T. H. Elsasser

Relative to a short daily (24-h) photoperiod, exposure to a long daily photoperiod increases the milk yield of dairy cows. However, the endocrine basis for this phenomenon is unknown. The present study was designed to test the hypothesis that a long daily photoperiod is associated with increased circulating insulin-like growth factor (IGF)-I, a hormone that is galactopoietic in ruminants. Forty lactating cows were exposed to either a natural photoperiod (< or = 13 h of light/d) or to a long daily photoperiod (18 h of light and 6 h of darkness) between January and April 1995. Cows were fed for ad libitum intake a total mixed diet formulated to meet the nutritional demands of lactation. Milk yield and dry matter intake were quantitated each day, and blood samples were collected by coccygeal venipuncture every 14 d. Plasma was harvested and assayed for IGF-I. The long photoperiod increased milk yield relative to the natural photoperiod (36.1 +/ 0.6 vs. 33.9 +/ 0.6 kg/d); the increase became significant after 28 d of treatment and was maintained for the duration of the study. In addition, cows exposed to a long photoperiod had greater circulating concentrations of IGF-I than did cows exposed to the ambient natural photoperiod (60.1 +/ 2.0 vs. 52.6 +/ 2.0 ng/ml). Concentrations of IGF binding protein -2 and -3 in plasma did not differ between treatments. These results support the hypothesis that a long daily photoperiod increases circulating concentrations of IGF-I in lactating cows and reveal a possible endocrine mechanism for the galactopoietic response to a long daily photoperiod.

The purpose of this study was to determine whether soluble CD14 (sCD14) in milk was affected by stage of lactation, milk somatic cell count (SCC), presence of bacteria, or lipopolysaccharide (LPS)-induced inflammation. Milk samples from 100 lactating cows (396 functional quarters) were assayed for sCD14 in milk to determine effects of stage of lactation, SCC, and intramammary infection. The concentration of sCD14 was highest in transitional milk (0 to 4 d postpartum) and in milk with high SCC (> 750,000 cells/ml). Most of the infected quarters (> 80%) were infected by coagulase-negative staphylococci and yeast. No difference was found between noninfected and infected quarters. One quarter of six healthy lactating cows was challenged with 100 microg LPS in order to study the kinetics of sCD14 during an LPS-induced inflammation. Milk samples were collected at various intervals until 72 h after injection. Rectal temperature, milk tumor necrosis factor-alpha, and interleukin-8 increased immediately after challenge. The increase in sCD14 paralleled the increase in SCC, peaked at 12 h, and started to decline after 24 h. Serum leakage, as characterized by the level of bovine serum albumin in milk, peaked at 4 h and then gradually decreased. All parameters remained at basal levels in control quarters throughout the study. In vitro experiments indicated that neutrophils released sCD14 in response to LPS in a dose-dependent manner. The results indicate that the concentration of sCD14 was significantly increased in milk after LPS challenge. The increase was not likely due to serum leakage. Instead, infiltrated neutrophils might be the main source of increased sCD14 in milk during inflammation.

The objective of this study was to determine whether neuropeptide Y (NPY) and recombinant human interleukin-1 receptor antagonist (IL-1ra) would: first, increase food intake; secondly, decrease concentrations of GH; thirdly, reduce GHRH-induced release of GH; and fourthly, reduce changes to concentrations of IGF-I in plasma during experimental endotoxemia in sheep. Six treatments were given to six castrated male sheep in a 6x6 Latin square treatment order. Osmotic mini-pumps were implanted at 0 h and a jugular vein was cannulated. Each sheep was continuously infused with saline (0.9%) or lipopolysaccharide (LPS) (20 micrograms/kg per 24 h, s.c.) at 10 microliters/h for 72 h via the osmotic mini-pumps. Blood samples (3 ml) were collected at 15-min intervals from 24 to 33 h. At 26 h, one of three treatments (artificial cerebrospinal fluid, NPY or IL-1ra) was injected i.c.v. within 30 s (0.3 microgram/kg), then infused i.c.v. from 26 to 33 h (600 microliters/h) at 0.3 microgram/kg per h. GHRH was injected i.v. (0.075 microgram/kg) at 32 h after which blood samples were collected at 5, 10, 15, 30, 45 and 60 min. Feed intake was reduced up to 50% for 48 h in LPS-treated compared with non-LPS-treated sheep. NPY restored feed intake in LPS-treated sheep and induced hyperphagia in non-LPS-treated sheep from 24 to 48 h. In contrast, IL-1ra did not affect appetite. Injection of NPY increased concentrations of GH from 26 to 27 h, while IL-1ra had no effect. Infusion of NPY suppressed GHRH-induced release of GH. However, no treatment altered pulse secretion parameters of GH. Concentrations of IGF-I were 20% higher at 72 h in LPS-treated sheep given NPY than in sheep treated with LPS alone, and this may reflect increased appetite from 24 to 48 h. We concluded that reduced appetite during endotoxemia is due to down-regulation of an NPY-mediated mechanism. Furthermore, NPY stimulates release of GH in healthy sheep, does not reduce pulse secretion parameters of GH, but does suppress GHRH-induced release of GH in endotoxic sheep. Therefore, NPY may be an important neurotransmitter linking appetite with regulation of GH during endotoxemic and healthy states in sheep.

Twelve Holsteins in first lactation were used to investigate the relationship between energy balance and effects of bovine somatotropin (bST) on thyroid hormone metabolism and cytokine concentrations in serum. Six cows were fed for ad libitum intake and six cows were feed restricted to induce negative energy balance during two treatment periods of 6 d. During treatment periods, cows were administered vehicle or 40 mg of bST/d according to a crossover design. Between treatment periods was a 15-d recovery period, during which all cows were fed ad libitum. Cows that were fed ad libitum remained in positive energy balance during control and bST treatments, whereas cows that were fed for restricted intake were in negative energy balance during control and bST treatment periods. In both dietary groups, bST decreased energy balance. Milk production and the fat percentage of milk increased during bST treatment in both dietary groups. Fat-corrected milk yield was increased 13% by bST treatment. Serum concentrations of IGF-I did not differ between dietary groups but were greater during bST than control periods. Serum thyroxine concentration was decreased by bST treatment. Serum triiodothyronine and reverse-triiodothyronine were not altered by hormone treatment, but circulating concentrations of thyroid hormones were apparently reduced by dietary restriction. Neither hepatic nor mammary thyroxine 5'-deiodinase was affected by bST treatment. Plasma concentration of tumor necrosis factor-alpha, a potential regulator of thyroxine 5'-deiodinase, was not affected by bST treatment. Short-term treatment with bST did not influence thyroid hormone metabolism in lactating cows in positive or negative energy balance.

The ionophoretic antibiotics, monensin and lasalocid, bind numerous mono- and divalent cations, primarily in dimeric complexes that facilitate the passage of metal ions through hydrophobic lipid membranes. Ionophores vary in their affinity for metal ions. Similarly, transport rates of the resulting complexes depend in part upon the affinity constant of the drug ion-binding interaction, and in part, upon local environmental and physical factors. The normal uptake, transport and use of divalent minerals in the animal body is accomplished via numerous endogenous "ionophore" transport routes. We studied the possibility that exogenous ionophores such as monensin and lasalocid might alter normal intestinal uptake of divalent metal ions. In the first experiment, chickens were fed either monensin or lasalocid; 45Ca, 59Fe or 64Cu was individually instilled into an exteriorized isolated loop of the duodenum and absorption allowed for 1 h. Radioactivity was measured in the duodenal mucosa. Compared with controls, 59Fe and 64Cu were lower in tissues from animals given monensin, but higher in animals given lasalocid. 45Ca was lowered in gut mucosa by both drugs. In the second experiment, liver Cu, Fe and Zn were measured in chickens and sheep fed diets containing monensin or lasalocid. Small differences in basal tissue levels of ions were observed in both sheep and chickens fed the ionophoretic drugs. Drenching sheep with 100 mg X animal-1 X d-1 Cu2+ as CuSO4 resulted in enhanced Cu accumulation in all animals, with the largest accumulation measured in those fed monensin. These preliminary data suggest that adding monensin and lasalocid to diets may change the bioavailability, gut uptake and tissue deposition of divalent minerals.(ABSTRACT TRUNCATED AT 250 WORDS)