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item Ferrell, Calvin
item Jenkins, Thomas
item Freetly, Harvey

Submitted to: American Society of Animal Science Southern Section Meeting
Publication Type: Proceedings
Publication Acceptance Date: 11/22/2005
Publication Date: 1/3/2006
Citation: Ferrell, C.L., Jenkins, T.G., Freetly, H.C. 2005. Feed utilization and performance of crossbred tropically adapted cattle. Symposium on Tropically Adapted Breeds, Southern Cooperative Series Bulletin 405, American Society of Animal Science Southern Section Meeting, p. 144-153.

Interpretive Summary: Four studies were briefly reviewed to evaluate tropically adapted relative to breeds developed in temperate environments for feed utilization and energy requirements during growth. Findings were relatively consistent among studies and indicated crossbred steers sired by tropically adapted breeds (Brahman, Boran, Tuli) tended to consume less feed (13%), grow slower (11%), and have similar feed conversion as steers sired by Angus, Hereford, or MARC III bulls. Although some differences in site of digestion were observed among breeds, total tract digestibility of high quality diets appears to be similar. Visceral organ weights and response of those organs to altered nutritional status differed among breeds. Those differences appear to be associated with differences in feed intake, total heat production, perhaps to the animal's capacity to adapt to altered nutritional status. Differences in heat production among genotypes were observed, but those differences appear to be primarily associated with differences in feed intake. Fasting heat production and maintenance requirements appear to be similar among genotypes when evaluated in a good nutritional environment under temperate environmental conditions.

Technical Abstract: Four studies were conducted to evaluate tropically adapted breeds for feed utilization and energy use during growth. In study 1, 10 Bos indicus-sired (5 Boran, Bo; 5 Brahman, Br) and 10 MARC III steers were used to assess cattle age and breed influence on digestion of a high grain diet. Duodenal flows of total N, microbial N, nonmicrobial N, total amino acids, and total tract N digestibility were not different (P > 0.05) due to age or breed. In study 2, 1/4 (21), 1/2 (7), and 3/4 (9) Br were compared to MARC III (14) steers fed bromegrass hay or corn silage diets during a 119 d period. Br crosses ate less (14.6 vs. 16.3 lb/d) and grew slower (1.37 vs. 1.59 lb/d) than MARC III (P < 0.05), but ME/gain was similar (16.0 vs. 14.1 Mcal/lb; P = 0.40). When subsequently fed a high-corn diet, daily DM intake (16.8 vs. 18.7) and ADG (2.60 vs. 2.91 lb/d) were lower (P < 0.05) for Br steers. Br and MARC III had similar ME/gain during finishing (9.16 vs. 9.16 Mcal/lb; P = 0.98) and for the entire study (9.80 vs. 9.71; P = 0.79). Influences of Angus (A), Bo, Br, Hereford (H), and Tuli (T) sires on body composition and energy use during finishing was evaluated in study 3. Feed intake was least for Bo- and T-, intermediate for Br- and H-, and greatest for A-sired steers. Rates of weight, fat, and energy gains were similar for A-, H-, and Br-sired steers, but less (P < 0.01) for Bo and T when fed ad libitum. Liver weights differed (P < 0.01) among sire breeds (14.0, 10.0, 11.2, 13.4, and 10.7 lb for ad libitum fed A, Bo, Br, H, and T, respectively) and increased in response to increased daily feed intake in H (0.65), A (0.55), Bo (0.47), Br (0.38), and T (0.40). Maintenance and efficiency of energy use for gain differed (P < 0.05) among sire breeds. In study 4, fasting heat production (FHP) at 30 wk of age was highest for MARC III heifers and decreased as Br increased (0, 1/4, 1/2, 3/4). FHP decreased with aging, but the rate of decrease followed the same ranking, resulting in similar values at 86 wk. A number of differences between tropically and temperately adapted cattle were observed, but efficiency of feed use was similar.