Genome-wide association study on milk production and somatic cell score for Thai dairy cattle using weighted single-step approach with random regression test-day model.

Genome-wide association studies are a powerful tool to identify genomic regions and variants associated with phenotypes. However, only limited mutual confirmation from different studies is available. The objectives of this study were to identify genomic regions as well as genes and pathways associated with the first-lactation milk, fat, protein, and total solid yields; fat, protein, and total solid percentage; and somatic cell score (SCS) in a Thai dairy cattle population. Effects of SNPs were estimated by a weighted single-step GWAS, which back-solved the genomic breeding values predicted using single-step genomic BLUP (ssGBLUP) fitting a single-trait random regression test-day model. Genomic regions that explained at least 0.5% of the total genetic variance were selected for further analyses of candidate genes. Despite the small number of genotyped animals, genomic predictions led to an improvement in the accuracy over the traditional BLUP. Genomic predictions using weighted ssGBLUP were slightly better than the ssGBLUP. The genomic regions associated with milk production traits contained 210 candidate genes on 19 chromosomes [Bos taurus autosome (BTA) 1 to 7, 9, 11 to 16, 20 to 21, 26 to 27 and 29], whereas 21 candidate genes on 3 chromosomes (BTA 11, 16, and 21) were associated with SCS. Many genomic regions explained a small fraction of the genetic variance, indicating polygenic inheritance of the studied traits. Several candidate genes coincided with previous reports for milk production traits in Holstein cattle, especially a large region of genes on BTA14. We identified 141 and 5 novel genes related to milk production and SCS, respectively. These novel genes were also found to be functionally related to heat tolerance (e.g., SLC45A2, IRAG1, and LOC101902172), longevity (e.g., SYT10 and LOC101903327), and fertility (e.g., PAG1). These findings may be attributed to indirect selection in our population. Identified biological networks including intracellular cell transportation and protein catabolism implicate milk production, whereas the immunological pathways such as lymphocyte activation are closely related to SCS. Further studies are required to validate our findings before exploiting them in genomic selection.

Changes in genetic parameters for milk yield and heat tolerance in the Thai Holstein crossbred dairy population under different heat stress levels and over time.

The objectives of this study were to investigate changes in genetic parameters for milk yield (MY) and heat tolerance of the crossbred Thai Holstein Friesian population under different heat stress levels over time, and to investigate the threshold point of heat stress manifestation on milk production. Genetic parameters were estimated using single-step genomic REML (ssGREML) and traditional REML models. Data included 58,965 test-day MY records from 1999 to 2008 (old data) and 105,485 test-day MY records from 2009 to 2018 (recent data) from the first parity of 24,520 cows. The pedigree included 55,168 animals, of which 882 animals had genotypes. Variance components were estimated with the REMLF90 program using a repeatability model with random regressions on a function of temperature-humidity index (THI) for additive genetic and permanent environmental effects. Fixed effects included farm-calving season combination, breed group-months in milk combination, and age at first calving. Random effects included additive genetic (intercept and slope) effects, permanent environmental (intercept and slope) effects, and herd-month-year of test. The phenotypic mean for MY was 13.33 ± 4.39 kg/d in the old data, and 14.48 ± 4.40 kg/d in the recent data. Estimates over different THI levels for the intercept additive genetic variance using old data ranged from 2.61 to 2.77 and from 5.02 to 5.38 using recent data with the REML method. In ssGREML analyses (performed with recent data only) the estimates for the intercept additive genetic variance ranged from 4.71 to 5.05. Estimates for the slope additive genetic variance were close to zero in all cases, with the largest values (0.024-0.030) at the most extreme THI value (80). Using REML, the covariance between the intercept and the slope additive genetic effects (THI from 72 to 80) ranged from -0.001 to 0.019 with old data and from 0.027 to 0.060 with recent data. The same covariance ranged from 0.026 to 0.057 in ssGREML analyses. The covariance between the intercept and the slope permanent environmental effects ranged from -0.42 to -0.67 for all data and THI levels. Across THI levels, the genetic correlation between MY and heat tolerance varied from -0.06 to 0.13 with old data, from 0.16 to 0.30 with recent data in REML analyses, and from 0.15 to 0.30 in ssGREML analyses, suggesting that in the current population the top animals for MY are more resistant to heat stress. This was expected, because of the introduction of Bos indicus genes in the last years. Heritability estimates for MY ranged from 0.19 to 0.21 (old data) and from 0.33 to 0.40 (recent data) for REML analyses. Heritability estimates for MY using ssGREML ranged from 0.31 to 0.38. A decline in MY was found when the animals' breed composition had more than 97.3% of Holstein genetics, and it was greatest at THI 80. The heritability and genetic correlations observed in this study show that selection for MY is possible without a negative correlated response for heat tolerance. Although the inclusion of genomic information is expected to increase the accuracy of selection, more genotypes must be collected for successful application. Future research should address other production and fitness traits within the Thai Holstein population.

Genetic correlation and genome-wide association study (GWAS) of the length of productive life, days open, and 305-days milk yield in crossbred Holstein dairy cattle.

In this study, we estimated the genetic parameters and identified the putative quantitative trait loci (QTL) associated with the length of productive life (LPL), days open (DO), and 305-day milk yield for the first lactation (FM305) of crossbred Holstein dairy cattle. Data comprising 4,739 records collected between 1986 and 2004 were used to estimate the variance-covariance components using the multiple-trait animal linear mixed models based on the average information restricted maximum likelihood (AI-REML) algorithm. Thirty-six animals were genotyped using the Illumina BovineSNP50 Bead Chip [>50,000 single nucleotide polymorphisms (SNPs)] to identify the putative QTL in a genome-wide association study. The heritability of the production trait FM305 was 0.25 and that of the functional traits, LPL and DO, was low (0.10 and 0.06, respectively). The genetic correlation estimates demonstrated favorable negative correlations between LPL and DO (-0.02). However, we observed a favorable positive correlation between FM305 and LPL (0.43) and an unfavorable positive correlation between FM305 and DO (0.1). The GWAS results indicated that 23 QTLs on bovine chromosomes 1, 4, 5, 8, 15, 26, and X were associated with the traits of interest, and the putative QTL regions were identified within seven genes (SYT1, DOCK11, KLHL13, IL13RA1, PRKG1, GNA14, and LRRC4C). In conclusion, the heritability estimates of the LPL and DO were low. Therefore, the approach of multiple-trait selection indexes should be applied, and the QTL identified here should be considered for use in marker-assisted selection in the future.

Genetic evaluation of egg production curve in Thai native chickens by random regression and spline models.

The objective of this research is to investigate appropriate random regression models with various covariance functions, for the genetic evaluation of test-day egg production. Data included 7,884 monthly egg production records from 657 Thai native chickens (Pradu Hang Dam) that were obtained during the first to sixth generation and were born during 2007 to 2014 at the Research and Development Network Center for Animal Breeding (Native Chickens), Khon Kaen University. Average annual and monthly egg productions were 117 ± 41 and 10.20 ± 6.40 eggs, respectively. Nine random regression models were analyzed using the Wilmink function (WM), Koops and Grossman function (KG), Legendre polynomials functions with second, third, and fourth orders (LG2, LG3, LG4), and spline functions with 4, 5, 6, and 8 knots (SP4, SP5, SP6, and SP8). All covariance functions were nested within the same additive genetic and permanent environmental random effects, and the variance components were estimated by Restricted Maximum Likelihood (REML). In model comparisons, mean square error (MSE) and the coefficient of detemination (R2) calculated the goodness of fit; and the correlation between observed and predicted values [Formula: see text] was used to calculate the cross-validated predictive abilities. We found that the covariance functions of SP5, SP6, and SP8 proved appropriate for the genetic evaluation of the egg production curves for Thai native chickens. The estimated heritability of monthly egg production ranged from 0.07 to 0.39, and the highest heritability was found during the first to third months of egg production. In conclusion, the spline functions within monthly egg production can be applied to breeding programs for the improvement of both egg number and persistence of egg production.

Association of BoLA-DRB3 alleles with tick-borne disease tolerance in dairy cattle in a tropical environment.

Tick-borne disease is one of the most harmful tropical diseases in dairy production. Selection of dairy cows for tolerance to tick-borne disease is a challenging concept for dairy breeders in the tropics. The objectives of this study were (1) to detect specific tick-borne pathogen in cattle of different genetics and (2) to examine the polymorphisms of DRB3.2 alleles in Thai dairy cattle and find the allelic association with tick-borne disease tolerance. Specific primers to Anaplasma marginale (AM), Babesia bigemina (BG) and Babesia bovis (BB) were used to detect the infections by PCR. The results showed that the high proportion of infections were found in Bos indicus (Sahiwal, n=95) and crossbred Holstein × Zebu (75:25 Holstein:Zebu, n=101), compared to high Holstein fraction crossbreed (≥ 87.5% Holstein, n=187). The proportion of triple infections was also highly found in high Holstein fractions crossbreed. This study confirmed that Zebuine (Bos indicus) had a higher degree of tolerance, even when infected by tick-borne pathogens, compared to high Holstein fraction crossbred. The associated alleles of DRB3.2 for tick-borne pathogen infection tolerance were found: DRB3*14 and *41 were found to be tolerant to A. marginale; *14 to B. bovis; and *10 and *51 to B. bigemina. These tolerance alleles could be used as potential markers for selection in dairy genetic evaluation. The associated alleles for susceptibility were also found: *2 was found to be susceptible to A. marginale; *3 and *16 to B. bovis; and *20 to B. bigemina. These susceptibility alleles could be used as markers for culling, and selection favoring susceptibility alleles should be considered to maintain heterozygote advantage and pathogen-specific memories in the herd.

Insulin-like growth factor I gene polymorphism associated with growth and carcass traits in Thai synthetic chickens.

Four Thai synthetic chicken lines (Kaen Thong, Khai Mook Esarn, Soi Nin, and Soi Pet) originated from Thai native and exotic commercial chickens were evaluated for their growth and carcass traits with the purpose of developing a Thai broiler breeding program. Insulin-like growth factor I (IGF-I) gene is known to play an important role in growth, proliferation and differentiation. Consequently, we investigated the possibility of using the IGF-I gene for marker-assisted selection in Thai synthetic chickens. We looked for variations in the IGF-I gene and studied their association with growth and carcass traits; 1046 chickens were genotyped using PCR-RFLP methods. A general linear model was used to analyze associations of the IGF-I polymorphism with growth and carcass traits. Kaen Thong, Khai Mook Esarn, and Soi Nin chickens were found to carry similar frequencies of alleles A and C (0.40-0.60), while Soi Pet chickens had high frequencies of allele C (0.75). The IGF-I gene was significantly associated with some growth traits (body weight at hatching, and at 4, 8, 12, and 14 weeks of age; average daily gain during 0-12 and 0-14 weeks of age) in all synthetic chickens. Carcass traits (the percentage of dressing and pectoralis major) were significantly different only in Khai Mook Esarn chickens. We conclude that IGF-I can be used as a marker gene for the selection of growth and carcass traits of synthetic chickens in a marker-assisted selection program.

Short communication: genetic effects of heat stress on days open for Thai Holstein crossbreds.

Seasonality of days open (DO) for Thai crossbred Holsteins was examined and genetic effects of heat stress on DO open were determined. Data included 18,413 records for first and second parities of 12,162 cows that calved between 1990 and 2006. Least squares means for DO were estimated using a model with fixed effects of herd-year of calving, breed group based on percentage of Holstein genetics, calving month, calving age, and parity. A reaction norm model and solutions for calving month were used to calculate a heat stress index. Variance components were estimated with a multitrait random regression model. Days open were greatest for cows calving in March (summer) and fewest in October (late rainy season) for all breed groups and parities. Estimates of additive genetic and residual variances and heritability varied by calving month. Residual variances increased and additive genetic variance decreased with percentage of Holstein genetics and parity. Heritability estimates for DO ranged from 7.1 to 8.4% for first-parity cows with <87.5% Holstein genetics, 5.9 to 8.0% for 87.5 to 93.6% Holstein genetics, and 5.8 to 7.8% for ≥93.7% Holstein genetics and from 6.3 to 7.9, 4.9 to 7.3, and 4.5 to 7.7% for the corresponding breed groups for second parity. Genetic correlations between additive genetic effects on DO with and without heat stress considered were 0.43 for first-parity cows with <87.5% Holstein genetics, 0.46 for those with 87.5 to 93.6% Holstein genetics, and 0.52 for those with ≥93.7% Holstein genetics; correlations were 0.46, 0.51, and 0.55 for the corresponding breed groups for second parity. Effect of heat stress on DO was greater for second than first parity and was particularly large for cows with ≥93.7% Holstein genetics. Fewer DO can be achieved in Thailand through selective breeding of cows with <87.5% Holstein genetics.

Genetic effects of heat stress on milk yield of Thai Holstein crossbreds.

The threshold for heat stress on milk yield of Holstein crossbreds under climatic conditions in Thailand was investigated, and genetic effects of heat stress on milk yield were estimated. Data included 400,738 test-day milk yield records for the first 3 parities from 25,609 Thai crossbred Holsteins between 1990 and 2008. Mean test-day milk yield ranged from 12.6 kg for cows with <87.5% Holstein genetics to 14.4 kg for cows with ≥93.7% Holstein genetics. Daily temperature and humidity data from 26 provincial weather stations were used to calculate a temperature-humidity index (THI). Test-day milk yield varied little with THI for first parity except above a THI of 82 for cows with ≥93.7% Holstein genetics. For third parity, test-day milk yield started to decline after a THI of 74 for cows with ≥87.5% Holstein genetics and declined more rapidly after a THI of 82. A repeatability test-day model with parities as correlated traits was used to estimate heat stress parameters; fixed effects included herd-test month-test year and breed groups, days in milk, calving age, and parity; random effects included 2 additive genetic effects, regular and heat stress, and 2 permanent environment, regular and heat stress. The threshold for effect of heat stress on test-day milk yield was set to a THI of 80. All variance component estimates increased with parity; the largest increases were found for effects associated with heat stress. In particular, genetic variance associated with heat stress quadrupled from first to third parity, whereas permanent environmental variance only doubled. However, permanent environmental variance for heat stress was at least 10 times larger than genetic variance. Genetic correlations among parities for additive effects without heat stress considered ranged from 0.88 to 0.96. Genetic correlations among parities for additive effects of heat stress ranged from 0.08 to 0.22, and genetic correlations between effects regular and heat stress effects ranged from -0.21 to -0.33 for individual parities. Effect of heat stress on Thai Holstein crossbreds increased greatly with parity and was especially large after a THI of 80 for cows with a high percentage of Holstein genetics (≥93.7%). Individual sensitivity to heat stress was more environmental than genetic for Thai Holstein crossbreds.