Relationship of Thermal Status to Productivity in Heat-Stressed Dairy Cows Given Recombinant Bovine Somatotropin

Abstract

The responses of lactating Holstein cows to daily administration of bovine somatotropin (bST) were measured at thermoneutrality (Tn) and under both constant and cycled heat-stress conditions to determine the relationship between thermal status and bST-induced shifts in milk production. All tests included a 5-d acclimation period at Tn (18 degrees C), followed by a 2-d increase in ambient temperature to 28.5 degrees C. After d 3, ambient temperature was cycled between 28.5 (day) and 25.5 degrees C (night) for 4 d. Daily injections with either 31 mg of bST or saline began on d 1 of the experiment. Milk production, feed intake, and respiratory rate (RR) were measured daily. Intraperitoneal, telemetric temperature transmitters were used for a continuous measure of core body temperature (T(core)). Blood samples were collected during each phase to evaluate the changes in serum chemistry in response to bST and heat stress. Following a 15-d recovery, cows were switched across injection treatments and the study was repeated. Milk production decreased by approximately 18.4% below the initial yield at Tn by the end of 7 d of heat challenge. Although a reduction in milk production occurred during heat stress in both groups, milk production was higher in bST-treated cows compared with control cows during periods of constant and cyclic heat. Likewise, bST treatment during the entire period increased the milk-to-feed ratio over the control level by approximately 11.3%. Plasma insulin-like growth factor 1 and serum nonesterified fatty acids accompanied the increased growth hormone level with bST treatment (approximately 122.0 and 88.8%, respectively), whereas plasma urea nitrogen was reduced by approximately 13.3% to reflect the shift to lipid metabolism. There was no difference in T(core) of the treatment and control groups at Tn. Both bST and control cows increased RR and T(core) above the Tn level by approximately 94.8 and 2.9%, respectively, during constant heat, with a greater increase in T(core) of bST-treated compared with control cows (approximately 0.6%). The increase in RR during heat stress preceded T(core) by 1 d for both groups. During cyclic heat, T(core) decreased by approximately 0.4% compared with constant heat in both the control and bST-treated groups. Bovine somatotropin treatment increased milk production similarly during the Tn and heat-stress periods, approximately 8.3% over the control; however, the bST-induced increase in milk-to-feed ratio was greatest during the continuous and cyclic heat-stress phases, approximately 16.2%. This increase occurred together with the elevation in T(core).

The Effect of Thermal Environment on Daily Milk Yield of Dairy Cows

“…Therefore, higher yielding dairy cows need a longer period of acclimatization to reach milk production on a level similar to the one before the heat stress. Settivary et al (18) indicate that negative effect of heat stress on milk production is delayed up to 4 days after the end of an induced thermal stress. Heat stress compromises lactational performance not only when occurring during lactation (5), but also during the nonlactating period before parturition.…”

Effect of Age at First Calving on First Lactation Milk Yield in Holstein Cows from Costa Rican Specialized Dairy Herds

“…Among the environmental conditions related to productivity are the temperature [26], the relative humidity [27], the solar radiation [28], the wind speed [29], the length of day [30] and the daily rainfall [31]. In this case, the high precipitation could be one of the most important factors contributing to declining milk production in these areas, where the highly acidic soil, poor in microelements and low fertility, limiting the suitable growth and the protein content of the pastures [32].…”

Enfriamiento al inicio de verano para mitigar el estrés por calor en vacas Holstein del noroeste de México

“…It is important to mention that cows from this study received a subcutaneous application of bovine somatotropin (STB) as part of the herd management. The STB is a synthetic hormone with similar function to GH in bovine cattle, and its exogenous application is a potential enhancer of heat load in lactating cows under heat stress (13,30,31) , as well as blood concentrations of IGF1 (32)(33)(34)(35) . Therefore, administration of STB in this study could induce a direct effect on IGF1 levels, and consequently on PRL levels.…”

“…Vale la pena señalar que las vacas de este estudio recibían la aplicación de un producto comercial como manejo habitual a base de somatotropina bovina (STB). La STB es una hormona sintética cuya función es similar a la GH en el bovino y su administración exógena incrementa potencialmente la carga de calor en ganado lactante bajo estrés calórico (13,30,31) , así como también la concentración de IGF1 en sangre (32,33,34,35) . Por lo tanto, la administración de STB en este trabajo pudo inducir un efecto directo sobre los niveles de IGF1 y consecuentemente en los de PRL.…”