Fat digestibility in Equus caballus follows increasing first-order kinetics.

The digestibility of ether extract varies greatly from forages to grains and further to added fats consisting mainly of triglycerides. This variation has been attributed to two main factors, the presence of nonhydrolyzable substances in the ether extract, especially in leafy foods, and the dilution of endogenous fecal fat. A compilation of results from 188 equine digestion balance observations on five basal feeds and 18 test feeds with added fats demonstrated a true digestibility of fat approaching 100% and an endogenous fecal fat of 0.22 g x d(-1) x kg BW(-1). The results revealed that nonhydrolyzable ether extract and endogenous fecal fat were insufficient to account for the difference between true digestibility and apparent digestibilities of ether extract in basal feeds and partial digestibilities of added fats in test feeds. A third possible contributing factor was demonstrated: an increasing first-order relationship between observed digestibilities (D, %) and the fat content of the feed (F, g/kg): D = 92.0 - 92.0e(-F/342). r2 = 0.81, P < 0.001. This equation indicates that 46% digestibility (half maximum) occurs at an ether extract or fat content of 24 g/kg, which is common in forages. It is consistent with fat digestibility or efficiency of absorption being a function of the rate of lipolysis, especially when residence time in the small intestine is limited. Consequently, we suggest that the kinetics of lipases, which are difficult to measure, may contribute to low digestibility when substrate concentration in the small intestine is low due to a low fat content in food. The status of vitamins A and E might be affected by low dietary fat contents and might be improved by fat supplementation.

Determination of the lactate breakpoint during incremental exercise in horses adapted to dietary corn oil.

OBJECTIVE: To determine lactate breakpoint of horses and test for effects of training and dietary supplementation with corn oil on that breakpoint. ANIMALS: 7 healthy Arabian horses. PROCEDURES: Horses received a control diet (n = 4) or a diet supplemented with 10% corn oil (4). A training program, which comprised two 5-week conditioning periods with 1 week of rest, was initiated. Submaximal incremental exercise tests (IET) were conducted before the first and after both conditioning periods. Blood samples for determination of blood lactate and plasma glucose concentrations were collected 1 minute before IET and during the 15 seconds immediately preceding each speed change. Data collected were fit to one- and two-slope broken-line models and an exponential model. RESULTS: Good fits were obtained by application of the broken-line models (adjusted R2 > 0.92) to blood lactate concentration versus speed curves. Lactate breakpoints increased 41% after training. After training, slope 2 and peak blood lactate concentrations were greater in the corn oil group, compared with controls. Mean blood lactate concentration at the breakpoint was not affected by training or diet. Plasma glucose concentration versus speed curves also fit the broken-line models, and glucose breakpoints preceded lactate breakpoints by approximately 1 m/s in the second and third IET. CONCLUSIONS AND CLINICAL RELEVANCE: Lactate breakpoints can be determined for horses, using blood lactate concentration versus speed curves generated during submaximal IET and may be useful for assessing fitness and monitoring training programs in equine athletes.

Behavior of horses is affected by soy lecithin and corn oil in the diet.

To test the hypothesis that dietary fats may improve tractability of horses, the effects of four total mixed diets on behavior were compared. The control diet (CON) contained chopped hay, corn, oats, beet pulp, molasses and a mineral mix; the three test diets contained an additional 10% (by weight) corn oil (CO), soy lecithin-corn oil (SL-CO), or soy lecithin-soy oil (SL-SO). Eight horses were fed each diet in random order for four 3-wk periods. Behavior was observed during the last week of each feeding period. Spontaneous activity was evaluated using a pedometer and was less in horses fed SL-CO than in controls (P = .022). Reactivity was evaluated as responses to pressure, loud noise, and sudden visual stimuli. Compared with results for control horses, reactivity was less in horses fed SL-CO during the visual stimulus test (P = .036), in horses fed CO in the noise test, the pressure test, and the visual stimulus test (P = .093, .108, and .116 respectively), and in horses fed SL-SO during the visual stimulus test (P = .108). These results provide the first quantitative evidence that dietary fats reduce the activity and reactivity of horses.

Acid-base variables during incremental exercise in sprint-trained horses fed a high-fat diet.

Seven Arabian horses performed a standard incremental exercise test on a high-speed treadmill at 6% slope then were randomly assigned to two diets, a control diet of ground hay and concentrates and a similar diet with 10% added fat (by weight). Horses were sprint-trained 4 d/wk, and two additional exercise tests were performed at 5-wk intervals. Heart rates and rectal temperatures were monitored and venous blood samples were collected at rest and at each speed increment. Whole blood was analyzed for glucose, lactate, and hemoglobin concentrations, and plasma was analyzed for pH, pCO2, albumin, total protein, and sodium, potassium, and chloride concentrations. Bicarbonate concentration ([HCO3-]) and strong ion difference ([SID]) were calculated, and total weak acid ([Atot]) was estimated from total protein. During exercise, there were increases in plasma sodium and potassium concentrations (P < .001), whole blood lactate and glucose (P < .001), and hemoglobin concentrations (P < .01). There were decreases in plasma pH, [HCO3-], and chloride concentrations (P < .001). The decrease in plasma pH was associated with changes in [SID] and [Atot] that combined to offset a decrease in pCO2. After sprint training, heart rates at rest and during submaximal exercise were decreased (P < .01), whereas heart rates at the end of exercise were increased (P < .05). Sprint training also increased workrate and estimated oxygen consumption at a heart rate of 200 beats/min (P < .001). Training increased the duration of exercise and the speed attained at the end of exercise (P < .05). Training increased the blood hemoglobin response to exercise and decreased the pCO2 response (P < .01). There were diet x training interactions for pH, pCO2, and [SID] (P < .05). Horses consuming the high-fat diet had higher blood glucose during both standard exercise tests and higher lactate concentrations at fatigue (P < .05) during the last test. Fat adaptation involving sprint training of horses may influence glucolysis at the level of pyruvate during an incremental exercise test.

A conceptual approach to optimal nutrition of brood mares.

Cumulative nutritional demands on good brood mares are unrivalled among domestic livestock, but little attention has been given to the influence of nutrition on their reproductive performance and efficiency. We suggest that part of the decline in racing performance of progeny of mares over 10 years of age may be caused by suboptimal nutrition. This article contrasts the concepts of minimal and optimal nutrient requirements, revives Hammond's concept of nutrient partitioning to the conceptus and mammary gland, and discusses energy and nutrient requirements during gestation and lactation. Further consideration is given to the aged brood mare.

Dietary aspects of developmental orthopedic disease in young horses.

The clinician may choose between two approaches to nutritional intervention. One is to evaluate the ration and make a painstaking effort to identify those specific factors operating in a particular case, then correct them. The second is to evaluate the ration, inspect for obvious aberrations, and, if finding none, proceed with no further delay to formulate an optimal diet, or a series, for the animals, and design a feeding program to suit farm management. Veterinarians should counsel clients on the possible or probable consequences of level of feeding on growth rate and clinical expression of DOD. In our view, retardation of growth rate by feeding poor quality hay is irresponsible. At present, we suggest that the new approach to retarded growth in weanlings and yearlings--a carefully formulated diet that specifically restricts starch and protein while supplying NRC minimum requirements of other essential nutrients--should be confined to selected individuals and be conducted under strict professional supervision.

Energy utilization and blood traits of ponies fed fat-supplemented diets.

The digestibility and heat production values for three fats of different origin were determined. Four pony geldings (225 kg) were used in a study consisting of four successive digestion trials utilizing a 4 X 4 Latin square design. The four dietary treatments were basal alone and supplemented with 15% corn oil, blended fat or inedible tallow. The blended fat was composed of a mixture of animal and vegetable fats. A 7-d preliminary period preceded a 7-d total fecal collection period for each trial. Heat production values were obtained by indirect calorimetry and calculated from oxygen consumption data. Fat supplementation increased (P less than .05) dietary metabolizable energy from a basal value of 3,224 kcal.kg intake-1.d-1 to a mean value of 3,984 kcal.kg intake-1.d-1 for the three fat diets. No difference in heat production was observed among the diets, averaging 2,883 kcal.kg intake-1.d-1. Fats increased (P less than .05) the energy balance (metabolizable energy-heat production) approximately 88% over the basal. Corn oil and blended fat produced the greatest energy balance of the fats. Utilization of energy in fats, calculated by difference, was not different, but tended to be highest in blended fat and lowest in the corn oil. Apparent fatty acid digestibility increased (P less than .05) with the addition of fat to the basal, partially due to the dilution of endogenous fecal fat, but digestion coefficients were not different (P greater than .40) among the high fat diets.