Effects of stocking rate, breed, and stage of production on energy expenditure and activity of meat goat does on pasture
Beker, A., T. A. Gipson, R. Puchala, A. Askar, K. Tesfai, G. D. Detweiler, A. Asmare, and A. L. GoetschJournal of Applied Animal Research. 36:159-174. 2009
Sixteen Boer and 16 Spanish multiparous does were used to determine how stocking rate (SR), breed, and stage of production influence energy expenditure and behavioral activities on pasture and to develop a simple method of predicting energy used for activity. The experiment began in late spring at an average of 24 days after kidding. Litter size was two and kids were Boer and Spanish. Two does of each breed resided in eight 0.5-ha grass/forb pastures. There were five periods, 56, 60, 63, 64, and 73 days in length, corresponding to mid-lactation, early post-weaning, the late dry period, early gestation, and mid-gestation. During period 1 and the first part of period 2, two additional does with kids of each breed grazed in four High SR pastures, with other pastures designated as Low SR. Because of low available forage mass in period 3, grass hay was offered for ad libitum consumption in periods 3-5 and a concentrate supplement was provided in periods 4 and 5. Energy expenditure (EE) was estimated from heart rate (HR) on pasture and EE:HR for each doe determined in a calorimetry system. A leg position/movement monitoring system and a GPS collar with position and movement sensors were used to estimate distance traveled and time spent grazing/eating, resting while lying, resting while standing, and walking without grazing/eating. EE attributable to activity (EEa%), expressed as a percentage of the ME requirement for maintenance plus activity in confinement, was determined based on total EE, estimated milk production, and doe BW and ADG. Forage DM mass in the middle of periods was 696, 246, 125, and 196 kg/ha for the High SR and 1362, 967, 479, and 610 kg/ha for the Low SR in periods 1, 2, 3, and 4, respectively. Kid ADG at weaning after 73 days was lower (P < 0.05) for the High vs. Low SR (87 vs. 112 g). Distance traveled was not influenced by SR or breed but varied among periods (3.54, 3.76, 3.09, 3.08, and 4.10 km/day in periods 1, 2, 3, 4, and 5, respectively; SE = 0.193). Time spent grazing/eating tended (P < 0.07) to be greater for Boer vs. Spanish does (7.9 vs. 6.7 h/day) and differed among periods (8.0, 7.8, 7.6, 5.3, and 8.0 h/day in periods 1, 2, 3, 4, and 5, respectively; SE = 0.72). Total EE was greater (P < 0.05) for Boer than for Spanish does (13.4 vs. 11.4 MJ/day) and differed among periods (13.5, 11.6, 11.7, 11.8, and 13.4 MJ/day in periods 1, 2, 3, 4, and 5, respectively; SE = 0.41). Likewise, predicted ME intake was greater (P < 0.05) for Boer vs. Spanish does (14.2 vs. 12.2 MJ/day) and varied with period (16.1, 10.6, 12.8, 12.6, and 14.0 MJ/day in periods 1, 2, 3, 4, and 5, respectively; SE = 0.47). EEa% was not influenced by SR, breed, or period, averaging 49%. Behavioral activities were not highly related to EEa%, although no-intercept regressions against time spent grazing/eating and grazing/eating plus walking indicated an increase in EEa% of 5.79 and 5.05%/h, respectively. In conclusion, although EEa% was not affected by treatments of this experiment or highly related to behavioral activities monitored, it represents a sizeable cost of energy deserved of further study.
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