Investigating the relationship between lamb weaning age and forage diet on carcass and meat quality : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Animal Science, Massey University, Palmerston North, New Zealand

Abstract

Lamb carcass characteristics and meat quality are important components of the value chain that determine the carcass value and price obtained. On-farm factors can affect carcass characteristics and meat quality of lamb, however, the effect of early weaning and forage diet on carcass and meat quality characteristics is not well-known. Therefore, this thesis considers the relationship between weaning age and the forage diet for influencing carcass characteristics and meat quality of lamb.

The study compared carcass characteristics and meat quality of early weaned lambs (at eight weeks of age) grazing a plantain-clover mix, and conventionally weaned lambs (at 14 weeks of age) grazing a plantain-clover mix or perennial ryegrass-white clover pasture with all lambs finished for six weeks as one mob on perennial ryegrass-white clover pasture to achieve a target minimum live weight of 35 kg at slaughter (Chapter 3). Forty-three Romney ewes rearing twin lambs (86 lambs) were used in this study. Ewes and their lambs were allocated to one of four treatments: 1) lambs weaned early (eight weeks of age) on a plantain-clover mix (EARLY), 2) lambs with dam grazing a plantain-clover mix (HERB), 3) lambs with dam grazing perennial ryegrass-white clover pasture >1200 kgDM/ha (HIGH), and 4) lambs with dam grazing perennial ryegrass-white clover pasture <1200 kgDM/ha (LOW). Lambs in treatments 2, 3, and 4 were weaned at 14 weeks of age.

Lambs in the HERB treatment had the fastest growth rate, yielding heavier carcasses and a higher dressing out percentage compared to EARLY and LOW lambs. HIGH lambs had intermediate growth rates, carcass weights and dressing out % (Chapter 5, Table 8). Physical dissection of the hind leg showed lambs in the EARLY treatment had the least dissectible fat compared to HIGH and LOW lambs which had the most, with HERB lambs intermediate. In addition, lambs in the EARLY treatment had a similar fat% and muscle% compared to HERB and LOW lambs but produced lower fat% and higher muscle % than lambs in the HIGH treatment (Chapter 5, Table 9).

Objective measurements of lamb meat quality only showed a difference among treatments for sarcomere length and total shear force work (Chapter 5, Table 10). Lambs in the EARLY and HIGH treatments had the longest sarcomere lengths and lambs in the HERB treatment the shortest, with intermediate lengths recorded for LOW lambs. Meat from lambs in the EARLY, HERB and LOW treatments required less total shear force work than lambs in the HIGH treatment. Although statistically significant the relative difference in results was not substantial, indicating that generally the treatments had no effect on meat quality.

Early weaning of lambs onto a plantain-clover mix does not have negative effects on carcass and meat quality. However, the slower growth rate of early weaned and restricted perennial ryegrass pasture raised lambs resulted in lower carcass weights in this study indicating that a lower nutritive diet as a consequence of using grass species or a lack of milk intake will mean lambs will need more time to achieve a set finishing weight.