Study of growth, DNA polymorphisms, and fertility in Bos indicus x Bos taurus beef cattle

The hypothesis that measures of growth and novel DNA polymorphisms could be associated with, and (or) serve as predictors of fertility trait levels in beef heifers was tested in two separated studies. In the first study, phenotypic trends in growth and reproductive traits from 1972 to 2006 were evaluated in a Brangus herd managed in a Chihuahuan Desert Beef production system. Autumn cow weight gradually increased until 1997 and then gradually decreased 0.6 kg/yr, whereas pregnancy rate decreased gradually until 1995 and then slightly increased 0.2%/yr. A quadratic effect appeared to describe these 2 variables (P < 0.01). A similar quadratic effect best described the trends across years for growth curve parameters. Asymptotic weight slightly decreased 2.2% from 1990 to 1996 (P < 0.01), whereas asymptotic age decreased 27% through from 1983 to 1996 (P < 0.05). Significant correlations (P < 0.01) were detected among maturing rate with age at first calving (r = --0.42), calving interval (r = --0.18), pregnant as yearling (r = .21), calved as 2-year old (r = 0.20) and first-calf heifer rebreeding (r = 0.21).;In the second study, beef heifers from the breeds Angus, Brahman, and Romosinuano, and their reciprocal crosses in a diallele design were used to evaluate 75 DNA polymorphisms from genes of the GH/IGF axis on chromosome 5 as predictors of reproductive traits. Three SNP had minor allele frequency >10%. Two of these SNP were in the PAPPA2 gene and 1 in the STAT2 gene. The 2 allele from PAPPA2_0665 SNP was the most favorable allele (P < 0.05), which reduced calving interval and days to calving (∼31 d), and increased pregnancy rate (∼7%). Similarly, the 1 allele from PAPPA2_2590 SNP appeared advantageous (P < 0.05) for these traits, as it was associated with reduced calving interval and days to calving (∼20 d), and increased pregnancy rate (∼4%). Advantageous alleles and favorable haplotype showed substitution effect, but their influence on fertility traits appeared non-additive (P < 0.05). No significant association was detected between STAT2_060 SNP with any reproductive trait; however, this SNP interacted with ancestral clusters for prediction of the traits calving interval (P < 0.10) and days to calving (P < 0.05).;In summary, measures of growth and DNA polymorphisms in genes of the GH/IGF axis on chromosome 5 appeared to be associated with fertility traits in Bos indicus x Bos taurus cross cattle.