GrowthSept2020.pdf

ASB 321 (Meat Science) Growth and Body composition of meat animals Thursday, 24 September 2020 --mhd-- 1 Thursday, 24 September 2020 --mhd-- 2  Module Objectives...

ASB 321 (Meat Science) Growth and Body composition of meat animals Thursday, 24 September 2020 --mhd-- 1 Thursday, 24 September 2020 --mhd-- 2  Module Objectives Upon completion, learners should be able to; o Explain and discuss animal growth o Discuss and describe tissue deposition in meat animals o Discuss use of growth promoters and their effects in meat animals o Explain/discuss carcass characteristics 24 September 2020 --mhd-- 3  Growth is a complex biological phenomenon It Involves interactions between nutrients, genetics, hormones & environmental factors Muscle/bone/fat tissues & wool/fibre are all involved in the process of growth The number of muscle fibres for an animal is fixed at birth or immediately thereafter Genetics set the upper limit for an individuals’ maximum growth The endocrine system (hormones) coordinates these interactions with sex as a major effect Thursday, 24 September 2020 --mhd-- 4  Understanding the pattern of growth helps in control & manipulation of specific end products; eg. lean vs fat deposits Growth does not only involve increase in size, but development also; Change in body ‘shape, composition and function’ Attributable to cellular differentiation (hyperplasia/hypertrophy) Thus of interest in meat science/production Gives us a guide to those desirable portions of an animal that are of value Their yield can thus be maximised – lean (edible) tissue Reduce adipose material Consequently, reduce food waste Thursday, 24 September 2020 --mhd-- 6  Muscle growth and distribution Thursday, 24 September 2020 --mhd-- 11  Function determines/influences growth and structure of muscles Differential patterns of muscle growth Standard anatomical muscle groups Factors affecting muscle growth and distribution sex breed stage of maturity weight loss/growth pattern Growth genes’ mutation ✓ double muscling condition ✓ callipyge condition Thursday, 24 September 2020 --mhd-- 12  Phases of muscle growth Phase I: The ante-natal phase Muscle growth that occurs in-utero. Muscle growth is thought to be stimulated by passive tension through skeletal elongation. Phase II: The immediate post-natal phase The immediate post-natal phase is one of great change in muscle weight/ development as the animal adapts to a new environment. Changes in muscle weight and development in this period are largely a result of functional responses. Phase III: Sexual maturity The growth of the musculature in both males and females undergo changes at puberty. Phase IV: Maturing phase This phase comprises the major phase of growth over which animals are presented for slaughter and yet it is the period of growth where the changes are perhaps the smallest. The changes during this period tend to be gradual as the animal moves towards a mature composition. Thursday, 24 September 2020 --mhd-- 13  Anatomical Muscle Groups Gp 1 Proximal muscle of the hindlimb Gp 2 Distal muscle of the hindlimb Gp 3 Muscles of the spinal column Gp 4 Abdominal muscles Gp 5 Proximal muscles of the forelimb Gp 6 Distal muscles of the forelimb Gp 7 Muscles attaching thorax to the forelimb Gp 8 Muscles attaching the neck to the forelimb Gp 9 Intrinsic muscles of the thorax Thursday, 24 September 2020 --mhd-- 14  The effect of sex on mature muscle distribution in sheep (%) Muscle Group Rams Ewes Maturing Pattern Gp 1 Proximal hindlimb 27.3 30.1 early Gp 2 Distal hindlimb 4.6 5.0 very early Gp 3 Spinal column 16.9 17.0 average Gp 4 Abdomenal muscles 9.4 9.8 E late, R very late Gp 5 Proximal forelimb 11.0 11.5 early Gp 6 Distal forelimb 2.7 2.9 early Gp 7 Thorax/forelimb 6.7 6.3 late Gp 8 Neck/forelimb 8.4 7.7 late Gp 9 Intrinsic thorax 13.0 9.8 E early, R late Total muscle weight (kg) 18.0 11.4 Thursday, 24 September 2020 --mhd-- 15  Heritabilities for lean in a joint Joint h2 Leg 0.21 Chump 0.28 Loin 0.46 Best end neck 0.07 Breast 0.35 Middle neck 0.15 Shoulder 0.33 High priced joints 0.65 Wolfe et al. (1981) Thursday, 24 September 2020 --mhd-- 18  Muscle growth How can we manipulate muscle mass?? ✓ hypertrophy (fibre size) (example: Callipyge) ✓ hyperplasia (fibre number) (example: Double muscling) Thursday, 24 September 2020 --mhd-- 19  Muscle distribution in DM animals greatest increase in proximal limbs least in the distal limbs greatest increase in the hindlimb than the forelimb greater in superfical than the deep muscles greater increase in late maturing muscles lower collagen content Thursday, 24 September 2020 --mhd-- 20  Double Muscling lower reproduction/increase in dystocia higher birth weights Production related lower feed intake higher carcass dressing out percentage (%) higher Muscle/Bone ratio Meat Production lower fat and bone content related favourable muscle distribution, more lean tissue yield – more meat Pale cuts Thursday, 24 September 2020 --mhd-- 21  DM - Myostatin mutation Hyperplasia ( cell #) Predominantly prenatal Result - more muscle - pale cuts - dystocia Callipyge Hypertrophy ( cell size) Predominantly postnatal Greater calpastatin Result - more muscle - pale cuts - tougher meat Thursday, 24 September 2020 --mhd-- 23  Callipyge Normal Calpain and Calpastatin of Biceps Femoris of Koohmarie et al. (1995) Normal and Callipyge Lambs 2.5 2 Activity 1.5 Normal 1 Callipyge 0.5 0 u-calpain m-calpain calpastatin Thursday, 24 September 2020 --mhd-- 24  Growth Promoting Agents Growth Promoting steroids Synthetics (anabolic steroids) based on natural sex hormones Androgens act like male hormone testosterone Oestrogens act like female hormone oestrogen Progestagens act like female hormone progesterone Promote growth through reduction of protein degradation instead of protein synthesis, eg: Trenbolone acetate Zeranol Effects based on sex of animal, males respond better to female based agents and vice versa Castrates respond better to a combination of both sex agents Banned in 1988 in EU due to health concerns but still used in other countries USA, RSA, Australia, Mexico, etc Thursday, 24 September 2020 --mhd-- 25  Growth Promoting Agents β-adrenergic Agonists Similar structurally to natural hormones adrenaline (epinephrine) and noradrenaline (norepinephrine) Their effect on cells is through acting on the β-receptors on cell membranes – thus so named eg. Ractopamine/paylean, clenbuterol, cimaterol Able to alter muscularity of animals Lean to fat ratio is improved They have repartitioning effect – more lean and less fat deposition Reduction of fat deposition (lipogenesis) and increase fat breakdown (lipolysis) Overall effect: They promote protein synthesis – results in more lean, more meat, unfortunately the meat tends to be tougher !! Thursday, 24 September 2020 --mhd-- 26  Carcass Yield and Composition Carcass Yield That part of a carcass saleable as meat Differs across meat species and carcass dressing codes, indicated through killing (dressing) out percentage Killing/dressing out % = (carcass weight/live weight) * 100 Influenced by; Breed Carcass conformation Species (monogastrics vs ruminants) Level of fatness Sex Age Different husbandry systems Carcasses lose water (1.5 – 2%) through evaporation Thus should be aware of which weight was used Hot carcass weight (HCW) or Cold carcass weight (CCW/CDM) 24 September 2020 --mhd-- 27  Typical Killing/dressing-out percentage for different species Species Killing-out (%) Sheep ~50 Cattle ~53 Pigs ~75 Broiler chickens ~72 Note: Differences between monogastrics and ruminants 24 September 2020 --mhd-- 28  Typical Carcass Components of a steer based on live weight Component Weight (kg) Percentage of LW Carcass 265 53 Gut contents 64 13 Hide 49 10 Gut 41 8 Head, lungs, trachea, diaphragm 31 6 Blood lost at slaughter 20 4 Liver and kidneys 11 2 Gut fat 8 2 Other small components 11 2 Totals 500 100 24 September 2020 --mhd-- 29  Carcass Conformation Refers to carcass shape Better in beef vs dairy ones Better in bulls vs steers Males vs females generally within age/breed 24 September 2020 --mhd-- 30  Message Muscle growth can be manipulated to our advantage Meat/lean production Know the mechanism - know the benefits - know the possible drawbacks Thursday, 24 September 2020 --mhd-- 31