Section 3.3 Production-Defining Factors

Section 3.3 Production-defining factors

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Introduction

As stated in Section 3.2, potential animal production is essentially determined by animal species and breeds. Their genetic potential can only be fully expressed in the appropriate climatic and agro-ecological circumstances (Figure 3.3.1). Changes in climate and management conditions affect bio-diversity leading to imminent loss of locally adapted breeds. This can compromise potential production in the future, if circumstances change.

Figure 3.3.1 Climatographs for cattle in Europe and Asia, showing conditions of temperature and humidity for some breeds.
(Source: WILLIAMSON, G. ; PAYNE, W.J.A. "An introduction to animal husbandry in the tropics". - (3rd ed.). - (Tropical Agriculture Series). - London : Longman, 1978. - p....,fig.1.7)

The production defining factors are presented in 4 sections:

1. mechanisms of thermoregulation for homoiothermic animals;
2. direct climatic factors: temperature, humidity, day-length and altitude;
3. most important domestic animal species and breeds;
4. processes determining animal reproduction.

3.3.1 Thermoregulation

Most domestic animals used for production are homoiotherms. As their metabolic processes only function within a limited temperature range, homoiothermic animals need to preserve a thermal balance (Figure 3.3.2). This balance is the result of the metabolic heat produced and the heat lost from skin and respiratory passages. When the animals body temperature goes outside its zone of thermal indifference, it has to adjust his temperature by changing the amount of heat produced or by the amount of heat lost.

Figure 3.3.2

Section 3.3 Production-defining factors

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3.3.1 Thermoregulation

Pathways to maintain thermal balance

Multiple pathways intervene in the thermal balance (Figure 3.3.3). Heat exchange with the environment can be negative, but also positive:

• conduction = heat lost to or gained from surrounding surfaces by direct contact with skin, when the surfaces’ temperature is lower or higher, respectively;
• convection = heat lost to or gained from the air. Is influenced by wind velocity and temperature of surrounding air;
• radiation = heat gained by radiation: a white coat will absorb 20 % of visible radiation and a black skin 100 %. Invisible radiation is completely absorbed irrespective of skin colour. Most known radiation is infra-red, also used for medical treatments;
• heat lost or gained by adjusting the temperature of ingested food to the body temperature.

Figure 3.3.3

Section 3.3 Production-defining factors

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3.3.1 Thermoregulation

Comfort zone

Within a range of environmental temperatures, compensatory responses of homoiothermics are absent. This zone is called the zone of thermal indifference or thermoneutrality (B-B' in fig.3.3.4), and varies for species and age. Moreover, each species has a range of body (core) temperatures most suitable for optimal biological activity. This temperature is most easily maintained within the zone of thermal comfort (A-A' in fig.3.3.4). For mammals, optimal core temperature ranges from 37 - 39 oC and for birds from 40 - 44 oC (see BOX 1).

Figure 3.3.4

Homoiothermic animals will react if ambient temperatures are outside the zone of thermoneutrality. If ambient temperature is lower, they try to increase heat production to keep their body warm (see BOX 2). If ambient temperature is higher they try to cool their body to maintain an optimal core temperature.

BOX 1: Average body temperature for various animal species.

Average body temperature for various animal species

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BOX 2: The sequence of reactions of homoiothermic animals to high temperatures

Section 3.3 - BOX 2
The sequence of reactions of homoiothermic animals to high temperatures

When the environmental temperature increases above the zone of thermal indifference, the animal activates its mechanisms for cooling. These mechanisms take place in approximately the following order:

1. changes in vascular blood flow (vasodilatation of veins in the skin);
2. initiation for sweating and increased respiration rate;
3. changes in hormone secretion and endocrine activity;
4. changes in behavioural patterns (e.g. moving into the shade);
5. increase of water intake, changes in the use of body water and in the state of hydration;
6. increase of body temperature, reduction of feed intake and production.

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3.3.1 Thermoregulation

Mechanisms for temperature regulation

When environmental temperature moves outside the zone of thermal indifference, the animal activates mechanisms for cooling or warming. Failure to maintain the thermal balance leads to progressive degeneration and finally to death. To prevent lethal stress from low or high temperatures, animals adjust:

• vascular blood flow (vasodilatation or constriction of veins in skin): e.g. vasodilatation of veins in the skin transports heat from the interior body to the skin thus facilitating amongst others evaporation from the skin;
• position of hairs: through pilo-erection animals reduce air movement between their hairs or feathers. The air layer isolates and prevents heat loss from the skin to the environment;
• behaviour: e.g. by huddling together;
• energy use: to facilitate cooling or to produce of more metabolic heat, energy is needed and thus part of the ingested food. As a consequence, less energy is available for production.

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3.3.1 Thermoregulation

Metabolic size

Body weight and body surface are important aspects for thermo-regulation. Experiments showed that body surface area is not linearly related to body weight (Table 3.3.1).

Table 3.3.1

Relation between body weight and skin surface area
Body weight (kg) / 1 / 2 / 25 / 50 / 100 / 200 / 400 / 600
Surface area (m2) / 0.09 / 0.14 / 0.76 / 1.2 / 1.9 / 3.0 / 4.9 / 6.4
(Source: BIANCA, W. 1976 "The significance of meteorology in animal production". - International Journal of Biometeorology, 1976, 20(2)139-156. - (adapted).)

This non-linear relation has three consequences:

• the size of homoiothermics is limited;
• within species, the zone of thermal indifference is inversely related to size or weight (Figure 3.3.5);
• energy need for basal metabolism and maintenance of domestic animals decreases with increasing weight/surface ratios.

For the last two reasons, nutrient requirements of domestic animals for basal metabolism and maintenance are calculated in relation to their metabolic weight. Experiments in closed chambers with regulated environmental conditions and instruments to measure exchanges of the animal with environment, confirmed this. The metabolic size of most farm animals is calculated as: W0.75

Figure 3.3.5

(Source: BIANCA, W. 1976 "The significance of meteorology in animal production". - International J. of Biometeorology, 1976, 20(2)139-156. - p....,fig.2. - (adapted).)

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3.3.1 Thermoregulation

Metabolic energy

Metabolic energyis produced in the body as a result of:

1. maintenance processes such as respiration, heart beat, maintenance of body temperature (i.e. basal heat production);
   
2. daily maintenance, e.g. feed collection and digestive processes. The amount of energy produced varies with type of feed, type of digestive system and type of management (e.g. zero-grazing versus grazing on far away pasture) (Section 3.4);
   
3. behavioural needs (Sub-section 3.5.2), e.g. body care, environmental exploration;
   
4. performance, such as growth, milk production and reproduction.

To decrease the amount of energy produced, some processes can be influenced more readily than others. The management regime can be adjusted to reduce or to increase metabolic energy production. In zero-grazing systems animals do not have to walk to collect their feed, and consequently, produce less metabolic energy. The temperature of all ingestedwater and food of homoiotherms is adjusted to body temperature. In this way animals can either loose or gain heat, if the temperature of ingested feed or water is lower or higher, respectively, than of the body.

For small animals it is hard to maintain body temperature in cold environments. Their skin surface is relatively large compared to their weight. Small animals collect food all day long to maintain body temperature. For large animals it is hard to maintain body temperature in hot environments. Elephants have large ears, increasing their skin surface and their potential to cool. Water buffaloes go into the water to cool.

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Section 3.3 Production-defining factors

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3.3.1 Thermoregulation

Evaporative heat loss

Transforming water (or sweat) into vapour requires energy. Energy from the skin is used and, hence, skin temperature decreases. Animal species and breeds differ with respect to their evaporative capacity. The evaporative capacity of an animal depends on:

• the density of sweat glands;
• the lung surface;
• amount of moisture available to the animal.

Beside this, the evaporative energy loss depends on the environment: air temperature, air humidity and air movement. Dry and warm air can contain more vapour than humid and cool air. Therefore, evaporation is easier under dry and warm conditions. Evaporation is higher in windy environments, except when all air is vapour-saturated. Wind removes vapour-saturated air and brings non-saturated air close to the skin.

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Section 3.3 Production-defining factors

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3.3.2 Direct climatic factors

Temperature and humidity

Ambient temperature and humidity are major factors in the thermal balance of homoiotherms, i.e. domestic animals. Temperature and humidity also effect the storage life of animal products (see BOX 3).

When homoiothermics have to cool or to warm themselves, they spend energy. The more meteorological stress must be fought, the less energy is available for production of meat, milk or eggs. In a cool environment, e.g. pigs have to eat more than in a warm environment to maintain a certain level of daily weight gain, because part of the feed is used for metabolic heating.

In a hot environment all animals reduce feed intake. High producing milk cows reduce feed intake already at ambient temperatures just above 20 C, because they must reduce metabolic heat production (Figure 3.3.6). As a consequence, milk production drops. Non-lactating cows only reduce intake if environmental temperature approaches body temperature.

Figure 3.3.6

BOX 3: Ambient temperature and preservation of animal products

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3.3.2 Direct climatic factors

Day-length

Day-length effects physiological processes related to reproduction and hair-growth, through the release patterns of hormones (Figure 3.3.7). Day-length triggers a seasonal ovulation pattern in some species or breeds and it affects fowls egg production (Section 3.3.4).

Figure 3.3.7

The seasonal hair growth cycle of cattle breeds of temperate regions is influenced by day-length. They shed their hairs in spring and its growth accelerates in autumn. Some individuals of temperate cattle do not shed their winter coat in the tropics, because day-length varies insufficiently to trigger shedding (Figure 3.3.8). Individuals unable to adapt to new ambient conditions will experience more heat stress and will never reach normal adult weight and production. The non-adapted hair-coat is only an expression of the non-adaptation.

3.3.2 Direct climatic factors

Climate, animal species and breeds

Climate is a combination of elements that include temperature, humidity, rainfall, air movement, radiation conditions, barometric pressure and ionisation. Of these, temperature, rainfall and humidity are the most important for plant and animal production. A simplified classification of climate distinguishes seven categories: boreal, temperate, mediterranean, humid/hot, sub-humid/hot, semi-arid and arid/hot. Arid regions are hardly of interest for animal production.

For an overview of climate and vegetation type see (in Dutch):
access check: 19dec2004)

A close relationship exists between these climatic zones, soils and the major vegetation types and thus the animal breeds that developed in these climate zones.

Two major management options are available to human in relation to climate and animal production. The most common management option is the housing of domestic animals (Sub-section 3.3.5). As species and breeds developed and throughout history adapted to various specific climates, human can choose the most adapted species and breeds for specific ambient conditions (Sub-section 3.3.3).

3.3.3 Animal species and animal breeds

Introduction

As stated in Section 3.2 potential animal production is essentially determined by animal species and breeds. Their genetic potential can only be fully expressed in the appropriate climatic and agro-ecological circumstances.

There are some 40 species of domestic animals. In total, these comprise some 4500-5000 breeds. Between 6000 and 10,000 years ago, man started to domesticate those animal species that provided products they needed or highly appreciated. Some sources indicate first domestication was for religious reasons. Selection under pressure of the environment - "survival of the fittest" - and by humans induced a large genetic variation (Figure.3.3.9).

Main domesticated species are cattle, buffalo, sheep, goat, pig, poultry, rabbit, camel, llamoids, horses and donkeys. Fish and some reptiles are not really domesticated, but are also bred and produced under controlled conditions.

3.3.3 Animal species and animal breeds

Cattle

All European cattle breeds belong to the species Bos taurus (BOX 4). In other parts of the world both Bos indicus and Bos taurus are represented (Figure 3.3.9). Bos indicus and Bos taurus are adapted to distinct climatic conditions (Table E3.3.2). Adult females weigh between 150 and 1000 kg according to breed; adult bulls weigh 50 to 500 kg more.

Cattle breeds are classified according to purpose:

• Multi-purpose, beef, dairy and draught.
  
• Double purpose, e.g. beef and dairy Maas-Rhine-IJssel and Mont-Beliard.
  
• Beef, e.g. Charolais and Brandrode, a Dutch endangered species. Individual beef production as well as production per hectare varies largely between production systems and nutrition schemes. In intensive production systems, beef carcass output reaches 600 kg per hectare per year.
  
• Dairy, most important dairy breeds are Holstein-Friesian, Jersey and Brown Swiss (Table E3.3.1). The Holstein-Friesianis the highest yielding dairy breed, and used worldwide. Actual mean production in the Netherlands is 8000 kg per lactation. Highest production levels (12.000 kg per lactation) seem to affect robustness and longevity of cows. Brown Swiss is known for its robustness. Most other breeds yield milk with higher protein and fat content (e.g. Jersey, respectively >3.5% protein and >5% fat).

In less developed countries, most cattle are multi-purpose or double-purpose animals (Table E3.3.1). Hariana, Sahiwal and Kankrej are famous double-purpose breeds of India, combining dairy and draught characteristics. Also Holstein-crosses are bred for these purposes, e.g. in the Amish communities of North America.

3.3.3 Animal species and animal breeds

Sheep

All domestic sheep belong to the species Ovis aries. The existing sheep breeds are adapted to various climatic circumstances (see BOX 5). They vary largely in size and adult weight (females 20–100 kg; males 30-150 kg) and body and production characteristics (Figure 3.3.11 and Table E3.3.3).

Figure 3.3.11

(Link to sources: (latest access check: 18dec2002) ;
- (latest access check: 18dec2002))

Various criteria are used for classifying sheep:

• wool or hair type: length, diameter, fleece quality and fleece weight;
• ability for mutton (meat) production or milk production;
• fat-tail or fat-rump breeds, stocking reserve body-fat in tail or rump ;
• length of legs (long-legged (nomadic) sheep);
• size: dwarf sheep, breeds with short legs and relatively large body. Most dwarf sheep are also tolerant to trypanosomiasis, e.g. the West African dwarf sheep, also represented in Europe as pet animal.

Most sheep are at least double-purpose: meat and wool. In the Netherlands, the Texel is a typical double-purpose breed, but with low litter size (i.e. number of lambs: mean littersize < 2). The Swifter, a crossbreed between Texel and Flemish/Finnish, combines higher litter size with high growth rates.

Resemblance between sheep and goat, also from the sub-family Caprinae, can be great. Goats have an erect tail and a beard, whereas sheep have a hanging tail and no beard. Goats are more individually grazing animals, whilst sheep are flock animals.

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3.3.3 Animal species and animal breeds

Goat

The domestic goat belongs to the species Capra hircus (see BOX 6). Goats are divided into three categories based on height at withers and adult weight: large (over 65 cm; 20-65 kg); small (51-65 cm; 19-40 kg); dwarf (< 51 cm; 18-25 kg). The European milk breeds and the long-legged desert goats of Asia and Africa (Table E3.3.4) belong to the group of large goats.

Breeds can also be classified according to production aim:

• multi-purpose: goats in less-developed countries are used for milk, meat and skin;
• wool: e.g. the Angora produces mohair and the Cashmir pashima;
• milk.

Goat are more efficient milk producers than cattle due to their lower maintenance requirement related to their size. Therefore, they are still the dairy producers for the poor, e.g. Malabar and Jamnapari in India (Figure 3.3.12). Some very productive breeds - Saanen, Toggenburger, and Dutch landrace - are used in intensive production systems. These farms keep 200 to 2000 dairy goat, and produce between 500 and 1500 kg milk per year per goat. In the Netherlands, highest individual milk production approaches 2000 kg milk per year (Table E3.3.4).

Figure 3.3.12

(Link to sources: (latest access check: 18dec2002) ;
- (latest access check: 18dec2002))

The global distribution of goats is partially explained by their ability to survive and thrive in environments with extremely sparse vegetation. When feed condition are good, litter size of goat is at least 2. The temperate goat breeds are photosensitive and reproduce once a year. Most breeds perform best in the drier environments. Dwarf goats are better adapted to humid conditions.

BOX 6: Classification of the genus Capra

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3.3.3 Animal species and animal breeds

Pigs or Swine

All pig breeds belong to the genus Sus. World-wide, two groups of swine breeds with different origin are important (see BOX 7):