Heat stress can cause reduced rumen function and lower feed intake, which leads to a reduced energy supply and impacts dairy performance. Milk yield and milk components are reduced. Milk loss is linked to both heat stress levels and duration of exposure. Lallemand Animal Nutrition developed a more precise categorization of losses thanks to several scientific publications that represent different situations all around the world. For dairy cows, the common threshold used by the scientific community was 68 (Burgos and Collier. 2013). However, practical field studies show that heat stress can impact dairy cattle starting at a temperature-humidity index (THI) of 62. Hammani (et al., 2013), studied heat stress in northern Europe and defined that heat stress can impact cows at 62. Bourraoui (et al., 2002) found higher losses in milk, fat and protein yields in Mediterranean regions.
Check out the mapTemperature (째C 째F)
& Humidity (%)
FROM
17.2°C (63°F)
TO
21.7°C (70°F)
50%
FROM
22.7°C(72°F)
TO
25°C (77°F)
50%
FROM
25.6°C(78°F)
TO
30.6°C(87°F)
50%
ABOVE
31.1°C (88°F)
50%
THI
Tresholds
< 62
No stress
62-67
Low Stress
68-72
Mid-moderate Stress
73-79
Mild Stress
> 80
Severe stress
62
72
79
80
Range of performance losses due to heat stress
Milk yield
-1.0 ; -2.1 kg/day
Milk
fat (%)
-
Milk
protein (%)
-
Milk yield
-3.0 ; -5.5 kg/day
Milk
fat (%)
-0.1
Milk
protein (%)
-
Milk yield
-4.9 ; -7.8 kg/day
Milk
fat (%)
-0.3
Milk
protein (%)
-0.2
Milk yield
-6.6 ; -9.8 kg/day
Milk
fat (%)
-0.5
Milk
protein (%)
-0.4
Temperature (째C 째F)
& Humidity (%)
Below
25°C (77°F)
50%
FROM
25.6°C(78°F)
TO
28.9°C(84°F)
50%
FROM
29.4°C(85°F)
TO
32.8°C (91°F)
50%
ABOVE
32.8°C (91°F)
50%
THI
Tresholds
< 72
No stress
73-77
Mid-moderate stress
78-82
Mild stress
> 82
Severe stress
62
77
82
100
Range of performances losses due to Heat Stress
Daily gain
-60 ; -90 g/day
Daily gain
-120 ; -160 g/day
Daily gain
-130 ; -170 g/day
Daily gain
- 220 ; -250 g/day
Temperature (째C 째F)
& Humidity (%)
Below
23.3°C(74°F)
50%
FROM
24.4°C(76°F)
TO
25.6°C(78°F)
50%
FROM
26.1°C(80°F)
TO
28.9°C(84°F)
50%
ABOVE
28.9°C (84°F)
50%
THI
Tresholds
< 70
No stress
71-73
Mid-moderate stress
74-77
Mild stress
> 77
Severe stress
62
74
77
100
Range of performance losses due to heat stress
Milk yield
-0,22 kg/day
Dairy sheep
-0,13 kg/day
Dairy goat
Milk yield
-0,57 kg/day
Dairy sheep
-0,32 kg/day
Dairy goat
Milk yield
-0,87 kg/day
Dairy sheep
-0,59 kg/day
Dairy goat
Milk yield
-1.19 kg/day
Dairy sheep
-0,92 kg/day
Dairy goat
As temperatures are rising, heat stress is a common and growing concern in ruminant production and experts are now fully aware that it is not limited to two summer months or tropical regions. Heat stress could be an issue for long periods. Cattle naturally change their behavior to help alleviate stress, which can disrupt digestion, increase inflammation, reduce performance, and impact their health.