No abstract

Three experiments were conducted to evaluate negative feedback action of estradiol-17~ (E2) on luteinizing hormone (LH) release in ovariectomized heifers and to determine the response at different ages. In the first experiment, iv injections of .2 or 2.0/~g E2/kg body weight (BW) reduced serum concentrations of LH by arresting episodic mode of secretion. Results of a second experiment indicated a positive relationship (P<.05) between dose of E2 and duration of LH suppression. Mean duration of suppression with the high (2.0/~g E2/kg BW), medium (2 #g E2/kg BW) and low (.1 /~g E2/kg BW) doses was 6.5, 4.5 and 3.5 h, respectively. Neither magnitude nor rate of LH suppression was related (P>.25) to dose in the first two experiments. Results of third experiment showed that both magnitude and duration of suppression were directly proportional to dose of E2 (0, .1 and 1.0 #g E:/kg BW). The response lasted longer in heifers 4 mo stitutes of Health, for donating luteinizing hormone used for iodination, luteinizing hormone antisera and luteinizing hormone used for standards, and the Upjohn Company for donating estradiol-tyrosine methyl ester. We also thank Dr. R. H. Stauffacher for assistance with surgery; Mr. E. Hoch, Mr. P. Bringie, Mr. J. Kane and Ms. J. Hillstrom for their excellent technical assistance, and Ms. S. Kading for typing this manuscript. 3 Trainee of the Endocrinology-Reproductive Physiology Program. 4 Dept. of Meat and Anita. Sci. and Wisconsin Regional Primate Research Center.of age than in heifers 8 and 12 mo of age. E2 was also more effective in reducing LH pulses in heifers 4 mo of age than in heifers 8 and 12 mo of age. These results show that E2 inhibits LH release by influencing pulsatile mode of secretion, and that the threshold to negative feedback increases as heifers approach puberty. (

The effects of somatotropin (STH) and energy intake on serum concentrations of glucose (GLU), insulin (INS), nonesterified fatty acids (NEFA), urea nitrogen (UN) and insulin-like growth factor-I (IGF-I) were determined in 40 Angus heifers. At 7 mo (208 +/- 8 d) of age heifers were assigned to four treatment groups: 1) vehicle (V) + high energy (HE; 2.68 Mcal ME/kg DM), 2) recombinant DNA-derived STH (20.6 mg/d; s.c.) + HE, 3) V + low energy (LE; 2.22 Mcal ME/kg DM) or 4) STH + LE. Animals remained on treatments until an average of 15.5 mo of age. Blood samples were taken every 30 min for 4 h at 9, 11, 13 and 15 mo of age to determine circulating concentrations of metabolites and hormones. Serum IGF-I was increased (P less than .01) by STH injections, but this effect appeared to diminish with age (STH x age; P less than .01). Energy intake did not influence IGF-I levels. Somatotropin increased (P less than .01) serum GLU in heifers fed the HE diet but only tended (P = .08) to increase GLU in those fed the LE diet (STH x energy; P = .05). Although STH increased (P less than .01) serum INS in both energy groups, the response in heifers fed the HE diet was greater (P less than .02) than that in heifers fed the LE diet (STH x energy; P less than .05). Heifers fed LE had higher (P less than .01) concentrations of NEFA than heifers fed HE.(ABSTRACT TRUNCATED AT 250 WORDS)

Women have not had the authority to define the conditions of animal agriculture or to develop strategies for addressing its problems because the field of animal science has been and remains dominated by men. Therefore, criteria for assessing the professional performance of animal scientists reflect the views of men and the experiences of masculinity. Recent attempts to improve the retention rates of women in the animal science profession have focused on socializing female protégés to the norms and expectations of the discipline. This approach is based on traditional liberal beliefs that all humans are essentially alike and that embodiment and(or) social location are irrelevant in understanding the world. Such socialization assumes that problems of gender inequity can be solved by providing opportunities for women to succeed in the existing system, with its existing norms. This approach ignores the possibility that the structure of women's lives and the normative commitments arising from women's experiences may be quite different from those of men. Professional reward structures that favor the life experiences and perspectives of men and ignore those of women coerce women into adopting values that may be incompatible with their identities. This not only devalues their perspectives and contributions, it forces them to commit self-betrayal. This is both harmful and antithetical to the idea of an empirically relevant science that blends multiple perspectives and understands diverse values. Substantive diversity in the animal science community requires standards that reflect and accommodate the pluralism in which we live.

Experiments were conducted to determine the role of estrogens on endogenous PGF2 alpha secretion and luteolysis following injection of cloprostenol in heifers. In Exp. 1, eight luteal-phase heifers were used to evaluate tamoxifen (T) as an estrogen antagonist. Heifers received T (35 mg i.v.) or ethanol:saline vehicle (ES) every 4 h for 44 h. All received cloprostenol (500 micrograms i.m.) immediately after the start of T or ES, and received estradiol-17 beta (500 micrograms i.m.) 12 h later. Each ES heifer had a surge of luteinizing hormone (LH) within 48 h of estradiol injection, whereas T-treated heifers did not. Estrus was observed in three ES-treated heifers, but not in T-treated heifers. In Exp. 2, 10 heifers received T (35 mg i.v.) or ES every 4 h for 64 h beginning on d 15 postestrus. Cloprostenol (500 micrograms i.m.) was injected 16 h after the start of treatment. Concentrations of LH were similar (P greater than .05) in both groups. In ES heifers, concentrations of 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) increased; in T-treated heifers, PGFM remained at pre-cloprostenol levels. Luteolysis was induced in all heifers. Progesterone (P4) decreased to less than or equal to 1 ng/ml at similar (P greater than .05) rates in ES-treated and T-treated heifers. Mean concentration of P4 288 h post-cloprostenol was greater (P less than .05) in ES-treated than in T-treated heifers. Three ES-treated heifers, but no T-treated heifers, were in standing estrus. We conclude that T effectively antagonizes estrogen in cattle.(ABSTRACT TRUNCATED AT 250 WORDS)