Bio-thermal responses and heat balance of a hair coat sheep breed raised under an equatorial semi-arid environment

Do newborn lambs with black and white hair-coats in an equatorial semi-arid environment maintain homeothermy?

We assessed newborn lambs from two hair-coat sheep breeds, the black Santa Ines (n = 29) and white Dorper (n = 26), to determine how they behaviourally and physiologically respond to the prevailing thermal conditions in an equatorial semi-arid environment. Measurements of hair-coat surface temperature, rectal temperature and the lambs' exposure to sun were recorded across the first 24 h of life every hour, after the lambs had received colostrum. Lambs and ewes were kept in a lambing pen and could freely move between a shaded area or be exposed to sun. During the study period, the air temperature ranged between 20 ºC and 34 ºC. When exposed to sun, lambs and ewes could experience as much as 1200 W m-2 of solar irradiance. Santa Ines lambs exhibited higher (highest density interval at 95%, HDI) hair-coat surface temperatures than did Dorper lambs. Overall, both Santa Ines and Dorper lambs sustained homeothermy, with a mean rectal temperature ranging from 38.7 ºC to 39.1 ºC between night and daytime phase, and a mean amplitude of ~ 0.8 ºC. Nevertheless, from 10:00 to 15:00, some lambs were found to be moderately hyperthermic. Five Santa Ines and three Dorper lambs had rectal temperatures above 40 ºC, and one Santa Ines lamb, while exposed to sun, had a rectal temperature of 41.3 ºC. Over this time period, lambs were more likely to move to shade (HDI at 95%). From 00:00 to 06:00, despite the air temperature being lower than the hair-coat surface, favouring high rates of sensible heat loss to the environment, no lamb exhibited signs of hypothermia (rectal temperature < 37.5 ºC). In conclusion, haired newborn lambs coped well with high levels of radiant heat during the daytime and lower temperatures at night. However, providing access to shade during the daytime is important to improve the welfare of newborn lambs delivered in equatorial semi-arid regions.

Thermal stress index for native sheep

The first objective of this study was to develop a thermal stress index for sheep based on environmental and animal data collected in a climate chamber under various environmental conditions. The second objective was to compare published indices of thermal comfort and the proposed index, testing them with the data from this study, with the objective of pointing out the most adequate index to be used by breeders when choosing management procedures. A total of 3024 data were obtained for the physiological variables of the sheep exposed to the eight thermal conditions in the climatic chamber and in ambient condition, kept three days in each thermal condition. A principal component analysis summarized the measurements of physiological variables into only one variable (y1). Using SigmaPlot software, multiple regression of y1 with the environmental variables and their combinations produced a number of indices. The equation chosen was the heat stress index for sheep, TSI = 24.153 - (0.0523*A_T) + (0.746*B_GT) + (4.104*Vp), with R² = 0.668. The correlations presented high values, where these correlation values were assumed to indicate the efficiency of each index as indicators of the animals' response to the environment. Thus, it was assumed that the TSI presents a high efficiency.

Morphology of coat and skin of small ruminants reared in the Brazilian semi-arid region

The structure of the coat and integument of small ruminants reared in semi-arid regions have valuable characteristics that favor their adaptation to the region. The objective of this study was to evaluate the structural characteristics of the coat and integument and sweating capacity of goats and sheep in the Brazilian semi-arid region, using 20 animals, 10 of each breed, 5 males and 5 females of each species, grouped in a completely randomized design in a 2 x 2 factorial scheme (2 species and 2 genders) with 5 replicates. The animals were already being kept under the influence of high temperatures and levels of direct solar radiation before the day of the collections. At the time of the evaluations, ambient temperature was high, with low relative humidity. The pattern of epidermal thickness and sweat glands per body region was superior in sheep (P < 0.05), and the number of hair follicles and sweat rate were similar (P > 0.05) between the species. There was no difference (P > 0.05) in the evaluated characteristics between the genders, showing that they are not influenced by hormones. The morphology of the coat and skin of these animals showed a superiority of goats compared to sheep.

Reliability of methods to determine cutaneous evaporative water loss rate in furred and fleeced mammals

We used a high-precision weighing system and flow-through respirometry to quantify cutaneous evaporative water loss rates in woolly sheep (wool thickness, ca. 6.5 cm) and haired goats (coat thickness, ca. 2.5 cm), while simultaneously recording parallel data obtained from (1) a flow-through ventilated capsule, (2) a closed hand-held electronic evaporimeter chamber, and (3) a closed colorimetric paper disc chamber. In comparison to the weighing system and respirometry, used here as a "gold standard" measure of cutaneous evaporative water loss rate, we found relatively good agreement with data obtained from the flow-through ventilated capsules. However, we found poor agreement with data obtained from the closed electronic evaporimeter chambers (underestimated by 60%, on average) and the closed colorimetric paper disc chambers (overestimated by 52%, on average). This deviation was likely associated with a requirement for shaved skin in the closed chamber methods. Our results therefore cast doubt on the validity of the closed chamber methods for measurement of cutaneous evaporative water loss rates in furred and fleeced mammals, and instead show that more accurate values can be obtained using flow-through ventilated capsules.

Sheep meat production in the Brazilian semi-arid region: crossing between indigenous breeds

Investigations in the Brazilian semi-arid region evaluating the performance and carcass traits of sheep of indigenous breeds and their crossings have been performed; however, these studies use exotic breeds which produce precocious lambs with heavier carcasses, but not adapted to climatic conditions and the extensive production system, jeopardizing the sustainability of the sheep production system. We crossed between three indigenous breeds: Morada Nova (MN - maternal breed); Rabo Largo (RL - paternal breed), and Santa Inês (SI - paternal breed) with the objective of evaluating the effect of genotype and sex on the performance and carcass traits of purebred and crossbred animals. A total of 30 lambs, males and females, reared in a semi-intensive system were evaluated. Birth and weaning weights were 2.26 ± 0.53 and 7.31 ± 1.85, respectively. All lambs were slaughtered at 10 months of age. A completely randomized design in a 3 × 2 factorial scheme (three genotypes and two sexes) was used. Multivariate techniques were also performed to reduce group and discriminate variables. Birth and weaning weight were similar (P > 0.05) among genetic groups and sexes. The weight gain, carcass and morphometric trait characteristics, and the main commercial cuts were higher in crossbred lambs (P < 0.05). All indicators have discriminatory power between genotypes and sexes, but the carcass traits have a higher discriminatory power (P < 0.001). All genotypes, regardless of sex, have particular characteristics, i.e. MN × SI was characterized by greater forelimb and ham perimeters (P < 0.001), and the MN × RL by higher hot carcass weight and finish (P = 0.001). The cluster analysis and the heatmap plot revealed associations between SI and the size of cuts and RL with the cut commercial yield and the reduction in weight loss due to cooling. Our findings confirm the hypothesis that crossing between indigenous breeds represents an adequate alternative in sheep meat production systems in semi-arid regions. Finally, we encourage the use of indigenous breeds for sheep meat production with breed identity in order to favor the conservation of genetic resources and the sustainability of the production system.

Comparative methods analysis on rates of cutaneous evaporative water loss (CEWL) in cattle

Closed colorimetric paper disc chambers and flow-through ventilated capsules are the most employed methods of measuring rates of local cutaneous evaporative water loss in cattle. However, we do not know if these methods show a close agreement with the total rate of cutaneous evaporative water loss derived from the weighing system (i.e., the gold standard method). We therefore combined a high-precision weighing system and flow through respirometry to accurately quantify the cutaneous evaporative water loss rates in shaded heifers, while simultaneously recording parallel data obtained from a flow-through ventilated capsule, and a closed colorimetric paper disc chamber. Least square means of the local surface-specific cutaneous evaporative water loss rate (g m^-2 h^-1) derived from the colorimetric paper discs and ventilated capsules show close agreement to the total rate of surface-specific cutaneous evaporative water loss (g m^-2 h^-1) derived from the weighing method. Likewise, fitted linear regression lines also showed that they were well correlated (e.g., R² = 0.93 and r = 0.96 for ventilated capsule vs weighing method; and R² = 0.81 and r = 0.91 for colorimetric paper discs vs weighing method). However, the mean square deviation revealed various sources of disagreement between the local measurements and those derived from the weighing method, in which the local rate of cutaneous evaporative water loss derived from colorimetric paper discs showed greater deviation. In conclusion, given the importance of cutaneous evaporative water loss for assessing temperature requirements and heat tolerance of cattle, our findings show large discrepancies derived from the closed colorimetric paper discs chamber when compared with parallel data derived from the gold standard method, which is sufficient to call into question previous findings obtained by employing such methods. Moreover, the flow-through ventilated capsule appears to be the most accurate method to assess the local rate of cutaneous evaporative water loss in cattle.