Effect of temperature - humidity index on the onset of post- partum ovarian activity and reproductive behavior in Bos indicus cows.

Ramiro Fernando Díaz,Jose Luis Pablos,Jaime Gallegos Sánchez,Emilio Manuel Aranda,Carlos Salvador Galina,Lorenzo Armando Aceves

doi:10.21451/1984-3143-ar2019-0074

Abstract

The effect of climatic factors on ovarian activity and reproductive behavior (RB) was evaluated in 46 Bos indicus cows kept under grazing conditions. Temperature-humidity index (THI) was used as an indicator of stress and divided in alert, damage and emergency levels. Fat thickness (FAT) was taken during the last trimester of gestation (LTG) to approximately 90d postpartum (PP). At 30d PP animals received a progesterone (P4)-releasing device (CIDR) which was withdrawn 9d later. Ovarian activity was assessed by blood progesterone on days 21, 24, 27, 30, 49, 51, and 54 PP. Animals were divided into three groups, higher, and moderate RB and non-behavior. Sixty percent presented a THI >74 increasing dramatically from June to September up to >78. During LTG, animals lost 27% of their body reserves contrasting to PP where an increase of 2.6% (P=0.002) was observed. The percentages of cyclic and non-cyclic animals were 57 and 43%, respectively (P> 0.05). Seventy-two percent displayed RB and 28% were non-behavior (P<0.05). A negative correlation (r = -0.307; P = 0.038) between THI and RB, and a positive correlation (r = 0.427; P = 0.003) between the onset of ovarian activity and RB were observed. Differences in THI during the LTG (P<0.01) were observed between cyclic and non-cyclic animals. Non-behavior cows in the LTG had a higher THI (P <0.05). High levels of THI have a negative effect on the resumption of ovarian activity and RB in Bos indicus especially if high THI occurs during the last trimester of gestation.

Highlights

The direct effect of climate on livestock production in the tropics has been studied for a long time (Gwazdauskas, 1985; Hansen, 2007)
Where: THI, is the temperature-humidity index; T, is the mean temperature expressed in °C; and RH, is the average relative humidity expressed in percentage
The estimators of the model effects that were selected were those with the lowest standard error according to the assumed structure of the model errors. In this case we considered the structures of independence, autoregressive of the first order (AR1), interchangeable and without structure (Song, 2007)

Summary

Introduction

The direct effect of climate on livestock production in the tropics has been studied for a long time (Gwazdauskas, 1985; Hansen, 2007). The temperature-humidity index (THI) has been widely used as an indicator of thermal stress in livestock (Hansen, 2007), forming the basis of the Livestock Weather Safety Index (Livestock Conservation Incorporated, 1970). THI above 74 has been targeted as an indicator of climatic stress for cattle (Arias et al, 2008).

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