Sumpun Thammacharoen

Effects of long-term administration of recombinant bovine somatotropin on milk production and plasma insulin-like growth factor and insulin in crossbred Holstein cows

The objective of the study was to determine the in vivo relationship between the long-term administration of recombinant bovine somatotropin (rbST), circulating levels of IGF-I and insulin, mammary blood flow and other variables relevant to milk synthesis, in crossbred, Holstein cattle. Ten first-lactation, non-pregnant, crossbred, Holstein dairy cattle were divided into two groups of five animals each: an experimental group and a control group. Animals in each group were fed with rice straw, treated with 5 kg urea dissolved in 100 litres water per 100 kg dry rice straw as the source of roughage. Four consecutive study periods were carried out in each group. These consisted of a pretreatment period (45 days postpartum before lactation peak) and three treatment periods during early lactation (105 days postpartum), mid-lactation (165 days postpartum) and late lactation (225 days postpartum). During the treatment periods, animals that had completed 60 days of lactation were injected subcutaneously at fortnightly intervals with 500 mg of recombinant bovine somatotropin (rbST) (POSILAC, Monsanto, USA) in the experimental group, while animals in the control group were injected subcutaneously at fortnightly intervals with 800 mg of sterile sesame oil, without rbST, as a placebo. During the pretreatment period, there were no significant differences in plasma concentrations of IGF-I, insulin and other parameters between the control group and the experimental group. During the treatment periods, the increase in the concentration of plasma IGF-I in rbST treated animals was significantly higher than in the control animals throughout the lactation period. Plasma glucose, protein and triglyceride concentrations in each group remained stable throughout the study. The total daily dry matter intakes were not significantly different between the groups. Milk yield increased by 20% with rbST treatment and it was 22% greater than that of the control animals receiving placebo in early lactation. Milk yield of rbST treated animals rose to a peak in early lactation and then gradually declined. In late lactation, milk yield of rbST-treated animals decreased by 19% as compared with early lactation. Udder plasma flow and udder blood flow markedly increased with rhST treatment and there were no significant changes in the control animals. The ratio of udder blood flow to the rate of milk production increased in mid- and late lactation in controls and the rbST treated animals. These findings suggest that the short persistency of lactation in rbST treated animals was similar to that in the control animals receiving placebo. Changes in milk production during the progress of lactation in rbST treated animals might not be controlled systemic;lily only but also locally within the mammary gland. The lack of effect of higher plasma IGF-I levels on persistency of lactation in rbST treated animals, may be due to changes in the pattern of IGF-I binding proteins and paracrine production inhibiting IGF-I action.

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

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 animals (P<0·05). The relative values of both TOH and TBW as a proportion of body weight of control animals decreased, while no alteration was apparent in rbST-treated animals during the course of treatments. These differences were statistically significant (P<0·05). The absolute values of empty body water (EBW) of the control animals showed no significant changes, while animals treated with rbST tended to increase in absolute values of EBW throughout the course of treatments. The effects of these differences were statistically significant (P<0·05). There were no significant changes in relative values of EBW during the course of treatments in both controls and rbST-treated animals. These data demonstrated that the rbST exerts its galactopoietic action in part through increases in TBW, EBW and ECW in association with an increase in MBF, which partitions the distribution of nutrients to the mammary gland for milk synthesis. During this long-term administration of rbST, the stimulant effect for milk yield was less in late lactation despite a higher MBF. The decline in milk yield during rbST treatment without fall in MBF in late lactation must be attributed to a local change within the mammary gland.

A low degree of high ambient temperature decreased food intake and activated median preoptic and arcuate nuclei

High ambient temperature (HTa) activates both behavioral and autonomic responses. Decreased food intake (FI) is a well-known behavioral response under HTa. In general, this behavioral response seems to be mediated under the activation of the stress axis. The present study, however, revealed that decreased FI after a low degree of HTa appeared to be activated earlier than stress axis activation. By comparing low and high levels of HTa exposure in rats, the present experiment demonstrated that the HTa-induced decrease in FI was clear in both conditions. However, only the high degree HTa rats showed prominent physiological responses to HTa. The results indicated that low degree HTa exposure decreased FI earlier than activated physiological responses. Using the low degree HTa condition, the next experiment revealed that only the median preoptic nucleus (MnPO) and arcuate nucleus (Arc) were activated. These results suggested that the MnPO and Arc (MnPO-Arc) are apparently involved in the low degree HTa effect on FI and that the paraventricular hypothalamic nucleus, which is the upper part of the stress axis, was not associated with this effect. A separate experiment also showed no differences in the corticotropin-releasing factor (CRF) concentrations from many selected nuclei. This result suggested that the effect of HTa to decrease FI via the MnPO-Arc was not associated with CRF. The current findings introduce a new behavioral aspect of the HTa effect on FI, representing important information to explain the mechanism of obesity relative to environmental conditions.

The effect of dietary ions difference on drinking and eating patterns in dairy goats under high ambient temperature

Objective The present study was carried out to evaluate the effect of high dietary cation and anion difference (DCAD) rations on diurnal variations in eating and meal patterns, water intake and urination patterns in dairy goats fed under high ambient temperature (HTa). Methods Ten crossbred dairy goats during peri-parturition period were selected and divided into two groups of five animals each. Experimental diets were control DCAD (control, 22.8 mEq/100 g dry matter [DM]) and high DCAD (DCAD, 39.1 mEq/100 g DM). The composition of two diets consisted of 44% corn silage and 56% concentrate. From the 2nd week to 8th week postpartum, goats were fed ad libitum twice daily either with the control or DCAD total mix ration with free access to water. The spontaneous eating and drinking patterns were determined. Results The environmental conditions in the present experiment indicated that goats were fed under HTa conditions (average peak THI = 85.2) and were in heat stress. In addition to the typical HTa induced tachypnoea in both groups, the respiratory rate in the DCAD group was significantly higher than the control group (p<0.05). Although the goats from both groups showed comparable level of eating, drinking and urination during experiment, the meal pattern and water intake were different. High DCAD apparently increased eating and meal patterns compared with the control. At week 8 postpartum, goats from high DCAD group had significant (p<0.05) bigger meal size and longer meal duration. Moreover, high DCAD appeared to increase night-time water intake (p<0.05). Conclusion Both meal pattern and night-time drinking effects of DCAD suggested that feeding with high DCAD ration may alleviate the effect of heat stress in dairy goat fed under HTa conditions.

Effects of Hindbrain Infusion of an Estrogen Receptor Antagonist on Estrogenic Modulation of Eating Behavior

Estradiol (E2) inhibits eating behavior in females via activating estrogen receptors (ERs) within the brain. Activation of hindbrain ERαs has been shown to be sufficient to inhibit eating behavioral pattern. To investigate the involvement of hindbrain ERαs in estrogenic control of eating behavior, intracerebroventricular infusion (4th i.c.v.) of an estrogen receptor antagonist, ICI 182780 (ICI), was performed in ovariectmized female rats. Significantly lower daily food intake was observed in rats after estradiol benzoate (EB) injections. The effect of EB on food intake was significantly compromised by 4th i.c.v. infusions of both 4 and 8 nM ICI solutions. The results suggest that hindbrain infusions of ICI can significantly attenuate the inhibitory effect of E2 on food intake. Importantly, 4th i.c.v. infusions during 12 days exerted no effect per se on eating. Further, there was no difference in the number of ERα immunopositive neurons in the selected hypothalamic nuclei and nucl. tractus solitarius. We conclude that the 4th i.c.v. infusions with ICI attenuated the exogenous estrogenic effect on food intake in ovariectomized rats, and the hindbrain is an important site pro viding estrogenic control of food intake.