Effects of evaporative cooling on the regulation of body water and milk production in crossbred Holstein cattle in a tropical environment

Abstract

The aim of this study was to determine how evaporative cooling modifies body function with respect to water metabolism and other variables relevant to milk synthesis in crossbred cattle. The study was conducted on two groups of 0.875HF:0.125RS crossbred Holstein cattle (87.5%) housed in an open-sided barn with a tiled roof (non-cooled animals) and in a close-sided barn under an evaporative cooling system (cooled animals). The maximum ambient temperature and relative humidity for the non-cooled group were 33 degrees C and 61%, with the corresponding values for the evaporatively cooled barn being 28 degrees C and 84%, respectively. The temperature humidity index (THI) of under non-cooled conditions was higher (P < 0.05) than that in the cooled barn. Rectal temperatures and respiration rates of non-cooled animals were higher (P < 0.05) than those of cooled animals. Daily dry matter intake (DMI) of cooled animals was higher while water intakes were lower (P < 0.05) than those of non-cooled animals. The mean absolute values of plasma volume, blood volume, and extracellular fluid (ECF) of cooled animals were significantly higher (P < 0.05) than those of non-cooled animals throughout all stages of lactation. Milk yields of cooled animals were higher by 42%, 36% and 79% on average than those of non-cooled animals during early-, mid- and late-lactation, respectively. The decline in milk yields as lactation advances was markedly apparent in late-lactating non-cooled animals, while no significant changes in milk composition at different stages of lactation were observed in either group. Mean arterial plasma concentrations, arteriovenous concentration differences (A-V differences) and the extraction ratio across the mammary gland for acetate, glucose and triglyceride of cooled animals were not significantly different compared with values for non-cooled animals. No differences were seen in plasma hormonal levels for triiodotyronine (T(3)) and insulin-like growth factor-1 (IGF-1), but plasma cortisol and thyroxine (T(4)) levels tended to be lower in non-cooled animals. This study suggests that low cooling temperature accompanied by high humidity influences a galactopoietic effect, in part through increases in ECF, blood volume and plasma volume in association with an increase in DMI, which partitions the distribution of nutrients to the mammary gland for milk synthesis. Cooled animals were unable to maintain high milk yield as lactation advances even though a high level of body fluids was maintained during long-term cooled exposure. The decline in milk yield, coinciding with a decrease in net energy for lactation as lactation advances, could be attributed to a local change within the mammary gland.

Heat stress and ACTH administration on cortisol and insulin-like growth factor I (IGF-I) levels in lactating Holstein cows

“…Similar results were previously described (McGuire et al 1991;Hirayama et al 2004;Chaiyabutr et al 2008). Other authors, in opposition to the aforesaid, reported that bovine somatotropin treatment, under heat stress, increased milk production, IGF-I release and RT in dairy cows (Sarko et al 1994;Jousan et al 2007).…”

“…In the same way, while some authors have reported that growth hormone (GH) and insulin-like growth factor I (IGF-I) are negatively influenced by heat stress (Sarko et al 1994;Rhoads et al 2010;Wheelock et al 2010), others mentioned that IGF-I levels during heat stress are similar to those obtained within thermal comfort zone (McGuire et al 1991;Hirayama et al 2004;Chaiyabutr et al 2008;Collier et al 2008). For these reasons, the interactions between heat stress and CORT and between IGF-I and environmental heat remain controversial.…”

“…During heat stress, dairy cows expend more energy for circulatory adjustments to increase respiratory rate (RR), sweating and panting (Srikandakumar & Johnson 2004). In those animals, heat stress has also been associated with lower food intake, increase in the negative energy balance and loss in milk production (Igono et al 1992;Chaiyabutr et al 2008;Shehab-El-Deen et al 2010). In general, cortisol (CORT) is an appropriate biological endpoint for the investigation of hypothalamic-pituitary-adrenal (HPA) axis, and exogenous administration of adrenocorticotropic hormone (ACTH) can be used to study the relationship between the HPA axis activity, cortisol release and stress in domestic animals (Negrão et al 2004(Negrão et al , 2010.…”

“…Although some studies have demonstrated that CORT levels are not related to heat stress (Ronchi et al 2001;Zähner et al 2004;Chaiyabutr et al 2008), others have associated it with high CORT levels (Satterlee et al 1977;Du Preez 2000). These results can be explained by the acclimation, which is a process driven by the endocrine system to preserve animal welfare regardless of environmental challenges (Bernabucci et al 2010).…”

Prediction of drinking water intake by dairy cows

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