Genetic background of walking ability and its relationship with leg defects, mortality, and performance traits in turkeys (Meleagris gallopavo).

This study aimed to explore the genetic basis of walking ability and potentially related performance traits in turkey purebred populations. Phenotypic, pedigree, and genomic datasets from 2 turkey lines hatched between 2010 and 2023 were included in the study. Walking ability data, defined based on a scoring system ranging from 1 (worst) to 6 (best), were collected on 192,019 animals of a female line and 235,461 animals of a male line. Genomic information was obtained for 46,427 turkeys (22,302 from a female line and 24,125 from a male line) using a 65K single nucleotide polymorphism (SNP) panel. Variance components and heritability for walking ability were estimated. Furthermore, genetic and phenotypic correlations among walking ability, mortality and disorders, and performance traits were calculated. A genome-wide association study (GWAS) was also conducted to identify SNPs associated with walking ability. Walking ability is moderately heritable (0.23 ± 0.01) in both turkey lines. The genetic correlations between walking ability and the other evaluated traits ranged from -0.02 to -0.78, with leg defects exhibiting the strongest negative correlation with walking ability. In the female line, 31 SNPs were associated with walking ability and overlapped with 116 genes. These positional genes are linked to 6 gene ontology (GO) terms. Notably, genes such as CSRP2, DDX1, RHBDL1, SEZ6L, and CTSK are involved in growth, development, locomotion, and bone disorders. GO terms, including fibronectin binding (GO:0001968), peptide cross-linking (GO:0018149), and catabolic process (GO:0009057), are directly linked with mobility. In the male line, 66 markers associated with walking ability were identified and overlapped with 281 genes. These genes are linked to 12 GO terms. Genes such as RB1CC1, TNNI1, MSTN, FN1, SIK3, PADI2, ERBB4, B3GNT2, and BACE1 are associated with cell growth, myostatin development, and disorders. GO terms in the male line are predominantly related to lipid metabolism. In conclusion, walking ability is moderately heritable in both populations. Furthermore, walking ability can be enhanced through targeted genetic selection, emphasizing its relevance to both animal welfare and productivity.

Growth Rate Distribution and Potential Non-Linear Relationship between Body Weight and Walking Ability in Turkeys.

The aim of this study was to investigate the potential non-linear relationship between growth and walking ability (WA). The phenotypic data included body weights at 12 and 20 weeks and WA at 20 weeks of age measured on 276,059 male turkeys. The growth rate at three age periods (0 to 12, 12 to 20 and 0 to 20 weeks) was calculated. Each bird was assigned to one of the quartiles of the growth rate distribution for each age period. Between the first and fourth quartiles, the incidence of score 1 (bad WA) increased by 31, 18, and 33% for the first, second, and third age periods, respectively. For good WA (scores 4, 5, and 6), the incidence decreased by 55, 66, and 72% between the first and fourth quartiles for the first, second, and third age periods, respectively. Estimates of heritability of WA ranged between 0.18 and 0.26. The genetic correlations between adjacent growth rate quartiles were high and decayed as the interval between quartiles increased. The magnitude of the variation in the incidence of walking scores and genetic correlations across the growth rate quartiles point towards a non-linear relationship between growth and mobility suggesting other factors may affect walking ability.

Research Note: Analysis of body weight and walking ability in turkeys and the prediction of categorical responses across systematic effect classes using a linear threshold model.

Heavy selection for growth in turkeys has led to a decay in leg soundness and walking ability. In this study, different models and traits were used to investigate the genetic relationships between body weight (BW) and walking ability (WA) in a turkey population. The data consisted of BW and WA traits collected on 276,059 male birds. Body weight was measured at 12 and 20 wk and WA at 20 wk of age. For WA, birds were scored based on a 1 (bad) to 6 (good) grading system. Due to the small number of records with scores 5 and 6, birds with WA scores of 4, 5, and 6 were grouped together resulting in only 4 classes. Additionally, a binary classification of WA (scores 1 and 2 = Similarly, an estimate of the genetic correlation between WA and BW at 20 wk was -0.45, indicating a more pronounced class 1; scores 3, 4, 5, and 6 = class 2) was evaluated. The inheritability estimates of WA ranged between 0.25 and 0.27 depending on the number of classes. The Heritability of BW at 12 and 20 wk was 0.44 and 0.51, respectively. The genetic correlation between WA and BW at 12 wk was around -0.35, indicating that heavy birds tend to have poor WA. antagonistic relationship between BW and WA. The genetic correlation between BW at 12 and 20 wk was positive and high (0.80). The residual correlation between WA and BW at 12 and 20 wk of age was -0.07 and -0.02, respectively. The residual correlation between body weight traits was 0.57. Similar results were observed when a binary classification was adopted for WA. The probability of an individual with a given genetic merit expressing a certain class of WA was determined for different fixed effect designations. Predictive probabilities clearly showed that birds when hatched in the winter would have a small chance to exhibit good WA phenotypes.

Multiphasic mixed growth models for turkeys.

Growth models are important for optimization of feed formulation and breeding programs in turkeys. The objectives of this study were 1) to compare sex and line differences in turkeys in parameter estimates of mono- and di-phasic Gompertz growth models, and 2) to evaluate mono and diphasic mixed Gompertz growth models to determine the variation in parameter estimates in a group of female line turkey toms. A total of 1,056 manually recorded weekly average body weight (BW) observations from male and female turkeys of a male and female line from weeks 1 to 20 were used for objective 1. Daily median values of automatically collected individual BW of female line turkey toms were used for objective 2 and random components associated with individual subject animals related to mature weight and/or timing of maximum gain during each phase were introduced in the Gompertz model. Growth curve shapes were different between male line toms, male line hens, female line toms, and female line hens (P < 0.001). However, inflection points were similar between male and female line toms and between male and female line hens (14.06 vs. 13.72 wk and 11.22 and 10.71 wk, respectively), while mature BW differed between lines by 6.49 and 3.81 kg for toms and hens, respectively. The normalized growth rate constant (growth rate constant corrected for mature weight) was around the same magnitude between male and female line toms (0.0031 vs. 0.0038, respectively), but slightly lower in male line hens compared to female line hens (0.0072 vs. 0.0091, respectively). Diphasic Gompertz models described growth better in all line × sex combinations compared to the monophasic models (P < 0.001) and mixed diphasic Gompertz models showed improved fit over mixed monophasic Gompertz models. The correlation structure of the random components identified that individuals with a higher mature weight had a later inflection point and lower growth rate coefficients. These results provide tools for improved breeding practices and a structure to evaluate the effects of dietary or environmental factors on growth trajectories.

Turkeys have been bred for several purposes over the past decades. We studied growth patterns of turkeys of two genetic lines bred for either meat production or egg production. Mathematical equations were designed and fitted to describe the average bodyweight of several consecutively grown groups of turkeys. Similarly, individual body weight was measured and studied in one group of male turkeys, to detect differences in growth patterns between individual turkeys. It showed that there were differences between both sexes as well as between both lines in the shape of the growth curve. The age at which males and females grew fastest was similar between meat production and egg production type turkeys, for males around 13 to 14 wk and for females around 10 to 11 wk. Males of the meat production line grew 6.5 kg heavier than males of the egg production line, whereas females of the meat production line grew 3.8 kg heavier than females of the egg production line. Individual turkeys that have a heavier mature weight grow at a slower pace and delay the growth spurt associated with sexual maturation. With these outcomes, turkey feed producers and genetic companies can better study and steer the desired growth of turkeys.

Single-Step Methodology for Genomic Evaluation in Turkeys (Meleagris gallopavo).

Genomic information can contribute significantly to the increase in accuracy of genetic predictions compared to using pedigree relationships alone. The main objective of this study was to compare the prediction ability of pedigree-based best linear unbiased prediction (PBLUP) and single-step genomic BLUP (ssGBLUP) models. Turkey records of feed conversion ratio, residual feed intake, body weight, breast meat yield, and walking ability were provided by Hybrid Turkeys, Kitchener, Canada. This data was analyzed using pedigree-based and single-step genomic models. The genomic relationship matrix was calculated either using observed allele frequencies, all allele frequencies equal to 0.5 or with a different scaling. To avoid potential problems with inversion, three different weighting factors were applied to combine the genomic and pedigree matrices. Across the studied traits, ssGBLUP had higher heritability estimates and significantly outperformed PBLUP in terms of accuracy. Walking ability was genetically negatively correlated to body weight and breast meat yield; however, it was not correlated to feed conversion ratio (FCR) or residual feed intake (RFI). Body weight showed a moderate positive genetic correlation to feed conversion ratio, residual feed intake and breast meat yield. Feed conversion ratio was strongly correlated to residual feed intake (0.68 ± 0.06). There was almost no genetic correlation between breast meat yield and feed efficiency traits. Larger differences in accuracy between PBLUP and ssGBLUP were observed for traits with lower heritability. Results of the three weighting factors showed only slight differences and an increase in accuracy of prediction compared to PBLUP. Slightly different levels of bias were observed across the models, but were higher among the traits; BMY was the only trait that had a regression coefficient higher than 1 (1.38 to 1.41). We show that incorporating genomic information increases the prediction accuracy for preselection of young candidate turkeys for the five traits investigated. Single-step genomic prediction showed substantially higher accuracy estimates than the pedigree-based model, and only slight differences in bias were observed across the alternate models.

Assessment of residual body weight gain and residual intake and body weight gain as feed efficiency traits in the turkey (Meleagris gallopavo).

BACKGROUND: Since feed represents 70% of the total cost in poultry production systems, an animal's ability to convert feed is an important trait. In this study, residual feed intake (RFI) and residual body weight gain (RG), and their linear combination into residual feed intake and body weight gain (RIG) were studied to estimate their genetic parameters and analyze the potential differences in feed intake between the top ranked birds based on the criteria for each trait. METHODS: Phenotypic and genetic analyses were completed on 8340 growing tom turkeys that were measured for feed intake and body weight gain over a four-week period from 16 to 20 weeks of age. RESULTS: The heritabilities of RG and RIG were 0.19 ± 0.03 and 0.23 ± 0.03, respectively. Residual body weight gain had moderate genetic correlations with feed intake (-0.41) and body weight gain (0.43). All three linear combinations to form the RIG traits had genetic correlations ranging from -0.62 to -0.52 with feed intake, and slightly weaker, 0.22 to 0.34, with body weight gain. Sorted into three equal groups (low, medium, high) based on RG, the most efficient group (high) gained 0.62 and 1.70 kg more (P < 0.001) body weight than that of the medium and low groups, yet the feed intake for the high group was less (P < 0.05) than that of the medium group (19.52 vs. 19.75 kg). When separated into similar partitions, the high RIG group (most efficient) had both the lowest (P < 0.001) feed intake (18.86 vs. 19.57 and 20.41 kg) and the highest (P < 0.001) body weight gain (7.41 vs. 7.03 and 6.43 kg) relative to the medium and low groups, respectively. CONCLUSIONS: The difference in feed intake between the top ranked birds based on different residual feed efficiency traits may be small when looking at the average individual, however, when extrapolated to the production level, the lower feed intake values could lead to significant savings in feed costs over time.