**7. Environmental modifications to minimize effects of stress in dairy cattle**

Use of environmental modifications such as shade and cooling systems is critical in arid and semi-arid zones affected by heat stress in order to maintain milk production, milk component levels, reproductive performance, and animal welfare.

The most basic attempt to reduce heat load from direct solar radiation in cattle is the use of shades. They can be from natural or artificial materials and are considered practical and economical ways for reducing heat stress. Trees are considered the most effective shade since they protect from the sun and capture radiation through the evaporation of humidity in the leaves (Avendaño, 1995). The wood or leaves of palms are materials also used for shade although corrugated steel sheets are the most widely used material because they last longer and of low maintenance costs (Armstrong, 1994).

Buffington et al. (1983) pointed out that painting of white color the upper part of the shade unit and installing a 2.5 cm thick of isolating material may considerable reduce solar radiation. For arid and semi-arid zones, areas of 3.5 to 4.5 m2 per lactating cow are recommendable. A more reduced area could provoke lesions in the udder due to competition of cows for shade

space, while an area greater than 4.5 m2/cow have little or no benefit (Armstrong, 1994; Berman, 2006). Height of shades in the corral must be from 3.6 to 4.2 m2 in order to guarantee reduction in solar radiation. However, the shade structure should be high enough from the ground to allow circulation and tractor access for corral cleaning.

Orientation of shades is also important to minimize heat load during summer months. North-South orientation will expose the surface to the sun under the shade during the morning and the afternoon, helping to maintain it dry, but under extremely hot conditions and low rainfall (10 to 12 cm), the East-West orientation could be preferable, although it requires greater labor for maintaining the surface under the shade in dry conditions. In any case, shades must be placed in the center of the corral and should avoid accumulation of humid material under the structure. If concrete floors are used, shade orientation is indistinct (Avendaño, 1995). Figure 4 shows an example of a shade for dairy cattle made from artificial material.

**Figure 4.** A group of cows seeking for shade during hot weather. Shade structure is from artificial materials.

Cooling systems alleviate heat load from dairy cows by using the principle of evaporation, combining water misting and forced ventilation through use of spray and fans, and are frequently placed inside free-stall barns or under shades in open space corrals (Berman, 2006). Even though responses have varied, cooling techniques have consistently improved feed intake and milk production in areas with high environmental temperatures (Armstrong, 1994; Ryan et al., 1992).

176 Milk Production – An Up-to-Date Overview of Animal Nutrition, Management and Health

shows an example of a shade for dairy cattle made from artificial material.

ground to allow circulation and tractor access for corral cleaning.

space, while an area greater than 4.5 m2/cow have little or no benefit (Armstrong, 1994; Berman, 2006). Height of shades in the corral must be from 3.6 to 4.2 m2 in order to guarantee reduction in solar radiation. However, the shade structure should be high enough from the

Orientation of shades is also important to minimize heat load during summer months. North-South orientation will expose the surface to the sun under the shade during the morning and the afternoon, helping to maintain it dry, but under extremely hot conditions and low rainfall (10 to 12 cm), the East-West orientation could be preferable, although it requires greater labor for maintaining the surface under the shade in dry conditions. In any case, shades must be placed in the center of the corral and should avoid accumulation of humid material under the structure. If concrete floors are used, shade orientation is indistinct (Avendaño, 1995). Figure 4

**Figure 4.** A group of cows seeking for shade during hot weather. Shade structure is from artificial

materials.

In general, cooling systems based on spray and fans consist of conventional fans of variable diameter (60 to 90 cm) suspended from the ceiling of the shade. There are lines with water sprinklers in front of them, that creates a kind of breeze with small water droplets which completely moisture the cow surface and skin and support loss of heat by evaporation. These cooling systems can operate at different time intervals which vary according climatic conditions. One disadvantage is the accumulation of moisture under the cooling area because cows spend hours under this area, so urine and feces build up very easily. More labor is required to maintain clean resting areas where the cooling is installed (Avendaño, 1995). Figure 5 shows a cooling system based on spray and fans located in a free stall barn to improve comfort of cows during feeding.

**Figure 5.** A cooling system based on spray and fans placed over the head-locks, next to the feedbunk.

Traditionally, dry cows are provided little or no protection against heat stress because they are not producing milk and it is erroneously assumed they are less prone to heat stress. However, dry cows are experiencing many physiological changes (milk-producing tissue formation, colostrum secretion, accumulation of antibodies, and final fetal growth) that may increase their susceptibility to hot weather and have a critical impact on postpartum cow health, milk yield

and reproduction (Avendaño-Reyes et al., 2010a). Avendaño-Reyes et al. (2006) allocated a group of dry cows in a pen with a cooling system based on spray and fans and compared them to a group with just shade in the pen. Cooled dry cows showed better physiological status than control dry cows. Fat content and fat-corrected milk production at eight week postpartum was significantly higher in cooled cows, as well as conception rate; however, calf birth weight and milk yield showed a trend to be higher in the cooled group. In addition, culling rate was higher in the control group and there was a benefit for using the cooling system during 60 d prepartum in Holstein cows. The physiological rationale for improved postpartum productivity in response to prepartum cooling is not entirely clear, but heat stress was found to negatively influence secretory function of the udder by decreasing mammary blood flow, thereby reducing the efficiency of energy utilization for milk fat precursor synthesis (Kadzere et al., 2002).

Using a cooling system based on spray and fans and installed in the holding pen, previous to the milking parlor, in an arid zone with extreme hot temperatures, Avendaño-Reyes et al. (2010b) provided 1, 2 or 3 h of cooling to a mid-lactating Holstein cows bringing the cows to that site. They found that even though cows under the cooling management system with the highest time of cooling per day showed better milk yield (+2 kg/d of milk), their physiological status did not correspond to a those non-heat stressed lactating cows. So they conclude that is necessary to increase the time of cooling to effectively reduce heat load during severe summer heat conditions. Figure 6 illustrates an installation of a cooling system on the roof of the parlor holding pen, and Figure 7 exemplifies a cooling system based on evaporative environmental chambers.

**Figure 6.** A cooling system based on spray and fans installed in the roof of the holding pen, prior to the milking parlor.

and reproduction (Avendaño-Reyes et al., 2010a). Avendaño-Reyes et al. (2006) allocated a group of dry cows in a pen with a cooling system based on spray and fans and compared them to a group with just shade in the pen. Cooled dry cows showed better physiological status than control dry cows. Fat content and fat-corrected milk production at eight week postpartum was significantly higher in cooled cows, as well as conception rate; however, calf birth weight and milk yield showed a trend to be higher in the cooled group. In addition, culling rate was higher in the control group and there was a benefit for using the cooling system during 60 d prepartum in Holstein cows. The physiological rationale for improved postpartum productivity in response to prepartum cooling is not entirely clear, but heat stress was found to negatively influence secretory function of the udder by decreasing mammary blood flow, thereby reducing

the efficiency of energy utilization for milk fat precursor synthesis (Kadzere et al., 2002).

based on evaporative environmental chambers.

milking parlor.

Using a cooling system based on spray and fans and installed in the holding pen, previous to the milking parlor, in an arid zone with extreme hot temperatures, Avendaño-Reyes et al. (2010b) provided 1, 2 or 3 h of cooling to a mid-lactating Holstein cows bringing the cows to that site. They found that even though cows under the cooling management system with the highest time of cooling per day showed better milk yield (+2 kg/d of milk), their physiological status did not correspond to a those non-heat stressed lactating cows. So they conclude that is necessary to increase the time of cooling to effectively reduce heat load during severe summer heat conditions. Figure 6 illustrates an installation of a cooling system on the roof of the parlor holding pen, and Figure 7 exemplifies a cooling system

**Figure 6.** A cooling system based on spray and fans installed in the roof of the holding pen, prior to the

**Figure 7.** A cooling system based on evaporative chambers. Note at the curtains in one side of the corral to avoid water misting goes out the shade.

With milk production increases between 5 and 10% the benefits for investment in cooling equipment (spray and fans) is from 2 to 3 years. As production increases approach to 20%, the profit on cooling investment could be one year or even less. Management strategies that reduce the impact heat stress has on milk peak production can produce large economic returns to cows that are in their second or higher lactation. The benefit of reducing heat stress in first lactation cows is considerably less because of their inherent lower productivity (Avendaño, 1995; Berman, 2006).

In Table 2 are presented several results of milk production from the use of three environmental modifications against heat stress in different regions of the world. It can be noted that the milk production from the use of spray and fans has a obvious advantage over the use of just shades in the corrals. However, there is no clear evidence that cooling chambers has an advantage over the use of spray and fans, recalling that the cooling chambers are characterized by a considerable investment cost.

In general, Livestock Environmental Management is an emerging area in Animal Science that is getting more acceptance due to the Climatic Change. This new area is an attempt to avoid adverse environmental impacts on animal production systems and is also an effort to minimize the need for expensive environmental protection measures for domestic animals.


ab Milk yield means with different superscript differ (P<0.05)

**Table 2.** Milk production of Holstein cows cooled with different environmental modifications in several studies in arid and semi-arid zones of the world.
