Identification of a siderophore utilization locus in nontypeable Haemophilus influenzae.

Background: Haemophilus influenzae has an absolute aerobic growth requirement for either heme, or iron in the presence of protoporphyrin IX. Both iron and heme in the mammalian host are strictly limited in their availability to invading microorganisms. Many bacterial species overcome iron limitation in their environment by the synthesis and secretion of small iron binding molecules termed siderophores, which bind iron and deliver it into the bacterial cell via specific siderophore receptor proteins on the bacterial cell surface.

Endocrine response of postpartum anestrous beef cows to GnRH or PMSG.

Forty-one postpartum anestrous Hereford cows, maintained under range conditions, were used to determine the influence of gonadotropin releasing hormone (GnRH) or pregnant mare serum gonadotropin (PMSG) on ovarian function. Anestrous cows were identified by estrous detection with sterile bulls and concentrations of progesterone in plasma obtained weekly. At 45+/-2 days postpartum, cows were allotted to the following treatments: (1) control (saline), (2) 100 microg GnRH, (3) 200 microg GnRH, (4) 200 microg GnRH in carboxymethyl cellulose (CMC), (5) 500 IU PMSG, (6) 1,000 IU PMSG or (7) 2,000 IU PMSG.

Serum luteinizing hormone and testosterone in bulls during exposure to elevated ambient temperature.

Eight mature Angus bulls were used to evaluate the effects of exposure to 34 C on concentrations of serum luteinizing hormone (LH) and testosterone before and after treatment with gonadotropin releasing hormone (GnRH). After a 3-week period of adjustment at 22 C, the bulls were randomly assigned to either a control (22 +/- 1 C) or a heat stress ( 34 +/- 1C) treatment for 15 days. Blood was sampled via jugular cannula at 30-min intervals for 12 hr on days -2, 6 and 15 of treatment.

Influence of 48 hour calf separation on milk production and calf growth in range cows.

Hereford cows and their calves were either left together or separated for a 48-hr period between 50 and 80 days postpartum. Milk production and calf weights were determined 1 and 2 weeks prior to and 1 and 3 weeks after calf separation. Daily milk production of separated cows (5.