Browsing by Author "Greiwe-Crandell, Kathleen M."

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    The effects of added dietary fat on young exercising horses
    Greiwe-Crandell, Kathleen M. (Virginia Tech, 1990-02-05)
    Two groups of three horses each were fed either a control diet of ground hay and concentrates or a similar diet with 10.5% added fat. The horses were trotted at 2.9 m/sec to a heart rate (HR) of 160 beats per minute (BPM) 5 d/wk on an equine treadmill set at go for a training period of 12 wk. A standard exercise test (SET) was performed at wk 0, 6, and 12. Blood samples were taken before, during, and after exercise and analyzed for lactate, glucose, cholesterol, total serum protein, and free fatty acids (FFA). Muscle biopsies were taken before and after exercise during the SETs on wk 1 and wk 12. Differences between wk 0, 6, and 12 in blood levels were found: lactate (P < .01) and glucose (P < .001) decreased, while cholesterol (P < .01) and FFA (P < .05) for both groups, indicating a conditioning response. However, no differences were found in any of the blood factors between groups. In the final SET, pre-exercise muscle glycogen levels in the fat-fed horses were lower (13.61 vs 25.44 mg/g wet tissue). Post-exercise glycogen levels, however, were higher in the fat- fed horses (10.95 vs 8.27 mg/g wet tissue), indicating that there may have been a glycogen-sparing effect. The fat-fed horses avg .3 kg/d less in daily consumption, and avg .03 kg/d more in ADG (.36 kg/d for control vs .33 kg/d for fatfed). Differences in trotting times (time to HR 160 BPM) between groups were seen at the end of four (P < .05) and eight (P < .05) Wki control horses improved 39% while fatfed horses only 25% from wk 1 to wk 8. No differences were seen between groups from wk 9 to 12. Improvement over the 12 wk period was similar for both groups (control 61%, fatfed 67%). These results seem to suggest that although fat appears to be a reasonable source of energy for the horse, there may be a long adaptation period for horses fed higher levels of fat.
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    Vitamin A depletion and repletion in thoroughbred horses
    Greiwe-Crandell, Kathleen M. (Virginia Tech, 1996-11-18)
    The purpose of this research was to study vitamin A status in grazing horses throughout the year and to evaluate the effectiveness of vitamin A and β-carotene as supplements. Vitamin A status was assessed by serum retinol concentrations (SR) and the relative dose response (RDR) which was adapted for use in the horse. The horses (45 Thoroughbred mares) were divided into three diet groups: pasture and hay only (PH); pasture, hay and vitamin A-free concentrate (PHC); and hay and vitamin A-free concentrate (HC). The mares, as well as their foals, were assessed for vitamin A status during the summer, fall and winter. After eight months, each diet group was subdivided and supplemented with either: retinyl palmitate at two times the recommended level (A), the equivalent in water dispersible β-carotene (B), or a placebo (C). Supplementation continued for 20 months during which the vitamin A status was assessed every 60 days in the mares, and at birth in the neonates. During both the depletion and the repletion phase the mares were kept on a regular breeding schedule and the reproductive rates were determined as well as the general health of the mares and their offspring. The RDR proved more sensitive at detecting changes in vitamin A status than SR, and a combination of both was used. A measurable decline in vitamin A stores was seen in the HC group within 2 months, and in PH and PHC groups during the winter. The HC group remained lower in vitamin A status throughout the study. A seasonal fluctuation of vitamin A status was observed regardless of supplementation. Supplementation with retinyl palmitate improved vitamin A status in all three diet groups, however, supplementation with β-carotene did not. Both neonates and young growing horses were lower in vitamin A status than the adult. A respiratory infection observed in the weanlings affected vitamin A status as well. Supplementation of the dam had no effect on neonatal vitamin A status. Deleterious effects on reproductive rates and health were also observed with vitamin A depletion. Supplementation of β-carotene had a negative effect on reproductive rates in this study.