Prediction of Hourly Dry Matter Intake in Horses
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2009-12-07
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DOWLER, LAUREN ELIZABETH. Prediction of Hourly Pasture Dry Matter Intake in Horses. (Under the direction of Paul David Siciliano.)
Establishing hourly dry matter intake (DMI) rates for horses grazing pasture would allow for calculation of the required length of time for horses to consume only their daily caloric requirement; thereby preventing wasteful overconsumption of pasture. Unfortunately, estimates of hourly pasture DMI rates are scant. The objective of this two-part study was to use an herbage mass (HM) reduction method to determine pasture DMI over an 8-hr period (experiment 1- EXPT1) and to test the validity of these estimates (experiment 2 – EXPT2). Pasture DMI in EXPT1 was measured using eight horses of light horse breeding (7 mares, 1 gelding; mean ± body weight 576 ± 32 kg; mean age 15.6 ± 6.8yr) at three separate times throughout the year (October 2008, and February, and May of 2009 - hereafter referred to as periods 1, 2, 3, respectively). Horses grazed for two consecutive 4-h periods in each of two separate 5m x 5m cells following 12h of feed restriction. The HM of each cell was determined prior to and after each 4-hr grazing period and was used to determine hourly DMI rate. Mean pasture DMI rate over the entire 8-h grazing period was 0.166, 0.088, and 0.108 ± 0.013 kg DM · 100 kg BW-1 · h-1 in periods 1, 2, and 3, respectively. Mean DMI rate over 8h was different across periods (period 1 > 2 and 3; P < 0.005) and cells (cell A > B; P < 0.001). Experiment 2 immediately followed EXPT1 in each period. The same horses from EXPT1 were randomly assigned to one of two treatments: unrestricted grazing (UNRES; n=4) or restricted grazing (RES; n=4) for the 42d. Horses in the UNRES group grazed continuously; horses in the RES group grazed only for a time period calculated to allow for consumption of daily DEm requirement only. Daily DEm was calculated using the hourly DMI rates determined in EXPT1, pasture DE concentration, and daily maintenance DE requirements. Body weight was monitored weekly. Mean BW increased over time (P = 0.013) by 7.9 ± 17.91 kg in period 1 and decreased over time in both period 2 (P < 0.001) and 3 (P < 0.001) (11.5 ± 16.98 and 44.44 ± 17.45 kg, respectively), but neither treatment nor treatment x time interaction were significant in any period. When extrapolated to a 15 h grazing time each day, the hourly DMI estimates correspond to a daily DMI of 2.49, 1.32, and 1.62% BW for periods 1, 2, and 3, respectively. While the estimate from periods 1 and 3 seem reasonable and are within the range of the NRC (2007), the estimate from period 2 seems low, and is not within the range (NRC 2007). However, the change in BW in each period of EXPT2 suggests that hourly intake rate likely varies from day to day as well as with changes in environmental variables, season, and forage characteristics. Withholding feed prior to EXPT1, could have led to atypical hourly DMI rates. In future studies estimating hourly pasture DMI, it may be useful to alter horse management techniques. While this data suggests that herbage mass reduction is a useful tool for determining DMI, it may be most accurate under specific conditions. Studies comparing the estimates of hourly DMI rate obtained through different methods such as markers, short term weight changes, and measurement of fecal outputs and known DM digestibilities would be useful in determining the most useful and accurate method to obtain estimates in the future.
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Tall Fescue, Pasture, Dry Matter Intake, Horse
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Degree
MS
Discipline
Animal Science
