En un experimento dialélico entre las razas Hereford (H/H) y Aberdeen Angus (A/A) desarrollado entre los años 1994 y 2002 en la Estación Experimental Bernardo Rosengurtt de la Facultad de Agronomía-Udelar, Uruguay, se estimaron diferencias en efectos genéticos directos (gIA-gIH) y efectos genéticos maternos (gmA-gmH), efectos de heterosis individual (hIAH) y materna (hmAH) mediante modelos lineales para condición corporal al parto (CCP), peso al nacimiento (PN), y peso al destete (PD), y usando modelos lineales generalizados para porcentaje de destete (% D). En CCP los efectos raciales y la heterosis estimada no fueron significativas, en tanto para PN la diferencia en kg fue negativa, siendo superior H/H (-1,18±0,42 kg, P=0,0051). Para PD la diferencia entre efectos maternos (gmA - gmH) resultó positiva, con 4,87±1,01 kg (P=0,0001), y la heterosis individual fue de 5,12±1,24 kg (P=0,0001). Para el % D, la hIAH fue de 0,22± 0,03. La hmAH resultó significativa para PD (11,58±1,48 kg, P=0,0001). Al nacimiento los terneros H/H, A/H y H/A fueron más pesados que los A/A. En % D las madres cruza en promedio superan en 24,7 unidades (14,9 %) a las puras (85,0 vs 60,3). Al destete los terneros hijos de madres híbridas fueron significativamente más pesados (promedio 159,1 kg). Las madres Hereford destetaron los terneros significativamente más livianos (promedio 143,3 kg); mientras que los terneros hijos de madres Angus pesaron 151,6 kg.

In a diallelic experiment between Hereford (H/H) and Aberdeen Angus (A/A) breed, developed between 1994 and 2002 at the Bernardo Rosengurtt Experimental Station (College of Agriculture-University of the Republic, Uruguay) individual (giA-giH) and maternal (gmA-gmH) breed differences, individual (hiAH) and maternal (hmAH) heterosis were estimated, using linear models for body condition at calving (BCC), birth weight (BW), and weaning weight (WW), and generalized linear models for weaning percentage (% W). Racial and estimated heterosis effects were not significant for BCC, while for BW the difference in kg was negative, and H/H was superior (-1.18 ± 0.42 kg, P = 0.0051). For WW, the difference between maternal effects (gmA - gmH) was positive, with 4.87 ± 1.01 kg (P <0.0001), and individual heterosis was 5.12 ± 1.24 kg (P <0.0001). The hiAH for % W was 0.22 ± 0.03. The hmAH was significant for WW (11.58 ± 1.48 kg, P=0.0001). At birth, calves H/H, A/H and H/A were heavier than A/A. For % W, crossbred dams averaged 24.7 points (14.9 %) higher than pure breeds (85.0 vs. 60.3). Crossbred breed dams weaned calves significantly heavier (means 159.1 kg). Hereford dams weaned significantly lighter calves (means 143.3kg); while the calves of Angus dams weighed 151.6 kg.

The aim of this study was to investigate the genetic diversity within and among three breeds of sheep: Corriedale, Merino and Creole. Sheep from the three breeds (Merino n = 110, Corriedale n = 108 and Creole n = 10) were genotyped using the Illumina Ovine SNP50 beadchip®. Genetic diversity was evaluated by comparing the minor allele frequency (MAF) among breeds. Population structure and genetic differentiation were assessed using STRUCTURE software, principal component analysis (PCA) and fixation index (F ST). Fixed markers (MAF = 0) that were different among breeds were identified as specific breed markers. Using a subset of 18,181 single nucleotide polymorphisms (SNPs), PCA and STUCTURE analysis were able to explain population stratification within breeds. Merino and Corriedale divergent lines showed high levels of polymorphism (89.4% and 86% of polymorphic SNPs, respectively) and moderate genetic differentiation (F ST = 0.08) between them. In contrast, Creole had only 69% polymorphic SNPs and showed greater genetic differentiation from the other two breeds (F ST = 0.17 for both breeds). Hence, a subset of molecular markers present in the OvineSNP50 is informative enough for breed assignment and population structure analysis of commercial and Creole breeds.