Different responses in postprandial plasma ghrelin and GH levels induced by concentrate or timothy hay feeding in wethers.

Ghrelin and growth hormone (GH) play a key role in regulating energy balance, metabolic hormone secretion and food intake. Ghrelin and GH responses to dietary compositions have not yet been fully clarified, although there may be significant relationships between dietary compositions and ghrelin and GH responses. In the present study, therefore, we assessed whether dietary compositions influence postprandial plasma ghrelin and GH levels in wethers. Four wethers were respectively fed concentrate (C) or timothy hay (R) for 14 days. The levels of total digestive nutrients (TDN) and crude protein (CP) were adjusted to be at the same level. The basal ghrelin in both groups was rapidly and significantly decreased after feeding. Although the decline of ghrelin levels in C was greater and shorter than that in R, no significant difference was observed in the area under the curve (AUC) or in the incremental area. The plasma GH levels were also rapidly and significantly decreased after feeding in both groups and a significant difference was observed between the two groups for AUC of GH. Interestingly, the circadian changes in the plasma ghrelin levels were close to those in the GH levels in C, but this was not the case in R. These data suggest that dietary compositions influence postprandial plasma ghrelin and GH levels, and that these differences may be caused by several factors, including nutrients and ruminal fermentation.

Alterations in lipid metabolism induced by recombinant bovine tumor necrosis factor-alpha administration to dairy heifers.

Endotoxin induces marked changes in lipid metabolism via its effects on cytokines. To evaluate the role of tumor necrosis factor-alpha (TNF) in mediating changes of lipid metabolism in ruminants, we performed a crossover saline-controlled study in Holstein heifers (n = 8; 394.0 kg average BW), investigating the metabolic effects of a single intravenous administration of recombinant bovine TNF (rbTNF, 5.0 microg/kg). Blood samples were taken from a jugular vein at 0 (1100, just before injection), 0.5, 6, 12, and 24 h after each treatment. Dry matter intake in the heifers was not affected by single administration of the rbTNF. The rbTNF produced early as well as later hypertriglyceridemia (P < 0.05) in dairy heifers. The rbTNF also induced an early and sustained rise (P < 0.05) in the plasma NEFA concentration. Plasma retinol concentration was decreased (P < 0.05) at 24 h after rbTNF injection, whereas the a-tocopherol concentration was not significantly affected by rbTNF treatment. At 0.5 and 24 h, there was an increase (P < 0.05) in the plasma concentration of the very-low-density lipoprotein (VLDL) fraction in rbTNF-treated heifers. Between 6 and 24 h after rbTNF treatment, concentration of the low-density lipoprotein fraction declined (P < 0.05) but the high-density lipoprotein fraction was not altered in the rbTNF-treated heifers. These results indicate that TNF produces a hypertriglyceridemic response associated with an increase of the VLDL fraction and a disturbance of retinol metabolism in dairy heifers.

Effects of growth hormone-releasing hormone treatment on milk production and plasma hormones and metabolites in lactating Japanese Black cows under negative energy balance.

The current study was performed to clarify the effects of GHRH treatment on milk production and plasma hormones and metabolites in lactating Japanese Black cows (a beef breed) under negative energy balance (EB). Ten multiparous lactating beef cows were offered a normal-energy diet daily (110% of ME requirements for maintenance and lactation) until 5 d in milk (DIM) to standardize the cows before dietary treatment. From 6 DIM to the final days (63 DIM) of the experiment, the cows were allotted to experimental dietary treatments: 5 cows were offered a diet formulated for 130% [high-energy diet (HED)] and the remaining 5 cows were offered a diet formulated for 80% [low-energy diet (LED)] of ME requirements for maintenance and lactation. In addition, all cows received daily subcutaneous injections of 3 mg of bovine GHRH from 36 to 56 DIM (GHRH treatment period). Differences in BW of HED- and LED-fed cows at 63 DIM were +28.4 and -7.2 kg compared with BW at 6 DIM, and HED- and LED-fed cows were under positive EB (+23.7 MJ/d) and negative EB (-11.6 MJ/d) throughout the experiment period. Treatment with GHRH increased (P<0.01) the average daily milk yield to 6.2 kg in HED-fed cows compared with a milk yield of 5.3 kg for 7 d before the GHRH treatment period (pretreatment period); LED-fed cows had no increase in milk production from GHRH treatment. Plasma GH, IGF-1, insulin, and glucose concentrations increased (P<0.05) after GHRH treatment in both HED- and LED-fed cows; GHRH treatment also induced an increase (P<0.05) in the net area under the curve of plasma insulin after glucose challenge in both HED- and LED-fed cows. Plasma urea N concentrations were decreased (P<0.05) by GHRH treatment in HED-fed cows, but not in LED-fed cows. Plasma NEFA concentration was unaffected by GHRH treatment in both HED- and LED-fed cows. We conclude that GHRH treatment of lactating Japanese Black cows stimulates endogenous GH and subsequent IGF-1 secretion and might induce an increase in insulin resistance, irrespective of EB; however, compared with lactating dairy cows, both galactopoietic and lipolytic effects of GHRH might be insufficiently exerted under negative EB in lactating beef cows.

Biogenic amine production in grass, maize and total mixed ration silages inoculated with Lactobacillus casei or Lactobacillus buchneri.

AIMS: To investigate the effects of inoculating Lactobacillus casei or Lacobacillus buchneri on the production of biogenic amines (BA) in silage. METHODS AND RESULTS: Wilted festulolium (Lolium perenne x Festuca pratensis), whole crop maize or a total mixed ration, consisting of wet brewer grains, lucerne hay, cracked maize, sugarbeet pulp, soyabean meal and molasses, was ensiled with or without the inoculation of either L. casei (>10(6) CFU g(-1)) or L. buchneri (>10(6) CFU g(-1)). Silages were opened after 60 days of storage, and the concentrations of histamine, tyramine, putrescine and cadaverine were determined. The inoculation of L. casei decreased all the BA regardless of the silage type. The effects of L. buchneri varied between the three silages; the tyramine and putrescine were increased in maize but were lowered in festulolium. Histamine was reduced in festulolium and the by-products, whereas no change was found in the maize silage. None of the inoculant strains produced the four BA in a synthetic medium, accounting for the actual ensiling except for tyramine and putrescine in maize. CONCLUSIONS: Wide variation would be found in the production of BA owing to the ensiling materials. The inoculation of L. casei can lower the BA concentration, while the effects of L. buchneri may vary considerably. The screening of BA-producing activity may help to reduce the risk of BA contamination in inoculated silage. SIGNIFICANCE AND IMPACT OF THE STUDY: Strains of decarboxylase-negative L. buchneri can enhance the aerobic stability of silage without a concern regarding the large production of putrefactive BA.

Characteristics of developmental changes in the kinetics of glucose and urea in Japanese Black calves: comparison with Holstein calves.

The current study was conducted to clarify the characteristics of glucose and urea kinetics in male Japanese Black calves, using a glucose and urea dilution method with stable isotopes, at preweaning (3 wk of age) and postweaning (13 and 26 wk of age) stages, in comparison with the kinetics of glucose and urea in male Holstein calves. Six Japanese Black and 6 Holstein calves were arranged in a 2 (breed) x 3 (stage) factorial block design. These 12 suckling calves were fed only whole milk, offered concentrate and or chardgrass hay after 3 wk of age, and weaned at 6 wk of age. Under steady-state conditions, glucose challenges (1.0 mg/kg of BW; [U-13C]d-glucose) and urea challenges (both 2.2 mg/kg of BW; [13C]urea and [15N2]urea) were performed at the 3 stages examined. There were no significant differences in plasma glucose concentrations between Japanese Black and Holstein calves at any stage, but the glucose concentrations at 3 wk of age were greater (P <0.05) than those at 13 wk of age in both breeds. The glucose pool size in Japanese Black calves was smaller (P <0.05) than that in Holstein calves at all stages. Within each breed, there were no significant differences between the glucose pool sizes at 3 and 13 wk of age, but the glucose pool size was larger (P <0.05) at 26 wk of age. Moreover, Japanese Black calves had greater glucose irreversible loss rates (P <0.01) than Holstein calves at 3 wk of age, and the glucose irreversible loss rates were less (P <0.05) on and after 13 wk of age in both breeds. Japanese Black calves had greater plasma urea N concentrations (P <0.05) than Holstein calves at all stages, and in both breeds, the urea N concentrations increased (P <0.05) with age. The urea pool size was smaller (P <0.01) in Japanese Black calves than in Holstein calves at all stages, and in both breeds, the urea pool size increased (P <0.05) with age. In comparison with Holstein calves, Japanese Black calves had greater urea irreversible loss rates (P <0.05) on and after 13 wk of age and greater urea recycling rates (P <0.05) at 26 wk of age. In addition, in both breeds, urea irreversible loss rates and urea recycling rates increased (P <0.05) with age. We conclude that Japanese Black calves have partially different glucose and urea kinetics from Holstein calves and that the kinetics of these metabolites in both Japanese Black and Holstein calves are strongly influenced by weaning.

Hormonal and lactational responses to growth hormone-releasing hormone treatment in lactating Japanese Black cows.

Ten multiparous lactating Japanese Black cows (beef breed) were used to evaluate the effects of bovine growth hormone-releasing hormone (GHRH) analog on milk yield and profiles of plasma hormones and metabolites. The cows received 2 consecutive 21-d treatments (a daily s.c. injection of 3-mg GHRH analog or saline) in a 2 (group) x 2 (period) Latin square crossover design. The 5 cows in group A received GHRH analog during period 1 (from d 22 to 42 postpartum) and saline during period 2 (from d 57 to 77 postpartum), and those in group B received saline and GHRH analog during periods 1 and 2, respectively. Mean milk yield decreased in saline treated compared with that during the 1-wk period before treatment 7.4 and 19.1% during periods 1 (group B) and 2 (group A), respectively. Treatment with GHRH analog increased milk yield 17.4% (period 1, group A) and 6.3% (period 2, group B). Treatment with GHRH analog induced higher basal plasma concentrations of growth hormone (GH), insulin-like growth factor-1 (IGF-1), insulin, and glucose compared with saline-treated cows. In glucose challenge, the GHRH analog-treated beef cows had greater insulin secretion than the saline-treated beef cows. In insulin challenge, however, there were no significant differences in the areas surrounded by hypothetical lines of basal glucose concentrations and glucose response curves between GHRH analog- and saline-treated cows. These results demonstrate that GHRH analog treatment facilitates endogenous GH secretion in lactating Japanese Black cows, leading to increases in milk yield and plasma concentrations of IGF-1, insulin, and glucose.

Metabolic and lactational responses during recombinant bovine tumor necrosis factor-alpha treatment in lactating cows.

This study examined the effects of recombinant bovine tumor necrosis factor-alpha (rbTNF) administration on metabolic and hormonal responses and lactational performance in dairy cows. Twelve lactating Holstein cows were injected subcutaneously with rbTNF (2.5 microg per kg per d) or saline (3 ml per head per d) at 1200 h daily for 7 d (d 0-6) and used in a crossover design. The rbTNF treatment induced increases in plasma haptoglobin, nonesterified fatty acid, cortisol, and growth hormone levels compared with the control levels. The rbTNF-treated cows had lower triiodothyronine and insulin-like growth factor-1 concentrations than control cows. In a somatoliberin challenge on d 6, the somatotropin response to somatoliberin (0.25 microg/kg) was smaller in the rbTNF group than in the control. The rbTNF treatment also produced increases of the nitrite plus nitrate concentration in plasma and milk during the period between d 1 and 7. Milk yield was reduced by rbTNF administration from d 1 to 8. The percentage of milk fat was increased on d 1-7 by rbTNF treatment, but milk protein content in the rbTNF group was decreased on d 5 and 7 as compared with that in the control group. These results support the possibility that tumor necrosis factor-alpha is responsible for the changes in hormone secretion, milk production and composition, and inflammatory parameters observed during coliform mastitis.