Page 14 - National Poultry Newspaper

2018 HIGHLIGHTS
Dr Eugeni Roura
AFTER many years of research and farm tests, feather pecking remains one of the main unsolved challenges of the poultry industry, causing signifi- cant economic and wel- fare problems.
Feather pecking is a multi-factorial phenom- enon, which has been related to genetics, bird age, social transmission, hormonal profiles and nu- trient requirements.
For example, dietary nutrition imbalances/de- ficiencies, particularly in amino acids, have been identified as one of the major factors causing increased incidence of feather pecking.
Nutritional imbalances related to the onset of feather pecking events may only affect a few in- dividuals in the flock and could be a consequence of the prevalent commercial no-choice feeding prac- tices, with a single feed being formulated to max- imise flock productivity.
Thus, commercial feeds may not always meet the nutritional requirements of all the birds in the flock due to individual variation in digestive and
metabolic efficiencies which, in turn, are likely to cause marginal nutri- ent deficiencies in these individuals.
As a result, chickens with a higher demand of specific limiting nutrients will develop nutrient-spe- cific appetites that could hypothetically translate into feather appetites.
Feather pecking has been positively associated with feather ingestion.
In addition, there is ex- perimental evidence that feather eaters may use feathers as an alternative source of amino acids.
We hypothesize that individual differences in metabolism lead to nutri- ent-specific appetites that, in turn, relate to feather- pecking habits.
This study compared phenotypic parameters and nutrient-specific ap- petites between feather eating and non-feather eating birds.
Materials and methods
The trials were conduct- ed at the Poultry Research Unit (Gatton campus, Uni- versity of Queensland).
A first trial was de- signed aiming at the iden- tification of the feather-
eating status (FE v NFE) of 156 caged laying hens (60-week-old, ISA Brown) by assessing the content/ absence of feathers in the gastrointestinal tract after euthanasia at the end of the trial.
In addition, this study assessed several pheno- typic traits and their re- lationship with feather ingestion.
Feather density and open skin areas (cm2) were measured to deter- mine feather coverage condition.
Also, beak length, shank length, body weight and stress hormone level were compared between FE and NFE birds.
In trial two, 96 mature laying hens (54-week-old, ISA Brown) were indi- vidually caged, exposing them to a double choice test including ground wheat without (control) and with the treatment.
A training period con- sisting of simultaneously offering two feeds in sep- arated containers was per- formed two days before the double choice test, to make birds familiar with the choice paradigm.
The nutrients tested in DC were sugars (dextrose, fructose or sucrose) at 5, 10 or 15 percent inclu- sion, or amino acids (ly- sine, methionine, cysteine, tryptophan, glutamine, ar- ginine, histidine, glycine, proline, serine, tyrosine or alanine) at 0.2, 1 or 5 per- cent inclusion.
At the end of the trial, the hens were penned one additional week in groups of five to allow for feather-eating behav- iours to express before they were euthanised and their feather consumption assessed.
The consumption of the two feeds in each test (control v treatment) was analysed as a difference relative to the control feed consumed (consumption of treatment – consump- tion of control) or as a standard preference index (percent of treatment con- sumption over total con- sumption).
The preference values were statistically com- pared to the random choice value of 50 per- cent, while the difference of consumption was ana- lysed in contrast with the no difference (0g).
The feather-eating status was assigned to each bird based on presence (FE) or no-presence (NFE) of feathers in the upper GIT after the necropsy of the carcass.
Potential differences in appetite between the two groups of birds (FE v NFE), were compared using the GLM procedure of SAS.
Differences were con- sidered significant at P<0.05.
Results and discussion
FE birds showed a sig- nificantly higher prefer- ence for methionine and lysine than NFE (60.4±5.4 percent compared to 43.5±6.9 percent for me- thionine and 61.2±5.8 per-
cent compared to 39.0±7.0 percent for lysine, respec- tively).
Dietary amino acid de- ficiencies, particularly of the most limiting ly- sine and methionine plus cysteine (sulphur-amino acids), had been previ- ously reported to trigger feather-pecking behav- iours.
On the other hand, kera- tin, the main protein in beaks and feathers, is par- ticularly rich in sulphur- containing amino acids.
Interestingly, our chick- en studies from trial one showed FE birds had significantly shorter beak lengths than NFE birds (12.4±0.2mm v 12.9±0.2mm, respective- ly).
It is known both feath- ers and the outer shell of the beak are composed of keratin.
The SAA, methionine and cysteine play a sig- nificant role in feather and beak development.
Avian gastric and pan- creatic proteolytic en- zymes were reported in- effective to significantly digest keratin.
However, recent da- ta from Prescilla et al. (2017) showed feathers consumed by feather-eat- ing birds were partially digested, resulting in sup- plemental methionine and cysteine compared to the control birds.
Ultimately, it is tempt- ing to speculate that beak growth of laying hens may be limited by SA A avail- ability in FE birds.
These results would strongly suggest feather eating in laying hens was related to marginal lysine and SA A deficiencies af- fecting some individuals that, in turn, would affect beak and feather develop- ment.
On the other hand, NFE hens showed a significant- ly higher preference for glucose when compared to FE birds (65.7±5.1 and 39.6±7.2 percent, respec- tively).
However, chicken pref- erence for sugar is contro- versial, particularly since they lack the sweet taste receptor (T1R2) respon- sible for sweet taste in mammals.
According to Glendin- ning et al. (2010), it was stablished that the attrac- tion to sugars in mammals was not determined solely by taste.
The expression of the SGLT1 (glucose trans- porter) in the T1R taste cells in the oral tissue of mice and rats has been reported.
In the absence of functional T1Rs or α-gustducin, an in- crease of the expression of SGLT1 was observed when mice were offered a high-carbohydrate diet.
Also, post-oral activa- tion of SGLT1 in mice stimulated the preference for sweet compounds in a murine model.
Thus, SGLT1 has been referred to be responsible for the T1R-independent sweet sensitivity in mice.
Our data suggests laying hens sense sugar through a T1R2-independent sen- sory pathway.
In addition, we studied the degree of stress in FE and NFE by analysing corticosterone levels in egg albumen, showing the corticosterone level was higher in NFE compared to FE, indicating the first group was under higher stress (2.09±0.21ng/g and 1.63±0.15ng/g, respec- tively).
It can be speculated that the higher stress reported in NFE relates to being feather pulled and pecked.
Thus, NFE have a high- er chance to be feather pecked than FE birds.
Finally, chronic stress has been related to in- creased sugar consump- tion in mice.
Thus, our results suggest chronic stress shown by the corticosterone levels in NFE birds seems relat- ed to an increase in sugar appetite.
Conclusion
The differences of the nutrient-specific appetite in laying hens could result from individual variations in digestive and metabolic efficiencies on nutrient utilisation.
In the current study, we have found feather-eating and non-feather eating birds showed different preferences in the specific nutrients.
Our results indicate feather eating is partially explained by an increased appetite for lysine and SAA.
Dietary supplementation with additional lysine, methionine and glucose may help prevent the on- set of feather-pecking out- breaks.
These results provide evidence of nutrient- sensing variations in individual birds, par- ticularly in relation to feather appetite and nu- trient requirements, and may help improve feed formulation of laying hens to prevent feather- pecking behaviour.
In addition, simple sug- ars such as glucose seem to have the potential to improve the welfare status of feather-pecked hens. Future research
Solving the problem of feather pecking will only be possible with an accu- rate understanding of the underlying mechanisms.
Thus, our future studies will target a mechanistic interpretation of the ly- sine, SA A and sugar ap- petites in FE birds.
We hypothesize that nutrient-specific appetites will be related to allelic variance and/or increased expression of the genes involved in sensing the nutrients of interest (such as lysine, methionine and simple carbohydrates).
We will study potential genetic mutations (sin- gle-nucleotide polymor- phisms, SNP) and varia- tion in gene expression in the oral and GIT tissues, comparing FE to NFE birds.
Nutrient appetites in feather-pecking hens
Page 14 – National Poultry Newspaper, August 2018
Dr Eugeni Roura www.poultrynews.com.au