Wiebke Icken

Background: Avian eggs have a proteinaceous cuticle. The quantity of cuticle varies and the deposition of a good cuticle in the uterus (Shell-gland) prevents transmission of bacteria to the egg contents. Results: To understand cuticle deposition, uterus transcriptomes were compared between hens with i) naturally good and poor cuticle and, ii) where manipulation of the hypothalamo-pituitary-gonadal-oviduct axis produced eggs with or without cuticle. The highest expressed genes encoded eggshell matrix and cuticle proteins, e.g. MEPE (OC-116), BPIFB3 (OVX-36), RARRES1 (OVX-32), WAP (OVX-25), and genes for mitochondrial oxidative phosphorylation, active transport and energy metabolism. Expression of a number of these genes differed between hens laying eggs with or without cuticle. There was also a high expression of clock genes. PER2, CRY2, CRY1, CLOCK and BMAL1 were differentially expressed when cuticle deposition was prevented, and they also changed throughout the egg formation cycle. This suggests an endogenous clock in the uterus may be a component of cuticle deposition control. Cuticle proteins are glycosylated and glycosaminoglycan binding genes had a lower expression when cuticle proteins were deposited on the egg. The immediate early genes, JUN and FOS, were expressed less when the cuticle had not been deposited and changed over the egg formation cycle, suggesting they are important in oviposition and cuticle deposition. The uterus transcriptome of hens with good and poor cuticle deposition did not differ. Conclusions: We have gained insights into the factors that can affect the production of the cuticle especially clock genes and immediate early genes. We have demonstrated that these genes change their expression over the period of eggshell formation supporting their importance. The lack of differences in expression between the uterus of hens laying eggs with the best and worse cuticle suggest the genetic basis of the trait may lie outside the oviduct.

The cuticle is an invisible glycosylated protein layer that covers the outside of the eggshell and forms a barrier to the transmission of microorganisms. Cuticle-specific staining and in situ absorbance measurements have been used to quantify cuticle deposition in several pure breeds of chicken. For brown eggs, a pre-stain and a post-stain absorbance measurement is required to correct for intrinsic absorption by the natural pigment. For white eggs, a post-stain absorbance measurement alone is sufficient to estimate cuticle deposition. The objective of the research was to estimate genetic parameters and provide data to promote adoption of the technique to increase cuticle deposition and reduce vertical transmission of microorganisms. For all pure breeds examined here, i.e. Rhode Island Red, two White Leghorns, White Rock and a broiler breed, the estimate of heritability for cuticle deposition from a meta-analysis was moderately high (0.38 ± 0.04). In the Rhode Island Red breed, the estimate of the genetic correlation between measurements recorded at early and late times during the egg-laying period was ~ 1. There was no negative genetic correlation between cuticle deposition and production traits. Estimates of the genetic correlation of cuticle deposition with shell color ranged from negative values or 0 in brown-egg layers to positive values in white- or tinted-egg layers. Using the intrinsic fluorescence of tryptophan in the cuticle proteins to quantify the amount of cuticle deposition failed because of complex quenching processes. Tryptophan fluorescence intensity at 330 nm was moderately heritable, but there was no evidence of a non-zero genetic correlation with cuticle deposition. This was complicated furthermore by a negative genetic correlation of fluorescence with color in brown eggs, due to the quenching of tryptophan fluorescence by energy transfer to protoporphyrin pigment. We also confirmed that removal of the cuticle increased reflection of ultraviolet wavelengths from the egg. These results provide additional evidence for the need to incorporate cuticle deposition into breeding programs of egg- and meat-type birds in order to reduce vertical and horizontal transmission of potentially pathogenic organisms and to help improve biosecurity in poultry.

Upcoming nesting behaviour traits, such as the exact oviposition time or the time spent in the nest, have a direct impact on economically relevant aspects. Hens which stay for a long time inside the nest box, require more nest capacity which result in higher investments for the farmer. This is similar to flocks in which most of the layers have the need to lay their eggs in a short time frame during the day. For both of these nesting behaviour traits, published data have shown strain differences. While brown layers are more relaxed in terms of their oviposition time, almost 90% of a white layer flock lay their eggs within 3 hours during the morning. Additionally, a white layer on average occupies the nest 15 minutes longer than a brown layer. The estimated heritabilities for both traits are on a medium level of around h² = 0.25, and are therefore susceptible to genetically-linked changes. Lower heritabilities are estimated for indirect nesting behaviour traits such as the time interval between two consecutively laid eggs (h² = 0.09) or the total clutch size (h² = 0.25). Ranging behaviour traits also show heritabilities on a medium level. The published heritability for the frequency of passages as well as for the length of stay in the winter garden is h² = 0.24, however, their relationship to the most important selection trait ‘egg number’, is negative. The laying performance tested with the Funnel Nest Box (FNB) show differences to the recorded egg number of full sibs which have been tested in cages. Tabled genetic parameters showed low correlations for the egg number at peak production (r_g = +0.2 to r_g = +0.4) which could be explained by genotype x environment effects. Other traits like egg weight, early egg production and body weight show high correlations between both testing environments.

Title of the paper: Genetic analysis of the laying pattern in floor management in terms of new performance parameters for breeding In order to facilitate a specific selection of laying hens which are suitable for alternative housing systems, it will be of advantage if the individual hens were tested in their later husbandry environment. Therefore, a new technology has been developed, the »Weihenstephan Funnel Nest Box«, which enables the automatic recording of these essential performance and nesting behaviour parameters of the individual hens in a group housing system. The exact oviposition times of 263 laying hens of Lohmann Silver line were recorded and used to analyse the laying pattern. Some results which were already pointed out in literature were thus confirmed, other brought new cognitions in terms of the oviposition pattern and about the pause following a laying sequence. A positive genetic correlation between the length of a laying sequence and the subsequent pause durations (r_g=+0.49) confirmed the tendency to longer breaks following an increasing laying sequence. The duration of a break was, however, not such an essential criteria for the productivity of a hen. More important in this context was the number of pauses which rises constantly with the number of laying sequences over the whole observation period. When the hens laid in shorter sequences, it was observed that the proportion of sequences grew, which was reflected as smaller number of registered eggs per hen (r_g =−0.73). The logical conclusion was the highly positive correlation between the length of a laying sequence and the number of registered eggs (r_g =+0.82). Closely associated with the length of a laying sequence, as well as the laying performance, was the parameter time interval between two laid eggs. The time interval between two laid eggs was significant shortened from the first to the third egg within one laying sequence and eventually reached for more than 24 h for most of the hens. The phenotypic and genetic correlation between the time interval and the laying performance was negative (r_p =−0.46 and r_g =−0.46). The heritability for the time interval was estimated at h²=0.17 which was similar to the heritability for number of eggs (h²=0.20). Slightly higher heritabilities were estimated for the indirect parameter of the time interval, the oviposition time of the third to the fifth egg in a laying sequence (h²=0.25, h²=0.34 and h²=0.29). Valuations in this range would be in regard of new performance testing parameter competitive to the parameter number of eggs and therefore, be tested in further investigations.

1. Over twelve 28-d laying periods (almost one year), 272 laying hens of the Lohmann Silver strain, individually tagged with transponders, were monitored on their ranging behaviour and laying performance in an aviary system with an adjacent winter garden. 2. From laying periods 1 to 12, the daily frequency of passages between the barn and the winter garden of individual hens, showed an antagonistic trend compared to the average duration of single visits. While the frequency of passages decreased until the end of the recording period to 8 passages per hen and day, the average duration of single visits increased to a maximum of 32 min per hen. 3. The heritability estimates for the traits, length of stay in the winter garden and frequency of passages were higher for the last 5 laying periods than at the beginning of the recording period. For the last 5 laying periods, the estimates for the duration of stay in the winter garden varied between h ² = 0·21 and 0·32 and for the frequency of passages, between h ² = 0·30 and 0·49. 4. Most of the estimated heritabilities for the rate of lay were on an expected medium level (h ² = 0·09 to 0·45). Deviant h ²-values to a few laying periods were based on low additive genetic variances or high environmental variance. 5. Genetic correlations between both free range traits and the laying performance were negative (r _{g length of stay} = −0·34 and r _{g passage frequency} = −0·08). 6. Generally, there seems to be a possibility to influence the ranging behaviour through selection. Further investigations with different genotypes and varying dates of exposure to the laying environment, should be carried out to clarify possible influences on other traits and the negative correlation with laying performance.