The objective of this study was to investigate the association of the signal transducer and activator of transcription 5A (STAT5A) gene with fertilization rate, embryonic survival, and milk production and composition in cattle. The STAT proteins are transcription factors that are specifically activated to regulate gene transcription when cells encounter cytokines and growth factors. The STAT5A gene is a member of the interferon-tau (IFN-tau) and placental lactogen (PL) signaling pathway, which is involved in both milk production and initiation of pregnancy. Using the DNA-pooling sequencing approach, a total of 12 single nucleotide polymorphisms (SNP) were identified, 1 exonic and 11 intronic. For the study of association of these SNP with embryonic survival, 1,551 embryos were produced in vitro from 160 cows and 3 sires. Significant associations with embryonic survival were found for 7, 5, and 2 SNP for embryos produced from sires 1, 2, and 3 respectively. The association of fertilization rate with STAT5A polymorphisms was evaluated in more than 2,300 oocytes. Significant associations were found for 6, 2, and 2 SNP for sires 1, 2, and 3 respectively. For sire 1, 5 SNP showed significant associations with both embryonic survival and fertilization rate compared with 1 SNP for sires 2 and 3. To determine if embryonic losses had occurred before the blastocyst stage, 145 of the surviving embryos were harvested at d 7 of development and genotyped for the single exonic SNP12195. A significant segregation distortion was observed between oocytes produced from 2 sires carrying the same genotype. Thus, it is most likely that STAT5A is associated with 2 mechanisms of embryo death. One is a prefertilization mechanism involving sperm factors that cause low fertilization rate. The second is a postfertilization mechanism that causes incompatibility between the male pronucleus and the oocyte, which in turn leads to death of the embryo before the blastocyst stage. Association testing of SNP12195 (exon 8) and SNP14217 (intron 9) with milk composition revealed that allele G of SNP12195 was associated with a decrease in both protein and fat percentages. However, SNP14217 in intron 9 showed no significant association with milk production or health traits. The G allele of SNP12195 was also associated with low embryonic survival, making this SNP an attractive candidate for progeny testing programs in dairy cattle.
SummaryCovariance between direct and maternal genetic effects on body weight in random-bred ICR mice at 2 through 10 weeks of age was estimated from cross-fostering experiments. The covariance contributes only a few percent of phenotypic variance at 2 weeks, but increases to 10–15% at later ages. Nearly all estimates are positive. We suggest that genes active during later parts of growth affect maternal performance more than those active during early growth, causing increased covariance at later ages. A model of combined genetic and persistent environmental effects on maternal performance is presented. Persistent effects of genetic or environmental variation in recent ancestors can influence covariance between relatives and response to selection.
Our objective was to determine whether pregnancy rates in heat-stressed dairy cattle could be enhanced by timed embryo transfer of fresh (nonfrozen) or frozen-thawed in vitro-derived embryos compared to timed insemination. Ovulation in Holstein cows was synchronized by a GnRH injection followed 7 d later by PGF2 alpha and a second treatment with GnRH 48 h later. Control cows (n = 129) were inseminated 16 h (d 0) after the second GnRH injection. On d 7, a fresh (n = 133) or frozen-thawed (n = 142) in vitro-derived embryo was transferred to cows assigned for timed embryo transfer after categorizing the corpus luteum by palpation per rectum as 3 (excellent), 2 (good or fair), 1 (poor), and 0 (nonpalpable). Response to the synchronization treatment, determined by plasma progesterone concentration (ng/ml) < or = 1.5 on d 0 and > or = 2.0 on d 7, was 76.2%. Mean plasma progesterone concentration on d 7 increased as the quality of corpus luteum improved from category 0 to 3. Concentrations of progesterone in plasma were elevated (> or = 2.0 ng/ml) at 21 d in 64.7 (fresh embryo), 40.3 (frozen embryo), and 41.4 +/- 0.1% (timed insemination) of cows, respectively. Cows that received a fresh embryo had a greater pregnancy rate at 45 to 52 d than did cows that received a frozen-thawed embryo or timed insemination (14.3 > 4.8, 4.9 +/- 2.3%). Body condition (d 0) of cows influenced the pregnancy rate and plasma progesterone concentrations. In summary, timed embryo transfer with fresh in vitro-produced embryos in heat-stressed dairy cattle improved pregnancy rate relative to timed insemination.
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