Effect of withholding feed on concentration and composition of plasma very low density lipoprotein and serum nonesterified fatty acids in horses

OBJECTIVE: To measure and compare the concentration and composition of very low-density lipoprotein (VLDL) in plasma and selected lipids in serum of horses fed mixed grass hay ad libitum or denied feed for 36 hours. ANIMALS: 4 healthy adult mares. PROCEDURE: Mares were either fed mixed grass hay ad libitum or denied feed for 36 hours beginning at 8:00 AM. Blood samples were collected every 2 hours during the study period and analyzed for nonesterified fatty acid (NEFA), triglyceride (TG), VLDL, and glucose concentrations and composition of VLDL. RESULTS: Withholding feed significantly increased mean serum concentrations of NEFA. By 36 hours, a 16-fold increase in mean serum NEFA concentration and 2-fold increase in mean plasma VLDL concentration, compared with baseline values, were detected. Mean plasma TG concentrations significantly increased with time in feed-deprived horses. Significantly lower overall mean plasma glucose concentrations were detected in feed-deprived horses. Mean percentage of protein in VLDL was significantly lower in feed-deprived horses. Plasma VLDL concentrations varied widely among horses in response to withholding feed. Plasma TG and VLDL concentrations remained unaltered in 2 horses. CONCLUSIONS AND CLINICAL RELEVANCE: Withholding feed significantly increases blood lipid concentrations in horses, but individual horses respond differently. Serum NEFA concentrations were increased in all 4 horses denied feed, indicating mobilization of tissue triglyceride stores. Variation in plasma VLDL concentration in response to withholding feed suggests that its metabolism is strongly influenced by other, as yet undetermined, factors in horses. Differences in the plasma VLDL concentrations among horses in response to withholding feed may be used as an indication of susceptibility to the hyperlipemic syndrome of Equidae.     

Nutrient restriction differentially modulates the mammalian target of rapamycin signaling and the ubiquitin-proteasome system in skeletal muscle of cows and their fetuses

The mammalian target of rapamycin (mTOR) signaling controls nutrient-stimulated protein synthesis in skeletal muscle, whereas ubiquitin-proteasome systems control the degradation of myofibrillar proteins. The objective of this study was to elucidate the effect of nutrient restriction on the mTOR signaling and ubiquitin-proteasome system in the skeletal muscle of cows and their fetuses. Beginning 30 d after conception, 20 cows were fed either a control diet that provided 100% nutrient requirements or a nutrient-restricted diet at 68.1% of NE(m) and 86.7% of metabolizable protein requirement. Cows were slaughtered on 125 d of gestation, and the LM of both cows and fetuses was sampled for the measurement of mTOR, ribosomal protein S6, adenosine 5'-monophosphate-activated protein kinase (AMPK), and protein ubiquitylation. When comparing the muscle samples from nutrient-restricted and control cows and their fetuses, no difference was observed for the content of mTOR and ribosomal protein S6, but the phosphorylation of mTOR at Ser(2448) and ribosomal protein S6 at Ser(235/336) were greater (P < 0.05) in control muscle than in muscle from nutrient-restricted animals. Because the phosphorylation of mTOR and ribosomal protein S6 upregulates translation, these results showed that nutrient restriction inhibits protein synthesis in muscle. The activity of AMPK in the muscle of nutrient-restricted cows was significantly lower (P = 0.05) than that of control cows. The protein ubiquitylation, however, was greater (P < 0.05) in the muscle from nutrient-restricted cows, showing accelerated protein degradation. No difference in the protein ubiquitylation was detected for fetal muscle. Data suggested that the decreased protein synthesis and promoted protein degradation resulted in muscle atrophy of pregnant cows, but not in fetal muscle. Results of this study show that in response to nutrient restriction, protein degradation was differentially regulated between cow and fetal muscle. The atrophy of cow muscle during nutrient deficiency may involve the enhanced degradation of muscle proteins.     

Effect of dental correction on feed digestibility in horses

To test the hypothesis that routine dental correction (removal only of sharp hooks and points from molars and premolars) would improve digestion of a hay/grain ration whereas performance 'floats' (rounding and smoothing of the dental arcades) would adversely affect digestion, 8 mature horses free from dental correction for over a year were used. Five-day digestion trials were conducted before and 2 and 4 weeks after correction in all horses. Although all horses had sharp points and minor premolar hooks, none had severe dental abnormalities. There were no significant differences found in apparent digestion of dry matter, crude protein, neutral detergent fibre or acid detergent fibre relative to precorrection data or controls (uncorrected horses on same digestion trial). Apparent digestibility of crude protein and fibre, however, was reduced if the occlusal angle of premolar 307 was greater than 80 degrees relative to the vertical axis (flattened). It should be recommended that regular dental correction be continued. However, if only small points and hooks are present, correction will not significantly improve digestion. Performance floating does not adversely affect digestion 2-4 weeks after the procedure is performed. Alterations in molar occlusal surface angle may affect digestibility of protein and fibre.     

Developmental regulation of the activation of translation initiation factors of skeletal muscle in response to feeding in horses

Objective-To determine whether feeding-induced activation of translation initiation factors, specifically protein kinase B, ribosomal protein S6 kinase (S6K1), ribosomal protein S6 (rpS6), and eukaryotic initiation factor 4E binding protein 1, in horses is affected by age. Animals-6 yearlings, six 2-year-old horses, and 6 mature horses. Procedures-After an 18-hour period of feed withholding, horses consumed a high-protein meal (2 g/kg) at time 0 and 30 minutes (postprandial state) or continued to have feed withheld (postabsorptive state). Blood samples were collected for the duration of the experimental procedures and used to determine plasma concentrations of glucose, insulin, and amino acids. At 90 minutes, biopsy specimens were collected from a gluteal muscle and used to measure phosphorylation of translation initiation factors. Results-Plasma glucose, insulin, and amino acid concentrations were elevated for the postprandial state, compared with results for the postabsorptive state, regardless of age. Phosphorylation of protein kinase B, S6K1, rpS6, and eukaryotic initation factor 4E binding protein 1 was increased for the postprandial state. There was an effect of age with increased phosphorylation of S6K1 at Thr(389) and rpS6 at Ser(235/236) in the yearlings and mature horses, compared with results for the 2-year-old horses. Conclusions and Clinical Relevance-Food consumption resulted in an increase in the activation of translation initiation factors, with the highest degree of responsiveness in the yearlings. This indicated that increased muscle accretion seen during growth could be a result of increased rates of muscle protein synthesis in response to a meal stimulus.     

Effect of exercise on development of capillary supply and oxidative capacity in skeletal muscle of horses

OBJECTIVE: To determine whether postnatal development of oxidative capacity and capillary supply of skeletal muscle is affected by various movement regimens in horses. ANIMALS: 35 foals. PROCEDURES: Dutch Warmblood foals were allocated into 3 groups (box stall rest, box stall rest with training, and free pasture exercise). Training comprised an increasing number of gallop sprints from 1 week after birth to 22 weeks of age. From 22 to 48 weeks, the 3 groups were combined and allowed to exercise freely. Capillary supply (diffusion index [ie, area supplied by 1 capillary]), citrate synthase (CS) activity, and succinate dehydrogenase (SDH) activity were measured in biopsy specimens of deep gluteus medius muscle. RESULTS: During the first 22 weeks, diffusion index increased in all 3 groups (the training and pasture groups had a smaller increase, compared with the box stall rest group), total SDH activity increased in the training and pasture groups and decreased in the box stall rest group, and CS activity decreased in all groups. The effect of the various movement regimens on the diffusion index remained after the groups were combined. CONCLUSIONS AND CLINICAL RELEVANCE: Withholding of exercise had a negative effect on the capillary supply (ie, diffusion index increased) that remained after box stall rest was discontinued and on oxidative capacity. Box stall rest with training prevented the negative effects and eventually had the same positive effect as pasture exercise.     

Effect of diet on gentamicin-induced nephrotoxicosis in horses.

Gentamicin sulfate-induced nephrotoxicosis was compared in 2 groups of horses fed different rations. Four horses were fed only alfalfa hay, and 4 other horses were fed only whole oats. Seven days after initiation of the diet, all horses were given gentamicin IV (5 mg/kg of body weight) every 12 hours for 22 days. Urinary gamma-glutamyl-transferase to urinary creatinine (UGGT:UCr) ratio was calculated daily, and serum concentration of gentamicin was measured at 1 and 12 hours after drug administration. Results indicated that horses fed oats had greater renal tubular damage than did horses fed alfalfa. Mean UGGT:UCr for horses fed alfalfa was 47.1 +/- 18.8 and was 100.0 +/- 19.0 for horses fed oats (P = 0.007). The UGGT:UCr in horses fed oats was greater than 100 for a total of 54 days; horses fed alfalfa had UGGT:UCr greater than 100 for only 7 days. Two horses not given gentamicin were fed only oats and 2 were fed only alfalfa. These horses had mean UGGT:UCr of 17.6 +/- 2.2 and 30.5 +/- 3.0, respectively. Mean peak and trough concentrations of gentamicin were statistically different for horses fed oats and those fed alfalfa (peak 23.16 +/- 1.87 and 14.07 +/- 1.79 micrograms/ml, respectively [P = 0.0001], and trough, 1.81 +/- 0.69 and 0.71 +/- 0.70 micrograms/ml, respectively [P = 0.0270]). Mean half-lives of gentamicin (estimated from peak and trough concentrations) for horses fed alfalfa (2.58 +/- 0.26 hours) and horses fed oats (2.88 +/- 0.27 hours) were not significantly different. Horses fed only oats had greater degree of gentamicin-induced nephrotoxicosis than did those fed only alfalfa.     

Storage and mobilization of muscle glycogen in exercising horses fed a fat-supplemented diet

In a switchback experiment, six mature mares were fed a control and a fat-supplemented diet while being exercised in a galloping regimen. After three weeks adaptation to each diet, horses performed an exercise test (ET) consisting of four, 600-m gallops. Muscle biopsies were obtained before and after the ET, and blood samples were taken before, during and throughout recovery from the ET. Resting glycogen concentration in the biceps femoris muscle increased (P<.05) from 15.77 mg/g wet tissue when the horses were fed the control diet to 22.89 mg/g when they were fed the fats-supplemented diet. During the ET, the amount of glycogen mobilized by the muscle increased (P<.05) from 6.99 mg/g when the horses were fed the control diet to 13.09 mg/g when they were fed the fat-supplemented diet. When the horses were fed the fat-supplemented diet, they galloped faster (P<.09), at a constant heart rate, during the last two gallops of the ET. Thus, adapting exercising horses to a fat-supplemented diet increased muscle glycogen concentrations, which appeared to enhance their performance past the anaerobic threshold.     

Voluntary feed intake and leptin sensitivity in ad libitum fed obese ponies following a period of restricted feeding: a pilot study

The relation between plasma leptin and daily ad libitum roughage intake was evaluated during a 14‐day period in eight obese Shetland ponies. When the feeding strategy was changed from maintenance feeding to ad libitum feeding, feed intake increased the first day, decreased the second day and increased again during the following days to reach a constant level after 8 days. Plasma leptin concentration increased during the first 2 days, but remained constant afterwards. Although the same pattern was found in all ponies, the magnitude of the increase in leptin on day 1 and the resulting decrease in feed intake on day 2 differed between ponies. A lower anorectic effect was seen in ponies with higher initial leptin concentration, suggesting the presence of different degrees in leptin sensitivity in obese ponies. High leptin production in a attempt to compensate for the decrease in leptin sensitivity might explain large variations in plasma leptin among obese ponies with similar body condition score. Further research is necessary to clarify whether the reduced leptin sensitivity precedes obesity in equines or vice versa.     

Blood pathophysiological changes in sheep following a prolonged (18-hour) period of hypocalcaemia induced by Na2EDTA solution.

Six aged Merino ewes were used in an experiment in which five were infused with 4.7% Na2EDTA solution intravenously for 18 h at a rate designed to produce hypocalcaemia and maintain recumbency, and five with 0.9% sodium chloride solution at the same rate for the same period (four were infused at different times with both solutions). Blood samples were collected every 3 h and determinations made of plasma Ca, Na, K, Mg, and inorganic P (PiP), erythrocyte Na, K and Mg, and PCV. Three of the hypocalcaemic sheep took 36-64 h to regain their feet. Plasma Ca and K, and erythrocyte Na showed significant (all P less than 0.01) decreases in the group infused with Na2EDTA compared with the group infused with saline while PCVs were significantly (P less than 0.01) greater in the former group. The sheep model used could be suitable for the study of the effects of prolonged hypocalcaemia and recumbency in cows.     

ORIGINAL ARTICLE: Impact of feeding level on digestibility of a haylage‐only diet in Icelandic horses

Eight mature Icelandic geldings were used in an experiment arranged as a change‐over design to evaluate the effect of feeding level on the digestibility of a high‐energy haylage‐only diet. The horses were fed a low feeding level 10.7 g dry matter (DM)/kg body weight (BW) (maintenance) and a high feeding level 18.1 g DM/kg BW (1.5 × maintenance) during two 23 days experimental periods. Total collection of faeces was performed for 6 days at the end of each period to determine the coefficient of total tract apparent digestibility (CTTAD). The CTTAD for DM, organic matter, neutral detergent fibre (NDF), acid detergent fibre and energy was higher in horses fed at the low level of feed intake, while feeding level did not affect the CTTAD of crude protein. The largest difference in CTTAD between feeding levels was found for NDF. The content (/kg DM) of digestible energy in the haylage was 11.3 MJ at the low level of feed intake and 10.6 MJ at the high level of feed intake. It can be concluded that feeding level has a large impact on the digestibility and energy value of early cut haylage in Icelandic horses.     

Endoscopy via a gastric cannula to monitor the development of ulcers in the pars esophagea in pigs after consumption of a finely ground feed combined with a period of withholding of feed

OBJECTIVE: To develop an endoscopic technique for use in monitoring devlopment of gastric ulcers via a gastric cannula during withholding of feed and administration of a finely ground diet to pigs. ANIMALS: 6 pigs weighing between 60 and 70 kg. PROCEDURE: A gastric cannula was surgically inserted adjacent to the pars esophagea in each pig. Pigs were fed a finely ground diet for two 7-day periods that were separated by a 48-hour period during which feed was withheld. Endoscopic examination via the gastric cannula was used to monitor development of ulcers in the pars esophageal region of the pigs during the 48-hour period of feed withhold and subsequent 7-day feeding period. An ulcer score was assigned during each endoscopic examination. A final examination was performed during necropsy and compared with results for the final endoscopic examination. RESULTS: Consumption of a finely ground diet for 7 days resulted in progressive erosive damage to the pars esophageal region of the stomach. Further significant increases in ulcerative damage were detected after 24 and 48 hours of withholding of feed. Final examination during necropsy did not reveal significant differences from results obtained during the final endoscopic examination. CONCLUSIONS AND CLINICAL RELEVANCE: Endoscopic examination via a gastric cannula was an effective means of monitoring ulcer development in the pars esophagea of pigs. Feeding a finely ground diet and withholding of feed induced endoscopically observable ulcers in the stratified squamous epithelial region of the stomach. Direct visual examination during necropsy confirmed the accuracy of endoscopic examination.     

Effect on young calves of a one-hour feeding stop during a 19-hour road journey.

This study examined the effects of transporting calves less than four weeks of age on a journey at the limit of the maximum time laid down by recent EU legislation. In both summer and winter, 45 calves were transported by road for 19 hours. The journey included a one-hour break on the lorry in which the calves were given either a glucose/electrolyte solution, water, or nothing at all. Control groups of 15 calves remained on farm and were fed normally. The effects of the journey were greater during winter when liveweight loss was greater and more prolonged, and the calves suffered a depression in body temperature. Mid-journey feeding was of minimal benefit. Feeding electrolytes reduced the extent of dehydration as measured by changes in plasma total protein and albumin concentrations, but there was some indication that giving water alone was detrimental. Most of the variables which changed during the journey had recovered in line with the values in the control animals within 24 hours of the end of the journey, but the calves' liveweight and plasma creatine kinase activity took up to seven days to stabilise. The study highlighted the problem that young calves have in maintaining body temperature during transport, especially during colder weather.     

Effect of different blood‐guided conditioning programmes on skeletal muscle ultrastructure and histochemistry of sport horses

The effects of three different blood‐guided conditioning programmes on ultrastructural and histochemical features of the gluteus medius muscle of 2‐year‐old sport horses were examined. Six non‐trained Haflinger horses performed three consecutive conditioning programmes of varying lactate‐guided intensities [velocities eliciting blood lactate concentrations of 1.5 (v_1.5), 2.5 (v_2.5) and 4 (v₄) mm respectively] and durations (25 and 45 min). Each conditioning programme lasted 6 weeks and was followed by a 5‐week resting period. Pre‐, post‐ and deconditioning muscle biopsies were analysed. Although training and detraining adaptations were similar in nature, they varied significantly in magnitude among the three different conditioning programmes. Overall, the adaptations consisted in significant increases in size of mitochondria and myofibrils, as well as a hypertrophy of myofibrillar ATPase type IIA muscle fibres and a reduction in number of type IIx low‐oxidative fibres. Together, these changes are compatible with a significant improvement in both muscle aerobic capacity and muscle strength. The use of v_1.5 and v_2.5 as the exercise intensities for 45 min elicited more significant adaptations in muscle, whereas conditioning horses at v₄ for 25 min evoked minimal changes. Most of these muscular adaptations returned towards the pre‐conditioning status after 5 weeks of inactivity. It is concluded that exercises of low or moderate intensities (in the range between v_1.5 and v_2.5) and long duration (45 min) are more effective for improving muscle features associated with stamina and power in sport horses than exercises of higher intensity (equivalent to v₄) and shorter duration (25 min).     

Variations of serum vitamin E, cholesterol, and total serum lipid concentrations in horses during a 72-hour period

Fluctuations of serum vitamin E (alpha-tocopherol), cholesterol, and total lipids were monitored in 12 horses at 3-hour intervals for 72 hours. Mean coefficients of variation were 12, 5, and 15%, respectively. Statistical analyses were used to conclude that instrumentation error was accountable for only a small portion of the vitamin E variation. Results indicated that a single serum sample assay is an unsatisfactory indicator of vitamin E status in horses. These data have clinical application in the evaluation of horses suspected to be affected with equine degenerative myeloencephalopathy. The large variance of serum total lipids and the lack of correlation of it with serum vitamin E over time preclude the use of vitamin E/serum total lipids ratio in assessing vitamin E status.     

The effect of aerobic exercise after a period of inactivity on bone remodeling and calcium and phosphorus balance in mature horses

An experiment was conducted to determine the effect of aerobic training after a sedentary period on bone remodeling and Ca and P balance and serum concentrations in varying ages of mature horses. Eighteen stock-type geldings were blocked into three age groups (6 to 10, 11 to 15, and 16 and older years of age), within two groups of nine, with horses randomly assigned to one of two exercise treatments, exercised for 112 days (control) or idle for 56 days followed by 56 days of exercise (treated). Blood samples were taken at the beginning of period I and at 14-day intervals thereafter to determine serum concentrations of osteocalcin (OST), Ca, and P. Dorsal-palmar and lateral-medial radiographs were taken of the left third metacarpal bone on days 0, 56, 84, and 112 to monitor changes in bone density. Total fecal and urine collections were taken for 72 hours on days 0, 56, and 112. Mean serum OST concentrations were affected by treatment (P<.02), time (P<.001); and the interactions of treatment and age (P<.003), time and treatment (P<.001), and time, treatment, and age (P<.001). Overall dorsal (DBRAE), palmar (PRBAE), and medial (MRBAE) RBAE means were affected by time (P<.001), as was overall lateral (LRBAE) RBAE mean (P<.005). Overall DBRAE and PRBAE means were lower (P<.04) at day 56, and higher at day 84 (P<.02) and 112 (P<.001) as compared to day 0. Mean serum Ca concentration was affected by treatment (P<.003) and time (P<.001). Mean serum P concentration was affected by the interaction of time and treatment (P<.001). Mean apparent daily Ca balance was affected bythe interaction of time, treatment, and age (P<.03). Mean apparent daily P balance was affected by treatment (P<.02) and time (P<.001). Biochemical and radiographic data from this experiment suggest that bone remodeling as well as Ca and P balance and serum concentrations are affected by age, inactivity, and exercise in mature horses.