Heat stress and seasonal effects on reproduction in the dairy cow--a review.

By F. De Rensis, R. Scaramuzzi. Theriogenology, 2003

808 citations recorded by the source corpus.

In dairy cows inseminated during the hot months of the year, there is a decrease in fertility. Different factors contribute to this situation; the most important are a consequence of increased temperature and humidity that result in a decreased expression of overt estrus and a reduction in appetite and dry matter intake. Heat stress reduces the degree of dominance of the selected follicle and this can be seen as reduced steroidogenic capacity of its theca and granulosa cells and a fall in blood estradiol concentrations. Plasma progesterone levels can be increased or decreased depending on whether the heat stress is acute or chronic, and on the metabolic state of the animal. These endocrine changes reduce follicular activity and alter the ovulatory mechanism, leading to a decrease in oocyte and embryo quality. The uterine environment is also modified, reducing the likelihood of embryo implantation. Appetite and dry matter intake are both reduced by heat stress thus prolonging the postpartum period of negative energy balance and increasing the calving-conception interval, particularly in high producing dairy cows. The utilization of cooling systems may have a beneficial effect on fertility but dairy cows cooled in this way are still unable to match the fertility achieved in winter. Recent studies suggest that the use of gonadotropins to induce follicular development and ovulation can decrease the severity of seasonal postpartum infertility in dairy cows.

Subfields: Agronomy and Crop Science, Animal Science and Zoology, Genetics

View Paper: https://www.semanticscholar.org/paper/12395522a169096f5fa1e1bc6cd28109f7a535d2

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Citations in the corpus

• FACTORS INFLUENCING IN VITRO EMBRYO PRODUCTION (2006, background): “Moreover, the effect of heat stress may also interfere with follicular development and with the secretion of hormones such as LH and progesterone (Rensis and Scaramuzzi, 2003), thus causing alterations in oocyte quality.”
• A review of the causes of poor fertility in high milk producing dairy cows (2010, neutral): “Heat stressed animals may also have low LH pulse amplitude and frequency, low oestradiol concentrations and smaller dominant follicles which can extend the interval from calving to first ovulation (De Rensis and Scaramuzzi, 2003) .”