Temperature effect on energy partitioning and fast heat production of Anglo Nubian and Saanen goats
The objective of this work was to determine the effect of temperature on energy balance and basal metabolism of Saanen and Anglo Nubian goats, using indirect calorimetry system. Six dry and non-pregnant Saanen (53.7 ± 7.7 kg BW) and six dry and non- pregnant Anglo Nubian (56.4 ± 8.0 kg BW) goats, which were on average 5 years old, were used in a factorial design 2 x 3 (2 breeds and 3 temperatures). The experimental period consisted of three stages corresponding to the temperature of 10.0 ± 0.23°C, 20.0 ± 0.41°C and 35.0 ± 1.05°C. The adaptation period in each temperature lasted 21 days. Goats were allocated to individual metabolism cages to perform the metabolism assay and gas exchange measurements concomitantly. During feeding period, gas measurement was performed using an open-circuit facemask respirometry in groups of four animals (two of each breed). After that, goats were subjected to 60-h fasting (no feed) to estimate fasting heat production (FHP) or basal metabolism. Irrespective of breed, DM intake (DMI) and organic matter intake (OMI) decreased linearly as ambient temperature increased. During feeding period, rectal temperature was not affect by ambient temperature, but respiratory rate (BPM) and evaporative water loss (EWL) increased linearly with temperature elevation. Saanen´s rectal temperature and BPM were higher than Anglo Nubian´s. Irrespective of breed (P = 0.59), heat production (HP) showed a quadratic effect with the lowest values at 20ºC. Conversely, FHP showed a quadratic effect with a tendency of decreasing at increasing rate in temperature above 20º up to 35ºC. Consequently heat increment (HI) showed quadratic effect with a sharp increase when the ambient temperature rose from 20 to 35ºC. In conclusion, Saanen and Anglo Nubian goats are able to maintain homeostasis in environments between 10 and 35ºC. On the other hand, the increase in ambient temperature leads to lower intake, resulting in negative energy balances. Above 20°C, goats tend to decrease fasting heat production, as an attempt to spare heat load in hot environments.