Comparative Assessment of Thermotolerance in Dorper and Second-Cross (Poll Dorset/Merino × Border Leicester) Lambs

Abstract

The objective of this study was to compare the thermotolerance of second-cross (SC; Poll Dorset × Merino × Border Leicester) and Dorper lambs. Dorper and SC lambs (4–5 months of age) were subjected to cyclic heat stress (HS) (28–40 °C). The temperature was increased to 38–40 °C between 800 and 1700 h daily and maintained at 28 °C for the remainder of the day (30–60% relative humidity (RH)) in climatic chambers for 2 weeks (n = 12/group), with controls maintained in a thermoneutral (TN) (18–21 °C, 40–50% RH) environment (n = 12/group). Basal respiration rate (RR), rectal temperature (RT) and skin temperature (ST) were higher (p < 0.01) in SC lambs than in Dorpers. HS increased RR, RT and ST (p < 0.01) in both genotypes, but the levels reached during HS were lower (p < 0.01) in Dorpers. HS increased (p < 0.01) water intake to a greater extent in SC lambs, while feed intake was reduced (p < 0.05) by HS in SC lambs but not in Dorpers. HS increased (p < 0.01) blood urea nitrogen and creatinine in SC lambs only. Plasma non-esterified fatty acid concentrations were reduced (p < 0.05) by HS in SC lambs but increased (p < 0.05) in Dorpers. There was no effect of HS on pO2, cHCO3− and cSO2, but higher (p < 0.01) blood pH and lower (p < 0.01) pCO2 were recorded under HS in both genotypes. Blood electrolytes and base excess were reduced (p < 0.01) under HS, while a genotype difference (p < 0.05) was only observed in blood K+ and hemoglobin concentrations. Basal plasma prolactin concentrations were lower (p < 0.01) in Dorpers but were elevated at a similar level during HS (p < 0.01) in both genotypes. Dorper lambs are more resilient to HS than SC lambs. Future research should focus on confirming whether the better heat tolerance of Dorpers is translated to better returns in terms of growth performance and carcass traits over the summer months.

Impact of Heatwaves on the Physiology and Retail Meat Quality of Lambs

“…The increase in RR, RT and ST with exposure to a HW observed in this experiment agrees with previous research on HS in sheep [9,[24][25][26]. The increase in RT is a commonly used indicator of HS observed when ambient temperature exceeds the species temperature threshold, and the animal can no longer maintain its core body temperature.…”

“…We have previously shown that the muscle pH and meat quality in lamb was not affected after 2 weeks or 1 week controlled HS exposure (28-40 • C, 30-40% RH) [9,38]. Similar to the current study, we had observed that the lambs' physiological and blood gas parameters were significantly affected by HS but not the meat quality and muscle pH [26]. These results also agree with previous work of Lowe, et al [7], who reported that 12 h of HS did not change sheep meat quality.…”

“…From the limited effect result of muscle pH (1-day HW) and meat colour (1-and 3-day HW groups of LTL and SM), acute HS has limited effects on muscle pH (HW1) and meat colour (HW3 and HW1 of LTL and SM respectively) as was seen here as the lambs may not have enough opportunity to adapt to acute stress. It may take 2-3 days for lambs to adapt to an ambient temperature change, even if the lamb's physiological and blood parameters were changed [26]. The number of published studies focused on the relationship between short-term HS (less than 1 month) and meat quality is very limited and does not provide conclusive evidence.…”

Reducing the Fermentability of Wheat with a Starch Binding Agent Reduces Some of the Negative Effects of Heat Stress in Sheep

“…Continuous selection for high-yielding wool and meat traits has made the sheep population more susceptible to summer heat stress (HS) due to associated feed and metabolic energy requirements [ 1 , 2 ]. Many studies have reported a HS-associated elevation in the thermoregulatory responses [ 3 , 4 , 5 ] and a decline in the production parameters of sheep [ 6 ]. Often, there are reports of impaired reproduction variables such as pregnancy rate, embryo survival, and lambing rates [ 7 , 8 ]; therefore, researchers and farmers have increased attention into the use of feed or feed additives that can mitigate the seasonal effects of heat while using livestock with a high genetic gain [ 9 , 10 ].…”

Productive characteristics of feedlot Santa Inês and Dorper lambs: intake, digestibility, feeding behavior, performance, carcass traits, and meat quality

“…Dorper is the result of the cross between Dorset Horn and Blackhead Persian, original transboundary breeds from South Africa. It presents high productivity with excellent performance, conformation, and uniform carcasses associated with meat quality (Ocak et al 2016;Issakowicz et al 2018;Joy et al 2020). Locally adapted breeds, such as Santa Inês, showed small bodyweight sizes compared to exotic specialized breeds (Malhado et al 2009).…”