caa a22 4500 388059915 CHVBK 20180307125117.0 cr unu---uuuuu 161130e199806 xx s 000 0 eng 10.1017/S1357729800009127 doi S1357729800009127 pii (NATIONALLICENCE)cambridge-10.1017/S1357729800009127 Serum somatotropin concentrations in Holstein heifers administered growth hormone-releasing factor and somatostatin [Elektronische Daten] Dose-response experiments were designed to determine the dosage of somatostatin (SRIF) necessary to alter serum growth hormone (GH) response to administration of GH-releasing factor (1·44; GRF) in cattle. The objective of this experimentation was to develop a GRF/SRIF challenge model that might be useful in early identification of animals which are genetically superior for milk production traits. In experiment 1, calves received either 0, 5 or 10 /JLg GRF per 100 kg body weight (BW) or GRF 1·29 at 1 ug per 100 kg BW. Both the 5 and 10 ug GRF per 100 kg BW dosages increased GH concentrations (P < 0·05). In experiment 2, animals received 3 ug GRF per 100 kg BW concurrent with administration of 0, 0·5, 1 or 2 ug SRIF per 100 kg BW at 0 min, with second dosage of GRF at +120 min. Administration of SRIF in those dosages did not alter GH response to GRF. In experiment 3, animals received 5 ug SRIF per 100 kg BW at -2, -1, 0 or +1 min relative to 3 ug GRF per 100 kg BW, with a second GRF injection at +120 min. No differences (P < 0·05) were found in response due to timing of SRIF administration. In experiment 4, animals were administered 0, 5, 10 or 20 Xg SRIF per 100 kg BW concurrent with 3 ug GRF per 100 kg BW. SRIF delayed (P < 0·05) the occurrence of maximum GH concentrations but did not affect the maximum concentration nor the area under the GH response curve (AUC) following either the first or second GRF injection. Utilizing data from experiment 4, individual animal response to GRF was reasonably consistent, as repeatabilities of AUCs for 1 h following first and second GRF injections were 0·80 and 0·65, respectively. Furthermore, sufficient among-animal variation existed so that animals could be distinguished from each other. Thus we conclude the method described herein might be useful in identifying superior dairy calves but accuracy would potentially be enhanced by collecting blood samples more frequently during the 20 min immediately after GRF injection. Copyright © British Society of Animal Science 1998 heifers nationallicence somatoliberin nationallicence somatotropin nationallicence somatostatin nationallicence Kazmer G. W. Department of Animal Science, Box U-40, University of Connecticut, Storrs, CT 06269-4040, USA Zinn S. A. Department of Animal Science, Box U-40, University of Connecticut, Storrs, CT 06269-4040, USA Animal Science Cambridge University Press 66/3(1998-06), 551-556 1357-7298 66:3<551 1998 66 ASC https://doi.org/10.1017/S1357729800009127 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1017/S1357729800009127 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Kazmer G. W. Department of Animal Science, Box U-40, University of Connecticut, Storrs, CT 06269-4040, USA NATIONALLICENCE 700 1- Zinn S. A. Department of Animal Science, Box U-40, University of Connecticut, Storrs, CT 06269-4040, USA NATIONALLICENCE 773 0- Animal Science Cambridge University Press 66/3(1998-06), 551-556 1357-7298 66:3<551 1998 66 ASC CC0 http://creativecommons.org/publicdomain/zero/1.0 nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-cambridge