Slide 1: Beat the Heat – Or It Will Beat You!
BEAT THE HEAT – OR IT WILL BEAT YOU! HEAT STRESS EFFECTS ACROSS THE LACTATION CYCLE Balchem Real Science Lecture 1 April 2025 G. E. Dahl Department of Animal Sciences Institute of Food and Agricultural Sciences gdahl@ufl.edu
Slide 2: Heat Stress Affects Entire Lactation Cycle
HEAT STRESS AFFECTS ENTIRE LACTATION CYCLE • Lactating cows Impact on efficiency, CH4 • Dry cows Milk yield, placental fxn, nulliparous heifers • In utero programming Reproduction, mammary development • Longevity effects of heat stress?
Slide 3: Heat Stress Effects on Yield Vary with DIM
HEAT STRESS EFFECTS ON YIELD VARY WITH DIM Figure 1. The milk yield responses of early (A), mid (B) and late (C) lactation heat- stressed or cooled cows during the treatment and post-treatment (gray area) periods. At each stage of lactation, cows had similar milk yield prior to the initiation of hea
Slide 4: Heat Stress Effects on Efficiency Vary with DIM
HEAT STRESS EFFECTS ON EFFICIENCY VARY WITH DIM Figure 2. The milk yield/DMI ratio of early (A), mid (B) and late (C) lactation heat-stressed or cooled cows. At each stage of lactation, cows had similar milk yield/DMI ratio prior to the initiation of heat treatment (Pre-HS). The Pre- HS milk yield/D
Slide 5: Heat Stress Reduces Total Daily CH4, Increases Yield and Intensity
HEAT STRESS REDUCES TOTAL DAILY CH4, INCREASES YIELD AND INTENSITY 370 18 14 CH4 intensity grams/Kg of ECM CH4 yield grams/Kg of DMI 350 16 12 Total CH4 grams/day 10 14 330 8 12 310 6 10 4 290 8 2 270 6 0 CL HS CL HS CL HS Trt 0.0016 Trt 0.0001 Trt 0.0039 Period 0.0001 Period 0.0754 Period 0.3472 Tr
Slide 6: Heat Stress Effects on Yield Persist
HEAT STRESS EFFECTS ON YIELD PERSIST Tao & Dahl, J. Dairy Sci. 96:4079-4093
Slide 7: Dam
Milk yield? Metabolism? Immune function? Placental Function? Late gestation DAM vs. DAUGHTER Cow performance? Thermoregulation? Survival? Calf health? Calf growth? Heifer growth? Reproduction?
Slide 8: Gainesville, Florida, USA
Gainesville, Florida, USA • Sand bedded free stalls • Fans over stalls • Soakers over feedline • Fans on at 70o F (21.1oC) • Soakers on 1 min every 5 min at 72o F
Slide 9: Cooling Dry Cows Increases Milk
COOLING DRY COWS INCREASES MILK 45 Treatment effect: P = 0.03 40 Milk Production, kg/d 35 30 25 20 15 10 5 0 1 4 7 10 13 16 19 22 25 28 31 34 37 40 Weeks in milk Tao et al., J. Dairy Sci. 94:5976–5986
Slide 10: Cooling Dry Cows Increases Milk
COOLING DRY COWS INCREASES MILK 50 Heat Stressed 45 Cooled 40 Milk, kg/d 35 30 25 20 15 10 5 0
Slide 11: Heat Stress Decreases Alveoli Number
HEAT STRESS DECREASES ALVEOLI NUMBER H&E Stain
Slide 12: Dry in Cool Months Improves Performance
Dry in COOL Months Improves Performance Thompson & Dahl, Prof. Anim. Sci. 28:628-631
Slide 13: Dry in Cool Months Improves Reproductive Performance
Dry in COOL Months Improves Reproductive Performance Thompson & Dahl, Prof. Anim. Sci. 28:628-631
Slide 14: Late Gestation Cooling
LATE GESTATION COOLING • Do I have to cool cows the entire dry period? • Do heifers need to be cooled pre- partum?
Slide 15: Heat Stress Increases Rectal Temperature and Respiration Rate
HEAT STRESS INCREASES RECTAL TEMPERATURE AND RESPIRATION RATE Fabris et al. , J. Dairy Sci. 102:5647-5656.
Slide 16: Heat Stress Decreases Gestation Length and Dry Period Length
HEAT STRESS DECREASES GESTATION LENGTH AND DRY PERIOD LENGTH AT ANY TIME P < 0.05 P < 0.05 P < 0.05 P < 0.05 P = 0.05 P = 0.05 Fabris et al. , J. Dairy Sci. 102:5647-5656.
Slide 17: Heat Stress Alters Placental Function: Estrone Sulfate
Heat Stress Alters Placental Function Estrone Sulfate: Shade vs. No Shade Collier et al., J. Anim. Sci. 54:309–319.
Slide 18: Heat Stress Alters Placental Function: Pregnancy Specific Protein B
Heat Stress Alters Placental Function Pregnancy Specific Protein B: HT vs. CL Thompson et al., J. Anim. Sci. 91:168–173
Slide 19: Dry Period Heat Stress Reduces Placental Capacity
DRY PERIOD HEAT STRESS REDUCES PLACENTAL CAPACITY Casarotto et al. , J. Dairy Sci. 108:1125- 1137.
Slide 20: Heat Stress in Dry Period Reduces Milk Yield
HEAT STRESS IMPOSED AT ANY TIME IN THE DRY PERIOD REDUCES MILK YIELD P P < 0.05 Fabris et al. , J. Dairy Sci. 102:5647-5656.
Slide 21: Effects on First Calf Heifers: Cooling Decreases RR and RT
EFFECTS ON FIRST CALF HEIFERS: COOLING DECREASES RR AND RT Week Relative to Calving Week Relative to Calving Davidson et al, J. Dairy Sci. 104:2357-2368
Slide 22: Effects on First Calf Heifers: Cooling Increases Yield
EFFECTS ON FIRST CALF HEIFERS: COOLING INCREASES YIELD Davidson et al, J. Dairy Sci. 104:2357-2368
Slide 23: Daughter
Milk yield? Metabolism? Immune function? Placental Function? Late gestation DAM vs. DAUGHTER Cow performance? Thermoregulation? Survival? Calf health? Calf growth? Heifer growth? Reproduction?
Slide 24: Cooling Increases Calf Birth Weight
COOLING INCREASES CALF BIRTH WEIGHT 45 Treatment effect: P < 0.01 Birth Weight, kg 40 35 30 36.7 kg 42.4 kg 25 20 Heat stress Cooling Tao et al., J. Dairy Sci. 95:7128-7136
Slide 25: Cooling Improves Total IgG and AEA
COOLING IMPROVES TOTAL IgG AND AEA 40 3,000 30 Heat Stress AEA, % 20 2,500 Cooling Total IgG (mg/dl) 10 0 2,000 Heat stress Cooling 1,500 1,000 500 0 1 2 3 4 5 6 7 8 9 10111213141516171819202122232425262728 Days of Age Tao et al., J. Dairy Sci. 95:7128-7136
Slide 26: In Utero HT Accelerates Gut Closure
IN UTERO HT ACCELERATES GUT CLOSURE Ahmed et al. , JDS Commun. 2:https://doi.org/10.3168/jdsc.2021-0098.
Slide 27: Retrospective Analysis of Calf Records from Studies 2007–2011
Retrospective analysis of records of calves from 5 studies between 2007 and 2011 Monteiro et al. , J. Dairy Sci. 99:8443-8450.
Slide 28: Heat Stress Experiments 2007 - 2011
Heat Stress Experiments 2007 - 2011 Bulls Heifers Total Cooling 31 41 72 Heat Stress 30 44 74 Total 61 85 147 Monteiro et al. , J. Dairy Sci. 99:8443-8450.
Slide 29: In Utero Heat Stress Decreases Calf Bodyweight to Puberty
IN UTERO HEAT STRESS DECREASES CALF BODYWEIGHT TO PUBERTY 400 350 Cooling Heat Stress 300 Body Weight (kg) 250 trt: P < 0.05 200 150 100 50 P = .03 0 0 2 3 4 5 6 7 8 9 10 11 12 Months of Age Monteiro et al. , J. Dairy Sci. 99:8443-8450.
Slide 30: In Utero HS Decreases Calf Survival
IN UTERO HS DECREASES CALF SURVIVAL Monteiro et al. , J. Dairy Sci. 99:8443-8450.
Slide 31: In Utero HS Decreases Reproductive Performance
IN UTERO HS DECREASES REPRODUCTIVE PERFORMANCE Monteiro et al. , J. Dairy Sci. 99:8443-8450.
Slide 32: AMH Concentrations Were Higher in CL Calves
AMH CONCENTRATIONS WERE HIGHER IN CL CALVES FROM D1 TO D56 Cooled Heat Stressed Anti-Müllerian Hormone, pg/ml 2000 1500 # 1000 ** ** ** ** 500 ** Trt: 0.03 ** # Day: <0.0001 Trt*Day: 0.02 0 1 7 14 21 28 35 42 49 56 Days of Age Davidson et al. , J. Dairy Sci. 104:Abstract.
Slide 33: Ovarian Size in Heifers at Birth and D63
CLOvarian HEIFERS:size was notOVARIAN INCREASED differentSIZE at AT birth D63 In utero cooled In utero heat stressed 25 10 1500 800 Ovary Volume, mm3 Ovary Length, mm Ovary Weight, mg 20 8 Ovary Width, mm 600 1000 15 6 Birth 10 4 500 400 200 5 2 D63 0 0 0 0 Trt: 0.58 Trt: 0.72 Trt: 0.66 Trt: 0.58 #
Slide 34: In Utero Heat Stress Reduces Mammary Development
IN UTERO HEAT STRESS REDUCES MAMMARY DEVELOPMENT Dado-Senn et al. , J. Anim. Sci. 100:1-11.
Slide 35: In Utero Heat Stress Reduces Mammary Development
IN UTERO HEAT STRESS REDUCES MAMMARY DEVELOPMENT Dado-Senn et al. , J. Anim. Sci. 100:1-11.
Slide 36: In Utero Heat Stress Reduces Milk Production
IN UTERO HEAT STRESS REDUCES MILK PRODUCTION P = .03 Monteiro et al. , J. Dairy Sci. 99:8443-8450.
Slide 37: In Utero Heat Stress Does Not Affect Mature Bodyweight
IN UTERO HEAT STRESS DOES NOT AFFECT MATURE BODYWEIGHT P = .03 Monteiro et al. , J. Dairy Sci. 99:8443-8450.
Slide 38: In Utero Heat Stress Alters Lifetime Yield
In Utero Heat Stress Alters Lifetime Yield 1st Lactation; 2.2 kg/d 3rd Lactation; 3.9 kg/d 2nd Lactation; 2.3 kg/d Laporta et al. , J. Dairy Sci. 103:7555-7568.
Slide 39: In Utero Heat Stress Reduces Survival in Herd
IN UTERO HEAT STRESS REDUCES SURVIVAL IN HERD Laporta et al. , J. Dairy Sci. 103:7555-7568.
Slide 40: Impact on Longevity?
IMPACT ON LONGEVITY? - In utero HT induces fetal programming - Alters methylation patterns in multiple tissues, ages - Phenotype persists to F2
Slide 41: Birth Season Impacts Cow Longevity in Florida
Birth Season Impacts Cow Longevity in Florida Cool Season THI= 58.4 ± 0.5 Hot Season THI= 77.0 ± 0.2 Lactation Cow Birth Season Number Number Cool Season Hot Season 5 968 686 282 6 423 321 102 7 129 96 33 8 47 26 21 Total Cows 1,567 1,129 (72%) ** 438 (28%) ** ** P < 0.01 Toledo et al., 2024 JDS Com
Slide 42: Birth Season Impacts Cow Longevity in California
Birth Season Impacts Cow Longevity in California Cool Season THI= 52.7 ± 0.5 Hot Season THI= 73.5 ± 0.2 Lactation Cow Birth Season Number Number Cool Season Hot Season 5 908 484 424 6 507 318 189 7 204 108 96 8 50 29 21 Total Cows 1,669 939 (56.3%) ** 730 (43.7%) ** ** P < 0.01 Toledo et al., 2024 J
Slide 43: Hot Birth Season Increases Cows Sold for Reproductive, Feet and Leg Issues, Mastitis
Hot Birth Season Increases Cows Sold for Reproductive, Feet and Leg Issues, Mastitis Toledo et al., 2024 JDS Communications. 5:674-678.
Slide 44: California: Birth Season Alters Death Loss
California: Birth Season Alters Death Loss Toledo et al., 2024 JDS Communications. 5:674-678.
Slide 45: Birth Season Affects Dairy Cow Longevity
Birth Season Affects Dairy Cow Longevity Birth Season Cow Longevity Cows Longevity Cows Sold Cows Dead Toledo et al., 2024 JDS Communications. 5:674-678.
Slide 46: rs gestation FO “~_. lactation FO
rs gestation FO “~_. lactation FO Mammary gland ae production < @—e— e™ voltae Mammary protein expression Behavior e B involution _ Gestation length _ Cell proliferation ¢ Ag ys ? Cotyledon number and surface | ==> DNA methylation 1 Lactation F1 2™ Lactation F1 3” Lactation F1 — - =) = © ™] ‘Birth w