Methods of restricting forage intake in horses

Abstract

Horses have evolved to be hindgut fermenters, requiring small amounts of forage to be consumed throughout the day [1]. However, due to the recent increase in equine obesity [2-4], it has become necessary to restrict the amount of feedstuffs a horse consumes, often resulting in a restriction of forage intakes. In order to maintain a healthy gastrointestinal system, management strategies should attempt to replicate a horse's natural foraging habits. The objectives of the following studies were: 1) to investigate the effectiveness of decreasing pasture forage intakes via use of a grazing muzzle, and whether the effectiveness could be altered by grass morphology and palatability, 2) to investigate the effectiveness of "slow-feed hay nets" at increasing time to consumption of a preserved forage meal in stalled horses and 3) to observe the effects of increased time to consumption of daily rations on the post-prandial metabolic response. To determine objective 1, a two-year study was designed where four horses were used in a Latin square design in Year 1, while 3 horses were used in a completely randomized design in Year 2. Horses were grazed for 4 hours on monoculture plots four days per month for four months. Initial herbage mass and residual herbage mass measurements were taken to determine forage intakes. For objective 2, 8 horses were used in a replicated Latin square design, with 2 horses assigned to a treatment at a time. There was a control (C) of feeding hay on the ground, as well as three treatments: small-opening net (SN), medium-opening net (MN) and large-opening net (LN). Horses were allowed 4 h to consume their hay meal. Time to consumption and dry matter intake rate were measured using a stopwatch and any orts remaining after the 4 h were collected and weighed. To estimate objective 3, 8 overweight horses were enrolled in a randomized complete block design. Horses were blocked by bodyweight, BCS, and gender. Horses were fed a control diet of hay at 2% BW for a period of 10 days, and were then switched to a restricted diet of hay fed at 1.08% and ration balancer fed once daily at a rate of 0.001% BW. Horses were assigned to one of two treatments: hay fed off the floor (FLOOR) and hay fed in a small-opening hay net (HN). Serial 24 h blood samples were taken on day 0, when horses were still on baseline diet, as well as days 14 and 28. Plasma glucose, insulin, cortisol, and leptin values were estimated.Results of objective 1 found that grazing muzzles were effective at decreasing pasture intakes by 30% (P < 0.0001). Species had no effect on intakes in Year 1 (P = 0.27), but did impact intakes in Year 2 (P = 0.042). Results of objective 2 found that SN and MN were effective at increasing total time to consumption (P < 0.0001) compared to horses on the control and LN, more closely mimicking a horses' natural foraging behavior. Results of objective 3 found that hay nets decreased overall stress of horses on a restricted diet (P < 0.05), however length of sampling and weight loss had a larger impact on post-prandial metabolite. Horses on day 28 of the trial had higher average glucose, insulin and cortisol values, as well as lower AUC cortisol. Increasing time to consumption of forages is a healthy method of decreasing body weight while maintaining healthy post-prandial metabolite values.