Soybean Hulls as an Energy Source for Weanling Horses

Soybean hulls have been used as a feed ingredient for horses for many years and are generally used as a fiber source. The NRC (11) gives them an energy value of 1.88 Mcal DE/kg DM, which is comparable with a medium quality grass hay. Recent evidence suggests that soybean hulls may have a higher energy value. Two feeding trials were conducted to evaluate the energy value of soybean hulls by using them to replace oats in a concentrate for weanling horses. In Exp. 1, 16 Thoroughbred and Quarter Horse weanlings, 145.2 4.1 d of age, were paired within breed and gender subgroups and assigned at random to either the oats or soybean hull-based concentrate. Soybean hulls replaced oats at 25% of the concentrate. Concentrates were fed individually to appetite for two, 1.5-h feeding periods daily with the concentrate restricted to the lesser amount consumed by the pair based on percentage of BW. Coastal bermudagrass (Cynodon dactylon) hay (12.8% CP) was group fed at 1.0 kg/100 kg BW daily. The BW and measurements of the weanlings were made at 14-d intervals for 112 d, and the weanlings were radiographed for bone mineral deposition determinations at the start and conclusion of the study. Experiment 2 used 13 weanlings starting at 143.8 ± 4.2 d of age and was identical to Exp. 1 except the source of the Coastal bermudagrass hay was different and the concentrate intake was fed ad libitum during the two, 1.5-h feeding periods. In Exp. 1, no differences in feed or nutrient intake, BW, or body measurement gains were detected (P > 0.05) except for body length gain, which was greater for the weanlings on the oat-based concentrate (P < 0.05). The weanlings gained 0.73 and 0.70 kg/d on the oat and soybean hull-based concentrates, respectively. In Exp. 2, the protein content of the hay (7.0% CP) was less than the previous year, resulting in a protein intake below NRC (11) recommendations. No differences in BW, withers height, or body length gain were detected (P < 0.05), but heart girth (P < 0.05) and hip height gain (P < 0.05) were both greater for the weanlings fed the oat-based concentrate. The weanlings gained 0.74 and 0.61 kg/d on the oat and soybean hull-based concentrates, respectively. Bone mineral deposition was not different between diet groups for either experiment. Results suggest that soybean hulls have an energy value for weanling horses that is similar to oats when fed with medium quality grass hay. When fed with low quality grass hay, soybean hulls do not seem to be as valuable as oats, perhaps because of either the slow energy release or the availability of protein in the foregut.     

Influence of Energy and Protein Content of the Concentrate and Restricting Concentrate Intake on Growth and Development of Weanling Horses

Forty-four Thoroughbred and Quarter Horse weanlings were used in three experiments to evaluate the effects of energy content, protein content, and feeding levels of the concentrate on growth and development when fed with Coastal bermudagrass hay. The animals were confined to drylot paddocks and fed the assigned concentrate in individual feeding stalls. The hay was group-fed in the paddocks. In the first experiment, the concentrate was fed at 1.5 kg/100 kg BW daily or ad libitum for two 1.5-h feeding periods daily. The ad libitum-fed weanlings had greater withers height gain (P<0.01), and hip height gain (P<0.05) than the limit-fed weanlings. Bone mineral gains were numerically greater for the ad libitum-fed weanlings (P>0.10). None of the other body measurements were different (P>0.05). In Exp. 2, weanlings were fed a basal concentrate ad libitum for two1.5-h feeding periods daily or a fat-added concentrate at equal amounts to the hay intake. Nutrients were balanced to meet NRC recommendations. The fat-added concentrate resulted in numerically greater withers height (P>0.10), heart girth (P>0.10), body length (P>0.10), hip height (P>0.10), and bone mineral (P>0.10) gains. Weight gain and feed efficiency favored the basal diet. In Exp. 3, weanlings were fed concentrates providing either 14 or 18% CP as described previously. The BW gains favored the high protein diets for three of the first four periods (P<0.05), and some numerical advantage persisted to the end of the trial (P>0.10). None of the other growth measurements were different for the two diets. Calculations on nutrient intake and BW gains of the animals on the three experiments revealed that lysine intake appears to be a greater factor than energy or protein in influencing BW gain of weanlings.     

Influence of chromium tripicolinate on growth and glucose metabolism in yearling horses

Thoroughbred and Quarter Horse yearlings (n = 24; 335+/-7 d of age) were used in a 112-d feeding trial to determine whether chromium (Cr) supplementation would alter growth, development, and energy metabolism of growing horses on high-concentrate diets. The horses were assigned at random within breed and gender subgroups to one of four treatment groups: A) basal concentrate; B) basal plus 175 microg of Cr/kg concentrate; C) basal plus 350 microg of Cr/kg concentrate; and D) basal plus 700 microg of Cr/kg concentrate. Chromium was provided via Cr tripicolinate (Prince Agri Products, Quincy, IL). The horses were weighed, measured for withers and hip height, heart girth, and body length and underwent ultrasound evaluation for croup fat thickness. The concentrate was fed for ad libitum consumption for two, 1.5-hr feeding periods daily. Coastal bermudagrass (Cynodon dactylon) hay was group-fed (six animals/group) at 1% of BW daily. Feed intake was 60% concentrate and 40% hay, resulting in a supplemental Cr intake of 0, 105, 210, and 420 microg/kg diet for groups A, B, C, and D, respectively. Colts consumed more concentrate and total feed than did fillies (P < .05), but no dietary effect on feed intake was detected. Colts weighed more than fillies at the completion of the experiment (P = .0754), but no dietary effects on weight, body measurements, or croup fat were detected. An i.v. glucose tolerance test (.2 g of glucose/kg BW) and an i.v. insulin sensitivity test (.1 IU of insulin/kg BW) were conducted on each animal during the third 28-d period of the experiment. Plasma glucose peaked immediately following injection and decreased more rapidly in animals consuming the high-Cr diet than in those consuming the control diet (P < .01). Mean glucose fractional turnover rate values increased (P = .0369) and mean half-life of glucose decreased (P = .0634) in response to the high Cr supplementation. Plasma glucose depletions in animals fed the other two diets were between and not different from (P > .10) the depletions in control animals or in those fed high-Cr diets. No difference in insulin sensitivity was detected (P > .10). Results indicate that Cr tripicolinate supplementation of yearling horses increases the rate at which glucose is metabolized and may lower the plasma glucose concentration. No effect of Cr supplementation on development of the animals was detected.     

Influence of dietary methionine concentration on growth and nitrogen balance in weanling Quarter Horses

Twenty-four Quarter Horse weanlings (120 ± 10 d) were blocked by age into 4 groups (n=6) for a 56-d trial to evaluate the influence of dietary Met concentration on growth and N balance. Weanling horses were housed by block and individually fed concentrates twice daily at 1.75% BW (as-fed basis). Weanling horses were randomly assigned to 1 of 4 concentrate treatments: basal (0.20 Met), basal + 0.03% Met (0.23 Met), basal + 0.07% Met (0.27 Met), and basal + 0.11% Met (0.31 Met). Diets were formulated to be isonitrogenous and isocaloric and contained equal amounts of Lys and Thr. Coastal bermudagrass hay (Cynodon dactylon) was individually fed at 0.75% BW (as-fed basis). Growth measurements, BW, rump fat, and plasma were obtained every 7 d. The final 4 d consisted of total collection of urine and feces. Feed, fecal, and urine samples were analyzed for N content, and N balance was calculated. Urine was analyzed for urea and ammonia concentrations. Plasma was analyzed for urea concentration. Grain, hay, and fecal samples were analyzed for nutrient composition. Data were analyzed using the PROC MIXED procedure of SAS. Linear, quadratic, and cubic effects were tested in the form of contrasts. There was no influence (P>0.25) of treatment on growth measurements, N balance, or urinary urea or ammonia. Intake of Lys and Thr did not differ (P>0.08) among treatments. Methionine intake increased as expected with increasing Met inclusion in the diet (P<0.01). Plasma urea N responded quadratically (P=0.04) to treatment. An unexpected peak in PUN was observed with 0.27 Met. The results indicate future studies that can ensure Met as the only dietary variable are necessary to better explain the Met requirements of weanling horses.     

Effects of supplementing with calcium salts of palm oil fatty acids or hydrogenated tallow on ewe milk production and twin lamb growth

Two experiments were conducted with Polypay ewes nursing twin lambs to evaluate the effects of supplementing fat (calcium salts of palm oil fatty acids or hydrogenated tallow) on ewe lactation. In Exp. 1, ewes were fed a 52% concentrate:48% hay-based diet (as-fed basis) consisting of alfalfa hay (n = 4), endophyte-free fescue hay (n = 4), or fescue hay with 3.7% fatty acids (n = 4) from d 4 to 56 of lactation. In Exp. 2, ewes were fed similar diets that had endophyte-free fescue hay (n = 6), fescue hay with 3.7% fatty acids (n = 5), or fescue hay with 3.1% tallow (n = 6) from d 14 before lambing until d 57 of lactation. Diet formulations with supplemental fat were more nutrient dense, and treatments were fed to meet ewe nutrient requirements; this caused diets with added fat to be offered at 10 and 17% lower rates than unsupplemented diets in Exp. 1 and 2, respectively. Lambs were maintained to consume only ewe milk. Ewe milk production and composition were determined using a portable milking machine following a 3-h separation from lambs. In Exp. 1, milk fat content was increased (P < 0.01) when ewes consumed fescue hay with fatty acids vs. the fescue hay diet (11.4 vs. 8.3%). Ewes fed fescue hay with fatty acids lost the most (P < 0.05) weight over lactation (-8.6 kg) compared with ewes fed the alfalfa hay (-2.4 kg) and fescue hay (-3.8 kg) diets. Other milk measures, lamb gain, and production efficiencies were not changed. In Exp. 2, ewes supplemented with fatty acids produced more (P < 0.05) milk fat than those fed tallow (290 vs. 210 g/d). The proportion of synthesized milk fat 14:0 was decreased (P < 0.01), but the percentage of incorporated 16:0 increased (P < 0.05) when fatty acids were fed. Dietary fat digestibility by ewes was increased (P < 0.01) by fatty acid supplementation but decreased (P < 0.01) when tallow was added. Although ewe weight measures were not changed in Exp. 2, twin lamb gain per ewe organic matter intake was most efficient (P < 0.05) when ewes were supplemented with fatty acids. Results suggest that feeding hydrogenated tallow decreased nutrient availability for ewe milk fat production. A complete diet based on endophyte-free fescue hay can replace a traditional alfalfa hay diet, whereas supplementing with the calcium salts of palm oil fatty acids may be more feasible when energy is limiting during ewe lactation.     

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

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<.05) feed:gain ratios (6.3 vs 7.3) than weanlings fed the control diet. Gain in heart girth circumference was greater (P<.05) for the fat fed weanlings (20.1 cm) than the control weanlings (17.9 cm). All other linear measurements of growth were similar between treatments. There were no radiographic indications of abnormalities in the physes of horses on either treatment. Closure of the physes occurred at normal rates in foals on both treatments. Radiographic bone density was not different between treatments, and there was an expected increase in bone density in weanlings on both treatments over time. Digestibilities of protein and energy were similar between treatments, while ether extract and neutral detergent fiber digestibilities were higher (P<.05 and P<.06, respec tively) in those horses consuming the fat-supplemented diet (65.39 vs 57.67% and40.55 vs 35.62%, respectively). These data indicate that fat can be used as an energy source to support growth and development in weanling horses.     

Effects of starch and fibre in pelleted diets on nutritional status of mule deer (Odocoileus hemionus) fawns

To compare the effects of a low-starch, high-fibre diet [LSHF; 51.6% neutral detergent fibre (NDF), 3.0% starch, 14.8% crude protein (CP)] and a high-starch, low-fibre diet (HSLF; 33.3% NDF, 20.0% starch, 19.6% CP) on the nutritional status of captive exotic ruminants, 16 mule deer (Odocoileus hemionus) were fed one of these two diets ad libitum with ≤25% alfalfa hay cubes from 10 days to 68 weeks of age. During five sampling periods beginning in November and spaced 6-12 weeks apart thereafter, feed intake, rumen and blood chemistry, faecal scores, growth and body condition were measured. Dry matter intake, digestible energy intake, time spent ruminating and feeding and blood acetate concentration were greater for deer fed LSHF (p < 0.05 for all). Lower dietary CP led to reduced blood urea nitrogen for deer consuming LSHF (p = 0.004). Deer had the same faecal scores, growth and body fat among treatments (all p > 0.05). These findings show pelleted diets with less starch, more fibre, and reduced protein met the energy and protein requirements of growing mule deer, a medium-sized browsing ruminant, as well as traditional grain-based diets while more closely mimicking natural forages and stimulating a more natural feeding behaviour.     

Influence of dietary fat and time of hay feeding on growth and development of yearling horses

Seventeen Thoroughbred and Quarter Horse yearlings were used in a 2×2 factorial experiment to determine 1) whether adding fat (5% corn oil) to the concentrate would influence feed intake, growth and development and 2) whether time of hay feeding would influence energy metabolism on the basal and added fat diets. Yearlings were assigned at random, within breed and gender subgroups, to one of four diets: B-I, basal concentrate with Coastal Bermuda grass (Cynodon dactylon) hay fed immediately after the concentrate; B-D, basal with hay fed 3.5 hr after the concentrate; F-I, basal + fat with the hay fed immediately; and F-D, basal + fat with the hay fed 3.5 hr after the concentrate. The basal concentrate was formulated to meet or exceed NRC (1989) recommendations when fed with the hay. The basal + fat concentrate was formulated at 9.7% higher digestible energy than the basal concentrate and all of the other nutrients were increased proportionately so if the intake was reduced, the yearlings would still meet nutrient needs. The concentrates were fed individually to appetite for two 1.5-hr feeding periods daily in 1.5×3.0 m slip stalls. Hay was group fed in the paddocks at a rate of 1.0 kg/100 kg BW daily divided into two equal feedings. Animals were housed in four 9.1×34.9-m drylot paddocks with three, four, or five animals in each paddock. The mean age at the start of the experiment was 377±8 days. Weight and body measurements for withers height, heart girth, body length, and hip height were taken at the start of the experiment and at 28-day intervals for 84 days. Radiographs for bone mineral estimates were made at the start and completion of the experiment. During the final 28-day period of the feeding trial, three animals from each experimental group were randomly selected for a 24-h period of blood sampling to evaluate the effects of the diets on blood glucose and insulin.Fat addition to the concentrate reduced the daily concentrate DM (P=0.0187) and total feed DM (P=0.0021) intake. When feed intake was expressed as a function of BW, concentrate and total feed intakes were 1.33 and 2.14 kg/100 kg BW daily and were not influenced by diet (P>0.1). Colts consumed more concentrate DM (P=0.0039) and total feed DM (P=0.0022) than fillies. The yearlings gained an average of 0.60 kg/d for the 84 days. Weight gain, body measurements and bone mineral deposition were not influenced by gender or diet. Mean plasma glucose concentrations were higher (P=0.05) in yearlings consuming the basal concentrate with hay fed immediately than when hay feeding was delayed. When fat was fed, the time of hay feeding had no effect on plasma glucose concentrations (P>0.05). Plasma glucose and insulin were lowest just prior to the morning feeding and peaked two to three hours after both morning and afternoon feedings. Fat supplementation reduced plasma insulin (P=0.001). Results suggest that the addition of 5% corn oil to a yearling concentrate may reduce feed intake but will not reduce growth and development of the animal if other nutrients are supplied at concentrations that provide for the animal's daily needs. Delaying hay feeding may be advantageous to growing horses as it may allow the concentrate to move down the tract at a slower rate reducing the glucose peaks.     

Effects of direct-fed microbial supplementation on digestibility and fermentation end-products in horses fed low- and high-starch concentrates

A study was conducted to determine whether direct-fed microbials (DFM) could be used to increase digestibility and minimize the risk of acidosis associated with feeding an increase in the amount of starch fed to horses. Fifteen mature Thoroughbred geldings were randomly assigned to 1 of 3 treatments in a 3 x 3 Latin square design balanced for carryover effects. Within each 26-d period, horses were offered grass hay + low-starch concentrate (LS; 1.2 g of starch x kg of BW(-1) x meal(-1)) from d 1 to 13 and then were abruptly changed to hay + high-starch concentrate (HS; 2.4 g of starch.kg of BW(-1)x meal(-1)) on d 14 continuing through d 26. The DFM treatments were offered in concentrate pellets at a target dosage of 10(8) cfu/(50 kg of BW x d) as follows: no DFM (CON; control), Lactobacillus acidophilus (LAC1; single-species DFM), or a mixture of L. acidophilus, Lactobacillus casei, Bifidobacterium bifidum, and Enterococcus faecium (LAC4; multiple-species DFM). Total feces were collected over 72 h from d 11 to 13 (LS; low dietary starch collection), from d 15 to 17 (AC; abrupt change in dietary starch collection), and at the end of each experimental period, from d 24 to 26 (HS; high dietary starch collection). Data collected consisted of total DM intake and fecal output, fecal pH, fecal acetate and propionate concentrations, and viable numbers of DFM in the feed. With the exception of Fe digestibility, there were no starch x DFM interactions. There was an effect of starch level (P 0.10). Horses supplemented with LAC4 had increased ether extract (P < 0.05) and a tendency for decreased Na (P < 0.10) digestibilities compared with CON horses. All DFM-supplemented horses had increased Cu (P < 0.05) and Fe and numerically increased Zn digestibilities compared with CON horses. Fecal pH decreased (P < 0.05), and fecal propionate concentration increased (P < 0.05) as dietary starch content changed from LS to HS. There was a tendency for elevated fecal pH (P < 0.10) in LAC1 horses compared with CON horses. These results confirm that increasing starch in the equine diet can enhance nutrient digestibility of the diet. Supplementing equine diets with either a single or mixed strain direct-fed lactic acid bacteria had limited effects on nutrient digestibility or on reducing the risk of acidosis associated with feeding high-starch concentrates to horses. The potential response of DFM supplementation should be evaluated when a more acute acidotic state is induced in horses than in the current study.     

Digestibility and dry matter intake of diets containing alfalfa and kenaf

Two experiments were conducted to determine the dietary value of pellets containing kenaf (Hibiscus cannabinus cv. 'Everglade 41') hay. Averaged across both experiments, kenaf pellets contained 82.6% kenaf hay, 16.6% liquid molasses, and 0.8% mineral oil. The chemical composition of the kenaf pellet was 12.6% crude protein (CP), 41.2% neutral detergent fiber (NDF), and 14.4% acid detergent fiber (ADF). In Exp. 1 (digestion and N balance trial), 18 lambs (body weight [BW] = 36.4 kg) were blocked by BW. Lambs were randomly assigned within a block to Diet 1 (59.5% corn and 40.5% alfalfa pellet), Diet 2 (59.7% corn, 28.4% alfalfa pellets, and 11.9% kenaf pellets), or Diet 3 (59.6% corn, 16.5% alfalfa pellets, and 23.9% kenaf pellets). Diets were formulated so that CP was the first-limiting nutrient. Each diet was limit-fed at 2.4% of BW. Replacing alfalfa pellets with kenaf pellets tended to decrease (P = 0.10) CP and ADF intakes, but increased (P = 0.01) DM digestibility. Diet had no effect (P = 0.33) on N balance. In Exp. 2 (dry matter [DM] intake trial), 32 lambs (BW = 30.4 kg) were blocked by gender and BW. Within a block, lambs were randomly assigned to one of four diets in a 2 x 2 factorial arrangement. Main effects were hay (bermudagrass or fescue) and supplemental protein source (kenaf or alfalfa pellets). Lambs were housed in individual pens with ad libitum access to the assigned hay. Supplemental protein was fed (185 g of DM) once daily. Hay intake was measured weekly for 8 wk. Lambs consumed more (P = 0.002) fescue than bermudagrass hay (743 vs 621 g/ d). Lambs fed fescue hay gained weight more rapidly (P = 0.001) than lambs fed bermudagrass hay (120 vs 72 g/d). Hay intake and ADG were similar (P = 0.90) for lambs fed alfalfa or kenaf pellets. Kenaf hay mixed with molasses and mineral oil can be formed into a pellet. In the diets used in this experiments, kenaf pellets can replace alfalfa pellets in diets fed to lambs without altering forage intake, gain, or N retention.     

Digestion and performance responses to lasalocid and concentrate supplements by beef cattle fed bermudagrass hay.

Beef cattle consuming bermudagrass hay were not supplemented or received a limited amount of ground corn alone or with a mix of protein meals to determine influences of concentrate supplementation on digestion and performance when the ionophore lasalocid (200 mg daily) was given. With limited feed intake, supplement treatment did not change the acetate to propionate shift in beef cows occurring with lasalocid (P < 0.06). Lasalocid did not affect sites of digestion of organic matter or nitrogen with any supplement treatment. However, lasalocid decreased (P < 0.10) ruminal digestion of neutral and acid detergent fibre. Live-weight gain by growing beef calves ingesting bermudagrass hay ad libitum was higher (P < 0.05) with than without supplementation and tended (P < 0.12) to be greater for corn plus protein meals than for corn alone. Lasalocid did not affect or interact with supplement treatment in feed intake or live-weight gain of heifers (236 kg; no growth stimulant) or steers (237 kg; treated with 200 mg progesterone and 20 mg estradiol benzoate). Lasalocid at 200 mg daily did not improve digestion characteristics or influence performance by beef cattle consuming a Basal diet of bermudagrass hay. Further, effects of lasalocid were not modulated by supplementation with concentrate, concentrate type or sex or growth stimulant usage.     

Effect of diet composition and feed intake level on diet digestibility and ruminal metabolism in growing lambs.

Lambs (29 +/- 2.5 kg) were fed three diets at various intakes to determine whether diet composition or level of intake was reflected in changes in diet digestibility or ruminal fluid characteristics. In Exp. 1, a 90% concentrated, pelleted diet or a whole shelled corn diet with a pelleted protein supplement was fed at three levels of intake: ad libitum and 92.5 and 85% of ad libitum (n = 15). Exp. 2 compared the 90% concentrate diet with diets in which the energy density was diluted to 55 or 72.5% concentrate by including alfalfa hay as a possible method of restricting energy intake (n = 6). Lambs were adapted to diets for 13 d; feces were collected for 6 d and ruminal fluid was collected 0, 3, and 6 h after feeding on the day following fecal collection. Restricting intake in Exp. 1 did not affect DM digestibility or digestibility of CP or starch. Digestibility of ADF was increased (P less than .10) by restricting intake. Ruminal fluid pH, ammonia concentration and VFA concentrations were affected little by either restricted intake level. Digestibility of DM was 4% higher (P less than .001) and starch 5% higher (P less than .001) for the whole shelled corn diet than for the pelleted, high-concentrate diet. Ruminal pH of lambs fed the whole shelled corn diet was higher and fluctuated less than the ruminal pH of lambs fed the high-concentrate, pelleted diet. In Exp. 2, diet digestibility was reduced (P less than .01) and ruminal pH was increased (P less than .002) by addition of hay. Restricted feeding of lambs did not seem to increase diet digestibility or alter ruminal conditions.     

Fat Supplementation to Alfalfa Diets for Refeeding the Starved Horse

The objective was to examine the metabolic responses of chronically starved horses using two isoenergetic diets consisting of either 100% alfalfa hay (AH) or 80% alfalfa hay with 20% corn oil (AO), on a caloric basis. Two 10-d trials were conducted using 14 emaciated, but otherwise healthy, horses with an initial mean body condition score of 1.8 ± 0.9 and mean BW of 336 ± 31 kg. The initial DE intake of 50% of maintenance was gradually increased to 100% during the 10-d refeeding period. Two of the horses receiving the AH diet were euthanized, thus 12 horses (AH, n = 7; AO, n = 5) survived the 10-d study. One preprandial and four postprandial venous blood samples were collected daily. Dietary effects (P<0.01) were shown for blood serum or plasma free fatty acids (FFA), phosphate, magnesium, and 2,3-diphosphoglycerate (2,3-DPG), but not glucose, insulin, or potassium concentrations. The response of insulin and FFA during the 10-d study showed differences (P<0.05) between AH and AO diets. Serum phosphate concentration in horses on both diets exhibited a general slow decline with concentrations below normal reference range during d 5 through 10, thus indicating hypophosphatemia. Serum magnesium increased in horses consuming the AH diet, whereas concentrations in horses consuming the AO diet consistently were below reference range, leading to mild hypomagnesemia. Hypokalemia did not develop in either treatment group, as all serum potassium concentrations remained in the normal reference range. The substitution of corn oil in isoenergetic alfalfa diets was not advantageous in minimizing or preventing hypophosphatemia or hypomagnesemia for refeeding starved horses. The AH diet is recommended as more supportive in refeeding starved horses because of the greater intake of dietary phosphorous and magnesium.     

The effect of replacing nonstructural carbohydrates with soybean oil on the digestibility of fibre in trotting horses

The hypothesis tested was that the intake of extra fat at the expense of an isoenergetic amount of nonstructural carbohydrates reduces fibre utilisation in horses. In a crossover trial with feeding periods of 42 days each, 6 mature trotting horses (age 4-12 years, bodyweight 340-476 kg) were given either a control or test diet. The test concentrate was formulated to contain 37% of net energy in the form of soybean oil. The control concentrate contained an isoenergetic amount of corn starch plus glucose. The concentrates were fed in combination with the same amount of hay so that the control and test diet contained 25.13 and 86.66 g crude fat/kg dry matter, respectively. Apart from the amounts of fat and nonstructural carbohydrates, the 2 diets were identical. The test diet reduced the apparent total tract digestibilities of crude fibre, neutral and acid detergent fibre by 8.0 (P = 0.007), 6.2 (P = 0.022) and 8.3 (P = 0.0005) percentage units, respectively. It is suggested that a high fat intake by horses may increase the amount of fat entering the large intestine to levels that depress fermentation by cellulolytic bacteria. The observed interaction between fat content of the diet and fibre utilisation may have consequences for practical horse feeding in that calculating the energy content of test diets on the basis of feedstuff tables leads to overestimating the amount of energy provided by the high-fibre ingredients of the diets.     

Rice mill feed as a replacement for broiler litter in diets for growing beef cattle

The efficacy of replacing broiler litter with rice mill feed was evaluated in four experiments. In Exp. 1, 40 predominantly Angus steers (initial BW = 277+/-18.2 kg) were fed four dietary treatments for 112 d (five steers per pen; two pens per diet). Dietary treatments (DM basis) were as follows: 1) 47% broiler litter:53% corn; 2) 60% rice mill feed:40% corn; 3) 50% rice mill feed:50% corn; and 4) 40% rice mill feed:60% corn. All diets, along with bermudagrass hay, were fed free choice. Daily gains were faster (P < 0.10) for the 50:50 and 40:60 diets (1.26 and 1.30 kg/d, respectively) than for the broiler litter diet (0.89 kg/d). Daily DMI was less (P < 0.10) by steers consuming rice mill feed-based diets than by those consuming broiler litter-based diets. In Exp. 2, 16 Angus x Charolais steers (initial BW = 277+/-22.7 kg) were fed the same four diets used in Exp. 1 while housed in individual metabolism stalls for determination of nutrient digestibility. Daily DMI was not different (P > 0.10) among diets. Nutrient digestibilities did not differ among diets (P > 0.10). In Exp. 3, 40 Continental cross steers (initial BW = 257+/-21.3 kg) were fed one of four dietary treatments for 112 d (five steers per pen; two pens per diet). On a DM basis, diets were as follows: 1) 47% broiler litter:53% soyhulls; 2) 70% rice mill feed:30% soyhulls; 3) 60% rice mill feed:40% soyhulls; and 4) 50% rice mill feed:50% soyhulls. All diets, along with bermudagrass hay, were fed free choice. Daily gains were less (P < 0.05) for the broiler litter diet than for the 60:40 and 50:50 diets (1.05, 1.16, and 1.28 kg/d, respectively), and steers fed the broiler litter diet consumed less DM than did steers fed the varying rice mill feed-based diets (P < 0.10). In Exp. 4, 16 Angus x Charolais steers (initial BW = 292+/-21.1 kg) were fed the same four diets as in Exp. 3 while housed in individual metabolism stalls for determination of nutrient digestibility. Daily DMI was less (P < 0.01) for the broiler litter diet (5.0 kg/d) than for the 70:30, 60:40, and 50:50 diets (7.8, 7.9, and 7.9 kg/ d, respectively). Digestibilities for DM, OM, and ADF did not differ (P > 0.10) among treatments; however, CP digestibility was greatest (P < 0.10) for the 60:40 diet, and NDF digestibility was least (P < 0.10) for the 70:30 diet. Rice mill feed can be used to replace broiler litter to formulate low-cost diets for stocker calves. Soyhulls and corn can be blended with rice mill feed to produce acceptable backgrounding diets for growing beef calves.     

Growth and development of yearling horses fed either alfalfa or coastal bermudagrass: Hay and a concentrate formulated for bermudagrass hay

Two experiments were conducted with yearling horses to determine whether the use of a concentrate designed to be fed with Coastal bermudagrass hay would cause growth differences or skeletal abnormalities when fed with western alfalfa hay. In experiment 1, 13 thoroughbred and quarterhorse yearlings, 332.8 ± 8.5 days, of age were assigned at random within breed and gender subgroups to 1 of 2 diets: (1) alfalfa hay plus a 12.7% CP concentrate and (2) coastal bermudagrass hay plus the same concentrate. The horses were housed in drylot paddocks in groups of 3 or 4 animals and group fed the hay at 1 kg/100 kg BW daily. The concentrates were fed individually to appetite for two 1.5-hour feeding periods daily for 112 days. Orts were weighed back daily. The animals were weighed, measured, and blood samples collected at the start of the experiment and at 28-day intervals for 112 days. Radiographs of the third metacarpal were made on day 0, 56, and 112 for estimation of bone mineral content. In experiment 2, 15 thoroughbred and quarterhorse yearlings, 345.6 ± 8.4 days of age, were used to repeat the experiment. The concentrate fed in this experiment contained 12.4% CP. In experiment 1, the hay protein content was less than anticipated, resulting in a protein intake below NRC¹ recommendations. In experiment 2, the hay protein was higher and more typical of NRC¹ values. In both experiments, feed intake of the 2 diets was not different (P > .10). Weight gain (P = .0136, P = .0330), heart girth gain (P = .0084, P= .0044), and hip height gain (P = .0165, P = .0137) were higher for the alfalfa fed yearlings for experiment 1 and experiment 2, respectively. Withers height gain (P = .0079) and body length gain (P = .0232) were also greater for the alfalfa fed yearlings on experiment 2. Bone mineral content and bone metabolism indicators were not influenced by diet (P > .10).     

Concepts in Protein Digestion and Amino Acid Requirements of Young Horses

There are numerous industry situations in which horses are N sufficient, but amino acid deficient. Although simple formulation of diets and consideration of nutrient-to-calorie ratios against requirements may appear to produce feeding programs that are suitable for horses, other factors, such as diet, rate of intake, site of nutrient absorption, horse age, and growth rate, must be considered when determining whether or not requirements are actually met. As an example, some yearlings kept in confinement consume concentrate and hay that fail to satisfy amino acid requirements. Other yearlings grazing very high quality pastures with no supplemental feed are able to meet their lysine requirement and achieve moderate growth. Field studies have documented that trends to manage weanlings and yearlings in a similar nutritional fashion are contributing to problems associated with rapid growth. Weanlings cannot process roughage at levels used effectively in yearlings, yet farms typically provide concentrate-to-hay ratios for weanlings inconsistent with NRC requirements and recommendations. Research on protein intake, site of absorption, concentrate type and intake, and grazing behavior must all be combined to be precise regarding adequate supply of protein quality to horses.     

Effect of yeast culture on in vitro fermentation of a high-concentrate or high-fiber diet using equine fecal inoculum in a Daisy II incubator

Two experiments were conducted to evaluate the use of a closed system, fermentation apparatus (Daisy II incubator) and determine the effects of a yeast culture (YC) preparation (Saccharomyces cerevisiae) on in vitro microbial populations, diet digestion, and fermentation patterns in horses. In Exp. 1, 4 mature horses were fed a pelleted concentrate and alfalfa cubes in a 50:50 (%, as-fed) ratio. Fecal samples were taken from each horse to form the inoculum and placed in 4 separate incubation vessels. Twenty nylon bags (10 with 0.25 g and 10 with 0.50 g of the total mixed diet) were placed in each vessel, and in vitro fermentation was carried out for 48 h to determine DM, NDF, and ADF digestibility. In Exp. 2, fecal samples were taken from 4 mature horses consuming either a high-concentrate (HC) or high-fiber (HF) diet. Filter bags containing the HC or HF diet were added to the 4 incubation vessels along with their respective inoculums. Yeast culture was added to 2 of the vessels containing the HC or HF diet, whereas the other 2 vessels served as controls. Vessels were incubated as in Exp. 1 with samples taken at 24 and 48 h. Filter bags were used to determine DM, NDF, ADF, and OM digestibility, whereas vessel fluid was analyzed for lactate, ammonia, VFA, and microbial concentrations. Results of Exp. 1 indicated that DM, NDF, and ADF digestibility were greater (P < 0.05), whereas the corresponding CV was lower (P < 0.05) for the 0.25- vs. the 0.50-g sample size. In Exp. 2, YC tended (P = 0.10) to decrease ammonia concentrations in the HF diet and increased (P < 0.05) acetate production in the HC diet when compared with the control. There were no effects of YC on pH, lactate, or the measured microbial populations, as well as DM, NDF, or ADF digestibility. The results did, however, show that in vitro and in vivo DM digestibility estimates were similar within a diet. Data from Exp. 1 indicated that the 0.25-g sample size provides a more accurate estimate of DM digestibility with less variation. Although YC had little, if any, effect in Exp. 2, the results indicated that the Daisy II incubator does provide valid estimates of total tract DM digestibility in the horse. These data provide further evidence that this process would be an effective and practical means of approximating the digestibility of diets with varying concentrate to forage ratios.     

Fiber digestion and voluntary intake in horses after adaptation to extensive large-colon resection

Each of 3 digestion trials (3 forage diets) was performed on 2 groups of horses 6 to 12 months after sham operation (group 1; n = 3) or large-colon resection (group 2; n = 5). Diets were alfalfa pellets, alfalfa hay, and grass hay. Feed and fecal analyses were performed to determine apparent digestion of dry matter, organic matter, and crude protein and true digestion of dry matter, organic matter, crude protein, total plant cell wall, hemicellulose, cellulose, and lignin. Additional fecal and metabolic variables determined were percentage of fecal water, total fecal water, metabolic organic matter, metabolic crude protein, and metabolic nitrogen. Large-colon resection decreased the digestion of plant cell wall because of decreased digestion of cellulose in alfalfa pellet and grass hay diets, but not in alfalfa hay diet. Insufficient digestible energy and/or protein from grass hay was obtained by horses with colon resection, and significant (P less than 0.05) weight loss was observed. Voluntary intake was significantly (P less than 0.05) increased by horses with colon resection. Of the diets studied, alfalfa hay was the most appropriate forage diet, compared with average grass hay and alfalfa pellet diet, for horses after extensive large-colon resection. Additionally, horses with colon resection may have higher levels of feed intake than do horses without colon resection.     

Effects of feeding ergovaline on lamb performance in a heat stress environment

Lambs exposed to a heat-stressed environment (33 degrees C, 50% relative humidity) were used in three experiments to determine whether ergovaline (EV) is the primary toxin involved in fescue toxicosis. The first study evaluated the effects of feeding diets containing increasing levels of endophyte-infected tall fescue seed (E+) and decreasing levels of endophyte-free tall fescue seed (E-). The second and third study evaluated the response to a diet that contained synthetic EV added to an E- diet and the response to a diet containing endophyte-infected ryegrass seed (R+) with an elevated concentration of EV. In Exp. 1, lambs were fed diets of: 1) 10% E- and 0% E+, 2) 5% E- and 5% E+, or 3) 0% E- and 10% E+. Increasing the percentage of E+ in the diet resulted in a linear decrease (P < 0.01) in feed intake (as-fed basis), skin temperature, thermocirculation index (TCI), and serum prolactin. Body weight gain also decreased (P < 0.06). Respiratory rate and core body temperature were not affected by the 5 or 10% E+ diets. In Exp. 2, lambs were fed diets that contained: 1) 10% E-, 2) 10% E- with synthetic EV added at a level equivalent to the 10% E+ diet, or 3) 10% E+. Feed intake (as-fed basis), body weight gain, and skin temperature did not differ for lambs fed the E- and EV diets. The EV diet elicited a decrease (P < 0.05) in TCI and prolactin compared with the E- diet. The TCI for lambs fed EV did not differ (P > 0.10) from the E+ lambs; however, serum prolactin was lower (P < 0.05) for lambs on the E+ diet than for those fed EV. Core body temperature was not affected (P > 0.10) by feeding EV or E+ fescue seed in Exp. 2. In Exp. 3, lambs were fed diets that contained: 1) 10% E-, 2) 3.24% R+ and 6.76% E-, which added an equivalent amount of EV to E+ diets but reduced concentrations of other ergot alkaloids, or 3) 10% E+. Lambs fed the E+ diet and maintained at 33 degrees C had lowered feed intake (as-fed basis), skin temperature, and TCI compared with lambs fed the E- or R+ diets (P < 0.05). Lambs fed the E+ diet had increased rectal temperatures and lowered serum prolactin compared with lambs on the R+ diet (P < 0.05). Lambs on the R+ diet had a greater rectal temperature and lower serum prolactin than lambs on the E- diet (P < 0.05). These results suggest that EV is a fescue toxin; however, other alkaloids might work synergistically with EV, causing the full expression of fescue toxicosis.