The aim was to conduct a literature review on the estrus detection and its interference on the reproductive efficiency of dairy cattle. Efficient and accurate estrus detection of cattle and artificial insemination in an assertive time are essential to increase pregnancy rate, estrus detection rate, and consequently good reproductive efficiency. Methods of estrus detection that are widely used on farms do not have good rates.  This is because the physiological and behavioral changes of the animals, as well as the period of the duration of the estrus cycle, are being expressed in low intensity and short duration. In addition, they are very variable and difficult to measure. Thus, it is of utmost importance to use electronic methods to improve estrus detection.

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In dairy cattle farming there are different breeding systems, which can influence the thermal comfort of the animals. The cattle, in turn, have mechanisms of thermal regulation to maintain homeostasis and a zone of thermoneutrality. However, these animals have significant sensitivity to solar radiation and have thermoneutral zones with lower temperatures than most Brazilian regions. This fact has had a great impact on the dairy economy due to the negative effects on the welfare, production, reproduction and behavioral changes of dairy cows, in addition to affecting the entire production chain, from gestation, growth of calves and reproduction of males. Thus, the present bibliographic review aims to analyze the effects of thermal stress on the different aspects of dairy cattle, showing how harmful it can be.

The present study assessed the influence of environmental variables at birth (birth season, temperature, relative humidity, THI - temperature and humidity index) and newborn serum protein level of 450 Holstein heifers on growth (body weight, and mortality rate) and reproductive performance (weight and age at puberty, age at first conception, and conception rate at first artificial insemination). The immune passive transfer was positively related to the weights at 30 and 60, with a trend at 90 days, which consequently affected weight at puberty, age at puberty, and age at conception. Therefore, it reinforces the importance of protocols with newborns that allow the assessment of the passive transfer of immunity. Calves born during the warmer months exhibited 4.2 and 12.28 kg less weight at weaning and puberty, respectively, compared to calves born during winter. Thus, calves born in an environment with higher THI showed changes in development, health, and reproductive efficiency in the short, medium, and long term. These findings reinforce the importance of adopting better colostrum management and welfare conditions, especially in warm season, to allow successful immune passive transfer and increase system efficiency.

A produção de leite no mundo é crescente, pois representa parte da economia mundial. Diante deste cenário, a preocupação com a quantidade e qualidade do leite e do rebanho tem sido relevante. O estresse por calor é a consequência da ausência de sombra nas propriedades rurais, prejudicando a produção e reprodução dos animais. Neste intuito, os sistemas silvipastoris têm sido favoráveis para o desempenho de vacas leiteiras, uma vez que o sombreamento promove efeitos positivos na produção de leite, bem estar, conforto e fertilidade, além disso, aumentam a disponibilidade de nutrientes no solo, melhorando as pastagens. Portanto, objetivou-se com esta revisão apresentar os benefícios do sombreamento proporcionado pelos sistemas silvipastoris na produção de leite e conforto térmico dos animais.