Physiological responses and lactational performances of late-lactation dairy goats under heat stress conditions

Abstract

Eight Murciano-Granadina dairy goats in late lactation were exposed to different ambient conditions, using metabolic cages in a climatic chamber. The experimental design was a crossover (2 periods of 35 d and 4 goats each) and conditions were (1) thermal neutral (TN; 15 to 20 °C day-night) and (2) heat stress (HS; 12-h day at 37 °C and 12-h night at 30.5 °C). Humidity was maintained at 40% and light-dark was constant (12-12h). The forage:concentrate ratio was adjusted daily for maintaining similar value in TN and HS goats (70:30). Water was freely available at ambient temperature. Rectal temperature and respiratory rate (0800, 1200 and 1700 h) and milk yield were recorded daily, whereas milk composition, nonesterified fatty acids and haptoglobin in blood were analyzed weekly. At d 25, additional blood samples were taken for analysis of metabolites and indicators of the acid-base balance. Digestibility coefficients and N balance were determined (d 31 to 35) and body weight was recorded (d 35). Compared with TN goats, HS goats experienced greater rectal temperature (+0.58 °C), respiratory rate (+48 breaths/min), water intake (+77%) and water evaporation (+207%). Intake of HS goats rapidly declined until d 7 (-40%), partially recovered from d 7 to 19, and steadied thereafter (-14%). No changes in digestibility or N balance were detected. Blood nonesterified fatty acids and haptoglobin peaked at d 7 in HS goats but did not vary thereafter. Although milk yield did not vary by treatment, milk of HS goats contained -12.5% protein and -11.5% casein than TN goats. Panting reduced concentration and pressure of CO₂ in the blood of HS goats, but they were able to maintain their blood pH similar to the TN group by lowering HCO₃(-) and increasing Cl(-) concentrations in their blood. In conclusion, HS dairy goats showed dramatic physiological changes during the first week of treatment and partially recovered thereafter. They were able to maintain milk yield by losing body mass, but milk protein content and protein yield were depressed. Further research is needed to assess the response of dairy goats to HS at earlier stages of lactation.

Effects of season on the quality of Garfagnina goat milk

“…The negative correlations between temperature and some short-chain FAs are in agreement with studies showing the reduction in the FAs synthesised from the breast (de novo) as a result of the increase of temperatures, usually combined with a reduced intake of feed (Hamzaoui et al 2013). Some authors have suggested that, to cope with the lack of energy due to decreased feeding, goats do not mobilise body fat, but change the rumen fermentation and rumen volatile FA profile (Salama et al 2014).…”

“…The decrease in feed intake could be the adaptive mechanism to produce less body heat (Marai et al 2007). Since in lactating animals most of the blood glucose is used by the breast for the lactose synthesis, it could be speculated, according to Hamzaoui et al (2013), that the reduction in lactose secretion is a strategy to maintain stable glycaemia.…”

Influence of seasonal changes on physiological variables, haematology and serum thyroid hormones profile in male Red Sokoto and Sahel goats

“…In goats, if the THI is below 65 or above 75, the animal may experience thermal stress (Hamzaoui et al 2013). In the present study, the AT and THI were higher than the thermoneutral zone in the afternoon hours of the HDS and RAS, suggesting that the goats experienced heat stress in these seasons.…”

Thermoregulatory responses related to coat traits of Brazilian native ewes: an adaptive approach

“…Certainly the thermolysis mechanisms, especially latent heat loss, were triggered to maintain the animals' normal temperatures, confirming their homeothermic capacity. Hamzaoui et al (2013) reported that animals keep under heat stress condition into climatic chambers, presented the highest values of RT and RR during the first week, but after this period were observed slight decreasing of these variables, which indicates a partial adaptation to the heat stress conditions. These results could explain the low variability of RT and RR of animals among environmental conditions (from groups 1 to 5), possibly animals were acclimated to high radiation and air temperature in which they were exposed over the years.…”

“…On the other hand, maintaining RRs high for a long time can cause some physiological disturbance, such as acid-basic disequilibrium (Srikandakumar et al 2003;Hamzaoui et al 2013). However, we found that, considering the natural environmental conditions analysed, there were no changes in stress response parameters, such as RR and RT, as shown in Figure 1.…”