Can IGF-I be used as an indirect selection criterion for beef cattle

Abstract

Proc. Aust. Soc. Anim. Prod. 1996 Vol. 21 CAN IGF1 BE USED AS AN INDIRECT SELECTION CRITERION FOR BEEF CATTLE? A.N. FERNSA, R.M. HERDB, R. WOODGATEB, C. QUINNB, K. ZIRKLERA and K.H. ODDY B ACRC for the Cattle and Beef Industry, University of New England, Armidale, N.S.W. 2351 B N.S.W. Agriculture, CRC for the Cattle and Beef Industry, University of New England, Armidale, N.S.W. 2351 Concentration of insulin-like growth factor-l in blood (IGFl) is moderately to highly heritable in cattle and phenotypically associated with a range of important production traits (Herd et al. 1995). IGFl is lower in cattle aged a few days old than at 9 and 11 months (Herd et al. 1995; Herd 1992). If IGFl was to be considered as an indicator trait in young animals then any change in its concentration as the animal grows and its relationship with production traits must be known. This study is of IGFl from birth to weaning in Angus calves from the High, Control and Low growth-rate selection lines used in our previous studies. The calves were born in late 1994 near Armidale, N.S.W., and were weighed and bled at birth and then fortnightly until 3 months of age, then monthly until weaning. Blood samples were stored on ice until centrifuged and plasma frozen for radiommunoassay (Hall et al. 1992). The males were castrated at 3 months of age. High-line calves showed the highest and Low-line calves the lowest liveweight increase to weaning. After 12 weeks liveweight differed (PcO.05) between the selection lines. Differences in IGFl between male calves from the 3 selection lines were small at birth: High-line 98 + 15 (mean t SE); Control-line 114 2 14 and Low-line 12 1- 13 ng/mL. IGFl rose to plateau within 4 weeks of birth. At weaning there was no difference + between the High and Low-line calves (214 + 11 v 216 + 10 ng/mL), with the Control-line calves having lower levels (180 + 1 lng/mL; PcO.05). IGFl did nit increase-with age to the same extent in heifer calves, being 120 2 12,89 +7 and 108 t 13 ng/mL at birth, and 165 +14,117 t 7 and 130 +7 ng/mL at weaning in the High, Control and Low-line respectively. The means for the High and Control-line heifers differed (PcO.05). For all animals from the 3 lines considered together, no variation in birth weight was explained by IGFl at birth (?=O.OO), nor was any variation in weaning weight explained by variation in IGFl at birth (r =O.Ol) or at weaning (r-%.02). These results were consistent with our earlier work which was also unable to demonstrate consistent differences in IGFl between the growth rate selection lines and/or a close relationship between growth rate and IGFl in these cattle. This is in contrast to other studies in young cattle that have demonstrated a strong correlation between IGFl and growth rate (Davis and Bishop 1994). In our study IGFl levels rose quickly in male calves between birth and 1 month of age, then appeared to plateau. Unpublished data of M. Bishop for Angus calves in Ohio, U.S.A. showed that IGFl remained low until after weaning before beginning a slow prepubertal rise to levels 3-fold higher at 10 months of age in bulls and 12 months in heifer calves. Patterns of increase with age of IGFl intermediate to those described by us and Bishop was reported in male calves by Skaar et al. (1994). Moreover the levels of proteins that bind circulating IGFl also change with age and this may influence the action of IGFl in young dairy calves (Skaar et al. 1994). These differences in both increase with age, and reported associations of IGFl with production traits between studies suggest that, if selection using IGFl to manipulate feed efficiency or body composition is to be successful, then more basic information on how IGF 1 operates is vital. DAVIS, M.E. and BISHOP, M.D. (1994). Anim. Prod. 59: 3 15-20. HALL, D.G., HOLST, P.J. and SHUIT, D.A. (1992). Aust. J. Agric. Res. 43: 325-37. HERD, R.M. (1992). Proc. Aust. Assoc. Anim. Breed. Genet. 10: 404-7. HERD, R.M., ARTHUR, P.F., ZIRKLER, K., QUINN, C. and ODDY, V.H. (1995). Proc. Aust. Assoc. Anim. Breed. Genet. 11: 694. SKAAR, T.C., BAUMRUCKER, CR., DEAVER, D.R. and BLUM, J.W. (1994). J. Anim. Sci. 72: 421-7. 403