Abstract
The objective of this research project was to investigate the effects of nutrition and stress related factors on basic physiological parameters. Studies were designed and conducted independently to evaluate (1) the effects of monensin on postpartum interval to first estrus (PPI) and serum luteinizng hormone (LH) response to 0, 1, 2 or 4 mg estradiol-17(beta) (E2) and (2) the effects of epinephrine (E), norepinephrine (NE) and(or) gonadotropin releasing hormone (GnRH) on serum LH. In the first trial, 48 Brangus cows were randomly stratified into a 2 x 4 factorial design with the main effects of dietary monensin (0 or 200 mg/hd daily) and E2 dose (0, 1, 2 or 4 mg/hd). Average PPI was shortened (P < .01) from 86 to 65 days by monensin treatment (M; 200 mg/hd daily). The proportion of cows with PPI less than 85 days was higher (P < .05) in the M group. Interval to initiation of the LH response (ILH) and interval to peak LH response (ILHP) were extended (P < .05) in M cows receiving 4 mg E2.</p> Forty prepuberal Simmental X Brahman-Hereford heifers were randomly assigned to groups. Treatments consisted of (I) 100 (mu)g GnRH at 0 min (n = 8); (II) 50 mg NE at -15 min and 0 min (n = 8); (III) 50 mg E at -15 min and 0 min (n = 8); (IV) 100 (mu)g GnRH at 0 min plus 50 mg NE at -15 min and 0 min (n = 8); and (V) 100 (mu)g GnRH at 0 min plus 50 mg E at -15 min and 0 min (n = 8). Initial LH response to GnRH was delayed (P < .05) by concomitant treatment with NE (Trt. IV) or E (Trt. V). These data indicate that monensin may be useful in aleviating the problem of extended PPI in beef cows. Additionally, the potential exists for stress intervening in reproductive function via the catecholamines based upon the detrimental effects observed here.
Hardin, Daniel Ra (1982). An investigation of some basic factors associated with the influence of nutrition and stress on reproductive efficiency of the bovine. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -516100.