Nitrogen Balance in Patients with Chronic Renal Failure on Diets Containing Varying Quantities of Protein

Twenty-four nitrogen balances have been performed in 16 patients with chronic renal failure, with a protein intake of 0·23 to 1·0 g./kg./day. The results show that most patients with chronic renal failure require about 0·5 g./kg./day (35 g. for a 70-kg. man) to remain in nitrogen balance. The proportion of high-quality protein in the diets varied from 40 to 98% and the calorie intake from 23·6 to 59·0 calories/kg./day (1,330 to 3,310 calories/day). Within these ranges the proportion of high-quality protein and the calorie content did not have a detectable effect on the nitrogen balance.It is concluded that when other forms of treatment for renal failure are available, reduced protein diets should be used for only short periods, and that the protein intake should be 0·5 g./kg./day to maintain the patient in nitrogen balance.     

Effect of ipriflavone on bone changes induced by calcium restricted, vitamin D deficient diet in rats

The preventive effect of ipriflavone, 7-isopropoxy-isoflavone, on the development of experimental osteopenia in rats was studied. Male Wistar rats (4 weeks old) on a calcium restricted, vitamin D deficient diet were given a daily oral administration of ipriflavone. The administration of ipriflavone (100 mg/kg BW/day) for 40 days significantly inhibited a decrease in the cortical thickness (14.0 +/- 1.6 vs. 17.1 +/- 2.9%, mean +/- SD, p less than 0.05) and bone calcium content (62 +/- 4 vs. 67 +/- 2 mg, p less than 0.05) in the femora of rats induced by a mild calcium restricted (0.3%), vitamin D deficient diet. This compound did not affect serum calcium levels in this condition. But a dose of 20 mg/kg BW/day of ipriflavone was insufficient to inhibit a decrease in bone calcium content. In rats fed on a more severe calcium restricted (0.03%), vitamin D deficient diet, the administration of ipriflavone (100 mg/kg BW/day) did not significantly affect the cortical thickness or calcium content. Intestinal calcium absorption measured by the in situ loop method was not significantly different between rats fed with a severe calcium restricted (0.03%), D deficient diet with or without ipriflavone (20 or 100 mg/kg BW/day) These results demonstrate that the new compound, ipriflavone, partially prevents bone calcium loss induced by a mild calcium restricted (0.3%), vitamin D deficient diet in rats. However, the precise mechanism of action of this compound remains unknown.     

Suppression of voluntary ethanol consumption in rats by gamma-butyrolactone

The effect of gamma-butyrolactone (GBL) on voluntary ethanol intake was studied in a group of Wistar rats in which a stable preference had been induced by exposure to increasing ethanol concentrations. These rats drank 60% of their daily fluid intake as 15% ethanol solution, corresponding to about 6 g ethanol/kg/day. GBL, injected intraperitoneally at the dose of 200 mg/kg, twice daily for 3 consecutive days, decreased ethanol intake by about 80% on the days of treatment, but did not reduce total fluid intake. Ethanol intake remained significantly reduced up to the 5th day following cessation of GBL administration. GBL, up to a concentration of 10(-3) M, inhibited neither alcohol-dehydrogenase nor aldehyde-dehydrogenase in rat liver homogenates, nor dopamine-beta-hydroxylase in homogenates of adrenal medulla or hypothalamus of rats. It is suggested that inhibition of firing in dopaminergic neurons mediates the suppressant effect of GBL on ethanol preference.     

Daily copper supplement effects on copper balance in trained subjects during prolonged restriction of muscular activity

The aim of this study was to assess the effect of a daily intake of copper supplements on negative copper balance during prolonged exposure to hypokinesia (decreased number of kilometers per day). During hypokinesia (HK), negative copper balance is shown by increased, not by decreased, serum copper concentration, as it happens in other situations. Studies were done during a 30-d prehypokinetic period and a 364-d hypokinetic period. Forty male trained volunteers aged 22–26 yr with a peak oxygen uptake of 66.4 mL/min/kg and with an average of 13.7 km/d running distance were chosen as subjects. They were equally divided into four groups: unsupplemented ambulatory control subjects (UACS), unsupplemented hypokinetic subjects (UHKS), supplemented hypokinetic subjects (SHKS), and supplemented ambulatory control subjects (SACS). The SACS and SHKS groups took 0.09 mg copper carbonate/kg body weight daily. The SHKS and UHKS groups were maintained under an average running distance of 1.7 km/d, whereas the SACS and UACS groups did not experience any modifications in their normal training routines. During the 30-d prehypokinetic period and the 346-d hypokinetic period, urinary excretion of copper, calcium, and magnesium and serum concentrations of copper, calcium, and magnesium were measured. Copper loss in feces and copper balance was also determined. In both UHKS and SHKS groups, urinary excretion of copper, calcium, and magnesium and concentrations of copper, magnesium, and calcium in serum increased significantly when compared with the SACS and UACS groups. Loss of copper in feces was also increased significantly in the SHKS and UHKS groups when compared with the UACS and SACS groups. Throughout the study, the copper balance was negative in the SHKS and UHKS groups, whereas in the SACS and UACS groups, the copper balance was positive. It was concluded that a daily intake of copper supplements cannot be used to prevent copper deficiency shown by increased copper concentration. Copper supplements also failed to prevent negative copper balance and copper losses in feces and urine in endurancetrained subjects during prolonged exposure to HK.     

Effect of dietary calcium on renal prostaglandins.

The present study was designed to clarify the possible role of renal prostaglandins (PGs) on blood pressure (BP) regulation during calcium (Ca) restriction or supplementation. Twelve normotensive women with a mean age of 21.2 years participated in the study. After 1 week of normal Ca intake (mean +/- SE, 536 +/- 2 mg/day), a low-Ca diet (163 +/- 1 mg/day) was given for a further 1 week. Additional asparagine Ca (3 g as Ca/day) was also given to half of the subjects. BP, heart rate, and serum total and ionized Ca concentrations were measured at the end of each period. Levels of Ca, sodium, PGE2, 6-keto-PGF1 alpha and thromboxane (TX) B2 excreted into urine were also determined. The plasma level of ionized Ca was significantly increased without any change in total Ca in both groups. Low and high Ca intake decreased and increased urinary Ca excretion by 28% and 56%, respectively. BP was not altered after Ca deprivation or loading. However, urinary PGE2 excretion was significantly augmented from 668.9 +/- 68.1 to 959.7 +/- 183.1 ng/day by Ca loading, whereas Ca deprivation decreased PGE2 excretion (695.4 +/- 108.1 to 513.2 +/- 55.2 ng/day). No changes were observed in 6-keto-PGF1 alpha or TXB2 urinary excretion. These results suggest that renal PGE2 synthesis is stimulated or decreased by 1-week Ca loading or deprivation, indicating a possible antihypertensive role of renal PGE2 during high-Ca intake in hypertensives.     

No effect of the plant growth regulator, chlormequat, on boar fertility

Chlormequat is a commonly used plant growth regulator in agriculture. Defined levels of chlormequat residue are allowed in food and an acceptable daily intake is defined for humans. However, there are results in the literature suggesting that a daily intake below the acceptable level for human is detrimental for mammalian reproduction. In the present experiment we investigated the effect of chlormequat at levels up to that acceptable for humans on reproduction in male pigs. Chlormequat (also known as chlorocholine chloride (CCC)) was mixed into the diet and given to the experimental animals at three levels (three treatment groups), i.e. 0 mg CCC/kg BW per day (Control), 0.025 mg CCC/kg BW per day and 0.05 mg CCC/kg BW per day. Eight mother sows per treatment group were used in the experiment. From the day of insemination, the mother sows received the experimental diets. The piglets were weaned at 4 weeks of age and two boar littermates continued on the same treatment as the dam until maturity and delivery of semen for in vitro fertilization (IVF) and in vivo fertilization. Semen volume, sperm concentration and fraction of live sperms were not (P 0.46) detrimentally affected by chlormequat intake. The fraction of oocytes developing to more than the one-cell stage at day 5 after IVF was not (P = 0.88) detrimentally affected by chlormequat intake. Chlormequat intake did not detrimentally affect the fraction of gilts being pregnant after one insemination (P = 0.65) or the number of embryos in the pregnant gilts (P = 0.36). Serum chlormequat concentration was 0.9 μg/kg in the 0.025 mg CCC/kg BW per day group and 1.8 μg/kg in the 0.05 mg CCC/kg BW per day group, but was below the detection limit in control animals. In conclusion, the plant growth regulator chlormequat could not be proven to be detrimental to the selected reproduction traits in male pigs. This is in contrast to existing results from the male mouse.     

Aluminium related changes in brain histology: protection by calcium and nifedipine

Aluminium (Al; 50 mg AlCl3/kg body wt/day) treatment caused a marked change in histological picture of normal brain as indicated by an increased number of vacuolated spaces. These changes returned to normal partially by simultaneous treatment with nifedipine (0.7 mg/kg body wt/day) and completely by similar treatment with 50 ppm calcium (CaCl2; 12.5 mg/kg body wt./day). Neither nifedipine nor calcium treatment alone altered the normal histological condition. The histological changes could not be correlated with the decrease in calcineurin activities in brain as nifedipine decreases calcineurin activity without any histological changes. Hence the histological changes may be considered as specific for Al and not due to a general decrease in calcineurin activity.     

The effect of adrenal cortical hormones on the calcium content of rat aorta.

The administration of prednisone in a dose of 10 mg/kg b.w. per os and of deoxycorticosterone in a dose of 10 mg/kg i.p. to rats weighing 200--220 g 24 hours before the experiment did not affect significantly the calcium content of the aortic vascular tissue. Metopiron, which influences biosynthesis of the adrenal hormones, likewise did not affect the calcium content when administered i.p. in a dose of 500 mg/kg b.w. and did not inhibit reserpine-induced calcium depletion. The results thus failed to confirm the hypothesis that reserpine influences the calcium content of the vascular wall via stimulation of corticold release.     

Preliminary observations on the relationship of calcium ingestion to vitamin D status in the green iguana (Iguana iguana)

We hypothesized the vitamin D-deficient green iguanas with depleted calcium stores would seek to augment calcium intake by self-selection of a high calcium source. Eight green iguanas were offered free-choice ground oystershell in addition to their regular diet. Of these, two had not been exposed to ultraviolet (UV-B) radiation for > 5 years and were demonstrated to be vitamin D-deficient by low circulating levels of the principal vitamin D metabolite, calcidiol (25-hydroxy-cholecalciferol). The six others had been exposed to a UV-B emitting bulb for the previous 3 years and had high circulating calcidiol levels. Average daily food intake (expressed as dry matter per kg body mass) did not differ between the Low-D and High-D iguanas. The daily oystershell intake of the Low-D iguanas (0.02–0.03 g/kg) was lower than that of the High-D iguanas (0.06–0.70 g/kg), leading to a significant difference in calcium intake. The failure of iguanas to increase calcium intake in response to vitamin D-deficiency was puzzling and suggests that vitamin D, as a steroid hormone, may play some role in the expression of calcium appetite. Zoo Biol 16:201–207, 1997. © 1997 Wiley-Liss, Inc.     

Ingestion of difructose anhydride III enhances absorption and retention of calcium in healthy men

We examined the effects of a nondigestible disaccharide difructose anhydride III (DFAIII) on calcium absorption and retention by means of a human balance study of single-blind crossover design. Twelve healthy male subjects ingested 250 mg of shell powder as calcium carbonate (corresponding to 100 mg of calcium) with or without 1.0 g DFAIII three times a day for 13 d. In the last 4 d as a balance period, all urine and feces were collected and evaluated for calcium excretion. The apparent calcium absorption (mg/d) and rate of absorption (%) were higher, and those of retention were much higher, in the DFAIII group than in the control group. Furthermore, serum osteocalcin increased after the experimental period in the DFAIII group but not in the control group. These results indicate that DFAIII ingestion enhances intestinal calcium absorption, which might be beneficial for bone metabolism.     

Calcium intake, food sources and seasonal variations in eastern Croatia

The objective of this study was to examine the quantity of calcium intake among adults, the sources of calcium, differences among seasons, as well as the differences between sexes, correlation with body mass index (BMI), and age. The study included 161 healthy volunteers from the eastern part of Croatia. Each subject completed three food frequency questionnaires (FFQ) with 150 items, at an interval of 3-4 months. The mean calcium intake for whole population for all three FFQs was 965 mg/day. At the same time, the quantity of calcium for all subjects was 14.2 mg/kg, women 14.5 mg/kg, and men 13.6 mg/kg, respectively. There was an inverse relation between calcium intake and age for men (r = -0.32 p = 0.028), but not for women. Correlation between calcium intake and BMI was negative, but not significantly. Milk and dairy products were the main source of calcium. Marginally low mean calcium intake goes to show the needful to educate the population.     

Effect of dietary calcium on serum BGP (osteocalcin).

The present study was designed to clarify the effects of dietary calcium (Ca) intake on serum BGP (osteocalcin) levels. Twelve women with a mean age of 21.2 years participated in the study. After one week of normal Ca intake (mean +/- SE, 535 +/- 2 mg/day), a low-Ca diet (163 +/- 1 mg/day) was given for one further week. Additional asparagine Ca (3 g as Ca/day) was also given to half of the subjects. Serum total and ionized Ca concentrations as well as BGP, PTH and 1,25(OH)2D3 were measured at the end of each period. Amounts of Ca and hydroxyproline excreted in urine were also determined. The plasma level of ionized Ca was significantly increased without any change in total Ca in either group. Low and high Ca intake decreased and increased urinary Ca excretion by 28% and 56%, respectively. Serum levels of BGP and 1,25(OH)2D3 were significantly augmented along with a transient increase in urinary hydroxyproline excretion after Ca deprivation. These results suggest that serum BGP is increased after one week of Ca restriction in healthy subjects.     

Effect of a moderate variation in dietary energy intake on the retention and excretion of zinc,calcium, and magnesium

Mineral balance was studied by metabolic balance techniques in 13 healthy college females aged 21–23 yr. They were fed diet containing 1780 kcal, 2580 kcal, and 25 g protein in a 20-d experiment period. Both diets contained approximately 5.28 mg zinc, 216.85 mg calcium, and 364.3 mg magnesium. The diet consisted of habitually consumed foods. Blood, urine and fecal samples were collected for mineral analysis using atomic absorption spectrophotometry. Plasma mineral levels were not affected by the change in dietary energy intake. Fecal calcium and magnesium were significantly higher when subjects were fed the low calorie (1780 kcal) diet, whereas there was no significant difference in fecal zinc for the two levels of dietary energy. Urinary calcium and magnesium were also significantly higher when the diet provided 1780 kcal though, on the other hand, urinary zinc was significantly higher when the diet provided 2680 kcal (P<0.05). Urinary calcium and magnesium correlated negatively, whereas urinary zinc correlated positively, with the dietary energy intake (P ^o<0.05). Dietary energy intake has a significant effect on the mineral balance of the subjects.     

Alteration of the acute toxicity and various pharmacologic effects of streptomycin sulfate by calcium 4'-phosphopantothenate

The effect of calcium 4'-phosphopantothenate (CPP) on acute toxicity of streptomycin and the decrease by the antibiotic of the muscle working capacity, "holes" reflex, body temperature and oxygen intake was studied on 258 albino mice weighing 22-26 g. Medical calcium pantothenate (CPA) was used for control purposes. CPP is an antagonist of streptomycin sulfate. In a dose of 1/10 or 1/5 of the LD50 injected intraperitoneally CPP lowered acute toxicity of streptomycin and prevented its effect in a dose of 0.11--1.1 g/kg injected subcutaneously on the muscle working capacity, "holes" reflex and body temperature. The spectrum index of the CPP antitoxic effect was equal to 22.5. By its acute toxicity CPP (LD50 1.18 +/- 0.07 g/kg) did not differ from CPA (LD50 1.25 +/- 0.08 g/kg). The efficacy of CPP, by its antitoxic spectrum, was 1.8 times higher than that of CPA. CPA lowered the streptomycin effect on the "holes" reflex and body temperature, while CPP prevented it. Both the drugs did not influence the decrease in the oxygen consumption induced by streptomycin.     

Effects of dose and timing of calcium supplementation on bone resorption in early menopausal women.

Bone resorption follows a circadian rhythm that peaks at night, reflecting the circadian rhythm of serum parathyroid hormone. Our previous studies in early postmenopausal women have established that 1000 mg of calcium given at 9 p. m. reduced bone resorption markers overnight, but not during the day. In contrast, 1000 mg given as a divided dose (500 mg doses at 9 a. m. and 9 p. m. each) reduced bone resorption markers during the day, but not during the night. We have now evaluated the effect of 1500 mg of calcium given as a divided dose of 500 mg in the morning and 1000 mg in the evening on bone resorption. We studied 26 healthy women (median age 56 years) whose menopause was less than five years before. On two days, urine was collected from 9 a. m. to 9 p. m. (day collection), and from 9 p. m. to 9 a. m. (night collection); a further fasting (spot) urine sample was obtained at 9 a. m. at the end of the night collection. On the second day, 500 mg of calcium in the carbonate form was taken at 9 a. m. (at the start of the collection) and a further 1000 mg at 9 p. m. (at the start of the second night collection). Calcium supplementation decreased urinary deoxypyridinoline (DPyr/Cr) during the day (p = 0.08) and night (p < 0.05), as well as urinary pyridinoline (Pyr/Cr) both by day (p < 0.05) and night (p < 0.001). There were also decreases in urine hydroxyproline. We conclude that the acute administration of 500 mg of calcium in the morning and 1000 mg in the evening to early postmenopausal women suppresses bone resorption markers during both the day and night.     

Enhanced trabecular-bone calcium deposition in female rats with a high physiological dose of prolactin diminishes after ovariectomy

Although an increase in trabecular-bone calcium deposition has been shown to be regulated by prolactin during lactation, the physiological significance of prolactin in bone calcium metabolism in nonlactating rats remains unclear. This investigation sought to demonstrate the effects of endogenous prolactin and a high physiological dose of exogenous prolactin on bone turnover and bone calcium deposition in normal female rats, using the 45Ca-labeling technique. Our results showed that suppression of endogenous prolactin with 6 mg/kg bromocriptine for 15 days significantly enhanced bone formation, but not bone resorption, in primarily trabecular sites, resulting in a significant increase in calcium deposition in the sternum and vertebrae, from -0.20+/-0.07 to 0.40+/-0.09 (p<0.05) and -0.07+/-0.11 to 0.34+/-0.06 (p<0.05) mmol Ca.(g dry mass)-1, respectively. Similarly, 2.5 mg/kg prolactin, a high physiological dose, increased sternal and vertebral calcium deposition, from -0.20+/-0.07 to 0.24+/-0.09 (p<0.05) and -0.07+/-0.11 to 0.25+/-0.18 (p<0.05) mmol Ca.(g dry mass)-1, respectively, by increasing bone formation more than bone resorption. However, as expected, prolactin had no effect on the tibia or femur, which are primarily cortical sites. Because several actions of prolactin have been known to be estradiol-dependent, we further investigated the dependence of prolactin action on 17beta-estradiol. We found that 2.5 mg/kg prolactin did not increase sternal calcium deposition in ovariectomized rats. However, 10 microg/kg 17beta-estradiol supplementation restored the action of prolactin. Ovariectomized rats given 17beta-estradiol plus prolactin also manifested slightly but significantly higher sternal total calcium content than sham-operated rats, (4.58+/-0.12 vs. 4.36+/-0.11 mmol Ca.(g dry mass)-1 (p<0.05)). We concluded that a high physiological dose of prolactin promoted calcium deposition in primarily trabecular sites of nonlactating rats. This effect was diminished after ovariectomy. In addition, we showed that basal endogenous prolactin played a role in the maintenance of normal trabecular-bone turnover.     

Influence of sex and immunocastration on feed intake behavior,skatole and indole concentrations in adipose tissue of pigs

Feed intake behavior was studied between 9 weeks of age and slaughter in a total of 36 gilts, 32 immunocastrates, 33 surgically castrated barrows and 33 boars from 36 litters. Consequences for the concentration of substances contributing to off odor of pork (skatole, indole) were evaluated. Animals were kept in groups of 12 pigs of the same sex and treatment and fed ad libitum (13.4 MJ ME, 17% CP, 1.1% lysine). Individual feed intake behavior was recorded continuously by an electronic feeder. Immunocastration was carried out with two injections of Improvac with at least 4 weeks between both injections (1st: 12 to 17 weeks of age, 2nd: 19 to 21 weeks of age). Feed intake/day increased from an average of 0.91 ± 0.02 kg/day up to 3.15 ± 0.04 kg/day before slaughter. This increase was associated with a 50% reduction in the number of meals/day (from 15.8 ± 0.44 to 7.2 ± 0.29 meals/day). The larger meal sizes resulted from an increase in both, the duration of feed intake/meal and the feed intake rate (g/min). In addition, sex and treatment differences were observed: Feed intake in boars was lower than in all other groups due to a reduction in the number of meals/day and in the time spent feeding/day. In females, time spent feeding/day was quite similar to boars, but resulted from a higher number of meals of shorter duration. Barrows had a significantly higher feed intake because of a higher number of meals/day resulting in more time spent feeding/day. The feed intake rate was similar in boars, gilts and barrows and showed an increasing trend during the study, starting from about 15 g/min up to four times the amount. Immunocastration affected feed intake behavior severely, especially the meal size increased dramatically because of higher feed intake rate, which exceeded that of all other groups by 25% at the end of the study. The number of meals/day was not influenced by immunocastration and was almost identical to that of boars. Highest skatole concentrations were measured in fat of boars, whereas indole concentrations were higher in immunocastrates than in all other groups. In gilts and barrows, skatole concentrations were related to growth rate. Additionally, the feeding rate was an important factor explaining the variability in skatole/indole concentrations in adipose tissue. The physiological mechanisms however need further clarification.     

Effect of the rate of increase in concentrate allowance with concentrates high or low in starch on the performance of dairy cows in early lactation

The effect of the rate of increase in concentrate allowance after calving with two concentrate mixes (A and B) differing in composition was evaluated using 64 Finnish Ayrshire cows during the first 100 days of lactation. After calving, the concentrate allowance of multiparous cows was increased stepwise from 4 to 17 kg/day, and of primiparous cows from 3 to 13.5 kg/day over 12 days (F rate of increase; multiparous 1.08 kg/day, primiparous 0.88 kg/day) or 24 days (S rate of increase; mutiparous 0.54 kg/day, primiparous 0.44 kg/day). The concentrates were formulated to have similar crude protein and metabolizable energy concentrations but differing starch and NDF concentrations. For concentrate A the starch and NDF concentrations were 421 and 167 g/kg dry matter (DM) and for concentrate B 258 and 251 g/kg DM. All cows received grass silage ad libitum. The higher concentrate intake during weeks 1 to 4 of lactation with F compared with the S rate of increase caused higher DM, energy and protein intake. The higher concentrate intake for F than for S treatment in early lactation did not cause a large decrease in silage intake (8.8 v. 8.3 kg DM/day). The intake of concentrate A and B after calving did not differ for S treatment. However, for F treatment the intake of fibrous concentrate B increased faster than starch-rich concentrate A during weeks 1 to 4 of lactation. The concentrate composition had no effect on energy-corrected milk (ECM) yield during weeks 1 to 4 of lactation for S treatments, but with F treatments the cows fed B concentrate produced more milk. The F rate of increase in concentrate allowance compared with the S rate increased the calculated energy balance after calving. The rate of increase in concentrate feeding post partum or concentrate composition had no effect on DM, energy or protein intake during the whole 100-day experiment. The average ECM yield over days 1 to 100 of lactation was higher for S than for F treatments and tended to be higher with concentrate B than A. Results of this study showed that by the fast rate of increase in concentrate allowance after calving on a grass silage diet, it was possible to improve the energy status of the cows in early lactation. This had, however, no effect on production later in lactation.     

Sex-specific effects of prolactin on food intake by rats

While prolactin (PRL) has been reported to increase food intake by virgin female rats, its effects on food intake by male rats are relatively unexplored. The present studies examined the possibility that PRL has sex-specific effects on food intake by rats. In the first study, intact female and male rats were given subcutaneous injections of saline vehicle or ovine (o) PRL (1.0 mg/kg) twice daily at 08:00 and 20:00 h for 10 days. Food intake, body weight, and water intake were measured daily. Results indicate that oPRL administration increased food intake by an average of 4.5 g per day in female subjects, but did not significantly alter body weight or water intake. Male rats treated with oPRL did not significantly alter their food intake, even after an additional five days of treatment. In the second study, a wide range of oPRL doses (vehicle, 0.02, 0.2, 2.0, and 20.0 mg/kg/day) were tested in gonadectomized female and male rats. The results indicate that female rats responded to increasingly larger doses of oPRL with greater increases in food intake, with a maximum increase of approximately 6. 1 g per day at a dose of 20.0 mg/kg. In contrast, male rats maintained baseline levels of intake across all oPRL doses tested. These data suggest that PRL has sex-specific effects on food intake.     

How does the suppression of energy supplementation affect herbage intake,performance and parasitism in lactating saddle mares?

Agroecology opens up new perspectives for the design of sustainable farming systems by using the stimulation of natural processes to reduce the inputs needed for production. In horse farming systems, the challenge is to maximize the proportion of forages in the diet, and to develop alternatives to synthetic chemical drugs for controlling gastrointestinal nematodes. Lactating saddle mares, with high nutritional requirements, are commonly supplemented with concentrates at pasture, although the influence of energy supplementation on voluntary intake, performance and immune response against parasites has not yet been quantified. In a 4-month study, 16 lactating mares experimentally infected with cyathostome larvae either received a daily supplement of barley (60% of energy requirements for lactation) or were non-supplemented. The mares were rotationally grazed on permanent pastures over three vegetation cycles. All the mares met their energy requirements and maintained their body condition score higher than 3. In both treatments, they produced foals with a satisfying growth rate (cycle 1: 1293 g/day; cycle 2: 1029 g/day; cycle 3: 559 g/day) and conformation (according to measurements of height at withers and cannon bone width at 11 months). Parasite egg excretion by mares increased in both groups during the grazing season (from 150 to 2011 epg), independently of whether they were supplemented or not. This suggests that energy supplementation did not improve mare ability to regulate parasite burden. Under unlimited herbage conditions, grass dry matter intake by supplemented mares remained stable around 22.6 g DM/kg LW per day (i.e. 13.5 kg DM/al per day), whereas non-supplemented mares increased voluntary intake from 22.6 to 28.0 g DM/kg LW per day (13.5 to 17.2 kg DM/al per day) between mid-June and the end of August. Hence total digestible dry matter intake and net energy intake did not significantly differ between supplemented and non-supplemented mares during the second and third cycles. In conclusion, supplementing lactating mares at pasture should not be systematic because their adaptive capacities enable to increase herbage intake and ensure foal growth. Further research is needed to determine the herbage allowance threshold below which supplementation is required.