Energy Utilization by Pregnant and Non-Pregnant Heifers

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Abstract
Ninety Hereford heifers were used to study the utilization of dietary energy during pregnancy. Metabolism studies were, conducted using pregnant (5) and non-pregnant (3) heifers. Neither the DE nor ME content of the diet was altered due to pregnancy. Although DE was lower (.25 Mcal/kg) for heifers fed at the high (1.8 × maintenance) than for those fed at the low (1.3 × maintenance) level of intake, ME was not affected by feeding level. The fasting heat production (FHP) of pregnant heifers, estimated from CO2 production, was 500, 698, 1,779 and 4,613 kcal/day greater at 120, 160, 200 and 240 days of gestation, respectively, than the FHP of non-pregnant heifers. Ten heifers were slaughtered initially in a comparative slaughter experiment. Of the 72 remaining heifers, 46 were pregnant. Pregnant and non-pregnant heifers were fed at a high (215 kcal ME/Wkg¾/day) or a low (150 kcal ME/Wkg¾/day) level of intake. Pregnant and non-pregnant heifers from both the high and low levels were killed at times corresponding to 134, 189, 237 and 264 days of gestation for pregnant heifers. Using comparative slaughter techniques the non-pregnant heifers had a FHP of 68 kcal/Wkg¾/day and utilized ME with an efficiency of 73% for maintenance and 39% for gain. The efficiency of utilization of ME for energy retention in the gravid uterus, conceptus and fetus were 14%, 12.5% and 12.2%, respectively. No differences in size or metabolic activity of the liver, heart or kidney due to pregnancy were observed. The daily ME requirements for pregnancy were estimated to be 257, 1,021, 3,264 and 8,336 kcal ME on day 100, 160, 220 and 280 of gestation, respectively. Copyright © 1976. American Society of Animal Science . Copyright 1976 by American Society of Animal Science.

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