Genome-wide association study (GWAS) is a powerful approach to identify genomic regions and genetic variants associated with phenotypes. However, only limited mutual confirmation from different studies is available. We conducted a large-scale GWAS using 294,079 first-lactation Holstein cows and identified new additive and dominance effects on five production traits, three fertility traits, and somatic cell score. Four chromosomes had the most significant SNP effects on the five production traits, a Chr14 region containing
DGAT1
mostly had positive effects on fat yield and negative effects on milk and protein yields, the 88.07–89.60 Mb region of Chr06 with
SLC4A4, GC, NPFFR2
, and
ADAMTS3
for milk and protein yields, the 30.03–36.67 Mb region of Chr20 with
C6
and
GHR
for milk yield, and the 88.19–88.88 Mb region with
ABCC9
as well as the 91.13–94.62 Mb region of Chr05 with
PLEKHA5, MGST1, SLC15A5
, and
EPS8
for fat yield. For fertility traits, the SNP in
GC
of Chr06, and the SNPs in the 65.02–69.43 Mb region of Chr01 with
COX17, ILDR1
, and
KALRN
had the most significant effects for daughter pregnancy rate and cow conception rate, whereas SNPs in
AFF1
of Chr06, the 47.54–52.79 Mb region of Chr07,
TSPAN4
of Chr29, and
NPAS1
of Chr18 had the most significant effects for heifer conception rate. For somatic cell score,
GC
of Chr06 and
PRLR
of Chr20 had the most significant effects. A small number of dominance effects were detected for the production traits with far lower statistical significance than the additive effects and for fertility traits with similar statistical significance as the additive effects. Analysis of allelic effects revealed the presence of uni-allelic, asymmetric, and symmetric SNP effects and found the previously reported
DGAT1
antagonism was an extreme antagonistic pleiotropy between fat yield and milk and protein yields among all SNPs in this study.