Effects of acute thermal stress and amount of feed intake on concentrations of somatotropin, insulin-like growth factor (IGF)-I and IGF-II, and thyroid hormones in plasma of lactating Holstein cows2

Abstract

Our objective was to evaluate effects of acute thermal stress, independent of reduced feed intake caused by elevated temperatures, and of reduced feed intake in thermal comfort on plasma concentrations of somatotropin, insulin-like growth factors I and II, thyroxine, and triiodothyronine. Six Holstein cows (averaging 475 +/- 18 kg BW, 2.3 +/- .3 parities, and 96 +/- 12 d in lactation) surgically fitted with catheters in the hepatic portal vein, mesenteric vein, and intercostalis posterior artery were exposed to treatments of thermal comfort environments with ad libitum or restricted (75% of ad libitum) DM intake and a thermal stress environment with ad libitum intake in two balanced 3 x 3 Latin squares. Thermal stress increased rectal temperatures and respiration rates. Dry matter intake of the thermal-stressed cows offered feed ad libitum (11.1 +/- .7 kg/d) was similar to the experimentally imposed reduction in DM intake of the thermal comfort restricted group (11.5 +/- .7 kg/d). Dry matter intake of cows in thermal comfort was 15.1 +/- .7 kg/d. Plasma somatotropin concentrations tended (P less than .08) to decrease during thermal stress but were unchanged by amount of feed intake in thermal comfort environments. Concentrations of IGF-I were not affected by treatments. Concentrations of IGF-II tended (P less than .14) to increase with thermal stress compared with thermal comfort treatments. Thyroxine concentrations tended (P less than .15) to increase in the thermal stress treatment compared with the thermal comfort restricted intake treatment. Triiodothyronine tended (P less than .11) to decrease with restriction in feed intake in the thermal comfort environment.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic changes in early lactation and impaired reproductive performance in dairy cows

“…Thyroid hormones tended to decrease during feed restriction [65]. From recent epidemiological studies, thyroid hormones are suggested to play a role in the onset of ovarian activity.…”

“…Because the amount of stored body fat and the mobilization of fat is reflected in blood leptin concentrations, changes with regard to the concentration of this hormone in early lactation can be anticipated too [9,33]. Other hormones that tend to decrease during feed restriction and NEB are thyroid hormones [65] and insulin-like growth factors (IGF) [63]. These changes reflect the adaptational system of the cow which is activated in order to meet the demands for the increasing milk production and maintenance.…”

Influence of endemic goitre areas on thyroid hormones in horses

“…Thyroid hormones are important physiological indices commonly used in studies concerning metabolic rate (Chen and Riley, 1981), animal thermogenesis (McGuire et al, 1991;Bird et al, 1998), central nervous system development and changes in cognitive function in animals and humans (Schantz and Widholm, 2001;Helmreich et al, 2006;Long and Voice, 2007). Their supplementation increases the metabolic rate and promotes significant weight loss with dietary restriction (Graves and Schott, 2002).…”

Physiological variables of horses after road transport

“…Thyroid hormones are important physiologic indices which are commonly used in metabolic rate and animal -E-mail: esterina.fazio@tin.it thermogenesis studies (McGuire et al, 1991;Bird et al, 1998) and their supplementation may increase metabolic rate and promote significant weight loss with dietary restriction. In addition, hormonally mediated events play an important role in central nervous system development and function, and a number of researchers have speculated that changes in cognitive function are also mediated by thyroid hormones in humans and animals (Schantz and Widholm, 2001;Helmreich et al, 2006).…”