Trace mineral supplementation of yearling horses.

Thirty-three Thoroughbred and Quarter Horse yearlings were used in two experiments (18 in Exp. 1 and 15 in Exp. 2) to determine the influence of trace mineral (TM) supplementation on growth and bone mineral content in young growing horses from 340 to 452 d of age. In each experiment the yearlings were assigned at random within breed and sex outcome groups to one of three treatments. Horses were fed assigned concentrates individually to appetite for two 1.5-h feeding periods, daily and group-fed Coastal bermudagrass (Cynodon dactylon) hay in drylot paddocks at a rate of 1.0 kg/100 kg BW daily. In Exp. 1, the concentrates were A) basal, B) basal + complete TM premix, and C) basal + Cu. In Exp. 2, the concentrates were D) basal, E) basal + complete TM premix, and F) basal + Cu + Zn. The basal diet in both experiments provided Cu and Zn intakes below NRC (1989) recommendations. Trace mineral supplementation had no effect on growth and development of the yearlings in either experiment. Weight gains equaled or exceeded gains specified as rapid (NRC, 1989) for yearlings of the age and expected mature weight used in these two experiments. No gross skeletal abnormalities were detected. Bone mineral deposition was increased by supplementation of the diet with a complete TM premix (P < .05). The addition of copper or copper plus zinc to the diets of yearling horses did not increase bone mineral deposition (P > .10). Results suggest that other trace minerals (Fe, Mn, Co, or I) are critical for bone mineralization.

The mechanical properties of equine third metacarpals as affected by age.

Twenty-five pairs of equine third metacarpals (McIII) were collected from horses of varying breeds and ranging in age from 1 d to 27 yr. Standard three-point bending tests were performed on the McIII to obtain comparative data on breaking load (BL), breaking strength (BS), and elasticity (E). Broken bones were reassembled and 2-cm sections cut from the bone 1 cm below the nutrient foramen and at the site of the break. Bone mineral content (BMC) and geometrical properties of these sections were determined. Maximum BMC (17.3 g/2 cm) was reached at 6.0 +/- 1.8 yr of age. Horses in this study achieved 76% of maximum BMC by 1 yr of age. Maximum BL (1,888 kg) was reached at 4.6 +/- 1.8 yr of age. The coefficient of determination (r2) between BMC and BL was .92 (P < .001). Breaking strength peaked at 2,272 kg/cm2 at 6.3 +/- 1.2 yr of age. The correlation between BS and BMC was .84 (P < .0001). At 1 yr of age BS was 1,919 kg/cm2, or 85% of maximum BS. Elasticity increased linearly with log 10 age (r2 = .91). The r2 of BMC and E was .79 (P < .001). Area moment of inertia (I) of the cortex of the bone was best approximated by the area of an ellipse (r2 = .91; P < .01). Results suggest that bone strength in horses peaks after most race horses have completed their careers.

Serum biochemical indicators of liver function in neonatal foals.

Serum biochemical indicators of liver function were determined in healthy, age-matched foals during the first 270 days of life. Values were compared with those of healthy adult horses and with those determined on the day of birth (less than 12 hours old). Serum alkaline phosphatase, gamma-glutamyl transferase, and L-iditol dehydrogenase activities were increased during the first 2 weeks of life. Serum cholesterol, triglyceride, and total and unconjugated bilirubin concentrations peaked during this same period. During the early neonatal period (less than 12 hours old), globulin concentrations (mainly beta 2 and gamma fractions) were low and albumin/globulin ratios were high. However, individual values for all analytes were varied.

The influence of mineral supplementation on growth and skeletal development of yearling horses.

Forty-six Thoroughbred and Quarter Horse yearlings were used in two experiments to evaluate the effect of mineral supplementation on growth and skeletal development. In the first experiment, concentrate and bermuda-grass hay diets providing 2.82 Mcal DE/kg (estimated), 13.0% CP, .62% Ca and .43% P on a DM basis were supplemented with trace minerals (TM) by adding 0, .5 or 1.0% TM premix to the concentrate. The TM content of the three diets (concentrate and hay) in mg/kg DM were: Fe 150, 162 and 176; Mn 56, 60 and 64; Zn 36, 53 and 69; and Cu 7, 8 and 11 for the low, medium and high TM levels, respectively. No effects of TM intake on feed intake, weight gain or body measurements were detected, but bone mineral deposition was increased by the high TM intake (P less than .02). No gross skeletal abnormalities were detected. In the second experiment, a basal diet with Ca and P concentrations near NRC (1978) recommendations was supplemented with no TM, TM or TM + Ca + P. The basal diet had TM concentrations similar to the highest TM levels in the first experiment. The two groups fed added minerals consumed more concentrate and total feed (P less than .1) than those receiving the basal diet. Weight gain was increased by the TM supplementation (P less than .1). There was no other diet effect on growth or development of the animals. Colts gained more height than fillies did (P less than .05). Results of these two experiments suggest that TM supplementation may have a positive effect on bone mineral deposition in yearling horses, but only when the TM content of the natural diet is below NRC (1978) recommendations.

Serum ferritin, serum iron, and erythrocyte values in foals.

Twenty-one healthy Thoroughbred and Quarter Horse foals were studied from birth until 1 year of age. Foals had access to an iron-supplemented creep feed before weaning and were fed an iron-supplemented concentrate as part of their diet after weaning at 4 months of age. Initial blood samples were taken before foals were allowed to nurse. Serum iron concentration, total iron-binding capacity, and PCV decreased during the foal's first 24 hours of life. Serum iron concentration decreased rapidly from 446 +/- 16 micrograms/dl (mean +/- SE) at birth to 105 +/- 11 micrograms/dl at 3 days of age. Serum ferritin concentration increased from a mean of 85 +/- 8 ng/ml at birth to 159 +/- 11 ng/ml at 1 day of age. Thereafter, ferritin concentration decreased gradually to a minimum of 61 +/- 6 ng/ml at 3 weeks of age, and then at 6 months increased to values similar to those from reference adult horses. The ferritin concentration in colostrum at birth was 354 +/- 42 ng/ml, compared with 25 +/- 2 ng/ml in milk 1 day later. The decrease and then increase in serum ferritin concentration occurred concomitantly with opposite changes in serum total iron-binding capacity. The mean PCV decreased gradually to a minimum at 3 months of age. This decrease was associated with an increasing number of microcytes, as determined with a cell-size distribution analyzer.

Influence of level of feeding and nutrient content of the concentrate on growth and development of yearling horses.

Three experiments using 63 Thoroughbred and Quarter Horse yearlings were conducted to evaluate the influence of level of feeding, and protein and calculated energy content of pelleted concentrates on growth and bone development. Animals were housed in drylot paddocks and individually fed concentrates twice daily. Coastal bermudagrass (Cynodon dyctylon) hay was group-fed. Yearlings offered a corn-based concentrate (3.56 Mcal digestible energy [DE]/kg) consumed levels of dry matter similar to yearlings fed a mixed-grain concentrate (3.32 Mcal DE/kg but consumed slightly more digestible energy. No differences in growth or bone development were detected. Yearlings fed restricted levels of concentrate that provided approximate National Research Council (NRC) recommendations for protein and DE had lower weight and girth gains (P less than .05) than those provided ad libitum concentrate intake during two 1.5-h daily feeding periods. Restricting concentrate intake had no effect on skeletal growth (P less than .05) but resulted in numerically lower values for bone radiographic density. Protein addition to a diet restricted to approximate NRC energy intake recommendations had no effect on weight gain, body measurements or bone mineral deposition (P greater than .05) and growth and development was less than that resulting from higher intakes of a lower protein concentrate.

Serum protein reference values in foals during the first year of life: comparison of chemical and electrophoretic methods.

Normal reference values for serum proteins of foals from birth to 1 year of age have been established. Chemical and electrophoretic/refractometric methods for total protein, albumin, total globulin and Albumin/Globulin (A/G ratio) have also been compared. The biuret total protein method and Bromcresol Green (BCG) method on the Technicon SMA 12/60 autoanalyzer were used and compared with total protein determined via refractometry and albumin determined by Cellulose Acetate (CA) electrophoresis/densitometry. Globulin and A/G ratios were calculated from the chemical method data and compared with that obtained electrophoretically. Total protein, albumin, total globulins and A/G ratios all were in agreement at all sample times studied. Data on the subfractionation of serum globulins via CA electrophoresis is also presented. Wide variations in alpha and beta globulin levels were noted among the foal sera early in life. As a result, two distinct populations of foals with respect to both globulin content and A/G ratio were identified. One of these populations (Group A) appeared to have obtained passive immunity more slowly than the other (Group B) animals. Comparison of these data with clinical cases of foals in which failure of passive transfer was a part suggests that the A/G ratio may be useful in assessing adequate colostral antibody levels in the newborn foal.

Haematology of foals up to one year old.

Packed cell volume, haemoglobin concentration, erythrocyte counts, erythrocyte indices, serum iron, iron binding capacities, total and differential leucocyte counts, platelet counts, total plasma protein, fibrinogen, haptoglobin and icterus index values were determined at 14 different ages in eight Thoroughbred and 14 Quarterhorse foals during the first year of life. Absolute neutrophil numbers in blood decreased and lymphocyte numbers increased during the first months. Absolute eosinophil numbers tended to increase until three months old. Haemoglobin concentration and packed cell volume decreased significantly during the first two weeks and generally stayed in the lower portion of adult horse normal ranges during the remainder of the first year. Mean cell volume decreased to minimum values at approximately four months and then gradually increased. Serum iron was high at birth and decreased rapidly to a minimum at three days old. Total iron-binding capacity increased to a maximum at one month. Serum haptoglobin was generally within the adult normal range at birth. A moderate, but significant, decrease occurred at one week old. Fibrinogen concentration increased to a maximum at five months. Icterus index values decreased rapidly during the first two weeks of life. Minor changes occurred in other parameters measured. Possible causes for the various changes in haematological parameters are discussed.

Effect of exogenous gonadal steroids and pregnancy on uterine luminal prostaglandin F in mares.

Two experiments were conducted to assess the effect of exogenous hormone treatment on uterine luminal prostaglandin F (PGF). In the first experiment ovariectomized pony mares received either corn oil (21 days, n = 3), estradiol valerate (21 days, n = 3), progesterone (21 days, n = 3) or estradiol valerate (7 days) followed by progesterone (14 days, n = 4). Progesterone treated mares had higher (P less than .01) uterine luminal PGF compared with all other groups, and no differences were detected between other treatment comparisons. In Experiment II, uterine fluid was collected from 4 ovariectomized horse mares before and after treatment with estradiol valerate (7 days) followed by progesterone (50 days). Pretreatment uterine luminal PGF levels were lower (P less than .001) than post-treatment levels (.03 vs 76.80 ng/ml). In a third experiment PGF was measured in uterine fluid of pony mares on days 8, 12, 14, 16, 18 and 20 of the estrous cycle and pregnancy. In nonpregnant mares a day effect (P less than .03) was observed in which uterine fluid PGF increased during the late luteal phase and declined thereafter. In contrast, no day effect was observed in pregnant animals and uterine luminal PGF was lower (P less than .001) than in cycling animals. These studies indicate that exogenous progesterone administration results in a large increase in uterine luminal PGF, whereas, pregnancy results in suppression. Taken collectively with previous work from our laboratory, these results suggest that while the endometrium of pregnant mares is capable of producing large amounts of PGF, the presence of a conceptus impedes its synthesis and/or release which allows for luteal maintenance.

Acute experimentally induced aflatoxicosis in the weanling pony.

Nineteen weanling ponies and 1 adult pony were given a single oral dose of aflatoxin B1 (AFB1). Dosages were: 0, 0.5, 1, 2, 4, 5, 6, and 7.4 mg of AFB1/kg of body weight. Vital signs were monitored, and whole blood and serum collected for analysis of serum enzymes, prothrombin time, blood cell counts, and serum urea nitrogen. Ponies that died were examined for gross lesions, and tissues were collected for histopathologic examination and analysis of AFB1 and AFM1 residues. Two of the 4 ponies given the 2 mg/kg dose and all ponies given the larger dosages died within 76 hours. Clinical signs included increased rectal temperature, faster heart and respiratory rates, abdominal straining, bloody feces, and tetanic convulsions. At necropsy, ponies that died of acute aflatoxicosis showed visceral petechiae and hepatic focal lesions. Histopathologic changes included severe hepatic necrosis, vacuolation, and bile duct hyperplasia. Aflatoxins B1 and M1 were recovered from liver, kidney, skeletal muscle, and gastrointestinal contents. One other pony given the 2 mg/kg dose died 32 days after dosing, and 1 control pony died after 70 days. Continuous elevations in prothrombin time and serum aspartate aminotransferase, alanine aminotransferase, and gamma-glutamyl transpeptidase levels were observed in ponies dosed at 4 mg/kg or more. Significant (P less than 0.05) elevations in these values, which peaked 2 to 3 days after dosing, were seen in ponies given the 2 mg/kg dose. This group also had significant increases over controls in PCV and hemoglobin concentration 5 days after dosing.

Lysine supplementation of diets for yearling horses.

Forty-six Thoroughbred and Quarter Horse yearlings were used in two experiments designed to determine the amount of lysine in the concentrate necessary to promote maximum growth when fed the Coastal bermudagrass (Cynodon dactylon) hay provided at 1% body weight (BW)/day. In the first experiment, a 196-day trial, supplemental protein sources and analyses of the concentrates compared were: (1) soybean meal (SBM; 15.4% crude protein, .70% lysine); (2) SBM + .2% lysine (15.7% crude protein, .81% lysine), and (3) brewers dried grains + .2% lysine (15.9% crude protein, .59% lysine). Concentrate intake averaged 1.67% BW/day, and hay intake averaged .94% BW, for a total of 2.61% BW/day. Protein and lysine intakes (grams/day) for horses fed the three diets were, respectively: (1) 1,106, 48; (2) 1,091, 52 and (3) 1,077 and 40. Growth and efficiency responses for animals on treatments 1, 2 and 3 were, respectively: weight gain - 125, 123 and 114 kg; height gain - 9.5, 9.3 and 8.1 cm; girth gain - 21.6, 19.0 and 17.0 cm (P greater than .05); length gain - 14.5, 13.7 and 14.9 cm. and feed/gain - 15.3, 15.0 and 16.0. In the second experiment, a 140-day trial, SBM-based concentrates provided (1) 16.1% crude protein and .67% lysine, (2) 13.6% crude protein and.51% lysine and (3) 14.2% crude protein and .64% lysine. Concentrate averaged 1.99% BW and hay intake averaged .92% BW, for a total of 2.91% BW/day. Protein and lysine intakes (grams/day) for horses fed the three diets were (1) 1,432, 59; (2) 1,195, 46; and (3) 1,182, 53. Growth and efficiency responses for animals given the three treatments were: weight gain - 101, 87 and 101 kg (P greater than .05); height gain - 5.7, 6.0 and 6.4 cm; girth gain - 14.8, 12.2 and 16.3 (P greater than .05); length gain - 10.9, 10.9 and 11.9 cm, and feed/gain - 16.5, 17.9 and 15.0 kg (P greater than .05). No significant sex effects were detected. Results suggest that at least 1.9 g lysine/Mcal digestible energy is required to support maximum growth of yearling horses.

Effects of aflatoxins in young ponies.

Sixteen clinically normal, healthy ponies were randomly assigned to 4 groups and given aflatoxin B1 in doses of 0.045, 0.030, 0.015, and 0 (control) mg/kg of body weight per day for 21 days (or total doses of 0.945, 0.630, 0.315, and 0 mg/kg). The animals were allowed to recover for 3 months and then were reassigned to 4 treatment groups such that each group during the 2nd trial included a pony from each of the groups of the 1st trial. The animals in the new groups were intubated and were given aflatoxin in doses of 0.4, 0.2, 0.1, and 0 (control) mg/kg/day for 5 days ( or total doses of 2.0, 1.0, 0.5, and 0 mg/kg). Venous blood samples were drawn every other day to monitor for toxicosis; examinations were made for RBC and WBC counts, hemoglobin concentration, PCV, serum urea nitrogen, prothrombin time, and serum concentrations of aspartate aminotransferase, iditol dehydrogenase, alkaline phosphatase, albumin, gamma-glutamyl transferase, and arginase. There were no significant differences between treatment groups and controls (given no aflatoxin) in the toxicologic values examined for during the 1st trial. During the 2nd experiment, 2 of the ponies in the large-dose treatment gorup (2.0 mg/kg) demonstrated increased serum enzyme activities. These animals had been in the large-dose (0.945 mg/kg) and median-dose (0.63 mg/kg) groups during the 1st trial. Arginase, iditol dehydrogenase, and gamma-glutamyl transpeptidase activities became increased on the 4th day of treatment and continued to increase until the 6th day of the experiment (1 day after treatment was terminated). These enzymes approached control group values at 10 days after cessation of treatment. These increases were indicative of hepatocellular toxicity. It was concluded that the possibility of equine aflatoxicosis exists although ponies given high quality rations appear to be less susceptible than some other species. Prior exposure to aflatoxins may predispose to clinical toxicity on subsequent exposure, despite lack of expression of clinical signs.

Plasma concentration of iditol dehydrogenase (sorbitol dehydrogenase) in ponies treated with aflatoxin B1.

Twelve clinically normal Shetland ponies were allocated to one of four treatment groups. Aflatoxin B1 was administered at the dosage level of 2 mg/kg of body weight to group A, 1 mg/kg to group B, and 0.5 mg/kg to group C; a placebo was given to group D (controls). Plasma samples were assayed at 4-hour intervals for iditol dehydrogenase (ID) (sorbitol dehydrogenase) concentrations as an indicator of hepatic damage. One of the ponies in group A died 68 hours after dosing; another pony in group A died 76 hours after dosing. All other animals survived the experiment. The means of peak ID values were as follows: group A, 1514.0 IU/l (P < 0.05); group B, 192.6 IU/L (P < 0.05); group C, 8.5 IU/L (P < 0.05); and group D (controls), 2.7 IU/L. A square root transformation analysis of the postdosing response of ID values in relation to time demonstrated that the mean of group A became significantly higher (P < 0.05) than did the mean of the control group at 5 to 6 hours. The mean of group B at 12 to 16 hours and the mean of group C at 20 to 24 hours also were significantly higher (P < 0.05) than was the mean of the control group.

An equine fetal monster dicephalus tetrapus dibrachius.

Double monsters are structurally related to monozygotic twins and the reported frequency of these abnormalities in the equine species is low. Symmetrical, double development in both the cephalic region and caudal trunk was demonstrated along with a common undeveloped cervical mass. Anomalies found in the separate genito-urinary systems added another variant to this case.