Nutrient Metabolism trations in blood (3—5)and milk (6, 7). Using im munofluorescence techniques, Glimm et al. (8) demonstrated increased IGF-I in mammary tissue from lactating cows treated with exogenous bST. Re ceptors for somatomedins are present in bovine mammary tissue and increase in number during lacto genesis (9). Further, IGF-I stimulated DNA synthesis in bovine mamm@y tissue in vitro (10). Thus, effects of bST at the mammary gland may be mediated by the somatomedins (1). Nutritional status plays a well-established role in the regulation of circulating levels of somatomcdins in h@m*nq and rats (11).Breieret al.(12)demon strated that restriction of dry matter intake in growing steers affected basal blood concentrations of IGF-I and abolished the response of IGF-I and insulin like growth factor-U (IGF-II) to exogenous bST. Ronge and Blum (13) demonstrated similar effects of under nutrition on IGF-Iresponse to bST in growing heifers. 1Presented in part at the 82nd Annual Meeting of the American Society of Aninttl Science, August 1990, at Iowa State University, Ames, IA [McCuire, M. A., Bauman, D. E@, Miller, ?vLA. & Hart-S nell, C. F. (1990)Effect of esergy and protein nutrition on resposee oftheinsulin-likegrowthfactors@ICP) to recombinant n-metbionyl bovine somatotropin (bST, eometribove) in lactating cows. J. Anim. Sd. 68(SuppL 1): 436(abs.)J. 2Supported in part by Cornell University Agricultural F.x periment Station. 3To whom correspondence should be addressed. 4Present address: Food and Drug MniinI!Itration, Cent@ for Veterinary Medicine, Rockvillç I@D 20857. This article was written by M. A. Miller in her private capacity. No official support or endorsement by the agency is or should be inferred. 5Abbreviations used: bST, bovine soniatotropin, @P, crude pro tam1ici'-i,u@win-iik@ @@th factor-I, ICP-Il,insulin-likegrowth factor-Ui NA, not applicable, NE, net energy1NEFA, non-esterified fatty acids, PEG, polyethylene glycoL ABSTRACT Mid-lactation HOlstein COWS(n - 4) W515 assigned to four dIetai@vsequences In a 4 x4 LatIn square to determine energy and proteIn effects on somatomadins. Diets were designed so that Intakes were eIther high or lOWfor net energy (NE)or erode protein (CP) with the range being representativefor a lactation cycle. Each dietaiy treatment lasted 16 d and consisted of an adjustment period (d 1 to 7), a basal period (d 8 to 12) and a period of bovine somatotropin (bW@) (40 mg/d) administration (d 13 to 16). Blood was obtainedvlajugularcatheterseveiy4hond 11 to 16. Basal milk yield was decreased by NE or CP restriction. Milkyield was Increased for cows fed all diets with bST, but response was greatest for those fed the high NE/ high CP diet (31%, 7.7 k@Jd). Plasma Insulin-like growth factor (IOF)-l and IOF-ilconcentrations were not af faded by diet. Forall diets, bSTcausedan IncreaseIn plasma lOP-I (125%) and IOF-Il (21%), wIth the In crease being substantially greater for cows fed the high NE/high CP diet. Basal Insulin levels differed among diets and Increased with exogenous bST In cows fed the high NE/high CP diet. Results are consistent with a role of somatomedins Inthemechanismbywhichexogenous bST Increases milk yield, and variations In somatomedin response due to nutritional status may explaIn part of the differences In milk yield response to exogenous bST. J.Nutr.122: 128-136,1992. INDEXING KEY WORDS: . somatotropin •Insulin-like growth factor •energy •protein •cattle Administration of exogenous bovine somatotropin (bST)5 to lactating cows increases milk production (1). Although some of the effects of bST on tissues are direct, evidence to date suggests that bST has no direct action at the mnmmnry gland (2). Adminis tration of exogenous bST to lactating cows causes an increase in insulin-like growth factor-I (IGF-I) concen 0022-3166/92 $3.00 C 1992 American Institute of Nutrition. Received 19 April 1991. Accepted 2 July 1991. 128 Response of Somatomedins (IGF-I and IGF-II) in Lactating Cows to Variations in Dietary Energy and Protein and Treatment with Recombinant n-Methionyl Bovine in@2 MARK A. MCGUIRE, DALE E. BAUMAN,3 MARGARET A. MILLER*4 @ GARY F. HARTNELL* Department of Animal Science, Cornell University, Ithaca, NY 14853 and tAnimal Sciences Division, Monsanto Company, SL Louts, MO 63198 by guest on July 21, 2011 jn.nutrition.org Downloaded from