Effect of photoperiod before and during first gestation on milk production and prolactin concentration in dairy heifers

Holstein heifers (n = 45) were subjected to treatments according to a 2 × 2 factorial design where the main effects were the photoperiod treatments during the second isometric (ISO, 52-61 wk of age) and the second allometric (ALLO, 62 wk of age to 8 wk before calving) periods of mammary gland development. During the ISO period, heifers were subjected to either a short-day photoperiod (SDP; 8 h light, 16 h dark; n = 22) or a long-day photoperiod (LDP; 16 h light, 8 h dark; n = 23). During the ALLO period, the photoperiodic treatments were either maintained (SDP:SDP, n = 11; LDP:LDP, n = 11) or switched (SDP:LDP, n = 11; LDP:SDP, n = 12). The treatments ended 8 wk before calving. All animals were then subjected to about 16 h of light per day. Serum prolactin (PRL) concentration during the ISO period was greater in heifers exposed to LDP than in those exposed to SDP. For the first 20 wk of the ALLO period, heifers exposed to LDP had greater serum concentration of PRL than those exposed to SDP. On the other hand, previous exposure to LDP during the ISO period reduced the concentration of PRL compared with those exposed to SDP during that period. During the second 20 wk of the ALLO period, PRL concentration remained greater in the serum of heifers then exposed to LDP than SDP, but serum PRL was greater in heifers exposed to LDP during the ISO period. During the last weeks before calving, when all animals were exposed to LDP, previous exposure to LDP during the ALLO period reduced serum PRL. Early-lactation milk (wk 1-5) and energy-corrected milk (wk 2-6) production were higher in the heifers exposed to SDP than in those exposed to LDP during ALLO. Photoperiod had no effect on milk production after that period. In conclusion, the results do not support to the hypothesis that photoperiod affects mammary gland development during the second allometric phase. However, they confirm that a short-day photoperiod in late gestation enhances milk production in the following lactation in primiparous heifers. Using serum PRL as an indicator of the photoperiodic response, we can conclude that responsiveness to the photoperiodic signal is still conditioned by a previous photoperiod several months after it ends.

Carcass Composition and Resistance to Fasting in Neonatal Piglets Born of Sows Immunized against Somatostatin and/or Receiving Growth Hormone-Releasing Factor Injections during Gestation

Thirty-eight gestating sows were either immunized against somatostatin (SRIF) and/or injected with growth hormone-releasing factor (GRF). Treatment effects on carcass composition and resistance of newborn piglets to a 60-hour fast were investigated. Protein content of carcasses at birth was increased in piglets of sows receiving GRF or immunized against SRIF, however, when sows received both treatments there was a reduction in carcass protein content (p = 0.01). Other carcass components were unaltered by treatments, and none of the treatments affected metabolic or endocrine profiles of piglets at birth. Concentrations of GH, IGF-I (p less than 0.01), glucagon and cortisol (p less than 0.05) increased linearly with duration of fast, whereas glucose values decreased. Resistance to fasting was unaltered in piglets from any treatment thereby suggesting that exogenous GRF and/or SRIF immunization of sows during gestation are unlikely to improve survival of newborn piglets.

Utilization of lactoferrin to fight antibiotic-resistant mammary gland pathogens

The widespread use of antibiotics has lead to the increased presence of pathogens that are less susceptible to their antibacterial effect. Lactoferrin (Lf) is naturally produced by the mammary gland. Lactoferrin is the main whey protein in human milk and is also present in cow's milk but at a much lower concentration than in human milk. This protein appears to have many biological functions, including antibacterial and antiinflammatory activities. The best-known effect of Lf is to bind iron that is essential for bacterial growth. However, the cationic nature of this protein also appears to be important for the antimicrobial activity of this protein. Lactoferrin has a weak antibacterial effect when used alone, but interestingly, Lf appears much more effective when used at low concentration in combination with several antibiotics. The most striking observation is that Lf increases the inhibitory activity of penicillin up to 4-fold in most penicillin-susceptible Staphylococcus aureus strains, whereas this increase was 4- to 16-fold in penicillin-resistant strains. Indeed, Lf reduces beta-lactamase activity in S. aureus strains producing this enzyme. Transcription of beta-lactamase gene is dramatically repressed in the presence of Lf. We evaluated the efficacy of intramammary treatments containing penicillin G or bovine Lf (bLf), or both, to cure chronic mastitis caused by a clinical isolate of S. aureus highly resistant to beta-lactam antibiotics. In a first trial, mastitis was induced in lactating cows by injecting a low dose of S. aureus through the teat canal of all quarters. Bacterial cure rate was null for control quarters, 11.1% for bLf, 9.1% for penicillin, and 45.5% for the combination of bLf and penicillin. A second trial was undertaken to investigate the effect of an extended therapy on chronic mastitis acquired in a previous lactation. Quarters were treated with 100,000 IU of penicillin G with or without 250 mg of bLf for 7 d. Bacterial cure rate was greater for the bLf + penicillin combination (33.3%) compared with penicillin alone (12.5%). In conclusion, bLf added to penicillin is an effective combination for the treatment of stable S. aureus infections resistant to beta-lactam antibiotics.

Efficacy of a Lactoferrin-Penicillin Combination to Treat β-Lactam-Resistant Staphylococcus aureus Mastitis

The efficacy of intramammary (IM) treatments containing penicillin G (PG) alone or a combination of PG and bovine lactoferrin (bLF) was evaluated using a model of experimentally induced chronic bovine mastitis caused by a clinical isolate of Staphylococcus aureus highly resistant to beta-lactam antibiotics. First, we confirmed that this strain could cause mastitis and infection could not be cured with PG alone. In a second trial, chronic mastitis was induced in 19 late-lactating cows by injecting a low dose of Staph. aureus through the teat canal of all quarters. After 15 d, cows with stable infections in their 4 quarters had their mammary quarters randomly assigned, within cow, to 1 of 4 IM treatments as follows: 1) citrate buffer, 2) 100,000 IU of PG, (3) 1 g of bLF, or 4) 1 g of bLF + 100,000 IU of PG. Treatments were repeated twice a day for 5 d. A third trial was undertaken to investigate the effect of an extended therapy on chronic mastitis acquired in a previous lactation. One month before dry-off, 20 gravid cows regrouped by dates of calving were infected in their 4 quarters. Once infections were established, cows were dried off abruptly. After calving, aseptic milk samples were collected separately from all quarters for 4 wk to monitor infection. Mammary quarters from enrolled cows were then randomly assigned, within cow, to 1 of 2 treatments as follows: 1) 100,000 IU of PG or 2) 250 mg of bLF + 100,000 IU of PG. Treatments were administered IM twice a day for 7 d. For all trials, milk samples were taken to monitor bacterial concentration and somatic cell count. Bacteriological cure rate was determined using milk samples taken 3 and 4 wk after initiation of treatments. For the second trial, cure rate was null for control quarters, 11.1% for bLF, 9.1% for PG, and 45.5% for the bLF + PG combination. For cows infected in their previous lactation, cure rate was higher for the bLF + PG combination (33.3%) compared with PG alone (12.5%). In conclusion, bLF added to PG is an effective combination (i.e., 3- to 5-times higher cure rate) for the treatment of stable Staph. aureu infections highly resistant to beta-lactam antibiotics.

Effect of Stage of Lactation and Parity on Mammary Gland Cell Renewal

Milk production is a function of the number and activity of mammary epithelial cells, regardless of stage of lactation. Milk yield is generally higher in multiparous cows than in primiparous cows, but persistency is usually greater in the latter group. We compared several measures related to metabolic activity, apoptosis, and endocrine control of mammary cell growth in 8 primiparous and 9 multiparous cows throughout lactation. Mammary gland biopsies were taken in early [10 d in milk (DIM)], peak (50 DIM), and late (250 DIM) lactation to evaluate gene expression and determine DNA and fatty acid synthase (FAS) content. Milk samples taken the day before the biopsies were used to detect protease activities and to determine stanniocalcin-1 (STC) concentrations. Blood samples served to measure insulin-like growth factor-1, prolactin, and STC concentrations. Milk yield was higher in multiparous cows than in primiparous cows at the 10 DIM (32.8 +/- 1.3 and 25.2 +/- 0.8 kg/d) and 50 DIM (38.0 +/- 1.2 and 29.8 +/- 1.1 kg/d), but it was the same for both groups at 250 DIM (23.9 +/- 1.5 and 23.8 +/- 1.1 kg/d). Except for stearoyl-coenzyme A desaturase, expression of genes related to milk synthesis was not affected by stage of lactation. However, gene expression of acetyl-coenzyme A carboxylase, beta-casein, and FAS was lower in early lactation in primiparous cows. Expression of both proapoptotic bax and antiapoptotic bcl-2 genes was higher in primiparous cows, whereas the bax-to-bcl-2 ratio was not changed. Mammary DNA concentration was higher in multiparous cows, as was the amount of FAS protein in early lactation. Two bands of protease activity were found in milk samples, and one of the bands had an apparent molecular weight similar to gelatinase A and was dependent on the stage of lactation. Serum insulin-like growth factor-1 increased with day of lactation and was higher in primiparous cows. Serum prolactin decreased in late lactation, but peak values were observed in early lactation for primiparous cows and peak lactation for multiparous cows. Milk STC content increased with advancing lactation. The results are consistent with a lower degree of differentiation and a greater capacity for cell renewal in the mammary gland of primiparous cows.

Impacts of dietary protein level and feed restriction during prepuberty on mammogenesis in gilts

The possible roles of dietary protein level and feed restriction in regulating mammary development of prepubertal gilts were investigated. Cross-bred gilts were fed a commercial diet until 90 d of age and then divided into four nutritional regimens based on two pelleted diets (as-fed basis): a high-protein diet (HP = 13.8 MJ of ME, 1.0% total lysine, 18.7% CP) and a low-protein diet (LP = 13.8 MJ of ME, 0.7% total lysine, 14.4% CP). Nutritional regimens were as follows: 1) HP ad libitum until slaughter (n = 22, T1); 2) HP ad libitum until 150 d of age followed by LP until slaughter (n = 20, T2); 3) LP ad libitum until slaughter (n = 21, T3); and 4) HP with a 20% feed restriction until slaughter (n = 19, T4). Gilts were weighed, their backfat thickness was measured, and jugular blood samples were obtained on d 90, 150, and at slaughter to determine concentrations of prolactin, IGF-I, leptin, and glucose. Gilts were slaughtered 8+/-1 d after their first or second estrus (202.7+/-14.5 d of age). Mammary glands were excised, parenchymal and extraparenchymal tissues were dissected, and composition of parenchymal tissue (protein, fat, DM, DNA, protein/DNA) was determined. The T4 gilts weighed less (P < 0.01) and had less backfat (P < 0.01) than did gilts on other treatments on d 150 and at slaughter. Treatments had no significant effects on prolactin, IGF-I, or glucose concentrations, but there was a treatment x day interaction (P < 0.01) for leptin, with concentrations being lower at slaughter in restricted-fed (T4) vs. LP (T3) gilts (P < 0.05). There was less extraparenchymal mammary tissue (P < 0.01) in T4 gilts than in gilts from the other groups and a tendency (P = 0.13) for the amount of parenchymal tissue to be lower in T4 gilts. In conclusion, a lower lysine intake during prepuberty did not hinder mammary development of gilts, but a 20% feed restriction decreased mass of parenchymal and extraparenchymal tissues. The effect of feed restriction on extraparenchymal tissue is most likely associated with the lower fat deposition.

Blood melatonin and prolactin concentrations in dairy cows exposed to 60 Hz electric and magnetic fields during 8 h photoperiods

Two experiments were conducted to test the hypothesis that electric and magnetic field (EMF) exposure may result in endocrine responses similar to those observed in animals exposed to long days. In the first experiment, 16 lactating, pregnant Holstein cows were assigned to two replicates according to a crossover design with treatment switchback. All animals were confined to wooden metabolic cages and maintained under short day photoperiods (8 h light/16 h dark). Treated animals were exposed to a vertical electric field of 10 kV/m and a horizontal magnetic field of 30 microT (EMF) for 16 h/day for 4 weeks. In a second, similar experiment, 16 nonlactating, nonpregnant Holstein cows subjected to short days were exposed to EMF, using a similar protocol, for periods corresponding to the duration of one estrous cycle. In the first experiment, circulating MLT concentrations during the light period showed a small numerical decrease during EMF exposure (P < .05). Least-square means for the 8 h light period were 9.9 versus 12.4 pg/ml, SE = 1.3. Melatonin concentrations during the dark period were not affected by the treatment. A similar trend was observed in the second experiment, where MLT concentrations during the light period tended to be lower (8.8 pg/ml vs. 16.3 pg/ml, P < .06) in the EMF exposed group, and no effects were observed during the dark period. Plasma prolactin (PRL) was increased in the EMF exposed group (16.6 vs. 12.7 ng/ml, P < .02) in the first experiment. In the second experiment, the overall PRL concentrations found were lower, and the mean plasma PRL concentration was not affected by treatment. These experiments provide evidence that EMF exposure may modify the response of dairy cows to photoperiod.

Lack of effect of 10 kV/m 60 Hz electric field exposure on pregnant dairy heifer hormones

Sixteen pregnant Holstein heifers weighing 521 +/- 46 kg, at 3.3 +/- 0.7 months of gestation and 2.2 +/- 2.0 months of age were confined to wooden metabolism cages and were exposed to a vertical electric field (EF) of 10.0 +/- 0.4 kV/m and an artificial light cycle of 12 h light-12 h dark. The heifers were divided into two replicates of eight each. Each replicate was divided into two groups of four animals each, one group becoming the non-exposed and the second, the EF exposed group. The exposed group were housed in metabolism cages in an area where EF were generated, and the non-exposed group, in metabolism cages located in the adjacent area where the EF was less than 2% of that present in the exposed area. The test animals were subject to the different treatments for 4 weeks continuously. After 4 weeks, the animals switched treatment, the exposed group becoming the non-exposed group and vice-versa. Then the treatment continued for 4 more weeks. Catheters were inserted into the jugular vein of the animals, and blood samples were collected on twice a week to estimate the serum concentration of progesterone (P4), melatonin (MLT), prolactin (PRL), and insulin-like growth factor-1 (IGF-1). Feed consumption was measured daily and feed samples were collected twice a week. The results indicated that exposure of dairy cattle to EF similar to those encountered directly underneath a 735 kV high tension electrical power line carrying a maximum load of current, cannot be associated with any variation in the experimental variables mentioned above. An exception to this, is the variation in MLT, which was associated with the EF exposure. Due to the inconsistency of the MLT response in the different replicates, caution should be exercised in the interpretation of this phenomenon.

Specific window of prolactin inhibition in late gestation decreases mammary parenchymal tissue development in gilts

Prolactin is required from d 70 to 110 of gestation for normal mammary development of gilts. The goal of the present study was to determine the effect of inhibiting prolactin with bromocriptine during specific time windows during the second half of gestation on mammary gland development in gilts. Crossbred primigravid gilts were assigned as controls (n = 12) or received 10 mg of bromocriptine orally three times daily from d 50 to 69 (BR50, n = 12), d 70 to 89 (BR70, n = 12), or d 90 to 109 (BR90, n = 12) of gestation. Jugular blood samples were collected on d 50, 70, 90, and 109 of gestation and assayed for prolactin and estradiol. Gilts were slaughtered on d 109 of gestation and fetuses were counted and weighed. One row of mammary glands was used for dissection of parenchymal and extraparenchymal tissues, and for biochemical analyses. Tissue from the other row was used for measures of prolactin receptor number and affinity. Concentrations of prolactin were decreased markedly (P < 0.001) at the end of each bromocriptine treatment period compared with controls, but there was no overall treatment effect (P > 0.1) on estradiol concentrations. Extraparenchymal tissue weight of the mammary glands was unaffected by treatments (P > 0.1), but weight of parenchymal tissue, total DNA, and total RNA were lower (P < 0.01) in BR90 than control gilts. The percentage of DM in parenchymal tissue was unaffected by treatments (P > 0.1), but percentage of fat was higher and percentage of protein lower (P < 0.01) in BR90 gilts compared with controls. Cell size, as estimated by the protein:DNA ratio, also was lower (P < 0.01) in the BR90 group. Number and affinity of prolactin receptors in parenchymal tissue were not significantly altered by treatments. In conclusion, there is a specific time period in the second half of gestation, from 90 to 109 d, during which prolactin is essential for normal mammary parenchymal tissue development.

Effect of feeding prepubertal heifers with a high oil diet on mammary development and milk production

The objective of this study was to evaluate the effect of feeding prepubertal heifers a diet containing a high level of polyunsaturated fatty acids on mammary development and milk production. A total of 116 Holstein heifers were either fed a conventionally formulated concentrate or a high oil (HO) concentrate, using the same formulation but including 20% soybean oil, from birth to 6 mo of age. After 6 mo of age, all heifers were managed identically. Mammary gland development was evaluated on heifers slaughtered at 4 mo (n = 10) and 12 mo (n = 30) of age. Other heifers were bred when they reached 15 mo of age and milk production and feed intake were recorded every day from wk 4 to 18 of lactation. Feeding the high oil concentrate increased the concentration of linoleic acid in blood plasma (176%) and mammary fat pad (78%) at 4 mo of age and mammary fat pad (93%) at 12 mo of age. At 4 mo of age, mammary development was similar in both treatments. At 12 mo of age, total, parenchyma, and stroma weights of the mammary gland were not affected by treatments. However, lipid content was lower and concentration of DNA was higher in the parenchyma of heifers fed the high oil diet. Nevertheless, total parenchymal DNA and dry fat free tissue content did not reach statistical significance despite the fact that they were, respectively, 15 and 21% higher in HO heifers. Milk production and composition was not affected by treatments. In conclusion, feeding prepubertal heifers with a high oil concentrate slightly improved the mammary development but effects were too small to be translated into better lactating performances.

Responses of the estrous cycle in dairy cows exposed to electric and magnetic fields (60 Hz) during 8-h photoperiods

To study the effects of exposure to extremely low frequency (ELF) electric and magnetic fields (EMF) on the estrous cycle of dairy cows under short-day photoperiod, 16 non-lactating, non-pregnant Holstein cows were exposed to a vertical electric field of 10 kV/m and a horizontal magnetic field of 30 microT for 16 h per day in a cross-over design consisting of two sequences. Each sequence included three periods, and each period corresponded to the duration of one estrous cycle. All animals were maintained under short photoperiod (8 h light/16 h dark) during the trial. Exposure to EMF had an impact on the duration of a complete estrous cycle (P<0.01) and on the duration of the luteal phase (P<0.01). The mean duration of one cycle was 19.5+/-0.4 for the control and 21.3+/-0.4 days for the exposed animals, respectively. The mean duration of the luteal phase was 15.4+/-0.4 days for the control and 17.2+/-0.4 days for the exposed group. The total area under the progesterone (P(4)) curve, the amplitude of the curve or the slope of the P(4) rise at the onset of the luteal phase were not affected by EMF exposure. Results indicate that exposure to EMF may increase the duration of the estrous cycle.

Management of photoperiod in the dairy herd for improved production and health

Environmental influences on lactation efficiency are frequently associated with reductions in milk output. Heat stress, for example, leads to depressed feed intake and, subsequently, losses in production. Conversely, cold stress may limit nutrients available for milk synthesis. Fortunately, one environmental factor, photoperiod, can exert a positive effect on dairy performance when managed properly. Long days have consistently been shown to improve milk yield during established lactation. In addition, photoperiod management can be used to improve heifer growth and maximize accretion of lean tissue, including mammary parenchyma. There is, however, evidence of refractoriness to long day stimulation. Recent work has focused on the dry period as a time when photoperiod manipulation can influence subsequent milk production. In contrast to lactating cows, multiparous cows benefit from exposure to short days when the dry period is followed by long days or natural photoperiod after calving. Similarly, primiparous animals also respond positively to short days late in pregnancy when subsequently exposed to long days during lactation. Furthermore, emerging evidence suggests that short days positively influence immune function in cattle. Mechanistically, it appears that prolactin has a causal relationship with the observed dairy performance effects during the dry period and on immune function, via altered sensitivity to prolactin through differential expression of prolactin receptor in multiple tissues. The objectives of this paper include a review of fundamental aspects of photoperiod physiology, integration of applied and basic research findings, and development of management recommendations for the entire life cycle of the dairy cow to optimize performance.

Effect of electric and magnetic fields (60 Hz) on production, and levels of growth hormone and insulin-like growth factor 1, in lactating, pregnant cows subjected to short days

Electric and magnetic fields (EMF) are generated by the transmission of electricity through high tension lines traversing rural areas. Previous studies showed increased dry matter intake (DMI) and fat corrected milk in dairy cows exposed to EMF. Because EMF exposure has been shown to suppress pineal release of melatonin in some species, it was hypothesized that EMF effects resemble those of exposure to long days. Previous studies have shown that DMI and milk production increase in dairy cattle in response to long day photoperiods, and this has been observed in association with increased circulating insulin-like growth factor 1 (IGF-1), but not growth hormone (GH). The hypothesis that EMF act by modifying the response to photoperiod was tested by subjecting dairy cows to controlled EMF exposure while keeping them under short-day conditions. Sixteen lactating, pregnant Holstein cows were exposed to a vertical electric field of 10 kV/m and a horizontal magnetic field of 30 microT in a crossover design with treatment switchback. Two groups of eight cows each were exposed to EMF for 16 h/d in either oftwo sequences. Each sequence consisted of three consecutive 28-d periods. All animals were maintained under short day conditions (8 h light, 16 h dark) during the trial. DMI and plasma IGF-1 were increased (P < 0.01) during EMF exposure (17.03 vs.16.04 kg/d, SE = 0.4; 137 +/- 6 ng/ml vs 126 +/- 6, respectively). The mean GH concentration was not affected, but a treatment x hour interaction was detected, with GH lower for the EMF exposed animals during the first 16 h of the sampling period, and higher for the last 8 h. Overall, the yield of milk or its components was not affected by EMF exposure, but milk yield was significantly higher for the exposed animals during wk 4 of treatment.

Variations in mammary protein metabolism during the natural filling of the udder with milk over a 12-h period between two milkings: leucine kinetics

To define the temporal variations of whole body and mammary leucine kinetics over a 12-h period between two milkings, we used two groups of four Holstein cows, one in their second and the other in their third or fourth lactation. Cows were infused with L-[1-13C]leucine during the 12-h interval between two milkings. Blood was sampled every 30 min during that period from arterial and mammary sources. Timeafter milking did not affect whole body irreversible loss rate of leucine but affected whole body leucine oxidation, which broadly followed variations in arterial plasma leucine concentration. Similarly, mammary leucine irreversible loss rate and leucine used for protein synthesis were not affected by time after milking. Leucine oxidation by the mammary gland was, however, affected by time after milking. It increased by 15% from the first 2-h period to the following 4-h period and then decreased by 13% over the following 2-h period. A 21% increase in leucine oxidation was observed from 8 to 10 h after milking, and then it decreased by 26% over the last 2-h period. Protein degradation expressed as percentage of mammary leucine flux followed a similar temporal pattern. Leucine used for protein synthesis by the mammary gland was unaltered over time after milking, suggesting that the increased availability of leucine resulting from mammary protein breakdown would increase intracellular concentrations of leucine, which would have favored its catabolism. Overall, these results confirm the high metabolic activity of the mammary gland, as protein synthesis by the mammary gland averaged 43% of whole body protein synthesis.

Response of Staphylococcus aureus isolates from bovine mastitis to exogenous iron sources

Staphylococcus aureus can survive in conditions of extremely low iron concentration. The ability of S. aureus to use two exogenous hydroxamate types of siderophores (desferrioxamine and ferrichrome) and four iron-containing proteins found in cattle (hemin, hemoglobin, ferritin, and lactoferrin) were tested on 16 reference and clinical isolates. For all strains tested, ferrichrome and desferrioxamine showed strong growth-promoting activities in a disk diffusion assay and in liquid medium. The heme proteins hemin and hemoglobin were also found to support growth in culture media lacking other iron sources, while lactoferrin failed to do so. On media containing the iron chelator dipyridyl, ferritin induced a growth inhibition effect that was further enhanced in the presence of lactoferrin in seven of the 13 tested strains. Staphylococcus aureus was able to bind hemin and the level of binding activity was not increased after growth in iron-rich or -poor media. Dot-blot competition tests showed that biotin-labeled lactoferrin binds to S. aureus, and this binding can be inhibited by unlabeled lactoferrin. Expression of lactoferrin-binding activity was independent of the level of iron in the medium and the iron saturation status of lactoferrin. For each strain tested, ligand blots showed lactoferrin-binding proteins of molecular weights ranging from 32 to 92 kDa. Possible functions of these lactoferrin-binding proteins could not be related to iron acquisition mechanism in S. aureus.

Variations in mammary metabolism during the natural filling of the udder with milk over a 12-h period between two milkings

Two groups of four Holstein cows, one in their second and the other in their third or fourth lactation, were used to study temporal variations of mammary metabolism over a 12-h period between two milkings. Blood samples were collected every 30 min from an artery and a mammary vein during a 12-h interval between two milkings. Isoleucine, leucine, lysine, methionine, and phenylalanine mammary net fluxes varied or tended to change over time after milking with a similar pattern between whole blood and plasma. For these amino acids, whole blood and plasma net fluxes reached their maximum over the first 8 h after milking. Simultaneously, respiratory quotients decreased linearly and varied from 2.31 to 2.01 during the first 8 h of the period, suggesting active mammary lipogenesis. From 8 to 12 h after milking, mammary amino acid net fluxes decreased, while mammary oxygen uptake tended to increase with a concomitant decrease in the respiratory quotient reaching 1.84 to 1.40. These findings suggest that, beginning 8 h after milking, mammary uptake of amino acids starts to decrease and catabolic processes appear promoted; this phenomenon could help to explain the increase in milk production reported in the literature with increased milking frequency.

Delineating potential control mechanisms of mammary protein synthesis utilizing atropine

Amino acids (AA) and/or somatotropin (ST) were infused into a jugular vein of lactating cows receiving atropine to determine the effect on milk protein secretion. Atropine decreased milk protein yield by 35%. Plasma alpha-amino nitrogen, which was decreased by 31% due to atropine, was restored to control levels upon AA infusion. Plasma ST concentration was not affected by atropine and, upon ST infusion, increased by 236% in treated animals. Amino acids, ST, or the combination of the two were unable to return milk protein to control levels in atropine-treated animals. Plasma insulin concentration decreased by 37% in atropine-treated animals and was not significantly different for cows receiving atropine as well as ST, AA, or both ST and AA. Similarly, glucagon decreased by 36% in atropine-treated animals but was partially restored in cows receiving AA. Overall, the insulin-to-glucagon ratio was not significantly affected by treatment. Plasma glucose concentration was not affected by treatment. These data lend support to the importance of the insulin-to-glucagon ratio in terms of whole-body metabolism, with the exception of the mammary glands, which are glucagon-insensitive and, therefore, sensitive to the observed decrease in circulating insulin concentration.

Effect of lactoferrin in combination with penicillin on the morphology and the physiology of Staphylococcus aureus isolated from bovine mastitis

The objective of the present study was to evaluate the therapeutic potential of bovine lactoferrin or lactoferricin in combination with penicillin G against Staphylococcus aureus. Minimal inhibitory concentrations of lactoferrin, lactoferricin, penicillin, and combinations of lactoferrin or lactoferricin with penicillin were determined for 15 S. aureus strains including several strains resistant to beta-lactam antibiotics. The fractional inhibitory concentration index indicated a synergistic effect between lactoferrin and penicillin. Combination of lactoferrin with penicillin increased the inhibitory activity of penicillin by two- to fourfold and reduced the growth rate in S. aureus strains tested, whereas the increase in the inhibitory activity of lactoferrin by penicillin was 16- to 64-fold. The addition of iron to the medium containing a combination of penicillin and lactoferrin had no effect on growth inhibition. Electron microscopy revealed that concentration below the minimal inhibitory concentrations of penicillin induced important ultrastructure alterations, which were further enhanced by the presence of lactoferrin. When S. aureus cells were grown in the presence of a combination of penicillin and lactoferrin, changes in the protein profile of the bacteria, including the disappearance of several protein bands due to the presence of lactoferrin, were observed. These data suggest that bovine lactoferrin or lactoferricin in combination with beta-lactam antibiotics can increase the antibacterial activity of these antibiotics against S. aureus resistant to antibiotics.

Effects of insulin, recombinant bovine somatotropin, and their interaction on insulin-like growth factor-I secretion and milk protein production in dairy cows

This trial was designed to test the effects of insulin, recombinant bovine somatotropin (rbST), and their interaction on milk protein and selected blood parameters in dairy cows. Eight Holstein cows (86 +/- 10 d in milk) were divided in two groups and used in two replicates of a Latin square design with four animals, four periods, and four treatments: 1) intravenous infusion of saline, 2) infusion of saline and subcutaneous administration of 40 mg of rbST per day, 3) intravenous infusion of 12 mg of insulin per day coupled with glucose infusion, and 4) rbST administration combined with insulin and glucose infusion. The glucose infusion rate was adjusted to maintain euglycemia. Each experimental period lasted 14 d: treatments were administered during the first 6 d, and no treatment was administered during the following 8-d resting phase. The average daily amount of glucose infusion needed to avoid hypoglycemia was 2.8 kg/cow when only insulin was infused as opposed to 2.2 kg/cow when both insulin and rbST were administered, indicating that either rbST causes a peripheral resistance to insulin or rbST increased liver gluconeogenesis or both. Data from the last 3 d of infusion were analyzed by using the SAS system for mixed models. Percent protein of milk tended to be lower (2.84 vs. 2.79%) and milk urea content was lower (16.6 vs. 14.8 mg/dl) during rbST administration, regardless of insulin infusion. Insulin infusion increased percent protein (2.78 vs. 2.85%) and percent casein (2.36 vs. 2.46%) and decreased milk urea content (17.1 vs. 14.3 mg/dl) regardless of rbST administration. For milk yield, protein yield, casein yield, lactose percent, and lactose yield, there were significant interactions between insulin and rbST administration. For example, casein yield averaged 1.17, 1.12, 1.20, and 1.28 kg/d for saline, insulin, rbST, and insulin combined with rbST, respectively. Similarly, there was a significant interaction between insulin and rbST on IGF-I levels, which were 122.5, 181.3, 342.3, and 492.2 ng/ml for saline, insulin, rbST, and insulin combined with rbST, respectively. In conclusion, these results clearly demonstrated that insulin interacts with bST in early lactation to improve milk protein synthesis and yield in dairy cows. These effects are probably mediated through a combination of bST nutrient mobilization, bST-induced gluconeogenesis, bST-induced insulin peripheral resistance, and bST/insulin synergism on insulin-like growth factor-I secretion and on mammary epithelial tissue.

Effect of a differential allelic expression of kappa-casein gene on ethanol stability of bovine milk

Two main genetic variants of κ-casein, A and B, are found in Holstein cows. A positive association between the κ-casein B genetic variant and milk characteristics of economic importance have been reported (reviews: Creamer & Harris, 1997; Ng-Kwai-Hang, 1998). This can be explained, at least in part, by a higher κ-casein content of the casein in milk of cows having the κ-casein B genetic variant (Donnelly et al. 1984; Law, 1993). We have recently reported the presence of a differential allele-specific expression of the κ-casein gene in Holstein cows by comparing the content of allele-A and allele-B specific mRNA in the mammocytes of lactating cows genotyped κ-casein AB (Robitaille & Petitclerc, 2000). For some cows, the A- and B-specific κ-casein gene alleles were expressed in a similar manner. These cows are named HH here to indicate that they were homozygous for κ-casein gene expression. The other group of cows, cows HL, presented a differential allele specific expression of the κ-casein gene allele B which was overexpressed compared to allele A. The genetic polymorphism governing this differential allele-specific expression of the κ-casein gene is likely to affect the physico-chemical properties of casein micelles and, hence, the technological properties of milk, as κ-casein is considered to be the stabilizing component of the milk micelles. The objective of the study was to evaluate the effect of this expression polymorphism of the κ-casein gene on milk ethanol stability.

Relationships between energy balance and health traits of dairy cattle in early lactation

The objective of the study was to calculate phenotypic relationships between energy balance in early lactation and health and reproduction in that lactation. Data were 26,701 daily records of dry matter intake and milk production, periodic measures of milk composition and body weight, and all health and reproductive information from 140 multiparous Holstein cows. Daily energy balance was calculated by multiplying feed intake by the concentration of energy of the ration and subtracting the amount of energy required for maintenance (based on parity and body weight) and for milk production (based on yield and concentrations of fat, protein, and lactose). Six measures of energy balance were defined: mean daily energy balance during the first 20, 50, and 100 d of lactation; minimum daily energy balance; days in negative energy balance; and total energy deficit. Measures of health were the numbers of occurrences of each of the following during lactation: all udder problems, mastitis, all locomotive problems, laminitis, digestive problems, and reproductive problems. Reproductive traits were the number of days to first observed estrus and number of inseminations. Several significant relationships between energy balance and health were observed. Increased digestive and locomotive problems were associated with longer and more extreme periods of negative energy balance.

External pudic venous reflux into the mammary vein in lactating dairy cows

A representative blood sample from the mammary vein depends on the functional integrity of the valves in the external pudic vein (EPV). To determine if the EPV valves maintain blood flow into the inguinal direction during the second and subsequent lactations, we used eight lactating cows catheterized in the EPV, the lateral branch of the cranial mammary vein (MV), and the external pudic artery (EPA). The averaged daily milk yields were 25.0 +/- 1.8 kg in cows in second lactation and 31.5 +/- 2.9 kg in older cows. The relative time taken by a pulse dose of p-amino hippuric acid (PAH) injected into the EPV, to reach the EPA and the MV, was measured in a first trial. In a second trial, we assessed the extent of alteration of the mammary PAH blood concentration with blood originating from other tissues using a continuous infusion of PAH into the EPA simultaneously with blocking or not any EPV backflux. From the first experiment, the PAH injected into the EPV appeared first in the EPA and then in the MV in cows in second lactation, suggesting that blood flow was towards the inguinal region. But in a third-lactation cow, the order of appearance was reversed. In parallel, the occlusion trial demonstrated that the concentration of PAH in the MV was diluted by 14 to 39% with blood draining nonmammary tissues only in cows in third or fourth lactation. This resulting reversed flow from the EPV towards the MV would have a detrimental impact on conclusions of mammary gland metabolism studies conducted with cows in their third lactation or higher.

Inhibition of prolactin in the last trimester of gestation decreases mammary gland development in gilts

Prolactin is required for mammary development in various species but its possible role for mammogenesis in pigs is not known. The goal of the present study was therefore to determine the effect of prolactin inhibition by bromocriptine during the last third of gestation on mammary gland development in gilts. Twenty-eight primigravid gilts were assigned as controls (n = 15) or received 10 mg of bromocriptine orally thrice daily (n = 13) from d 70 to 110 of gestation. Jugular blood samples were collected on d 70 of gestation and every 8 d thereafter and were assayed for prolactin, IGF-I, estradiol, and progesterone. Gilts were slaughtered on d 110 of gestation and fetuses were counted and weighed. One row of mammary glands was used for dissection of parenchymal and extraparenchymal tissues and for determination of DNA, RNA, dry matter, protein, and fat contents. Tissue from the other row was used for measures of prolactin receptor number and affinity. Concentrations of prolactin were drastically reduced throughout the bromocriptine treatment period (P < .001), whereas there was no overall treatment effect on progesterone and IGF-I levels (P > .10). Total weight and extraparenchymal tissue weight of the mammary glands were unaffected by treatment (P > or = .1), but weight of parenchymal tissue, total DNA, and total RNA decreased (P < .01) with bromocriptine treatment. Percentages of fat and dry matter in parenchymal tissue increased with bromocriptine treatment (P < .01) and the percentage of protein decreased (P < .01). Number of prolactin receptors in parenchymal tissue decreased with bromocriptine treatment (P < .001) and receptor affinity increased (P < .001). Average fetal weight was lower in gilts receiving bromocriptine than in control gilts (P = .05), but fetal number did not differ (P > .1). These results clearly demonstrate that prolactin is essential for normal mammary gland development and can affect fetal growth during the last third of gestation in gilts.

Expression polymorphism of kappa-casein gene in Holstein cows

Several studies have reported associations between κ-casein (κ-CN) genetic variants A and B and milk composition and properties (for review, see Ng-Kwai- Hang, 1998). For instance, genetic variant κ-CN B was associated with higher protein, casein and κ-CN contents. The objective of the present study was to demonstrate a differential expression of κ-CN genetic variants A and B at the mRNA level in mammary epithelial cells during lactation.

Effects of electromagnetic fields on photophasic circulating melatonin levels in American kestrels

Birds reproduce within electromagnetic fields (EMFs) from transmission lines. Melatonin influences physiologic and behavioral processes that are critical to survival, and melatonin has been equivocally suppressed by EMFs in mammalian species. We examined whether EMFs affect photophasic plasma melatonin in reproducing adult and fledgling American kestrels (Falco sparverius), and whether melatonin was correlated with body mass to explain previously reported results. Captive kestrel pairs were bred under control or EMF conditions for one (short-term) or two (long-term) breeding seasons. EMF exposure had an overall effect on plasma melatonin in male kestrels, with plasma levels suppressed at 42 days and elevated at 70 days of EMF exposure. The similarity in melatonin levels between EMF males at 42 days and controls at 70 days suggests a seasonal phase-shift of the melatonin profile caused by EMF exposure. Melatonin was also suppressed in long-term fledglings, but not in short-term fledglings or adult females. Melatonin levels in adult males were higher than in adult females, possibly explaining the sexually dimorphic response to EMFs. Melatonin and body mass were not associated in American kestrels. It is likely that the results are relevant to wild raptors nesting within EMFs.

Testes-specific transgene expression in insulin-like growth factor-I transgenic mice

Insulin-like growth factor-I (IGF-I) is a low molecular weight peptide that mediates the cell proliferating actions of growth hormone. Evidence exists indicating that IGF-I is produced by various cell types and this growth factor has been implicated in a variety of reproductive processes. To investigate the effect of IGF-I over-expression on reproductive systems, we generated three independent lines of transgenic mice harbouring a human IGF-I cDNA (hIGF-I) under the control of a Cytomegalovirus immediate early (CMV) promoter. The CMV promoter was used in an attempt to direct expression of IGF-I into a variety of tissues both reproductive and non-reproductive. Yet expression of the foreign hIGF-I gene, determined by Northern blot, was found to occur only in the testicular tissues of the male mice, apparently due to methylation of the transgene in all the tissues tested except the testes, which demonstrate transgene hypomethylation. Evaluation of the transgene expression during testicular development revealed that expression begins between 10 and 15 days of development, coinciding with the appearance of the zygotene and pachytene primary spermatocytes during early spermatogenesis, therefore indicating germ line expression of the transgene. Extensive study of the CMV-hIGF-I transgenic lines of mice has revealed that the effects of the transgene expression do not extend beyond the testicular tissues. No significant differences (P > 0.05) in the IGF-I serum levels, growth rates, or testicular histology have been observed between transgenic and non-transgenic male siblings. The ability of transgenic males to produce offspring also appears unaffected. Evaluation of the IGF binding protein (IGFBP) levels in the testicular tissues of CMV-hIGF-I transgenic mice by Western ligand blot revealed an increase in the concentration of testicular proteins with molecular weights corresponding to IGFBP-2 and IGFBP-3. These results suggest that the testicular over-expression of IGF-I induces increased IGFBP localization in this tissue. Inhibition of IGF activity by the IGFBPs would explain the lack of a dramatic physiological effect in the CMV-hIGF-I transgenic mice, despite the presence of elevated testicular IGF-I. The observation that testis specific IGF-I overexpression induces localization of IGFBPs in this tissue confirms the existence of a well regulated testicular IGF system and supports the convention that this growth factor plays an important role in testicular function.

Administering exogenous porcine prolactin to lactating sows: milk yield, mammary gland composition, and endocrine and behavioral responses

Third-parity sows received s.c. injections of sterile water (CTL, n = 12) or 15 mg of recombinant porcine prolactin (pPRL, n = 12) at 0730, 1530, and 2330 from d 2 to 23 of lactation. Litters were standardized to 11 or 12 pigs and were weighed weekly until weaning (d 24). On d 22 of lactation, milk production was estimated, and a milk sample was obtained the next day. Jugular blood samples were collected from sows on d 2, 7, 14, and 21 of lactation. Sows were slaughtered and mammary glands collected at d 24. Injections of pPRL doubled the serum concentrations of prolactin (P < .001) on d 7, 14, and 21 of lactation and decreased IGF-I concentrations on d 14 (P = .07) and 21 (P < .01). Weight, backfat, and milk yield of sows and mean pig weights were not affected by pPRL (P > . 1), yet the mean duration of intervals between nursings was reduced by 4.2 min (P = .06) in pPRL litters (45.9 vs 41.7 min). Dry matter and fat percentages in milk were lower in pPRL sows (P < .01). Weights of parenchymal and extraparenchymal tissues were not altered by pPRL treatment (P > .1). Number of prolactin receptors in parenchymal tissue as well as receptor affinity were similar in both groups (P > .1). Results indicate that virtually all prolactin receptors were saturated in CTL sows. This is probably the reason why additional exogenous prolactin had negligible effects.

Plane of nutrition and folic acid supplementation between birth and four months of age on mammary development of dairy heifers

Forty-seven dairy heifers of approximately 10 d of age were assigned randomly to a 2 × 2 factorial design to study the effects of folic acid supplementation (0 vs. 40 mg) administered weekly i.m. and levels of feed intake after weaning on mammary development. Folic acid treatment started immediately and all heifers were weaned 5 wk later. Heifers were then either fed ad libitum grass hay and concentrates or restricted to a body weight gain of approximately 700 g d−1 until slaughter at 4 mo of age. Average daily gain was affected by feed intake level after weaning (615 vs. 954 g d−1P < 0.01); however, folic acid supplementation increased weight gain only during the 5-wk period following weaning (P < 0.05). Heifers fed ad libitum were 33% heavier before slaughter (P < 0.001) but there was no effect due to folic acid supplementation (P > 0.05). There was no effect of treatments on serum prolactin and growth hormone concentrations (P > 0.05); overall, prolactin increased and growth hormone decreased over the 16-wk sampling period. However, serum IGF-1 concentrations were significantly higher in heifers fed ad libitum following weaning as compared with the feed-restricted animals (P < 0.001); overall, IGF-1 concentrations increased linearly between weeks 2 and 16 (P < 0.001). Plane of nutrition did not have any effect (P > 0.05) on the total volume of parenchymal tissue in the mammary gland (61.6 vs. 63.6 cm3); however, ad libitum feeding increased significantly (P < 0.001) the volume of extraparenchymal tissue in the gland (262.0 vs. 1067.6 cm3). After adjusting data for the difference in body weight at slaughter, the amount of parenchymal tissue was smaller in animals fed ad libitum (P < 0.05); this adjustment did not change the effect of plane of nutrition on mammary extraparenchymal tissue. In conclusion, a fast rate of gain after weaning up to 4 mo of age induced a large accumulation of mammary fat, but did not negatively affect the total amount of parenchymal tissue in the mammary gland of dairy heifers. Key words: Plane of nutrition, folic acid, mammary gland, IGF-1

Mammary gland development of sows injected with growth hormone-releasing factor during gestation and(or) lactation

Twenty-four gilts received s.c. injections of saline or growth hormone-releasing factor (GRF) in late gestation and(or) lactation. Sows were sacrificed on day 30 of lactation and functional mammary glands were excised for chemical analyses. Weight of parenchymal (P = 0.004) and extra-parenchymal tissues (P = 0.002) were decreased with GRF injections during lactation. Parenchymal mass per milligram of DNA also decreased (P = 0.025) with GRF in lactation while parenchymal DNA concentration increased (P = 0.03). Exogenous GRF given to sows during lactation therefore decreased total parenchymal mass, increased cell density and decreased mammary cell size. Key words: Sow, mammary gland, growth hormone-releasing factor

Evolution of insulin-like growth factor-1, prostaglandin E2, and mitogenic activity of bovine mammary primary lymph during the dry period and lactogenesis

Four pregnant cows near the end of lactation were fitted with a catheter in a lymph duct afferent to the supramammary lymph node. Cows were dried off 3 d after surgery, and samples of lymph were collected daily from the day of surgery until 4 d postpartum. Samples of blood and mammary secretions were taken before and after drying off and at parturition. Concentrations of most metabolites were lower in lymph than in serum. Concentrations of IGF-I and prostaglandin E2 were not affected at drying off but decreased and increased, respectively, at parturition. All IGF-binding proteins that were present in serum were also present in lymph fluid, but the binding activity was lower. Mitogenic activities of lymph samples taken at various physiological stages were determined on mammary epithelial (MAC-T) and fibroblast cell lines. Lymph was mitogenic, but mitogenic activity was not related to physiological stages. The correlation was high between mitogenic activity of lymph on MAC-T cells and the content of prostaglandin E2 in lymph. Supplementation of lymph with additional prostaglandin E2 increased mitogenic activity, and neutralization of lymph by antibodies reduced mitogenic activity. Basal medium conditioned by the epithelial cell line contained 100 to 250 pg/ml of immunoassayable prostaglandin E2.

The effect of matrix attached regions (MAR) and specialized chromatin structure (SCS) on the expression of gene constructs in cultured cells and in transgenic mice

The flanking sequences of several genes have been shown to direct a position independent expression of transgenes. Attempts to completely identify the insulating sequences have failed so far. Some of these sequences contain a matrix attached region (MAR) located in the flanking part of the genes. This article will show that the MARs in cultured cells located in the 3' OH region of the human apolipoprotein B100 (Apo B100) and within the SV40 genome were unable to stimulate and insultate transgene expression directed by the promoters from a rabbit whey acidic protein (WAP) gene or from human cytomegalovirus (hCMV) early genes. In transgenic mice, the MAR from the Apo B100 and SV40 genes did not enhance the expression of a transgene containing the rabbit whey acid protein (WAP) promotor, the late gene SV40 intron (VP1 intron), the bovine growth hormone (bGH) cDNA and the SV40 late gene terminator. This construct was even toxic for embryos. Similarly, the specialized chromatin structure (SCS) from the Drosophila 87A7 HSP70 gene reduced chloramphenicol acetyl transferase (CAT) activity when added between a cytomegalovirus (CMV) enhancer and a Herpes simplex thymidine kinase (TK) gene promoter. This inhibitory action was almost complete when a second SCS sequence was added before the CMV enhancer. Sequences from the firefly luciferase and from the human gene cathepsin D cDNA used as control unexpectedly showed a similar inhibitory effect when added to the CMVTKCAT construct instead of SCS. When added before the CMV enhancer and after the transcription terminator in the CMVTKCAT construct, the SCS sequence was unable to insulate the integrated gene as seen by the fact that the level of CAT in cell extracts were by no means correlated with the number of copies in individual clones. From these data, it is concluded that i) a MAR containing the canonical AT rich sequences does not amplify the expression of all gene constructs ii) At rich MAR sequences do not have per se an insulating effect iii) Drosophila SCS from the 87A7 HSP70 gene has no insulating effect in all gene constructs (at least in mammalian cells) iv) and the addition of a DNA fragment between an enhancer and a promoter in a gene construct cannot be used as a reliable test to evaluate its insulating property.

The effect of various introns and transcription terminators on the efficiency of expression vectors in various cultured cell lines and in the mammary gland of transgenic mice

Various combinations of promoters, introns and transcription terminators were used to drive the expression of bovine growth hormone (bGH) cDNA in different cell types. In constructs containing the human cytomegalovirus (hCMV) promoter and the SV40 late genes terminator, the intron from SV40 genes (VP1) was much more efficient, than the intron from the early genes (t). The synthetic intron SIS generated by the association of an adenovirus splice donor and an immunoglobulin G splice acceptor showed the highest activity. The respective potency of these introns was similar in several mammalian (CHO, HC11 and COS) and fish (TO2 and EPC) cells. The rabbit whey acidic protein (WAP) gene promoter was highly efficient to drive the expression of bGH gene in the HC11 mammary cell lines. In contrast, the bGH cDNA under the control of the same promoter was much less efficiently expressed when the SV40 VP1 intron and transcription terminator were used. The rabbit WAP gene and the human GH gene terminators did not or only moderately enhanced the expression of the construct WAP bGH cDNA. Introduction of a promoter sequence from the mouse mammary tumor virus (MMTV) LTR in the VP1 intron increased very significantly the expression of the WAP bGH cDNA. Although several of these vectors showed high potency when expressed stably in HC11 cells, all of them were only moderately efficient in transgenic mice. These data indicate that the VP1 and the SIS introns may be used to express foreign cDNAs with good efficiency in different cell types. The addition of an enhancer within an intron may still reinforce its efficiency. However, transfection experiments, even when stable expression is carried out, are poorly predictive of the potential efficiency of a vector in transgenic animals.

The effect of feed intake and growth hormone-releasing factor on lactating dairy cows

Twenty-four lactating dairy cows, averaging 30.0 kg/d of milk and 159 d of lactation, were used to study the effect of feed intake and growth hormone-releasing factor in a 2 x 2 factorial arrangement. For the first 10-d period, cows had free access to a TMR and received a fixed amount of high moisture corn, protein supplement, and hay. In the second 10-d period, 12 cows were maintained on this high intake, and 12 cows received 70% of their previous intake (low intake). During the following 10-d period, each intake group was divided, and each of two subgroups (n = 6) received twice daily s.c. injections of saline or growth hormone-releasing factor (10 micrograms/kg of BW per injection). Feed restriction decreased milk production by 24%. Milk production increase was not different following growth hormone-releasing factor treatment for cows maintained at high intake (4.6 kg/d) or low intake (3.4 kg/d). Feed restriction increased concentration of growth hormone but did not affect IGF-I concentration. Growth hormone-releasing factor increased IGF-I concentration similarly for both intake groups but increased concentrations of insulin and IGF-binding proteins-1 and -3 only in the high intake group. Low intake did not affect growth hormone, IGF-I, or milk responses to growth hormone-releasing factor, but suppressed the increase in concentrations of insulin and IGF-binding proteins-1 and -3 following treatment with growth hormone-releasing factor for cows on high intake.

Long-term effects of human growth hormone-releasing hormone and photoperiod on hormone release and puberty in dairy heifers

Forty-eight Holstein dairy heifers (98.9 kg BW; 3 mo old) were subjected for 246 d to twice-daily s.c. injections of saline (CTL) or human growth hormone-releasing hormone (GRH; 5 micrograms/kg BW) and to photoperiods of 8 h of light (L): 16 h of dark (D) or 16L:8D according to a 2 x 2 factorial arrangement of treatments. Jugular blood samples were collected from 16 heifers at 3, 4, 8, and 11 mo of age to monitor prolactin, growth hormone, and estradiol-17 beta. Plasma progesterone concentrations were monitored weekly in all heifers as an index of puberty (> 1 ng/mL). Growth hormone release was induced by GRH (P < .001) throughout the trial; area under the GH curve (AUC) averaged 1,582 vs 3,643 ng.min-1.mL-1 in CTL vs GRH heifers. However, GRH-induced GH response was less (P < .05) after the second daily injection. There was also an interaction (P = .08) between GRH, photoperiod, and days of treatment on GRH-induced GH response; AUC was greater in GRH-16L:8D than in GRH-8L:16D heifers at 3 mo but less at 8 mo of age. The PRL concentrations were similar for both photoperiods at 3 mo (36.4 vs 41.7 ng/mL) and 8 mo (16.2 vs 12.8 ng/mL) of age but were greater in 16L:8D vs 8L:16D heifers at 4 mo (18.4 vs 39.3 ng/mL) and 11 mo (26.3 vs 44.1 ng/mL) of age (photoperiod x day interaction, P < .001). Photoperiod of 16L:8D vs 8L:16D reduced (P < .01) weight at puberty in CTL heifers (251 vs 303 kg BW) and to a lesser extent in GRH-treated heifers (271 vs 284 kg BW; GRH x photoperiod interaction, P = .10). In conclusion, GH response is maintained throughout 8 mo of GRH treatment, and a 16L:8D photoperiod will reduce age and weight at puberty in heifers. Furthermore, refractoriness to photoperiod-induced PRL changes was detected.

Effect of plane of nutrition before and during gestation on the concentration of hormones in dairy heifers

Forty heifers (1 yr of age; 313 +/- 27 kg of BW) were assigned to one of four treatments in a 2 x 2 factorial design. Main effects were plane of nutrition (ad libitum vs. moderate feeding) during the second isometric phase (1 yr of age to 3 mo of gestation) and during the second allometric phase (3 mo of gestation to 14 d before calving) of mammary development. Jugular blood samples were collected from 16 heifers before the onset of treatment, at the end of the isometric phase, and at the end of the allometric phase. Additional daily blood samples were collected from 32 heifers from 14 d before expected calving to 10 d postpartum and then thrice weekly until 70 d postpartum. High plane of nutrition reduced average growth hormone concentrations during the isometric and allometric phases. Serum concentrations of prolactin tended to be higher in heifers on ad libitum intake during the isometric phase and were higher during the allometric phase. Prolactin was positively correlated with BW and average daily gain during allometric phase. Plasma IGF-I concentrations were not affected by plane of nutrition. No effect was found for previous plane of nutrition on concentrations of growth hormone, prolactin, IGF-I, and progesterone during either prepartum or postpartum periods. Average postpartum IGF-I concentrations were negatively correlated with milk production. A positive relationship existed between mean postpartum concentrations of growth hormone and both peak milk production and feed intake during lactation.

Effect of plane of nutrition of dairy heifers before and during gestation on milk production, reproduction, and health

Fifty-nine heifers (1 yr of age; 320 +/- 12 kg) were assigned to one of four treatments of a 2 x 2 factorial design. Main effects were plane of nutrition (ad libitum vs. moderate feeding) during the second isometric phase (1 yr of age to 3 mo of gestation) and during the second allometric phase (3 mo of gestation to 14 d before calving) of mammary development. During the isometric phase, average daily gain were .72 and .84 kg/d for heifers fed a moderate or ad libitum diet, respectively. During the allometric phase, average daily gain was affected by previous plane of nutrition and averaged .84, .66, .95, and .73 for continuous ad libitum, ad libitum followed by moderate, moderate followed by ad libitum, and continuous moderate feeding, respectively. The BW at the end of gestation and BW after calving were increased by ad libitum feeding during the allometric phase (643 vs. 605; 588 vs. 558 kg, respectively). Milk production, protein content, and withers height were not affected by plane of nutrition. Milk fat was increased by ad libitum feeding during the isometric phase (3.9 vs. 3.6%). Cows on ad libitum feeding during the allometric phase had reduced average daily gain during lactation (.02 vs. .15 kg/d). The resumption of ovarian activity (progesterone > 1 ng/ml) was not affected by treatment, but days to first observed estrus increased with ad libitum feeding during the allometric phase. Finally, ad libitum feeding during isometric phase resulted in a higher incidence of displaced abomasum after calving, 9 versus 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Lactation performance of sows injected with growth hormone-releasing factor during gestation and(or) lactation

Fifty-two Yorkshire x Landrace gilts were equally allotted to four treatments: 1) controls, saline injections (CTL); 2) injections of 12 mg of growth hormone-releasing factor (GRF) (1-29)NH2 thrice daily (0700, 1500, and 2300) from d 100 of gestation until parturition (GEST); 3) injections of GRF thrice daily from d 3 to 29 of lactation (LACT); and 4) injections of GRF thrice daily during gestation (d 100 to parturition) and lactation (d 3 to 29) (GEST-LACT). Within 48 h of birth, litters were standardized to 9 +/- 1 pigs. Weights of the pigs were recorded weekly from birth (less than 24 h) until weaning (d 30) and on d 42 and 56. Weights of gilts at mating, d 110 of gestation, 1 d postfarrowing, and at weaning also were recorded. On d 24 of lactation, milk yield was estimated by the weigh-suckle-weigh method, and a representative milk sample was obtained the next day. Jugular vein cannulas were inserted into six sows per treatment on d 26, and a 6-h blood profile (sampling every 20 min from 0600 to 1200) was obtained on d 29. Daily feed consumption of sows was recorded throughout the study. Weights of the pigs at any one time or survival until weaning were not affected by treatments (P greater than .1). Sows injected with GRF during GEST (P = .05) and(or) LACT (P less than .01) were lighter than CTL sows at weaning; in addition, sows treated during lactation had less backfat (P less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Hormonal changes following an acute stress in control and somatostatin-immunized pigs

Sixteen Yorkshire pigs (49 +/- 2 kg BW at 17 weeks) were immunized against somatostatin (SRIF; 4 males, 4 females) or its conjugated protein, bovine serum albumin (BSA; controls; 4 males, 4 females). Immunizations were done at 10, 12 and 14 weeks of age. Jugular vein cannulae were surgically inserted at 17 weeks of age. Five d later, half of each sex from the control and SRIF-immunized groups were stressed. The other half were subjected to the same stress 48 hr later. On both days, remaining animals were used as unstressed controls. The stress consisted of 5 min of snare restraint. Blood samples were collected from all pigs on both days at -20, -15, -10, -5, 0 (beginning of stress), 2, 6, 10, 15, 20, 30, 40, 60, 90, 120, 150, 180 and 240 min. Samples were radioimmunoassayed for cortisol, growth hormone (GH), prolactin (Prl), insulin, triiodothyronine (T3), thyroxine (T4) and insulin-like growth factor I (IGF-I). Mean antibody titers against SRIF (1:150 dilution) at 15 weeks were 0.49 +/- .09% and 54.5 +/- 4.9% for control and SRIF immunized pigs, respectively. Gender and immunization against SRIF had no effect on any of the variables measured (P greater than 0.05), except for T3 levels which were greater in females than in males (P less than 0.05). The stress by time of sampling interaction was significant (P less than 0.01) for all hormones measured. Cortisol values almost tripled within 15 min of stress, reaching concentrations above 100 ng/mL. Maximal increases were seen at 2 min for T4 (14%), at 6 min for T3 (36%), at 15 min for Prl (46%) and at 10 min for insulin (141%). An increase of 129% in GH concentration was present at 20 min in stressed pigs; however, an increase of 97% was also seen at 120 min in control pigs. Concentrations of IGF-I decreased (21%) by 60 min in the stressed pigs and remained depressed for up to 150 min. Stress associated with snare restraint, therefore, induces major changes in the concentrations of a series of hormones in growing pigs. On the other hand, immunization against SRIF did not alter any of the hormonal profiles measured. Since snare restraint is widely used to handle pigs during jugular puncture, any study of hormonal secretion in this species should be carried out under carefully controlled conditions in terms of blood sampling technique.

Effect of long-term administration of human growth hormone-releasing factor and(or) thyrotropin-releasing factor on milk production, insulin-like growth factor-I and plasma constituents in dairy cows

Forty-seven Holstein cows (51 ± 7 d of lactation; 607 ± 78 kg BW) were randomly subjected to a 2 × 2 factorial arrangement based on milk production. Milk production and feed intake were recorded every day and milk and feed composition determined once a week for 33 wk (4 wk preinjection, 26 wk of injection and 3 wk postinjection). During the injection period, cows received daily s.c. injections (10:00 h) in the cervical area of saline (control), human growth hormone-releasing factor (1–29)NH2 (GRF; 10 μg kg−1 BW), thyrotropin-releasing factor (TRF; 1 μg kg−1 BW) or the combination of both releasing factors (10 and 1 μg kg−1 BW, respectively). Growth hormone-releasing factor enhanced milk production (P < 0.001; 22.1 vs. 24.2 kg 4% FCM per d), feed intake (P < 0.05; 19.0 vs. 19.8 kg DM per d), feed efficiency (P < 0.05; 1.14 vs. 1.21 kg 4% FCM per kg DM) and insulin-like growth factor-I concentrations (P < 0.05) but did not affect milk composition (P > 0.25) or average daily weight gain (P > 0.25). Thyrotropin-releasing factor did not affect nor did it interact with GRF on any of these variables except for average daily weight gain which was reduced by TRF (P < 0.05; 0.24 vs. 0.12 kg d−1) during the injection period. Milk production of GRF-treated cows returned to control levels after 3 wk following cessation of treatment. GRF treatment depressed (P < 0.05) serum urea, creatinine, triglycerides and glutamate pyruvate transaminase concentrations, while TRF treatment increased glucose levels (P < 0.05). In conclusion, daily s.c. injections of GRF for 6 months stimulated milk production by 9.5% and improved feed efficiency by 6.1% in dairy cows. Key words: GRF, TRF, milk production, plasma constituents, IGF-I

Effects of creep feeding and breed composition on growth of heifer calves and milk production of their dams

Heifer calves resulting from matings of Angus (A), Hereford (H), or Simmental (S) bulls with A and H cows were used to examine the effects of creep feeding (CREEP) and heifer genotype (CALFBRD; n = 14 AA, 18 HH, 10 AH. 10 HA, 19 SA, 15 SH) on their preweaning average daily gain (ADG) and the milk yield and milk composition of their dams during the 1987 and 1988 grazing seasons. Eight-hour milk yield was estimated by oxytocin-hand milking procedures at 62, 120, and 170 d from the beginning of the calving season. Dependent variables used in repeated measures analyses included heifer calf and cow ADG between consecutive sampling times, 8-h milk yield (MILK), milk composition (grams per 8 h and percent of fat, protein, and lactose in each sample (FATG, FAT%, PROTG, PROT%, LACTG, LACT%, respectively), fat-corrected milk (FCM) and solid-corrected milk (SCM) from each cow at each sampling time. Neither CREEP nor CALFBRD had any effect on any milk yield or milk composition variable except a slight effect of CALFBRD on LACT%. Year differences were found for cow ADG, FATG, FAT%, PROTG, PROT%, LACT%, FCM and SCM, but not for LACTG, MILK or calf ADG. Differences (P≤ 0.001) in calf ADG due to CREEP and CALFBRD were found. Age of cow was a significant source of variation for cow and calf ADG and all milk yield variables, but not for FAT%, PROT%, or LACT%. Time trends (within subject factors) were significant for all dependent variables. Time by Year effects were important for cow and calf ADG, MILK, SCM, PROTG, PROT%, and LACTG. Both the breed composition of calves and supplementation with creep feed influenced calf gains but had no effect on their dam's milk yield, milk composition, or changes in body weight. Key words: Beef cattle, creep feeding, milk yield, milk composition, average daily gain, repeated measurements

Effects of active immunization against somatostatin (SRIF) and/or injections of growth hormone-releasing factor (GRF) during gestation on hormonal and metabolic profiles in sows

The hormonal responses of gestating sows to immunization against somatostatin conjugated to bovine serum albumin (SRIF-IMM) and/or injections of growth hormone-releasing factor (GRF) were studied with thirty-eight second parity sows. Immunization against bovine serum albumin (BSA-IMM) was used as control. First immunizations were done on day 30 and boosters were given on days 44, 58, 72, 86 and 100 of gestation. Injections of GRF (9 mg of GRF (1-29)NH2 per injection) or saline were given at 0800, 1400 and 2000 hr daily from day 90 of gestation until parturition. Mean body weights of sows at 85 and 110 d of gestation were 196.3 and 210.5 kg, respectively (SE = 0.8). Jugular blood samples were collected from 0740 hr to 1100 hr at 20 min intervals on days 90, 101 and 112 of gestation. On day 112, additional samples were collected from 1340 hr to 1700 hr and from 2140 hr to 2300 hr. At 112 d of gestation, antibody titers against SRIF (% binding, 1:150 dilution) were higher (P less than 0.01) for SRIF-IMM (13.5%) vs BSA-IMM (0.95%) sows. There was no effect of SRIF-IMM nor was there a GRF by SRIF-IMM interaction on any variable measured (P greater than 0.05). Injections of GRF increased (P less than 0.01) the area under the curve (AUC) for growth hormone (GH; 305 vs 1623 ng/min/ml). The increase was greater as days of injection increased (P less than 0.05). Administration of GRF did not affect prolactin (Prl) AUC (P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Negative control by Sandostatin on pancreatic and duodenal growth: a possible implication of insulin-like growth factor I

This study was undertaken to evaluate the effects of Sandostatin, a potent somatostatin analogue, on pancreatic and intestinal growth and plasma and pancreatic levels of insulin-like growth factor I, a known growth factor. Rats weighing 320-330 g, equipped with an intravenous cannula were infused with either bovine serum albumin or Sandostatin at a dose of 5 micrograms kg-1 h-1 for 7 days. Sandostatin caused significant reductions in pancreatic and intestinal weights accompanied by decreases in total DNA, RNA in both organs and total protein in the intestine while total pancreatic enzymes were increased. Plasma cholecystokinin and insulin-like growth factor I were reduced whereas total insulin-like growth factor I pancreatic content was increased. It is suggested that Sandostatin may reduce growth of these two organs by decreasing cholecystokinin and insulin-like growth factor release and their specific effects at the pancreatic and duodenal cellular level.

Dynamics of growth hormone responsiveness to growth hormone releasing factor in aging rats: peripheral and central influences

The in vivo and in vitro dynamics of somatotroph responsiveness to rGRF (1-29) NH2 (rat growth hormone releasing factor) were evaluated in 2-, 4-, 8-, 12-, and 20-month-old male rats. In vivo, using pentobarbital-anesthetized animals, we observed that the rGH (rat growth hormone) responsiveness to 0.4 and 1.6 micrograms/kg rGRF started to decline at the higher dose in 12-month-old rats and was completely blunted at both rGRF doses in 20-month-old animals. In vitro, using freshly dispersed perifused pituitary cells, we also documented a decrease of rGRF-induced rGH secretion in 12- and 20-month-old rats. Moreover, as the animals aged, the rGRF-induced rGH secretion was differentially affected by the inhibiting action of somatostatin (p less than 0.001), suggesting a loss of pituitary sensitivity to somatostatin in the presence of a high concentration of rGRF. The pituitary rGH content increased until rats reached 12 months of age, but was diminished in 20-month-old rats. In contrast, the pituitary somatostatin content increased twofold in 20-month-old rats as compared with younger rats. The hypothalamic somatostatin content was highest in 8-month-old rats and only slightly diminished in 20-month-old animals. Finally, plasma insulin-like growth factor I concentrations were highest in 8-month-old rats and lowest in 20-month-old animals. Altogether, these results indicate that the physiological loss of somatotroph responsiveness associated with the process of aging starts around 12 months of age.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of growth hormone-releasing factor infusion on somatotropin, prolactin, thyroxine, insulin, insulin-like growth factor I and blood metabolites in control and somatostatin-immunized growing pigs

The aim of this study was to characterize the effects of prolonged infusion of growth hormone-releasing factor (1-29)NH2 (GRF) on plasma concentrations of hormones and metabolites when administered to control pigs and pigs immunized against somatostatin (SRIF). In the first experiment, eight purebred Yorkshire boars averaging 113 +/- 2 kg BW were immunized against SRIF conjugated to bovine serum albumin (BSA) (n = 4) or BSA alone (n = 4). Somatotropin (ST) response to four rates of GRF infusion (0, 1.66, 5 and 15 ng/min/kg BW) for 6 hr was evaluated using a double balanced 4 x 4 Latin square design. During the 4 hr before infusion, SRIF-immunized animals tended (P = 0.06) to have a higher ST release (613 vs 316 ng.min/ml, SE = 232) than controls. During infusion, GRF elicited a dose-dependent increase in ST release in both squares; the ST response was not better in SRIF-immunized animals than in controls (P greater than 0.05) (1435 vs 880 ng.min/ml; SE = 597). In the second experiment, ten purebred Yorkshire boars (5 controls and 5 SRIF-immunized animals) averaging 69 +/- 2 kg BW were continuously infused with GRF at the rate of 15 ng/min/kg BW for six consecutive d. Under GRF infusion, ST concentrations increased (P less than 0.05) from 805 to 4768 ng.min/ml (SE = 507) from day 1 to day 6 in both SRIF-immunized and control animals. Prolactin levels increased (P less than 0.05) with GRF infusion; pattern of increase was different (P less than .01) overtime in control and SRIF-immunized animals. Thyroxine levels increased from 2.53 to 3.45 micrograms/dl (SE = 0.16) after six d of infusion. Insulin-like growth factor I was higher (P less than 0.05) before (139 vs 90 ng/ml; SE = 11) and during (222 vs 185 ng/ml; SE = 11) GRF infusion in SRIF-immunized animals. A transient increase (P less than 0.05) in glucose and insulin was observed in both groups. Immunization against SRIF had no effect on blood metabolites; however, GRF infusion increased free fatty acids from 157 to 204 microEq/l (SE = 11) and decreased blood urea nitrogen from 4.1 to 3.5 mmol/l (SE = 0.2) from day 1 to day 6, respectively. In summary, active immunization against SRIF in growing pigs increased ST and IGF-I concentrations. Infusion of GRF continuously raised ST levels with days of infusion without any sign of decrease responsiveness.

Effect of human growth hormone-releasing factor and(or) thyrotropin-releasing factor on growth, carcass composition, diet digestibility, nutrient balance, and plasma constituents in dairy calves

Sixty male dairy grain-fed calves, raised from 70 to 223 kg BW in individual crates, were used in a 2 X 2 factorial arrangement to determine the effect of administration of human growth hormone-releasing factor (1-29)NH2 (GRF) and(or) thyrotropin-releasing factor (TRF). Calves received twice-daily s.c. injections of .9% NaCl (control), GRF (5 micrograms/kg BW), TRF (1 micrograms/kg BW) or GRF (5 micrograms/kg BW) plus TRF (1 micrograms/kg GTRF). Average daily gain and days on feed were not affected by treatments, but TRF treatment increased (P less than .05) total intake of dry matter (DM) and feed conversion ratio: 3.00, 3.02, 3.08, and 3.22 kg DM/kg weight gain for control, GRF, TRF, and GTRF, respectively. During two 7-d periods, after 66 and 75 d of treatment, feces and urine were collected from 40 calves (5 per treatment per period). Treatment with GRF increased (P less than .05) digestibility of DM, nitrogen (N), and energy and tended (P less than .20) to increase N retention. At slaughter, withers height was increased (P = .05) by GRF and carcass length was increased (P less than .05) by TRF. Pituitary and liver weights were increased (P less than .05) by TRF. The combination of GRF and TRF slightly increased (P less than .10) protein content and decreased (P less than .05) fat content of the 9-10-11th rib section. After d 1, GRF treatment chronically increased (P less than .05) insulin concentrations and also increased (P less than .10) IGF-I concentrations on d 29 and 57. In summary, chronic treatment with GRF and(or) TRF did not improve growth or efficiency, although GRF increased digestibility of DM, N, and energy and the GRF plus TRF combination resulted in slightly leaner carcasses.