Progress 01/15/04 to 01/14/08
Outputs
OUTPUTS: Our objective was to identify quantitative trait loci associated with economically important dairy traits using genotypic and phenotypic data from a crossbred Holstein x Jersey resource population. Females in our experiment were randomly mated to 7 crossbred Jersey x Holstein sires from February 2003 through October 2007. This produced approximately 650 backcross calves, of which 312 were female. In addition, these backcross females were mated to progeny tested Holstein sires to create 123 additional crossbred females in the subsequent generation. The crossbred sires were genotyped for 275 potentially informative microsatellites on the 29 bovine autosomes, and heterozygosity for individual sires ranged from 57.4% to 65.3%. From these, 172 markers that were heterozygous in at least four of seven sires were chosen for genotyping offspring. Extensive phenotypic data were collected, including information regarding: perinatal survival, birth weight, dystocia, total protein, immunoglobulin G, fecal consistency score, respiratory disease score, gestation length, and pre-weaning survival. Data collection for growing heifers will continue until August 2010, and this includes information regarding: body weight, hip height, body length, heart girth, body condition score, pelvic width, pelvic height, pelvic area, pelvic length, age at puberty, conception rate, canon bone circumference, and blood levels of alkaline phosphatase, cholesterol, total protein, glucose, urea nitrogen, calcium, sodium, potassium, chloride, magnesium, and phosphorous. Likewise, data collection in lactating cows will continue until December 2012, and this includes information regarding: dystocia, calf weight, calf survival, colostrum IgG content, milk yield, fat percentage, protein percentage, somatic cell count, milk urea nitrogen, ovulation status, conception rate, mastitis, milk fever, blood calcium, gestation length, embryonic loss, ketone level, retained placenta, displaced abomasums, lameness, hoof lesions, sole ulcers, hairy heel warts, locomotion score, body weight, body condition score, stature, strength, body depth, dairy form, rump angle, rump width, rear legs - side view, rear legs - rear view, foot angle, fore udder attachment, rear udder height, rear udder width, udder cleft, udder depth, udder tilt, front teat placement, and teat length. To date, 276 crossbred animals have been genotyped for 172 microsatellite markers. Because of recent developments in high-throughput genotyping of single nucleotide polymorphism (SNP) markers, genotyping of microsatellite markers has been discontinued. Fortunately, with the advent of cost effective, high density SNP genotyping, we can combine information from our 435 crossbred females with that of their 398 Holstein contemporaries, for which identical phenotypic data have been collected throughout the study, in a single, much larger genome scan. We are presently seeking funding to genotype these crossbred and Holstein females using the Illumina Bovine SNP50 BeadChip. PARTICIPANTS: The following individuals were directly involved in the project: Kent Weigel (PI) - Overall scientific leadership, coordination of collection of genotypic and phenotypic data, recruitment of personnel, compliance with animal care guidelines, supervision of statistical analysis. Patrick Hoffman (co-PI) - Experimental design, management of heifers, collection of phenotypic data from 3 months to 21 months of age. Valerie Schutzkus (technician) - Collection of blood samples, isolation of DNA, measurement of total protein, serum IgG, and colostrum IgG. Christian Maltecca (PhD student) - Genotyping of microsatellite markers, statistical analysis of associations between marker genotypes and calf phenotypes. Ryan Wernberg (technician) - Database development and data entry. Nancy Esser (technician) - Collection of phenotypic data in growing heifers. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Our initial work involved identification of quantitative trait loci (QTL) associated with birth weight, direct gestation length and passive immune transfer in our backcross (Holstein x Jersey) x Holstein resource population. A total of 276 calves were used in a microsatellite-based genome scan covering the 29 bovine autosomes. The study, performed through interval mapping with an animal model, identified several QTL associated with phenotypic differences between individual animals in the aforementioned traits. Putative QTL were identified on BTA7 and BTA14 for gestation length, on BTA2, BTA6, and BTA14 for birth weight, and on BTA20 for passive immune transfer. In total, these QTL accounted for 12%, 18%, and 1% of the phenotypic variance in direct gestation length, birth weight, and passive immune transfer, respectively. For direct gestation length, results from our experimental population were confirmed by an independent analysis involving a granddaughter design in a prominent Holstein sire family, which identified putative QTL on BTA7 and BTA14. In addition to our analysis of experimental data, the ability to identify QTL in experimental designs involving crosses of distant breeds was investigated via simulation. A single chromosome containing a QTL was simulated in a crossbred resource population derived from two purebred populations, which in turn branched from a common ancestral population. Power and precision to detect the QTL were investigated for 2 scenarios: a single QTL affecting a trait segregating in only one purebred population, and a single QTL segregating in two purebred populations that had been selected at different intensities. Both scenarios were compared with QTL detection in a single purebred population, and performance was evaluated in terms of power and precision of estimates of QTL position and estimates of magnitude of the QTL effect. In the simulation, the ability to correctly position the QTL was not affected by the design, whereas the power to detect the QTL in a crossbred population was significantly greater than in a purebred population. Our current focus is two-fold. First, we intend to secure funding to carry out dense SNP genotyping of the crossbred females and their Holstein contemporaries. Next year, we will seek renewal of this project through NRI, capturing increased statistical power through collaboration with colleagues with similar resource populations at Virginia Tech and North Carolina State. In the meantime, we will pursue opportunities to fund dense SNP genotyping through industry sources. Second, we intend to continue collection of detailed phenotypic information, as noted earlier. In addition to traits described in the previous section, we have begun collecting data regarding fatty acid profiles using mid-infrared spectrometry of milk samples, and we have begun measuring casein and whey protein content using reverse-phase HPLC.
Publications
- Maltecca, C., K. A. Weigel, H. Khatib, M. Cowan, and A. Bagnato. 2008. Whole genome scan for quantitative trait loci for birth weight, gestation length, and passive immune transfer in a Holstein x Jersey crossbred population. Animal Genetics (in press).
- Hoffman, P. C., K. A. Weigel, and R. M. Wernberg. 2008. Our Industry Today: Evaluation of equations to predict dry matter intake of dairy heifers. Journal of Dairy Science 91:3699-3709.
- Hoffman, P. C., K. A. Weigel, and R. R. Wernberg. 2007. Negative exponential models to predict dry matter intake of dairy heifers. Journal of Dairy Science 90(Suppl. 1):558.
- Maltecca, C., K. A. Weigel, H. Khatib, and V. R. Schutzkus. 2007. Quantitative trait loci affecting IgG serum protein levels, birth weight and gestation length in a Holstein x (Holstein x Jersey) backcross population. Journal of Dairy Science 90(Suppl. 1):597.
- Weigel, K. A., T. J. Halbach, C. Maltecca, and P. C. Hoffman. 2007. Performance and physical conformation of first parity backcross Holstein x Jersey cattle and their Holstein contemporaries. Journal of Dairy Science 90(Suppl. 1):420.
- Maltecca, C., H. Khatib, V. R. Schutzkus, P. C. Hoffman, and K. A. Weigel. 2006. Changes in conception rate, calving performance, and calf health and survival from the use of crossbred Jersey x Holstein sires as mates for Holstein dams. Journal of Dairy Science 89:2747-2754.
- Maltecca, C., H. Khatib, V. R. Schutzkus, P. C. Hoffman, and K. A. Weigel. 2006. Health, immune function, and survival of Holstein and crossbred Jersey x Holstein dairy calves. Proceedings of the 8th World Congress on Genetics Applied to Livestock Production, Belo Horizonte, Brazil, August 13-18.
- Maltecca, C., H. Khatib, V. R. Schutzkus, and K. A. Weigel. 2006. Mapping quantitative trait loci affecting calves immune function and birth weight in a Holstein x (Holstein x Jersey) backcross population. Journal of Dairy Science 89(Suppl. 1):274.
- Maltecca, C., K. A. Weigel, H. Khatib, V. R. Schutzkus, and P. C. Hoffman. 2006. Health, immune function, and survival of calves from Holstein dams and Holstein or crossbred Jersey x Holstein sires. Journal of Dairy Science 89(Suppl. 1):276.
- Hoffman, P. C., C. Simson, C. Maltecca, K. A. Weigel, P. Pacitto, and T. Worch. 2006. Growth parameters and blood profiles for Holstein and crossbred heifers according to phosphorous feeding level and breeding criteria. Proceedings of Midwest American Society of Animal Science / American Society of Dairy Science Annual Meeting, Des Moines, IA, March 20-22.
- Maltecca, C., and K. A. Weigel. 2004. Health parameters in F1 Jersey x Holstein, backcross (Jersey x Holstein) x Holstein, and pure Holstein calves. Journal of Dairy Science 87(Suppl. 1):87.
- Weigel, K. A., and C. Maltecca. 2004. Comparison of the fertility of pure Holstein sires and F1 Jersey x Holstein sires mated to pure Holstein cows in an experimental herd. Journal of Dairy Science 87(Suppl. 1):282.
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