L.W. Greene

Physiologic and metabolic response of exercising horses to added dietary fat

Summary Six mature Quarter Horse-type geldings were used in a replicated 3 × 3 Latin square experiment to determine the effects of adding 5 or 10% feed-grade rendered animal fat to the concentrate diet fed to performance horses. The experiment was conducted over a 14-day pre-trial period to acquaint horses to the experimental apparatus, a 28-day conditioning period and 3 diet treatment periods of 21 days, each conducted in a Latin square arrangement. The horses were exercised on a dirt track and diet effects were evaluated during and following a submaximal exercise test (SET) on an equine treadmill. Physiological responses to the SET were determined following each experimental period. Relative to the control, the horses required 21% and 25% less of the concentrate feed (P

Characterization of changes related to mineral balance and bone metabolism in the young racing Quarter Horse

Summary This study was conducted to determine physiologic responses reflective of bone metabolism during the onset of training and to relate those responses to the mineral requirements of young racehorses. Ten previously untrained Quarter Horse geldings were put into race training. They were fed a diet balanced to meet NRC recommendations for young horses in training. Feed, feces and urine were collected, weighed and analyzed over the experiment to determine mineral balance. Radiographs were taken of the left front leg to determine mineral content of a cross-sectional area of the third metacarpal. Blood samples were taken to determine osteocalcin, parathyroid hormone, 25-hydroxyvitamin D, Ca and inorganic P concentrations. Horses were gentled to ride, trained to gallop on the track and maintained in training for four 28-day periods. Blood serum was collected every 14 day, while radiographs and 72-hr total collections of urine and feces were taken every 28 d. Radiographs demonstrated that mineral content was lowest at day 56 in the dorsal, palmar and medial cortices of the third metacarpal. Urinary Ca declined dramatically from day 0 to day 28, then remained constant to day 56, before decreasing at day 84. Fecal Ca peaked at day 28 and remained elevated above day 0 amounts until day 112. calcium retention was negative at day 0, became slightly positive by day 28 and increased through day 112. Phosphorus and Mg balance remained relatively unchanged throughout the duration of the study. This study demon-strated changes in the mineral content of the third metacarpal and Ca balance during early training and suggests that further studies be performed.

EFFICACY OF A FAT-SUPPLEMENTED DIET ON MUSCLE GLYCOGEN CONCENTRATIONS IN EXERCISING THOROUGHBRED HORSES MAINTAINED IN VARYING BODY CONDITIONS

Abstract In a switchback experiment, twelve mature Thoroughbreds were randomly divided into three groups; each group was fed to achieve moderately low (ML), moderate (M) or moderately high (MI-I) body-fat content. Following a 28-day aerobic conditioning period, two horses from each group were fed a conventional, control diet and the other two were fed a fat-supplemented diet for a 21-day adaptation period. During the adaptation period, aerobic work continued as before, and the horses were also worked at a level to achieve anaerobiosis twice per week. After the adaptation period, horses performed a standardized exercise test consisting of four, 600-m sprints. Muscle biopsies were obtained from the biceps femoris before and after the test, and blood samples were taken before, during and throughout recovery from the test. Then, the horses were switched to opposite diets and the procedures were repeated. Muscle biopsies were obtained from biceps femoris before and after the exercise test, and blood samples were taken before, during and throughout recovery from the test. Pre-test muscle-glycogen concentrations were similar (P .05) in horses on all treatments. Thus, adapting Thoroughbred horses to a fat-supplemented diet inereased utilization of muscle glycogen, which may enhance performance that requires anaerobic energy production.

Lactation and reproductive performance of mares fed added dietary fat during late gestation and early lactation

Summary Eighteen pregnant mares were randomly allotted to one of two treatment groups. The control group was fed a conventional concentrate and the fat group was fed a concentrate containing 5% feed-grade rendered fat. Both concentrates had the same nutrient:calorie ratio and were fed in amounts required to maintain zero change in percent body fat of the mares. During the study, which began 60 d prior to expected foaling date and ended 60 d postpartum, mares were monitored for feed intake, body weight, rump fat thickness, ration digestibility, plasma glucose and lipid concentrations, milk composition and reproductive efficiency. Birth weight, growth rate, and plasma glucose and lipid concentrations were also measured in foals. Mares fed fat consumed less concentrate (P

Response of young horses in training to varying concentrations of dietary calcium and phosphorus

Summary This experiment was conducted to determine if additional mineral supplementation during early training would increase mineral retention and improve the strength of bone as indicated by the mineral content of the third metacarpal. Twelve previously untrained Quarter Horse geldings were randomly divided into two groups, broke to ride, trained to gallop on the track and maintained in training for four 28-day periods. One group of four horses served as controls and was fed a ration averaging 28.3 g of Ca/day and 21.9 g P/day while in training. Eight other horses were fed a ration averaging 34.9 g Ca/day and 26.4 g P/day while in training. Feed, feces and urine were analyzed to determine mineral balance. Radiographs were taken of the left front leg to examine bone density as indicated by radiographic bone aluminum equivalence (RBAE). The high mineral treatment group retained more Ca than controls (P

Adaptation to a Fat-Supplemented Diet by Cutting Horses

Summary In a crossover experiment, eight mature Quarter Horses were exercised by simulated cutting-horse training and fed either a control concentrate (C) or a 10% fat-supplemented concentrate (F) with Bermuda grass hay in a 60:40 ratio. The experiment consisted of two 28-day experimental periods with a 28-day standardization period between treatments. Digestion trials and standardized exercise tests (SET) were conducted every 7 days during experimental periods. Dietary fat had no detrimental effect on digestion of diet constituents, and all digestion coefficients were within expected ranges. Likewise, there was no significant difference in heart rates between treatments or SET days. Plasma lactic acid concentrations did not differ (P > .05) between treatments, however, there was a decline (P .05) in muscle glycogen over time when horses were fed C. On days 7, 14, and 28, muscle glycogen utilization increased (P

Growth, nutrient utilization, radiographic bone characteristics and postprandial thyroid hormone concentrations in weanling horses fed added dietary fat

Summary Thirty, 19-week-old Quarter Horses were utilized in a 112-d study to compare growth, nutrient utilization and post prandial thyroid hormone concentrations in weanling horses fed fat-supplemented or conventional diets. Concentrates were formulated to contain the same nutrient-calorie ratios and were fed with Coastal Bermuda grass hay in a 70:30 concentrate:hay ratio. Initially and at 28-d intervals the horses were weighed and measured for height, heart girth circumfer ence and subcutaneous fat thickness over the rump and ribs. Radiographs were taken of the right carpal and metacarpal phalangealjoints at the beginning and end of the experimental period for evaluation of bone density and physeal maturation. A digestion trial was conducted on each horse 10 d prior to completion of the study. On d 70, blood samples were col lected from 6 females in each treatment group over a 6-h collection period for evaluation of postprandial insulin, T4 and T3 concentrations in response to the diets. Horses in both groups consumed an average of 2.6% of body weight daily of total feed (Dry Matter). Weanlings consuming the fat-supplemented concentrate tended to have higher (P = .10) average daily weight gains (.80 vs .74 kg) and lower (P

Mineral balance in resting and exercised miniature horses

Summary Four mature Miniature Horse geldings were used in astudy to measure mineral losses from exercising horses. Mineral balance trials were conducted at rest and following workbouts after a four-week conditioning period. During the second mineral balance trial, the extent of mineral loss in the sweat of the exercising horses was quantified. Minerals lost in the sweat amounted to 1.8 g sodium, 3.9 g chloride, 5.9 g potassium, 8.5 mg calcium, and 10.7 mg phosphorus per Mcal DE consumed for work above maintenance. Dietary concentrations of calcium and phosphorus were adequate to meet the needs of the exercising horses, but a need for sodium, potassium and chloride supplementation of the diet was indicated. In this study, dietary requirements for Na, K and Cl during exercise were increased over basal dietary supply by threefold, seven-fold, and sixfold, respectively.

Physiologic and skeletal response to exogenous equine somatotropin (eST) in two-year-old Quarter Horses in race training

Summary This study was conducted to determine the physiologicand skeletal response to exogenous equine somatotropin (eST) in two-year-old horses in race training. Sixteen Quarter Horse geldings were paired by age (ave. age=26 months), and one horse from each pair was assigned at random to either the eST treatment group or the control. The experiment was conducted over 112 days during which the horses were broke to ride and trained on a dirt track in a regimen typical for racehorses in training. Radiographs were taken of the left third metacarpal on day 0,28, 42, 56, 70, 84 and 112. Jugular blood samples were collected every 14 days and analyzed for calcium (Ca), phosphorous (P), osteocalcin, 25-dihydroxyvitamin D (Vit D), parathyroid hormone (PTH), insulin-like growth factor-I (IGF-I) and growth hormone (GH). Daily injections of eST were well tolerated and resulted in no observed side effects. There was a trend (P= .14) for increased plasma GH concentrations in the treated horses as the trial progressed. Plasma IGF-I concentrations were increased (P .05). In this study, administration of eST was effective in elevating plasma IGF-I, which is stimulatory to osteoblasts, and serum osteocalcin, which is a product of osteoblastic activity.

COPPER BALANCE IN MINIATURE HORSES FED VARYING AMOUNTS OF ZINC

Summary Copper balance was examined in Miniature Horse geldings fed diets containing 12 ppm copper and either 73, 170, 400 or 580 ppm zinc in a 4×4 Latin square experiment. Horses were fed each diet for 14 days and were maintained in wood metabolism stalls during the last four days of each treatment period for total collections of feces and urine. Copper absorption ranged from 42.2% to 50.7% of intake, and copper retention as a percentage of copper absorption ranged from 89% to 94% across diet treatments. There was no alteration in copper absorption with increasing intake of zinc.