A 60% pregnancy success for inseminations is targeted to optimize production efficiency for dairy cows within a seasonal, pasture-grazed system. Routine measures of pregnancy success are widely available but are limited, in practice, to a gestation stage beyond the first 28 d. Although some historical data exist on embryonic mortality before this stage, productivity of dairy systems and genetics of the cows have advanced significantly in recent decades. Accordingly, the aim was to construct an updated estimate of pregnancy success at key developmental stages during the first 70 d after insemination. Blood samples were collected for progesterone concentrations on d 0 and 7. A temporal series of 4 groups spanning fertilization through d 70 were conducted on 4 seasonal, pasture-grazed dairy farms (n = 1,467 cows) during the first 21 d of the seasonal breeding period. Morphological examination was undertaken on embryos collected on d 7 (group E7) and 15 (group E15), and pregnancy was diagnosed via ultrasonography on approximately d 28 and 35 (group E35) as well as d 70 (group E70). Fertilization, embryo, and fetal evaluation for viability established a pregnancy success pattern. Additionally, cow and on-farm risk factor variables associated with pregnancy success were evaluated. We estimated pregnancy success rates of 70.9%, 59.1%, 63.8%, 62.3%, and 56.7% at d 7, 15, 28, 35, and 70, respectively. Fertilization failure (15.8%) and embryonic arrest before the morula stage (10.3%) were the major developmental events contributing to first-week pregnancy failures. Embryo elongation failure of 7% contributed to pregnancy failure during the second week. The risk factors for pregnancy success that were related to the cows included interval between calving and insemination, and d-7 plasma progesterone concentrations, whereas insemination sire was associated with pregnancy outcome. Most pregnancy failure occurs during the first week among seasonal-calving pasture-grazed dairy cows.

In dairy cows, mammary gland involution, and thus a decline in milk production, occurs following peak lactation. To examine the cell signaling pathways regulating involution of the mammary gland, signal transducer and activator of transcription factors (STAT5 and 3), suppressors of cytokine signaling (SOCS1-3 and CIS), insulin-like growth factors (IGF1 and 2), and protein kinase B (Akt) were examined. Mammary involution was induced by termination of milking, and alveolar tissue was collected from 52 nonpregnant, primiparous, mid-lactation Holstein-Friesian cows killed at 0, 6, 12, 18, 24, 36, 72, and 192h postmilking. Qualitative immunohistochemistry showed that activated (phosphorylated) STAT5-P was localized in nuclei of mammary epithelial cells at the early time points, with detection levels decreasing by 24h postmilking. In contrast, STAT3-P was barely detectable at the early time points, with detection levels increasing following longer postmilking periods. This was supported by Western analysis, which showed a decline in STAT5 and STAT5-P protein levels by 24h postmilking, no change in STAT3 levels, and an increase in STAT3-P protein (barely detectable at the early time points) by 72h postmilking. Quantitative real-time reverse transcription PCR analysis showed SOCS1 and SOCS3 mRNA increased by 72h postmilking compared with 6h postmilking. The SOCS2 mRNA remained unchanged across the time series, whereas CIS decreased by 18h postmilking and remained lower compared with that at 6h postmilking until 72h postmilking. The IGF1 mRNA increased by 192h postmilking, whereas IGF2 mRNA decreased by 18h postmilking compared with 6h postmilking. The IGFBP5 mRNA and protein levels of Akt and Akt-P remained unchanged over the time series. These results show that reciprocal activation of STAT5 and STAT3 occurs at the onset of mammary gland involution in the bovine, albeit at a slower rate than in rodents. Mathematical modeling of the pathways indicated that activated STAT3 could block the STAT5 pathway by upregulating SOCS3. The regulation of IGF1-Akt signaling suggests that by 192h postmilking in dairy cows, the involution process is still in the reversible phase, with quiescent mammary epithelial cells not yet in the senescent phase.

Processing bovine semen in fresh long life extender for use over 3 to 4 days after collection is a widely used technique in New Zealand (Shannon and Vishwanath 1995 Anim. Reprod. Sci. 39, 1-10). Advantages include greater use of valuable sires, transport without liquid nitrogen, and the possibility of more efficient use of sexed sorted semen. The new extender (Ext. A) also has the advantage of containing no egg yolk. This study compares this new long-life extender (Ext. A) with an existing product (Ext. B) and frozen/thawed semen. Semen from 12 different bulls was diluted to a concentration of 8 × 106 mL-1 and gradually cooled to 16°C. All samples were held at ambient temperature in the dark and motility was evaluated over a storage period of 4 days comparing the extenders. In this part of the trial Ext. A maintained motility better than Ext. B (P = 0.001) during the 4-day storage period (24 h: 90 v. 70%; 96 h: 85 v. 50%). The second part of the trial compared the conception rates (CR) in cows from the use of fresh long-term-extended semen and frozen/thawed semen. On 19 farms, 8546 cows were inseminated with fresh semen stored for 1 to 3 days and 7280 cows were inseminated with frozen semen. The overall CR at 7 to 8 weeks for the 19 farms was 73.7%. On 18 farms within the same farming group, 8498 cows received frozen semen and the CR was 71.1%. Pregnancy results were 2.6% (P = 0.001) higher CR at scanning in herds where fresh semen was used compared with the farms where only frozen/thawed semen was used (73.7 v. 71.1%). In the third part of the trial, semen from 4 different bulls were extended to 1 × 106 mL-1 in Ext. A and held at ambient temperature for 6 days prior to use for IVF. Our lab standard frozen/thawed bull semen was used as a control. Table 1 shows that semen held at ambient temperature in Ext. A for 6 days produced a similar percentage of transferable quality embryos to our IVP control frozen/thawed semen (26.9 v. 25.7%). We conclude that preserved bovine semen in fresh long-life extender for several days offers some advantages in AI and IVP programs compared with frozen semen. Table 1.Fresh semen extender (Ext.A) compared with frozen semen in IVP We appreciate the assistance of Liberty Genetics Ltd.