HL Groups Research Articles

Role of 12-lipoxygenase and oxidant stress in hyperglycaemia-induced acceleration of atherosclerosis in a diabetic pig model.

We previously showed that vascular smooth muscle cells and endothelial cells cultured under high glucose conditions produced more 12(S)-hydroxyeicosatetraenoic acid (12-HETE), the 12-lipoxygenase (12-LO) product of arachidonate metabolism, relative to normal glucose. Because the lipoxygenase (LO) pathway has been associated with oxidant stress and the pathogenesis of atherosclerosis, we now examined 12-LO activation in vivo in a pig model of diabetes-induced accelerated atherosclerosis which displays human characteristics. The animal model was developed in pigs who were fed a normal or high fat diet and given streptozotocin injections to produce normolipemic-normoglycaemic (NLNG), normolipemic-hyperglycaemic (NLHG), hyperlipemic-normoglycaemic (HLNG) and hyperlipemic-hyperglycaemic (HLHG) pigs. Tissue samples were obtained from key arterial beds to examine 12-LO expression at 20 weeks after the pigs began their diet. All HG pigs maintained threefold higher serum glucose concentrations. The HL groups developed atherosclerosis but diabetic HLHG pigs showed markedly accelerated atherosclerosis (twofold) relative to non-diabetic HLNG pigs. Immunostaining showed progressive increases in 12-LO in arteries in the order NLNG, NLHG, HLNG and HLHG. Leukocyte-type 12-LO protein (immuno-blotting) as well as mRNA expression (by competitive PCR) in abdominal and coronary arteries were significantly greater in HLHG pigs than in all the other three groups. Furthermore, increased oxidant stress was observed in monocytes from NLHG and HLNG pigs, and greatly potentiated in HLHG pigs. These results are consistent with the hypothesis that 12-LO activation plays a key role in accelerated atherosclerosis due to diabetes and hyperlipemia.

ENDOTHELIAL FUNCTION OF CONDUIT AND RESISTANCE ARTERIES IN NEPHROTIC RANGE PROTEINURIA

OBJECTIVE: To test the hypothesis that endothelial dysfunction occurs in nephrotic range proteinuria primarily as a consequence of dyslipidaemia. METHODS: Brachial artery and forearm microcirculatory endothelial function was compared among patients with nephrotic range proteinuria (NRP, n = 14 ), primary hyperlipidaemia (HL, n = 15) and normal controls (NC, n = 16). Endothelial function was studied by measuring post-ischaemic flow-mediated dilatation (FMD) of the brachial artery using high resolution ultrasonography. Endothelium-independent, glyceryl trinitrate (GTN) mediated brachial artery vasodilatation was also measured. Basal and post-ischaemic blood flow of the forearm microcirculation was measured using venous-occlusion strain gauge plethysmography. RESULTS: Serum creatinine was similar among groups. The proteinuric group had a mean albumin of 27.6g/L(1.8) and 24-hour urinary protein excretion of 6.3g(1.3). Plasma lipids and lipoproteins were not statistically different between the NRP and HL groups. Brachial artery FMD was significantly lower in the NRP and HL groups compared with the controls (NRP 4.7%(1.3)*, HL 4.9%(0.7)* and NC 8.3%(0.6), *p = 0.012 vs. NC); GTN mediated dilatation and basal and post-ischaemic forearm blood flow were not statistically different among the three groups. CONCLUSION: Patients with nephrotic range proteinuria have endothelial dysfunction of conduit arteries in the peripheral circulation, similar to that observed in patients with primary hyperlipidaemia. This suggests dyslipoproteinaemia is the principal cause of endothelial dysfunction of conduit arteries in nephrotic range proteinuria. Confirmation of this should be sought with an intervention trial of lipid-regulating therapy.

ENDOTHELIAL FUNCTION OF CONDUIT AND RESISTANCE ARTERIES IN NEPHROTIC RANGE PROTEINURIA

OBJECTIVE: To test the hypothesis that endothelial dysfunction occurs in nephrotic range proteinuria primarily as a consequence of dyslipidaemia.METHODS: Brachial artery and forearm microcirculatory endothelial function was compared among patients with nephrotic range proteinuria (NRP, n = 14 ), primary hyperlipidaemia (HL, n = 15) and normal controls (NC, n = 16). Endothelial function was studied by measuring post‐ischaemic flow‐mediated dilatation (FMD) of the brachial artery using high resolution ultrasonography. Endothelium‐independent, glyceryl trinitrate (GTN) mediated brachial artery vasodilatation was also measured. Basal and post‐ischaemic blood flow of the forearm microcirculation was measured using venous‐occlusion strain gauge plethysmography.RESULTS: Serum creatinine was similar among groups. The proteinuric group had a mean albumin of 27.6g/L(1.8) and 24‐hour urinary protein excretion of 6.3g(1.3). Plasma lipids and lipoproteins were not statistically different between the NRP and HL groups. Brachial artery FMD was significantly lower in the NRP and HL groups compared with the controls (NRP 4.7%(1.3)*, HL 4.9%(0.7)* and NC 8.3%(0.6), *p = 0.012 vs. NC); GTN mediated dilatation and basal and post‐ischaemic forearm blood flow were not statistically different among the three groups.CONCLUSION: Patients with nephrotic range proteinuria have endothelial dysfunction of conduit arteries in the peripheral circulation, similar to that observed in patients with primary hyperlipidaemia. This suggests dyslipoproteinaemia is the principal cause of endothelial dysfunction of conduit arteries in nephrotic range proteinuria. Confirmation of this should be sought with an intervention trial of lipid‐regulating therapy.

Endothelial function of conduit and resistance arteries in nephrotic range proteinuria

OBJECTIVE: To test the hypothesis that endothelial dysfunction occurs in nephrotic range proteinuria primarily as a consequence of dyslipidaemia. METHODS: Brachial artery and forearm microcirculatory endothelial function was compared among patients with nephrotic range proteinuria (NRP, n = 14 ), primary hyperlipidaemia (HL, n = 15) and normal controls (NC, n = 16). Endothelial function was studied by measuring post-ischaemic flow-mediated dilatation (FMD) of the brachial artery using high resolution ultrasonography. Endothelium-independent, glyceryl trinitrate (GTN) mediated brachial artery vasodilatation was also measured. Basal and post-ischaemic blood flow of the forearm microcirculation was measured using venous-occlusion strain gauge plethysmography. RESULTS: Serum creatinine was similar among groups. The proteinuric group had a mean albumin of 27.6g/L(1.8) and 24-hour urinary protein excretion of 6.3g(1.3). Plasma lipids and lipoproteins were not statistically different between the NRP and HL groups. Brachial artery FMD was significantly lower in the NRP and HL groups compared with the controls (NRP 4.7%(1.3)*, HL 4.9%(0.7)* and NC 8.3%(0.6), *p = 0.012 vs. NC); GTN mediated dilatation and basal and post-ischaemic forearm blood flow were not statistically different among the three groups. CONCLUSION: Patients with nephrotic range proteinuria have endothelial dysfunction of conduit arteries in the peripheral circulation, similar to that observed in patients with primary hyperlipidaemia. This suggests dyslipoproteinaemia is the principal cause of endothelial dysfunction of conduit arteries in nephrotic range proteinuria. Confirmation of this should be sought with an intervention trial of lipid-regulating therapy.

Immunocompetence and Viability Under Commercial Conditions of Broiler Groups Differing in Growth Rate and In Antibody Response to Escherichia coil Vaccine

Mortality and morbidity due to infectious diseases are an increasing source of losses to the broiler industry. Breeding chickens for improved disease resistance may reduce these losses. A study was designed to evaluate the contribution of selection for immune response to viability of broilers under farm conditions. The experimental populations consisted of six groups: two lines divergently selected for high (HH) or low (LL) antibody (Ab) response to Escherichia coli vaccination; commercial broilers (CC); and the HH × CC, LL × CC, and HH × LL crosses. Chicks were tested under standard vaccination program and management on commercial farms in two years (1997 and 1998). Mortality was recorded in the whole groups, each consisting of several hundred or thousand of chicks, whereas BW and Ab to natural exposure to E. coli and to vaccination with Newcastle disease virus (NDV) were determined in samples of 50 to 120 chicks/group per yr. Groups were clustered into three levels of BW: CC representing contemporary fast-growing broilers; HH, LL, and HL representing broilers 10 yr earlier; and HC and LC with intermediate BW. The HH and LL groups exhibited the highest and lowest E. coli Ab titers, respectively. Mean Ab of the CC group equaled the average of the selected lines, and all crosses exhibited mid-parent Ab titers, indicating additive genetic control. Group means for Ab to NDV were highly correlated with those of E. coli, suggesting a common genetic control for the immune response to these two antigens. In both years, the highest mortality was found in the fast-growing group (CC), and the lowest mortality was in the slow-growing HH, LL, and HL groups. In the crosses, despite their similar mean BW, mortality was one-third higher among LC vs. HC birds. These results suggest that Ab response and potential growth rate interact in their effect on mortality due to infectious diseases.

TEOAE-based estimation of the auditory threshold in the mid-octave frequencies.

The purpose of this study was to estimate the hearing levels, at the mid-frequencies, of 233 ears with sensorineural hearing loss by classifying the corresponding transiently evoked otoacoustic emissions (TEOAE) recordings into three threshold groups. A classification algorithm was based upon a discriminant analysis of fast Fourier transform (FFT) data, evoked by non-linear click stimuli of 80 (+/-2) dB SPL per ear. To validate the efficiency of the proposed methodology TEOAE recordings were initially grouped by mean hearing level values of the 1 kHz and 2 kHz octaves into three threshold ranges according to two strategy schemes: in the first, TEOAE data were assigned into 10-19 dB HL, 20-39 dB HL or > or = 40 dB HL groups. In the second, TEOAE data were assigned into 10-29 > dB H >, 30-39 dB HL or > or = 40 dB HL groups. The most accurate prediction estimates were obtained from the second strategy scheme with a 90.9% accuracy in the 10-29 dB HL group, 82% in the 30-39 dB HL group and 71.4% in the > or = 40 dB HL group.

Plasma hyperosmolality and arterial pressure regulation during heating in dehydrated and awake rats.

To gain better insights into the effect of dehydration on thermal and cardiovascular regulation during hyperthermia, we examined these regulatory responses during body heating in rats under isosmotic hypovolemia and hyperosmotic hypovolemia. Rats were divided into four groups: normovolemic and isosmotic (C), hypovolemic and isosmotic [L, plasma volume loss (DeltaPV) = -20% of control], hypovolemic and less hyperosmotic [HL1, increase in plasma osmolality (DeltaPosm) = 23 mosmol/kgH2O, DeltaPV = -16%], and hypovolemic and more hyperosmotic (HL2, DeltaPosm = 52 mosmol/kgH2O, DeltaPV = -17%). Hyperosmolality was attained by subcutaneous injection of hypertonic saline and hypovolemia by intra-arterial injection of furosemide before heating. Then rats were placed in a thermocontrolled box (35 degreesC air temperature, approximately 20% relative humidity) for 1-2 h until rectal temperatures (Tre) reached 40.0 degreesC. Mean arterial pressure in L decreased with rise in Tre (P < 0.001), whereas mean arterial pressure remained constant in the other groups. Maximal tail skin blood flow in L, HL1, and HL2 was decreased to approximately 30% of that in C (P < 0. 001). Tre threshold for tail skin vasodilation (TVD) was not changed in L, whereas the threshold shifted higher in the HL groups. Tre threshold for TVD was highly correlated with Posm (r = 0.94, P < 0. 001). Heart rate in the HL groups increased with rise in Tre (P < 0. 001), whereas it remained unchanged in C and L. Cardiovascular responses to heating were not influenced by V1 antagonist in C, L, and HL2. Thus isotonic hypovolemia attenuates maximal tail skin blood flow, whereas hypertonic hypovolemia causes an upward shift of Tre threshold for TVD and an increase in heart rate during hyperthermia. These results suggest that plasma hyperosmolality stimulates pressor responses in the hypovolemic condition that subsequently contribute to arterial pressure regulation during heat stress.

The Effect of Probucol on Intimal Thickening of Autologous Vein Grafts in Hyperlipidemic Rabbit

Probucol is used to treat hypercholesterolemia and also has an anti-atherogenic effect. The effects of probucol on intimal thickening of autologous vein graft in hyperlipidemic rabbits with poor distal run-off were investigated. A poor distal run-off model was prepared in the right hindlimb of 18 rabbits allocated to four groups depending on diet: normolipidemic commercial diet (NL group, n = 5); hyperlipidemic diet (HL group, n = 5); commercial diet with 1% probucol (NP group, n = 4); and hyperlipidemic diet with 1% probucol (HP group, n = 4). After 4 weeks the femoral vein grafts were implanted into normal ( n = 18) or poor ( n = 18) runoff limbs. Vein grafts were harvested 4 weeks after implantation. Intimal thickening of the graft was measured and macrophages therein examined immunohistochemically. The serum cholesterol level was not reduced by probucol treatment. The mean flow rate of the graft was significantly reduced in the poor run-off limb. On histological examination intimal thickening in the poor run-off limb was significantly greater than that of controls, while intimal thickening in the HL and HP groups was enhanced compared with that in the NL and NP groups, respectively. mean intimal thichening in each limb in HP group rabbits was significantly lower than that in HL rabbits (μm): control (HL/HP): 99.4(7.4)/58.8(0.7) ( P &lt; 0.05); poor run-off (HL/HP): 155.3(9.6)/130.3(7.3) ( P &lt; 0.05). There was no difference between NL and NP (μm): control (NL/NP): 44.6(24.7)/31.5(12.8); poor run-off (HL/HP): 115.3(13.8)/97.5(34.0). In addition, enhanced intimal thickening due to poor distal run-off was not suppressed. Immunohistochemical staining showed intimal macrophage infiltration in the HL and HP groups; however, macrophage infiltration in grafts in the HP group was less than in the HL group. In conclusion, under hyperlipidemic conditions, probucol decreased intimal thickening enhancement of the vein graft, and suppressed intimal macrophage infiltration. These findings were similar to the anti-atherogenic effect of probucol in the native artery. Hence, probucol administration after vascular reconstruction with vein grafts in patients with hyperlipidemia may be beneficial.

The effect of probucol on intimal thickening of autologous vein grafts in hyperlipidemic rabbit

Probucol is used to treat hypercholesterolemia and also has an anti-atherogenic effect. The effects of probucol on intimal thickening of autologous vein graft in hyperlipidemic rabbits with poor distal run-off were investigated. A poor distal run-off model was prepared in the right hindlimb of 18 rabbits allocated to four groups depending on diet: normolipidemic commercial diet, (NL group, n=5); hyperlipidemic diet (HL group, n=5); commercial diet with 1% probucol (NP group, n=4); and hyperlipidemic diet with 1% probucol (HP group, n=4). After 4 weeks the femoral vein grafts were implanted into normal ( n=16) or poor ( n=16) runoff limbs. Vein grafts were harvested 4 weeks after implantation. Intimal thickening of the graft was measured and macrophages therein examined immunohistochemically. The serum cholesterol level was not reduced by probucol treatment. The mean flow rate of the graft was significantly reduced in the poor run-off limb. On histological examination intimal thickening in the poor run-off limb was significantly greater than that of controls, while intimal thickening in the HL and HP groups was enhanced compared with that in the NL and NP groups, respectively. mean intimal thichening in each limb in HP group rabbits was significantly lower than that in HL rabbits ( μm): control (HL/HP): 99.4(7.4)/58.8(0.7) ( P<0.05); poor run-off (HL/HP): 155.3(9.6)/130.3(7.3) ( P<0.05). There was no difference between NL and NP ( μm): control (NL/NP): 44.6(24.7)/31.5(12.8); poor run-off (HL/HP): 115.3(13.8)/97.5(34.0). In addition, enhanced intimal thickening due to poor distal run-off was not suppressed. Immunohistochemical staining showed intimal macrophage infiltration in the HL and HP groups; however, macrophage infiltration in grafts in the HP group was less than in the HL group. In conclusion, under hyperlipidemic conditions, probucol decreased intimal thickening enhancement of the vein graft, and suppressed intimal macrophage infiltration. These findings were similar to the anti-atherogenic effect of probucol in the native artery. Hence, probucol administration after vascular reconstruction with vein grafts in patients with hyperlipidemia may be beneficial.

Effects of Seasonal Protein Restriction on Antlerogenesis and Body Mass in Adult Male White-Tailed Deer

Seasonal dynamics in protein availability vary with latitude throughout the geographic range of white-tailed deer (Odocoileus virginianus), but the effects of variability in the timing of protein availability on deer performance or antlerogenesis are understood poorly. We designed an experiment to examine the effects of a 12-week (spring or summer) protein restriction on deer performance. Eighteen male white-tailed deer (≥2 yr old) were blocked by past antler size, body mass, and age, then randomly assigned to one of 3 diet groups (LH, HL, HH) composed of 2 dietary levels of crude protein (CP), low (L, 7%) or high (H, 16%) during 1992-93. The HH group served as the control, receiving a high protein diet during the antlerogenic period (Mar-Aug) of each year. The LH and HL groups received a low protein diet for a 12-week period in spring (LH) or summer (HL) and a high protein diet in the opposite season. During fall and winter, all deer consumed a medium protein diet created by mixing the experimental diets. Body mass, feed intake, antler characteristics, and serum chemistries were examined. No diet effects were found for any antler characteristic measured. Body mass varied by a diet-month interaction in 1992 (P = 0.04) and in 1993 (P = 0.01), because deer on H diets from June to September gained mass faster than deer on L diets for the same period. Rapid gain of body mass was accomplished by increased feed efficiency rather than increased feed intake. Final body mass did not vary by diet (P = 0.587). In general, serum chemistry levels were consistent with those reported in the literature. Adult white-tailed deer compensated for a 12-week protein restriction within a 5-17-week realimentation period. Greater treatment effects during the second year of the study suggested cumulative effects of protein restriction on deer performance.

Time-course of photoadaptation in the symbiotic sea anemone Anemonia viridis

The time-course of photoadaptation in the symbiotic sea anemone Anemonia viridis (Forskal) was determined on freshly collected anemones which were maintained under low light (LL: 10 μE m-2s-1) or high light (HL: 300 μE m-2s-1) over a period of 35 d. Photosynthesis versus irradiance curves (P vs I) normalised to anemone dry weight were determined for anemones at the start of the experiment and for both groups at 7 d intervals. Photosynthetic parameters derived from the P vs I curves, P max gross (the maximum photosynthetic capacity of the zooxanthellae), α (an estimate of photosynthetic efficiency) and I k(the light-saturating irradiance), and the respiration rate, showed that anemones were high-light adapted before the experiment began. Thereafter, any observed changes occurred only in anemones adapting to the low-light regime. P max gross remained relatively constant over 35 d and there was no significant difference between LL and HL groups. In the LL group α increased and both I kand the respiration rate decreased significantly. These photoadaptive responses were most rapid in the first 7 d, after which change was gradual until about Day 28, when photoadaptation appeared to be complete. In order to predict the physiological mechanisms of photoadaptation to low light, P gross vs I curves normalised to zooxanthellae biomass were constructed for LL and HL anemones at 35 d. Zooxanthellae density and photosynthetic pigment content were also analysed. For LL-adapted anemones, α and chlorophyll a were higher, there were no differences in algal density and chlorophyll c 2 and I kwas lower. It is proposed that the size of the peridinin-chlorophyll a-protein complex (PCP) of the light-harvesting complex was increased to facilitate photoadaptation. Plotting P net vs I normalised to anemone dry weight on the 35 d-photoadapted anemones gave a measure of changes in the excess photosynthetically fixed carbon that was potentially available to the host. Net photosynthesis of the LL group was higher at subsaturating light intensities as a result of the increase in α, and at saturating light intensities P max net was higher as a result of a decrease in the rate of respiration of the whole symbiotic association.

Effect of plane of nutrition on body weight and birth weight of pregnant Gwembe Valley goats in Zambia

Pregnant Gwembe Valley goats, aged 18–24 months, with an average BW of 23.2±0.82 kg were used. In addition to hay, they were fed concentrate mixtures for 12 weeks that contained 12.2, 13.3 or 13.7 MJ GE/kg and 14.3, 13.4 and 12.2% CP. Three dietary treatments were high protein-low energy (HL), medium protein-medium energy (MM) and low protein-energy (LH). Voluntary daily intake of concentrate before kidding was 0.53±0.08, 0.62±0.10 and 0.48±0.08 kg/doe for HL, MM and LH, respectively; and intake was more ( P < 0.05) in MM. Average daily live weight gains were 25 ± 0.08, 43 ± 0.53 and 24 ± 0.08 g/doe for HL, MM and LH groups. Intakes of concentrates after kidding were not significantly different ( P > 0.05); however, hay intakes differed ( P < 0.05) between groups. Mean birth weights of kids were 1.24±0.41, 1.60±0.13 and 1.63±0.09 kg for HL, MM and LH groups. Birth weights of kids were not different ( P > 0.05) between MM and LH, but they differed slightly from the HL group. Apparent digestibility coefficients were significantly influenced ( P < 0.05) by levels of protein and energy. From these results, the estimated optimal protein and energy requirements in concentrate supplements for pregnant Gwembe Valley goats is 13.4% CP and 13.3 MJ GE/kg, since body weight and birth weight were best at that level.

Structural alterations and breaking strength of mouse femora exposed to three activity regimens

Mice were used as a model system to correlate loading, changes in cortical and trabecular bone growth and remodeling, and differences in breaking strength of the whole femur. BALB/c mice were raised for 30 days, starting at day 14, under three conditions of loading or exercise: (a) normal exercise control (NE), (b) 4 × normal gravity for a total of one h/day in addition to normal exercises (HG), and (c) chronic digging and burrowing (high-litter cage) (HL). Results indicate that both HG and HL groups significantly increased the cortical cross-sectional area of the mid-shaft of the femur, the moment of inertia in the antero-posterior direction at the mid-shaft, anterior wall thickness of the midshaft cross section, and changed the architecture of trabecular bone in the proximal one-third of the femur. The extent of these structural changes, however, was unique in each group. The HG group (high-intensity, short duration loading) demonstrated the greatest structural changes in the moment of inertia in the antero-posterior direction, which increased by 44% over the control ( p < .001), and in the architecture of trabecular bone. The HL group (lower-intensity, chronic exercise), demonstrated the greatest structural change in cortical bone cross-sectional area, which increased by 27% ( p < .0001). Despite the differences in loading and structural changes in the HG and HL groups, the breaking strength of the whole femur for both groups was approximately 64% greater than the controls ( p < .0001). A mechanical analysis of our data revealed that for our tests the contribution of bending to the total stress on the shaft may be over 50 times greater than that of either compression or tension. Further, the change in the geometry of the cortical bone may account for only approximately 50% of the increase in breaking strength; the remaining increase must be accounted for by changes in material properties and/or placement of trabeculae within the lumen of the shaft.

Atherosclerotic lesions in coronary arteries of hyperlipidemic swine: Part 2. Endothelial cell kinetics and leukocyte adherence associated with early lesions

The role of endothelial cells (EC) in the development and progression of early swine intimal cell mass (ICM)-derived coronary artery lesions in 55 swine fed either a mash or hyperlipidemic diet for 14, 49 or 90 days was investigated. Characteristics studied were endothelial cell turnover (using tritiated thymidine autoradiography), adhesion of leukocytes (presumably chiefly monocytes) to endothelium, and the presence or absence of endothelial cell denudation. The major findings were: (a) An increased adherence of leucocytes to endothelial cells over ICM-lesions in the HL-90 day group compared to the corresponding mash value at 90 days as well as to that of each of the other HL and mash groups. (b) Significant positive correlation between the labeling indices (LI) of endothelial cells lying over coronary artery lesion cells and the labeling indices of the underlying ICM-lesion cells; also, a significant positive correlation between the labeling indices of endothelial cells over lesions of the abdominal aorta and those of the coronary arteries. (c) At 90 days the endothelial cell LI over lesions in the HL group was significantly higher than the corresponding values in the mash group. Since the EC increase rates by growth in the two groups are also significantly different, the differences in LIs reflect at least in part EC growth differences and no strong conclusion can be made regarding possible cell turnover differences. (d) No frank endothelial denudation was found. The findings suggest that in swine coronary arteries participation by monocytes from circulating blood is a factor in the early progression of the lesion as well as smooth muscle cell proliferation.

Effect of herbage allowance during pregnancy and lactation on feed intake, milk production, body composition and energy utilization of ewes at pasture

SUMMARYIn two experiments Dorset ewes were offered low (LP) or high (HP) herbage allowances during pregnancy to induce light (45–50 kg) or heavy (60–65 kg) post-partum body weights, respectively. During the first 6 weeks of lactation three herbage allowances were offered in a 2 x 3 factorial design: 2 (LL), 5 (ML) and 8 (HL) kg D.M./ewe per day. In the first experiment (Expt 1) lambs were removed and ewes machine-milked twice daily. In the second (Expt 2) they were suckled by two lambs; a further group on the ML allowance (MML) was machine-milked. Ewes were slaughtered during early pregnancy, post-partum and after 6 weeks of lactation for determination of body composition. Diet selection and faecal output were measured during lactation.Absolute level of milk production was not affected by pregnancy nutrition when rearing two lambs and producing 2·0–2–7 kg milk/day or at 30–50% lower milk production when machine-milked. When expressed as g/kg W0·75 per day milk production was 14% greater in LP than in HP ewes. Milk fat content was higher at low allowances and was positively related to rate of body fat mobilization. Milk protein concentration was lower in suckled than in machine-milked ewes (40 ν. 47 g/kg) though total milk protein secreted (g/day) was similar. Milk production was 11–13% greater in ewes bearing twin lambs compared with those bearing singles whether machine-milked or suckling two lambs.Mean intakes during the 6 weeks of lactation were 58, 69 and 73 g DOM/kg W0·75 per day, respectively, for LL, ML and HL groups when machine-milked and 51, 75 and 83 g DOM/kg W0·75/day, respectively, for ewes rearing two lambs. LP ewes consumed 13% (Expt 1) and 17% (Expt 2) more feed (g DOM/kg W0·75/day) during lactation than HP ewes, though in absolute terms (kg D.M./day) there was no difference. The difference in OMD between herbage offered (OMD = 0·77) and consumed ranged from 0 when sheep grazed to a residual herbage mass of 910 kg D.M./ha to + 0·04 when residual herbage was &lt; 1600 kg D.M./ha.All sheep, irrespective of pregnancy nutrition, milk production or herbage allowance, were in negative body energy balance during lactation. Mobilization of body fat during lactation averaged 40 g/day for machine-milked and 150 g/day for suckled ewes and was greatest in HPLL groups (92 and 219 g/day in Expts 1 and 2, respectively). In LP groups body protein loss during pregnancy was 10 and 16 g/day in Expts 1 and 2, respectively, and little further net protein loss occurred during lactation. The maximum rate of body protein loss in HP groups was 30 g/day in ewes rearing two lambs on the low herbage allowance.Maintenance energy requirement during lactation averaged 0·238 MJ ME/kg W per day for ewes in both experiments; efficiency of use (Kl, (t)) of total energy available above maintenance for milk synthesis (namely, milk energy/ME intake - estimated energy requirement for maintenance (MEm + mobilized tissue energy) decreased from 0·84 to 0·51 with increasing rate of tissue energy mobilization. There was a positive relationship between Kl(t) and the proportion of mobilized energy derived from body protein.The overall energy requirement of lactating ewes well-fed during pregnancy was similar to previous estimates (Agricultural Research Council, 1980) but that of sheep undernourished during pregnancy was 10–20% greater.

The effects of level of feeding during rearing and early pregnancy upon reproduction in young female sheep

ABSTRACTTwo hundred and forty Suffolk × (Cadzow Improver × Scottish Blackface) female sheep were housed at 4 months of age and average live weight (± s.d.) of 30·6 ± 501 kg, and divided into four equal treatment groups: HH, HL, LH and LL. They were group-fed such that HH and HL sheep were 39·7 ± 5·27 kg, and LH and LL were 35·6 ± 4·64 kg, at puberty, which was recorded in all sheep. There were no differences in average date at puberty.After puberty the sheep were gradually transferred to different levels of feeding by the time of mating with fertile rams at the second oestrus such that HH and LH were group-fed 1·50, and HL and LL 0·75 of maintenance requirement. The sheep were slaughtered at return or 25 ± 3 days after mating.The proportion of sheep with live embryos was 0·48,0·40,0·50 and 0·41 for HH, HL, LH and LL groups respectively (NS). Ova wastage was 0·59, 0·68, 0·51 and 0·59 for the treatments, with statistically significant differences in losses between treatments in sheep with two corpora lutea (P&lt;0·05). Ovulation rate also differed between treatments (HH &gt; HL, P &lt; 0·01; HH &gt; LH and LL, P &lt; 0·05). Differences occurred between treatments in the proportion of multiple cycles between first and second oestrus (P&lt;0·05), and HL sheep had a greater proportion of sheep failing to return to service but without embryos (HH&gt;HL, P&lt;0·05). The pooled results showed that pregnant sheep were heavier at 4 months of age (P &lt; 0·05), but not at mating, than non-pregnant sheep. Sheep with two corpora lutea were more likely to be pregnant than sheep with one corpus luteum (P &lt; 0·05).

Effect of duration and pattern of underfeeding in early lactation on milk production and reproduction of dairy cows

Eighty cows of mixed breeds were fed so that they calved in moderate condition, and were then strip-grazed at different rates over the first ten weeks of lactation. Two levels of feeding were used factorially ; either ad libitum pasture intake (H) or an allowance of pasture which resulted in an intake of 7 kg of pasture dry matter cow-1 day-1 (L), for the first or second five-week period. After ten weeks, all cows were grazed as one group as well as seasonal conditions permitted. The effects of five-week periods of underfeeding on milk, milk fat and protein yield were equal and additive over the first ten weeks of lactation, HL and LH groups producing 11 kg and LL group 22 kg less milk fat than the HH group. Residual effects, however, from week 11 to the end of lactation differed markedly between treatments, the LH group producing the same as, but HL and LL groups producing 9 and 21 kg less than, the HH group. Residual effects of only 0.7 and 1.0 times the immediate effect were recorded for underfeeding in the first five and ten weeks of lactation, respectively. Cows underfed in early lactation gained more liveweight in later lactation at the expense of milk yield. An extra 10 kg pasture dry matter was required in early lactation to give an extra kilogram of milk fat over the lactation. The calving to conception interval in the LL group was 18 days longer than in the HH group (P &lt; 0.05). The delay was associated with both a longer post-partum anoestrus and a higher number of services per conception. There was no effect of stage of underfeeding (HL vs LH) on reproductive performance. The poor understanding of factors affecting residual effects from underfeeding in early lactation is highlighted. As pattern of underfeeding has little effect on lactation performance, this gives the farmer considerable flexibility in allocating feed supplies in early lactation.

Effects of Previous Calcium Intakes on Adaptation to Low and High Calcium Diets in Rats

To study adaptation to low and high calcium diets, female weanling rats were fed for two periods in one of four ways: 1) a low calcium diet (0.2%) throughout both periods (LL); 2) a low calcium diet followed by a high calcium diet (0.9%) (LH); 3) a high calcium diet followed by a low calcium diet (HL); or 4) a high calcium diet throughout both periods (HH). Rats (LL and LH), accustomed to low intakes of calcium, retained a larger percentage of the dietary calcium than rats (HL and HH) accustomed to higher amounts of the element, regardless of whether the present calcium intake was low or high. Up to 133 days of age, the bones of the LL and LH groups contained less calcium and phosphorus per unit of bone weight than did the bones of the HL and HH groups. At 156 days of age (end of experiment), however, the bones of all groups contained equal concentrations of calcium and phosphorus. These data were interpreted to mean that body calcium stores control calcium retention. Parathyroid activity, as estimated by parathyroid gland weight and urinary phosphate values, was greater in the LL group than in the HL group. These data demonstrated that the adaptation to both high and low calcium diets was affected by previous dietary calcium levels and confirmed the idea that body stores of calcium control its retention.

Further Evidence on Testcross Versus Line Performance in Maize1

A total of 169 S1 lines out of KrugIII synthetic were evaluated as (1) lines per se, (2) testcrosses to an unrelated tester, and (3) testcrosses to the parental population. The three highest‐ and three lowest‐yielding from each of the three evaluation series were used to study their intercross behaviour. The 18 lines were intercrossed. Composites of HH, HL, and LL crosses within each set of 6 lines and crosses between sets (H1H1, H1L1, L1H1 and L1L1) provided the material for test evaluation in 1965‐66. In each evluation series the superior lines [&gt;(p̄ + σp)] had been selected to form new cycle populations. These populations (Cycle IV) together with the parental, KIII synthetic, were included in the performance trials.The LL, HL, and HH groups from line per se selections exhibited a linear trend for yield. Selection on the basis of an unrelated tester resulted in the HL group ≥ the HH group. Intercrosses of lines selected on the basis of the parental population as the tester exhibited a linear yield trend but with evidence of partial dominance for high yield. Highest yields resulted from intercrosses of lines selected on the basis of performance in testcrosses with the parental population.With respect to the newly derived populations, that based upon selection from testcrosses with the parental population (KIV‐3) exhibited a 15% increase in yield relative to KIII synthetic. Line per se selection resulted in a 4% gain in yield, whereas no gain resulted from selection based upon evaluation in testcrosses with the unrelated tester parent.