The anatomical locations of proopiomelanocortin (POMC) and luteinizing hormone-releasing hormone (LHRH) neurons were examined in brain tissue from peripubertal female calves and from mature, luteal-phase cows. Biotin-avidin-peroxidase procedures were used for single- and double-labeled immunostaining. LHRH perikarya formed a loosely arranged continuum, extending posteriorly from the diagonal band of Broca, passing through the medial and lateral preoptic areas, and ending within the anterior hypothalamic area. LHRH fibers, apparently directed toward the median eminence, passed (1) posteroventrally in the periventricular area and through the arcuate nucleus, and (2) ventromedially lateral to the arcuate nucleus and medial to the supraoptic nucleus. POMC perikarya were located within and about the arcuate nucleus, some penetrating into the median eminence. Fibers from these POMC perikarya passed ventrally to terminate in the median eminence and to regions ventral to the mammillary nuclei. POMC fibers also projected dorsally and laterally from the arcuate nucleus to other hypothalamic regions as well as anteriorly along the third ventricular wall to the preoptic area, bed nucleus of stria terminalis, and stria terminalis. Less than 6% of the POMC or LHRH processes were in close anatomical apposition to LHRH perikarya and dendrites. Extensive intermingling of LHRH and POMC fibers occurred within zona externa of the median eminence.

Thirty-four mature Holstein cows were blocked into two groups on their 305-day, twice daily milked, mature equivalent milk production of the previous lactation; groups were assigned at random to a twice or thrice daily milking frequency. In addition, six pairs of paternal half-sisters and one pair of nonsibling heifers also were assigned to twice daily or thrice daily milking frequency. Half-sisters were assigned to milking frequency on alternate calvings, and the nonsibling pair was assigned at random. Milk production peaked at 6 wk lactation in mature cows in both treatments, at 7 wk for cows in first lactation milked twice daily, and at 9 wk for cows in first lactation milked thrice daily. Cows milked thrice daily reached higher peak milk production and were more persistent in milk production. Multiparous and first-lactation cows milked thrice daily produced 18.5 and 25.2% more milk than their counterparts milked twice daily, and after 15 wk heifers milked thrice daily were producing more milk per day than mature cows milked twice daily. The combined increased average production for cows and heifers milked thrice daily, 1299 kg, required only 92 kg more dry matter intake and resulted in an apparent preferential utilization of feed nutrients for milk production or higher rate of tissue catabolism in cows milked thrice daily. Milk composition was not influenced by milking frequency; total milk fat was 36 kg more for cows milked thrice daily. Reproductive performance measured as days to first estrus, days open, or services per conception also was not influenced by milking frequency.

Treatment with ACTH (100 i.u.) or hydrocortisone acetate (250 mg) twice daily for 12 days to increase cortisol concentrations blocked ovulation in all gilts. The preovulatory surge of LH was also blocked in the treated gilts. Oestrous cycle length and number of days in oestrus were similar for all treatments except that in one of the 2 experiments ACTH suppressed oestrus in 4 of the 5 gilts treated.

Hypothalamic growth hormone-releasing hormone (GHRH) and somatotropin release-inhibiting factor or somatostatin (SS) immunoreactive (ir) neurons were localized in pigs (n = 8) and cattle (n = 7) to identify neuroanatomical sites involved in the regulation of growth hormone secretion. Coronal and sagittal frozen sections (30–60 µm) of Zamboni’s fixed hypothalamic tissue, without prior colchicine treatment were incubated with GHRH or SS primary antisera for 48 h, then visualized by peroxidase-diaminobenzidine immunocytochemistry. Fusiform, bipolar SS-ir perikarya were located about the third ventricle in the periventricular nucleus, extending from rostral aspects of preoptic periventricular nucleus to a level approximate with caudal regions of the paraventricular nucleus. Rounded or fusiform, bipolar GHRH-ir perikarya were mostly located in ventrolateral portions of the arcuate nucleus in pigs and cattle, and within ventral aspects of the ventromedial nucleus in pigs but rarely in cattle. In both pigs and cattle, SS-ir and GHRH-ir fibers projected ventrally into the median eminence with dense and overlapping innervation of the external layer, especially dense in lateral regions. In pigs, but not as distinguishable in cattle, SS-ir fibers also densely innervated the ventromedial and arcuate hypothalamic nuclei. Double immunostained sections revealed close apposition of SS-ir fibers and varicosities with GHRH-ir perikarya in arcuate and ventromedial nuclei, and apposition of SS-ir and GHRH-ir varicosities in the median eminence.

Effects of fiber vs starch energy supplements on endogenous growth hormone (GH), insulin-like growth factor (IGF-1) and animal performance from weaning to breeding age were evaluated in 18, 9-mo-old beef heifers. Heifers had ad libitum access to wheat silage plus an average daily supplement intake of 1) 4.08 kg corn-soybean meal (SBM) (high energy-starch, HS), 2) 4.54 kg soyhulls (SH)-SBM (high energy-fiber, HF) or 3) 1.36 kg SH-SBM (low energy-fiber, LE). Serum samples were collected via jugular puncture every 10 d and were analyzed for IGF-1 by RIA. On d 45 and d 176, four heifers per treatment were fasted 18 h and serial blood samples collected via jugular cannulas every 15 min for 6.5 h. Arginine (.5 g/kg BW) was administered intravenously (ARG) to induce release of GH, and four additional samples of blood were collected. Samples were analyzed by RIA for GH. Mean fasted GH (6.4 +/- .4, 8.3 +/- .4 and 13.8 +/- .4 ng/ml for HS, HF and LE, respectively) varied with energy source and level (P less than .01). Mean GH following ARG was higher (P less than .01) in heifers receiving LE (46.2 +/- 4.7) than in those receiving HS and HF (23.5 +/- 4.4 and 24.1 +/- 4.6 ng/ml). Basal GH concentration and peak amplitude were higher (P less than .05) in LE than in HS and HF treatments. Diet did not influence number or frequency of GH peaks.(ABSTRACT TRUNCATED AT 250 WORDS)