Adsa Logo White Adsa Title White

Metabolic and productive characteristics of sensitive and heat-tolerant phenotypes in dairy sheep.

A. A. K. Salama




Metabolic and productive characteristics of sensitive and heat-tolerant phenotypes in dairy sheep.
B. Chaalia, S. Serhan, S. Gonzalez-Luna, X. Such, A. A. K. Salama*, G. Caja. Research Group in Ruminants (G2R), Universitat Autonoma de Barcelona Barcelona, Spain.

The objective was to evaluate the effects of heat stress (HS) on Manchega dairy ewes differing in their phenotypical heat tolerance. Dairy ewes (n = 24) in late-lactation (158 � 5 DIM) were submitted to a short-term (2 h) heat challenge (36�C, 43% humidity) in a temperature-controlled room. Rectal temperature (RT) and respiratory rate (RR) were recorded, and the ewes were classed by the RT and RR change ratio (CR = after/before HS). The CR values distributed normally and averaged 5.15 � 0.22. Ten ewes differing in CR (Tolerant: A, 4.61 � 0.24, n = 5; Sensitive: B, 5.69 � 0.14, n = 5; P < 0.01) with similar milk yield were used in a crossover design of 2 periods (3 wk each) and 2 climatic conditions: 1) thermo-neutral (TN; 15 to 20�C day-night), and 2) HS (day, 37�C; night, 30�C). Humidity (50%) and dark-light (12—12 h) were constant. RT and RR, milk yield, and feed and water intakes were recorded daily. Milk and blood samples were collected and analyzed weekly. At d 19 of each period, ewes were submitted to glucose tolerance test (GTT; 0.25 g/kg BW) with blood samples collected at 10 time points (min ?15 to 120) for the analysis of glucose and insulin. Compared with TN, HS ewes experienced increased (P < 0.001) RT (+0.54�C), RR (+177%), water consumption (+35%), whereas feed intake decreased (−20%; P < 0.001). Milk yield (0.63 � 0.05 kg/d) did not vary between treatments, but milk fat and milk protein contents decreased (P < 0.01) 14 and 17%, respectively in HS. The TN and HS ewes had similar blood glucose, insulin and NEFA, but HS had greater prolactin and creatinine values (+415 and 10%, respectively; P < 0.01). No differences were detected in RT, RR, feed intake, water consumption, milk yield, or milk composition between A and B phenotypes. Compared with TN, HS ewes had a similar insulin response to GTT (P > 0.10), but numerically greater (P = 0.17 to 0.19) glucose disposal. The A ewes under HS tended to have greater insulin secretion during GTT, but similar glucose disposal compared with B ewes. In conclusion, Manchega dairy ewes in were relatively tolerant to HS conditions, with few differences between A and B heat tolerance phenotypes.

Keywords: heat tolerance, metabolic indicators, dairy sheep.