Effects of induced hypothyroidism or hyperthyroidism on growth and reproductive performance of Brahman heifers

摘要: Prepubertal Brahman heifers (BW = 302 +/- 7.5 kg, body condition score [BCS] 5.4 .2, age 498 3.4 d: SEM) were used to study the effects of thyroid function on growth and reproduction. Seven controls (C). induced become hypothyroid by ingestion 4 mg/kg BW 6-n-propyl-2-thiouracil (PTU). hyperthyroid (T) daily s.c. injections triiodothyronine (T3, 1 mg/d). Treatments administered for 84 d followed an posttreatment period. Blood samples obtained twice weekly via tail venipuncture analysis T3, thyroxine, progesterone. The BW, BCS, rectal temperature (RT) recorded weekly. Estrus was monitored with aid a fertile bull equipped chin ball marker. Hyperthyroidism hypothyroidism successfully in T- PTU- treated heifers, respectively. During treatment period, PTU gained most BCS (72.4 kg; .93 .15 units), C intermediate (41.7 .43 T least (13.3 -.36 units; P < .05). RT also decreased (P .05) (-1.9 .2 degrees C) compared (-1.2 or (-.8 C). No exhibited estrus during (93.9 6.1 1.14 .13 (67.0 .86 +/-. 13 (22.2 -.14 reversal gains period corresponded periods transient hypo- hyperthyroidism Age at puberty pregnancy similar among all groups. lower (5.7 than (6.6 units). Induction resulted significant increases but these not sufficient dramatically affect reproductive performance heifers.