IDENTIFICATION AND UTILIZATION OF MECHANISMS RESPONSIBLE FOR THE ADAPTATION OF CATTLE TO STRESSORS OF THE SUBTROPICS
Title: Evaluation of two sources of Angus cattle under South Florida subtropical conditions
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 2, 2011
Publication Date: July 1, 2011
Citation: Riley, D.G., Arthington, J.D., Chase, C.C., Jr., Coleman, S.W., Griffin, J.L., Rae, D.O., Mader, T.L., Olson, T.A. 2011. Evaluation of two sources of Angus cattle under South Florida subtropical conditions. Journal of Animal Science. 89:2265-2272.
Interpretive Summary: Some cow-calf producers in the southeastern U.S. realize enhanced profitability in their operations by using Angus in straight or crossbreeding programs. No doubt, much of this value may be due to retained ownership and enhanced feedlot performance and meat quality of calves once shipped to more northern regions for backgrounding and finishing. Replacement females; however, must cope with the harsh subtropical environment and reproduce and raise a good calf annually for multiple years. There are not a lot of Angus seedstock producers in Florida, perhaps because they are not adapted to local conditions. At the Subtropical Agricultural Research Station in Brooksville, Florida, is an Angus herd formed in the 1950’s, primarily bred to bulls from Maryland through the 1970’s, and bulls primarily selected from within the herd for the last 40+ years. Angus cattle in this herd are visibly different than are modern Angus, primarily due to their smaller size throughout life. It is possible that these Angus have somewhat adapted to local conditions. This study compared performance and aspects of adaptability of this Florida Angus bloodline with cattle that are representative of modern Angus bloodlines in the subtropics of Florida. Embryos from both Angus sources (local and outside) were transferred to Brahman crossbred cows in South Florida over 3 years and 82 calves were produced. At weaning, outside-source calves were taller but not significantly heavier than local-source calves. Differences in inner ear (tympanic) temperature were not observed between sources. At 17 months of age, outside-source heifers were heavier and taller than local-source heifers. Outside-source heifers were younger (about 100 days) at first conception, and had greater pregnancy and calving rates than local-source heifers. Bulls from outside-source were heavier at 320 days, and from 14 to 17 months of age had larger scrotal circumference and tended to be heavier than local-source bulls. These results indicate no performance or adaption advantages for the local-source Angus through 17 months of age. The striking difference between sources in age at first conception is important and requires further study as does this influence on lifetime cow productivity.
The objective of this study was to compare performance and aspects of adaptability attributes of cattle from a Florida Angus bloodline (local source from a mostly closed herd for over 50 yr) to cattle that are representative of modern Angus bloodlines (outside source) in U.S. subtropical conditions. Embryos from both sources were transferred to Brahman-crossbred cows in South Florida, and calves (n = 82) were born in 3 yr. Before weaning, summer tympanic temperatures were recorded hourly for 3 d in each year. Heifers were placed with fertile bulls until diagnosed pregnant. Traits relative to sexual maturation of bulls were recorded at 1- or 2-mo intervals until approximately 17 mo of age. Calves from outside sources had greater hip height at weaning than calves from the local source (P < 0.001; 108.8 ± 0.62 and 104.7 ± 0.68 cm, respectively). Local-source calves (n = 37) had greater (P = 0.03) exit velocity (2.7 ± 0.3 m/s) than outside-source (n = 45) calves (2.0 ± 0.29 m/s), which may be indicative of more nervous or temperamental disposition. However, no source differences were detected for other assessments of disposition (chute or pen score, P > 0.8). Few source differences for minimum, maximum, or range of daily tympanic (inner ear) temperatures were detected. At 17 mo of age, outside-source heifers were heavier (P = 0.05) and had greater (P < 0.001) hip height than Angus heifers from the local source. Heifers from the outside source were younger (P < 0.001) at the time of their first conception (454 ± 17.5 d) than heifers from the local source (550 ± 16.9 d). Outside-source heifers also had greater (P < 0.02) pregnancy and calving rates (0.7 ± 0.119 and 0.62 ± 0.125, respectively) from exposure to bulls within a year from weaning than the heifers from the local source (0.29 ± 0.089 and 0.19 ± 0.077, respectively). Bulls from the outside source were heavier (P = 0.05) at 320 d of age than local-source bulls. From 14 through 17 mo of age, outside-source bulls had greater (P = 0.05) scrotal circumference and tended (P = 0.15) to be heavier than local-source bulls. There appeared to be no performance or adaptation advantages for the local-source Angus through 17 mo of age. The large source difference for age at first conception in heifers merits additional attention and comparison with cow lifetime production performance for the 2 sources.