**Characterisation of Goats' Response to Heat Stress: Tools to Improve Heat Tolerance Tools to Improve Heat Tolerance**

**Characterisation of Goats' Response to Heat Stress:** 

DOI: 10.5772/intechopen.70080

Juan M. Serradilla, María J. Carabaño, Manuel Ramón, Antonio Molina, Clara Diaz and Alberto Menéndez‐Buxadera Manuel Ramón, Antonio Molina, Clara Diaz and Alberto Menéndez-Buxadera Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

Juan M. Serradilla, María J. Carabaño,

http://dx.doi.org/10.5772/intechopen.70080

#### **Abstract**

This chapter aims to review present knowledge about the effects of heat stress on goats, summarising what is known about its measurement, its impact on the performances of the animals, mainly milk traits, the physiological and genetic bases of the animals' response and the improvement of resilience through selection. A short historic review of the climatic indexes used to measure heat stress, with special emphasis on the temperature humidity indexes, and the main consequences on milk yield and composition are followed by a description of the results of experiments carried out to study the physiological and metabolic consequences of heat stress. The results of the quantitative analyses of the genetic bases of heat stress using norm of reaction models and of the application of omic techniques, particularly transcriptomic and genomic, to understand the complexity of the genetic background of animal's reaction to thermal stress, constitute the next points. The chapter ends treating the possible ways and difficulties of applying selection to increase resilience to heat stress.

**Keywords:** heat stress, physiological response, genetic analysis, selection for resilience

#### **1. Introduction**

The extraordinary results obtained through artificial selection in all domestic animals had some undesirable side effects, such as low reproductive efficiency, increased susceptibility to diseases and higher sensitivity to sudden environmental changes [1]. In particular, artificial selection to increase milk yield has been proved to reduce heat tolerance in dairy cattle [2, 3] and dairy sheep [4]. Heat stress (HS) has also been proved to be one of the main causes of economic losses

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

[5, 6]. Temperature increase and rainfall reduction are expected during the next decades in many areas of the world and, particularly, in the Mediterranean region, where the largest part of goats in Europe are raised [7]; therefore, knowledge of the physiological and genetic bases of the response to the consequences of climate change is needed to reduce its impact. The study of physiological indicators and the quantification of the genetic variation of the response to HS, as well as the genomic and other –omic analyses to find candidate genes involved in this response and the changes in gene expression so induced, allow for the identification of animals with a positive response to HS and the design of methods to select them.

for solar load or wind speed [19], parameters of great impact on animal physiology, especially in grazing species. In addition, it does not take into account the breed, the genotype or other animal differences (e.g. age, level of production). Gaughan et al. [20] concluded that the THI may not adequately describe the effect of hot climatic conditions on livestock (and much less on the effects of cold conditions). Furthermore, with the exception of the case of cattle, most THIs have not been specifically designed for their own species (and much less for a specific breed exploited in certain geographic and climatic conditions). Thus, in the case of the goat species, the scarce number of studies carried out so far has used THI formulations developed for beef and dairy cattle, with the exception of the works carried out by our research group [21–24] in which a modification of the THI developed for sheep exploited under Mediterranean environmental conditions by Finocchiaro et al. [4] was used. Only very recently the feasibility and the validity of a heat stress score specifically developed for intensive dairy goat farms has been tested [25]. It is generally recognised that goats are more tolerant to HS than sheep, and both are superior to this respect than cows, due to the morphological and physiological differences between these species related to heat dissipation [26]. However, it is also well known that high temperatures and relative humidity values affect productivity of small ruminants [27, 28]. As opposed to the case of dairy cattle, few woks have dealt with the effects of HS on milk yield and composition in goats. In several studies lately carried out to quantify these effects on native breeds of goats, Murciano‐Granadina and Payoya [21], Florida [22], Malagueña [29], raised mostly in the South of Spain, it has been observed that the animals are exposed to stressing climatic conditions, due to high temperatures, during 45–55% of the year (**Figure 1**), generating losses of 1.9 and 3.1% of annual fat plus protein yields in Murciano‐Granadina and Payoya goats, respectively (**Figure 2**). Sano et al. [30] found milk yield losses of 3–13% in dairy Saanen goats exposed to moderate or severe HS for 4 days (THI, 81 or 89), respectively. Brown et al. [31] reported that

Characterisation of Goats' Response to Heat Stress: Tools to Improve Heat Tolerance

http://dx.doi.org/10.5772/intechopen.70080

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**Figure 1.** Evolution through the year of THI values in the South of Spain (from Ref. [22]).

Research works described in this chapter aimed to ascertain the effects of HS on milk traits and to study the physiological and genetic bases of these effects in order to allow for the inclusion of resilience to HS as a new goal in the selection programmes of three Spanish breeds of goats.
