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

Abstract

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 cow (Holstein) fertility, as well as seasonal influence on in vitro oocytes maturation and embryos development. Impact of heat shock (HS) effects on in vitro oocyte’s maturation and further embryo development after in vitro fertilization (IVF) was also evaluated. For such purpose the result of the first artificial insemination (AI) performed 60 to 90 days after calving of 6,300 cows 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 IVF. Further, to evaluate HS effect, 891 oocytes were collected in the cold moths (December, January, February and March) and divided in three groups treated to HS 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 IVF. Cleavage, morula and blastocyst development were evaluated respectively on day 2, 6, and 9 after IVF. A negative correlation between cow’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 HS 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.

Gene expression, oocyte nuclear maturation and developmental competence of bovine oocytes and embryos produced after in vivo and in vitro heat shock

“…Global warming, nutritional variability and increase of metabolic disorders are factors affecting both human and animal reproduction (Sirotkin, 2010), environmental heat stress is one of the major factors affecting animals, particularly lactating cows (Dunlap & Vincent, 1971; Badinga et al , 1985; Pavani et al , 2015b). Summer heat factors, such as high temperature humidity indexes (THI), are major problems for the dairy industry and contribute to economic losses among about 60% of the world's cattle population (Edwards et al , 2009).…”

“…It has been postulated that an increase in THI (≥72) affects the body temperature of dairy cows (Armstrong, 1994), which leads to hypothermia and impairs the cellular function of various tissues and parts of the reproductive system (Wolfenson et al , 2000). Heat-induced hypothermia studies, both in vivo and in vitro , have shown that rectal temperature may reach or exceed 41°C (Ealy et al , 1993), which impairs hormonal secretion, oocyte fertilization and embryo development (Wolfenson et al , 2000; Rivera & Hansen, 2001; Sartori et al , 2002), resulting in a decrease in pregnancy rate of approximately 25% for every 1°C increase in rectal temperature (Pavani et al , 2015b).…”

Studies on Gene Expression and Developmental Competence of Bovine Embryos Produced Under Different Conditions of Heat Stress

“…Experiments developed by our team show that exposing cumulus oocyte complexes (COCs) to 41°C did not alter the number of embryos that cleaved but reduced significantly the percentage of development in the blastocyst stage [9]. Additionally, the exposure of bovine embryos to heat shock during oocyte maturation leads to embryos with reduced development and induced alterations in protein synthesis and possibly gene expression as early as the two-cell embryos.…”

“…Before ovulation, there are several physiological factors that can disrupt establishment of pregnancy changes by elevated thermal heat. Heat shock effects endometrial prostaglandin secretion, oocytes during maturation period, and decreases low fertility of dairy cows in hot seasons [9]. Moreover, heat stress was suggested to be similar to oxidative stress, because of correspondences in the genes expressed after heat exposure, such as genes encoding heat shock proteins (HSPA14 gene), demonstrated heat-induced increase of reactive oxygen species (ROS) production, especially the superoxide anion.…”

“…The towering temperature causes several cellular changes during the maturation period and germinal vesicle stage in the oocytes [8]. Therefore, the heat stress influences and impacts on in vitro oocytes maturation, their nuclear maturation, and further embryos development to the stage of blastocysts after in vitro fertilization [9]. The low fertility of cattle females has led to an increased interest in in vitro embryo production (IVEP) technologies for achieving rapid genetic improvement and providing an excellent source of embryos for carrying out basic research on developmental physiology [10].…”