Effects of nutritional level and biological type on gonadotropin-releasing hormone-induced luteinizing hormone release and plasma progesterone, estrone and estradiol concentrations in pre- and post-partum beef heifers.
Forty-six beef heifers (16 to 23 mo) of two biological types (small = Red Poll-sired, large = Charolais-sired) were individually fed from d 90 of gestation through parturition to evaluate the effects of nutritional restriction on plasma LH and steroid hormone concentrations. Heifers were allotted to one of two nutritional treatments to achieve a BW reduction (loss, fed at 1% of BW/d) or to maintain initial BW (maintenance, fed 1.5% of BW/d) to parturition. Gonadotropin-releasing hormone (100 micrograms) was injected i.m. three times during gestation (d 130; d 200; d 270) and twice after parturition (d 1 to 14; d 23 to 36). Blood samples were collected at 20-min intervals after GnRH for 4 h. Maternal BW change from d 90 to parturition differed (P less than .01) between loss and maintenance heifers. Mean plasma progesterone concentrations were greater (P less than .05) at d 130 and 270 of gestation in small than in large heifers and were greater (P less than .01) at d 23 to 36 postpartum in maintenance than in loss heifers. Mean concentrations of estrone and estradiol were greater (P less than .05) in large than in small heifers at d 200 of gestation. Mean plasma LH concentrations following GnRH injection were greater (P less than .01) in loss than in maintenance heifers at 200 and 270 d of gestation. Metabolizable and retained energy were related inversely to LH release during mid and late gestation.(ABSTRACT TRUNCATED AT 250 WORDS)
Killen
J H
JH
Texas A&M University, College Station.
Forrest
D W
DW
Byers
F M
FM
Schelling
G T
GT
Baker
J F
JF
D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001835:Body Weight; D002417:Cattle / Q000378:metabolism*; D004032:Diet; D004958:Estradiol / Q000097:blood; D004970:Estrone / Q000097:blood; D005260:Female; D007743:Labor, Obstetric / Q000378:metabolism; D016018:Least-Squares Analysis; D007986:Luteinizing Hormone / Q000097:blood*; D010906:Pituitary Hormone-Releasing Hormones / Q000494:pharmacology; D049590:Postpartum Period / Q000378:metabolism*; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000378:metabolism*; D011374:Progesterone / Q000097:blood; D012044:Regression Analysis
D010906:Pituitary Hormone-Releasing Hormones; D004970:Estrone; D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone