Meat quality and fat characteristics of lambs finished on different summer forages : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand

Abstract

New Zealand lamb production systems are typically based on grazing perennial ryegrass/white clover pastures; however forage quality and growth tend to be inconsistent over the summer period leading to reduced intakes and animal performance. Summer-active forage crops can be included in the farm system to provide a source of high-quality forage over this crucial finishing period. In addition to this, ensuring consistently high eating quality lamb meat is paramount to maintain and expand export markets, thus any change to production systems need to consider the impact on the meat produced. Whilst alternative forages to perennial ryegrass/white clover have been studied extensively for their agronomic characteristics and animal performance, less is known about the impact of an alternative forage on the value chain from farmer to processor and in particular characteristics that can impact the consumer such as meat quality. This is particularly the case with the relatively new forage brassica species, Raphanobrassica. This collection of studies conducted a comprehensive assessment of lambs grazing Raphanobrassica, Chicory, Perennial ryegrass/white clover (Chapters 3-7), Leafy Turnip, Red Clover and Perennial ryegrass/white clover + concentrate (Chapters 3-4). Studies utilised a replicated farmlet design and measured lamb growth, carcass production, meat quality, fat characteristics, volatile profile and conducted a consumer sensory evaluation. Lambs grazing alternative forages had increased lamb growth rates, carcass weights and dressing out percentages (Chapters 3 & 5). Using Raphanobrassica or Chicory resulted in greater per hectare lamb performance (liveweight gain and carcass weight produced per hectare) over the summer and autumn period. The two forage types had different factors driving this increase, with lambs fed Chicory having greater per head performance and Raphanobrassica able to support a larger number of grazing lambs per hectare due to superior forage growth in dry conditions (Chapter 5). Instrumental measurement of meat quality (pH, meat colour, shear force and water holding capacity) demonstrated small and inconsistent effects of forage diet (Chapters 4 & 6). Grazing alternative forages resulted in greater fat deposition (V-GR and intramuscular fat %) from faster growth and heavier carcasses. Changes in fatty acid composition were small and explained by the differences in IMF deposited (Chapters 4 & 6). Assessment of different grazing durations over summer and autumn (32, 35 or 67 days) showed that length of time grazing had a greater effect on meat quality and fat deposition than the forages themselves, with longer grazing durations associated with heavier carcasses, greater fat deposition and a fatty acid profile that was more saturated (Chapter 6). A stepwise analysis was used to assess the volatile profile of lamb meat, with 10 key volatile compounds differentiating the forage grazed and grazing duration. Aldehydes, alcohols and ketones (derived from lipid oxidation), sulphur compounds and hydrocarbons (non-lipid volatiles) were identified as potential markers for the forage treatments (Chapter 6). A consumer sensory panel identified meat from Chicory fed lamb as being less tender, however this can be explained by the larger carcass weights achieved on this forage type. Scores for overall liking for Raphanobrassica were dichotomous, potentially due to Raphanobrassica having more frequent rankings for greatest flavour intensity, indicating flavour intensity could be a stronger driver of liking for some consumers compared to others (Chapter 7). This research has shown that alternative forages to perennial ryegrass/white clover can be grazed by lambs over the summer period to improve animal production per head and per hectare without compromising the quality of meat produced for the processor or consumer.