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Effects of length of pasture access on energy use by growing meat goats

T. Berhan, R. Puchala, R. C. Merkel, T. A. Gipson, G. Animut, A. L. Goetsch, T. Sahlu

E (Kika) de la Garza American Institute for Goat Research, Langston University, Langston, OK

Six Boer × Spanish wethers (21 ± 1.0 kg initial BW and 7 to 8 mo of age) were used in two simultaneous 3 x 3 Latin squares to determine effects of different lengths of access to pasture with high availability of cool-season annual forage on energy expenditure (EE), retained energy (RE), ME intake, and grazing behavior. Wethers grazed a 0.7-ha pasture of wheat (Triticum aestivum) and rye (Secale cereale) in the fall/winter period for 4 (1200 to 1600), 8 (0800 to 1600), or 24 h; 4- and 8-h wethers were confined as a group in an enclosed facility at other times. Periods were at least 18 d in length, with 4 d for total feces collection with bags, 2 d to measure heart rate (HR; Polar S610 monitor) and grazing behavior (IGER system), and 1 d without feed or water for assessing body composition from urea space and shrunk BW. EE was based on HR and the predetermined relationship between EE and HR for each wether, and ME intake was the sum of EE and RE. Available forage DM mass averaged 2,831, 2,176, and 2,443 kg/ha in period 1, 2, and 3, respectively. Energy expenditure was greatest (P < 0.05) for 24 h (4.96, 5.13, and 6.19 MJ/d; SE = 0.253), although RE was similar among treatments (0.88, 2.16, and 1.57 MJ/d for 4, 8, and 12 h, respectively; SE = 0.361). Intake of ME was greater for 8 and 24 h vs 8 (5.84, 7.30, and 7.76 MJ/d for 4, 8, and 24 h, respectively; SE = 0.530). Gain of fat (15.7, 50.3, and 33.7 g/d for 4, 8, and 24 h, respectively; SE = 9.80) was responsible for numerically greatest RE for 8 h, with similar gain of water, protein, and ash. As length of pasture access increased, number of steps (2,508, 4,569, and 6,412), time spent ruminating (4.42, 6.33, and 7.28 h), and time eating (3.77, 6.35, and 7.24 h) increased (P < 0.05) and idle time (15.81, 11.32, and 9.48 h) decreased (P < 0.05), whereas time lying was greater (P < 0.05) for 4 and 8 h vs 12 (8.39, 8.25, and 6.66 h for 4, 8, and 24 h, respectively; SE = 0.161). In summary, even though 4-h pasture access limited ME intake and eating time, EE was similar to that for 8 h. Full-day pasture access resulted in greater EE than for 8 h presumably because of differences in behaviors such as eating time and number of steps, yet ME intake was not different. In conclusion, these results suggest that with high availability of high-quality forage, limited pasture access of a minimal length could yield performance by growing meat goats at least comparable to that with continuous access.


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