The aim of this review is to present some aspects of environmental stress effect on reproduction of farm animals. It describes the following: neuroendocrinology of stress, types of stress, stress characteristics in the reproductive process and recommendations for control environmental stress. Stress is the result of confinement and an ambitious vision and uncaring by the man, who is in the interest of improving production, has participated unconsciously, by manipulating animal production in its way, even trying to tame new species, impossible to adapt to our environment healthy. At present, it has been concluded that stress is one of the environmental factors that affect handling and decrease the production of livestock, it is considered that the main factor which should be controlled in units animal production, since it is closely related to pathogens and infectious agents that may try to the health of animals. Finally, some recommendations are outlined to lessen stress for heat, by handling and by feeding.
At present, the need to produce more efficiently, the need to improve reproductive and productive parameters so that new technologies have been adopted which are becoming more sophisticated, all in order to increase the production in animals.
Despite the advances in technology are applied to animal production, few producers or farmers who have shown concern for improving the general environmental conditions of the animal production units, not realizing that these conditions are largely, are responsible for the health of animals, altering thereof and being significantly impacting on the presence of such problems reproductive and productive, significantly increasing production costs.
Stress is the result of confinement and an ambitious vision and uncaring by the man, who is in the interest of improving production, has participated unconsciously, by manipulating animal production in its way, even trying to tame new species, impossible to adapt to our environment healthy.
At present, it has been concluded that stress is one of the environmental factors that affect handling and decrease the production of livestock, it is considered that the main factor which should be controlled in units animal production, since it is closely related to pathogens and infectious agents that may try to the health of animals.
The man plays a very important role in creating the stress. It can provide the means to alleviate, remove or modify any potential stressor [
Mammals, respond to environmental changes by adaptation mechanisms, regulated by the release of hormones such as: Adrenocorticotropin (ACTH), glucocorticoids (GH) and catecholamine (CA), the amount of release depends on the type and intensity of the stress that comes along.
Under stress, there is a negative feedback effect of progesterone on luteinizing hormone (LH) increasing the first. Are elevated cortisol levels with subsequent depression, there are changes in the release of LH. The level of prostaglandin F2 alpha (PGF2 ∞) and ACTH increase. The levels of epinephrine and norepinephrine, also increase [
Solar radiation, wind speed, air temperature and humidity are all factors which are concerned with the presentation of heat stress. An early reproductive responses to heat stress are the decrease in the intensity of estrus and consequently low fertility [
Studies by [
Recent studies conducted by [
When the body temperature exceeds 40˚C, the developed follicles can suffer severe damage and become nonviable [
A study by [
Studies by under in vitro conditions, suggesting that exposure of pregnant domestic females at high ambient temperatures and humidity, which often occur during the summer months, can disrupt the balance between the biochemical and endometrial factors responsible for the maintenance of pregnancy. [
In 1994, [
It has been shown that during periods of severe heat stress, only 10% to 20% of inseminations can result in normal pregnancies [
Work performed in the United States, indicate that Holstein and Jersey cows set in hot, express signs of estrus for only 12 to 13 hours, which means a difference of 5 - 6 hours less than the normal duration of estrus animals warm places [
In the 2000 [
In other studies in Florida, by [
The best way to control the effects of heat stress are: 1) physical modification of the environment, 2) breeding races less sensitive to heat stress and, 3) good nutritional management [
In 1998, Zapiola said that in cattle, stress during transportation, has a detrimental effect on the physiology of the animal that the stress caused by lack of food and drink, for a period of equal length, which is because the blood flow is diverted from the internal organs, to the peripheral tissues in an attempt to reduce the body temperature by increasing heat losses. This mechanism leads to a reduction of blood flow, aimed at internal organs such as the uterus, fallopian tubes and ovaries, decreased blood supply to these organs also implies low nutrient availability and therefore low functional capacity [
Studies by [
Females consume less food during warm seasons, consequently, there may be insufficient nutrients are available, after the production of milk and therefore the ovaries do not function during the first 6 weeks of lactation [
Vitamin E may decrease moderately, the effects of heat stress during hot months, does not necessarily increase fertility [
The interactions between employees and animals influence the response of cattle to stress management known as [
In 2000, [
There are many driving situations can cause stress seriously affecting the reproductive process of the species, such as excessive mobilization of inseminated females before, the use of aggressive or driving the separation of animals, mobilization of animals on the sleeve of management for different purposes, etc. [
The time when stress management, represents greater adverse effects on reproduction, it is just no time to estrus [
The temperament of cattle can be classified as follows: 1) stand still while subject, 2) is restless, 3) shaken vigorously driving sleeve and 4) shakes violently management sleeve and tries to escape. Overall, in cattle, the Bos indicus have a more aggressive and nervous temperament than Bos taurus [
In 2000 [
Moreover, [
Cattle, is one of the most adaptable and homeocinéticos have mechanisms to maintain body functions at the expense of critical changes in other physiological functions, such as reproduction, so that the reproductive function is determined largely by the environment [
Constant maintenance of a normal body temperature is known as homeotermia and is vital to the functioning of the brain tissue. In cattle, the normal diurnal variation in body temperature should be from 0.6 to 1.2˚C. A further increase to 1.2˚C is a sign of illness or poor adaptation to temperature elevation. This temperature range is known as a zone of comfort, varies according to the species and animal breeds. When animals have a body temperature below or above their level of comfort, decreases or increases metabolic rate than normal, appearing in imbalance in animal welfare. Heat or body temperature can be eliminated by the following mechanisms: radiation, conduction, convection and evaporation [
Environmental stress can cause low sperm quality, which is closely related to low fertility in females, probably due to a combination of low fertilization rates and increased embryonic mortality [
Direct exposure of the testis at high temperatures, causes changes in certain critical stages of spermatogenic cycle, which is also directly related to the quality of the ejaculate.
Recent studies conducted by [
Sexual behavior and fertility rate are the main indicators of the mammalian female reproduction that are negatively affected by environmental stress. So that the programs undertaken in order to increase the fertility of domestic females, are less successful in hot weather than in temperate [
A temperature increase of 0.5˚C uterine during hot days, caused a decrease in the rate of fertilization. In cattle, heifers exposure to 32˚C for 72 hours after insemination, inhibit embryonic development, however, it is known that 48% of the females held 21˚C, can become pregnant without any problem. If heat stress is presented after 10 days after the service, fertility is not affected.
Fertility in lactating cows, varies by season. In the winter, decreases about 50%, 20% in the summer and fall is lower than in the winter. A few years earlier, Gilad et al., (1993) reported that conception rates in Israel fell from 52% in winter to 24% in the summer.
In summer, 80% of estrus may be undetectable [
Heifers and cows studies have indicated that the decline in oocyte quality in the early postpartum period is associated with negative energy balance and low body condition of the animals, which is expressed in developing embryos increased and abnormal having embryos resulting in loss of the hottest months of the year [
Several studies [
• Provide a ventilation system that controls body temperature.
• Implement water sprinklers.
• Animal protection against solar radiation, directly and indirectly, through shadows or appropriate ceilings.
• Provide shade in feeding and drinking, to increase feed intake in animals with heat stress.
• Provide water sprays.
• Provide animals, spray baths, in the hottest part of the day.
• Try to have animals with white fur, as they are the most easily absorb heat and therefore are less sensitive to heat stress.
• Develop genetically adapted in animals, as they may be less sensitive to heat stress.
• Implementation of frozen embryos.
• Insemination with frozen semen in less hot time.
• Provide free areas in the Production Unit and shaded.
• Provide the required area per animal, for comfort.
• Bathing females before service and 3 to 5 days.
• Breed or service in less hot periods.
• Implement estrus synchronization programs, to schedule inseminations or services.
• Do not isolate females long before artificial insemination or service.
• Balancing diets properly, providing the energy needed to offset declining intake presented.
• Reduce your intake of fiber and protein and increase energy.
The effects of the environment on the reproduction of farm animals, negatively affect reproductive performance in both females and males, in females, on the percentage of fertility, declining oocyte quality and therefore the quality of the embryo; in males negatively affect the quantity and quality of sperm. Therefore, it is recommended to follow the guidelines described in this paper to reduce the effect of environmental stress on reproduction of farm animals.