# Presentation: 730649

## Effect of temperature and humidity on gestation length

*H.D. Norman, J.R. Wright,* and J.B. Cole*
- Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350

- Abstr. M38

- _INTRODUCTION_
- High temperature and humidity have been shown to affect production traits but their effects on other traits has not been examined.
- More accurate prediction of gestation length (GL) could aid herd managers in assuring that appropriate nutrition and health actions are given to pregnant cows at the optimal time.

- _OBJECTIVES_
- Determine if monthly differences in GL are caused by temperature and humidity.
- Determine how various measures of temperature and humidity account for differences in GL.

- _DATA & METHODS __*(cont.)*_
- Edits:
- Inseminations initiating gestation must have been after February 1998 and subsequent calving parturition must have been before January 2006
- Holstein with >86% breed purity based on AIPL crossbred database
- Matings to identified AI sires only
- 10% sample selected for analysis (477,068 conceptions)
- Model:
- 	GL =	calf conception year
- 				(4 heifer groups, 8 cow groups)
- 			+ calf conception herd-year (absorbed)
- 			+ calf conception month (Jan., Feb., etc.)
- 			+ calf parturition code (8 groups based
- 				on multiple birth status and gender)
- 			+ age within parity at conception
- 				(5 heifer groups, 17 cow groups)
- 			+ lactation length (7 groups)
- 			+ milk yield (5 groups)
- 			+ THI (16 groups)
- 			+ residual (random)
- Analysis:
- Use SAS GLM to evaluate the following 16 measures of THI:
- Day of calving
- Individual days 1 to 13 prior to calving
- Mean THI of calving day and 6 days prior to calving (7 days)
- Mean THI of calving day and 13 days prior to calving (14 days)

- _DATA & METHODS_
- Lactation, reproductive, and dystocia records from the national dairy database at AIPL as supplied by dairy records processing centers, breed associations, and the National Association of Animal Breeders.
- Meteorological data from 238 weather stations supplied via subscription to the Southern Regional Climate Center, Louisiana State University.
- Meteorological data matched to herd ZIP code by choosing closest weather station based on distance between latitude/longitude of center of ZIP codes using Haversine formula to approximate distance.
- Trait definition:
- 		Temperature-Humidity Index (THI) =
- 			(1.8T + 32) – (0.55 – 0.0055H) (1.8T – 28)
- 	where T = temperature in Celsius and H = relative humidity expressed as a percentage.

- _RESULTS_
-  Frequency of records by THI level:
- Relationship of THI with GL:
- Comparison of various THI measures:
- 	A	=	conception year, conception herd-year, calf parturi-
- 				tion code, age within parity, lactation length, milk yield
- 		M	=	month of conception
- 		Tn	=	THI of day n prior to calving

- Model		Model
- effect(s)	R2	effect(s)	R2
**A****	****.1071****	****A,M,T****7****	****.1143**
**A,M****	****.1125****	****A,M,T****8****	****.1141**
**A,T****6****	****.1097****	****A,M,T****9****	****.1140**
**A,M,T****0****	****.1139****	****A,M,T****10****	****.1139**
**A,M,T****1****	****.1140****	****A,M,T****11****	****.1139**
**A,M,T****2****	****.1140****	****A,M,T****12****	****.1139**
**A,M,T****3****	****.1142****	****A,M,T****13****	****.1138**
**A,M,T****4****	****.1143****	****A,M,T****0-6****	****.1154**
**A,M,T****5****	****.1145****	****A,M,T****0-13****	****.1164**
**A,M,T****6****	****.1145**

- http://aipl.arsusda.gov/

- _RESULTS __*(cont.)*_
- Adding THI to the model including conception month increased prediction of GL only slightly.
- Only small differences between were found between various THI measures.
- THI measured at days 5 and 6 were slightly more effective than other single-day measures.
- THI mean of 7 days or 14 days was more useful in helping to predict GL than single-day measures.
- Solutions by THI group for model including all effects, conception month, and THI at 6 days prior to calving:

- _RESULTS __*(cont.)*_
- Adding THI to the model including conception month increased prediction of GL only slightly.
- Only small differences were found between various THI measures.
- THI measured at days 5 and 6 were slightly more effective than other single-day measures.
- THI mean of 7 days or 14 days was more useful in helping to predict GL than single-day measures.
- Solutions by THI group for model including all effects, conception month, and THI at 6 days prior to calving:

- _CONCLUSIONS_
- THI is useful in predicting GL but has limited value when conception month is included in the model.
- Effectiveness of THI in predicting GL is greater at higher temperatures.