0.05). Die höchsten GH‐und IGF‐I‐Konzentrationen waren bei den Bullen gefolgt von den Ochsen und Färsen festzustellen. Die GH‐Konzentrationen zeigten einen gewichtsabhängigen Abfall bei Ochsen und Färsen, während die GH‐Konzentrationen bei Bullen wahrscheinlich aufgrund von Streß nur tendenziell mit zunehmendem Gewicht abfielen. Mit zunehmendem Gewicht stiegen die IGF‐I‐und Insulin‐Konzentrationen an. Die Veränderungen des Blutplasmaspiegels der Hormone werden hinsichtlich der Geschlechts‐ und Wachstumseinflüsse diskutiert. Aufgrund der physiologischen Effekte der Hormone und ihrer Blutplasmakonzentrationen im Hinblick auf die Schlachtkörperzusammensetzung wird gefolgert, daß IGF‐I beziehungsweise die Somatotropin‐Achse in Beziehung zum Proteinansatz und dem Muskelfleischanteil am Schlachtkörper steht, während der Fettansatz und die Schlachtkörperverfettung eher durch die Insulin‐Konzentration wiedergegeben wird.

Concentrations of growth hormone (GH), insulin-like growth factor , insulin and glucagon were determined in the plasma of growing bulls, steers and heifers (no. = 138 in total, German Simmental breed). The animals were offered either a high level or a low level of energy resulting in relatively high and low average daily gain. Trials were subdivided into two experimental series and started at approximately 3 months of age at an average live weight of 110 kg. The animals were slaughtered at different body weights from 200 to 510 kg (heifers) or 660 kg (bulls, steers) . Blood samples (needle puncture) were collected at biweekly intervals. Frequent samples for time-course analysis of GH were taken by catheter from nine animals in total. Concentrations of GH declined during growth in steers and heifers as well as in bulls in blood samples collected by means of a catheter. IGF-1 and insulin concentrations increased from the start of the trial onwards up to different ages among the groups.Concentrations of glucagon constantly decreased from the start of the trial until slaughter. Significant differences (P < 0-05) in concentrations ofGH, IGF-1 and insulin could be observed between sexes and levels of nutrition, with the highest GH and IGF-1 levels in bulls followed by steers and heifers. In contrast insulin values were highest in heifers followed by steers and bulls. A high level of nutrition increased concentrations of IGF-1 and insulin in all sexes.

Abstract. The expression of the bovine growth hormone receptor (GHR) was detected in various tissues by a reverse transcription -polymerase chain reaction system (RT-PCR). For the quantification of the bovine 438 by GHR cDNA fragments a HPLC-UV detection system was used. bGHR amplificates were well detectable in liver from cows, heifers and in fetal liver. bGHR expression was also demonstrated in mammary gland, kidney and in adipose tissue. Lower but significant amounts of bGHR amplificates were obtained in skeletal muscle and in rumen villi, indicating a potential new mode of action of GH via affecting the gastrointestinal tract. bGHR mRNA was detected in various female and male reproductive tissues, i.e. in uterus, oviduct, corpus luteum, and in the vesicular gland. No bGHR expression was detectable in testes from adult bulls. A longterm treatment of heifers with a slow-release preparation of bovine growth hormone had no effect on either bGHR-mRNA expression in liver or on GH binding capacity on liver membrane preparations. These results demonstrate that the RT-PCR system together with a HPLC-UV detection system provides a useful strategy to study GHR expression and regulation in different tissues under various conditions.