The use of Texel, Dorper, Suffolk, and Rambouillet rams in terminal crossbreeding programs on fine wool type sheep to improve growth rate and carcass composition of offspring

Abstract

A crossbreeding study to compare the use of Texel, Dorper, Suffolk and Rambouillet rams as terminal sires on fine wool type sheep was conducted at Texas A&M University, College Station, Texas. Two-hundred fifty-five multiparous Rambouillet ewes were randomly divided into four breeding groups and mated to rams representing the test breeds. Ewes were maintained on native grass pastures and supplemented with concentrate or dry hay, when forage sources were deemed insufficient to meet ewes' dietary requirements according to NRC (1985) for gestating and lactating ewes. Ewes lambed and were maintained on pasture through weaning. Data collected and analyzed included birth weights, lamb vigor scores and death loss prior to weaning. Lambs were weaned at average age of 90d, weaning weights were taken and adjusted for age, sex, and type of birth/rearing. Seventy-eight lambs, 20 from each of the Rambouillet, Suffolk, Texel and 18 from the Dorper subgroups, were placed in the feedlot portion of this study. Lambs were fed ad libitum for 78d. Refusals were weighed back weekly and feed conversions calculated. After a 12hr shrink, final weights were obtained, post weaning average daily gain calculated, and lambs were slaughtered. Hot carcass weights were obtained and dressing percentages calculated. Cold carcass weights, loin eye area (LEA), 12[] rib fat thickness, leg circumferences and carcass lengths were measured. Leg conformation scores were assigned to each carcass after a 48h chill. Texel-sired lambs had a higher mean (P<.01) birth weight when compared to other sire breeds. Dorper-sired lambs had the highest mean (P<.01) vigor score. Texel- and Suffolk-sired lambs were similar in mean adjusted weaning weights, both higher than Dorper- and Rambouillet-sired lambs. No differences were observed for post weaning ADG or feed conversion (P>.10). Texel- and Suffolk-sired lambs had higher mean final weights (P<.01) than Dorper- and Rambouillet-sired lambs. Texel- and Suffolk-sired lambs had advantages in LEA and leg circumference (P<.01). Texel-sired lambs had the highest (P<.01) leg conformation scores. No difference was observed in 12[] rib fat thickness (P>.10) among breeds. Dorper-sired lambs had the lowest final weights, lightest hot carcass weights and shortest carcass lengths (P<.01).