Environmental Physiology of Livestock

R. J. Collier, J. L. Collier

• Publisher: Wiley-Blackwell
• Year: 2011
• ISBN:
  9781119949077
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Zoology
• Index: Biological Sciences

Environmental stress is one of the most significant factors affecting livestock performance and health, and it is only expected to increase with effects of global warming. Environmental Physiology of Livestock brings together the latest research on environmental physiology, summarizing progress in the field and providing directions for future research. Recent developments in estimating heat stress loads are discussed, as well as key studies in metabolism, reproduction, and genetic expressions.

Environmental Physiology of Livestock begins with a survey of current heat indexing tools, highlighting recent discoveries in animal physiology, changes in productivity levels, and new technologies available to better estimate stress response. Using this synopsis as a point of orientation, later chapters hone in on major effects of heat stress, including changing metabolic pathways and nutrient requirements, endocrine regulation of acclimation to environmental stress, and reduced reproductive performance. The text concludes with a thorough discussion of environmental effects on gene expressions, providing important insight for future breeding practices.

Environmental Physiology of Livestock is a globally contributed volume and a key resource for animal science researchers, geneticists, and breeders.

Chapter 1

From Heat Tolerance to Heat Stress Relief: An Evolution of Notions in Animal Farming

Amiel Berman

Introduction

The quest for heat tolerance has gained attention with the development of dairy farming in warmer climate regions. Heat tolerance, in its narrow sense, is defined here as the maintenance of homeothermy (Bligh, 2006), i.e., thermal stability of the body in heat-stress environments. As such, it is determined by the relationship between metabolic heat production and the capacity to dissipate excess heat. Heat tolerance, in this sense, does not involve reduction of ambient heat stress or increasing heat loss by human intervention. Heat-stress relief, in contrast, consists of a means to improve animal thermal balance in stressful environments. This review attempts to present the experience of the past and its lessons for the present with a look into the near prospective. It examines the evolution of breeds in the warm climates, the attempts to create dairy breeds adapted to warm climates, and the reduction of environmental constraints on dairy productivity.

Notions on Adaptability to Warm Climate

The deleterious effect of warm climates on animal performance is well known and is not new. This awareness emerged during the course of the early attempts and failures to introduce temperate climate breeds of farm animals into the warm climates during the 1920s and 1930s. It became more evident in the endeavor to increase dairy productivity in subtropical regions during the post-WW2 period and during the development of farming in warm regions of Central and South America. During all these stages of dairy industry development, a notion prevailed that breeds endogenous to a warm climate region are endowed with capacity for heat tolerance. The following discussion examines the limits within which this notion applies. This notion emerged around the mid-twentieth century and is best expressed in a review of the ecology of domesticated animals (Wright, 1954) of that time: “In subtropical or tropical climates no pure-bred temperate breed of cattle is really suited.” It cites from a large number of studies of crossbreeding in subtropical and tropical countries (e.g., West Indies, Philippines, Egypt, Jamaica, India, Cochin China, Cambodia, Malaysia, and East Africa) in which importing temperate zone breeds or backcrossing to temperate zone breeds were linked to regressive changes in the imported and crossbred animals. In retrospect, it is noteworthy that animals were maintained in the warm climate regions according to temperate region prevailing concepts, with the limited knowledge existent at that time of diseases caused by local ectoparasites and their prevention.

This notion probably has roots dating many decades back. It most likely dates from the formative period of modern agricultural systems in Western Europe, more than 150 years ago. During this period a multitude of cattle breeds were present; each was confined for generations to a limited ecological niche, in a specific climate, with static agricultural and socioeconomic conditions. It is likely that in such conditions a balance was reached between the specific environmental conditions of a region (i.e., climate, nutrition, disease, and management) and the genetic constitutions of animals in that region.

This balance was disturbed, however, by the advent of the mercantile society and with produce and animals shipping over great distances. Many agricultural systems in both developed and developing areas were in warm climates, in which heat stress limits animal productivity. The demand for animal products in these regions created the need to reassess the potential role of heat-tolerant breeds and heat-stress relief for increasing animal productivity in warm regions. This is carried out here for dairy cattle mostly, with only incidental reference to beef cattle, as the two are found in widely differing farming systems.

The Evolution of Warm-Climate Adapted Breeds

The nature of heat tolerance, the identity of heat-tolerant breeds, and their origins and evolution are not altogether clear. It is commonly stated that the Bos indicus cattle, the Zebu breeds, are better adapted to thrive in warm climates than Bos taurus. This notion is based on the distribution and survival of cattle types in different climates. The Zebu breeds are morphologically differentiated primarily by the presence of a thoracic or cervicothoracic hump, which is absent in taurine cattle (Epstein, 1971). Modern techniques opened new ways of examining the origin and evolution of Bos indicus and Bos taurus cattle by their paternal and maternal lineages, i.e., by their nuclear and mitochondrial DNA (mtDNA), respectively. The latter is better preserved, present in larger quantities in ancient specimens, and is therefore the main material on which ancestry is examined. The information made available by mtDNA, however, represents only about 40 mitochondrial genes, as compared to the 20,000 to 25,000 nuclear genes. The Bos indicus and Bos taurus types have been recognized as separate subspecies that evolved by speciation from wild oxen, Bos primigenius. Phylogeny estimation and analysis of molecular variance estimate the separation of the two mtDNA clades from the wild oxen at 200,000 years to 1 million years BCE according to one source (Loftus et al., 1994) and 1.7 to 2.0 million years ago by another source (Hiendleder et al., 2008). As domestication is thought to have occurred in approximately 10,000 BCE, ancestors of modern cattle originated in separate domestication of genetically discrete Bos primigenius strains (Avise et al., 1998). The Bos indicus subspecies that evolved in the warm areas between Pakistan and northwest India gave birth to the Asian cattle breeds. The Bos taurus subspecies that evolved in the Near East is the origin of both European and African cattle breed ancestors (Achilli et al., 2008; Hiendleder et al., 2008). The Bos indicus subspecies is presumed to be better adapted to heat owing to its evolution in hot climates.

Cattle types most probably did not remain clearly separate and distinct of each other. Evidence was found for later introgressions of Bos primigenius into ancient (Mesolithic and Neolithic) domestic cattle (Stock et al., 2009). Autosomal data of Bos taurus cattle breeds revealed considerable introgression from Bos indicus cattle; this was particularly apparent in cattle populations from Iraq in the east, and declined in the populations further west toward Anatolia. The pattern of introgression suggests the introduction of zebu cattle from the region corresponding to present-day Iran and northern Pakistan. In addition, maternal and paternal markers demonstrate that the movement of cattle into and within the Near East was complex (Edwards et al., 2007). The complexity is exemplified by the presence of a Bos indicus admixture in the maternal but not in the paternal lineage in Damascus cattle (Edwards et al., 2007; Loftus et al., 1999), though these cattle are devoid of the typical hump characteristic for Bos indicus (Hirsch and Schindler, 1957). The mtDNA and casein polymorphisms data indicate existence of hybrids between taurine and indicine cattle in the Ukrainian and Central Asian zones as well as into southern and southeastern European breeds (Kantanen et al., 2009).

Breeds domesticated in the Near East and introduced in Europe during the Neolithic diffusion after 6400 BCE probably also intermixed, at least in some regions of the Mediterranean basin, with African cattle introduced by terrestrial and maritime routes (Beja-Pereira et al., 2006).

Dairy Breeds in the Americas

In North America, the initial import of European dairy breeds was followed by a rapid development of dairy farming systems, with the Holstein as the dominant breed, characterized by its high productivity. The U.S. Holstein was re-introduced into Europe, to become a dominant dairy breed in some regions. The relatively recent development of farming systems in Central and South America stimulated a renewed interest in the role of breeds in agricultural productivity in warm climates. It is there that the mixing between indicine and taurine cattle that started in ancient times continues into present times. Cattle were introduced for the first time to the Americas by Spanish conquerors traveling from the Caribbean islands in 1492. The first cattle that arrived in Brazil from Portugal and Spain (Iberia) in the early sixteenth century were the humpless taurine (Bos taurus). In the nineteenth century, continental European cattle and later zebu cattle (Bos indicus) from India were imported. In the course of a few years the cattle population spread over the continent. Currently, almost all South American countries have Creole cattle, i.e., native breed descendants of Iberian cattle mixed with indicine cattle (Dani et al., 2008).

The ancestry of the Creole cattle may be examined by its maternal lineage as well as by its paternal lineage. The matrilineage of Creole cattle throughout the American continent was analyzed in published mtDNA sequences from Creole, Iberian, and African cattle breeds. The Western European haplogroup was the most common (63.6%), followed by the African (32.4%) and the Near Eastern haplogroups (4%), none of which were found in Bos indicus types (Liron et al., 2006).

The paternal lineage in Creole cattle breeds was examined in a study of the geographic distribution and frequency of Y-chromosome haplotypes in Bos taurus and Bos indicus. Taurine and indicine haplotypes were detected in 85.7 and 14.3% of the males, respectively. The geographic distribution of this polymorphism suggests a male mediated pattern of zebu introgression. The highest frequencies of the Zebu Y-chromosome are found in Brazilian populations (43–90%), in the eastern part of the continent, while absent in the southernmost breeds from Uruguay and Argentina. Bolivian breeds, at the center of the continent, exhibit intermediate values (17–41%). Differences between breeds in genetic diversity reflect the impact of modern breeding. The Creole breed consistently showed higher levels of genetic diversity among populations than the Holstein (Giovambattista et al., 2001).

In the main, aforementioned studies support the view that, with the possible exception of breeds in Pakistan and India, introgression between breeds is the rule rather than the exception. As many breeds evolved in warm climates, it may be assumed that they shared attributes of heat tolerance. The identity of these attributes is not clear, however. Neither is it clear the extent to which they constitute a relative advantage to breeds in the modern dairy-farming context. The identity of heat tolerance attributes presumably carried by indicine breeds and possibly by taurine breeds therefore is of major interest.

Elements Affecting Heat Tolerance and Their Prevalence

Heat tolerance may be defined as the ability to maintain thermal stability at warm temperatures. This definition is narrower than the earlier used, which included elements of disease and deficient nutrition. In this sense, it does not comprise resistance to ectoparasites, which would be valuable for grazing beef cattle. As such, heat tolerance is determined by the relationship between heat dissipation capacity and metabolic heat production.

Heat dissipation is determined by relative surface area, sweating rates, external insulation, and respiratory heat loss. A larger relative body surface may transmit larger sensible and insensible heat loss from the animal's body surface to the environment. However, crossing the Jersey with the Red Sindhi did not increase the relative body surface of the daughter generation (McDowell et al., 1954).

The high sweating rate of 1.5 kg m−2 h−1, which is typical for humans (Grucza, 1990), is a most effective means for increasing the range of tolerable environmental temperatures. Reports contrast the low sweating rate in cattle that ranges from a minimum of 0.1 to a maximum 0.6 kg m−2 h−1 in Gir and Hariana (Bos indicus) cattle housed indoors (Joshi et al., 1968), sun-exposed African zebu Fulani cattle (Egbunike et al., 1983), Jersey and Jersey × Red Sindhi (Pan et al., 1969), and in-shaded lactating Holstein in Israel (Berman and Morag, 1971). The sweating rates reported in association with the slick hair gene initially found in Senepol (Bos taurus) and Carora (mixed Bos taurus and Bos indicus) cattle and introduced into the Holstein (Dikmen et al., 2008) are in the lower range of the above ...

Table of contents

• Cover
• Title Page
• Copyright
• Dedication
• Contributors
• Foreword
• Chapter 1: From Heat Tolerance to Heat Stress Relief: An Evolution of Notions in Animal Farming
• Chapter 2: Physiological Basics of Temperature Regulation in Domestic Animals
• Chapter 3: Heat Stress and Evaporative Cooling
• Chapter 4: Regulation of Acclimation to Environmental Stress
• Chapter 5: Environment and Animal Well-Being
• Chapter 6: Effects of Environment on Metabolism
• Chapter 7: Impact of Hot Environment on Nutrient Requirements
• Chapter 8: Effects of Environment on Animal Health: Mechanisms and Regulatory Inputs
• Chapter 9: Effect of Environment on Immune Functions
• Chapter 10: Strategies for Improvement of Thermal and Reproductive Responses under Heat Stress
• Chapter 11: Prospects for Improving Fertility during Heat Stress by Increasing Embryonic Resistance to Elevated Temperature
• Chapter 12: Environmental Heat Stress Impairs Placental Function, Fetal Growth and Development, and Postnatal Performance in Livestock
• Chapter 13: Effects of Photoperiod on Domestic Animals
• Chapter 14: Rethinking Heat Index Tools for Livestock
• Chapter 15: Strategies to Reduce the Impact of Heat and Cold Stress in Dairy Cattle Facilities
• Chapter 16: Genotype by Environment Interactions in Commercial Populations
• Chapter 17: Responses of Poultry to Environmental Challenges
• Index
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