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Energy expenditure was measured in four geldings (433 to 520 kg) during submaximal exercise on a racetrack using a mobile open-circuit indirect respiration calorimeter. A total of 304 5-min measurements of O2consumed and CO2produced were taken. Measurements were made with and without riders. The amount of energy expended by the horses was exponentially related to speed and was proportional to the body weight of the riderless horse or the combined weight of the horse plus rider and tack. Total energy expended by the four horses walking, trotting, cantering was best described by the equation:where Y = energy expended (cal·kg−1·min−1) and × = speed (m/min). Digestible energy (DE) required above maintenance was calculated as

Energy balance studies using indirect calorimetry were conducted with four mature equids ranging in weight from 125 to 856 kg. Each animal was fed three different levels of intake of the same diet. The amounts of digestible and metabolizable energy required for zero energy balance were determined by calculating regression equations for energy balance against energy intake. It was concluded that the maintenance requirements of equids vary linearly with body weight. No advantage was found for the use of weight75for the comparison of equids within the range studied. The digestible energy (DE) requirement for equids confined to metabolism stalls was DE (kcal/d) = 975 + 21.28 × W where W equals body weight in kg. If a factor for activity similar to that suggested by the National Research Council was included, the requirement could be calculated by the equation: DE (kcal/d) = 1,375 + 30.0 × W.

The energy requirements of lactating pony mares were studied. Twenty-two mares were divided into three groups and fed one of three diets consisting of different ratios of corn, alfalfa meal and soybean meal. All three diets were fed at a level of intake that supplied the National Research Council (NRC) recommended amount of crude protein for pony mares during the first 3 mo of lactation. Diets 1, 2 and 3 supplied 93.0, 74.8 and 57.2 kcal of digestible energy (DE)• kg body weight−1•d−1, respectively. The DE content of each diet was determined in a 3 × 3 Latin square digestion trial using mature pony geldings fed at a rate of 1.5% body weight/d. Mares and foals remained on trial for an 11-wk period. The mares and foals were weighed each week, and foal heart girths and heights at withers were measured. Least-squares regression of foal average daily gain with mare weight and energy intake of the mare as independent variables showed no significant effect of energy intake of the mare on foal growth. A regression equation that describes the influence of energy intake of the mare on mare weight change is Y = .0031−.0033 X1+ .0531 X2, where Y is average daily weight change of the mare (kg), X1= postfoaling mare weight (kg) and X2= measured daily energy intake of the mare (Meal DE/d). Using this equation, a 200-kg mare fed 12.37 Meal DE/d, or 85% of the NRC recommendation for lactating pony mares, would be expected to maintain body weight during the first 3 mo of lactation. A 200-kg mare fed the NRC recommended amount (14.58 Mcal/d) would be expected to gain 5% body weight over this period.

The Ca:oxalic acid ratios varied from 1.9 to 7.8 in 22 samples of alfalfa pellets and varied from 1.7 to 3.9 in 11 samples of alfalfa hay. The correlations between protein and oxalic acid, and Ca and oxalic acid were not considered large enough to be of predictive value. Metabolism studies were conducted with eight mature ponies fed diets containing alfalfa hays with different Ca:oxalic acid ratios. One hay contained 14.8 mg of Ca and 5 mg of oxalic acid/g of dry matter (Ca:oxalic acid ratio of 3.0) and the other hay contained 14.6 mg of Ca and 8.7 mg of oxalic acid/g of dry matter (Ca:oxalic acid ratio of 1.7). The diets were 33% hay and 67% oats. No significant differences in apparent or estimated true digestibility of Ca, P or Mg were found between diets. The alfalfa hays used in these studies were considered to be excellent sources of available Ca for ponies.

Absorption, excretion and tissue distribution of stable Zn and 65Zn in mature ponies were studied in three experiments. In the first experiment, the metabolism of stable, dietary Zn and intravenously administered 65Zn was studied in three ponies in a 3 × 3 Latin square design. The ponies were fed a corn and beet pulp diet containing 35 mg Zn/kg or the same diet with 250 or 520 mg of supplemental Zn as ZnO. The ponies absorbed and retained more stable Zn when fed 250 mg of supplemental Zn than when fed the basal diet alone or the basal diet plus 520 mg of supplemental Zn. The ponies retained more 65Zn (percentage of dose) when fed the basal diet or the same diet with 250 mg of supplemental Zn. The intestinal tract was the major route of excretion of stable Zn and 65Zn. In the second experiment, the retention of an oral dose of 65Zn was studied in three ponies in a 3 × 3 Latin square design. The ponies were fed a beet pulp, corn starch and alfalfa meal diet containing 15 mg Zn/kg or the same diet with 240 or 480 mg of supplemental Zn as ZnO. The ponies retained a greater percentage of a dose of 65Zn when fed the basal diet or the basal diet plus 240 mg of supplemental Zn than when fed 480 mg of supplemental Zn. In the third experiment, four ponies fed a commercial pelleted diet containing 125 mg Zn/kg were given an intravenous dose of 6SZn. The ponies were killed 7 or 14 days after receiving the dose and tissues were counted for radioactivity. Parenchymatous organs such as liver, pancreas, kidney, heart and lung contained a greater percentage of 65Zn than did structural organs such as bone and muscle. The wall of the gastrointestinal tract contained more radioactivity than did the contents.

Two experiments were conducted to study the effect of varying the temporal distribution of conditioning sessions on equine learning behavior. In the first experiment, 15 ponies were trained to clear a small hurdle in response to a buzzer in order to avoid a mild electric shock. Three treatments were used. One group received 10 learning trials daily, seven times a week; one group was trained in the same fashion two times a week and one group was trained once a week. The animals conditioned only once a week achieved a high level of performance in significantly fewer sessions than the ones conditioned seven times a week, although elapsed time from start of training to completion was two to three times greater for the former group. The twice-a-week group learned at an intermediate rate. In the second experiment, the ponies were rearranged into three new groups. They were taught to move backward a specific distance in response to a visual cue in order to avoid an electric shock. Again, one group was trained seven times a week, one group was trained two times and one group was trained once a week. As in the first experiment, the animals trained once a week achieved the learning criteria in significantly fewer sessions than those trained seven times a week, but, as in trial 1, elapsed time from start to finish was greater for them. The two times-a-week group learned at a rate in-between the rates of the other two groups.

Differences in forage digestibility by ruminal and cecal microbes were studied using a nylon bag and in vitrotechniques. The microbes were from a cow fed hay, from the cecum of a pony fed hay and from the cecum of a pony fed hay and grain. Digestibility of cell wall and dry matter digestibility of timothy hay, orchard grass, and wheat straw was greater when exposed to ruminal microbes than when exposed to cecal microbes for 24 to 48 hours. The digestibility of these forages was greater by the microbes from the hay adapted cecum than by microbes from the hay plus grain adapted cecum when the nylon bag method was used but not by the in vitromethod. Alfalfa digestibility was similar in all microbial environments.The ruminal microbes fermented all forages but alfalfa at a faster rate than did the cecal microbes. Rates of digestion by microbes from the hay adapted cecum and from the hay plus grain adapted cecum were similar.

IntroductionWhat is an herbivore? According to Webster's dictionary (Anon, 1971), an herbivore is a plant eating mammal with a stout body and a long small intestine. Many zoologists consider herbivores to be those animals that eat plants in contrast to those that fed on meat or a mixture of both (Landry, 1970). Thus animals that eat seeds and fruits would be considered as herbivores. However in this paper, an herbivore will be defined as an animal (vertebrate or invertebrate) that can subsist on a diet consisting primarily of fibrous plant material. Nonruminant herbivores include a wide range of nonruminating species such as the hippopotamus, hamster, kangaroo, sloth and certain primates in which a voluminous, compartmentalized or sacculated stomach serves as the primary site of microbial activity (Moir, 1965; Kerr, 1972). But the majority of the nonruminant herbivores rely on the hind gut as the primary site of fermentation. The following discussion will deal with the latter group.

Potassium metabolism and some metabolic interractions of K, Mg and Ca were studied in a series of balance trials with ponies. The kidney was the primary pathway of K excretion. Increasing K intake markedly affected the renal excretion of K but had only small effects on fecal excretion. Increasing K intake increased retention and apparent digestibility of K. High levels of dietary Ca (3.4%) did not influence K metabolism but the highest level of Mg (.81%) increased the apparent digestibility of K. A level of 3.4% K did not decrease Mg, P or Ca digestibility and retention. The maintenance requirement of K was estimated to be 48 mg/kg of body weight. The estimates did not account for sweat and dermal loss of K. The small intestine appeared to be the site of greatest apparent net K absorption but a significant amount of K was absorbed from the large intestine.

The horse industry has increased greatly during the past 25 yr. During that period universities and experiment stations have greatly expanded their equine teaching and research programs. Although several research areas such as genetics and behavior have been investigated, the primary areas have been nutrition and reproduction. Recent advances in these latter areas are reviewed and suggestions for further research are given. It is concluded that significant advances toward a better understanding of equine nutrition and reproduction have been made but much more research is needed. Universities are encouraged to continue to supply highly trained individuals to an industry that is becoming more complex.

Weight, height, and cannon bone measurements were obtained on 1,992 Thoroughbred foals. Colts were heavier than fillies at birth and the differences increased with age. Dams under 7 years of age and older than 11 years had foals of lighter weight at birth than mares 7 to 11 years of age and the differences persisted at 510 days of age. Foals born in April, May, or June were heavier than foals born in January, February, or March. Year of birth also influenced body weight. The trends for height at withers and cannon circumference were similar to those of body weight.

A pelleted ration was fed limited or ad libitumto two groups of seven Shetland 8-month-old ponies for 117 days. During the last 56 days, gelatin was added to the diets of four animals in each of the two intake groups. Gelatin was added at levels of 30 and 90 g per 100 kg body weight for the first and second 28-day periods, respectively.Ponies fed the diet ad libitumconsumed 180% more feed, had 50% greater rate of hoof growth (.384 ± .009 vs.254 ± .008 mm/d), 200% greater increase in height at the withers and 425% greater increase in body weight than ponies fed the limited level. The hoofs of ponies fed ad libitumhad 82% greater surface area at the sole border than those fed limited amounts. The addition of gelatin did not affect (P<.05) hoof growth, base area, compression strength (yield point or elasticity), moisture, iron, zinc or nitrogen content. Rate of hoof growth declined with age. Hind hoofs grew faster than front hoofs. Sex of animals did not affect hoof growth or quality.The average compression yield strength of hoof wall was 146 ± 5 meganewtons per meter (mN/m2). The tangent modulus of elasticity just prior to failure was 3.722 ±.111 mN/m2. Neither yield strength nor elasticity were changed by level of diet intake or gelatin supplementation or by iron, zinc, or nitrogen content of the hoof wall.The zinc content of the hoofs of limited fed ponies (136 ± 3 ppm) was higher (P<.01) than those that were fed ad libitum(114 ± 2 ppm). Hoof nitrogen, and moisture content were not different (P<.05) between groups. Hoof wall iron content was greater for limited fed ponies. Nitrogen content averaged 17.7 ±.1%. Moisture content of all postmortem hoof samples averaged 27.8 ± .2%. Specific gravity of limb bones was greater (P±.05) for the ponies fed ad libitum.

The relationship of ultrasonic measurements to actual fat cover, the value of such measurements for the prediction of total body fat, and the effect of exercise and level of diet intake on fat cover were studied in horses and ponies in four trials. In trial 1 eight ponies were allowed feed ad libitumand seven ponies were fed a limited amount of the same diet for 41/2 months. Ultrasonic rump fat thickness was highly correlated (r = .85), with actual rump fat thickness. The ponies fed ad libitumhad greater live weights and rib and rump fat thickness than ponies fed restricted amounts. Twelve horses were evaluated by ultrasound for fat thickness over the shoulder, rib and rump after 0, 30 and 90 days of exercise in the second trial. Shoulder fat and rump fat decreased after 30 days, although rib fat and body weight did not change.In a third experiment, eight horses were evaluated for fat thickness by ultrasound, then slaughtered and analyzed for chemically ex-tractable fat. Rump and shoulder fat were correlated with extractable fat, (r = .93 and r = .71, respectively). The relationship between rump fat determined ultrasonically (X, cm) and extractable fat (Y, %) was described by the equation: Y = 8.64 + 4.70 X (r2= .86).Ultrasonic measurements were made at 30 and 80 days on five exercised and six control ponies in a fourth experiment. The animals were slaughtered and extractable fat determined. Rib fat, rump fat thickness and extract-able fat were lower for the exercised than control groups. The relationship between rump fat (X, cm) and extractable fat (Y, %) was described by the equation: Y = 3.83 + 5.58X (r2= .64).It was concluded that fat cover in horses and ponies can be estimated by ultrasound and that rump fat measurement is useful in the prediction of total body fat.

Factors affecting glucose tolerance and the effect of volatile fatty acids on plasma glucose were studied with five ponies in two 5×5 latin square trials. The treatments were equimolar infusions of glucose, acetate, propionate, butyrate and isontonic saline in fed or fasted ponies.Animals fasted for 72 hr. exhibited a markedly lower glucose tolerance than those fed ad libitum. Propionate appeared to be the only VFA stimulating a significant glucose response in the fasted animals, but no response was noted in the fed animals. The data suggest that length of fast is an important variable in evaluating glucose tolerance in the horse, and that plasma glucose control may be mediated in part by different mechanisms than in the ruminant species.

Ground barley was separated according to particle size into two fractions—high fiber (11.3 %) and low fiber (2.5%). Growing pigs fed the low fiber fraction gained weight faster and more efficiently than pigs fed ground barley. The high fiber fraction was not as efficiently utilized as ground barley by pregnant sows or beef bulls, but there was no effect upon reproductive performance of the sows or weight gains of the bulls. It was suggested that under certain conditions, more efficient use of barley could be obtained if the barley were separated according to particle size and the low fiber fraction fed to growing pigs and the high fiber fraction fed to ruminants.

A 3 × 3 latin square design balance trial was conducted with three mature ponies fed diets containing 0.16, 0.31 or 0.86% magnesium. Increasing the dietary level of Mg increased Ca absorption but did not affect P absorption. Increasing the Mg intake increased Mg retention, urinary losses and apparent and true digestibility of magnesium. Estimated endogenous fecal and urinary Mg losses were 2.2 mg and 3.9 mg of Mg/kg of body weight, respectively. The maintenance requirement for ponies was estimated to be 12.8 mg Mg/kg of body weight.

IN the course of previously reported studies of calcium, phosphorus and protein metabolism of the horse, data concerning Mg metabolism were obtained from 72 balance studies. The relationship of retention to intake indicated that horses require about 13 mg of Mg/kg of body weight/day for maintenance. Other studies demonstrated that the primary site of Mg absorption was the small intestine. The magnesium in diets in which the primary protein source was milk products was more available than in diets in which the primary protein source was linseed meal. Magnesium absorption was decreased in diets containing high levels of phosphorus. The levels of Mg used in these trials did not appear to affect digestibility.

Two balance trials were conducted with mature gelding ponies. In the first trial the addition of isonitrogenous amounts of urea, soybean meal or linseed meal to the basal diet increased nitrogen retention and apparent protein digestibility. The percent retention of the absorbed nitrogen was similar for ponies fed all three supplemented diets. In the second trial, feeding urea or putting urea directly into the cecum resulted in similar increases in nitrogen retention and apparent digestibility of protein. The results were compared to several other recent reports on urea utilization in horses and ponies and it was concluded that equines can utilize urea to increase nitrogen retention when fed low protein diets but that in general the efficiency of the utilization of the absorbed N from urea is less than that of N from performed protein.

Two feeding trials and one metabolism trial were conducted with 56 young horses fed isonitrogenous diets containing either milk products or linseed meal as the primary source of supplemental protein. Daily gain, nitrogen retention and feed/gain were greater when the diet contained milk products or when lysine was added to the linseed meal diet. At least some of the greater response appeared to be due to the higher lysine content of the milk products. The calcium and phosphorus of the diets containing milk products were more available than those in the linseed meal diets.

Two trials were conducted in which ponies were fed varying forage-grain ratios to study the effects of the various ratios on digestibility, molar percentages of volatile fatty acids (VFA) in intestinal fluid and blood glucose levels in ponies. No interactions or associative effects on digestibility due to forage-grain ratio were observed. Blood glucose levels were not influenced by the forage-grain ratio. The total concentration of VFA in cecal fluid and the percentage of acetate was decreased and the percentages of propionate, isovalerate and valerate were increased when high grain diets were fed.

Eleven ponies were fed diets containing 1:0, 3:2 or 1:4 forage-grain ratios for 30 days. Animals were killed 4 hr. after feeding and the entire digestive tracts were removed and segments isolated. Digestion coefficients were calculated for dry matter, protein, available carbohydrate (ACHO) and neutral detergent fiber (NDF) by Cr2O3-nutrient ratio for seven segments of the gut.The major site of ACHO and protein digestion was prececal; whereas, the major sites of NDF digestion were the colon and cecum regardless of the hay:grain ratio. Therefore the relative importance of digestion in the lower gut increased with increased levels of forage.

Three feeding trials with a total of 120 pigs and one trial with 24 rats were conducted to evaluate the supplementation of barley-cotton-seed meal diets.Additions of riboflavin, pantothenic acid and vitamin B12to diets containing alfalfa meal did not increase rate of gain or feed efficiency of pigs in trial 1. In trial 2, additions of riboflavin, niacin, pantothenic acid or vitamin B12to all-plant diets (no alfalfa meal) increased rate of gain of pigs in the growing period (30 to 60 kg.) but not in the finishing period (60 to 90 kg.) and when analyzed overall there was no effect. In trial 1, substituting soybean meal or soybean meal plus meat and bone scraps for cottonseed meal did not improve performances of pigs fed diets containing 16% crude protein (dry matter basis). In trials 2 and 3, lysine supplementation of barley-cottonseed meal diets containing lower levels of protein increased rate of gain and apparently improved feed efficiency. A similar response was obtained with rats in trial 4. None of the carcass characteristics measured were influenced by lysine supplementation except the protein content was increased and the fat content decreased in samples of lean taken from the loin. Methionine supplementation was tested in trial 3 but did not improve rate of gain, feed efficiency or carcass characteristics.

Five pairs of horses were used to study the effect of pelleting on the nutritive value of horse rations. The horses were pair-fed, one member receiving a pelleted ration and one member receiving the same ration but not pelleted. The trial was conducted for 63 days. Pelleting the ration did not influence rate of gain or efficiency of feed utilization. There were no significant differences in digestibility of the pelleted and the nonpelleted rations except for ether extract of the pelleted ration, which was significantly more completely digested than in the nonpelleted ration. Rate of passage was apparently faster for the pelleted ration. The pelleted ration was consumed in a significantly shorter period of time, and the fresh feces of horses fed the nonpelleted ration contained a significantly higher percent of dry matter than the feces of horses fed the pelleted ration.

The predominant species of algae grown on sewage were Chlorellaspp., Scenedesmus obliquusor S. quadricauda, depending upon the season. In the feeding trials algae had to be pelleted with other feeds to insure consumption and prevent sorting. Algae contained 51% crude protein, which was 73% digestible when fed to cattle and sheep, but only 54% digestible when fed to pigs. The digestible energy content for cattle and sheep was 2.6 kcal./gm. Two feeding trials indicated that algae supplied adequate protein to supplement barley for growing-finishing pigs. Alfalfa-algae pellets resulted in higher gains than alfalfa pellets, when fed to lambs on dry summer range. Although algae grown on sewage are not a high-energy feed because of a high ash content and low digestibility of the nonprotein, nonfat organic matter, it appears to have potential as a livestock feed because of the high content of protein, plus significant amounts of carotene, phosphorus, calcium and trace minerals.

A series of digestion trials with steers and sheep was conducted on soybran flakes and soybean hulls. Soybran flakes had a significantly higher digestibility than either ground or unground soybean hulls when they were used as the only feed. However, when hay was added to the ration, the digestibility of the soybran flakes, ground soybean hulls and unbran flakes, soybran flakes and hay, soybean hulls and hay were extremely similar at all observation times, thus they were averaged together. Therefore the line labeled “other comparisons” is the average of nine observations. The curve for soybean hulls fed alone is the average of three observations. The similar excretion patterns for soybran flakes fed with and without hay are in agreement with Johnson et al. (1962). The soybean hulls were excreted at a faster rate than the other ground soybean hulls was markedly increased and there was no longer any large difference between them. Although the hulls contained 36.4% fiber they were highly digested and the TDN was calculated to be 72.9%.The rates of passage were studied, using a stained particle technique, and a faster rate was observed when raw soybean hulls were fed alone than for soybran flakes fed with and without hay and for raw soybean hulls fed with hay.

A SERIES of balance trials were conducted with ponies to determine the utilization of phosphorus (P) in wheat bran and factors which affect its utilization. The average estimated true digestibility of P in diets in which wheat bran supplied a significant amount of the total dietary P was 29.5±3.0%. The addition of Ca or steeping wheat bran in 50 C water for 1 hr. did not influence P utilization but feeding 83,000 IU of vitamin D3daily to ponies increased digestibility by about one third. It was concluded that the P in wheat bran is about one half as available as the P in supplements such as NaH2PO4, dicalcium phosphate and bone meal and differences in availability should be considered when balancing rations for horses.