BackgroundBirth weight (BW) is an economically important trait in beef cattle, and is associated with growth- and stature-related traits and calving difficulty. One region of the cattle genome, located on Bos primigenius taurus chromosome 14 (BTA14), has been previously shown to be associated with stature by multiple independent studies, and contains orthologous genes affecting human height. A genome-wide association study (GWAS) for BW in Brazilian Nellore cattle (Bos primigenius indicus) was performed using estimated breeding values (EBVs) of 654 progeny-tested bulls genotyped for over 777,000 single nucleotide polymorphisms (SNPs).ResultsThe most significant SNP (rs133012258, PGC = 1.34 × 10-9), located at BTA14:25376827, explained 4.62% of the variance in BW EBVs. The surrounding 1 Mb region presented high identity with human, pig and mouse autosomes 8, 4 and 4, respectively, and contains the orthologous height genes PLAG1, CHCHD7, MOS, RPS20, LYN, RDHE2 (SDR16C5) and PENK. The region also overlapped 28 quantitative trait loci (QTLs) previously reported in literature by linkage mapping studies in cattle, including QTLs for birth weight, mature height, carcass weight, stature, pre-weaning average daily gain, calving ease, and gestation length.ConclusionsThis study presents the first GWAS applying a high-density SNP panel to identify putative chromosome regions affecting birth weight in Nellore cattle. These results suggest that the QTLs on BTA14 associated with body size in taurine cattle (Bos primigenius taurus) also affect birth weight and size in zebu cattle (Bos primigenius indicus).

The reproductive performance of bulls has a high impact on the beef cattle industry. Scrotal circumference (SC) is the most recorded reproductive trait in beef herds, and is used as a major selection criterion to improve precocity and fertility. The characterization of genomic regions affecting SC can contribute to the identification of diagnostic markers for reproductive performance and uncover molecular mechanisms underlying complex aspects of bovine reproductive biology. In this paper, we report a genome-wide scan for chromosome segments explaining differences in SC, using data of 861 Nellore bulls (Bos indicus) genotyped for over 777,000 single nucleotide polymorphisms. Loci that excel from the genome background were identified on chromosomes 4, 6, 7, 10, 14, 18 and 21. The majority of these regions were previously found to be associated with reproductive and body size traits in cattle. The signal on chromosome 14 replicates the pleiotropic quantitative trait locus encompassing PLAG1 that affects male fertility in cattle and stature in several species. Based on intensive literature mining, SP4, MAGEL2, SH3RF2, PDE5A and SNAI2 are proposed as novel candidate genes for SC, as they affect growth and testicular size in other animal models. These findings contribute to linking reproductive phenotypes to gene functions, and may offer new insights on the molecular biology of male fertility.

ABSTRACT. The aim of this study was to evaluate a genome wide association study (GWAS) approach to identify single nucleotide polymorphisms (SNPs) associated with fertility traits (early puberty) in Nellore cattle (Bos indicus). Fifty-five Nellore cows were selected from a herd monitored for early puberty onset (positive pregnancy at 18 months of age). Extremes of this phenotype were selected; 30 and 25 individuals were pregnant and non-pregnant, respectively, at that age. DNA samples were genotyped using a high-density SNP chip (>777.000 SNP). GWAS using a case-control strategy highlighted a number of significant markers based on their proximity with the Bonferroni correction line. Results indicated that chromosomes 5, 6, 9, 10, and 22 were associated with the traits of interest. The most significant SNPs on these chromosomes were rs133039577, rs110013280, rs134702839, rs109551605, and rs41639155. Candidate genes, as well as quantitative trait loci (QTL) previously reported in the Ensembl and Cattle QTLdb databases, were further investigated. Analysis of the regions close to the SNP on chromosomes 9 and 10 revealed that four QTL had been previously classified under the reproduction category. In conclusion, we have identified SNPs in close proximity to genes associated with reproductive traits. Moreover, U6 spliceosomal RNA was present on three different chromosomes, which is possibly associated with age at first calving, suggesting that it might be a strong candidate for future studies.

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Irenilza de A. NÄÄS 2 RESUMOCom o objetivo de estimar a perda de calor sensível em cordeiros em confinamento e quantificar a energia metabolizável utilizada para manutenção da temperatura corporal, sob estresse térmico pelo frio, foram utilizados 24 cordeiros cruzados e não castrados, (média de 120 dias de idade, 26,3 kg de peso vivo e sob dieta com 2,94 kcal animal -1 dia de energia metabolizável). Destes, selecionou-se aleatoriamente seis animais, que foram referência para coleta dos seguintes parâmetros do ambiente de alojamento: temperatura do ar mínima e máxima, velocidade do ar, umidade relativa do ar e luminosidade. Para estimar o gasto energético foram consideradas as temperaturas superficiais médias das regiões de cabeça, orelhas e pernas, obtidas com o auxilio da câmara termográfica infravermelho e respectivo software. Durante o período foi verificado que a temperatura ambiente ficou abaixo da zona de conforto térmico e que a temperatura superficial corporal média dos cordeiros foi de 11,48 ± 0,92 °C, indicando que houve uma interação entre os parâmetros climáticos avaliados, promovendo o resfriamento do ambiente e influenciando na redução da temperatura superficial. A dissipação total de calor sensível por animal nas partes analisadas foi de 39,18 W, o que corresponde ao consumo de 0,388 kcal 12 h -1 . Constatou-se que, 26,4% da energia metabolizável diária ingerida pelos cordeiros, nos dias de temperatura abaixo da zona de conforto térmico, foi utilizada para termogênese. Contudo, foi verificado que, por estarem abaixo da zona de conforto térmico, os cordeiros dissiparam o calor sensível por convecção e radiação, utilizando parte da energia metabolizável da dieta para manter a temperatura corporal, situação que pode acarretar perdas econômicas para a produção.Palavras-chave: energia metabolizável, ovinos, termografia 1 Mestrando em Zootecnia-UFGD. afonsohostalacio@hotmail.com 2 Pesquisadora Visitante Senior-UFGD.