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1255
WS Winter grazing or confinement feeding heifer development strategies differ in energetics as measured by 24 hour heart rate and activity
ABSTRACT: A heifer’s ability to thrive is partially due to traits including behavioral/metabolic adaption and genetic background. Type of weaning and development program implemented creates an environment replacement heifers must adapt to flourish. This study was designed to determine if heifers developed in confinement or grazing native range use different adaption and coping processes by measuring activity such as distance traveled and percent resting time in 24 hr along with resting heart rate and average heart rate per day. Spring-born, crossbred heifers were stratified to 1 of 2 treatments at weaning (start of Period 1): (1) fence-line weaning on native range (NR) with self-fed salt-mineral protein supplement (n = 118) and after weaning received a hand fed daily energy supplement or a self fed protein supplement, or (2) weaned into a dry lot (DL) and fed a corn silage diet formulated to gain 0.68 kg/d (n = 53). Ad libitum grass hay was made available in mid-December due to snow coverage resulting in range forage inaccessibility. Heifer BW were taken every 28 d from initiation of weaning. Each month (except February and June) a cohort of 7 heifers from each treatment were fitted with equine heart rate monitors (Polar Equine RS800CX) and QSTARZ CR-Q1100P GPS tracking recorder. Data were recorded for 48 hr. On April 9, 2014 (Period 2) the two supplement groups grazing NR and DL heifers were combined into a common pasture. Heifers receiving DL had greater (P < 0.01) BW throughout the entire study. Resting heart rate was influenced (P < 0.01) by an interaction of period and weaning/development management. The rankings of resting heart rate were reversed from period 1 to period 2. Resting heart rate was also shown to influence BW. Resting heart rate relationship with BW was negative suggesting that lower resting heart rate is related greater BW. The analysis suggests that for every 2.2 decline in resting HR there is an additional 0.45 kg of BW. This study indicates that resting heart is negatively related to BW implying that animals with lower resting heart rate may have a production advantage.
Keywords: beef heifers, heart rate, heifer development