The effects of experimental increase in insulin-like growth factor 1 on feather growth rate, moult intensity and feather quality in a passerine bird

Moulting is a crucial, yet often overlooked life-history stage in many animals, when they renew their integumental structures. This life-history stage is an energetically demanding somatic growth event that has particular importance in birds because feathers play a crucial role in flight, insulation and communication. Somatic growth processes are regulated by the evolutionarily conserved peptide hormone, insulin-like growth factor 1 (IGF-1). However, the role of IGF-1 in feather growth remains unknown. In this study, we captured 41 juvenile free-living bearded reedlings (Panurus biarmicus) that had started their first complete moult and brought them into captivity. Then we manipulated their circulating IGF-1 levels using poly-(lactid-co-glycolid acid) microparticles (microspheres) that provide a sustained release of IGF-1. The treatment increased IGF-1 levels but did not affect the feather growth rate. However, two weeks after the treatment, birds in the increased IGF-1 group were moulting more feathers simultaneously than the controls and were at a more advanced stage of moult. Birds with experimentally increased IGF-1 levels had better quality feathers (measured by a lower number of fault bars) than the controls. These results suggest that an increase in IGF-1 does not speed up feather growth, but may alter moult intensity by initiating the renewal of several feathers simultaneously. This may shorten the overall moulting time but may imply costs in terms of IGF-1 induced oxidative stress.

Feather growth, bodyweight and body temperature in broiler lines with different feathering rates

Two early feathering sire lines (B1 and B2), two late feathering dam lines (A1 and A3), and an early feathering dam line were evaluated to determine differences in growth, in lengths of primary feathers, in under-wing and rectal temperatures, and in feed intake until the birds were 20 weeks old. The chicks were hatched from eggs collected from 35-week-old hens of pure line broiler flocks. Data were collected at hatch, and at 1, 2, 4, 6, 8, 12, and 20 weeks old Thirty males and 30 females were evaluated for each line. The early feathering genotypes (A2, B1 and B2) had longer primary feathers until they were six weeks old. They also had higher under-wing and rectal temperatures and higher live weight compared with the late-feathering lines (A1 and A3) at one and two weeks old. The males were heavier than females at all ages. However, under-wing and rectal temperatures were similar in males and females at all ages. A positive correlation was observed between the length of primary feathers and live weight in A2, B1, and B2 at six weeks, whereas a negative correlation was observed between the rectal temperature and the length of primary feathers in A1 and A3 at 4 and 20 weeks old.

Describing the growth and molt of modern domestic turkey (Meleagris gallopavo) primary wing feathers

The use of feathers as noninvasive physiological measurements of biomarkers in poultry research is expanding. Feather molting patterns and growth rates, however, are not well described in domestic poultry. These parameters could influence the measurement of these biomarkers. Therefore, the objective of this study was to describe the juvenile primary feather molting patterns and feather growth rates for domestic turkeys. The 10 primary wing feathers of 48 female turkeys were measured weekly from week 1 (0 d of age) to week 20. Feathers were manually measured, and the presence or absence of each primary feather was recorded weekly. Generalized linear mixed models were used to investigate if feather growth differed between the primary feathers. The molting of the juvenile primary feathers followed a typical descending pattern starting with P1 (5 wk of age), while P9 and P10 had not molted by the end of the study (20 wk of age). The average feather growth rate was 2.4 cm/wk, although there was a significant difference between the 10 primary feathers (P < 0.0001, 2.1 to 2.8 cm/wk). Over time, feather growth followed a pattern where the growth rate reaches a peak and then declines until the feather is molted. The results of this study provide a critical update of patterns of molting and feather growth in primary wing feathers of modern turkeys. This can have implications for the interpretation of physiological biomarkers, such as the longitudinal deposition of corticosterone, in the feathers of domestic turkeys.

A brief report on the development of dorsal air sacs in hand reared Von der Decken’s hornbills (Tockus deckeni)

Several species of hornbills are known to develop dorsal air sacs after hatching, which present as a pocket of air under their skin. These increase in size as the chicks grow, and gradually disappear as the chicks develop feathers. However, this feature is not well-described, nor do we know the extent it occurs in Bucerotids. Here, it is reported in a clutch of hand-reared Von der Decken’s hornbills ( Tockus deckeni) ( n = 5) at Jurong Bird Park, Singapore. Air sacs were not present at hatch, but developed within 24 h, increasing in size until about 10 days of age. They gradually recede from this age and are not always inflated, disappearing at about 16 days of age when the chick has considerable feather growth. The functions of this unique feature are largely unclear, but it is thought to be mostly related to thermoregulation. Further research is required to determine this, possibly using captive specimens from zoological institutions as it is more difficult to collect data from wild birds.