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The Effects of Inbreeding in a Flock of Hampshire Sheep^1,2,3,

Oregon State University, Corvallis 97331

Abstract

A registered flock of Hampshire sheep that had been predominantly closed for about 30 yr was utilized to study the effects of inbreeding on productivity of the 1980 and 1981 lamb crops. Five generation pedigrees for ewes and rams were used to calculate inbreeding coefficients. The median inbreeding coefficient of 598 lambs was 10.7%, and ranged from 1.4 to 29.6%. The median inbreeding coefficient of 212 ewes was 4.3%, and ranged from .0 to 28.1%. Regression techniques were used to determine the effects of ewe inbreeding on 6-mo fleece weight and ewe breeding weight and the effects of both ewe and lamb inbreeding on days from ram introduction to conception, fertility, prolificacy, lamb survival to 7 and 90 d of age, weight of lamb at birth, 30, 60, and 90 d and weight of lamb weaned/ewe exposed. A 1% increase in lamb inbreeding reduced (P<.01) survival to 7 d by 1.1%, reduced (P<.01) survivial to 90 d by 1.3% and reduced (P<.05) weight of lamb weaned/ewe exposed by .59 kg. A 1% increase in ewe inbreeding decreased (P<.10) ewe breeding weight by .27 kg, increased (P<.10) days from ram introduction to conception by .35 d and decreased (P<.05) fertility by 1.2%. The effect of ewe inbreeding on 6-mo fleece weight and the effects of lamb and ewe inbreeding on prolificacy and lamb weight at birth, 30, 60 and 90 d were not significantly different from zero. The negative effect of lamb inbreeding on weight of lamb weaned/ewe exposed was attributed as follows: 11% to its effect on fertility, 6% to its effect on prolificacy, 80% to its effect on survival and 3% to its effect on 90-d weaning weight.

¹ Technical Paper No. 6138, Oregon Agr. Exp. Sta. Contribution to North Central Regional Project NC-111, "Increased Efficiency of Lamb Production."

² The authors wish to express their sincere appreciation to R. W. Hogg and Sons Hampshires for providing animals and facilities for this project. Ronald and Glenn Hogg have dedicated over 50 yr of their lives to the breeding of Hampshire sheep. It has been a privilege to know and work with these seedstock producers.

³ Dept. of Anim. Sci.

⁴ Present address: Dept. of Anim. Sci., Univ. of Nebraska, Lincoln 68583.

⁵ Present address: Dept. of Anim. Sci., Univ of Illinois, Urbana 61801.

⁶ Dept. of Statist.