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
To limit the impact of heat stress on the performance of your herd, consider how you will tackle the following challenges: Feed intakes The challenge: When temperatures exceed 25 °C feed intakes can decline by as much as 12 per cent. When cows are suffering from heat stress they will be less inclined to move to sources of feed and will also try to limit the amount of heat energy they produce when digesting feed. In high temperatures, cows also tend to sift feed and focus on intake of easily digestible concentrates, rather than forage. This can lead to the development of acidosis due to an imbalance in rumen pH. Solution: Aim to feed 60-70 per cent of rations between 8pm and 8am, when temperatures are cooler. Research has shown that by feeding at these times, dairy producers can increase feed intakes and milk production of their herd during spells of hot weather. Increasing the energy density of your cow’s diet by using C:16 or hydrogenated fats will help offset lower dry matter intake and maintain milk quality. Also consider the use of a rumen buffer, live yeast or rock salt to buffer rumen pH to maintain cow health and performance. Hydration The challenge: Keeping your cows hydrated during hot weather is vital to reduce the risk of acidosis and maintain optimal rumen function and feed utilisiation.
Youngstock and cow fertility The challenge: When ambient temperatures are high, cows are less sexually active and will experience reduced follicular activity and increased risk of early embryonic death. Hot weather can therefore significantly hamper breeding programmes and increase calving intervals due to decreased fertility and conception rates. If cows suffer from heat stress during the precalving period, calf birth weight can be reduced by 4 percent and the chance of calf mortality during labour increases by 6 per cent. Solution: It is vital to keep breeding and pregnant cows as cool as possible. Providing sources of shade, increasing air exchange within housing and supplying plenty of water can help keep achieve this. More attention must be paid to heat detection and ensure high dry matter intakes for in-calf cows to maintain adequate supplies of energy to support pregnancy.
Water Intake
a.m. milking
p.m. milking
Solution: During the warmer months, cows will have a peak water intake in early afternoon and early evening (see graph below) so ensure that you plan provision of water accordingly.
Cows suffering from heat stress can drink an extra 100 litres of water a day, so a plentiful supply of fresh, preferably cool, water is essential to avoid dehydration. A good rule of thumb is 5 litres of water per litre of milk produced.
For more information about managing heat stress please speak to your ForFarmers Account Manager. 0
6
12
18
24 hrs
Time of day Summer drinking: a higher afternoon peak
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