The effect of a limit-fed diet and slow-feed hay nets on morphometric measurements and postprandial metabolite and hormone patterns in adult horses.

Modern horse management systems tend to limit a horse's opportunity to forage, rely on meal feeding, and may contribute to the increase in equine obesity. The use of slow-feed hay nets represents an opportunity to extend foraging time while feeding a restricted diet. The objectives of this study were to determine if limit feeding combined with a slow-feed hay net would affect morphometric measurements and postprandial metabolite and hormone patterns in overweight adult horses. Eight adult Quarter horses (BW 563 kg ± 4.6 kg; BCS 7.2 ± 0.3) were used in a randomized complete block design, with 4 horses assigned to feeding hay off the stall floor (FLOOR) and 4 horses assigned to feeding from a slow-feed hay net (NET). Horses were fed in individual stalls at 1% BW each day, split evenly between 2 meals at 0700 and 1600 h. Body weight, BCS, neck and girth circumference, cresty neck score, and ultrasound measurements of average rump fat, longissimus dorsi (LD) depth, and LD thickness were taken on d 0, 14, and 28. Three 24-h blood samplings were conducted on d 0, 14, and 28 and were analyzed for glucose, insulin, cortisol, and leptin concentrations. Samplings occurred every 30 min for 3 h postfeeding, with hourly samples occurring between feedings. Horses feeding from the FLOOR took less time to consume their hay meal compared with horses feeding from the NET ( < 0.001). All horses lost weight over the 28-d period ( < 0.0001); however, no difference was observed between treatments. There was no difference in BCS, neck and girth circumference, cresty neck score, rump fat, or LD depth between days or treatments ( ≥ 0.25). There was an effect of day on LD thickness in horses feeding from the NET. Longissimus dorsi thickness was lower on d 28 compared with that on d 0 ( = 0.0257). Only time to peak insulin and peak cortisol were affected by treatment ( ≤ 0.037), with horses feeding from the NET having lower values than horses feeding from the FLOOR. Average glucose, insulin, cortisol, and leptin were affected by day ( ≤ 0.0102). Glucose and insulin values increased, whereas cortisol and leptin levels decreased throughout the 28-d study. The use of a slow-feed hay net coupled with a limit-fed diet appears to be an effective method for decreasing BW and maintaining more homeostatic levels of postprandial metabolites and hormones when feeding overweight adult horses.

Plasma and synovial fluid concentration of doxycycline following low-dose, low-frequency administration, and resultant inhibition of matrix metalloproteinase-13 from interleukin-stimulated equine synoviocytes.

REASONS FOR STUDY: To determine whether low-dose, low-frequency doxycycline administration is capable of achieving chondroprotective concentrations within synovial fluid (SF) while remaining below minimum inhibitory concentration 90 (MIC90 ) of most equine pathogens and would be an option in the management of osteoarthritis. OBJECTIVES: To determine whether low-dose, low-frequency oral administration of doxycycline can attain in vivo SF concentrations capable of chondroprotective effects through reduction of matrix metalloproteinase (MMP)-13 activity, while remaining below MIC90 of most equine pathogens. STUDY DESIGN: Descriptive pharmacokinetic study with crossover design. METHODS: Two groups of 6 horses received oral doxycycline. Plasma and SF doxycycline concentrations were measured using high performance liquid chromatography. Group 1 received 5 mg/kg bwt q. 24 h with 21 blood and 8 SF samples collected over 120 h; Group 2 received 5 mg/kg bwt q. 48 h with 27 blood and 11 SF samples collected over 192 h. Cultured synoviocytes were treated with interleukin-1α (1 ng/ml) for 24 h to stimulate MMP synthesis, and then SF was added to the culture medium for 96 h. MMP-13 protein and mRNA were measured in synoviocyte culture medium and synoviocytes, respectively. RESULTS: Mean doxycycline concentration ≥0.043 µg/ml (previously demonstrated to inhibit MMP-13) was achieved in plasma by t = 0.25 h and SF by t = 48 h in Group 1, and in plasma by t = 0.17 h and SF by t = 1 h in Group 2. Synoviocyte culture medium containing doxycycline from Groups 1 and 2 had significantly decreased active MMP-13 protein concentration, and synoviocytes cultured in this medium had significantly decreased MMP-13 gene expression compared to controls. Plasma doxycycline concentration in both groups and SF doxycycline concentration in Group 2 demonstrated a cumulative effect. CONCLUSIONS: Low-dose orally administered doxycycline achieves SF concentrations in vivo capable of diminishing MMP-13 expression. This study supports the use of doxycycline as a disease modifying osteoarthritic drug.