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Long-term progesterone influence on feed efficiency, body composition, non-esterified fatty acids and metabolic hormones in mature Rambouillet ewes
The objectives of this study were to evaluate the effects of long-term progesterone (P4) treatment on changes in feed efficiency, BW, body composition, NEFA and metabolic hormones in mature Rambouillet ewes. Thirty, multiparous, 5- and 6-yr-old Rambouillet ewes were stratified by age and metabolic BW and assigned randomly to receive long-term P4 administration using a sequential replacement of either a P4-containing controlled internal drug release device (CIDR) or non-P4-containing CIDR (CIDRX). Initially, ewes were synchronized for estrus using a 7 d CIDR and PGF2a protocol. All ewes exhibited estrus within 72 h after PGF2α. Twelve d after estrus (d = 0), each ewe received either a CIDR (n = 15) or a CIDRX (n = 15). Every 14 d thereafter, the CIDR or CIDRX was removed from each ewe and replaced with a new CIDR or CIDRX for 126 d. Jugular venous blood samples were collected from each ewe at the time of CIDR or CIDRX replacement. Serum samples were assayed for P4, NEFA, insulin (INS), triiodothyronine (T3) and thyroxine (T4). Individual feed intake was recorded using GrowSafe units, beginning at d 0 following a 3-wk adaptation period. Ewes were fed a mixed grass hay diet ad libitum that met the nutrient requirements for maintenance. BW for each ewe was collected every 14 d when CIDR or CIDRX were replaced. Back fat (BF) and rib-eye area (REA) were measured for each ewe every 28 d using ultrasonography. BW, residual feed intake, BF and REA did not differ (P > 0.10) between CIDR- and CIDRX-treated ewes. Calculated estimates of body composition did not differ (P > 0.10) between CIDR- and CIDRX-treated ewes. NEFA, T3 and T4 concentrations did not differ (P > 0.10) between CIDR- and CIDRX-treated ewes. However, INS concentrations did differ (P < 0.05) between CIDR- and CIDRX-treated ewes. In conclusion, long-term P4 treatment did not appear to alter feed efficiency and partitioning of nutrients. However, maintaining P4 may alter the homeostatic relationship between INS and carbohydrate metabolism in ewes.
Keywords:
carcass traits, ewe, metabolism, progesterone, residual feed intake