Environmental Modifications

Global climate change models predict an increase of heat stress events, as well as general warming in some areas. Therefore, methods that will alleviate the impact of these events should be considered, especially if alternative land use or species/ breed use is not an option. Beede and Collier (1986) suggest three management options for reducing the effect of thermal stress in cattle which have application for all livestock and poultry. The options are: (1) physical modification of the environment; (2) genetic development of breeds with greater heat tolerance and (3) improved nutritional management during periods of high heat load.

Numerous methods of environmental modifications to ameliorate heat stress in livestock and poultry are found in the literature, ranging from provision of shade through environmental control using mechanical air conditioning (e.g., Hahn and McQuigg 1970; Hahn 1989; Bucklin et al. 1991; Bull et al. 1997; Mader et al. 1999a; Valtorta and Gallardo 1998; Mitlohner et al. 2001; Spiers et al. 2001; Pagthinathan et al. 2003; Champak Bhakat et al. 2004; Correa-Calderon et al. 2004; Mader and Davis 2004; Lin et al. 2006). However, while all are technologically feasible, not all are economically viable or acceptable from a management perspective.

Shade: In many cases, the most economical solution to high heat load is the provision of shade. Shade is a simple method of reducing the impact of high solar radiation (Bond et al. 1967; Fuquay 1981; Curtis 1983), but has little impact on air temperature. Black globe temperatures under shade structures can be as much as 12°C lower than the black globe temperature in the sun (36°C vs. 49°C) (J. Gaughan, 2007, personal communication). Shade can be either natural or artificial. It has been suggested that shade from trees is more effective (Hahn 1985) and is preferred by cattle (Shearer et al. 1991). However, Gaughan et al. (1998) reported that dairy cows preferred the shade from a solid iron roof even when they had access to shade trees. This result may have been a result of differing shade density, leading to a greater reduction in radiation heat load under the roof. Aspects concerning design and orientation of shades have been widely published (Buffington et al. 1983; Hahn 1989; Bucklin et al. 1991; Valtorta and Gallardo 1998). Many species, even those deemed to be heat tolerant will seek shade under hot conditions if it is an option. Shades are effective in reducing heat stress and the effects of heat stress in cattle (Davison et al. 1988). Valtorta et al. (1996b) found that cattle with access to shade had lower rectal temperature and respiration rate in the afternoon, and yielded more milk and greater milk protein compared to unshaded cows. Khalifa et al. (2000) reported that exposure to solar radiation (46°C black globe temperature) and 27% RH, significantly increased rectal temperature, skin temperature, ear temperature, respiration rate and pulse rate of goats without access to shade compared to those in shade. However, exposure to solar radiation significantly decreased temperature gradients from the skin to air and from rectal to ear temperatures.

Air movement: Air movement is an important factor in the relief of heat stress, since it affects convective and evaporative heat losses (Armsby and Kriss 1921; Mader et al. 1997; Yahav et al. 2005). Air movement whether outside or in buildings is critical if cooling is to be effective. The use of natural ventilation in animal buildings should be maximized by the construction of open-sided sheds (Ferguson 1970; Bucklin et al. 1991), sheds with ridge top ventilation (Baxter 1984) and good separation distance between buildings (Ferguson 1970). Forced or mechanical ventilation, provided by fans, is an effective method for enhancing air flow, if properly designed and maintained (Baxter 1984; Xin and Puma 2001). Numerous methods of increasing air movement in animal buildings ranging from simple overhead fans, mechanically driven curtains which open or close depending on ambient temperature, tunnel ventilation systems to fully controlled computer operated systems can be found in the literature. Shelters, shade and wind breaks, if not designed correctly, can lead to micro-climate conditions that may induce severe heat stress in animals.

Using water for cooling livestock: Direct access to water such as in dams, ponds and rivers is effective in cooling animals in grazing situations. It is not unusual to see cattle standing belly deep in water. Intensively housed dairy cattle, feedlot cattle and pigs will also use water troughs for similar purposes if they can gain access. Where access is limited water splashing and dunking the head in the trough is a common practice. Pigs will use nipple drinkers to spray water over their bodies in an effort to keep cool. Where animals are housed there are several methods which are commonly used, including misting, fogging, and sprinkling systems. A large number of studies have investigated the efficacy of these systems in reducing the incidence of heat stress in domestic animals (Berman et al. 1985; Hahn 1985; Armstrong and Wiersma 1986; Schultz 1988; Turner et al. 1989; Strickland et al. 1989; Bucklin et al. 1991; Armstrong 1994; Armstrong et al. 1999; Brouk et al. 2001, 2003a; Pagthinathan et al. 2003; Gaughan et al. 2004; Marcillac et al. 2004; Barbari and Sorbetti Guerri 2005; Calegari et al. 2005; Gaughan and Tait 2005).

Evaporative coolers may be effective in reducing air temperature especially when relative humidity is low and there is adequate ventilation and air movement. Evaporative coolers are effectively used to cool the air in cattle, pig, sheep and poultry buildings in areas characterized by a hot dry environment. Misting is routinely used in the dairy industry and is especially effective in dry climates (e.g. Israel, Saudi Arabia, and Arizona) (Armstrong et al. 1993), and is also used for cooling the ventilation air entering poultry and swine buildings (Xin and Puma 2001; Brouk et al. 2003b). However, misting systems can be effective even when relative humidity is high e.g. Hawaii (dairy cattle) (Armstrong et al. 1993), Florida (dairy cattle) (Taylor et al. 1986; Beede 1993; Mearns et al. 1992), Missouri (dairy cattle, swine and poultry) (Brouk et al. 2003b) and Iowa (poultry) (Xin and Puma 2001) provided that there is sufficient air movement. Misting or fogger systems are not generally recommended in hot humid environments (Bucklin et al. 1991; Bottcher et al. 1993; Turner et al. 1993). However, misters do have the advantage of low water usage (Lin et al. 1998).

Direct water application: Direct application of water to the skin is an effective method of cooling buffalo, cattle, pigs, and poultry. Adding water to the body surface increases the latent heat loss from an animal. It is the evaporation of the water from the surface that results in the cooling of the animal. Under the right conditions, water application will reduce heat load on animals (Fig. 7.7). However, the use of water for cooling livestock may lead to an increase in relative humidity, especially where there is limited air movement, and this reduces the ability of the animal to dissipate heat via evaporation (Frazzi et al. 1997; Xin and Puma 2001; Correa-Calderon et al. 2004). Gaughan et al. (2003) demonstrated that wetting cattle exposed to high temperature and humidity had only minor short term effects

Time of day, h

Fig. 7.7 The effect on rectal temperature when cattle have been sprinkled (DW) between 1,200 and 1,600 h or not sprinkled (NW) (Adapted from Gaughan et al. 2004)

Time of day, h

Fig. 7.7 The effect on rectal temperature when cattle have been sprinkled (DW) between 1,200 and 1,600 h or not sprinkled (NW) (Adapted from Gaughan et al. 2004)

on relative humidity, provided that ventilation was adequate. The negative impacts of high relative humidity and/or limited air movement on the animals ability to dissipate heat may be magnified when insufficient water is used e.g. foggers or misters or there is insufficient ventilation to remove the moisture laden air. In these circumstances water particles may form a cover over the hair or pelage of the animal trapping heat and thereby increasing the level of heat stress (Hahn 1985).

Continuous application of water is not required to achieve heat stress alleviation. Morrison et al. (1973) used a 30 min cycle where cattle were wetted for 30 s and then exposed to forced air ventilation for 4.5 min. The 30 min cycle was repeated nine times a day. The dairy cows which were exposed to the cooling strategy had a lower (0.5-0.9°C) rectal temperatures than those not cooled. In a later study Morrison et al. (1981) using feed conversion efficiency and rate of gain as indicators did not find any benefit from wetting cattle. However, feed intake was greater in the cooled cattle. Flamenbaum et al. (1986) wetted dairy cows for either 10, 20 or 30 s followed by forced ventilation (1.5 m/s at cow height) for either 15, 30 or 45 min. They found that the 20 and 30 s wetting followed by the 30 and 45 min forced ventilation reduced rectal temperature by 0.7°C and 1.0°C respectively. Igono et al. (1987) reported effective cooling when where sprinklers were used for were used for 20 minutes on and were then off for 10 min. Using beef cattle in Florida, Garner et al. (1989) used a 3 min on 30 min off when temperature was greater than 26.7°C. Fans were also used in this study however air speed at animal height was not mentioned. Lin et al. (1989) used 3 min on and 15 min off. Two and a half minutes on and 7 min off was used by Turner et al. (1992). Beede (1993) recommended approximately 1-2 mm per dairy cow per 15 min wetting cycle, or just enough water to wet the back. In a study by Brouk et al. (2001) used a cycle of 3 min on and 12 min off, while Gaughan et al. (2008b) used 5 min on and 15 min off.

Brouk et al. (2001) suggests that the coat of dairy cows should be allowed to dry between water applications, however Gaughan et al. (2008b) reported that beef cattle which were completely dry within 10-15 min of water application had an increase in respiration rate. It is likely that these animals were under some degree of heat stress, albeit for short periods of time, because water was evaporating from the skin but not removing sufficient body heat (Frazzi et al. 2000). This suggests that the 15 min interval between wettings was too long given the ambient conditions to which the cattle were exposed or that the duration of water application was too short or that the amount of water supplied was insufficient.

Before considering water application, a number of factors need to be considered. These include: infrastructure and running cost, water availability, how will water be removed from the site, provision of sufficient air movement, and micro-climate effects.

Livestock managers need to be especially vigilant when applying water to animals. Changes in micro-climate (e.g., an increase in relative humidity) may reduce evaporative cooling from the animal's surface. Therefore increased wetting frequency may be required. Furthermore, consistency in application is important. Once started, wetting needs to continue until high heat load has abated (Gaughan et al. 2004, 2008b).

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