Utilization of energy and nitrogen by yearling Holstein cattle fed direct-cut alfalfa or orchardgrass ensiled with formic acid plus formaldehyde.

First-growth orchardgrass and alfalfa were harvested at two stages of maturity, treated with formic acid plus formaldehyde, and ensiled as direct-cut silage during 1978 and 1979. The 1978 silages were fed to eight yearling Holstein heifers (average BW 273 kg), and the 1979 silages were fed to eight yearling Holstein steers (average BW 264 kg) in replicated 4 x 4 Latin square experiments to measure total energy and N balance using the Beltsville open-circuit respiration calorimeters. Silage was offered daily at 70 g of DM/kg.75 BW, a rate that was essentially ad libitum for late-maturity orchardgrass, but restricted for the other three silages within each experiment. Cattle fed alfalfa used ME for growth with greater efficiency (55%) than did cattle fed orchardgrass (40%). Cattle fed orchardgrass achieved the same tissue N retention at a lower total N intake than did cattle fed alfalfa. Differences in tissue N retention were accounted for by differences in N intake insoluble in autoclaved ruminal fluid, but soluble in acid detergent, a fraction termed available N. At equal intake of ME and available N, cattle fed alfalfa gained more tissue energy than those fed orchardgrass and gained tissue protein similarly to cattle fed orchardgrass. Fractions composing digestible OM were different between forage types but similar within forage type between maturities at harvest. More efficient use of ME for growth by animals fed alfalfa compared with orchardgrass may be related to differences in digestible OM composition, load of digestive tract content, and composition of absorbed nutrients.

Effect of bovine somatotropin on metabolism of lactating dairy cows: energy and nitrogen utilization as determined by respiration calorimetry.

Effects of exogenous bovine somatotropin (bST) on energy and nitrogen utilization by high producing dairy cows were examined. Nine cows received bST (51.5 IU/d) or exipient (control) in a single reversal design involving 14-d treatment periods. Energy and nitrogen balances were measured in open-circuit respiration chambers. Yield of 4% solids-corrected milk was increased by 22% with bST treatment. Dry matter intake and the apparent digestibilities of dry matter, energy and nitrogen were not altered by treatment. The only significant component of nitrogen utilization that was altered by bST treatment was an increase in milk nitrogen secretion. Cows were in negative tissue nitrogen balance during the control period (-21 g/d) and tended to become more negative during the bST treatment period (-34 g/d). Heat energy loss and milk energy secretion were increased with bST treatment. Tissue energy balance was -1.1 Mcal/d during the control treatment period and the use of energy reserves with bST treatment decreased tissue energy balance to -9.8 Mcal/d. Changes in heat production with bST treatment were equal to those predicted from the changes in milk and body tissue. Overall, the results demonstrated that bST treatment increased yield of milk and milk components even when cows were in negative nitrogen and energy balance. Effects of bST were predominantly associated with nutrient partitioning, and observed heat loss (associated with maintenance and partial efficiencies of milk synthesis and tissue utilization) did not differ from predicted heat loss.

Effect of bovine somatotropin on metabolism of lactating dairy cows: influence on rates of irreversible loss and oxidation of glucose and nonesterified fatty acids.

Effects of bovine somatotropin (bST) on irreversible loss rate (ILR) and oxidation rate of glucose and nonesterified fatty acids (NEFA) were examined. Nine lactating cows received bST or excipient in a single reversal design using 14-d periods. Kinetic variables were estimated by compartmental analysis of blood metabolite and expired CO2 specific activity values obtained during infusion of [U-14C]glucose or [1-14C]palmitate. With bST treatment, milk energy yield increased by 31% but feed intake was unchanged. Blood glucose concentrations were not affected by treatment or correlated with any glucose kinetic variables. In the control period, glucose ILR was 12.1 mol/d with 66.5% utilized for milk lactose synthesis and 17.4% oxidized to CO2. Treatment with bST increased glucose ILR (+1.5 mol/d) and reduced glucose oxidation (-0.4 mol/d); this accommodated the additional glucose (+1.3 mol/d) required for the increase in lactose secretion. Increases in milk energy yield with bST treatment caused cows to be in a substantial negative net energy balance (-9.8 Mcal/d). No acute lipolytic response occurred with bST treatment, but plasma NEFA were chronically elevated (+104 mumol/L) and NEFA ILR increased (+2.3 mol/d). Increased NEFA turnover was primarily used for increased oxidation to CO2 (+0.5 mol/d) and 41% increase in milk fat (equal to approximately 1.3 mol fatty acids/d). For NEFA, plasma concentrations were correlated with ILR (r = +0.80), oxidation to CO2 (r = +0.74) and net energy balance (r = -0.78). Overall, bST resulted in an exquisite coordination of metabolism to meet nutrient needs for increased synthesis of milk components.

Prediction of empty body components in steers by urea dilution.

Empty body composition of 68 mixed-breed and 50 Angus steers was determined by chemical analysis of the right half-carcass and entire noncarcass fraction of each steer. Chemical composition was used to develop prediction equations for empty body protein (EBPRO) and fat (EBFAT) in steers using urea space (US) and body weight measurements. Previous research showed a significant positive correlation between empty body water (EBH2O) and urea space in these steers. For all steers studied, the percentage of EBH2O ranged from 44.8 to 69.2 (mean = 56.0), the percentage of EBPRO ranged from 14.1 to 19.8 (mean = 17.0) and the percentage of EBFAT ranged from 6.1 to 38.1 (mean = 22.1). The best predictions obtained were multiple regression equations with actual weight of body components as dependent variables and US and empty body weight (EB) as independent variables. Urea space alone was a poor predictor of EBFAT, but US improved predictions based on live weight (LW) or EB alone. Coefficients of determination for the best predictions of percentage of composition were not as high as coefficients of determination for the best predictions of actual weight of body components. These data suggest that US measurements can be used to predict empty body composition of live steers, but this may require repeated measurements and an independent estimate of EB from LW for greatest accuracy.

Effect of bovine growth hormone administration on metabolism of growing Hereford heifers: protein and lipid metabolism and plasma concentrations of metabolites and hormones.

The objectives were to determine the effects of daily injection of bovine growth hormone (bGH) on the metabolism of [1-14C]leucine and [1-14C]palmitate and on hormone and metabolite concentrations in growing Hereford heifers. The experimental design was a 28-d single reversal with two 14-d injection periods of placebo or bGH. Energy intake was restricted to a level slightly above maintenance. Injection of bGH did not affect circulating concentrations of glucose, beta-hydroxybutyrate, urea nitrogen, prolactin, triiodothyronine or thyroxine. Plasma concentrations of insulin and nonesterified fatty acids (NEFA) were chronically elevated whereas leucine concentration was chronically decreased after 1 wk of bGH injection compared to placebo injection. Leucine oxidation was lower and whole-body protein synthesis was higher during bGH injection than during placebo injection. There were increases in both total irreversible loss and oxidation of NEFA during bGH injection compared to placebo injection. These results suggest mobilization of stored fatty acids and increased reliance on NEFA to provide energy for cellular processes. The dual and reciprocal effects of bGH on nitrogen and NEFA metabolism demonstrate its role as a homeorhetic regulator, affecting metabolism of several body tissues to support lean body accretion in Hereford heifers at near-maintenance intake of metabolizable energy.

Effect of bovine growth hormone administration on metabolism of growing Hereford heifers: dietary digestibility, energy and nitrogen balance.

The objective was to determine the effect of daily s.c. injection of bovine growth hormone (bGH) on nitrogen and energy balance in six Hereford heifers. In addition, effects on urinary excretion of 3-methylhistidine and hydroxyproline and on serum mineral concentrations were monitored. A single reversal design was used with two 14-d injection periods of placebo or bGH (29.2 IU/d). Measurements were made on d 8-14 of each period. Injection of bGH did not alter apparent digestibility of dry matter, energy or nitrogen, nor urinary excretion of 3-methylhistidine or hydroxyproline. Serum concentrations of calcium, phosphorus and magnesium were normal with bGH treatment. Nitrogen retention was higher and urinary nitrogen excretion was lower when the heifers were injected with bGH than with the placebo demonstrating an effect of bGH on postabsorptive metabolism of nitrogen. Total energy balance was not altered by treatment. Energy retained as protein was higher after bGH treatment than after the placebo, implying decreased energy retained as fat and demonstrating a role for GH in altering energy partition in growing animals. Total heat production was not altered by treatment indicating no change in the gross efficiency of metabolizable energy use with bGH treatment.

Estimation of empty body water in steers by urea dilution.

Urea dilution has been proposed as a practical method for estimating body composition in live cattle. The objectives of this study were to evaluate the urea dilution technique by comparing urea space to direct measurement of empty body water in steers and to develop prediction equations for empty body water in live steers using urea space parameters. Urea space was determined in 68 mixed-breed and 50 Angus steers ranging in live weight from 210 to 517 kg by the measurement of change in plasma urea nitrogen concentration before and 12 minutes after the midpoint of an intravenous infusion of 130 mg urea (20% solution w/v in 0.9% saline infused over 2 minutes) per kg live weight. Water in ground samples from carcass and digesta-free non-carcass fractions was determined by lyophilization. Linear relationships for pooled data of both groups of steers existed between empty body water and urea space (r = 0.96, P less than 0.001). Prediction of empty body water in live steers was improved by including live weight as an independent variable in a multiple regression equation (Sy X x = 7.2 kg for pooled data). Live weight alone predicted empty body water with a standard error of the estimate 36% larger than the multiple regression prediction using urea space and live weight.