An in vivo model to assess the thermoregulatory response of lactating Holsteins to an acute heat stress event occurring after a pharmacologically-induced LH surge.
J Therm Biol
; 78: 247-256, 2018 Dec.
Article
en En
| MEDLINE
| ID: mdl-30509643
Hyperthermia occurring 10-12â¯h after LH surge reduces quality of maturing oocyte, thereby reducing fertility. Objective was to examine consequences of an acute heat stress and the influence of certain hormones on the thermoregulatory responses of lactating cows during this critical period. Between the months of February through May, cows were transported to a facility and maintained at a temperature-humidity index (THI) of 65.9⯱â¯0.2 (thermoneutral) or exposed to changes in THI to simulate what may occur during an acute heat stress event (71-86â¯THI; heat stress); cows were rapidly cooled thereafter. Mixed model regressions with repeated measures were used to test respiration rates (RR) and rectal temperature (RT). Within 40 and 110â¯min of increasing THI, RR increased in a quadratic fashion (Pâ¯<â¯0.001); RT increased by 0.04⯱â¯0.1⯰C (Pâ¯<â¯0.001) per unit THI. Changes in RR lagged THI and preceded rises in RT. Average THI 3-days before treatment (prior THI) influenced RR (Pâ¯=â¯0.050) and RT (Pâ¯<â¯0.001) changes. Increased RR was more noticeable in heat-stressed cows when prior THI was in the 40â¯s. Rectal temperature of heat-stressed cows was 0.8⯱â¯0.02⯰C lower when prior THI was in the 40â¯s versus low 60â¯s. Levels of progesterone and luteinizing hormone before treatment were predictive of thermoregulatory response in heat-stressed cows. Rapid cooling decreased RR by 0.6⯱â¯0.1 bpm (Pâ¯<â¯0.001) and RT by 0.02⯱â¯0.002⯰C per min (Pâ¯<â¯0.002). Speed and magnitude of thermoregulatory changes to an acute heat stress and after sudden cooling emphasizes importance of strategic cooling before ovulation. Efforts to do so when prior THI approaches levels expected to induce mild stress are especially important. Respiration rate is a useful indicator of the degree of hyperthermia a lactating cow is experiencing.
Palabras clave
Texto completo:
1
Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Regulación de la Temperatura Corporal
/
Lactancia
/
Bovinos
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Hormona Luteinizante
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Respuesta al Choque Térmico
Tipo de estudio:
Prognostic_studies
Límite:
Animals
Idioma:
En
Revista:
J Therm Biol
Año:
2018
Tipo del documento:
Article
País de afiliación:
Estados Unidos
Pais de publicación:
Reino Unido