Graduate Thesis Or Dissertation
 

Creep-feeding to stimulate metabolic imprinting in nursing beef heifers : impacts on heifer growth, reproductive, and physiological parameters

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  • The following experiment presented herein compared growth, physiological, and reproductive responses of beef heifers with (MI) or without (CON) access to a creep-feeder, as a manner to stimulate metabolic imprinting while nursing their dams. On d 0 of the experiment, 60 Angus × Hereford heifers were ranked by initial BW and age (140 ± 3 kg and 68 ± 3 d, respectively) as well as dam age and BCS, and assigned to pairs so all ranking criteria were similar between heifers within each pair. On d 1, pairs were randomly assigned to MI (n = 15) or CON (n = 15). From d 1 to 51, MI pairs and their dams were allocated to 15 drylot pens where heifers had ad libitum access to a corn-based supplement through a creep-feeder. The CON pairs and their dams were maintained in an adjacent single drylot pen. From d 52 to 111, cattle from both treatments were managed as a single group on a semiarid range pasture. On d 111, heifers were weaned and allocated to 2 pastures according to treatment, receiving hay and a corn-based concentrate until d 326. Full BW was recorded prior to (d -1 and 0) and at the end of the creep-feeding period (d 50 and 51), whereas shrunk BW was collected on d 112 and 326. On d 0, 51, 111, 187, 261, and 325, blood was collected and real-time ultrasonography for LM depth and backfat thickness assessment was performed. Blood was also collected every 10 d from d 113 to 323 for puberty evaluation via plasma progesterone concentrations. Liver and subcutaneous fat biopsies were performed on d 51, 111, 261, and 325. Average daily gain was greater (P < 0.01) for MI than CON from d 1 to 51, tended (P = 0.09) to be greater for CON than MI from d 112 to 326, whereas BW on d 326 was similar (P = 0.87) between treatments. On d 51, MI had greater (P ≤ 0.01) plasma IGF-I and glucose concentrations, as well as mRNA expression of hepatic pyruvate carboxylase and adipose fatty acid synthase than CON. On d 261 and 325, plasma insulin concentrations were greater (P ≤ 0.03) in CON than MI. Mean mRNA expression of hepatic IGF-I and adipose peroxisome proliferator-activated receptor gamma were greater (P ≤ 0.05) in MI than CON. Heifers assigned to MI attained puberty earlier (P = 0.04) during the experiment than CON, although age and BW at puberty were similar (P ≤ 0.74) between treatments. In conclusion, supplementing nursing heifers via creep-feeding for 50 d altered physiological and biochemical parameters suggestive of a metabolic imprinting effect, but did not impact heifer age or BW at puberty.
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