Dr. Jose Santos presented this information for DAIReXNET on March 19th, 2012.

1. NUTRITION PROGRAMS FOR LACTATING
DAIRY COWS UNDER HEAT STRESS
J.E.P. Santos and C.R. Staples
Department of Animal Sciences
University of Florida

2. Heat-Stressed Dairy Cow
• Spends less time lying down (9 to 10 h vs. 11 to 13 h)
• Spends less time ruminating
• Increases CO2 losses due to hyperventilation
• Increases rumen retention time: greater fermentability of feeds
• Has a deficit of HCO3-, Na, and K
• Has reduced blood flow to the portal-drained viscera (PDV)
• Has reduced nutrient uptake by the PDV
• Has reduced blood flow to the mammary gland
• Has increased energy requirements for maintenance (dissipate heat)
LESS PRODUCTIVE

3. Consequences for Dairy Cattle
– Reduced dry matter intake
– Reduced yields of milk and milk components
– Decreased fat and protein content in milk
– Reduced growth rates
– Decreased reproductive performance
– Increased incidence of health disorders, particularly
retained placenta, metritis, and lameness

4. The Better-Producing Cows Suffer the
Most from Heat Stress
n = 230
40.0 39.8 n = 170
39.6
Body Temp, C
39.1
39.2 38.9 38.9
38.8
38.4 37
28 37 28
38.0
Milk Production, kg FCM Production, kg
Missouri Israel

5. Controlled heat stress in AZ:
- Temperature increased from 80 to
104 ºF
-Pair-fed cows under thermoneutral
conditions keep nutrient intake similar
- Duration of 9 days
-Body temperature increased from 101
to 104.5 ºF
- Respiration rate increased from 40 to
70 breaths/min

6. Heat stress intake by ~ 30%
Heat stress yield ~45%
Underfeeding yield by ~19%
feed intake only accounted for 50% of the reduction in milk yield
Rhoads et al. (2009) J. Dairy Sci. 92:1986-1997

7. Nutritional Management During Heat Stress
• DMI
• Feeding frequency and feed delivery
• Fiber feeding
• Energy sources
• Protein feeding
• Mineral manipulation

8. Water, the forgotten nutrient……

9. Cows Drink More Water When Experiencing
Ruminal Acidosis
• Subacute ruminal acidosis (SARA) was induced by
replacing 25% of the TMR with a 50:50 mix of
barley:wheat pellets fed twice daily.
• Cows could choose to drink water containing
– No sodium bicarbonate or
– 2.5 g of sodium bicarbonate per liter of water
Cottee et al., 2004, JDS 87:2248

10. Ruminal pH and Water Intake During the 3
Hours of Lowest Ruminal pH
Control SARA
Mean ruminal pH 6.02 5.45*
NaHCO3- water intake, % of
total water intake 39 36
Water intake, L 14.4 18.9*
Cottee et al., 2004, JDS 87:2248

11. Drinking Water Reduces Ruminal Acidity
(Cottee et al., 2004)
6.4 0.15 Before
6.19 After
6.2 0.24
6.04 Drinking Bout
Ruminal pH
6.0 5.91
5.8 5.67
5.6
5.4
Control SARA
Cottee et al., 2004, JDS 87:2248

12. Feeding Frequency and Feed Delivery
• Increasing feed frequency increases DMI
– Fresh feed available
– Stimulatory effect of feed delivery
– Push up feed does not seem to have the same effect
• Feed consumption during heat stress:
– Greater after milkings
– Greater during the cooler periods of the day ( early in the
morning and during the night)

13. Frequency of Feed Delivery and Eating Behavior
100
Milking Milking
80 ── Delivery 1 x daily
% of cows eating
60 ── Delivery 2 x daily
40
20
── Delivery 2 x daily
0
04:00 07:00 10:00 13:00 16:00 19:00 22:00
100
01:00 04:00
── Delivery 4 x daily
Hour Milking Milking
% of cows eating
80
60
40
20
0
04:00 07:00 10:00 13:00 16:00 19:00 22:00 01:00 04:00
DeVries et al (2005) J. Dairy Sci. 88: 3553-3562
Hour

14. Dietary Fiber
• Cows under heat stress might require a more nutrient dense
diet to compensate for the lower DM intake
• Greater heat production associated with fiber feeding
• Metabolic pathway to synthesize acetate produces CH4 (Loss of
energy)
• Efficiency of metabolizable energy utilization increases with low
forage diets (Tyrrel et al., 1979)
• At the same ME diet, high forage diets increases portal blood
flow and O2 utilization by the PDV (Reynolds et al., 1991)

15. Fiber Level and Heat Stress
(West et al, 1999)
DMI, % BW
DMI 5.00
24
4.75
23
22 4.50
21 4.25
% BW
kg/d
20 4.00
19
3.75
18
3.50
17
16 3.25
15 3.00
30.2 33.8 37.7 42 30.2 33.8 37.7 42
Cool Hot Cool Hot

16. Fiber Level and Heat Stress
(West et al, 1999)
3.5% FCM
Milk
34
34
32
32
30
30
kg/d
28
kg/d
28
26 26
24 24
22 22
20 20
30.2 33.8 37.7 42 30.2 33.8 37.7 42
Cool Hot Cool Hot

17. Effect of Heat Stress on Ruminal pH of
Holstein Cows (JAS 30:1023)
6.8 6.5 Diet by Environment Interaction, P < 0.01
6.5
6.1 6.1
6.2
Ruminal pH
5.9
5.5
C C
5.6 O H O
O O O H
5.3 O
L T L
5 T
High Forage Diet High Concentrate Diet

18. Effect of Heat Stress on Ruminal Activity
Environ. Rectal Ruminal
Reference Temp, F Temp, F Contractions
Florida Shade 38.7a 2.4/mina
JDS 64:844 No shade 39.6b 1.7/minb
Missouri 18 C 38.4a 2.2/min
JAS 29:734 38 C 40.9b 1.7/min
Remastication rates
Maryland 20 C 39.2a 90/mina
JAS 17:326 35 C 40.3b 80/minb

19. Cows Under Heat Stress Are at Greater Risk for
Rumen Acidosis

20. Month of Diagnosis of 1st Lameness Case
August to November
May to July
December to April

21. Dietary Fat
• Fat contains 2.5 to 3 x more calories than CHO
• Fat is a source of non-fermentable energy
• Fatty acids: DE content = ME content (no gas or urinary
losses)
• Fat may alleviate heat production during periods of
thermal stress

22. Effect of Fat and Heat Stress on Performance of Dairy Cows
Treatment
Cool Hot P<
Control HF Control HF Fat FxE
DMI, kg/d 20.2 19.9 14.2 14.9 NS NS
FCM, kg/d 32.3 35.0 26.1 27.9 0.05 NS
Milk
Fat, % 3.16 3.42 3.15 3.51 0.05 NS
Protein, % 2.82 2.84 2.62 2.56 NS NS
Adapted from Knapp and Grummer (1991)

23. Effect of Supplemental Fat on NEL Intake and Milk
Yield During Moderate and Hot Weather
46 35
45 34
44 33
43 32
kg/d
Mcal/d
42
31
41
30
40
39 29
38 28
Moderate Heat Stress Moderate Heat Stress
Control PFA Control PFA
Huber et al. (1994) J. Dairy Sci.

24. Dietary Protein
• Diets with a high CP content usually are detrimental to cows
under heat stress
• Protein degradability and quality affects performance of heat-
stressed dairy cows
• Balance diets for metabolizable protein and limiting essential
amino acids that allows to reduce the total dietary CP
– Corn/corn silage and alfalfa based diets – methionine and lysine
– Grass silage/barley-oat based diets - histidine

25. Effect of Decreasing RDP on Milk Yield
% RDP as a % Milk yield
Location
of CP increase
Arizona
65% 60% 3.3 kg/d
JDS 72:2554
Arizona
61% 47% 6.0 kg/d
JDS 74:243
Greece
69% 61% 2.4 kg/d
WRAP 30:21
Arizona 58% 58%
3.1 kg/d
JDS 76:819 lysine

26. Mineral Nutrition
• Heat stress: metabolic alkalosis due to hyperventilation
• Blood pH increases, but total HCO3- drops
• Ruminant sweat is high in K
• Thermal stress reduces DM intake, milk yield and milk fat content
• Altering the concentration of some macro minerals in the diet
influences:
– rumen metabolism
– blood buffering
– yields of milk and milk fat

27. Relationship Between DCAD and DM Intake
in Lactating Dairy Cows (69 diets)
Recommended DCAD: +30 to +40 mEq/ 100 g DM
Hu and Murphy, 2004 JDS 87:2222

28. Relationship Between DCAD and Milk Yield
in Lactating Dairy Cows (69 diets)
Recommended DCAD: +30 to +40 mEq/100 g DM
Hu and Murphy, 2004 JDS 87:2222

29. Yeasts and Fungal Cultures
• Yeasts (Saccharomyces cerevisiae either as live yeast or yeast
culture) and fungal cultures (Aspergillus oryzae) act as rumen
microbial modifiers:
– Stimulate fiber digestion
– Reduce lactic acid accumulation in the rumen fluid
– Typically improve efficiency of feed conversion into milk or 3.5% FCM
http://www.chemistrydaily.com/
chemistry/upload/0/09/
Saccharomyces_cerevisiae.jpg

30. Summary of Responses of Lactating Dairy
Cows Fed 3 g/day of Aspergillus oryzae
Number of experiments
16
14
12
10 6 4
8
6
4 8 8
2
0
DM intake Milk yield Rectal temp
No change Significant improvement
Huber et al. (1994) J. Dairy Sci.

31. Effect of Feeding Yeast Culture (YC)1 on
Lactating Dairy Cow Performance in Summer
Site Diets DMI, kg/day Milk kg/day Efficiency
CA, 2010 Cont 26.0 42.2a 1.62
YC 25.8 43.4b 1.68
GA, 2007 Cont 26.2 39.2a 1.50a
YC 25.6 41.0b 1.60b
SD, 2004 Cont 23.1 34.9 1.49a
YC 22.1 35.3 1.59b
IL, 2000 Cont 15.2 25.9 1.70
Jerseys YC 16.5 27.2 1.65
1Diamond V Mills ‘XP’ or Vi-Cor AMAX-Xtra a, b P ≤ 0.10

32. Effect of feeding increasing amounts of live yeast to cows under heat stress on
rumen fluid composition
Live yeast1, g/d P
0 0.5 1 Linear
Rumen pH 5.99 ± 0.11 6.03 ± 0.11 6.30 ± 0.11 0.04
Rumen pH < 5.8, % (n/n) 45.0 (9/20) 36.8 (7/19) 10.5 (2/19) 0.02
Lactate 4.9 ± 1.8 4.5 ± 1.8 1.3 ± 1.9 0.18
Detectable lactate, % 70.0 (14/20) 57.9 (11/19) 57.9 (11/19) 0.58
(n/n)
Lactate > 1 mM, % (n/n) 35.0 (7/20) 21.1 (4/19) 5.3 (4/19) 0.04
VFA, mM 123.4 ± 5.8 124.7 ± 5.9 125.3 ± 6.1 0.82
1 Levucell SC (Lallemand Animal Nutrition) Marsola et al. (2009) J. Dairy Sci.

33. Recommendations
• Feed cows more frequently during periods of heat stress
• Cows under heat stress should be fed the highest quality
forage available - Minimizes the need for high-starch feeds
• In my opinion, NDF should be increased from the traditional 28-
30 to 31-33%
– When forage quality is a problem, then replace part of the starch with a
highly digestible NDF source
• Formulate diets with moderate concentration of CP
– Review the metabolizable protein needs of the cows and formulate
based on MP and essential amino acids.
– Keep rumen-degradable protein at ~ 10% of the diet DM

34. Recommendations
• Feed moderate to high (up to 5% of the diet DM) fat diets, but avoid
excessive amounts of unsaturated fatty acids
• Increase Na and K
– Add 1 to 1.2% of the total ration as sodium bicarbonate to increase the
total Na up to 0.4 to 0.5%
– Increase the K content up to 1.6 to 1.8% with potassium carbonate
– DCAD of the ration should be between 300 and 400 mEq/kg of DM
• Dietary Mg should be at 0.35 to 0.4% in high K diets
• Incorporate a live yeast or yeast culture to the ration
– Improve production of fat-corrected milk
– Improves feed efficiency
– Reduces the risk of rumen acidosis

35. Got questions?
This project was supported by Agriculture and Food Research Initiative Competitive
Grant no. 2010-85122-20623 from the USDA National Institute of Food and
Agriculture.