Manejo De Borregos

Genetic and physiological determinants of maternal behavior and lamb survival:
Implications for low-input sheep management
C. M. Dwyer
J ANIM SCI 2008, 86:E246-E258.
doi: 10.2527/jas.2007-0404 originally published online August 20, 2007

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Genetic and physiological determinants of maternal behavior and lamb
survival: Implications for low-input sheep management1,2
C. M. Dwyer3
Sustainable Livestock Systems Group, SAC, Edinburgh, EH9 3JG, UK

ABSTRACT: The relatively intensive supervision afforded many ewes at lambing time is a barrier to thedevelopment of low-input sheep management systems.
However, in some flocks, reduction in this level of supervision may initially affect lamb mortality and animal
welfare. In this review, possibilities for optimizing behavioral interaction between the ewe and lamb are considered, with the goal of improving lamb survival without the need for high levels of human supervision. At
birth, ewes showspecific behavioral patterns (e.g., licking or grooming, low-pitched bleats, udder acceptance)
that facilitate the transition of the lamb from pre- to
postnatal life and that accompany the formation of an
exclusive olfactory memory for the lamb. The lamb also
performs a specific sequence of behaviors directed toward standing, finding the udder, and sucking. The
successful accomplishment of thesebehavior patterns
is vital for the formation of a strong attachment between both partners, and for lamb survival. The expression of maternal behavior in the ewe is affected by her
previous maternal experience, by nutrition in pregnancy, by breed, by temperament, and, to some extent,
by the behavior of her lamb. The maternal care ex-

pressed by a ewe at parturition is indicative of herbehavior throughout that lactation and in successive
pregnancies, suggesting an underlying basis to maternal care intrinsic to that ewe. Studies with Scottish
Blackface and Suffolk ewes show that ewes expressing
high levels of maternal care have elevated plasma estradiol in late gestation compared with ewes with poorer
maternal care, and that circulating estradiol concentration is correlated withmaternal behaviors. Although
the genetic basis of maternal behaviors has still to be
fully determined, there are possibilities of improving
maternal behavior by selection, and a better understanding of the neuroendocrine processes underlying
individual differences in maternal behavior may help
in developing selection strategies. In addition, selection
on lamb behaviors, which show somegenetic basis, may
also be a route to improve lamb survival. Because behavior of both the ewe and lamb is affected by environmental factors, appropriate management, through
pregnancy and at parturition, will enhance the expression of maternal behavior and lamb vigor, and so contribute to improving lamb survival.

Key words: estradiol, genetics, lamb survival, management, maternal behavior, sheep©2008 American Society of Animal Science. All rights reserved.

INTRODUCTION
Traditionally, domestic ewes have been subjected
to relatively intensive supervision at lambing time to

1
Acknowledgements: SAC receives financial support from the Scottish Executive for Environment and Rural Affairs Department.
Thanks to J. FitzSimons, M. Ramsay, and H. Brown for assistance
with animal husbandryfor the studies described here; to K. McLean,
J. Chirnside, L. Deans, S. Robson, S. Jarvis, J. Stevenson, J. Ogg, J.
Mann, M. Farish, K. McIlvaney, E. Baxter, L. Maggs, M. Farnsworth,
J. Donbavand, and L. Smith for technical assistance at lambing time;
and to I. Swanson and F. Pitt at MRC (Edinburgh), F. Gebbie, K.
Mackie, J. Rooke, and J. Conington at SAC for help with hormone
assays and...