Effects of stage of lactation and level of feed intake on energy utilization by Alpine dairy goats
Tovar-Luna, I., R. Puchala, T. Sahlu, H. C. Freetly, and A. L. GoetschJournal of Dairy Science 93:4829-4837. 2010
Thirty-six lactating Alpine does were used to determine effects of stage of lactation and level of feed intake on energy utilization. Twelve does were assigned to measurement periods in early, mid-, and late lactation (wk 5, 13, and 27, respectively). For six does of each group, after ad libitum consumption of a 60% concentrate diet feed intake was restricted to near the ME requirement for maintenance (MEm) for 8 d followed by fasting for 4 d. Fasting was immediately after ad libitum consumption for other does. Intake of ME was similar among stages of lactation with ad libitum intake (22.1, 22.1, and 19.8 kJ/d, respectively). The efficiency of ME utilization for maintenance determined with does fed near MEm averaged 81%. Fasting heat energy was greater with ad libitum vs. near MEm consumption (368 vs. 326 kJ/kg BW0.75) and was numerically lowest among stages in late lactation with near MEm intake (334, 350, and 295 kJ/kg BW0.75) and ad libitum consumption (386, 384, and 333 kJ/kg BW0.75 in early, mid-, and late lactation, respectively). The efficiency of use of dietary ME for lactation was greater for consumption near MEm than for ad libitum intake (67.9 vs. 58.6%) and with ad libitum consumption tended to decrease with advancing stage of lactation (63.9, 57.3, and 54.5% for early, mid-, and late lactation, respectively). Estimated MEm was greater with ad libitum than near MEm intake and was lowest during late lactation (429, 432, and 358 kJkg BW0.75 with near MEm intake, and 494, 471, and 399 kJ/kg BW0.75 with ad libitum consumption in early, mid-, and late lactation, respectively). Although, because of increasing BW as the experiment progressed, MEm in MJ/d was similar among stages of lactation with both levels of intake. The efficiency of ME use for maintenance and lactation was similar among stages of lactation and greater with intake near MEm than ad libitum (77.1 vs. 67.7%). In conclusion, the MEm requirement in kJ/kg BW0.75 of does in late lactation was less than in early and mid-lactation. There was marked effect of restricted feed intake subsequent to ad libitum consumption on estimates of efficiency of energy use for maintenance and lactation compared with use of nonlactating animals. Level of feed intake can have substantial effect on estimates of energy utilization by lactating dairy goats.
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