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1. Introduction
Reproductive performance has been shown to be greatly affected by changes in environmental factors, such as temperature. The most economically important reproductive performance traits of farm animals may be endangered by high environmental temperature [1]. In tropical countries and in summer of temperate countries, the reproductive performance of dairy cattle is low [2, 3]. Bloemhof et al. [1] observed that the pregnancy outcomes of sow decrease in the hot weather. Furthermore, the reproductive efficiency of Holstein cows is lower in autumn than in winter, suggesting a late effect of high temperature during the summer [4]. Both male and female reproductive processes are sensitive to high temperature. High environmental temperature has adverse effect on spermatogenesis and oocyte development and maturation [5, 6]. Fortunately, the reduced quality of the sperm and ova during the hot season has been overcome to some extent by artificial insemination (AI) and embryo transfer techniques [6]. However, overcoming the problems resulting from exposure to elevated ambient temperatures during pregnancy is more complicated. Ealy et al. [7] reported that exposure to elevated temperatures at day 1 of pregnancy in cow compromises early embryonic development. In mice, several studies have shown that exposure to elevated temperatures for 12 h soon after mating disturbs normal embryonic development [8–11]. On the other hand, exposure of pregnant ewes to high temperatures during midgestation causes reduced foetal weights [12].
The recent climate changes and global warming have led to renewed interest in the study of the effects of exposure to elevated ambient temperatures on pregnancy outcomes and offspring growth with special attention to the time of exposure that leads to more deleterious effects on pregnancy outcomes. Determining the pregnancy stage that is most sensitive to heat exposure will assist in the design of environmental modification systems that provide an optimal temperature at critical period of pregnancy to improve the pregnancy rates and outcomes in hot climates. Therefore, the current study was intended to determine the effects of exposure to elevated ambient temperature during different pregnancy stages on reproductive outcomes and offspring growth and to determine the stage...