Opportunities for exercise during pullet rearing, Part I: Effect on the musculoskeletal characteristics of pullets

Abstract

Increased load-bearing exercise improves bone quality characteristics in a variety of species, including laying hens. Providing increased opportunities for exercise during the pullet rearing phase, a period of substantial musculoskeletal growth, offers a proactive approach to reducing osteoporosis by improving bone composition. The main objective of this study was to determine whether differing opportunities for exercise during rearing influences pullet musculoskeletal characteristics. Two flock replicates of 588 Lohmann Selected Leghorn-Lite pullets were reared in either standard, conventional cages (Conv) or an aviary rearing system (Avi) from day-old chicks until 16 wk of age. The keel bone and the muscles and long bones of the wings and legs were collected at 16 wk to measure muscle growth differences between rearing treatments and quantify bone quality characteristics using quantitative computed tomography (QCT) and bone breaking strength (BBS) assessment. Keel bone characteristics and muscle weights were adjusted for BW and analyses for QCT and BBS included BW as a covariate. At 16 wk of age, rearing system had an effect on the majority of keel bone characteristics (P < 0.05). The length of the keel metasternum, caudal tip cartilage length, and the overall percentage of cartilage present on the keel at 16 wk was greater in the Avi pullets compared to the Conv pullets (P < 0.01). Wing and breast muscle weights of the Avi pullets were greater than the Conv pullets (P < 0.001), but leg muscle weights were greater in the Conv pullets (P = 0.026). Avi pullets had greater total bone density, total cross-sectional area, cortical cross-sectional area, total bone mineral content, and cortical bone mineral content than Conv pullets for the radius, humerus, and tibia (P < 0.001). Avi pullets had greater BBS compared to the Conv pullets for the radius, humerus, and tibia (P < 0.01). Increased opportunities for exercise offered by the aviary rearing system increased muscle and bone growth characteristics in pullets at 16 wk of age.

Effects of outdoor ranging on external and internal health parameters for hens from different rearing enrichments

“…This coincides with observations on commercial farms that assessed damage via both dissection (Kolakshyapati et al, 2019) and palpation (Larsen et al, 2018) and found no association between individual ranging and keel damage. It was expected that rearing with structural enrichments may have reduced the later occurrence of fractures (Casey-Trott et al, 2017b), but this was not supported by the current study. The actual relationship between range use and keel damage might be inconclusive because painful keel fractures might prevent birds passing through the pop holes (Richards et al, 2012) and ultimately reduces range access.…”

“…This would also correspond with the higher empty gizzard weight observed in the ranging hens, similar to findings of larger gizzards in free-range versus caged hens (Yang et al, 2014). The reduction in body weight might also be a result of greater energy utilisation during locomotion, although greater exercise opportunities have previously been shown to increase bone and muscle development (Casey-Trott et al, 2017a;Regmi et al, 2016) which was not found in the outdoor hens. Other measured skeletal properties rather than overall mass may have revealed differences between ranging groups although recent work showed no effect of ranging on multiple tibial measurements across hens from a commercial aviary-free-range system (Kolakshyapati et al, 2019).…”

“…Furthermore, it is well documented both within Australia and internationally that range use varies by individual choice, with some hens ranging daily while others do not range at all (Larsen et al, 2017;Pettersson, Freire & Nicol, 2016b). This variation could result in large differences in activity and diet between hens which may impact health and welfare such as influencing body composition by lowering body fat accumulation (Crespo & Esteve-Garcia, 2001; Renema et al, 1999;Sun et al, 2006) and strengthening the bones (Regmi et al, 2016) and muscles (Casey-Trott et al, 2017a), although recent work with commercial free-range layers showed no relationship between range use and tibial bone strength (Kolakshyapati et al, 2019).…”

Peer Review #3 of "Effects of outdoor ranging on external and internal health parameters for hens from different rearing enrichments (v0.2)"

“…This would also correspond with the higher empty gizzard weight observed in the ranging hens, similar to findings of larger gizzards in free-range versus caged hens (Yang et al, 2014). The reduction in body weight might also be a result of greater energy utilisation during locomotion, although greater exercise opportunities have previously been shown to increase bone and muscle development (Casey-Trott et al, 2017a;Regmi et al, 2016) which was not found in the outdoor hens. Other measured skeletal properties rather than overall mass may have revealed differences between ranging groups although recent work PeerJ reviewing PDF | (2019:11:43210:2:0:NEW 3 Feb 2020)…”

“…Furthermore, it is well documented both within Australia and internationally that range use varies by individual choice with some hens ranging daily while others do not range at all (Larsen et al, 2017;Pettersson et al, 2016b). This variation could result in large differences in activity and diet between hens which may impact health and welfare such as influencing body composition by lowering body fat accumulation (Crespo & Esteve-Garcia, 2001;Renema et al, 1999;Sun et al, 2006) and strengthening the bones (Regmi et al, 2016) and muscles (Casey-Trott et al, 2017a ). Although recent work with commercial freerange layers showed no relationship between range use and tibial bone strength (Kolakshyapati et al, 2019).…”