Relationships were assessed between circulating concentrations of urea, creatinine, thyroxine (T4) and triiodothyronine (T3), measured at 5, 9 and 13 months of age in young Romney rams, and performance of ram's ewe progeny. Five rams were chosen at random from each of the fleeceweight- selected and control lines of a long-term selection experiment. Average performance of their progeny (n = 6 to 12 per ram) was evaluated for hogget greasy fleeceweight (adjusted for age-of-dam, birth rank, date-of-birth) and yearling ultrasonic backfat depth (adjusted as previously but also for liveweight). There was no significant relationship between progeny yearling backfat depth and sire's urea, creatinine or T4 concentration at any age of measurement of the sires. However, backfat depth of the progeny was negatively correlated with sire's circulating T3 levels at both 5 months (r = 0.76, P<0.01) and 13 months (r = -0.59, P<0.10) of age. Hogget greasy fleeceweight was negatively associated with both urea (r= -0.48 and r= -0.45, respectively at 5 and 13 months) and creatinine (r= -0.63 and r= -0.53, respectively at 5 and 13 months) concentrations in the sire at 9 and 13 months of age respectively, but only the association with creatinine concentrations was significant (P<0.05). Progeny hogget fleeceweight was positively associated with sire T3 levels at 5 months of age (r= 0.62, P<0.10) but negatively associated with sire T4 levels at both 5 months (r= -0.55, P<0.10) and 9 months (r= -0.65, P<0.05) of age. Results of this preliminary study suggest that plasma concentrations of creatinine, T3 and T4 may be worthy of more extensive investigation as potential markers of genetic merit for backfat depth and fleeceweight in sheep.
Proceedings of the New Zealand Society of Animal Production, Volume 53, , 287-290, 1993
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