Testis size and endocrine parameters in rams as predictors of
aseasonality in their daughters
Z.Z. Xu, M.F. McDonald, S.N. McCutcheon, H.T. Blair
Department of Animal Science, Massey University, Palmerston
North, New Zealand
Proceedings of the New Zealand Society of Animal Production.
1992, 52: 195-198
A progeny test involving Romney (n=5) and Poll Dorset (n+5)
rams mated to Romney ewes was conducted to examine the relationship
between testis size and endocrine parameters, measured during the
transitional period from the non-breeding to the breeding season, in
rams, and reproductive performance of their daughters in the first and
second breeding seasons. More of the Poll Dorset cross hoggets reached
puberty during the first breeding season (80 v. 60%; P<0.01) associated
with earlier onset (13 v. 22 May; P<0.10) at younger ages (264 v. 276
days; P<0.10) and more oestrous cycles (2.7 v. 2.0; P<0.05) than for
Romney hoggets. The date of onset of the second breeding season was
influenced by breed (P<0.001) and sire within breed (P<0.05). These
differences between Romney and Poll Dorset cross animals in reproductive
performance were associated with differences between their sires in the
pattern of seasonal variation in testis size and plasma gonadotrophin
concentrations. However, within-breed correlations between testicular
and endocrine parameters in the sires and date of onset of the breeding
season in the offspring were low. It is concluded that, while some of
the testis and endocrine parameters could potentially be used as
selection criteria for date of onset of the breeding season in ewes,
further studies are needed before these parameters can be incorporated
into selection programmes.
Keywords: NZSAPAB;
Testis size; LH; FSH; gonadotrophin; GnRH; breeding season;
puberty.
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Last Updated 25-01-1997
