Heat shock proteins (Hsp) are induced by various stressors such as heat, cold, toxins, and oxygen deprivation. Our objective was to determine the relationship among polymorphisms in the Hsp70 gene, forage system, and calving rates. Genomic DNA for 77 cows was purified from the buffy coats of EDTA-treated whole blood. The cows were Angus (n = 20), Brahman (n = 26), and reciprocal crosses (n = 31). Cows were assigned to and remained on their respective forage system for the duration of the experiment (8 years). Forage systems were endophyte-infected toxic tall fescue (E+) or common bermudagrass (CB). Specific primers for bovine Hsp70 (HSP1778F: CGCTGGAGTCGTACGCCTTC; HSP2326R: CTTGGAAGTAAACAGAAACGGG) were used for PCR amplification of a 523-base segment (based on GenBank accession number U09861). The PCR product was sequenced in both directions. Seven single nucleotide polymorphisms (SNP) were identified, and they were located at base positions 1851 (n = 6), 1902 (n = 4), 1917 (n = 4), 1926 (n =4), 2033 (n = 20), 2087 (n = 6), and 2098 (n =4). Concentrations of Hsp70, Julian date, and lifetime calving rate were analyzed by ANOVA, with each SNP represented as the main effect in the model. Two SNP resulted in altered peptide sequences, also known as mis-sense mutations (1926, aspartic acid to glutamic acid, and 2033, glycine to alanine). Five unique haplotypes were deduced based on the SNP profile (GCGCGCT, GCGCCCT, ACGCGCT, GCGCGGT, GTTGGCA, respectively, for haplotype 1, 2, 3, 4, and 5). Plasma concentrations of Hsp70 were affected by an interaction (P < 0.05) between Hsp70 haplotype and forage system. Cows with haplotypes 4 and 5 consuming fescue had higher plasma Hsp70 concentrations than other cows (5.4, 5.1, 3.8, 5.1, 5.2, 5.1, 5.7, 4.2, 22.4, and 9 MSE 1.5 ng mL^-1, respectively, for 1-5 CB and 1-5 E+). That same interaction tended (P < 0.09) to be associated with lifetime calving percentage. Cows with haplotype 4 consuming bermudagrass had the lowest calving rate (58%). These results suggest that the Hsp70 gene in cattle is polymorphic, and those polymorphisms are related to cattle fertility.