Responses of hair sheep breeds to high heat load index conditions

TitleResponses of hair sheep breeds to high heat load index conditions
Publication TypeJournal Article
Year of Publication2016
AuthorsTadesse, D, Puchala, R, Gipson, TA, Tsukahara, T, Goetsch, AL
JournalJournal of Animal Science
Volume94
IssueE-Supplement 94
Start Page823
AbstractFourteen Dorper (D; 59±3.2 kg), 13 Katahdin (K; 58±2.5 kg), and 8 St. Croix (SC; 50±3.0 kg) female sheep (>1.5 yr) were used to evaluate responses to high heat load index (HLI) conditions. After 4 wk of thermoneutral conditions (70 HLI), in sequential 2-wk periods daytime HLI was regulated near 85, 90, and 95 and that at night was 70, 77, and 81, respectively. Data were analyzed with a mixed model containing breed, week within period, measurement time (0700, 1300, and 1700 h), three-way interactions, and baseline covariates. Rectal temperature (RT) at 1300 and 1700 h was lowest for SC (38.36, 38.87, and 38.96 for D, 38.31, 38.85, and 38.87 for K, and 38.29, 38.64, and 38.66 ºC for SC at 0700, 1300, and 1700 h, respectively; SE=0.046). A similar interaction (P=0.052) occurred in panting score (PS, 0-4.5; 0.10, 0.64, and 0.54 for D, 0.09, 0.70, and 0.58 for K, 0.02, 0.42, and 0.40 for SC at 0700, 1300, and 1700 h, respectively SE=0.064). Breed differences in PS resulted from highest HLI in period 3 (0.07, 0.17, and 1.03 for D, 0.08, 0.15, and 1.14 for K, 0.04, 0.06, and 0.73 for SC in period 1, 2, and 3, respectively; SE=0.080). Period, week, and time interacted (P<0.001) in respiration rate (RR) (period 1: 41, 102, and 97 in wk 1, 50, 124, and 115 in wk 2; period 2: 56, 158, and 124 in wk 1, 65, 160, and 134 in wk 2; period 3: 76, 219, and 161 in wk 1, 130, 164, and 148 in wk 2 at 0700, 1300, and 1700 h, respectively; SE=6.6). There was a corresponding interaction (P<0.001) in RR:RT as an index of energy expended to minimize RT (period 1: 0.40, 1.00, and 0.96 in wk 1, 0.05, 1.22, and 1.14 in wk 2; period 2: 0.57, 1.55, and 1.22 in wk 1, 0.66, 1.58, and 1.31 in wk 2; period 3: 0.75, 2.14, and 1.58 in wk 1, 1.28, 1.61, and 1.44 in wk 2 at 0700, 1300, and 1700 h, respectively; SE=0.064). In conclusion, some measures suggest greater tolerance of high HLI by SC than D or K. There appeared considerable adaptation in RR from wk 1 to 2 of period 3 to minimize RT in the early afternoon, which was at least partially facilitated by higher RR in the early morning before HLI increased.