The Assessment of Genetic Expression and Nutritional Effects on Lamb Eating Quality

Summary

Objectives

Priorities: specific to MLA

1. Determine sire effects on lamb eating quality and provide a benchmark for a lamb eating quality estimated breeding value (EBV).

2. Determine the effects of Carwell genotype on carcass yield and meat quality.

Test the validity of the current GR site measurement for fat on lamb carcasses of a range of weights and seek a superior measurement for heavy lamb carcasses

Brief methodology

Sixty-four 12-week-old lambs selected from a group of 190 were placed in single pens for individual feeding. The remaining lambs were maintained on improved pasture. The lambs were from BL x Merino ewes and sired by Poll Dorset rams either from two rams known to express the Carwell gene or from two CPT non-Carwell sires.

The pen-based lambs were weighed weekly and assessed for fat score and subjected to an ultrasound scan for eye muscle depth monthly. Individual feed intake was recorded by weighing the feed offered and the uneaten residues daily. The ration for the pen based lambs was approximately 16% CP and 11 MJ ME/kg DM. Paddock lambs were weighed monthly and assessed for fat score and subjected to an ultrasound scan twice during the trial.

A total of 105 lambs (64 from the pen trial and 41 paddock lambs) were used to represent progeny from the Carwell and non-Carwell sires. They ranged in carcass weights and GR fat measures and after slaughter were used for meat quality (including eye muscle depth, carcass length, loin characteristics, muscle measurements, fat and bone) and retail yield.

Meat Quality measurements included: Warner Bratzler shear force, cooking loss, meat colour, ultimate pH, and aging rate of the LL. In addition to the GR tissue depth measure, measurements of the loin area included: GRb (the amount of muscle at the GR site), C fat (fat over the deepest part of the eye muscle), J fat (thickest layer of fat over the 12th rib), and eye muscle area (length and width at the 12th rib).

Main results and conclusions

Carwell and non-Carwell lambs were finished to slaughter weights (approximately 50 kg live weight) on either wheat/lupin rations (containing protected (starch, protein and lipid) or unprotected nutrients) or at pasture. After processing at a commercial domestic works LL of the carcase was assessed for pH, tenderness, cooking loss and colour. The right side of the carcase was cut into six primal joints.

Lambs fed protected and unprotected nutrients had significantly higher ADG’s and greater carcase weights and GR than those grown at Pasture. Sire type was not found to significantly affect growth rates or carcase weights.

The hindleg primal, the bone-in loin and loin eye were found to be significantly heavier in Carwell sire-31 and Carwell sire-32, when adjusted to a standard carcase weight.

WB shear was found to be significantly higher in Carwell sire-32 and non-Carwell sire-14 at 2 days after slaughter and remained significantly higher in Carwell sire-32 at 7 days after slaughter. There was no significant difference between sires for tenderness (WB) at 14 days.

Lambs pen-fed protected and unprotected nutrients had significantly higher WB at 2 days than the lambs grown at pasture. There were no significant differences at 7 days or 14 days.

Sire type and nutrition had no significant effects on cooking loss of the LL but non-Carwell sire-14 gave significantly greater cooking loss in the SM.

From this work it is concluded that individual sires can have significant impact on meat quality traits. Nutrition can also significantly affect meat quality. It remains to be determined whether sensory panel work elucidates the differences found using objective measures.