Abstract. Heat stress is among the most challenging environmental conditions affecting commercial poultry. It severely affects growth and egg production, particularly in tropical and subtropical regions. This study aimed to examine physiological responses -including triiodothyronine (T 3 ) levels, enzymatic activity of creatine kinase (CK) and lactate dehydrogenase (LDH), respiratory rates, and cloacal temperature -to acute heat stress associated with different genotypes of the HSP70 gene and to evaluate the association of these polymorphisms with growth and egg production. Genotyping was performed by single-strand conformation polymorphism analysis. The polymorphisms identified were A258A, A258G, and G258G. Twenty 12-week old birds were randomly selected from each genotype and exposed to 40 • C ambient temperature for 1 h. Blood samples were collected at 0 and 1 h following heat stress. Respiratory rate and cloacal temperature were measured following 0, 30, and 60 min of exposure. After 1 h, the A258A genotype exhibited lower levels of CK activity and plasma T 3 . Neither respiratory rate nor cloacal temperature displayed a significant association with the genotypes. Body weight gain differed among the genotypes for males (F = 3.268, P = 0.041) and females (F = 14.029, P < 0.001), and the A258A genotype exhibited the greatest weight gain at 0-16 weeks of age for both genders. There were no significant differences among genotypes regarding egg weight at first egg or the number of eggs laid until 40 weeks of age. The A258A genotype displayed higher heat tolerance with no negative effects on growth performance and egg production.

Several oocyte-derived genes/proteins are essential to early embryonic development. The expression and stability of these proteins are influenced by the autocrine/paracrine activity of factors released by oocytes and cumulus cells. This study investigated the paracrine and autocrine activity of follistatin (FS), which is secreted by oocytes and cumulus cells as part of porcine embryogenesis. Immunohistochemical (IHC) localization of follistatin was conducted on 100 randomly selected early- and late-cleaving two-cell embryos. Dissociated cumulus cells were treated with various doses of follistatin for determination of the follistatin gene (FST) mRNA expression levels by quantitative real-time PCR analysis. Microinjection of siRNA induced a downregulation of FST mRNA during embryonic development, thereby decreasing the proportion embryos developing to the blastocyst stage (19.33%). Immunolocalization analysis showed enhanced staining for follistatin in early-cleavage stage embryos. Quantitative real-time PCR indicated a significantly lower FST transcript level in cumulus cells after application of the highest dose of follistatin (100 ng/ml). Exogenous follistatin treatment of in vitro maturation embryos resulted in statistically significant dose-dependent changes during development. Application of the highest concentration (100 ng/ml) of follistatin decreased the maturation rate of the oocytes. On the other hand, the application of 10 ng/ml follistatin resulted in an increase in the number of embryos. The observed differential effect of exogenous follistatin might be due to maternal FST and autocrine/paracrine factors secreted by cumulus cells.

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