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Information Resources on the Care and Welfare of Horses

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Feeding Restrictions

Christensen, R.A., K. Malinowski, A.M. Massenzio, H.D. Hafs, and C.G. Scanes (1997). Acute effects of short-term feed deprivation and refeeding on circulating concentrations of metabolites, insulin-like growth factor I, insulin-like growth factor binding proteins, somatotropin, and thyroid hormones in adult geldings. Journal of Animal Science 75(5): 1351-1358. ISSN: 0021-8812.
NAL Call Number: 49 J82
Abstract: Two studies were performed with Standardbred geldings 7 to 21 yr of age to determine the sequence of changes in blood plasma concentrations of some hormones and metabolites during feed deprivation for 48 h and for 12 h after refeeding. Plasma hormone and metabolite concentrations were determined with methods validated for horse plasma. Insulin-like growth factor binding proteins (IGFBP) were determined with radioligand analysis following SDS-PAGE electrophoresis. In both experiments, plasma concentrations of triiodothyronine and thyroxine decreased (P < .01) during feed deprivation and increased (P < .01) during refeeding. Plasma glucose and IGF-I either decreased or were not altered during feed deprivation. In contrast, plasma concentrations of NEFA and urea nitrogen increased (P < .01) during feed deprivation and decreased (P < .01) during the refeeding period. Plasma somatotropin (ST) increased (P < .01) approximately 80% at 24 to 36 h of feed deprivation, declined (P < .01) to control values at 48 h of feed deprivation, increased (P < .01) nearly three fold at 3 h after refeeding, and returned to control values by 6 h after refeeding. We identified five IGFBP, and their plasma concentrations were not significantly altered during feed deprivation or following refeeding. We conclude that metabolite availability during feed deprivation and following refeeding alters the secretion of thyroid hormones, ST, and possibly IGF-I, thereby maintaining homeostasis in horses.
Descriptors: horses, American Trotter, food deprivation, refeeding, blood plasma, insulin like growth factor, binding proteins, triiodothyronine, thyroxine, blood sugar, fatty acids, urea, somatotropin, homeostasis.
Notes: Meeting Information: Paper presented at "Stressors That Alter Animal Growth" at the Midwest ASAS/ADSA meetings March 18-20, 1996, Des Moines, IA.

Frank, N., J.E. Sojka, and M.A. Latour (2003). Effect of hypothyroidism and withholding of feed on plasma lipid concentrations, concentration and composition of very-low-density lipoprotein, and plasma lipase activity in horses. American Journal of Veterinary Research 64(7): 823-828. ISSN: 0002-9645.
NAL Call Number: 41.8 Am3A
Descriptors: horses, metabolism, hypothyroidism, feeding practices, plasma lipid concentration, lipoprotein, plasma lipase activity.

Frank, N., J.E. Sojka, and M.A. Latour (2002). Effect of withholding feed on concentration and composition of plasma very low density lipoprotein and serum nonesterified fatty acids in horses. American Journal of Veterinary Research 63(7): 1018-1021. ISSN: 0002-9645.
NAL Call Number: 41.8 Am3A
Descriptors: mares, food deprivation, blood lipids, very low density lipoprotein, blood plasma, fatty acids, blood serum, variation, unrestricted feeding, triacylglycerols, blood sugar.

McManus, C.J. (2001). Effect of food restriction and pharmacological repartitioning of energy intake on reproductive activity in the mare. Dissertation, University of Kentucky: Lexington, Kentucky, USA.
Descriptors: horses reproduction, sexual behavior of animals, mares feeding and feeds, fertility effect of drugs on, mares fertility, fertility nutrition.
Notes: Thesis (Ph. D.)--University of Kentucky, 2001.

McManus, C.J. and B.P. Fitzgerald (2000). Effects of a single day of feed restriction on changes in serum leptin, gonadotropins, prolactin, and metabolites in aged and young mares. Domestic Animal Endocrinology 19(1): 1-13. ISSN: 0739-7240.
NAL Call Number: QL868.D6
Abstract: In a variety of species, short-term feed restriction leads to restriction leads to rapid changes in the reproductive axis and reduces serum levels of leptin. Two experiments were performed to test the hypothesis that a single day of feed restriction in aged and young mares would cause a suppression of the gonadotropins and serum leptin concentrations. The estrous cycles of 12 aged (>eight years; Exp. 1) and eight young (<five years; Exp. 2) mares were synchronized and the mares were conditioned to twice-daily meal feeding. On the seventh day after synchronization, restricted mares (n=6 for Exp. 1; n=4 for Exp. 2) were not fed for 24 hr; all mares were fed the second day. In Exp. 1, serum leptin concentrations significantly decreased in restricted mares, but not in controls. In Exp. 2, serum leptin concentrations declined in restricted mares and no decline was seen in the controls. Serum glucose concentrations did not change in response to feed restriction or refeeding, but in both experiments feed restriction caused an increased in free fatty acids. For both experiments, prolactin, FSH, and LH serum concentrations were not significantly altered by feed restriction. The observed of suppression may reflect the maintenance of sufficient levels of metabolizable fuels, rather than a failure of leptin to signal nutritional status to the reproductive axis of the mare.
Descriptors: mares, restricted feeding, refeeding, hormones, FSH, LH, prolactin, hormone secretion, blood serum, blood sugar, blood lipids, blood plasma, fatty acids, estrous cycle, synchronized females, age.

Messer, N.T., P.J. Johnson, K.R. Refsal, R.F. Nachreiner, V.K. Ganjam, and G.F. Krause (1995). Effect of food deprivation on baseline iodothyronine and cortisol concentrations in healthy, adult horses. American Journal of Veterinary Research 56(1): 116-121. ISSN: 0002-9645.
NAL Call Number: 41.8 Am3A
Abstract: Six healthy, adult horses, with normal (mean +/- SEM) baseline serum concentrations of total triiodothyronine (T3, 1.02 +/- 0.16 nmol/L), free T3 (FT3, 2.05 +/- 0.33 pmol/L), total thyroxine (T4, 19.87 +/- 1.74 nmol/L), free T4 (FT4, 11.55 +/- 0.70 pmol/L), total reverse T3 (rT3, 0.68 +/- 0.06 nmol/L), and cortisol (152.75 +/- 17.50 nmol/L), were judged to be euthyroid on the basis of response to a standardized thyroid-stimulating hormone response test. Serum concentrations of T3, FT3, T4, FT4, rT3, and cortisol were determined immediately before and every 24 hours during a 4-day period of food deprivation, when water was available ad libitum. Similar variables were measured 72 hours after refeeding. Decreases (to percentage of baseline, prefood deprivation value) in circulating T3 (42%), T4 (38%), FT3 (30%), and FT4 (24%) concentrations were maximal after 2, 4, 2, and 4 days of food deprivation, respectively (P < 0.05). Increases (compared with baseline, prefood deprivation value) in rT3 (31%) and cortisol (41%) concentrations were maximal after 1 and 2 days of food deprivation, respectively (P < 0.05). Refeeding resulted in increase in serum T4 and FT4, and decrease in rT3 and cortisol concentrations toward baseline values, after 72 hours (P < 0.05). Refeeding did not effect a return of T3 or FT3 concentration to baseline values after 72 hours (P < 0.05). Food deprivation appears to cause changes in serum concentrations of T3, FT3, T4, FT4, rT3, and cortisol in horses that are similar to those in human beings. This effect of food deprivation should be considered when results of serum thyroid hormone and cortisol assays are interpreted in the face of clinical. disease. These results further emphasize the invalidity of making a clinical diagnosis of hypothyroidism on the basis of baseline, serum thyroid hormone concentrations in horses, especially if the horses have been anorectic or inappetent.
Descriptors: horses, food deprivation, triiodothyronine, hydrocortisone, thyroxine, blood serum, total-thyroxine, free-thyroxine, total-triiodothyronine, free-triiodothyronine, reverse-triiodothyronine.

Meyer, H. (1996). Influence of feed intake and composition, feed and water restriction, and exercise on gastrointestinal fill in horses. 2. Equine Practice 18(9): 20-23. ISSN: 0162-8941.
NAL Call Number: SF951.E62
Descriptors: feed intake, water uptake, hay, feeds, physical activity, digestive system, dry matter content, moisture content, feed and water restriction, effects of exercise.

Murray, M.J. and E.S. Eichorn (1996). Effects of intermittent feed deprivation, intermittent feed deprivation with ranitidine administration, and stall confinement with ad libitum access to hay on gastric ulceration in horses. American Journal of Veterinary Research 57(11): 1599-1603. ISSN: 0002-9645.
NAL Call Number: 41.8 Am3A
Descriptors: horses, stomach ulcers, food deprivation, restricted feeding, gastrointestinal agents, stomach mucosa, lesions, acidity, unrestricted feeding, feeding behavior, grazing, hay.

Murray, M.J. and T.C. Grady (2002). The effect of a pectin-lecithin complex on prevention of gastric mucosal lesions induced by feed deprivation in ponies. Equine Veterinary Journal 34(2): 195-198. ISSN: 0425-1644.
NAL Call Number: SF955.E6
Descriptors: horses, food deprivation, lesions, stomach mucosa, pectins, phosphatidylcholines, disease prevention, stomach ulcers, pronutrin.

Nadal, M.R., D.L. Thompson Jr., and L.A. Kincaid (1997). Effect of feeding and feed deprivation on plasma concentrations of prolactin, insulin, growth hormone, and metabolites in horses. Journal of Animal Science 75(3): 736-744. ISSN: 0021-8812.
NAL Call Number: 49 J82
Abstract: Two experiments were conducted to determine 1) the prolactin response to different kinds of feedstuffs in stallions and 2) the effects of total feed deprivation on prolactin secretion in mares and its interaction with the prolactin response to feeding. Experiment 1 was performed with stallions as a 6 X 6 Latin square: A) no feed; B) pelleted feed fed to meet 82.5% of the horses' CP requirements; C) pelleted feed at 25% of the amount in B; D) pelleted feed as in B plus water ad libitum; E) cracked corn at the weight in B; and F) chopped alfalfa at the weight in B. The positive prolactin responses (P < .05) to feeding were similar for treatments B through F. The insulin response to feeding was highest (P <.05) in stallions fed water with the pelleted feed. In Exp. 2, 72 h of feed deprivation did not affect (P > .1) daily prolactin secretion. Feeding of a meal on the 3rd d of deprivation increased (P < .05) plasma prolactin, insulin, and glucose concentrations similarly in all mares. There was a positive growth hormone response (P < .1) after feeding in feed-deprived mares but not in fed mares. The prolactin response (P <.001) to thyrotropin-releasing hormone was greater (P = .083) for feed-deprived mares than for controls, whereas the response to sulpiride (P < .001) only tended to differ (P = .16) between groups. We conclude that prolactin secretion may be stimulated by aspects of eating other than the feedstuff itself. Total feed deprivation had little effect on the subsequent prolactin response to a meal or to other known secretagogues.
Descriptors: stallions, starvation, pelleted feeds, drinking water, mares, blood plasma, prolactin, insulin, blood sugar, fatty acids, maize, alfalfa, thyrotropin releasing hormone.

Powell, D.M. (1999). Effect of short- and long-term calorie restriction and diet composition on thyroid hormone and the metabolic responses to meal feeding and exercise in horses. Dissertation, University of Kentucky: 135 p.
Descriptors: horses feeding and feeds, horses exercise, Thoroughbreds.
Notes: Thesis (Ph. D.)--University of Kentucky, 1999.

Powell, D., L.M. Lawrence, T. Brewster Barnes, B. Fitzgerald, L.K. Warren, S. Rokuroda, A. Parker, and A. Crum (1999). The effect of diet composition and feeding state on the response to exercise in feed-restricted horses. Equine Veterinary Journal 30(Suppl.): 514-518. ISSN: 0425-1644.
NAL Call Number: SF955.E6
Abstract: Eight Thoroughbred horses were used to determine the effects of long-term calorie restriction and diet composition on serum T4 and T3 concentrations and metabolic responses with exercise. Horses were randomly assigned to 2 treatment groups (n = 4): Group 1, horses were fed a calorie-restricted diet designed to have 70% of the calories from the roughage source (RHR); Group 2, horses were fed a calorie-restricted diet designed to have 70% of the calories from the concentrate source (RHC). Horses then completed 2 step-wise exercise tests; one following a 12 h fast and one 2 h after a meal of 2 kg of a grain mix. Glucose concentrations declined (P < 0.01) in fed horses on the RHR diet but did not change in fed horses on the RHC diet. Fasted horses receiving the RHR diet had a more rapid increase in glucose concentration during exercise compared to fasted horses receiving the RHC diet (P < 0.01) as well as the highest glucose concentration at fatigue (P < 0.05). Insulin concentrations were higher (P < 0.05) at fatigue in fed horses on the RHR diet. Fasted horses receiving the RHR diet had higher (P < 0.01) pre-exercise FFA concentrations and a more rapid decline (P < 0.01) in FFA during exercise. Serum T3 concentrations increased (P < 0.01) in response to exercise within all treatments. The differences in thyroid hormone, glucose and FFA responses to exercise suggest that calorie source may be important in the hormonal regulation and energy metabolism of horses consuming calorie deficient diets.
Descriptors: food deprivation, thyroid hormones, fatty acids, heart rate, insulin, muscle fatigue, Thoroughbreds, effects of long-term calorie restriction, composition of diet, serum T4 and T3 concentrations, effects of execise.

Powell, D.M., L.M. Lawrence, B.P. Fitzgerald, K. Danielsen, A. Parker, P. Siciliano, and A. Crum (2000). Effect of short-term feed restriction and calorie source on hormonal and metabolic responses in geldings receiving a small meal. Journal of Animal Science 78(12): 3107-3113. ISSN: 0021-8812.
NAL Call Number: 49 J82
Abstract: The metabolic effects of short-term feed restriction and dietary calorie source were studied in horses receiving high-roughage or high-concentrate diets. Four Thoroughbred geldings were assigned to four treatment groups in a 4 x 4 Latin square experiment. The four treatments were 1) a nutritionally adequate high-roughage ration (70% roughage, 30% concentrate; AHR), 2) a nutritionally adequate high-concentrate ration (40% roughage, 60% concentrate; AHC), 3) 70% of the intake of the AHR diet (RHR), and 4) 70% of the intake of the AHC diet (RHC). Diets AHR and AHC were designed to meet the caloric need of horses undergoing moderately intense work. Blood samples were taken on the first 7 d of each period for analysis of serum T4 and T3 concentrations. On d 9 of each feeding period, each horse was fed 1.0 kg of oats as the morning meal. Jugular blood was sampled before and immediately after, as well as at 30 min after, completion of the meal and subsequently every hour for 7 h. Daily serum T4 and T3 concentrations were not affected by day, feeding level, or diet composition. Meal feeding produced an increase (P < 0.01) in T4 and T3 concentrations when horses were adapted to the AHR and AHC diets but not the RHR or RHC diets. Thyroxine concentrations were lowest (P < 0.05) when horses were adapted to the AHC diet. Glucose (P < 0.05), insulin (P < 0.01), and NEFA (P < 0.01) concentrations were higher in response to the meal when horses received RHR than for the other diets. These results indicate that nutrient restriction alters responses to meal feeding in horses and that this response may also be affected by the dietary roughage:concentrate ratio.
Descriptors: horses, restricted feeding, diets, roughage, hay, oats, blood serum, l thyroxine, triiodothyronine, blood sugar, blood lipids, fatty acids, insulin, digestive absorption, body weight.

Spader, B.R., P.R. Buff, and D.H. Keisler (2002). Fasting and re-feeding responses of plasma leptin in pony mares. Journal of Animal Science 80(Suppl. 2): 35. ISSN: 0021-8812.
NAL Call Number: 49 J82
Descriptors: horses, feed management, effects of feed deprivation, endocrinology.
Notes: Meeting Information: Meeting of the American Society of Animal Science, Southern Section, Orlando, Florida, USA; February 01-06, 2002.

Sticker, L.S., D.L. Thompson Jr., L.D. Bunting, J.M. Fernandez, and C.L. DePew (1995). Dietary protein and (or) energy restriction in mares: plasma glucose, insulin, nonesterified fatty acid, and urea nitrogen responses to feeding, glucose, and epinephrine. Journal of Animal Science 73(1): 136-144. ISSN: 0021-8812.
NAL Call Number: 49 J82
Abstract: Sixteen light horse mares (8 to 9 yr of age; 457 to 579 kg BW) were fed Bermudagrass hay and a corn/cottonseed hull-based supplement formulated to contain either 100% (control) or 50'7c (restricted) of the protein and(or) energy requirements for maintenance in a 2 X 2 factorial arrangement of treatments. Daily measurements of intake, BW, and plasma hormones and metabolites were made for 33 d. Plasma glucose, insulin, NEFA, and urea N were measured in hourly samples drawn on d 27, and parallel with an i.v. glucose tolerance test (IVGTT) and epinephrine challenge on d 29. Energy restriction increased daily NEFA concentrations (P < .001) and urea N (P = .013), whereas protein restriction decreased (P = .002) urea N concentrations. These effects of protein and energy restriction occurred within 24 h and were consistent (day effect, P > .1) throughout the remaining 24 d. Normal meal consumption elevated plasma glucose, insulin, and urea N concentrations (time effect, P < .08). Plasma NEFA concentrations did not change after feeding in mares fed control energy, but decreased in mares fed restricted energy (energy X time interaction, P = .005). After IVGTT, areas under the curve for plasma glucose and insulin were smaller in mares fed restricted protein (P < .05), whereas glucose area was larger in mares fed restricted energy (P = .009). After epinephrine injection, energy restriction increased the initial magnitude of the NEFA response, but after 50 min, reduced plasma NEFA below pre-injection concentrations (energy X time interaction, P = .06). We conclude that metabolic responses occur within 24 h of dietary changes and that plasma constituents are altered by protein and(or) energy restriction. during feeding, glucose, and epinephrine challenges.
Descriptors: mares, restricted feeding, energy intake, protein intake, body weight, blood sugar, blood plasma, insulin, fatty acids, urea, glucose tolerance, epinephrine.

Sticker, L.S., D.L. Thompson Jr., L.D. Bunting, J.M. Fernandez, C.L. DePew, and M.R. Nadal (1995). Feed deprivation of mares: plasma metabolite and hormonal concentrations and responses to exercise. Journal of Animal Science 73(12): 3696-3704. ISSN: 0021-8812.
NAL Call Number: 49 J82
Abstract: Twelve light horse mares were fed a control diet that provided 100% of their maintenance protein and energy requirements for 7 d and were then either continued on the control diet or totally deprived of feed (with access to water) for 3 d. Plasma samples were drawn twice daily throughout the experiment, at 15-min intervals for 9 h beginning 45 h after feed removal, and at 10-min intervals around an exercise bout beginning 73 h after feed removal. Feed deprivation increased (P < .06) whole blood beta-hydroxybutyrate and plasma NEFA, urea N, L-lactate, and glucagon concentrations, decreased (P = .02) IGF-I concentrations, and did not change (P > .1) plasma glucose, insulin, prolactin, triiodothyronine, and thyroxine concentrations. Exercise increased (P < .05) plasma NEFA, prolactin, and growth hormone (GH) concentrations in all mares. Plasma NEFA concentrations increased (P < .001 ) after exercise and remained increased in fed mares, but rapidly decreased in deprived mares (time X diet interaction, P = .006). Plasma glucose concentrations following exercise increased in deprived mares but decreased in fed mares (time X diet interaction, P = .07). The plasma prolactin response after exercise also differed between groups (P = .09). Feed-deprived mares had greater (P = .02) plasma GH concentrations before exercise (73 h after feed withdrawal) and had a greater (P < .001) GH peak at 10 min after initiation of exercise. The increase in secretion rate of GH due to feed deprivation in these mares was similar to that reported for other domestic species but was not nearly as great in magnitude.
Descriptors: mares, starvation, duration, blood plasma, exercise, fatty acids, urea, lactic acid, glucagon, insulin like growth factor, blood sugar, prolactin, hydrocortisone, somatotropin, thyroid hormones.

Suwannachot, P., C.B. Verkleij, S. Kocsis, E. Enzerink, and M.E. Everts (2000). Prolonged food restriction and mild exercise in Shetland ponies: effects on weight gain, thyroid hormone concentrations and muscle Na+K+-ATPase. Journal of Endocrinology 167(2): 321-329. ISSN: 0022-0795.
NAL Call Number: 448.8 J8293
Descriptors: horses, skeletal muscle, effects of food supply, effects of training, blood chemistry, endocrine system, growth.

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