Effect of lasalocid on the GnRH-induced LH and testosterone release during puberal development in the Brahman bull.
To determine the effect of lasalocid on endocrine patterns associated with puberty, 12 half-sib prepuberal Brahman bulls were allotted by age and weight (174 to 256 d of age; 141 to 243 kg) to control or lasalocid treatments. Bulls in the control treatment were fed a 4:1 corn:cottonseed meal concentrate plus Coastal bermudagrass hay to which the bulls were given ad libitum access. The lasalocid treatment was identical except for the addition of 200 mg of lasalocid.animal-1.d-1. Blood samples were collected frequently before and after GnRH (200 micrograms, i.m.) on d 7, at 28-d intervals thereafter, and within 14 d after puberty (defined as 50 x 10(6) sperm cells with 10% motility). By d 7, bulls fed lasalocid released more LH (P less than .05), but not testosterone (T;P greater than .10), in response to GnRH than controls. At the time that the first sperm cells were observed in an electroejaculate (FS), lasalocid-fed bulls released more (P less than .05) LH and T than controls. At puberty, there was no difference (P greater than .10) between treatments in amount of T released, although lasalocid-fed bulls released more LH (P less than .05). Before puberty, concentrations of LH were positively correlated with concentrations of T in samples collected 1 and 2 h later. Both groups of bulls exhibited a linear increase in T response with advancing age (P less than .005). Release of LH decreased with age in the control bulls (P less than .10) but was unaffected by age in lasalocid-fed bulls. Both groups showed a decreased (P less than .001) LH:T response ratio with advancing age. Results of this study with bulls confirm previous reports in heifers of the enhancing effect of an ionophore on reproductive function.
Rutter
L M
LM
Texas A&M University Agricultural Research and Extension Center, Overton 75684.
Neuendorff
D A
DA
Randel
R D
RD
Peterson
L A
LA
D000818:Animals; D002417:Cattle / Q000502:physiology*; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism; D007832:Lasalocid / Q000097:blood / Q000494:pharmacology*; D016018:Least-Squares Analysis; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D008297:Male; D012044:Regression Analysis; D012741:Sexual Maturation / Q000187:drug effects*; D013739:Testosterone / Q000378:metabolism*
D007987:Gonadotropin-Releasing Hormone; D013739:Testosterone; D007986:Luteinizing Hormone; D007832:Lasalocid