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Heat tolerance in Tuli-, Senepol-, and Brahman-sired F1 Angus heifers in Florida.

1998; Oxford University Press; Volume: 76; Issue: 6 Linguagem: Inglês

10.2527/1998.7661568x

1544-7847

A. C. Hammond, C. C. Chase, E J Bowers, T. A. Olson, R.D. Randel,

Genetic and phenotypic traits in livestock

We investigated heat tolerance and growth rate in two trials under ambient conditions in central Florida. Trial 1 (1994) involved 38 Brahman (B), 21 Senepol (S), 19 B × Angus (A), 20 S × A, and 20 Tuli (T) × A heifers. Trial 2 (1995) involved 13 A, 35 B, 30 S, 23 B × A, 17 S × A, and 28 T × A heifers. Measurements were made on three consecutive weeks during the hotter and cooler seasons of each year and included rectal temperature (RT, °C), respiration rate (RR, bpm), temperament score (TS; 1 = very docile, 5 = very aggressive), blood packed-cell volume (PCV), and plasma cortisol concentration (CORT). Data for RT were transformed (log10 [RT - 37]) before analysis. On the hottest date in Trial 1, log10 RT was not different between B (.39 ± .011) and B × A (.37 ± .016) or between T × A (.35 ± .015) and B × A, but log10 RT was lower (P < .05) in S × A (.30 ± .015) than in either S (.35 ± .015) or T × A. On all dates in Trial 1, RR was lower (P < .05 to .001) and PCV was higher (P < .05 to .001) in B than in B × A. There were few differences in TS except on two dates when B scored higher (P < .01 to .001) than B × A, and these differences were associated with higher (P < .05) CORT in B than in B × A. Using initial BW as a covariate, adjusted ADG (kg) of T × A (.52 ± .023) was not different from adjusted ADG of B × A (.57 ± .024) or S × A (.54 ± .023). On the hottest date in Trial 2, log10 RT and RR were higher (P < .001) in A (.59 ± .017, 74 ± 2.7) than in B (.47 ± .010, 39 ± 1.6), S (.42 ± .011, 50 ± 1.8), and crossbred heifers (.47 ± .011, 60 ± 1.8; .43 ± .014, 55 ± 2.4; and .50 ± .012, 48 ± 2.0 for T × A, S × A and B × A, respectively), and RR was higher (P < .001) in B × A than in B. On the coolest date in Trial 2, RR was slightly lower in B (32 ± .5) than in A (34 ± .7, P < .01) and B × A (36 ± .6, P < .001) and was associated with higher PCV in B than in A. On both dates, TS and CORT were higher (P < .01) in B than in A. In Trial 2, adjusted ADG (kg) was higher (P < .01) in B (.43 ± .017) than in A (.32 ± .033), higher (P < .001) in S (.45 ± .018) than in A, and higher (P < .001) in crossbreds (B × A [.53 ± .023] + S × A [.44 ± .025] + T × A [.46 ± .019]) than in A. These data indicate that heat tolerance in F1 crosses of tropically adapted breeds (Tuli, Senepol, Brahman) with a temperate breed (Angus) is similar to heat tolerance displayed by purebred tropical breeds (Senepol, Brahman).