Sarlo, Kaitlyn Mary (2016-08). Reciprocal Differences in F2 and F3 Nellore-Angus Halfblood Steers for Growth and Health Traits. Master's Thesis.
Nellore-Angus halfblood reciprocal F2 and F3 steers (n = 372) produced in the Texas A&M AgriLife Research McGregor Genomics project were evaluated for weight and growth through different stages of life, including after a standardized bovine viral diarrhea virus (BVDV) challenge. The F2 steers were sired by F1 Nellore-sired (NA) or Angus-sired (AN) bulls out of F1 NA and AN dams (4 reciprocal calf types of ANAN, ANNA, NAAN, NANA, where the breed type of the bull is listed first). The F3 steers resulted from F2 NANA parents. There were no differences due to calf type for birth weight. From birth to weaning the F3 steers gained between 0.10 and 0.13 kg less (P < 0.05) per d than the F2 steers. The F3 steers were lighter than all F2 calf types at weaning, a year of age, through a 42-d health trial, and 15 mo of age. The NAAN steers were the heaviest (P < 0.05) calf type for weaning weight, yearling weight and weight at 15 mo. During the 42-d health and feeding trial, weights of F2 steers out of AN dams were 7 to 10 kg heavier (P < 0.05) than F2 steers out of NA dams. A similar pattern existed for ADG; ADG of the F3 steers was not significantly different from F2 steers out of NA dams. The F2 steers out of AN dams also had higher (P < 0.05) monocyte counts than F2 steers out of NA dams. Although monocyte count was not correlated to ADG during the 42-d health trial, it was lowly and positively correlated (r = 0.14, P = 0.008) with ADG from weaning to a year of age. Different patterns of relationship were present stages among the different calf types. For the NANA (r = -0.52, P = 0.003), F3 (r = -0.22, P = 0.003) and NAAN (r= -0.20, P = 0.003) steers there was a negative correlation of rectal temperature change and ADG from d 0 to 14 post challenge. Rectal temperature change post BVDV challenge was positively correlated with ADG from weaning to yearling weight for NANA (r = 0.62, P = 0.002) and ANNA (r = 0.28, P = 0.026) steers. Only ANAN steers had a relationship of preweaning ADG with rectal temperature change from BVDV challenge (r = 0.43, P = 0.046). In these cattle, the apparent trade-offs between growth and health responses appear inconsistent. The nature and interpretations of these reciprocal differences remain unclear and warrant additional research.