Anatomical and biomechanical traits of broiler chickens across ontogeny. Part II. Body segment inertial properties and muscle architecture of the pelvic limb

Abstract

In broiler chickens, genetic success for desired production traits is often shadowed by welfare concerns related to musculoskeletal health. Whilst these concerns are clear, a viable solution is still elusive. Part of the solution lies in knowing how anatomical changes in afflicted body systems that occur across ontogeny influence standing and moving. Here, to demonstrate these changes we quantify the segment inertial properties of the whole body, trunk (legs removed) and the right pelvic limb segments of five broilers at three different age groups across development. We also consider how muscle architecture (mass, fascicle length and other properties related to mechanics) changes for selected muscles of the pelvic limb. All broilers used had no observed lameness, but we document the limb pathologies identified post mortem, since these two factors do not always correlate, as shown here. The most common leg disorders, including bacterial chondronecrosis with osteomyelitis and rotational and angular deformities of the lower limb, were observed in chickens at all developmental stages. Whole limb morphology is not uniform relative to body size, with broilers obtaining large thighs and feet between four and six weeks of age. This implies that the energetic cost of swinging the limbs is markedly increased across this growth period, perhaps contributing to reduced activity levels. Hindlimb bone length does not change during this period, which may be advantageous for increased stability despite the increased energetic costs. Increased pectoral muscle growth appears to move the centre of mass cranio-dorsally in the last two weeks of growth. This has direct consequences for locomotion (potentially greater limb muscle stresses during standing and moving). Our study is the first to measure these changes in the musculoskeletal system across growth in chickens, and reveals how artificially selected changes of the morphology of the pectoral apparatus may cause deficits in locomotion.

Variety, sex and ontogenetic differences in the pelvic limb muscle architectural properties of leghorn chickens (Gallus gallus domesticus) and their links with locomotor performance

“…Similar to findings in broiler chickens across ontogeny (Paxton et al. ), there was no difference in relative fascicle length between juvenile and mature cohorts in the parallel‐fibred muscles. Sex differences, however, were already present in the fascicle lengths of the IC and PIFL in juveniles.…”

“…The skeletal muscle architectural properties of broiler breeders and ancestral jungle fowl, including at differing ontogenetic stages, have been comprehensively described (Paxton et al. , ). Intra‐ and inter‐breed variations in the muscle architecture of chickens selected for their egg‐laying productivity, however, have yet to be investigated.…”

Post‐Hatching Growth of the Pectoralis Muscle in Pigeon and Its Functional Implications

“…In the black tern ( Anous minutus ), a semi‐precocial bird, the pectoralis MM exhibited strong positive allometry, presenting 25‐fold increase over the period leading up to first flight, with a further doubling associated with functional flight (Bennett, ). The growth pattern of FL was only reported for leg muscles, and it showed a mixed scaling pattern among different species (Lamas et al, ; Paxton et al, ). This is the first report on the ontogenetic allometry of the FL of the pectoralis.…”

Peer Review #1 of "Ontogenetic scaling patterns and functional anatomy of the pelvic limb musculature in emus (Dromaius novaehollandiae) (v0.1)"

“…Few studies have quantified the ontogenetic scaling patterns of limb musculature in birds (Carrier & Leon 1990;Dial & Carrier 2012;Paxton et al 2014;2012b;Picasso 2014), but positive allometry predominates in the muscle masses involved in the major adult mode of locomotion (flying vs. cursorial). In the Californian gull, the M. gastrocnemius scaled isometrically but the M. pectoralis had strong positive allometry with an inflection point when the fledglings started exercising their wings (Carrier & Leon 1990).…”

“…In the Californian gull, the M. gastrocnemius scaled isometrically but the M. pectoralis had strong positive allometry with an inflection point when the fledglings started exercising their wings (Carrier & Leon 1990). Paxton et al (2014;also 2010) recently reported the ontogenetic scaling patterns of the musculature of a highly modified galliform, the broiler chicken. These birds, unsurprisingly due to their selective breeding, were found to have positive allometry of muscle masses of the main pelvic limb muscles but isometry of the fascicle lengths (Paxton et al 2014), a pattern that is nonetheless similar to our findings.…”