Post-natal growth and development of Simmental calves derived from in vivo or in vitro embryos

Abstract

Large fetuses arising from embryos produced in vitrohave been shown to exhibit altered organ developmentin utero, but it is not known whether this persists postnatally. Post-natal growth and development was examined in 18 Simmental bullsderived from in vivo frozen-thawed(n = 6), in vitrofrozen- thawed (n = 6) orin vitro fresh (n = 6)embryos and reared together post weaning on anad libitum diet until slaughter at approximately 13months old. Calves weighing less than 60 kg at birth (n= 11) were classified as normal, and heavier calves(n = 7; all from in vitroembryos) as oversize. Lifetime growth rates and slaughter weights apparentlywere unaffected by embryo source or birthweight. Mean (&plusmn; s.e.m.) postmortem liver and kidney weights were unaffected by embryo source, but heartsof bulls from in vitro frozen embryos were heavier than those of bulls fromin vivo frozen embryos (2.7 &plusmn; 0.04v. 2.3 &plusmn; 0.07 kg,P&lt;0.025). Heart weight per kilogram body weight atslaughter for the 7 perinatally oversize males (4.01 &plusmn; 0.08 g) exceededthat of the other 5 bulls from in vitro embryos (3.60&plusmn; 0.10 g kg <emph type="7">-1 ;P&lt;0.04) and the 6 in vivo males(3.56 &plusmn; 0.12 g kg <emph type="7">-1 ;P&lt;0.02). Overall, one-third of the variation in heartweight at slaughter (r <emph type="7">2 =0.35; P = 0.01) was due to variation inbirthweight. This is the first study to demonstrate birthweight-relateddevelopmental effects on post-natal organ weight following the transfer ofembryos produced in vitro.