**6. Effect of evaporative cooling system on dry matter intake and daily milk yield of dairy cows**

Dry matter intake, expressed as kilograms per day (kg of DM/day) was greater (P<0.05) in cooled (12.0 0.2 kg/d) than uncooled cows (9.1 0.2 kg/d). DMI increased (P<0.05) from wk 1 to 22 of lactation in both groups of cows but treatment x week postpartum did not affect (P>0.05) it (Figure 2) [50].

**Figure 2.** Weekly changes in average daily DMI for the cooled and uncooled cows during the first 22 week postpartum.

**Figure 3.** Weekly changes in average daily milk production for the cooled and uncooled cows during the first 22 week postpartum.

Daily milk yield was greater (P<0.001) in cooled (16.9 0.3 kg/d) than uncooled (12.6 0.2 kg/d) cows. Daily milk yield increased (P<0.001) from wk 1 to wk 22 of lactation in both groups of cows but treatment x week postpartum did not affect (P>0.50) daily milk yield (Figure 3). The 4% FCM also differ (P<0.001) between cooled and uncooled cows. Cooled cows had more persistent milk production than uncooled cows. Milk composition did not differ (P>0.50) between the groups of cows over the 12 week study (Table 2) [50].

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

**Figure 2.** Weekly changes in average daily DMI for the cooled and uncooled cows during the first 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 **Week Postpartum**

Uncool Cool

Uncool Cool

**Figure 3.** Weekly changes in average daily milk production for the cooled and uncooled cows during

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 **Week Postpartum**

week postpartum.

**Milk yield (kg/day)**

0

2

4

6

8

**Dry matter intake (kg)**

10

12

14

16

the first 22 week postpartum.


**Table 2.** Dry matter intake, milk production and milk composition of cooled and uncooled cows during the 12 week study.

In this study, rectal temperature was positively correlated with air temperature and THI but negatively correlated with DMI. Dry matter intake was positively correlated with milk production. Milk yield and DMI exhibited a significant decline when maximum THI reached 77 [51]. There is a significant negative correlation between THI and DMI [52,53], and the effect of THI is probably mediated through the effects of increasing body temperature on cow performance.

Mean air temperature had the greatest influence on milk yield for Holstein cows under hot conditions [48]. The mean daily ambient temperature was highly correlated with the p.m. rectal temperature and milk yield was highly correlated with the cows p.m. rectal temperature. The elevated p.m. rectal temperatures were associated with concomitant reductions in DMI and milk yield [54]. Uncooled cows, in this study, had rectal temperatures exceeded 39C at both the a.m. and the p.m. milking, when cow temperatures should have been near their lowest and highest points, respectively. Such consistently elevated rectal temperatures, result in a significant decline in DMI and milk yield when compare with the cooled cows which had a lower rectal temperature.

The negative effects of heat stress on milk production could be explained by decreased nutrient intake and decreased nutrient uptake by the portal drained viscera of the cow [55]. Blood flow which moves to peripheral tissues for cooling purposes may alter nutrient metabolism and contribute to lower milk yields during hot weather. Providing cows with supplemental shade and cooling to mitigate heat stress has been evaluated in economic terms using the increase in milk production data [2]. Adding sprinklers and fan cooling increased the feed intake (7.1 to 9.2%) and milk production (7.1 to 15.8%), and decreased rectal temperature (-0.4 to -0.5 C) and respiration rate (17.6 to 40.6 %) [56].

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