Genetic parameters for lameness, mastitis and dagginess in a multi-breed sheep population

Abstract

The objective of the present study was to quantify the extent of genetic variation in three health-related traits namely dagginess, lameness and mastitis, in an Irish sheep population. Each of the health traits investigated pose substantial welfare implications as well as considerable economic costs to producers. Data were also available on four body-related traits, namely body condition score (BCS), live weight, muscle depth and fat depth. Animals were categorised as lambs (<365 days old) or ewes (⩾365 days old) and were analysed both separately and combined. After edits, 39 315 records from 264 flocks between the years 2009 and 2015 inclusive were analysed. Variance components were estimated using animal linear mixed models. Fixed effects included contemporary group, represented as a three-way interaction between flock, date of inspection and animal type (i.e. lamb, yearling ewe (i.e. females ⩾365 days but <730 days old that have not yet had a recorded lambing) or ewe), animal breed proportion, coefficients of heterosis and recombination, animal gender (lambs only), animal parity (ewes only; lambs were assigned a separate 'parity') and the difference in age of the animal from the median of the respective parity/age group. An additive genetic effect and residual effect were both fitted as random terms with maternal genetic and non-genetic components also considered for traits of the lambs. The direct heritability of dagginess was similar across age groups (0.14 to 0.15), whereas the direct heritability of lameness ranged from 0.06 (ewes) to 0.12 (lambs). The direct heritability of mastitis was 0.04. For dagginess, 13% of the phenotypic variation was explained by dam litter, whereas the maternal heritability of dagginess was 0.05. The genetic correlation between ewe and lamb dagginess was 0.38; the correlation between ewe and lamb lameness was close to zero but was associated with a large standard error. Direct genetic correlations were evident between dagginess and BCS in ewes and between lameness and BCS in lambs. The present study has demonstrated that ample genetic variation exists for all three health traits investigated indicating that genetic improvement is indeed possible.

Factors affecting ewe longevity on sheep farms in three European countries

“…Indeed, Larsgard and Vaabenoe (1993) and Waage and Vatn (2008) observed, when previously assessing mastitis in Norwegian sheep breeds, that the incidence of mastitis increased as litter sizes increased. Previous research from Ireland also found that the incidence of mastitis increased with ewe age (O'Brien et al, 2017). This, coupled with the large proportion of terminal sire bloodlines represented in the Irish data (Texel, Suffolk and Charollais), which are also often associated with high lamb growth rates, may explain why mastitis features highly as an end reason in the Irish data.…”

Genetic analyses of live weight and carcass composition traits in purebred Texel, Suffolk and Charollais lambs

“…The carcass composition traits in the present study showed similar results to those previously reported in the literature for purebred Irish lambs. An earlier study conducted in Ireland (O'Brien et al, 2016) showed a mean of 33.21and 7.55 mm for muscle and fat depth traits, respectively. The first study carried out in the UK on live weight and carcass composition traits in terminal sire sheep was reported by Simm and Dingwall (1989) from which selection indices for terminal sire breeds were implemented in practice for the UK sheep industry and responses to selection reported.…”

Low-density genotype panel for both parentage verification and discovery in a multi-breed sheep population

“…Several traits constitute sheep breeding objectives (Santos et al, 2015), including those in Ireland that differ in estimated heritability. For example, the heritability of lamb survival is up to 0.09 (McHugh et al, 2017), the heritability of lameness is 0.10 (O'Brien et al, 2017), and the direct heritability of live weight is 0.25 (O'Brien et al, 2017). The proportional reduction in genetic gain for these three example traits with a 10% sire error (Berry et al, 2018) is illustrated in Figure 3.…”