New Zealand Journal of Agricultural Research abstracts

---

Threshold model analysis of lamb survivability in Romney sheep

C. S. Welsh^1,2*
D. J. Garrick^2,3
R. M. Enns²
G. B. Nicoll⁴

¹National Animal Germplasm Program
National Center for Genetic Resources Preservation, ARS, USDA
Fort Collins, CO 80521, USA
carrie.welsh@ars.usda.gov

²Department of Animal Sciences
Colorado State University
Fort Collins, CO 80523, USA

³Institute of Veterinary, Animal and Biomedical Sciences
Massey University
Private Bag 11222
Palmerston North 4442, New Zealand

⁴Landcorp Farming Limited
PO Box 44
Rotorua 3010, New Zealand

Abstract   Lamb survivability is a major determinant of the reproductive efficiency of the flock. The objective of this study was to estimate variance components for direct, maternal, and permanent environmental components of lamb survivability. Threshold model procedures were used to estimate variance components from 25 362 lamb survival observations representing 136 sires from two Romney flocks in New Zealand with an average lamb survival of 80.8%. Lambs were born between 1997 and 2000. Fixed effects fitted in the model included sex and contemporary group, defined as the interaction of age of dam, flock, and birth date class. Median heritabilities were 0.106 ± 0.010 for direct, 0.082 ± 0.005 for maternal, and a median proportion of phenotypic variation 0.098 ± 0.003 for permanent environmental effects. The direct-maternal correlation was - 0.75 ± 0.03. Estimated breeding values on the underlying scale were back-transformed to the phenotypic probability scale. For direct lamb survivability, the highest performing sire’s lambs had a 14.8% greater chance of survival than the lowest performing sire’s lambs for flocks with an average lamb survivability of 80%. Although heritabilities for both components of lamb survivability are low, selection for this trait can be accomplished and is of economic importance for the sheep breeder.

Keywords   lamb survival; sheep; estimated breeding values; heritability; threshold model

A06028; Online publication date 11 October 2006
Received 6 May 2006; accepted 11 August 2006

^*Mention of a trade name or proprietary product does not constitute a guaranty or warranty by the USDA and does not imply approval to the exclusion of other products that may be suitable. USDA, Agricultural Research Service, Northern Plains Area, is an equal opportunity/affirmative action employer. All agency services are available without discrimination.

New Zealand Journal of Agricultural Research, 2006, Vol. 49: 411–418
0028–8233/06/4904–0411  © The Royal Society of New Zealand 2006

PDF file of entire paper: Print-quality (304K) | screen-quality (364K)

---

This year's abstracts | Journal home page | All abstracts | Publishing home page