Genetic effects for reproductive performance of straightbred and crossbred Romosinuano and Angus cows in a temperate zone

Abstract

The objectives of this work were to: (1) estimate heterosis and breed direct effects for cow reproduction traits of Romosinuano, Angus, and F1 cows in a temperate climate, and (2) assess the effects of the type of forage grazed (bermudagrass, endophyte-infected and endophyte-free tall fescue) during the breeding season on traits and genetic effects. Calving and weaning rate (n=666 records) were evaluated for 145 cows from 2005 through 2012. Calving interval (n=400) and day of conception within breeding season (n=547) were recorded. Mixed models included combinations of fixed effects: year of record or cow age within year of record, breed type parameterized as main and interaction effects of sire breed and dam breed of cows with records. Additive genetic effects were included as a random component. The sire breed-dam breed interaction was characterized by lower (P<0.005) Angus calving and weaning rates (0.75±0.03, 0.65±0.04, respectively) than other groups, which ranged from 0.88±0.02 (Romosinuano) to 0.92±0.04 (Romosinuano-sired F1) for calving rate and ranged from 0.81±0.03 (F1 sired by Angus) to 0.82±0.03 (Romosinuano-sired F1) for weaning rate. Romosinuano cows conceived later (P<0.02) in the breeding season (25.2±2.3d) than other groups (range from 16.9±3.1 to 17.3±1.8d). Calving and weaning rates were highest (P<0.05) for cows grazing bermudagrass during the breeding season (0.98±0.02, 0.93±0.03), and lowest for cows grazing endophyte-infected tall fescue (0.85±0.03, 0.78±0.04); cows grazing endophyte-free tall fescue were intermediate (0.94±0.02, 0.88±0.03). No interaction of forage type with sire or dam breed was detected (P>0.24). Estimates of heterosis were 0.09±0.03, 0.11±0.04, and –3.7±2.0d (P<0.05) for calving and weaning rate, and conception day within breeding season, respectively. Romosinuano direct effects for these traits were large (P<0.003) and favorable for calving and weaning rate (0.14±0.05, 0.2±0.05), but unfavorable for conception day within breeding season (8.7±2.9d; P<0.05). Angus cows had the greatest proportion of calf loss (0.33) and cows that died or were culled (0.8). Romosinuano may merit consideration for inclusion in breeding programs across forage types in temperate climates.