El componente racial influencia la resistencia a la infección con el virus de la leucosis bovina / The racial component influences resistance to infection with the bovine leukemia virus

RESUMEN El virus de la leucosis bovina (VLB) es un retrovirus que afecta principalmente el ganado lechero, reduciendo la producción de leche entre el 2,5 y 5%. La raza criolla colombiana Blanco Orejinegro (BON) es una raza rustica, bien adaptada, que ha mostrado resistencia in vitro a las infecciones ocasionadas por los virus de la fiebre aftosa y la estomatitis vesicular, así como las originadas por la bacteria Brucella abortus. El objetivo del presente estudio fue determinar si la raza BON y su cruce con Holstein son resistentes a la infección por el VLB. Se tomaron 124 muestras de sangre (59 Holstein, 40 BON y 25 BON x HOL) del mismo hato, se extrajo el DNA y se realizó una PCR-anidada correspondiente a una región del gen env de VLB. Se obtuvo un fragmento de 444 pb en los animales positivos. La prevalencia molecular del hato fue 33% para VLB. Se encontró diferencia significativa para infección por VLB entre los tres grupos raciales (p < 0,05). El porcentaje de infección fue del 55,9% para la raza Holstien, 5% para las vacas BON y 24% para el cruce BON x HOL; este último presentó una reducción en el porcentaje de infección del 32% respecto a la raza Holstein, lo cual puede ser atribuido a la presencia de genes de resistencia en la raza BON. Se comprobó que el nivel de infección es menor en vacas lecheras del cruce BON x HOL que en la raza lechera Holstein.

ABSTRACT The bovine leukemia virus (BLV) is a retrovirus that primarily affects dairy cattle, reducing milk production between 2.5 and 5%. The Colombian Blanco Orejinegro (BON) is a well-adapted, rustic, creole breed resistant to in vitro infections of Foot-and-mouth disease virus and vesicular stomatitis virus, as well as to Brucella abortus. This study aimed to determine if the crossing of BON and Holstein breeds is resistant to infection by BLV. Blood samples of 124 individuals (59 Holstein, 40 BON, and 25 BON x HOL) of the same herd were taken. The DNA was extracted, and a nested PCR was performed related to a region of the env gene of BLV. A fragment of 444 bp was obtained for positives animals. The molecular in-herd prevalence was 33% for BLV. A significant difference for BLV infection was found among the groups (p<0.05). The infection rate for the Holstein group was 55.9%, for BON cattle 5%, and for BON x HOL cattle 24%. The latter showed a reduction in the infection rate of 32% to the Holstein breed, which can be attributed to the presence of resistance genes in the BON breed. It was found that the level of infection is lower in BON x HOL cattle in contrast with Holstein dairy cows.

Association between a polymorphism in intron 3 of the bovine growth hormone gene and growth traits in Holstein heifers in Antioquia.

The aim of this study was to determine the association between a polymorphism in intron 3 of the bovine growth hormone (BGH) gene and growth traits related to the start of the reproductive life of Holstein heifers. This research was conducted using 480 Holstein heifers belonging to eight herds in three municipalities in the Department of Antioquia (Colombia). The phenotypic information used corresponded to information that had been historically recorded for each of the herds and was supplemented with information obtained through bimonthly visits to the herds over a period of 24 months. Genotyping was performed using the PCR-RFLP technique with DNA extracted from peripheral blood using the salting out technique. To determine association, statistical analyses were performed using parametric methods. Allele frequencies for the alleles (+) and (-) were 0.91 and 0.09, respectively. The genotype frequencies were 0.77, 0.2 and 0.03 for the genotypes (+/+), (+/-) and (-/-), respectively. There was an association between genotype and weight at first estrus and first calving (P < 0.01). The regression coefficients for both characteristics were significant, indicating that for each (+) allele, weight at first estrus and first calving decreased by 9.24 and 16.07 kg, respectively. The results indicated the existence of an association between a polymorphism in intron 3 of the BGH gene and both weight at first estrus and first calving, which can be used to facilitate the selection of animals with these genotypes for use in breeding programs.

Effect of two single nucleotide polymorphisms on milk yield and composition.

The bovine prolactin (PRL) and bovine growth hormone (bGH) genes exhibit several polymorphisms. Some of them can be detected by molecular techniques using restriction endonucleases, such as RsaI for the PRL gene and MspI for the bGH gene. We examined the relationship between the PRL-RsaI and bGH-MspI polymorphisms and some economically important characteristics of Holstein cows. Research was conducted on 315 Holstein cows from 5 municipalities in the Department of Antioquia, Colombia. Individuals were genotyped using PCR/RFLP. The statistical analysis was carried out using generalized linear models and a regression analysis. Polymorphism of the bGH gene was found to have a significant association with the percentage of protein in milk and milk yield. Genotype (-/-) was favorable for dairy yield, while genotype (+/+) was favorable for protein percentage. The PRL gene showed no significant association with any of the evaluated characteristics. The bGH gene appears to be a candidate for the implementation of marker-assisted selection programs. To determine the effect of the prolactin gene, research should be conducted with a larger sample size and a group of animals with more balanced genotypes.