Effects of long-term exogenous bovine somatotropin on water metabolism and milk yield in crossbred Holstein cattle

Abstract

The present study was conducted to evaluate the effects of long-term administration of recombinant bovine somatotropin (rbST) on the regulation of body fluids, mammary blood flow (MBF) and other variables relevant to milk synthesis, in crossbred dairy cattle (0·875 of Holstein–Friesian (HF) genes and 0·125 Red Shindi (RS) genes. Ten first lactation, non-pregnant, animals were chosen and divided into the control and experimental groups of five animals each. Four consecutive measurements were carried out in each group beginning on days 45 (pre-treatment), 105, 165 and 225 of lactation. Animals that had completed 60 days of lactation were injected subcutaneously every 14 days with 500 mg of rbST (POSILAC, Monsanto, USA) in the experimental group, while animals in the control group were injected subcutaneously every 14 days with 800 mg of sterile sesame oil, without rbST, as a control. All animals were fed with rice straw treated with 50 g urea/l as the source of roughage in combination with a similar concentrate throughout the experiments. During the treatment periods, the daily dry matter intake (DMI) was numerically greater for rbST-treated animals than for control animals, while the relative values of DMI per kg body weight and water intake showed no differences.Animals in both groups gained weight throughout the experiment with no significant differences between the groups. Animals receiving rbST for 45 days increased their peak milk yield from 13·4 kg/day per animal during pre-treatment to 15·9 kg/day per animal (18·7% increase) on day 105 of measurement and this peak yield was higher (19·5%) than those of control animals in the same period. Milk yields on days 225 in late lactation of both groups significantly decreased (P<0·05) in comparison with the early and mid-lactating periods. Over the course of the experiment, milk yield of the rbST-treated animals was significantly higher than those of the control animals (P<0·01). The administration of rbST significantly increased MBF (P<0·05) and mammary plasma flow (MPF) (P<0·01). The ratio of MBF to milk yield slightly increased as lactation advanced in both controls and rbST-treated animals. The administration of rbST significantly increased the absolute values of both plasma volume (P<0·01) and blood volume (P<0·05) when compared with the control animals. The control animals showed no significant changes in values of extracellular water (ECW) throughout the course of treatment periods. The rbST-treated animals increased in both the absolute values and the relative (proportion of body weight) values of ECW throughout the experiment (P<0·05). The estimated values of intracellular water (ICW) in both groups showed no significant changes during the course of treatments. There were no significant changes in the water turnover rate (WTO) and the biological half-life of tritiated water in different periods of lactation in both groups. The absolute values of total body water space (TOH) and total body water (TBW) were significantly greater in rbST-treated than control an...

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

“…Thermal stress, with high body temperatures or high respiratory rates, does not in itself act as an extramammary factor causing a reduction in milk production in crossbred HF animals. Other factors might be involved, since crossbred HF animals treated with bovine somatotropin under high thermal environments have been shown to increase milk yield (Chaiyabutr et al 2007b).…”

“…The increase in ECF and TBW could be an important factor influencing the process of lactation, since increases in ECF and TBW coinciding with increased milk yield in tropical crossbred HF cattle treated with bovine somatotropin have been noted (Chaiyabutr et al 2007b). However, the pattern of progressive decline in milk yield of cooled animals, despite a higher level of both ECF and plasma volume, implies that evaporative cooling does not involve a decline in mammary function as lactation advances.…”

Effects of long‐term administration of recombinant bovine somatotropin on the concentration of metabolites in milk in different stages of lactation in crossbred Holstein cattle

“…It is known that the rate of blood flow to the mammary gland determines the rate of nutrient uptake by the mammary gland. During the long‐term administration of rbST in crossbred dairy cattle, it has been noted that milk yield increased with an increase in MBF in early lactation, but rbST has a less stimulating effect for milk yield as lactation advances to late lactation, despite a high level of MBF (Chaiyabutr et al . 2007).…”

Control of Mammary Function During Lactation in Crossbred Dairy Cattle in the Tropics

“…This proposal was indicated that humoral factors were responsible, especially the level of plasma growth hormone in the regulation of mammary circulation and milk production between 87.5%HF and 50%HF cattle. A number of studies have demonstrated that similar proportion increases in milk secretion and mammary blood flow occurred during growth hormone treatment in goats and cows (Hart et al, 1980;Chaiyabutr et al 2007). A marked decline in blood flow to the mammary gland during the transitional period from early lactation to mid-lactation in 87.5%HF cattle with the constancy of the plasma volume and blood volume were apparent (Chaiyabutr et al 2000a).…”

“…Many studies have demonstrated the efficacy of bST for improvement in milk yield (Breier et al, 1991 ;Burton et al, 1994). Long term exogenous recombinant bovine somatotropin (rbST) in 87.5% crossbred Holstein cattle increased in milk yield which accompanied with an increase in the rate of mammary blood flow, but the stimulant effect for milk yield was less in late lactation despite a high level of mammary blood flow (Chaiyabutr et al 2007). It is not known which factors are the cause and which factors are the effects for such reduction.…”