An analysis of creeping belly in the Carnarvon Afrino sheep flock

 

M.A. Snyman# & W.J. Olivier

Grootfontein Agricultural Development Institute, Private Bag X529, Middelburg (EC), 5900, South Africa

Corresponding author: Gretha Snyman

 

In many of the dual purpose wool sheep breeds, breeders discriminate strongly against creeping bellies, even to the extent of culling animals superior in terms of the economically important traits. Negative genetic correlations of –0.33 ± 0.23 and –0.25 ± 0.20 were estimated in 1995 between creeping belly assessed at two-tooth age and lifetime total weight of lamb weaned and number of lambs weaned respectively in the Carnarvon Afrino flock. However, at that stage, no creeping belly data were available on reproducing ewes. The data used for this study were collected on 5130 14-month old Afrino ram and ewe lambs from 1990 to 2011, as well as on 1078 reproducing Afrino ewes from 2004 to 2011 in the Carnarvon Afrino flock. Creeping belly was assessed on a linear scale from 1, indicating a severe creeping belly, where belly type wool was found more than halfway up the side, to 50, for sheep with no creeping belly. At 14 months of age, rams had more creeping bellies than ewes (35.6 ± 0.2 vs. 37.7 ± 0.2). Weaning status and year of birth also significantly influenced the occurrence of creeping bellies, more so in rams than in ewes. Single born lambs and lambs born in years with higher rainfall and subsequent better grazing conditions, had less creeping bellies. Differences in creeping belly score of reproducing ewes were observed among years, but not among age groups. Repeatability of creeping belly from 14 months until 8 years of age was estimated as 0.23 ± 0.06. Putting a lot of emphasis on crimp quality, together with the emphasis on fibre diameter, led to a correlated increase in the appearance of creeping belly in the Carnarvon Afrino flock, which is evident from the genetic trend in creeping belly from 1990 until 2000 (y = -0.1163x - 1.0869). Since 2001, less emphasis was put on fibre diameter and crimp quality, especially with the selection of young ewes, and more emphasis on wool weight. The resultant genetic trend in creeping belly until 2011 was y = 0.2494x - 5.0111. No significant relationship between weight of lamb weaned or number of lambs born or weaned and creeping belly was found in this dataset. A positive relationship was found between greasy fleece weight and creeping belly score (y = 3.6201x + 24.257) as well as between fibre diameter and creeping belly score (y = 0.6517x + 20.5322). As far as creeping belly is concerned, more data are needed to quantify the economic implications if less selection pressure is placed against creeping belly. In the meantime, it is proposed that only animals with extreme creeping bellies be culled.

 

Published

Proceedings 47th SASAS congress, Pretoria