**8. Effect of evaporative cooling system on energy balance and body weight of dairy cows**

Responses of dairy cow to heat stress include panting and sweating. If these are not successful in alleviating the heat load, body temperature will rise. Increased body temperature will result in reduced feed intake, higher maintenance requirements (panting) and less efficient productive ability. The higher maintenance requirements dictates that cows need to increase feed intake to maintain milk production. However, this not possible as feed intake declines when ambient temperatures exceeded 26C. For uncooled cows in this study, as a result of this increase in requirement and a decrease in intake, milk production may decline as much as 25-30%, and typically they mobilize body reserves and lose body weight to maintain milk production until the intake of feed can match or exceed nutritional requirements [9,10], thus entering a state of negative energy balance.

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

In this study the cooling system improved cow comfort and milk production. The cooling system decreased ambient temperatures and THI. The cows with this cooling system had decreased rectal temperatures and respiration rates, and increased feed intake (30.9 %) and milk production (42.5%). In addition, an analysis of the economics in the this study showed that the rate of return on investment in cooling equipment and additional feed plus electric

There are questions that arise regarding the cost effectiveness of an evaporative cooling system over a period of years. In this study, an economic analysis of the evaporative cooling system showed that cows in the tunnel ventilation barn produced 5.1 kg/cow/day more than the cows housed outside. The milk price was 11.50 baht/kg. Therefore, the use of tunnel ventilation cooling increased revenue by 58.65 baht/cow/day and increased feed costs by

The cost of the fan and water pump operation was 6.88 baht/cow/day. The total equipment and supply cost to build the tunnel barn facility was 125,000 baht (for 18 cows), which, when depreciated over the expected life of the equipment (including maintenance costs of 25,000 baht over 5 years), was 4.11 baht/cow/day. Thus, the cows housed in the tunnel barn earned 25.49 baht/day or 3823.50 baht more than the cows housed outside over the 22-week study

Item Difference Income-Cost

**Table 3.** The economic analysis of the evaporative cooling system over the first 22 week of lactation in

Responses of dairy cow to heat stress include panting and sweating. If these are not successful in alleviating the heat load, body temperature will rise. Increased body temperature will result in reduced feed intake, higher maintenance requirements (panting) and less efficient productive ability. The higher maintenance requirements dictates that cows need to increase feed intake to maintain milk production. However, this not possible as feed intake declines when ambient temperatures exceeded 26C. For uncooled cows in this study, as a result of this increase in requirement and a decrease in intake, milk

**8. Effect of evaporative cooling system on energy balance and body** 

Milk yield (kg/cow/day) 5.1 58.65 DMI (kg/cow/day) 2.9 -22.17 Electric cost (fan & water pump operation) -6.88 Equipment and maintenance cost (5 years) -4.11 Total 25.49

(Baht/cow/day)

costs of this cooling system, showed it was profitable in hot and humid conditions.

**7. Economic analysis of the utilizing evaporative cooling system** 

22.17 baht/cow/day. Thus, income over feed cost was 36.48 baht/cow/day.

(Table 3).

dairy cows.

**weight of dairy cows** 

The energy balance and body weight of dairy cows is presented in Figure 4 and Figure 5. During 12 wk of lactation, average body weight of postpartum cows was greater in cooled than uncooled cows. In both groups of cows, body weight decreased between wk 1 and 4, and increased between wk 5 and 22. Week postpartum (P<0.001) and treatment (P<0.001) affected EB but treatment x week postpartum was not significant. Cows in both groups entered into NEB immediately after calving. Averaged EB was greater (P<0.001) in cooled (0.916 0.194 Mcal/day) than uncooled cows (-0.268 0.195 Mcal/day). During the 12 week study, the week of EB nadir was at wk 2 in both groups and the degree of EB nadir did not differ significantly (P>0.50) between the groups, although the average was lower in uncooled than cooled cows. After reaching the EB nadir, uncooled cows required more days to reach a positive energy balance than the cooled cows. The first week that EB was greater than zero was at wk 5 in cooled cows and at wk 7 in uncooled cows. Because of dry matter intake in uncooled cows was lower (P<0.05) than in cooled cows. Resulting in uncooled cows having a prolonged period of negative energy balance and postpartum body weight in these cows were lesser (P<0.05) than in cooled cows [50]. The negative energy balance is directly related to the postpartum interval to first ovulation, and follicle size was adversely affected by negative energy balance in early postpartum dairy cows [9]. The average EB during the first 4 week of lactation was negatively correlated to the postpartum interval to first ovulation [57].

**Figure 4.** Weekly changes in energy balance for the cooled and uncooled cows during the first 12 week postpartum.

**Figure 5.** Weekly changes in average body weight for the cooled and uncooled cows during the first 22 week postpartum.
