Temperature and humidity in the Brazilian tropical summer affecting the in vivo embryo production of Nelore breed in superovulation program

Abstract

This study used Nelore embryo donors to evaluate the effects of summer temperatures and humidity in a tropical area on embryo recovery. Seventeen cows were randomly assigned to three groups (G1, G2 and G3) as well as 28 heifers into four groups (G4, G5, G6 and G7), and underwent a consecutive 4 d superovulation protocol (Day 0 to 3) and two artificial inseminations (AI; Day 4 and 5). Cortisol concentrations were determined on Day 0, 4 and 5. Temperature and humidity index (THI) was recorded from Days 0 to 7. Embryos were recovered on Day 11, and evaluated for quality and quantity. Heifers experienced higher thermal load than cows, however, there was no difference in the cortisol and reproductive parameters measured between both. The THI measured throughout the experiment oscillated between 65.8 and 85.2 (76.1 ± 3.9), which is a dangerous range for thermal comfort, especially above 78. Animals from G5 were subjected to high THI throughout the experimental protocol, approaching a dangerous condition (78.7 ± 0.9) on Day 4 (first AI). The THI for G2 cattle was also high, as in the other groups, but increased to over 80 two days after AI. Animals from group G5 had the lowest viable production being 2.4 ± 0.9 embryos (38% of viability), followed by cattle from group G2 (3.0 ± 0.9 viable, P<0.05). Thus, high thermal load in the summer expressed by high THI, on the day and post- insemination days (during embryo cleavage), compromises embryo numbers, viability and consequently reproductive performance of Nelore females.

Shading effect on physiological parameters and in vitro embryo production of tropical adapted Nellore heifers in integrated crop-livestock-forest systems

“…When the ambient temperature reaches critical temperatures higher than TCZ, the efficiency of the heat loss processes is reduced and the animal enters heat stress (HS) (Silanikove 2000), which leads to a consequent activation of thermoregulation mechanisms (Rodrigues et al 2010). As responses, changes in animal behavior, body temperature, respiratory frequency, heart frequency, and sweating rate (Paranhos da Costa 2004), as well as alterations in adrenal activity and immune response, are observed (Geraldo et al 2012), Macedo and Zúccari 2012). Reduction of weight gain (Navarini et al 2009), food consumption (Geraldo et al 2012), and consequently a reduction on reproductive performance has also been reported (Lima et al 2013).…”

Importance of the silvipastoral system on the animal health and welfare of dairy cattle

“…According to Silanikone (2000), when the environmental temperature exceeds the ZCT the thermolysis mechanisms are reduced and the animal goes into heat stress and this leads to a consequent inactivation of thermoregulatory processes (RODRIGUES et al, 2010). As a response to heat stress, changes in the animal's behavior, body temperature, respiratory rate, as well as changes in the activity of the autonomous nervous system and immunity of the animals will be observed (PARANHOS DA COSTA 2004;GERALDO et al 2012;MACEDO;ZÚCCARI 2012).…”