LIVESTOCK PERFORMANCE AND ENVIRONMENT
*T. Sathyabama and P. Selvaraj
*Corresponding author; Email: drtsbama@gmail.com
Department of Veterinary Physiology,
Veterinary College and Research Institute, Namakkal.
Tamil Nadu Veterinary and Animal Sciences University
The capacity of an animal to produce differs between species, breeds and strains as a result of genetic factors. However, a complex of inter-related factors in the animal husbandry will influence the animal’s ability to utilize that capacity for growth, development and production. Progress in breeding and feeding for further increase in production and efficiency can be limited by environmental factors. Animal housing design is mainly concerned with the physical environment, in particular climatic and mechanical factors, but all other factors should also be considered in order to create a good layout, where healthy, high yielding animals can be provided with correct feeding, can be easily handled and can produce without stress or suffering physical harm.
All domestic livestock are homeotherms; i.e., they maintain relatively constant internal body temperatures, usually within a 1 to 2° C range. The body temperature of most domestic animals is considerably higher than the environmental temperature to which they are exposed most of the time. They maintain their body temperatures by balancing internal heat production and heat loss to the environment. The hypothalamus gland acts as a body thermostat by stimulating mechanisms to counteract either high or low ambient temperatures.
- Environmental Temperature
The over-riding environmental factor affecting the physiological functions of domestic animals is temperature. For most farm animals a mean daily temperature in the range 10 to 20°C is referred to as the “comfort zone”. In this range the animal’s heat exchange can be regulated solely by physical means such as constriction and dilation of blood vessels in the skin, ruffling up the fur or feathers and regulation of the evaporation from lungs and skin.
At the upper and lower critical temperatures the physical regulation will not be sufficient to maintain a constant body temperature and the animal must, in addition, decrease or increase its metabolic heat production. A further decrease or increase in temperature will eventually bring the temperature to a point beyond which not even a change in heat production will be sufficient to maintain homeothermy.
A very young animal, lacking fully developed temperature-regulating mechanisms, particularly the ability to increase heat production by increased metabolism, is much more sensitive to its thermal environment and requires higher temperatures.
- Relative Humidity
In a hot-dry climate evaporation is rapid, but in a hot humid climate the ability of the air to absorb additional moisture is limited and the inadequate cooling may result in heat stress.
Too low humidity in the air will cause irritation of the mucous membranes, while too high humidity may promote growth of fungus infections. High humidity may also contribute to decay in structures. If possible keep the relative humidity in the range of 40 to 80%.
Poultry do not have sweat glands, so all evaporative heat loss must originate from the respiratory tract. Other livestock species have varying abilities to sweat and in descending order they are as follows: Horse, donkey, cattle, buffalo, goat, sheep and pig.
- Solar Radiation
The heat load on a grazing animal can be considerably increased by direct solar radiation and radiation reflected from clouds or the ground. A white hair coat will absorb less radiant energy than a dark, but the heat penetrates deeper in a white, loose coat. Air movements will dispel the heat and reduce the differences. Furthermore, solar radiation may adversely affect the animal’s skin in breeds having non pigmented skin.
Heat gain by radiation can be effectively reduced by the provision of a shaded area. It must, however, be sufficiently large to allow space between the animals so that the heat loss by other means is not reduced. Grass covered ground in the surroundings of the shade will reflect less radiation than bare soil.
- Air Movements
Air movements will assist in heat loss by evaporation and by conduction/ convection as long as the air temperature is lower than the skin temperature. When the air temperature approaches the skin temperature rapid air movements are experienced as comfortable, but at low temperatures it will lead to excessive cooling of unprotected skin areas (cold draught).
Air movements are required to remove noxious and toxic gases and to supply the animal with fresh air for breathing. A wind velocity of 0.2m/s is generally regarded as a minimum requirement, but it can be increased to 1.0m/s, when the temperature is nearing the upper critical, or more when it goes beyond that.
- Precipitation/Rainfall
Heavy rain my penetrate the fur of an animal and decrease its insulation value. A strong wind can lead to excessive cooling. However, a naturally greasy hair coat will resist water penetration and with the provision of a shelter for the animals the problem may be avoided altogether.
- Others
Acoustical factors have a marginal effect on the animal’s development and production. Nervous animals may, however, react adversely to intermittent sudden noises. Pig squeals prior to feeding can become a hazard to the stockman’s hearing. Soft radio music in a milking parlour may have a smoothing effect on the cows.
Day length or photoperiod varies with latitude and season and has a direct influence on animal performance, especially on the breeding season for sheep and egg production of poultry. Under natural conditions, there is a correlation between length of day and rate of laying. Artificial light is used in the temperate zone to equalize egg production throughout the year. Additional hours of light before dawn and after dusk are recommended in hot climates to encourage the hens to take feed during the cooler hours. Dust can carry micro-organisms, which may cause an outbreak of disease.
Toxic and noxious gases are produced by manure may accumulates in buildings or storages especially agitation of manure slurry stored in a pit release harmful gases. However, problems with gases are not likely to arise in the open-sided buildings used in the tropics.
The heat and moisture produced by the animals confined in a structure must be removed by ventilation. In the tropics, sufficient ventilation flow is usually provided for by the use of opensided structures.
The maximum ventilation rate should remove enough of the sensible heat produced so that a small temperature difference, usually 2 to 4°C, can be maintained between inside and outside. It should be noted that ventilation alone can only maintain the building temperature at slightly above ambient.
Livestock Performance
In tropical and subtropical countries an animal may often be under heat stress. When the environmental temperature exceeds the upper critical level (18 to 24°C, depending on the species) there is usually a drop in production or a reduced rate of gain. Furthermore, when the temperature falls outside the comfort zone, other climatic factors assume greater significance. Humidity becomes increasingly important as do solar radiation and wind velocity.
Dairy Cattle show a reduced feed-intake under heat stress resulting in lowered milk production and reduced growth. Reproduction is also adversely affected. There are, however, important differences between breeds. European cattle (Bos taurus) produce well at temperatures ranging from 4 to 24° C even at high humidity. Much lower temperatures (-10°C) have little effect as long as fluctuations are not too rapid or frequent. On the other hand, a drop in milk production results with temperatures exceeding 25°C. The drop may be as much as 50% at temperatures of 32°C or higher. In contrast, Zebu cattle (Bos indicus), which are native to warm climates, have a comfort zone of 15 to 27° C and milk production begins to drop only when temperatures rise above 35°C.
Horses do not require warm surroundings, but they do not easily tolerate draughts, dampness and high humidity. When exposed to high temperatures and vigorous exercise, horses sweat and the evaporation of this perspiration cools the skin and helps to maintain normal body temperature.
Sheep can tolerate a wide range of temperatures but should be protected from wind and rain. However, a long period of high ambient temperatures inhibits reproduction. Heat stress also reduces lambing percentage, decreases the incidence of twinning, and decreases the birth weight of lambs. When temperatures are below 7°C at breeding time, ewes show improved reproductive efficiency.
Goats are affected by temperature, humidity and rain. In hot climates, goats need shelter from intense heat during the day. In humid areas they need protection from prolonged heavy rain. Excessive wetting from rain can cause pneumonia and an increase in parasitic infestation
Pigs require a change in ambient temperature as they age and grow, and like cattle, they show a decreased feed intake when under heat stress. Piglets survive and develop best at 30 to 32°C initially followed by a gradual reduction to 20°C over the first three weeks. Feeder pigs (30 to 65 kg) make good gains in the temperature range of 10 to 25°C with 24° C reported optimum. The optimal ambient temperature for pigs weighing 75 to 120 kg is 15° C. Brood sows do well at 15°C but suffer badly at 25°C and above, since they do not perspire when hot. Reproduction rates fall under heat stress and sows are more apt to trample their baby pigs in the discomfort of hot weather.
Poultry, the environmental requirements for poultry vary with age. Chicks should be started at 35° C. After one week the temperature is reduced gradually to 24°C by the fifth week. Broilers and young turkeys reared at ambient temperatures below 18°C are heavier than similar stock reared within the 18 to 35°C range, but their feed conversion efficiency will be less. Laying birds produce the greatest number of eggs and the largest sized eggs at 13 to 24° C. The best feed conversion efficiency is achieved between 21 to 24° C. With increasing environmental temperature there is a decrease in feed intake and alterations in behaviour. Within the temperature range of 5 to 30°C there is a reduction of about 1.6% in feed intake for every 10°C increase in ambient temperature. Above 24°C there is a reduction in egg production and egg size. A continued rise in temperature to 38°C or more may prove lethal. High humidity at high temperature creates condition that is more likely to be lethal because of a breakdown in body cooling through respiration.
Rabbits are affected most by sun and heat, wind, rain and draughts. Sunlight is of benefit to breeding stock and the growing young, but it will also fade the coat of coloured rabbits and discolour a white one. Because of their thick fur coats they tolerate cold, better than extreme heat, but they are susceptible to chilling from draughts. Rabbits also need protection from rain and dampness.
https://www.pashudhanpraharee.com/impacts-of-climate-change-on-dairy-cattle/
https://www.fao.org/partnerships/leap/en/
