Genetic Improvement Of Lamb Survival In The Australian Merino

Author : Samantha Leanne Bickell
Publisher :
ISBN 13 :
Total Pages : 346 pages
Book Rating : 4.:/5 (93 download)

DOWNLOAD NOW!

Download or read book Does the Selection on Temperament in Merino Sheep Significantly Affect the Establishment of the Ewe-lamb Bond Or Lamb Survival? written by Samantha Leanne Bickell and published by . This book was released on 2009 with total page 346 pages. Available in PDF, EPUB and Kindle. Book excerpt: The selection of Merino sheep for a calm temperament has been previously proposed to improve lamb survival by improving the expression of maternal behaviour in calm ewes. However, the effects of the selection process on ewe and lamb behaviour and the establishment of a mutual bond are still unknown despite these temperament traits having been selected over 15 years. The aim of this thesis was to study in detail the extent to which the selection on temperament had affected the establishment of the ewe-lamb bond and lamb survival, and its means of transmission from mother to young. This study shows that selection for temperament in Merino sheep does not affect the early process of ewe-lamb bonding. In a two-choice recognition test, both calm and nervous ewes recognised their lambs at 6 hours after parturition. Likewise, calm and nervous lambs showed a preference for their own mother at 18 hours after birth even though differences in temperament were detected in the lambs at one week of age. Even in the presence of a novel object, known to be a strong stressor for the nervous ewes, calm and nervous ewes did not differ in their ability to recognise their own lamb in a two-choice test. Unexpectedly however, the nervous lambs expressed better discriminative abilities than the calm lambs in the presence of the novel object in the two-choice test. In addition, when the ewes were housed indoors in individual pens, both temperament lines expressed adequate maternal behaviour. Hormonal secretion patterns of oestradiol, progesterone and prolactin, hormones involved in the onset of maternal behaviour during the pre and post-partum period, were similar between the two lines, providing further evidence to suggest that both calm and nervous mothers had the capacity to express adequate maternal behaviour. Under outdoor lambing conditions with minimal human disturbance, calm ewes licked their lamb more and tended to stay longer on the birth site, while nervous lambs stood up earlier and started to perform exploratory behaviour earlier. However, these differences in behaviour did not lead to differences in lamb mortality between the two lines. Finally, it was demonstrated that genotype rather than non-genetic behavioural transmission determines the temperament of Merino lambs at weaning. It is to be noted that, because a cross fostering experimental design was used, other maternal influences on the development of the offspring can not be ruled out since the prenatal uterine environment can also affect the epigenetics of mammalian offspring. This study concludes that the differences in ewe behaviour and lamb survival previously reported were not due to an effect of temperament on maternal behaviour per se, but to some interaction of temperament with the presence of the human observer. These results demonstrate that the expression of a trait like temperament is mostly in response to a triggering stimulus and the consequence of the expression depends on the context in which it occurs.