FEEDING FOCUS July 2016 • Issue 16
How to tackle heat stress
With the warm weather we’ve experienced over the last month set to continue it is important to remember the negative impact that heat stress can have on the performance of your cows. Understanding heat stress To ensure optimum cow performance, the ideal ambient temperature should be between 5°C and 25°C, though this range will be influenced by weight, breed and feeding levels. Any prolonged exposure to temperatures in excess of these limits will result in a negative impact on cow performance. Overheated cows will attempt to cool themselves by increasing their internal blood flow, drooling and panting; all of which require energy that could be used for milk production. Dairy cows generate a lot of heat energy (1.4kW for a 600kg cow producing 30 litres/day), so it does not take a large increase in temperature to result in heat stress (see chart).
Relative Humidity
Temp oC
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
19.0
61
61
62
62
63
64
65
65
66
66
67
67
68
68
69
69
19.5
61
62
62
63
64
65
65
66
66
67
67
68
68
69
69
70
20.0
62
62
63
64
65
66
66
66
67
67
68
68
69
69
70
70
20.5
62
63
64
65
66
66
66
67
67
68
68
69
69
70
70
71
21.0
63
64
65
66
66
66
67
67
68
68
69
69
70
70
70
71
21.5
64
65
66
66
67
67
67
68
68
69
69
69
70
70
71
71
22.0
65
66
66
67
67
67
68
68
69
69
69
70
70
70
71
71
22.5
66
66
67
67
68
68
68
69
69
69
70
70
71
71
72
72
23.0
66
66
67
67
68
68
68
69
69
70
70
71
71
72
73
73
23.5
67
67
67
68
68
69
69
70
70
70
71
71
72
72
73
73
24.0
67
68
68
68
69
69
70
70
71
71
72
72
73
73
74
74
24.5
68
68
69
69
70
70
71
71
72
72
73
73
74
74
75
75
25.0
68
69
69
70
70
71
71
72
72
73
73
74
74
75
75
76
25.5
69
69
70
70
71
71
72
73
73
74
74
75
75
76
76
77
26.0
69
70
70
71
71
72
73
73
74
74
75
76
76
77
77
78
26.5
70
70
71
72
72
73
73
74
75
75
76
76
77
78
78
79
27.0
70
71
72
72
73
73
74
75
75
76
77
77
78
78
79
80
27.5
71
71
72
72
73
73
74
75
76
76
77
77
78
79
80
81
28.0
71
71
72
73
73
74
75
75
76
77
77
78
79
79
80
81
28.5
71
72
73
73
74
75
75
76
77
78
78
79
80
80
81
82
29.0
72
73
74
75
75
76
77
78
78
79
79
81
81
82
83
84
29.5
72
73
74
75
75
76
77
78
78
79
80
81
81
82
83
84
30.0
73
74
74
75
76
77
78
78
79
80
81
81
81
82
83
84
30.5
73
74
75
76
77
77
78
79
80
81
81
82
83
84
85
86
31.0
74
75
76
76
77
78
79
80
81
81
82
83
84
85
86
86
MILD
HIGH
SEVERE
Temperature Humidity Index (THI) – heat stress indicator