Plasma glucose and insulin responses of Thoroughbred mares fed a meal high in starch and sugar or fat and fiber

Plasma concentrations of glucose and insulin following a meal were compared in twelve Thoroughbred mares fed a pelleted concentrate (PC), a traditional sweet feed high in sugar and starch (SS), or a feed high in fat and fiber (FF). The feeds had similar DE and CP but differed in fat (19, 32, and 166 g/kg DM, respectively), NDF (199, 185, and 369 g/kg DM, respectively) and nonstructural carbohydrates (574, 645, and 247 g/kg, respectively). Mares were randomly assigned to two groups balanced for foaling date and weight. All mares received PC in late gestation; then, after foaling, one group was fed SS and the other FF for trials in early and late lactation. Mares were placed in stalls and deprived of feed overnight. A series of blood samples was collected via a jugular catheter from 0 (baseline) to 390 min after consumption of 1.82 kg of feed. Plasma was analyzed for glucose and insulin. Baseline values, peak values, and areas under curves (AUC) were compared by ANOVA. Baseline values were 74.7 +/- 10.9 mg/dL for glucose and 5.86 +/- 1.80 mIU/L for insulin for all diets and stages. Responses to PC did not differ between the two groups (P > 0.34), indicating the groups were metabolically similar. Peak plasma glucose and insulin concentrations were higher (P < 0.001) in the SS group than in the FF group during early and late lactation. Similarly, glucose and insulin AUC were larger (P < 0.003) in SS than in FF during early and late lactation. These results indicate that metabolic fluctuations are moderated by the replacement of sugar and starch with fat and fiber. This replacement may reduce the risk of certain digestive and metabolic disorders that have been linked to feeding meals of grain-based concentrates to pregnant or lactating mares.     

The effect of oral metformin on insulin sensitivity in insulin-resistant ponies

Metformin may be an effective therapeutic option for insulin-resistant (I-R) horses/ponies because, in humans, it reportedly enhances insulin sensitivity (SI) of peripheral tissues without stimulating insulin secretion. To determine the effect of metformin on insulin and glucose dynamics in I-R ponies, six ponies were studied in a cross-over design by Minimal Model analysis of a frequently-sampled intravenous glucose tolerance test (FSIGT). Metformin was administered at 15 mg/kg bodyweight (BW), orally, twice-daily, for 21 days to the metformin-treated group. The control group received a placebo. A FSIGT was conducted before and after treatment. The Minimal Model of glucose and insulin dynamics rendered indices describing SI, glucose effectiveness (Sg), acute insulin response to glucose (AIRg) and the disposition index (DI). The body condition score (BCS), BW and cresty neck score (CNS) were also assessed. There was no significant change in SI, Sg, AIRg, DI, BW, BCS or CNS in response to metformin, or over time in the control group. There were no measurable benefits of metformin on SI, consistent with recent work showing that the bioavailability of metformin in horses is poor, and chronic dosing may not achieve therapeutic blood concentrations. Alternatively, metformin may only be effective in obese ponies losing weight or with hyperglycaemia.     

Obesity and diet affect glucose dynamics and insulin sensitivity in Thoroughbred geldings

Insulin resistance is considered a risk factor in obesity, laminitis, exertional rhabdomyolysis, and osteochondrosis. The objective was to use the minimal model to estimate glucose effectiveness (Sg) and insulin sensitivity (Si) in nonobese to obese horses initially adapted to forage only, then adapted to forage plus supplements rich in starch and sugar (SS) or fiber and fat (FF). Ten Thoroughbred geldings, with BCS of 5 (nonobese), 6 (moderately obese), and 7 to 8 (obese), were adapted to pasture and hay, allocated to two groups, and fed SS or FF in a switch-back design with 8 wk of adaptation. Modified frequent-sampling i.v. glucose tolerance tests were applied after adaptation to forage, SS, and FF. For the tolerance tests, horses were kept in stalls overnight and provided hay, and venous catheters were placed the next morning. Baseline samples were collected, 0.3 g of glucose/kg of BW was given i.v., and blood was sampled at 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 14, 16, and 19 min. At 20 min, 30 mU of insulin/kg of BW was given, followed by sampling at 22, 23, 24, 25, 27, 30, 35, 40, 50, 60, 70, 80, 90, 100, 120, 150, and 180 min. Plasma was analyzed for glucose and insulin, and Si, Sg, acute insulin response to glucose, and the disposition index were calculated. Normality was tested using the Shapiro-Wilk statistic. Body condition effects were analyzed using a mixed model with repeated measures. Diet effects were analyzed using a Wilcoxon signed rank test. The Sg was higher in obese than nonobese (P = 0.003) and moderately obese (P = 0.007) horses; Si was lower in obese than nonobese (P = 0.008) horses, and acute insulin response to glucose was higher in obese than nonobese (P = 0.039) horses. Effects of diet were likely confounded by body condition, but horses had lower Si (P = 0.066) when fed SS compared with FF, especially when nonobese. In conclusion, the minimal model effectively estimated Sg, Si, acute insulin response to glucose, and disposition index in horses. Obese geldings were insulin-resistant and seemed to rely primarily on Sg for glucose disposal. Feeding a diet rich in sugar and starch decreased insulin sensitivity of horses. Maintenance of body condition and avoidance of grain-based meals rich in sugar and starch would be beneficial to decrease the risk of developing insulin resistance and associated metabolic syndromes in horses, especially for horses at risk for these syndromes.     

Glucose clearance in grazing mares is affected by diet,pregnancy, and lactation

The glucose tolerance test in the horse may be used to determine metabolic responses to diet, disease, or physiologic state. The objective of this study was to determine the effect of reproductive stage (gestation and lactation) and supplemental dietary energy source (sugar and starch [SS] or fiber and fat [FF]) on glucose metabolism in grazing mares using an oral glucose tolerance test. Twelve mares, six on each supplement, were examined on three occasions: one in the third trimester of pregnancy, the second in early lactation, and the third in late lactation. During each test, venous samples were taken at 30 and 1 min before, and 30, 60, 90, 120, 150, 180, 240, and 300 min after a nasogastric dose of glucose at 0.2 g/kg of BW. Plasma was assayed for glucose, insulin, and cortisol. Statistical analysis was a mixed model with repeated measures with horse, diet, and reproductive stage as fixed effects. The incremental glucose area under the curve (AUC) in response to oral glucose was lower in SS than in FF mares (P = 0.022). Mares tended to have a lower incremental glucose AUC in early lactation than in late gestation (P = 0.057), and insulin AUC was lower in early lactation than in late gestation (P = 0.002) and late lactation (P = 0.013). Glucose clearance was more rapid (P = 0.007) in SS than in FF mares. The glycemic response to the oral glucose tolerance test was consistent with adaptation to dietary sugar and starch as well as metabolic changes associated with pregnancy and lactation. Feeding twice-daily grain meals rich in SS influenced glucose metabolism in horses to an extent that the natural adaptation of glucose metabolism to pregnancy was moderated. Feeding a diet rich in FF more closely mimics the natural grazing state of pasture and allows for adaptation of glucose metabolism to pregnancy and lactation.     

Use of proxies and reference quintiles obtained from minimal model analysis for determination of insulin sensitivity and pancreatic beta-cell responsiveness in horses

OBJECTIVE: To develop proxies calculated from basal plasma glucose and insulin concentrations that predict insulin sensitivity (SI; L.min(-1) x mU(-1)) and beta-cell responsiveness (ie, acute insulin response to glucose [AIRg]; mU/L x min(-1)) and to determine reference quintiles for these and minimal model variables. ANIMALS: 1 laminitic pony and 46 healthy horses. PROCEDURE: Basal plasma glucose (mg/dL) and insulin (mU/L) concentrations were determined from blood samples obtained between 8:00 AM and 9:00 AM. Minimal model results for 46 horses were compared by equivalence testing with proxies for screening SI and pancreatic beta-cell responsiveness in humans and with 2 new proxies for screening in horses (ie, reciprocal of the square root of insulin [RISQI] and modified insulin-to-glucose ratio [MIRG]). RESULTS: Best predictors of SI and AIRg were RISQI (r = 0.77) and MIRG (r = 0.75) as follows: SI = 7.93(RISQI) - 1.03 and AIRg = 70.1(MIRG) - 13.8, where RISQI equals plasma insulin concentration(-0.5) and MIRG equals [800 - 0.30(plasma insulin concentration 50)(2)]/(plasma glucose concentration - 30). Total predictive powers were 78% and 80% for RISQI and MIRG, respectively. Reference ranges and quintiles for a population of healthy horses were calculated nonparametrically. CONCLUSIONS AND CLINICAL RELEVANCE: Proxies for screening SI and pancreatic beta-cell responsiveness in horses from this study compared favorably with proxies used effectively for humans. Combined use of RISQI and MIRG will enable differentiation between compensated and uncompensated insulin resistance. The sample size of our study allowed for determination of sound reference range values and quintiles for healthy horses.     

Plasma progesterone concentration in beef heifers receiving exogenous glucose, insulin, or bovine somatotropin

Three experiments were conducted to evaluate plasma concentrations of glucose, insulin, IGF-I, and progesterone (P4) in pubertal beef heifers receiving exogenous glucose, insulin, or sometribove zinc. All heifers used had no luteal P4 synthesis but received a controlled internal drug-releasing device containing 1.38 g of P4 to estimate treatment effects on hepatic P4 degradation. In Exp. 1, 8 pubertal, nulliparous Angus × Hereford heifers (initial BW = 442 ± 14 kg; initial age = 656 ± 7 d) were randomly assigned to receive, in a crossover design containing 2 periods of 10 h, intravenous (i.v.) infusions (10 mL) of insulin (1 μg/kg of BW; INS) or saline (0.9%; SAL). Treatments were administered via jugular venipuncture in 7 applications (0.15 μg insulin/kg BW per application) 45 min apart (from 0 to 270 min). Blood samples were collected immediately before each infusion as well as at -120, -60, 330, 390, and 450 min relative to the first infusion. Heifers receiving INS had greater (P < 0.01) plasma insulin, reduced (P ≤ 0.04) plasma glucose and IGF-I, and similar (P = 0.62) plasma P4 concentrations compared with SAL heifers. In Exp. 2, the same heifers were assigned to receive, in a similar experimental design as Exp. 1, i.v. infusions (10 mL) of 1) insulin (1 μg/kg BW) and glucose (0.5 g/kg BW; INS+G) or 2) SAL. Heifers receiving INS+G had greater (P ≤ 0.02) plasma insulin, glucose, and P4 but reduced (P = 0.01) plasma IGF-I concentrations compared with SAL heifers. In Exp. 3, the same heifers were assigned to receive, in a crossover design containing 2 periods of 14 d, subcutaneous (s.c.) injections of 1) 250 mg of sometribove zinc (BST) or 2) SAL. Blood samples were collected 3 h apart (0900, 1200, 1500, and 1800 h) from heifers on d 6, 8, and 10 relative to treatment administration (d 1). Heifers receiving BST had greater (P < 0.01) plasma glucose and IGF-I and similar (P ≥ 0.67) plasma insulin and P4 concentrations compared with SAL heifers. Results from this series of experiments suggested that concurrent increases in glucose and insulin are required to reduce hepatic catabolism and increase plasma concentrations of P4 in bovine females.     

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.     

Effects of body condition score at parturition and postpartum supplemental fat on metabolite and hormone concentrations of beef cows and their suckling calves

To determine the effects of BCS at parturition and postpartum lipid supplementation on blood metabolite and hormone concentrations, 3-yr-old Angus x Gelbvieh beef cows, which were nutritionally managed to achieve a BCS of 4 +/- 0.07 (479.3 +/- 36.3 kg of BW) or 6 +/- 0.07 (579.6 +/- 53.1 kg of BW) at parturition, were used in a 2-yr experiment (n = 36/yr). Beginning at 3 d postpartum, cows within each BCS were assigned randomly to be fed hay and a low-fat control supplement or lipid supplements with either cracked high-linoleate or high-oleate safflower seeds until d 61 of lactation. The diets were formulated to be isonitrogenous and isocaloric, and the safflower seed supplements were formulated to achieve 5% DMI as fat. On d 31 and 61 of lactation, blood samples were collected preprandially and then hourly postprandially (at 0, 1, 2, 3, and 4 h). Serum insulin (P = 0.27) and glucose (P = 0.64) were not affected by BCS at parturition. The mean concentrations of plasma NEFA (P = 0.08) and beta-hydroxybutyrate (P = 0.08) tended to be greater, and serum IGF-I was greater (P < 0.001) in BCS 6 than BCS 4 cows. Conversely, serum GH was greater (P = 0.003) for BCS 4 cows, indicating that regulation of IGF by GH may have been uncoupled in BCS 4 cows. The postpartum diet did not affect NEFA (P = 0.94), glucose (P = 0.15), IGF-I (P = 0.33), or GH (P = 0.62) concentrations. Oleate-supplemented cows had greater (P = 0.03) serum insulin concentrations, whereas control cows had greater (P = 0.01) plasma beta-hydroxybutyrate concentrations. Concentrations of NEFA (P = 0.05) and glucose (P < 0.001) were greater, and beta-hydroxybutyrate tended (P = 0.07), to be greater at d 3, whereas serum IGF-I was greater (P = 0.003) at d 6 of lactation. Similar concentrations of NEFA, glucose, GH, and IGF-I indicate that the nutritional status of beef cows during early lactation was not influenced by lipid supplementation. However, perturbations of the somatotropic axis in BCS 4 cows indicate that the influence of energy balance and BCS of the cow at parturition on postpartum performance should be considered when making managerial decisions.     

Insulin Sensitivity in Thoroughbred Geldings: Effect of Weight Gain,Diet, and Exercise on Insulin Sensitivity in Thoroughbred Geldings

The effects of dietary energy source, controlled weight gain, and exercise restriction on insulin sensitivity (SI) were studied in mature Thoroughbred geldings with body condition scores (BCS) of 4.3 ± 0.1. Two dietary energy sources were used, one high in starch and sugar (HS; n = 9) and one high in fat and fiber (HF; n = 7), and horses were fed 20 Mcal digestible energy (DE)/day above maintenance requirements to encourage weight gain. Using the minimal model of glucose and insulin dynamics, no differences in SI between groups were noted before initiation of treatment concentrate feeding. After dietary acclimation, SI was decreased in HS (P < 0.01) as compared with HF. After 32 weeks of controlled weight gain (90.8 kg; final BCS, 7.0 ± 0.1), SI remained lower in HS (P = 0.07) but did not change from the preweight gain value. SI in HF did not change between the start and end of weight gain. After completion of weight gain, exercise was restricted for 2 weeks, resulting in a reduction in SI in HF (P = 0.03) but no change in HS. It was concluded that dietary energy source may be more influential than weight gain on SI in the mature Thoroughbred gelding between BCS 4 and 7. The higher SI found in horses consuming the HF diet appeared to be partially dependent on some level of physical activity.     

Relationship between body weight and level of fat supplementation on fatty acid digestion in feedlot cattle

Eight Holstein steers with cannulas in the rumen and proximal duodenum were used in a split-plot design experiment to evaluate the interaction of body weight (175 vs. 370 kg) and level of fat supplementation (0, 3, 6, and 9% yellow grease) on characteristics of digestion and feeding value of fat in finishing diets. Dry matter intake was restricted to 2% of BW. There were no interactions between BW and level of fat supplementation (P > 0.10) on ruminal or total-tract digestion. Level of supplemental fat decreased (linear, P < 0.01) ruminal digestion of OM and NDF, and increased (linear, P < 0.05) ruminal N efficiency. There were no treatment effects (P > 0.10) on postruminal digestion of OM, NDF, and N. There tended to be an interaction (P < 0.10) between BW and level of fat supplementation on postruminal starch digestion. Increasing level of fat supplementation increased postruminal digestion of starch in heavier steers but did not affect starch digestion in lighter steers. There were no interactions (P > 0.10) between BW and level of fat supplementation on postruminal fatty acid digestion. Increasing level of fat supplementation decreased (linear, P < 0.01) postruminal fatty acid digestion, which was due to a decreased (linear, P < 0.01) postruminal digestion of C16:0 and C18:0. Supplemental fat decreased (linear, P < 0.01) total-tract digestion of OM and NDF. The estimated NEm (Mcal/kg) of yellow grease averaged (linear, P < 0.01) 6.02, 5.70, and 5.06 for the 3, 6, and 9% of level supplementation, respectively. We conclude that intestinal fatty acid digestion (FAD, %) is a predictable function (r2 = 0.89; P < 0.01) of total fatty acid intake per unit body weight (FAI, g/kg BW): FAD = 87.560 - 8.591FAI. Depressions in fatty acid digestion with increasing level of intake were due primarily to decreased intestinal absorption of palmitic and stearic acid. Level of fatty acids intake did not appreciably affect intestinal absorption of unsaturated fatty acid. Changes in intestinal fatty acid digestion accounted for most of the variation in the NE value of supplemental fat.     

Porcine somatotropin alters insulin response in growing pigs by reducing insulin sensitivity rather than changing responsiveness

Exogenous porcine somatotropin (pST) treatment consistently improves growth performance and reduces fat deposition in pigs, and it is hypothesized that one component of the mechanism is through altering the sensitivity and/or responsiveness to insulin. Therefore, a study was conducted to investigate the effect of pST treatment on whole-body glucose metabolism in response to varying doses of insulin. Eight barrows were surgically prepared with indwelling catheters and randomly assigned to one of two treatment groups (0 or 120 μg pST/kg BW · d) for 13 d. Whole-body glucose kinetics were measured during infusion of [6-(3)H]-glucose under basal conditions and during hyperinsulinemic-euglycemic clamps at various insulin infusion rates (7, 28, and 140, and 14, 70, and 280 ng insulin/kg BW · min) and alterations in the dose-response parameters were calculated with nonlinear regression. Treatment with pST increased basal plasma concentrations of glucose (36%; P = 0.005), insulin (276%; P = 0.001), and NEFAs (177%; P = 0.01) and decreased the rate of glucose disappearance (-59%; P = 0.001). The responsiveness (maximum response) for steady state glucose infusion rate to maintain glycemia was not altered by pST (112 vs 106 μmol/min · kg; P = 0.78), whereas the sensitivity (effective dose at 50% of maximum response) was increased almost 7-fold (1.3 vs 8.7 ng/mL; P = 0.027). Similar responses were observed for rate of glucose disappearance and insulin-dependent glucose utilization. Therefore, pST-induced insulin resistance with regard to whole-body glucose uptake is due to a reduced sensitivity to insulin, rather than a change in responsiveness.     

The effect of stage of growth and implant exposure on performance and carcass composition in steers

Angus and Angus x Limousin cross steers (n = 182; initial BW = 309 +/- 27.8 kg) were used to evaluate the influence of an estradiol-trenbolone acetate implant (containing 24 mg of estradiol and 125 mg of trenbolone acetate) on production efficiency and carcass traits when administered at specific stages of growth. Treatments were 1) control, no implant (NI); 2) early implant (EI) on d 1 (BW = 309 kg); or 3) delayed implant (DI) on d 57 (BW = 385 kg). Comparisons were also made between the NI and implanted treatments (I; EI + DI). Steers were procured at weaning and were backgrounded (47 d) before the initiation of the experiment. Initial predicted carcass composition was 14.9% protein, 13.3% fat, 54.6% moisture, and 17.2% bone. Days on feed were constant across treatment. After 56 d, ADG and G:F were improved (P < 0.01) by implants, NI vs. EI (1.68 vs. 1.90 kg and 0.227 vs. 0.257). At d 57, predicted carcass composition did not differ among treatments. From 57 to 112 d, DI caused higher ADG than NI or EI (NI = 1.65, EI = 1.57, and DI = 1.78 kg; P < 0.05) and higher G:F (NI = 0.155, EI = 0.150, and DI = 0.173; P < 0.01). Cumulative ADG and G:F were improved by implants (1.65 vs. 1.73 kg; P < 0.05) and (0.175 vs. 0.186; P < 0.01) for NI vs. I, respectively, with no differences between treatments that involved implants. Cumulative DMI was similar for all treatments. Implanting increased dressing percentage (63.5 vs. 64.1%; P < 0.05) and increased (P < 0.01) hot carcass weight (341 vs. 353 kg) and LM area (76.5 vs. 81.4 cm(2)) for NI vs. I, respectively. Rib fat and kidney, pelvic, and heart fat were not affected by treatment, and treatment had no effect on the whole carcass proportions of fat, protein, or water. Implants advanced maturity scores (NI = A(51) vs. EI + DI = A(59); P < 0.01). Marbling scores were decreased (P < 0.05) by EI but not by DI (NI = Small(65), EI = Small(20), DI = Small(36)). The percentage of i.m. fat content of the LM was decreased (P < 0.10) by EI and was not affected by DI (NI = 5.1, EI = 4.0, DI = 4.8%). Treatment affected (P < 0.10) the proportion of carcasses with marbling scores greater than Modest(0) (NI = 23.6, EI = 7.8, DI = 22.6%). The results of this study suggest that growth of i.m. fat is sensitive to anabolic growth promotants administered during early periods of growth.     

Intake, digestion, and digestive characteristics of Neotyphodium coenophialum-infected and uninfected fescue by heifers offered hay diets supplemented with Aspergillus oryzae fermentation extract or laidlomycin propionate

Tarentaise heifers fitted with a rumen cannula (539 +/- 7.5 and 487 +/- 15.7 kg avg initial BW in Exp. 1 and 2, respectively) were used in two Latin square metabolism experiments having 2 x 2 factorial treatment arrangements to determine the effects of supplementation with Aspergillus oryzae fermentation extract (AO) or laidlomycin propionate (LP) on intake, digestion, and digestive characteristics of Neotyphodium coenophialum-infected (IF) or uninfected (FF) tall fescue (Festuca arundinacea) hay diets consumed ad libitum. Heifers were housed in individual stanchions in a metabolism facility with ambient temperatures controlled to range between 26.7 and 32.2 degrees C daily. Total feces and urine were collected for 5 d following a 21-d dietary adaptation period. In situ DM and NDF disappearance and ruminal fermentation characteristics were also determined. In Exp. 1, DMI was 24% greater (P < 0.01) by heifers offered FF than by those offered IF (6.7 vs 5.4 kg/d). Heifers fed 2 g/d AO tended (P = 0.09) to consume 4% more DM than those fed a diet without AO. Degradable DM and NDF fractions of IF were greater (P < 0.01) than those of FF, but AO supplementation did not affect situ disappearance (P > or = 0.42). In Exp. 2, DMI was 18.9% greater (P < 0.01) by heifers offered FF than by those offered IF (6.6 vs 5.5 kg/d). Heifers fed LP (50 mg/d) consumed 10.6% less (P < 0.05) DM than those not fed LP (5.7 vs 6/5 kg/d). Digestibility of NDF tended to be greater (P = 0.08) and digestibility of ADF was greater (P < 0.05) from FF than from IF. Conversely, apparent N absorption (%) was greater (P < 0.05) from IF than from FF. Heifers fed LP had lower (P < 0.05) ADF digestibility than those not fed LP. In situ degradable DM and NDF fractions were greater (P < 0.01) from IF than from FF. Diets supplemented with LP had higher (P < 0.01) indigestible DM and NDF fractions than those without LP. Propionic acid and total VFA concentrations were greater (P < 0.05) from heifers offered FF than from those offered IF and from heifers fed LP than from those not fed LP. Therefore, it appears the major effect of N. coenophialum was a reduction in forage intake and total-tract fiber digestibility in certain situations. Response to the feed additives was similar whether heifers were offered IF or FF and no evidence was apparent that either additive would improve performance substantially by animals consuming low-quality fescue hay diets.     

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.     

Effects of roughage source and distillers grain concentration on beef cattle finishing performance, carcass characteristics, and in vitro fermentation

Two experiments were conducted to evaluate the effects of wet distillers grains plus solubles (DG) and roughage source on finishing cattle performance, carcass characteristics, and in vitro fermentation. In Exp. 1, crossbred beef steers (n=224, initial BW=349 kg) were used in a randomized complete block design with a 2 × 3 + 1 factorial arrangement of treatments. Experimental diets were a standard steam-flaked corn (SFC)-based control (no DG and 10% alfalfa hay), and either 15 or 30% DG (DM basis) with roughage sources of alfalfa hay (15-AH and 30-AH), Coastal bermudagrass hay (15-BG and 30-BG), or sorghum silage (15-SS and 30-SS). Within each DG concentration, roughages provided an equivalent percentage of NDF to 7.5% AH. Steers consuming 15% DG had greater (P < 0.04) final BW, ADG, and G:F than those fed 30% DG. Feeding AH as the roughage source with DG resulted in decreased final shrunk BW and ADG (P < 0.02) compared with BG and SS. Feeding SS as the roughage source decreased (P=0.01) G:F relative to BG. Hot carcass weight was greater (P < 0.01) for steers consuming 15 vs. 30% DG, tended to be least for diets with AH as the roughage source (P=0.06), and did not differ for the control vs. the other diets (P=0.86). Control cattle had an increased (P=0.05) proportion of USDA Choice or greater carcasses compared with the average of the other treatments. In Exp. 2, the same 2 × 3 +1 factorial arrangement as in Exp. 1 was used to examine the effects of roughage source and DG on IVDMD, culture fluid osmolality, and gas production kinetics. In vitro DMD tended (P < 0.09) to be greater for BG compared with SS at 6 and 36 h of incubation and was greater for AH vs. the mean of BG and SS at 18 h (P=0.01). Culture fluid osmolality, asymptotic maximal gas production, fractional rate of gas production, and lag time of gas production did not differ among treatments (P > 0.14). Overall, feeding 15% DG in SFC-based diets increased ADG, BW, and HCW relative to 30% DG. In addition, feeding AH tended to decrease ADG, final BW, and HCW relative to the other 2 roughage sources, whereas BG improved G:F over SS. These data suggest that including the smaller amount of DG and BG as the roughage source resulted in improved performance relative to other combinations, and that substituting roughages on the basis of equivalent NDF concentration might not be ideal for optimizing performance when feeding SFC-based finishing diets that contain DG.     

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.     

Daily treatment of growing foals with equine somatotropin: pathologic and endocrinologic assessments at necropsy and residual effects in live animals

This experiment assessed the effects of 12 mo of daily treatment of young horses with recombinant equine somatotropin (eST) on 1) carcass and internal organ traits at necropsy and 2) residual effects in live horses for 60 d after cessation of treatment. Seven horses received eST daily at 20 microg/kg BW; seven others received vehicle (controls). Four horses from each group were killed at the end of treatment. There were few effects of eST treatment on hematologic assessments or histopathologic evaluations of internal organs. Treatment with eST increased the weights of the right adrenal gland (P = 0.090), left (P = 0.085) and right (P = 0.013) kidneys, liver (P = 0.012), tended to inrease the weights of pancreas (P = 0.082), spleen (P = 0.008), and heart (P = 0.102), and decreased (P = 0.032) somatotropin (ST) content in the adenohypophysis. Loin-eye area at the 10th rib was also greater (P = 0.01) in eST-treated horses than in controls. There was no difference (P > 0.15) between groups in left adrenal, brain, parathyroid glands, or thyroid gland weights or in 10th-rib fat thickness. In the remaining two control and three eST-treated horses (one control horse died), plasma IGF-I concentrations were higher (P = 0.001) in treated animals through d 6 after cessation of treatment and then dropped precipitously. Insulin concentrations in treated animals tended to be elevated (P = 0.08) only on d 0. There was a treatment x day interaction (P = 0.04) for plasma urea nitrogen levels, which increased in treated horses. A decrease (P < 0.05) in BW in the treated animals was observed by 21 d after treatment. There was no difference (P > 0.15) in insulin or glucose response to glucose tolerance tests given on d 0 through 60 after cessation of treatment. Overall ST response to secretagogue was reduced (P < 0.05) in eST-treated horses compared with controls. In summary, long-term treatment of growing horses with eST decreased endogenous ST response to secretagogue and increased plasma IGF-I concentrations and many internal organ weights but had little effect on hematologic or histopathologic characteristics at necropsy. The effects on IGF-I concentrations were lost within 6 d, and BW in treated horses decreased within 3 wk after cessation of treatment.     

Effect of nonwaxy and waxy sorghum on growth, carcass traits, and glucose and insulin kinetics of growing-finishing barrows and gilts

Two experiments were conducted to determine the effect of nonwaxy (amylose and amylopectin starch) or waxy (amylopectin starch) sorghum on growth, carcass traits, and glucose and insulin kinetics of pigs. In Exp. 1 (95-d), 60 crossbred barrows or gilts (initial and final BW of 24 and 104 kg) were allotted to three treatments with five replications of four pigs per replicate pen in a randomized complete block design. The dietary treatments for Exp. 1 were 1) corn-soybean meal (C-SBM) diet, 2) sorghum-SBM (red pericarp, non-waxy), and 3) sorghum-SBM (red pericarp, waxy). In Exp. 2, 28 crossbred barrows (initial and final BW of 24 and 64 kg) were allotted to two treatments with three replications of four or five pigs per replicate pen in a randomized complete block design. Growth data were collected for 49 d, and then 20 barrows were fitted with jugular catheters, and then a glucose tolerance test (500 mg glucose/kg BW), an insulin challenge test (0.1 IU of porcine insulin/kg BW), and a feeding challenge were conducted. The dietary treatments for Exp. 2 were 1) sorghum-SBM (white pericarp, nonwaxy) and 2) sorghum-SBM (white pericarp, waxy). In Exp. 1, ADG (P = 0.10) and ADFI (as-fed basis; P = 0.02) were increased (P = 0.10) and gain:feed was decreased (P = 0.04) in pigs fed the sorghum-SBM diets relative to those fed the C-SBM diet. These responses may have resulted from the lower energy content of sorghum relative to corn. Plasma NEFA concentration (collected after a 16-h fast on d 77) was decreased (P = 0.08) in pigs fed the waxy sorghum-SBM diet relative to those fed the nonwaxy sorghum-SBM diet. Kilograms of carcass fat was decreased (P = 0.07) in pigs fed the waxy sorghum-SBM diet relative to those fed the nonwaxy sorghum-SBM diet. In Exp. 2, there was no effect (P = 0.57 to 0.93) of sorghum starch type on growth performance by pigs. During the glucose tolerance and insulin challenge tests, there were no effects (P = 0.16 to 0.98) of diet on glucose or insulin kinetics. During the feeding challenge, glucose (P = 0.02) and plasma urea N (P = 0.06) area under the response curves from 0 to 90 min were decreased in pigs fed the waxy sorghum-SBM diet. Feeding waxy sorghum had minimal effects on growth and carcass traits relative to pigs fed corn or nonwaxy sorghum. Waxy sorghum vs. nonwaxy sorghum had no effect on glucose or insulin kinetics in pigs.     

Influence of ruminal or duodenal soybean oil infusion on intake, ruminal fermentation, site and extent of digestion, and microbial protein synthesis in beef heifers consuming grass hay.

Six heifers (two Hereford X Jersey, four Hereford X Longhorn; average BW 278 kg) cannulated at the rumen and duodenum and fed a grass hay (fescue/orchardgrass) diet were used in a replicated 3 X 3 Latin square. Treatments were either no infusion (C), 150 ml of duodenally infused soybean oil (DI), or 150 ml of ruminally infused soybean oil (RI)/heifer twice daily for a total daily infusion of 300 ml of soybean oil. Periods of the Latin square included 18 d for adaptation and 5 d for collection. Forage OM, ADF, NDF, and N intakes were not affected (P greater than .10) by soybean oil infusion. Ruminal (P = .11) and total tract (P less than .10) OM digestibilities were decreased by RI compared with C or DI, but ADF and NDF digestibilities were not affected by treatment. Duodenal N (P less than .05) and microbial N flows were increased (P less than .10) for C and RI compared with DI. Microbial efficiency (g of N/kg of OM truly fermented) was improved (P less than .10) by RI compared with DI but did not differ (P greater than .10) from C. Ruminal pH was lower (P less than .05) with RI than with either C or DI. Ruminal NH3 N, total VFA, and acetate were not affected (P greater than .10) by treatment. Propionate (mol/100 mol) was greater (P less than .05) with RI than with DI and C, but the proportion of butyrate did not differ among treatments. These data indicate minimal direct benefits for improving forage usage as a result of soybean oil infusion with a 100% grass diet; however, animals should realize benefits from additional dietary energy provided by infused lipid.