Determining the variation in premaxillary and dentary bone morphology that may underlie beak shape between two pure layer lines

Beak treatment is an effective method of reducing the damage inflicted by severe feather pecking (SFP) but there is significant pressure to eliminate these treatments and rely solely on alternative strategies. Substantial variation in beak shape exists within non-beak treated layer flocks and beak shape appears to be heritable. There is the potential to use this pre-existing variation and genetically select for hens whose beak shapes are less apt to cause damage during SFP. To do this, we must first understand the range of phenotypes that exist for both the external beak shape and the bones that provide its structure. The objective of this study was to determine the variation in premaxillary (within the top beak) and dentary (within the bottom beak) bone morphology that exists in 2 non-beak treated pure White Leghorn layer lines using geometric morphometrics to analyze radiographs. Lateral head radiographs were taken of 825 hens and the premaxillary and dentary bones were landmarked. Landmark coordinates were standardized by Procrustes superimposition and the covariation was analyzed by principal components analysis and multivariate regression using Geomorph (an R package). Three principal components (PCs) explained 85% of total premaxillary bone shape variation and showed that the shape ranged from long and narrow with pointed bone tips to short and wide with more curved tips. Two PCs explained 81% of total dentary bone shape variation. PC1 described the dentary bone length and width and PC2 explained the angle between the bone tip and its articular process. For both bones, shape was significantly associated with bone size and differed significantly between the two lines. Bone size accounted for 42% of the total shape variation for both bones. Together, the results showed a range of phenotypic variation in premaxillary and dentary bone shape, which in turn may influence beak shape. These bone phenotypes will guide further quantitative genetic and behavioral analyses that will help identify which beaks shapes cause the least damage when birds engage in SFP.

The impact of beak tissue sloughing and beak shape variation on the behavior and welfare of infrared beak-treated layer pullets and hens

This research examined how infrared beak treatment (IRBT), sloughing of the treated beak tissue, and the variations in beak shape that can occur post-IRBT impact the welfare and mortality of Lohmann LSL-Lite (LW) and Lohmann Brown (LB) pullets and hens. Two experiments were conducted and birds for both experiments were treated on the day of hatch. IRBT equipment settings were adjusted to create 4 specific beak shapes: shovel (SHV), step (STP), standard (STAN), and an untreated sham control (C). Experiment 1 pullets (n = 80 per strain) were reared in bioassay cages from 1 to 29 D of age (4 replicates per treatment). Data collected included time and presence of beak sloughing, pecking force, behavioral expression, and mortality. Experiment 2 pullets (n = 320 per strain) were reared in floor pens from 1 D to 18 wk of age (2 replicates per treatment) and then conventional cages from 18 to 60 wk of age (6 replicates per treatment). Data collected for Experiment 2 included behavioral expression, feather cover, comb damage, and mortality. Data were analyzed using PROC MIXED (SAS® 9.4) with Tukey's test to separate means. Differences were significant when P ≤ 0.05. IRBT and sloughing had no effect on pecking force or mortality throughout rearing. The variations in post-IRBT beak shape had minor effects on behavior. During rearing, STAN pullets were more active than C pullets but STP and STAN pullets performed less exploratory pecking. During the laying period, SHV and STP hens preened more than C hens. The IRBT treatments, regardless of beak shape, reduced feather loss, comb damage, and cannibalism-related mortality during the laying period. Overall, the results indicate that LW and LB pullets and hens can cope with the change in beak shape that occurs with IRBT, and that welfare is not negatively impacted if some variation in beak shape occurs.

The effect of beak tissue sloughing and post-treatment beak shape on the productivity of infrared beak-treated layer pullets and hens

Infrared beak treatment (IRBT) results in a change in beak shape; however, it is unclear what effect variations in post-treatment beak shape have on young pullets. Additionally, the impact of sloughing of the treated beak tissue is not fully understood. Two experiments were conducted to determine the effects of beak tissue sloughing and post-treatment beak shape on the productivity of infrared beak-treated Lohmann Brown (LB) and Lohmann LSL-Lite (LW) pullets and hens. Birds were treated on day of hatch and IRBT equipment settings were adjusted to create 4 specific beak shapes: shovel (SHV), step (STP), standard (STAN), and an untreated sham control (C). Experiment 1 pullets (n = 160) were housed in cages from 1 to 29 d of age and had access to water through chick founts or 360° nipple drinkers (2 replicate cages per treatment). Data collected included body weight (BW), feed intake (FI), feed efficiency (FE), and water disappearance (WD). Experiment 2 pullets (n = 640) were housed in floor pens from 1 d to 18 wk of age (2 replicate pens per treatment) then conventional cages during the laying period (6 replicate cages per treatment). Data collected included BW, FI, egg production, and egg quality. Data were analyzed using PROC MIXED (SAS® 9.4) and differences were significant when P ≤ 0.05. During early life, the IRBT treatments and sloughing had minor effects on FI, FE, and BW. At 4 wk of age, STAN pullets were lighter than C pullets; however, differences were no longer apparent after this age. Pullets with STP or STAN beak shapes had lower WD than C pullets when allowed access to water via nipple drinkers but this did not result in reduced growth. Throughout the laying period, SHV hens laid more saleable eggs than C hens, with no other effects on production. Overall, variations in beak shape and sloughing of the beak tissue had minimal impacts on the productivity of LW and LB pullets and hens.