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Survival of Red Maasai, Dorper and crossbred lambs in the sub-humid tropics

Published online by Cambridge University Press:  18 August 2016

R. Nguti ,
P. Janssen ,
G.J. Rowlands ,
J.O. Audho  and
R.L. Baker
R. Nguti
Affiliation:
University of Nairobi, PO Box 30197, Nairobi, Kenya
P. Janssen
Affiliation:
Limburgs Universitair Centrum, B-3590 Diepenbeek, Belgium
G.J. Rowlands
Affiliation:
International Livestock Research Institute (ILRI), PO Box 30709, Nairobi, Kenya
J.O. Audho
Affiliation:
International Livestock Research Institute (ILRI), PO Box 30709, Nairobi, Kenya
R.L. Baker*
Affiliation:
International Livestock Research Institute (ILRI), PO Box 30709, Nairobi, Kenya
*
†Email: L.Baker@cgiar.org
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Abstract

The survival rates of Dorper, Red Maasai and crossbred lambs born over a period of 6 years at Diani Estate, Coast Province, Kenya were compared using the Cox mixed proportional hazards model with a random (frailty) term for sire. Of the 1785 lambs born, proportionately 0·44 died before they were 1 year old. Almost half of these deaths occurred before weaning; a third were associated with mis-mothering and a fifth with gastro-intestinal nematode parasite (endoparasite) infections. Half of the deaths post weaning were associated with endoparasite infections, predominantly Haemonchus contortus. The Red Maasai lambs had a lower risk of death than the Dorper lambs with a relative hazard of 0·27 pre-weaning and 0·25 post weaning. Other crosses and back crosses had relative hazards in between these values and 1; there was no evidence of heterosis. Survival rates were different among years and appeared to be associated to some degree with variations in rainfall. There were highly significant effects of both birth weight and weaning weight on survival. Body weight, together with packed red cell volume and faecal egg count, were also introduced into the proportional hazard model as time-varying covariates. All three variables had major influences on survival. The risk of death over the following month in animals individually treated with an anthelmintic drug pre weaning was reduced by 0·61 compared with those not treated. The sire frailty variance estimate was similar to its standard error pre-weaning but larger post weaning. When adjusted for lamb body weight the sire variance post weaning increased to three times its standard error.

Keywords

survival analysismortalitysheeptropical Africa
Type
Research Article
Information
Animal Science , Volume 76 , Issue 1 , February 2003 , pp. 3 - 17
Copyright
Copyright © British Society of Animal Science 2003

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