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Metabolic and productive characteristics of sensitive and heat-tolerant phenotypes of Murciano-Granadina dairy goats.

S. González-Luna


Metabolic and productive characteristics of sensitive and heat-tolerant phenotypes of Murciano-Granadina dairy goats.
S. Serhan1, S. González-Luna*1,2, B. Chaalia1, X. Such1, A. A. K. Salama1, G. Caja1. 1Group of Research in Ruminants (G2R), Universitat Autonoma de Barcelona Bellaterra, Spain, 2F.E.S. Cuautitlan, Universidad nacional Autónoma de México Cuautitlan, Mexico.

Thirty-three Murciano-Granadina does in mid-lactation (2.45 ± 0.14 kg/d milk; 40.9 ± 1 kg BW) were submitted to a short-term challenge (2 h) passing from thermo neutral (TN, THI = 65) to heat stress (HS, THI = 86) conditions. Variation of thermophysiological traits (RT, rectal temperature; RR, respiratory rate) were used to calculate the change ratio (CR = Σ after/before) and to select does differing in tolerance (TO, tolerant, 4.20 ± 0.21, n = 9; SE, sensitive, 6.25 ± 0.24, n = 10; P < 0.01). The does were allocated to a crossover of 2 periods (12-d each) with 2 climatic conditions: TN (15 to 20°C; THI = 63—65), and 2) HS (30 to 37°C; THI = 88—79). RT, RR and lactational traits were recorded daily, whereas milk and blood samples were collected weekly. At the end of each period a glucose tolerance test (GTT; glucose, 0.15 g/kg BW; samples, min —15 to 120) was done. The HS does, increased RT 0.82°C (0.58 and 1.05°C a.m. and p.m. respectively; P < 0.001), RR 224% (164 and 285%, a.m. and p.m. respectively; P < 0.001) and water consumption (74%; P < 0.001), whereas decreased feed intake (—10%; P < 0.001), in comparison to TN. Milk yield increased by 5% (P < 0.005) but energy-corrected milk (2.0 ± 0.1 kg/d) did not vary by HS. Milk fat (—16%), protein (—14%) and lactose (—4%) contents decreased (P < 0.01) by HS. Blood glucose, insulin, and urea did not change, but HS goats had huge PRL and greater creatinine (819 and 14%, respectively; P < 0.01) than TN. Blood insulin did not vary between TN and HS does, but glucose disposal was greater in HS. Comparing TO and SE phenotypes, no differences were detected in RR, but p.m. RT was lower in the SE goats. No differences were detected in feed and water intakes, milk yield and composition, as well as in basal blood metabolites. AUC glucose at 60 min tended to be lower (P < 0.07) in SE than in TO goats. In conclusion, Murciano-Granadina goats, in terms of thermophysiological and lactational traits and blood metabolites, were moderately affected by HS. Responses to GTT indicated that HS increased insulin resistance and that TO and SE goats employed different mechanisms to keep blood glucose levels under HS conditions.

Keywords: heat tolerance, challenge, dairy goat.