Abstract
Abstract This study’s objective was to determine the relationship between retained energy, lactation maintenance energy requirement (MER), and dry period voluntary feed intake (VOL) in beef cows. Twenty-four mature fall-calving Angus cows were used in an 82-d study during lactation to establish maintenance energy requirements followed by a voluntary feed intake study after weaning. During the lactation MER experiment, cows were housed in 2 drylot pens and limit-fed a mixed hay/concentrate diet (17.8% CP, 2.6 Mcal/kg ME, DM basis) individually once per d in a stall barn. Cows were adapted to the diet and feeding management for the first 16 d. Subsequently, cows were weighed and feed allowance adjusted at 14-d intervals to achieve BW and BCS stasis. Milk yield and composition were determined on d – 10, 49, and 77 using a milking machine. Retained energy was calculated as average daily maternal tissue energy change plus average daily milk energy yield. During the post-weaning VOL experiment, cows were provided ad libitum access to a grass hay diet for 41 d (8.15% CP, 1.8 Mcal/kg ME, DM basis) using five individual feed intake monitoring units (SmartFeed, C-Lock, Inc). Each one unit increase in metabolizable energy intake, kcal/kg BW0.75 was associated with a 0.86 ± 0.28 kcal/kg BW0.75 increase in total retained energy (P = 0.005). Using this partial efficiency coefficient, ME required for maintenance declined by 0.80 ± 0.11 kcal ME/kg BW0.75 for each additional kcal net energy retained/kg BW0.75 (P < 0.0001). There was no relationship between lactation-period retained energy and post-weaning VOL forage dry matter intake. The present study results contradict previous reports suggesting that maintenance requirements increase with increasing productivity.
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