Induced lactation in heifers: Effects of dexamethasone and age at induction on milk yield and composition

Milk production in heifers induced into lactation is lower than that of postpartum primiparous cows. A method to improve milk production in induced lactations may provide opportunities for increased profitability as well as increase our understanding of the mechanisms that regulate mammary gland development and colostrum composition. The present study was conducted to determine if dexamethasone administration at the onset of milking or age at lactation induction would affect milk production in heifers induced into lactation. Holstein heifers at 14 [n=20; 354 ± 38 kg of body weight (BW)] and 18 mo of age (n=20; 456 ± 30 kg of BW) were assigned randomly to dexamethasone (DEX) or control (CON) treatment groups in a 2 × 2 factorial arrangement with age and dexamethasone treatment as the 2 factors. Heifers were induced into lactation with daily subcutaneous injections of estradiol-17β and progesterone (0.075 and 0.25 mg/kg of BW per d, respectively) on experimental d 1 to 7. They also received bovine somatotropin (bST) every 14 d beginning on experimental d 1. Milking began on experiment d 18 (lactation d 1). Dexamethasone (10mg) was administered on lactation d 1 and 2 following the morning milking; CON heifers did not receive dexamethasone. Milk yield from d2 to 15 of lactation of heifers receiving DEX (7.8 kg/d) was greater than that of CON heifers (6.0 kg/d) but was similar thereafter through 305 d of lactation (18.2 kg/d). Milk production to d 11 was similar for 14- and 18-mo-old heifers but was greater for 18- (18.9 kg/d) than for 14-mo-old animals (17.4 kg/d) through 305 d in milk. Milk fat percentage increased initially and was greater in DEX (4.51%) compared with CON (3.53%) heifers until 21 d in milk. Milk protein and lactose concentrations were not affected by DEX treatment. Age at induction did not affect milk fat, protein, or lactose percentages. Mean milk IgG concentration declined from 107.4 mg/mL on d 1 to 5.0mg/mL on d 7 of lactation, tended to be greater for 18- compared with 14-mo-old heifers, and was not different due to DEX treatment. Administration of DEX to heifers induced into lactation increased initial milk production during the first 2 wk of lactation but this effect did not persist through 305 DIM. Treatment with DEX appeared to stimulate mammary cell differentiation but did not change the rate of decline of milk IgG concentrations. Higher milk yield in 18-mo-old heifers may be due to greater mammary epithelium, higher body mass, or both.

17Beta-estradiol and estrone concentrations in plasma and milk during bovine pregnancy

Estrone (E1) and 17beta-estradiol (E2) are present in milk, but the mechanism(s) that regulate their appearance in milk are not known. The objectives of this study were to determine the impact of stage of pregnancy on the concentrations of E1 and E2 in plasma and milk and to determine the correlations between plasma and milk E1 and E2 and with milk components throughout pregnancy. Blood and milk samples were collected from 13 cows every 28 d throughout pregnancy. The E1 and E2 were quantified in plasma and milk using RIA after organic solvent extractions and Sephadex LH-20 column chromatography. Plasma E1 concentrations averaged 0.8, 16.9, and 41.8 pg/mL in trimesters 1, 2, and 3, respectively. The respective E1 concentrations in milk averaged 0.6, 7.9, and 27.1 pg/mL. The E2 concentrations in plasma averaged 0.5, 0.9, and 2.0 pg/mL; milk E2 averaged 0.3, 0.9, and 5.0 pg/mL. Plasma and milk E2 concentrations were greater in trimester 3 compared with trimesters 1 and 2. The E1 concentrations in milk were significantly correlated with plasma E1 concentrations (r = 0.77), percentage of milk fat (r = 0.50), and milk yield (r = -0.43). The E2 concentrations in milk were significantly correlated with plasma E2 concentrations (r = 0.93), percentage of milk protein (r = 0.63), and milk yield (r = -0.57). The milk-to-plasma ratio of E2 increased from 0.4 during trimester 1 to 2.2 in trimester 3, which suggested that the mechanism(s) regulating the appearance of E2 in milk may change over the course of pregnancy.

Concentrations of 17β-Estradiol in Holstein Whole Milk

Some individuals have expressed concern about estrogens in food because of their potential to promote growth of estrogen-sensitive human cancer cells. Researchers have reported concentrations of estrogen in milk but few whole milk samples have been analyzed. Because estrogen associates with the fat phase of milk, the analysis of whole milk is an important consideration. The objectives of this study, therefore, were to quantify 17beta-estradiol (E2) in whole milk from dairy cows and to determine whether E2 concentrations in milk from cows in the second half of pregnancy were greater than that in milk from cows in the first half of pregnancy or in nonpregnant cows. Milk samples and weights were collected during a single morning milking from 206 Holstein cows. Triplicate samples were collected and 2 samples were analyzed for fat, protein, lactose, and somatic cell counts (SCC); 1 sample was homogenized and analyzed for E2. The homogenized whole milk (3 mL) was extracted twice with ethyl acetate and once with methanol. The extract was reconstituted in benzene:methanol (9:1, vol/vol) and run over a Sephadex LH-20 column to separate E2 from cholesterol and estrone before quantification using radioimmunoassay. Cows were classified as not pregnant (NP, n = 138), early pregnant (EP, 1 to 140 d pregnant, n = 47), or midpregnant (MP, 141 to 210 d pregnant, n = 21) at the time of milk sampling based on herd health records. Mean E2 concentration in whole milk was 1.4 +/- 0.2 pg/mL and ranged from nondetectable to 22.9 pg/mL. Milk E2 concentrations averaged 1.3, 0.9, and 3.0 pg/mL for NP, EP, and MP cows, respectively. Milk E2 concentrations for MP cows were greater and differed from those of NP and EP cows. Milk composition was normal for a Holstein herd in that log SCC values and percentages of fat, protein, and lactose averaged 4.9, 3.5, 3.1, and 4.8, respectively. Estradiol concentration was significantly correlated (r = 0.20) with percentage fat in milk. Mean milk yield was 18.9 +/- 0.6 kg for the morning milking. The mean E2 mass accumulated in the morning milk was 23.2 +/- 3.4 ng/cow. Likewise, using the overall mean concentration for E2 in milk, the mean E2 mass in 237 mL (8 fluid ounces) of raw whole milk was 330 pg. The quantity of E2 in whole milk, therefore, is low and is unlikely to pose a health risk for humans.

Major Advances in Teaching Dairy Production

A survey of 38 universities that grant 4-yr degrees as well as 12 institutions that grant technical degrees of 2 yr or less revealed that degree programs in dairy production remain popular, but have changed significantly over the last 25 yr. Enrollment in dairy production programs remains strong (1,189 and 417 students in baccalaureate and nonbaccalaureate degrees, respectively) even though this is viewed as a traditional industry. There are significant differences in size of programs across the United States, and some are struggling to maintain both the visibility and faculty numbers to keep pace with the industry. The percentage of students enrolled in 4-yr programs who are female has increased to the majority. More students hail from a nondairy farm background in our university programs today than in 1994. Computer and information technology has become a mainstream part of our educational programs. A high percentage of undergraduate students elect to engage in an internship or work experience, and there is a high correlation between internship and career paths selected by our students. The dairy industry initiated and financially supports the North American Intercollegiate Dairy Challenge; an educational activity among university teams to foster skills in analyzing a dairy farm business. This collaboration between universities and private industry is strong evidence that our undergraduate programs are relevant to the dairy industry. Extracurricular activities like dairy science clubs also remain popular, and are perceived by faculty members to be an important part of our educational experience. An analysis of nonbaccalaureate degree programs was not reported previously, but was a part of the present survey. In the nonbaccalaureate institutions that responded to the survey, there were 417 students enrolled in 12 dairy programs across the United States in 2004. This student population in nonbaccalaureate programs has a higher percentage of female enrollment than in 1994, but enrollment is still predominantly male. Computer and information technologies are an important part of their curricula and a very high percentage of these students remain in production agriculture upon graduation. Many of the challenges in undergraduate education described previously continue to be challenges in 2005. However, there are many reasons for optimism; as the number of students electing enrollment in dairy production remains strong, there is great interest in keeping the curricula relevant and interaction with and support by the dairy industry continues to be significant.

Automatic Cluster Remover Setting Affects Milk Yield and Machine-On Time in Dairy Cows

The primary objectives of this study were to examine effects of automatic cluster remover (ACR) settings on milk yield and machine-on time, and to describe variation in cow body weight (BW) associated with day of bovine somatotropin (bST) cycle. Automatic cluster removal settings of 0.48, 0.6, and 0.8 kg/min were used to regulate the end of milk removal. The setting was changed every 2 wk for 12 wk and followed the sequence 0.8, 0.6, 0.48, 0.48, 0.6, and 0.8 kg/min. Milk yield, machine-on time, and BW were measured for 60 Holstein cows at each milking. Milk yield averaged 19.7, 19.9, and 19.3 kg/cow per milking for ACR settings of 0.48, 0.6, and 0.8, respectively. There was a 2.5% reduction in milk yield at the high setting, but yields were similar for the others. Machine-on time was 6.3, 5.9, and 5.6 min for ACR settings of 0.48, 0.6, and 0.8, respectively. There was an 11.1% reduction in milking time between the 0.8- and 0.48-kg/min settings. The middle ACR setting yielded a shorter milking time than the low setting without reducing production. Milk yield and cow BW increased over the 14-d bST cycle, peaking by d 8, and then declining through d 14. Automated collection of milk yield, milking time, and BW at each milking can be used to establish normal patterns for individual animals, which could be useful in making management decisions.

Induced Lactation in Nonpregnant Cows: Profitability and Response to Bovine Somatotropin

Significant culling of high-producing cows with low fertility reduces profitability of dairy farms as those cows are replaced with heifers. Induced lactation of nonpregnant cows may be a management alternative to reduce culling and increase profits. The objectives of this study were to evaluate the efficacy of bovine somatotropin (bST) to increase milk production in cows induced into lactation with estrogen plus progesterone, and to determine the profitability of inducing cows into lactation vs. using replacement heifers entering the herd as first-lactation cows. Parity 1 or greater, nonpregnant, healthy Holstein cows (n = 28) were induced into lactation by administration of estradiol-17beta (0.075 mg/kg of body weight [BW] per d) and progesterone (0.25 mg/kg of BW per d) for 7 d. Milking began on d 18. Cows were randomly assigned to control or bST treatment groups on d 37 +/- 20 of milking, and milk production was compared for 70 d. After the 70-d comparison, all cows received bST for the duration of lactation. Cows receiving bST produced more milk (28.4 kg/d) than controls (24.1 kg/d), with variable yields among cows. For the economic analysis, induced cows were compared to first-lactation cows in the same herd using fair market value for costs and multiple component pricing for milk. Net present value for an induced cow (1966 dollars) was significantly greater than that for a first-lactation cow (1446 dollars). Our data suggest that bST use in induced cows is profitable. If a reliable method were developed and approved by the FDA, inducing nonpregnant cows into lactation could be used by dairy producers to increase profitability.

Purification of porcine beta-casein, N-terminal sequence, quantification in mastitic milk

The objectives of the study were to purify porcine beta-casein from sow's milk, to determine N-terminal amino acid sequence, to develop specific antisera against porcine beta-casein, and to use that antisera to evaluate milk samples from a mastitis study. Milk was collected by hand milking a Yorkshire by Duroc crossbred sow following oxytocin administration on d 27 of lactation. A casein-enriched fraction was then prepared by iso-electric precipitation. Porcine beta-casein was then purified by liquid chromatography on a Mono Q anion-exchange column, and checked for purity with SDS-PAGE. An apparent molecular weight of 29,000 Da was estimated from SDS-PAGE. N-Terminal amino acid sequence was determined by Edman degradation to be RAKEELNASGETVE. Rabbits (n = 2) were immunized with beta-casein mixed with Freund's complete (primary) or incomplete (boosters) adjuvant at 4-wk intervals. Antiserum collected from one rabbit 112 d after primary immunization detected 30 to 100 ng beta-casein by Western blot procedure when used at a dilution of 1:2 x 10(6). The antiserum was specific for porcine beta-casein, but showed some cross-reactivity with equine casein. It was determined by Western blot procedure that mammary inflammation induced by lipopolysaccharide infusion resulted in a 41% decrease in the beta-casein concentration of sow milk.

The effects of accelerated growth rates and estrogen implants in prepubertal Holstein heifers on growth, feed efficiency, and blood parameters

Sixty-eight Holstein heifers were used to determine the effects of accelerated growth rates by increased nutrient intake and estrogen implants on feed efficiency, structural growth, and blood parameters in heifers between 19 and 39 wk of age. At the beginning of the treatment period, the heifers were assigned to one of four treatment groups by using a randomized complete block design in a 2 x 2 factorial arrangement. The treatments were standard growth rate (700 g/d), accelerated growth rate (1000 g/d), standard growth rate with an estradiol implant, and accelerated growth rate with an estradiol implant. All heifers received the same diet, but dry matter intake was adjusted weekly to achieve the target rate of gain. Accelerating heifer growth rates from 705 to 1007 g/d improved feed efficiency 5.1%, increased the rate of withers height, heart girth, and hip width growth 12, 27, and 27%, respectively, and body condition scores 0.25 points. Estradiol implants improved feed efficiency 2.4% and decreased the rate of withers height 6% and heart girth growth 3.5%. Increased nutrient intake and average daily gain depressed mean plasma growth hormone and urea nitrogen content 17 and 7%, respectively, while elevating insulin-like growth factor-1 levels by 10%. Estradiol implants increased mean plasma growth hormone content by 29% and insulin-like growth factor-1 levels by 17%, but decreased urea nitrogen content by 11%. Feeding prepubertal heifers for accelerated growth rates increased structural growth with a small increase in body condition, whereas estradiol implants improved feed efficiency and decreased the growth rate of withers height and heart girth without affecting the rate of hip width growth.

The effects of accelerated growth rates and estrogen implants in prepubertal Holstein heifers on estimates of mammary development and subsequent reproduction and milk production

The objectives of this study were to determine the effects of accelerating growth rates and of imposing estrogen implants in prepubertal heifers on mammary development and subsequent reproduction and milk production. Sixty-eight Holstein heifers were assigned to 1 of 4 treatment groups by using a randomized complete block design in a 2 x 2 factorial arrangement. The treatments were standard growth rate (700 g/d) or accelerated growth rate (1000 g/d) and estrogen implant or no estrogen implant. The treatments were imposed over 20 wk, beginning at 4.5 mo of age and 130 kg of body weight (BW). During the treatment period, all heifers were fed individually and received the same diet, but the dry matter intake of each heifer was adjusted weekly to achieve the designated growth rate. The estrogen implants were removed at the end of the treatment period at 9.5 mo of age. After the treatment period, the heifers were group fed according to BW and age to allow the heifers to have a similar BW and age at calving. The accelerated growth regimen decreased age at puberty by 32 d. Age, BW, and body condition scores at calving were not significantly different among treatments. The accelerated prepubertal growth regimen decreased first lactation fat-corrected milk yield 7.1%. Prepubertal heifers given estrogen implants produced 5.2% less fat-corrected milk during first lactation than did heifers not implanted with estrogen. Estrogen implants stimulated a large increase in teat length growth during the treatment period, but the advantage was lost posttreatment. Over both the treatment and posttreatment periods, the estrogen implants reduced teat length growth by 30%. Accelerated growth rates from 700 to 1000 g/d and estrogen implants in prepubertal heifers decreased first lactation milk production.

Effects of elevated blood insulin-like growth factor-I (IGF-I) concentration upon IGF-I in bovine mammary secretions during the colostrum phase

The objectives of these studies were to determine if the concentration of insulin-like growth factor-I (IGF-I) in mammary colostrum secretions could be altered through manipulation of IGF-I concentrations in blood and to compare the temporal changes of IGF-I in mammary secretions to those occurring for IgG1. Milking of 15 pregnant Holstein cows was stopped at 8 weeks prepartum and they were randomly assigned to one of three treatments. A control (C) treatment consisted of feeding the animals 100% of NRC requirements for protein and energy. A second group of cows was fed as the control group and injected with 1.8 mumol bovine GH/day. The third group was fed at 70% of NRC requirements for protein and energy to cause a moderate nutrient restriction (NR). Body weight was measured weekly. Blood was collected by tail venepuncture at 4 h intervals for 24 h. Mammary secretions were collected and pooled among contralateral front and rear quarters (diagonal) for measurement of volume, IGF-I and IgG1 concentrations. Samples were collected at -7, -5, -2, 0 and 1 week postpartum. Cows on the NR treatment failed to gain weight during the dry period compared with C cows (P < 0.05). Blood GH and IGF-I concentrations (P > 0.1) were unaffected by NR treatment. Cows treated with GH had higher (P < 0.01) serum GH and IGF-I levels throughout the entire treatment period, and higher serum IgG1 at 5 and 2 weeks prepartum (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of the hepatic growth hormone receptor and serum growth hormone-binding protein during pregnancy in the mouse: effects of litter size

The regulation of hepatic GH receptor (GHR) and serum GH-binding protein (GHBP) during pregnancy in the mouse was investigated by manipulating the number of conceptuses carried by the dam. Animals carrying 1-4 conceptuses had significantly lower amounts of hepatic GHR (GH-binding activity) than mice carrying 10-13 conceptuses on days 9 and 13 of pregnancy. There was no significant difference in hepatic GHR on day 17 of pregnancy between animals carrying 1-4 and 10-13 conceptuses. Animals carrying 1-4 conceptuses had significantly lower concentrations of GHBP in serum than animals carrying 10-13 conceptuses on days 9, 13, and 17 of pregnancy. The relative amounts of liver GHR- and GHBP-encoding messages in animals with low and high conceptus numbers were investigated by Northern analysis. There were higher levels of both messages in animals carrying 10-13 conceptuses than in mice carrying 1-4 conceptuses. On day 13 of pregnancy, animals carrying 10-13 conceptuses had significantly higher levels of GHBP-encoding message than animals carrying 1-4 conceptuses. Total hepatic mass was not significantly different between animals with low and high conceptus numbers. No significant difference was found in GHBP concentration between blood from the uterine vein and the trunk in 17-day pregnant animals. Mouse placental lactogen-I (mPL-I), mPL-II, GH, and corticosterone concentrations were measured by RIA and related to hepatic GHR activity and serum GHBP concentration. Hepatic GHR activity and serum GHBP concentration were significantly correlated with each other on days 9, 13, and 17 of pregnancy. Hepatic GHR activity was significantly correlated with mPL-I and mPL-II on day 9 of pregnancy. GHBP concentration was significantly correlated with mPL-I and mPL-II on day 9 of pregnancy and with mPL-II and GH on day 13 of pregnancy. Data are consistent with the hypothesis that mPL-I, mPL-II, and GH may affect hepatic expression of the GHR/GHBP gene during pregnancy in the mouse.

Binding and bioactivity of ovine and porcine prolactins in porcine mammary tissue

Differential binding of homologous and heterologous prolactin was investigated in porcine mammary tissue. Specific binding of ovine prolactin to porcine mammary membranes or tissue slices was significantly greater than specific binding of the homologous porcine prolactin. Ovine prolactin was also more potent than porcine prolactin in stimulating proliferation of Nb2 cells. In contrast, stimulation of glucose metabolism in porcine mammary explants by porcine prolactin was greater than that by ovine prolactin. Differences in specific binding were probably not due to damage during iodination, as low concentrations of iodinated prolactins were similar to unlabelled prolactins in their abilities to stimulate proliferation of Nb2 cells. Furthermore, electrophoretic analysis of medium from binding reactions suggested that differences in specific binding were not due to proteolytic cleavage of the homologous prolactin into large (greater than 10 kDa) fragments. These studies suggest that ovine prolactin either binds to sites in addition to the authentic lactogenic receptor in porcine mammary tissue or that a significantly higher affinity of ovine prolactin for the porcine lactogenic receptor has little effect on its biological activity.

Endocytosis and degradation of ovine prolactin by Nb2 lymphoma cells: characterization and effects of agents known to alter prolactin-induced mitogenesis

Rat Nb2 node lymphoma cells proliferate in response to lactogens, but the signal transduction mechanism involved remains unclear. Specific binding, internalization, and degradation of ovine PRL (oPRL) were examined under a variety of experimental conditions to characterize the metabolism of receptor-bound hormone by these cells. Stationary-phase cells were incubated with [125I]oPRL in Fischer's medium containing horse serum. Cell suspensions were centrifuged, and the cell pellets were assayed to determine specific cell-associated radioactivity. Internalized ligand was measured by exposing the cells to an acidic buffer before centrifugation to dissociate hormone from plasma membrane receptors, and cell-surface ligand was calculated by subtracting internalized hormone from the total [125I]oPRL bound by the cells. Hormone degradation was assessed by measuring the radioactivity in an acid-soluble fraction prepared from the incubation medium. Endocytosis of [125I]oPRL was observed within 30 min at 37 C, and the internalized component accounted for approximately 50% of the bound hormone under steady-state conditions. Hormone degradation was detectable within 1 h at 37 C and continued at a relatively linear rate thereafter; by 4 h, 8% of the added [125I]oPRL was acid soluble. Chloroquine (0.2 mM), methylamine (20 mM) and monensin (20 microM) prevented [125I]oPRL degradation and elevated both cell-surface and intracellular hormone 2-fold during a 4-h incubation. Leupeptin (0.2 mM) decreased degradation by only 15% under the same conditions. Phorbol 12-myristate 13-acetate (PMA; 20 nM), a comitogen for lactogen-stimulated Nb2 cells, increased cell-surface hormone by 20% and decreased intracellular hormone by a corresponding amount 1 h after administration. Calcium ionophore A23187 (1 microM) produced similar changes, and a synergistic effect was noted when cells were exposed to both agents for 4 h. Amiloride (125 microM), an inhibitor of Nb2 cell mitogenesis, decreased [125I]oPRL degradation by 25% during a 4-h incubation. This response was abolished when the cells were exposed simultaneously to PMA. These experiments demonstrate that receptor-bound oPRL is rapidly internalized and extensively degraded via the endosome-lysosome pathway when Nb2 cells are maintained at 37 C. The inhibitory effect of PMA on oPRL internalization may help to explain the comitogenic action of this phorbol on Nb2 cells. Since amiloride also produced major changes in oPRL metabolism, post-binding events in lactogen processing by target cells could play an important role in the mitogenic response elicited by such hormones.

Effect of exogenous bovine somatotropin on mammary lipid metabolism and milk yield in lactating dairy cows

Eight lactating Holstein cows were used to study the effect of bovine somatotropin on mammary lipid metabolism, milk production, and milk composition. Eight cows were injected with either excipient (n = 4) or 50 IU somatotropin/d (n = 4). A 2-wk adjustment period preceded a 10-d period when treatments were administered. On d 9, serial blood samples were collected from 2 to 5 h post-injection to determine concentrations of somatotropin and metabolites in plasma. Mammary tissue biopsies were obtained 2 to 3 h after a.m. milking on d 10 to determine lipoprotein lipase activity and in vitro rates of acetate incorporation into fatty acids and acetate oxidation by mammary tissue slices. Activity of lipoprotein lipase in milk and mammary tissue and rate of acetate metabolism by mammary tissue were not affected by treatment. The following means for placebo and somatotropin, respectively, were: milk production (21.5 and 24.8 kg/d), milk fat (3.8 and 4.0%), and 4% FCM (20.7 and 25.1 kg/d). Plasma concentrations of somatotropin (3.0 and 43.4 ng/ml) and free fatty acids (105.6 and 219.5 mu eq/L) were significantly elevated with somatotropin. The injection of somatotropin into lactating dairy cows did not affect the mechanisms of fatty acid synthesis or metabolism evaluated in this study.

Relationships among prolactin binding, prolactin concentrations in plasma and metabolic activity of the porcine mammary gland

The current studies were designed to investigate relationships among prolactin (PRL) binding, PRL concentrations in plasma and metabolic activity of porcine mammary glands. Preliminary studies revealed specific high-affinity binding of oPRL to porcine mammary gland. Conditions for optimal specific binding were similar to those observed for other species. To address the main objectives of the study, four mammary biopsies and blood samples were obtained from each of four gilts during lactogenesis and lactation (d-11, 4, 21 and 42 of lactation) to measure in vitro rates of metabolic activity, PRL binding to mammary membranes and PRL concentrations in plasma. Metabolic activity, as measured by oxidation of glucose or acetate to CO2 and incorporation into lipid, was low during pregnancy, increased two- to five-fold on d 4, and then paralleled the lactation curve for sows. There were highly significant positive correlations between PRL binding and all measures of mammary metabolism when data from pregnancy and lactation were utilized. Coefficients were positive but generally not statistically significant when lactation data only were utilized. During lactation, significant negative correlations were observed between concentrations of PRL in plasma and PRL binding and between PRL in plasma and mammary metabolic rate. These data provide evidence that binding of PRL to its receptor is an important effector of milk production in sows. Furthermore, oPRL is a suitable ligand to quantify PRL binding to porcine mammary tissue.

Quantitation of prolactin-dependent responses in porcine mammary explants

A system was developed to quantitate prolactin-dependent responses in porcine mammary tissue obtained from pregnant gilts. Metabolic responses to prolactin (Prl) and cortisol (C) in the presence of varying doses of insulin (I) were examined in mammary explants cultured on the surface of the medium or submerged in medium, under an atmosphere of humidified air. Explants suspended on grids at the surface of medium oxidized 45% more glucose (P less than .05) and incorporated 67% more glucose into lipids (P less than .05) than explants submerged in culture medium. In explants cultured on grids, both 100 and 1,000 ng I/ml increased glucose oxidation (by 50%) and glucose incorporation into lipids (by 150%) compared with 10 ng/ml (P less than .05), but responses to 100 and 1,000 ng I/ml were not different. Therefore, in subsequent studies, explants were cultured on grids with 100 ng I/ml. Rates of glucose metabolism for mammary explants cultured with I + C for 48 or 72 h were not different from those in fresh tissue. However, addition of Prl (200 or 1,000 ng/ml) increased oxidation rate 130% and fat synthesis 400% compared with I + C (P less than .05). Addition of triiodothyronine to I + C + Prl further increased rate of fat synthesis by 87%. Dose-dependent responses to Prl were demonstrated and were within the concentrations of Prl found in blood of gestating gilts. These studies demonstrate that the lactogenic complex of I, C and Prl induces metabolic activity in porcine mammary tissue from late pregnancy.

Effect of added dietary fat and bovine somatotropin on the performance and metabolism of lactating dairy cows

Four early lactation Holstein cows (44 to 105 d postpartum) were used in a 4 X 4 Latin square experiment in a 2 X 2 factorial arrangement of treatments to study effects of added dietary fat and/or bovine somatotropin on performance and metabolism. Treatments were: 1) control diet plus placebo injection; 2) 5% added dietary fat (hydrolyzed blend of animal and vegetable fat) + placebo injection; 3) control diet + 50 IU bovine somatotropin/d; and 4) 5% added dietary fat + 50 IU bovine somatotropin/d. Dietary fat reduced dry matter intake (21.6 vs. 22.7 kg/d) and elevated plasma triglycerides (34.7 vs. 29.2 mg/100 ml). Injection of somatotropin lowered blood urea nitrogen, increased plasma free fatty acids, and increased plasma somatotropin. Milk production, milk fat percent, and 4% FCM production were increased by the injection of somatotropin. Milk protein percent was decreased (3.30 vs. 3.44%) with added fat and tended to be lower with somatotropin. The percentage of short-chain fatty acids (C6 to C14) in milk fat decreased with added fat while the percentage of stearic and oleic acids in milk fat increased. Production responses for fat plus somatotropin and somatotropin treatments were similar. Under the conditions of this study, the addition of dietary fat with injection of somatotropin had little effect on production parameters compared with that found with somatotropin alone.

Relationship of estrone and prolactin with growth and survival of piglets to 35 d of age

The relationship between estrogen or prolactin (Prl) status of pigs at birth and subsequent performance was examined in ten (Study 1) or seven (Study II) Yorkshire litters. In both studies, piglets were bled (3 ml) from the suborbital sinus at birth, and then hourly for 12 h. Hematocrit (Hct) and concentrations of plasma protein (PP) and estrone (E1) were determined on all samples. Concentrations of Prl were determined only in samples at birth. Weights at 3 and 5 wk of age as well as percent survival to 5 wk were obtained. Mean concentrations of E1 and Prl in piglets at birth were 6.97 +/- 44 ng/ml and 9.12 +/- .32 ng/ml, respectively. A decrease in E1 occurred over the first few hours after birth. Hematocrit values also decreased postnatally, whereas concentrations of PP increased. Sex of neonate did not affect any of the blood characteristics studied. Correlations between E1, PP, Hct and Prl at birth and body weights at birth, 3 and 5 wk were nonsignificant. However, piglets with higher Prl values at birth showed a greater survival rate. In Study II, half of the piglets in each litter were implanted at birth with silicone rubber implants containing estradiol-17 beta. Estrone concentrations were significantly higher in implanted piglets than in controls over the subsequent 12-h period, but Hct and PP values were not affected by treatment, suggesting that treated piglets did not consume more colostrum.(ABSTRACT TRUNCATED AT 250 WORDS)

Native and recombinant bovine growth hormone antagonize insulin action in cultured bovine adipose tissue

The current study was undertaken to determine if pituitary bovine GH (pbGH) and recombinant bGH (rbGH) antagonized insulin action in bovine adipose tissue after acute (2-h) and chronic (48-h) exposure and whether this was an intrinsic property of bGH. Insulin action (measured as the effect on incorporation of acetate-carbon into long-chain fatty acids) was unaffected by bGH in short term incubations regardless of whether hydrocortisone (HC) was present. After 48 h of culture, however, both pbGH and rbGH similarly antagonized the ability of insulin to maintain lipogenic capacity. This antagonism was dependent upon the presence of HC and was dose dependent, with half-maximal inhibition of insulin action occurring at about 0.5 ng/ml bGH. Bovine PRL did not mimic the effects of bGH on insulin action. These results establish that bGH antagonizes insulin action in bovine adipose tissue and that this effect is dependent upon long term exposure and the inclusion of HC in the culture medium. The fact that both rbGH and pbGH acted similarly indicates that this is an intrinsic property of bGH. The effect of bGH on insulin-dependent maintenance of lipogenic capacity may play an important role in redirecting nutrients away from adipose tissue to other tissues, such as muscle or mammary tissue. It is speculated that this metabolic effect of bGH plays an important role in the adaptive response to chronic bGH treatment, which increases milk yield of dairy cows and growth performance of beef cattle.

Effect of environmental temperature and dietary fat on growth and physiological responses of newborn calves

Effects of cold environmental temperature and supplemental dietary fat (energy) on growth rate and physiological responses of young dairy calves fed a milk replacer diet were studied. Thirty-six Holstein bull calves were randomly assigned to one of six treatments allotted in a 2(-4 degrees C or 10 degrees C) X 3(10, 17.5, or 25% dietary fat) factorial arrangement of treatments Calves began the experiment at an average of 6 d of age and received .6 kg dry milk replacer in 4 L of water daily for 3 wk. Average daily gains (kg/d) over the 3-wk trial for calves fed 10, 17.5, and 25% fat diets were-.04, .02, and .09 at -4 degrees C and .15, .22, and .20 at 10 degrees C. Gains were significantly lower for calves housed at -4 degrees C. Rectal temperatures were lower for calves at -4 degrees C than at 10 degrees C and for calves fed 10% versus 25% fat diet. Respiratory rates and water intakes were lower for calves housed at -4 degrees C but were not affected by diet. Concentrations of plasma glucose and prolactin were lower for calves housed at -4 degrees C while concentrations of plasma free fatty acids and growth hormone were not affected by temperature. Plasma free fatty acids were increased by dietary fat, and plasma growth hormone was reduced as dietary fat increased. Calves housed at -4 degrees C had higher maintenance energy requirements (.133 Mcal metabolizable energy/kg.75) than calves housed at 10 degrees C (.101 Mcal metabolizable energy/kg.75).(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma somatotropin response to exogenous growth hormone releasing factor in lambs

Two experiments were performed to examine the ability of human pancreatic growth hormone releasing factor (hGRF) administration to stimulate endogenous growth hormone (GH) secretion in lambs. Each study utilized eight Dorset wether lambs in replicated 4 X 4 Latin square experiments. Growth hormone response (integrated area under the curve for 150 min post-injection) for 0, 1, 5 and 10 micrograms hGRF/kg body weight averaged 13, 23, 92 and 134 units, respectively. While the 1-microgram hGRF dose was not different (P greater than .05) than the response to saline injection, there was an increased (P less than .01) GH response to 5 or 10 micrograms hGRF. Overall the GH response increased in a log dose-response fashion. There was distinct variation between lambs in their response to hGRF. Study II examined the optimal method to administer 40 micrograms hGRF/kg body weight to maximize GH concentration over 24 h. Continuous infusion (CI) was compared with eight (8X), four (4X), or two (2X) injections/d. Hourly blood samples were obtained from all lambs. Growth hormone response (area under the curve for 24 h) was 162, 305, 306 and 220 units for CI, 8X, 4X and 2X, respectively. Growth hormone response to CI was inferior to discrete injections, and the GH response to 4X or 8X was superior to 2X/d. Results demonstrate that, in spite of lamb-to-lamb variation, one can utilize exogenous hGRF to enhance GH secretion in lambs. Thus, the ability of exogenous hGRF to enhance growth performance merits further study.

Effect of number of conceptuses on maternal hormone concentrations in the pig

This study examined the effect of number of conceptuses on maternal concentrations and profiles of estrogen sulfate, estrone, estradiol-17 beta, progesterone and prolactin in gilts. Estradiol-valerate injections were used to induce pseudopregnancy (O conceptuses; n = 5) and oviduct ligation or no treatment were utilized to obtain pregnant gilts with 4 to 7 (n = 4), or 8 to 11 (n = 4) conceptuses, respectively. Blood samples were collected every 10 d from d 10 through 110 of pregnancy or pseudopregnancy. At 110 d after onset of estrus, all gilts were slaughtered and numbers and(or) weights of fetuses, corpora lutea, placentae and the empty uterus were determined. Concentrations of estrogen sulfate and estrone, but not progesterone or prolactin, were associated with fetal number, total fetal weight, total placental weight or empty uterine weight. In contrast, only progesterone was highly correlated with number of corpora lutea. Results suggest that most conjugated estrogen, estrone and estradiol were of fetal-placental origin, whereas little, if any, placental production of progesterone or prolactin occurred. Increases in estrogen sulfate and estrone concentrations were observed at gestation d 30 and from d 70 to 100. The latter increase coincides with previously established increases in the rate of maternal mammary development and fetal growth.

Ultrastructural changes in porcine mammary tissue during lactogenesis

Ultrastructural changes occurring in porcine mammary tissue were characterised between Day 90 of pregnancy and Day 4 of lactation. Porcine mammary tissue on Day 90 of pregnancy was composed of alveoli which contained negligible to moderate amounts of secretion. Epithelial cells of these alveoli were relatively undifferentiated. The appearance and distribution of cellular organelles suggested that mammary epithelial differentiation had been initiated by Day 105 of pregnancy in the pig. A further increase in intracellular lipid droplets and granular endoplasmic reticulum suggested that differentiation had progressed by Day 112. On the day of parturition, secretions within the alveolar lumina assumed the appearance of normal milk (as opposed to colostrum) and the epithelia displayed a distinct cellular polarity characteristic of lactating mammary tissue. By Day 4 of lactation, differentiation of epithelial cells appeared to be complete, with dilated cisternae of the granular endoplasmic reticulum and with numerous secretory vesicles. Elongated microvilli were present and numerous cells contained lipid droplets which were being extruded into the lumina. Data from this and previous studies indicate that lactogenesis in the pig occurs in two stages. Stage 1 occurs between Days 90 and 105 of pregnancy, and Stage 2 between Days 112 of pregnancy and early lactation when the predominant feature is active milk secretion.

Endocrine regulation of fetal and postnatal meat animal growth

Evidence is discussed which indicates that nutrient partitioning between muscle and adipose tissue can be altered by growth hormone administration in meat animals. In the limited number of studies conducted with meat animals, growth rate, feed efficiency and carcass composition were improved by growth hormone administration. When insulin was administered to normally growing swine no improvement in growth performance was observed. The mechanisms by which growth hormone affects growth performance are not clear but considerable data from rodent studies exist to indicate that many of the growth promoting effects of this hormone are due to somatomedins. However, few data are available for meat animals to indicate whether the growth promoting effects of growth hormone are mediated by somatomedins. Knowledge about the mechanisms that regulate growth hormone synthesis, secretion and biological action is accumulating. It is apparent that growth hormone administration induces an insulin-resistant state in rodents and meat animals. It is not clear whether chronic growth hormone administration in meat animals induces a growth hormone resistant state. Based on the available information, manipulation of systemic hormone concentrations and(or) tissue sensitivity to hormones involved in growth and differentiation may result in means to manipulate fetal and postnatal growth and development.

Nucleic acid, metabolic and histological changes in gilt mammary tissue during pregnancy and lactogenesis

Changes in mammary gland histology, dry weights, nucleic acids and in vitro rates of substrate oxidation in incorporation into lipid were measured in mammary biopsies of three gilts each on d 30, 45, 60, 75, 90, 105 and 112 of pregnancy, and d 1 and 4 of lactation. Histological changes noted were progressive duct growth early in pregnancy followed by rapid lobulo-alveolar development between d 75 and 90 to complete mammogenesis. Colostrum and lipid were evident by d 105 with marked distension of alveolar lumina on d 112. Complete differentiation of the secretory process was apparent on the day of parturition. Concentrtion of dry, fat-free tissue (DFFT) and DNA changed little before d 60 but increased fourfold between d 75 and 90. No further increases in DFFT or DNA were noted. RNA concentrations paralleled DNA through d 90, after which they steadily increased. Rates of acetate and glucose oxidation increased transiently during midpregnancy then declined and remained low until initiation of lactogenesis. Substrate incorporation into lipid increased slightly at midpregnancy and again at d 105, after which it increased markedly. Collectively, results indicate that mammogenesis is complete by d 90, after which lactogenesis is initiated in a two-stage process. Metabolic rates expressed on a DNA basis indicated considerable rates of oxidation, but not of lipogenesis by proliferating mammary tissue. Preferential metabolism of acetate vs glucose near parturition suggests coordination of metabolism between the mammary gland and other maternal tissues.

Season and treatment effects on serum prolactin and milk yield during induced lactation

Nineteen nonpregnant, nonlactating dairy cows were allotted to three treatments to induce lactation during winter, 1976, or spring, 1977. All groups received 17 beta-estradiol (.1 mg/kg) days 1 to 7. Groups 2 and 3 also received progesterone (.25 mg/kg) days 1 to 7. Groups 1 and 2 were given reserpine (5 mg intramuscular) on days 8, 10, 12, and 14. Group 3 received reserpine (5 mg intramuscular) on days 2, 5, 8, 11, and 14. Blood samples were collected for prolactin analysis just prior to and 3 h after reserpine injection. Mean daily temperatures were 11.9 C for spring group and -6.5 C for winter group. Comparisons of spring with winter for basal prolactin concentrations, reserpine-stimulated prolactin concentrations, and 100-day milk yields were 44 with 10 ng/ml, 482 with 199 ng/ml, and 1991 with 862 kg. Differences in prolactin concentrations and milk yields among hormone and reserpine treatments could not be detected, but cows on treatment 3 in the spring gave the largest yield of milk. Prolactin concentrations were correlated with milk yields among cows and among cows within seasons. Seasonal differences demonstrate the critical role of prolactin in the treatment to induce lactation.