Reproductive Performance of Holstein Dairy XXXX Grazing in Dry-summer Subtropical Climatic Conditions: Effect of Heat Stress and @entity1457 on Meiotic Competence and In vitro Fertilization.

@entity52 @entity1457 @entity291
The present study was designed to evaluate how environmental factors in a dry-summer subtropical climate in Terceira-Azores (situated in the North Atlantic Ocean: 38   43' N 27   12' W) can affect dairy @entity291 (Holstein) fertility, as well as seasonal influence on in vitro oocytes maturation and embryos development. Impact of @entity1457 ( @entity1457 ) effects on in vitro oocyte's maturation and further embryo development after @entity52 ( @entity52 ) was also evaluated. For such purpose the result of the first artificial insemination (AI) performed 60 to 90 days after calving of 6,300 @entity291 were recorded for one year. In parallel, climatic data was obtained at different elevation points (n = 5) from 0 to 1,000 m and grazing points from 0 to 500 m, in Terceira island, and the temperature humidity index (THI) was calculated. For in vitro experiments, oocytes (n = 706) were collected weekly during all year, for meiotic maturation and @entity52 . Further, to evaluate @entity1457 effect, 891 oocytes were collected in the cold moths (December, January, February and March) and divided in three groups treated to @entity1457 for 24 h during in vitro maturation at: C (Control = 38.5  C), HS1 (39.5  C) and HS2 (40.5  C). Oocytes from each group were used for meiotic assessment and @entity52 . Cleavage, morula and blastocyst development were evaluated respectively on day 2, 6, and 9 after @entity52 . A negative correlation between @entity291 's conception rate (CR) and THI in grazing points (-91.3%; p<0.001) was observed. Mean THI in warmer months (June, July, August and September) was 71.7  0.7 and the CR (40.2  1.5%) while in cold months THI was 62.8  0.2 and CR was 63.8  0.4%. A similar impact was obtained with in vitro results in which nuclear maturation rate (NMR) ranged from 78.4% (  8.0) to 44.3% (  8.1), while embryos development ranged from 53.8% (  5.8) to 36.3% (  3.3) in cold and warmer months respectively. In vitro @entity1457 results showed a significant decline (p<0.05) on NMR of oocytes for every 1  C rising temperature (78.4  8.0, 21.7  3.1 and 8.9  2.2, respectively for C, HS1, and HS2). Similar results were observed in cleavage rate and embryo development, showing a clear correlation (96.9 p<0.05) between NMR and embryo development with respect to temperatures. Results clearly demonstrated that, up to a THI of 70.6, a decrease in the CR occurs in first AI after calving; this impairment was confirmed with in vitro results.
