ABSTRACT
In the detection phase of a bovine marker assisted selection program, this paper investigated the genetic variability of three microsatellites on the chromosome 18 (BTA 18). The possible associations between genotypes or alleles of these markers versus weight at first calving and a lifetime calving interval (as indicators of reproductive performance) were evaluated in a beef cattle herd (5/8 Aberdeen Angus x 3/8 Nelore). Eleven alleles were detected in TGLA227 and ILSTS002 and three in BMS3004, the most frequent being TGLA227*79, ILSTS002*133, ILSTS002*135 and BMS3004*129. Polymorphic information content ranged from 0.41 to 0.84, while heterozygosity ranged from 49 percent to 86 percent, with an average value of 77 percent. The association analyses performed between genotype classes for the genetic markers versus weight at first calving indicated no significant result. Also, no correlation was observed between calving interval (CI) and TGLA227 genotypes. However, positive associations were detected between ILSTS002 and BMS3004 and CI. Animals carrying at least one ILSTS002*135 allele presented a CI about 39 days longer than the individuals with other genotypes; animals heterozygous for BMS3004 presented a CI about 35 days shorter than the homozygous. On these grounds, it can be concluded that these markers can be useful as an aid to fertility selection, in this herd.
Na fase de detecção, em um programa de seleção assistida por marcadores, em bovinos, este trabalho investigou a variabilidade genética de três microssatélites no cromossomo 18 (BTA 18). As possíveis associações entre genótipos ou alelos destes marcadores versus o peso ao primeiro parto e o intervalo entre partos (como indicadores do desempenho reprodutivo) foram avaliados em um rebanho de gado de corte (5/8 Aberdeen Angus x 3/8 Nelore). Onze alelos foram detectados em TGLA227 e ILSTS002 e três em BMS3004, os mais freqüentes sendo TGLA227*79, ILSTS002*133, ILSTS002*135 e BMS3004*129. O conteúdo polimórfico de informação variou de 0,41 a 0,84, enquanto a heterozigosidade variou de 49 a 86 por cento, com média de 77 por cento. As análises de associação efetuadas entre classes genotípicas dos marcadores genéticos versus o peso ao primeiro parto não indicaram resultados significantes. Da mesma forma, nenhuma correlação foi observada entre o intervalo entre partos (IEP) e os genótipos de TGLA227. Entretanto, associações positivas foram detectadas entre ILSTS002 e BMS3004 com o IEP. Animais portadores de pelo menos um alelo ILSTS002*135 apresentaram IEP cerca de 39 dias mais longo que os indivíduos com outros genótipos, e animais heterozigotos para BMS3004 apresentaram IEP cerca de 35 dias mais curto que os homozigotos. Assim, pode-se concluir que esses marcadores podem ser úteis como auxiliares na seleção para fertilidade, o rebanho em questão.
ABSTRACT
The aim of the present study was to verify associations between reproductive efficiency and four microsatellite markers located in synteny with genes involved in the regulation of reproductive mechanisms. A sample of 107 females from a Brangus Ibagé population (5/8 Aberdeen Angus x 3/8 Nelore) was characterized for ETH225 (D9S1) and MM12E6 (D9S20) microsatellites, mapped on chromosome 9, and HEL5 (D21S15) and AFZ1 (D21S37) on chromosome 21. Associations between the genetic markers and reproductive efficiency were determined by one-way analysis of variance using calving interval (CI), live weight at calving (LWC), live weight at first calving (LW1C) and live weight at second calving (LW2C) as dependent variables. The genotypes were classified according to allele size into homozygous for long alleles, homozygous for short alleles and heterozygous. A longer CI was observed for individuals homozygous for long alleles at the HEL5 locus compared with the others (p = 0.022). For the AFZ1 locus, an inverse correlation between allele size and calving interval was observed (p = 0.022), suggesting that homozygosity for long alleles at this microsatellite could be advantageous. Analysis of the combined effect of favorable genotypes at HEL5 and AFZ1 indicated that animals with unfavorable genotypes (homozygous for long alleles at HEL5 and homozygous for short alleles at AFZ1) presented a significantly longer CI (p = 0.003) when compared to the other genotypes. The ETH225 and MM12E6 systems did not present any association with CI. None of the systems studied showed any significant association with LWC, LW1C or LW2C.