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Effect of dexamethasone and confinement stress on estrous cycle length in beef heifers
THERIOGENOLOGY
EFFECT
OF D E X A M E T H A S O N E A N D C O N F I N E M E N T STRESS ESTROUS CYCLE L E N G T H IN BEEF HEIFERS
S.H.
ON
Pool*, R.A. Godke and R.H. I n g r a h a m D e p a r t m e n t of Animal S c i e n c e and School of V e t e r i n a r y M e d i c i n e L o u i s i a n a State U n i v e r s i t y Baton Rouge, LA 70803
Thirty-two pasture reared c r o s s b r e d h e i f e r s (263 to 497 kg) w e r e equally and r a n d o m l y a l l o t t e d to four t r e a t m e n t groups as follows: (A) f i e l d - c o n t r o l (FLD-C), (B) fielddexamethasone (FLD-DEX), (C) p e n - c o n t r o l (PEN-C), and (D) pendexamethasone (PEN-DEX). Heifers w e r e a s s i g n e d to t r e a t m e n t groups on day 16 of the estrous cycle (estrus = day 0) and placed in either 0.8 ha field lots or 44 m 2 c o v e r e d pens (four/pen). DEX heifers in (B) and (D) r e c e i v e d 20 mg (IM) of A z i u m ~ on cycle d a y 16 followed by 30 mg (IM) on cycle days 17 through 20 (1730 hr) while control heifers in (A) and (C) r e c e i v e d equal v o l u m e s of 0.9% saline on c o r r e s p o n d ing days. Blood samples w e r e c o l l e c t e d daily (1725 hr) from all heifers via jugular v e n i p u n c t u r e f r o m day 16 t h r o u g h day 7 of the s u b s e q u e n t cycle and o v a r i a n structures p a l p a t e d at 48-hr intervals. Plasma p r o g e s t e r o n e (PRG) c o n c e n t r a t i o n s w e r e m o n i t o r e d by RIA. M e a n cycle lengths (• for FLD-C and PEN-C heifers (21.1• and 21.6• days) w e r e shorter (P<.001) than that for F L D - D E X and P E N - D E X heifers (40.7• and 29.0• days). Those in the P E N - D E X group had a cycle length that was shorter than that of the F L D - D E X group(p<.04). M e a n interval from d e c r e a s e d PRG levels (
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JANUARY 1979 VOL. 11 NO. 1
EFFECT
OF D E X A M E T H A S O N E A N D C O N F I N E M E N T STRESS ESTROUS CYCLE L E N G T H IN BEEF HEIFERS
S.H.
ON
Pool*, R.A. Godke and R.H. I n g r a h a m D e p a r t m e n t of Animal S c i e n c e and School of V e t e r i n a r y M e d i c i n e L o u i s i a n a State U n i v e r s i t y Baton Rouge, LA 70803
Thirty-two pasture reared c r o s s b r e d h e i f e r s (263 to 497 kg) w e r e equally and r a n d o m l y a l l o t t e d to four t r e a t m e n t groups as follows: (A) f i e l d - c o n t r o l (FLD-C), (B) fielddexamethasone (FLD-DEX), (C) p e n - c o n t r o l (PEN-C), and (D) pendexamethasone (PEN-DEX). Heifers w e r e a s s i g n e d to t r e a t m e n t groups on day 16 of the estrous cycle (estrus = day 0) and placed in either 0.8 ha field lots or 44 m 2 c o v e r e d pens (four/pen). DEX heifers in (B) and (D) r e c e i v e d 20 mg (IM) of A z i u m ~ on cycle d a y 16 followed by 30 mg (IM) on cycle days 17 through 20 (1730 hr) while control heifers in (A) and (C) r e c e i v e d equal v o l u m e s of 0.9% saline on c o r r e s p o n d ing days. Blood samples w e r e c o l l e c t e d daily (1725 hr) from all heifers via jugular v e n i p u n c t u r e f r o m day 16 t h r o u g h day 7 of the s u b s e q u e n t cycle and o v a r i a n structures p a l p a t e d at 48-hr intervals. Plasma p r o g e s t e r o n e (PRG) c o n c e n t r a t i o n s w e r e m o n i t o r e d by RIA. M e a n cycle lengths (• for FLD-C and PEN-C heifers (21.1• and 21.6• days) w e r e shorter (P<.001) than that for F L D - D E X and P E N - D E X heifers (40.7• and 29.0• days). Those in the P E N - D E X group had a cycle length that was shorter than that of the F L D - D E X group(p<.04). M e a n interval from d e c r e a s e d PRG levels (
106
JANUARY 1979 VOL. 11 NO. 1