Genetic parameters for bodyweight, wool, and disease resistance and reproduction traits in Merino sheep. 2. Genetic relationships between bodyweight traits and other traits

Abstract

The Australian Merino is the predominant genetic resource for both the prime lamb and sheep meat industries of Australia. There are very few studies that provide good information on the relationships between wool and non-wool traits. The objective of this paper was to describe genetic relationships within bodyweight traits and between bodyweight and other traits recorded in Merino sheep. The genetic correlation between bodyweight, fleece weight and fibre diameter was positive (0.1 to 0.2). While fibre diameter coefficient of variation, staple length, staple strength, mean fibre curvature, and faecal egg count were not correlated with bodyweight. Scrotal circumference (0.4), number of lambs born (0.1), and number of lambs weaned (0.1) were positively correlated with bodyweight. Results indicate that selection for an increase in bodyweight will have a positive effect on eye muscle depth, fleece weight, and reproduction traits, while selection for an increase in bodyweight will have a negative effect on fibre diameter and fibre diameter coefficient of variation.

Sire carcass breeding values affect body composition in lambs — 1. Effects on lean weight and its distribution within the carcass as measured by computed tomography

“…This contradicts previous findings from smaller studies where PWWT had no effect , though it does support the general principle that lambs selected for high post weaning weights would have a larger mature size (Huisman & Brown, 2008) and therefore they will be physiologically less mature when compared at the same weight (Berg & Butterfield, 1968;Butterfield et al, 1983;Hegarty, Shands, et al, 2006) …”

“…This change in body composition may be suggestive of low PFAT animals having a larger mature size, however, previous research has demonstrated little genetic or phenotypic correlation between sire PFAT and adult weight (Huisman & Brown, 2008) or growth rate (Kelman et al unpublished). Thus it seems likely that these compositional differences will still be present when the animals reach their mature size.…”

“…However if maturity was implicated then there should also have been proportionately more bone (Berg & Butterfield, 1968;Butterfield, Zamora, Thompson, Reddacliff, & Griffiths, 1984;Fourie et al, 1970). Furthermore, Huisman & Brown (Huisman & Brown, 2008) have demonstrated no phenotypic or genetic correlation between PEMD and mature weight. Therefore the more muscular composition appears to be independent of maturity.…”

“…Whilst there is evidence that a strong emphasis on PWWT ASBV will increase growth rate and mature size (Huisman & Brown, 2008), there is little data showing the effects of this ASBV on carcass composition. It has been shown that lambs growing at a faster rate are proportionately leaner when compared at the same weight, largely due to a correlated increase in mature weight (Bennett, Kirton, Johnson, & Carter, 1991;Butterfield, 1988).…”

The impact of genetics on retail meat value in Australian lamb

“…This was a reflection of their greater lean weight across all three carcass sections compared to both Merino and Maternal sired lambs, consistent with their larger mature size and therefore reduced maturity when compared at the same weight (Huisman & Brown, 2008). On the basis of these differences the carcasses of Terminal sired lambs were worth $9.57 and $14.36 more than the Merino and Maternal sired lambs.…”