Identifying indicator traits for breech strike in Merino sheep in a Mediterranean environment

Abstract

Abstract. Data from 2833 unmulesed Merino lambs from 49 sires and 1535 dams that were born from 2005 to 2009, were used to identify indicator traits for breech strike in a Mediterranean environment. Sheep were managed in a normal production environment where no preventative treatments were applied to protect them from being struck by flies, but were immediately treated when found to be fly struck. Seventy-seven skin, body conformation, wool, disease and production traits that may contribute to breech strike and that could qualify as potential indicator traits were recorded on progeny at birth, weaning, postweaning, yearling, spring and at pre-and post-hogget age at~18 months of age. In all, 31% of ewes and 22% of rams were fly struck in the breech area between birth and hogget shearing. The heritability of and the phenotypic and genetic correlations between the potential indicator traits and breech strike were estimated. The results showed that breech strike is a heritable trait (h 2 = 0.51 AE 0.10), and that the most important indicator traits for breech strike were dags, scored at any time, especially at hogget age (r g = 0.81 AE 0.15), spring (r g = 0.77 AE 0.13) or at weaning (r g = 0.64 AE 0.00), urine stain scored at weaning (r g = 0.54 AE 0.13) and marking (r g = 0.51 AE 0.15), neck wrinkle at hogget age (r g = 0.46 AE 0.13) and breech cover (r g = 0.32 AE 0.15) scored at post-weaning shearing. These traits could be used to select indirectly for breech strike resistance in a Mediterranean environment.

Genetic parameters for wool traits, live weight, and ultrasound carcass traits in Merino sheep1

“…The change in direction of the genetic correlations between bWT and yWT may be due to the growth of the animal and the associated increase in skin surface area that impact on wrinkle. Several studies have shown a reduction in BRWR scores as sheep age, with the largest change occurring between the marking and yearling assessments (Brown et al, 2010;Bird-Gardiner et al, 2014;Greeff et al, 2014;Hatcher and Preston, 2015). Two separate studies have also clearly shown that selection for increased skin folds (wrinkle) resulted in a correlated response of lower live weight (Turner et al, 1970;Crook and James, 1991), with a realized genetic correlation of −0.22 (Crook and James, 1991).…”

Genetic parameters for breech cover, wrinkle and wool coverage scores and their implications for Merino sheep breeding programs and flock management

“…Producers have since taken heed of the problems of the past, and as a result there has been a reduction in the degree of wrinkling in the modern Australian Merino http://dx.doi.org/10.1016/j.smallrumres.2015.07.023 0921-4488/Crown Copyright © 2015 Published by Elsevier B.V. All rights reserved. (Roberts, 1959;Baillie, 1978;Donnelly, 1978;Hatcher et al, 2009), particularly since 1999 when ram breeders became more aware of the need to breed sheep that do not have to be mulesed (Brown et al, 2010) due to increased public awareness that questioned the animal welfare aspects of surgical mulesing (Greeff et al, 2014).…”

“…However, increasing the degree of wrinkling not only resulted in increased wool cuts (Beattie, 1962;Lewer et al, 1995;Hatcher et al, 2009), but a greater susceptibility to and incidence of flystrike (Donnelly, 1978;Scholtz et al, 2010), fleece rot (Raadsma et al, 1988) and wool yellowing (Crook and James, 1991). These changes resulted in sheep that required an increased level of management (Roberts, 1959;Baillie, 1978) including surgical mulesing, regular crutching, jetting with insecticides and treating individually fly struck sheep with chemicals (Greeff et al, 2014). Other correlated effects associated with increased wrinkling included a higher number of dry ewes (Baillie, 1978) and higher birth weights (Dun and Wall, 1962) which were associated with an increased incidence of dystocia (Dun and Wall, 1962;Donnelly, 1978).…”

“…Implementing a genetic reduction in wrinkles requires accurate estimation of genetic parameters for a range of breech, wrinkle and wool coverage traits and knowledge of the correlations between these traits. Previous studies have shown that breech wrinkle is a highly heritable trait (Brown et al, 2010;Bird-Gardiner et al, 2014;Greeff et al, 2014), neck and body wrinkle scores are moderately (Beattie, 1962;Mortimer and Atkins, 1993;Lewer et al, 1995) to highly heritable (Hatcher et al, 2009;Mortimer et al, 2009;Brown et al, 2010;Bird-Gardiner et al, 2014;Greeff et al, 2014) and estimates for breech cover vary from moderate to high (Bird-Gardiner et al, 2014;Greeff et al, 2014). However, the earlier reports used various non-standard scoring systems, selection can change the genetic relationships within a population (Turner and Young, 1969) and there are no published reports on phenotypic and genetic correlations between breech cover, breech-, body-and neck-wrinkle or wool coverage at various ages.…”

Short communication: Divergent selection for reproduction affects dag score, breech wrinkle score and crutching time in Merinos

“…Scobie et al (2005) reported an up to 20% increase in the shearing period, directly proportional to the number of blows required for sheep with high wrinkle scores. Wrinkle score is genetically and phenotypically correlated to dag score (Greeff & Karlsson, 2009;Smith et al, 2009). It therefore stands to reason that animals in the L line took longer to crutch.…”