Role of prolactin, growth hormone and insulin-like growth factor 1 in mammary gland involution in the dairy cow

Bovine mammary involution, an important process for subsequent lactations, is characterized by loss of epithelial cells by apoptosis, but its hormonal regulation is still not well defined. Prolactin (PRL) and growth hormone (GH) play a specific role on rat mammary gland apoptosis, through insulin-like growth factor 1 (IGF-1) and the IGF binding protein (IGFBP) system. The purpose of our investigation was to determine the possible role of PRL, GH, and IGF-1 on cell survival and on IGFBP-5 expression in the bovine mammary gland. Mammary gland explants were cultured in the presence of cortisol, 17beta-estradiol, progesterone, insulin, PRL, GH, and IGF-1 and with the same treatment but without PRL, GH or IGF-1, respectively. After 24 h of culture, we determined the level of apoptosis through evaluation of DNA laddering in the oligonucleosomal fraction and examined IGFBP-5 messenger RNA (mRNA) expression. The results show a high level of DNA laddering and an increase in IGFBP-5 mRNA content in mammary explants cultured in the absence of PRL, GH, or IGF-I with respect to explants treated with all hormones. Moreover, explants cultured in presence of PRL, GH, or IGF-I show a low level of DNA laddering and IGFBP-5 expression with respect to explants cultured without any hormones. These data demonstrate a relationship between levels of apoptosis and IGFBP-5 mRNA expression in the bovine mammary gland and confirm the involvement of this binding protein programmed cell death and its relationship with the main lactogenic hormones.     

Effects of genetic selection for milk yield on somatotropin, insulin-like growth factor-I, and placental lactogen in Holstein cows

Cows from static, low-merit control (CL) and contemporary, high-merit select (SL) lines that differed in milk yield by more than 4,000 kg/305-d lactation (SL > CL) were used to determine effects of selection for milk yield on blood serum concentrations of somatotropin (ST), insulin-like growth factor (IGF-I), and placental lactogen (PL). Cows were exposed to the same environment and management conditions and fed the same diets. Serum and milk samples were collected from primiparous (18 CL, 18 SL) and multiparous (12 CL, 18 SL) cows relative to day of lactation (from −28 to 280 d for nonpregnant cows and to subsequent calving for cows that conceived). Data were analyzed as repeated measures using mixed model procedures. Serum ST increased at calving, remained elevated for a longer interval in SL than in CL cows, and was greater in SL than in CL cows. Serum IGF-I decreased at calving, remained low through 14 DIM, and gradually returned to precalving concentrations as lactation progressed. Postpartum concentrations of IGF-I were less in SL than CL through 84 DIM and were similar through the remainder of lactation, resulting in a line by day interaction. Serum IGF-I and PL were not affected by merit during gestation. There was an interaction of merit and postconception interval on IGF-I, with the difference in IGF-I concentration between lines decreasing as gestation progressed. Change in serum IGF-I and PL appeared to be synchronous. Results indicate that selection for milk yield increased serum ST, prolonged the postpartum reduction in serum IGF-I, and did not alter serum PL. Results also indicate a positive relationship between PL and IGF-I and support the concept that PL plays a role in the regulation of serum IGF-I during gestation.     

Serum prolactin and growth hormone responses to thyrotropin releasing hormone in postpubertal cattle.

Serum prolactin increased 9 to 20 and growth hormone 2.5 to 4 times following administration of thyrotropin releasing hormone in 6 heifers during an estrous cycle, in 26 heifers during pregnancy, and in 16 cows during lactation. Stage of the estrous cycle or pregnancy did not affect quantity of prolactin or growth hormone released after administration of thyrotropin releasing hormone. There was a tendency for the quantity of prolactin released by thyrotropin releasing hormone to be greater at 2 mo than at 4, 6, 8, or 10 mo of lactation. During lactation, growth hormone release after thyrotropin releasing hormone was greatest at 2 mo. Prolactin release after thyrotropin releasing hormone was 6 to 16 times greater in summer than in spring or fall in pregnant heifers and approximately 3 times greater in spring, summer, and fall than during the winter in lactating cows. Season did not affect release of growth hormone after thyrotropin releasing hormone. Season of year more importantly affects capacity of the anterior pituitary to release prolactin than stages of the estrous cycle, pregnancy, or lactation. On the other hand, season does not affect induced release of growth hormone by thyrotropin releasing hormone. There is, however, an increased capacity of the anterior pituitary to release growth hormone during early lactation, coincident with maximal milk yield.     

Response of bovine serum prolactin and growth hormone to duodenal, abomasal, and oral administration of thyrotropin-releasing hormone.

Thyrotropin-releasing hormone was injected into the duodenum of two 500-kg steers, placed into the abomasum of two prepubertal bulls, and fed to four bull calves (1 to 3 wk of age) to test the effect on concentrations of prolactin and growth hormone in blood serum. Before 20 and 200 mg of thyrotropin-releasing hormone were injected into the duodenum, prolactin in serum averaged 7.5 and 9.4 ng/ml and increased to 52.5 and 129.6 ng/ml at 45 and 35 min after treatment. Average growth hormone concentration of serum was increased also, but the response was more variable than prolactin. Peak concentrations of prolactin and growth hormone in blood serum were 5 to 10 times greater after treatment with thyrotropin-releasing hormone (40 mg/100 kg body weight into abomasum) than before treatment. Within 30 min after oral administration of thyrotropin-releasing hormone (0, .5, 1, and 2 mg/kg body weight) growth hormone concentration of serum was 30, 306, 356, and 317% greater than pretreatment. Prolactin concentration of serum, however, was increased in only one calf.     

Arginine infusion stimulates prolactin, growth hormone, insulin, and subsequent lactation in pregnant dairy cows

L-Arginine or saline was administered intravenously by rapid infusion into 16 late-pregnant Holstein cows to study changes of prolactin, growth hormone, insulin, total protein, urea nitrogen, and subsequent lactation. Arginine was infused daily at .1 g/kg body weight starting about 7 days prior to predicted calving until calving. Blood was sampled via a jugular cannula at 0700, 0715, 0730 (infusion immediately followed 0730 h sample), 0745, 0815, 0845, 1100, 1300, 1500, 1700, and 1900 h. Arginine infusion evoked dramatic but transient increase of concentrations of blood serum prolactin, growth hormone, and insulin. Urea nitrogen also was elevated in blood serum but not total protein. The secretory response of prolactin, growth hormone, and insulin to daily arginine infusion during the entire prepartum period was not diminished. Milk production for the first 22 wk of lactation tended to be higher (by about 10%) for cows infused with arginine as compared to cows infused with saline. Therefore, repeated arginine infusion in late-pregnant cows dramatically increased prolactin, growth hormone, and insulin and tended to increase subsequent milk yield.     

Polymorphism in the bovine growth hormone gene affects endocrine release in dairy calves

The objective was to test whether calves with the Leu/Leu genotype release more growth hormone (GH) than calves with Leu/Val and Val/Val genotypes. Danish Holstein (n = 286), Danish Red (n = 68), and Danish Jersey (n = 61) calves were genotyped for the Leu/Val polymorphism in the GH gene and assessed for GH release following inducement by the growth hormone releasing hormone (GHRH). Three GH traits were assessed for each calf: BASELINE, PEAK, and RATE. BASELINE and PEAK are the mean concentration of GH in blood sampled before and after GHRH inducement. RATE is the disappearance rate of GH in blood sampled after GHRH inducement. Danish Jersey calves with Leu/Leu genotype had a higher PEAK and RATE than calves with the Val/Val genotype, whereas the Leu/Val genotype had an intermediate response. The contribution of the Leu/Val polymorphism to the total genetic variation of the BASELINE, PEAK, and RATE traits was 5, 30, and 27%, respectively. By contrast, the amount of GH released by the Danish Holstein and Danish Red calves was not influenced by their GH genotype. Further studies involving calves with all three genotypes are required to further elucidate whether this polymorphism has a functional role or whether it works through a linked-gene effect specific to certain cattle breeds.     

Milk yield, feed intake, prolactin, growth hormone, and glucocorticoid response of cows to supplemented light

Milk production and dry matter intake of 21 cows subjected to 16 h of fluorescent light and 8 h dark and of 21 cows subjected to natural light 9 to 12 h daily between October 25 and March 14 were measured beginning in early (37 to 74 days postpartum) and late (94 to 204 days postpartum) lactation. Cows that received 16 h of fluorescent light produced 6.7% (1.4 kg) more milk per day (adjusted for parity and pretreatment production) than cows exposed to natural photoperiods. Increases of milk production with 16 h of fluorescent light were similar for early and late lactation. Photoperiod did not alter percent of fat in milk. Dry matter intake increased 6.1% for cows in 16 h of light, and this increase could account for increased milk yields. Basal prolactin in serum and that released by thyrotropin releasing hormone were 1.5 to 1.8 times greater for cows exposed to 16 h of light than for cows in 9 to 12 h of natural light daily. Photoperiod did not affect release of prolactin by milking. Cold ambient temperatures reduced basal prolactin and prolactin released by thyrotropin releasing hormone but had no effect on concentrations of growth hormone or glucocorticoids. Compared with cows in late lactation, cows in early lactation released 2.4 times more prolactin after milking, but they released similar amounts of prolactin after thyrotropin releasing hormone. Photoperiod did not affect concentrations of growth hormone or glucocorticoids in blood sera.     

Genetic polymorphism of kappa‐casein,growth hormone and prolactin genes in Turkish native cattle breeds

A total of 259 cattle of four Turkish native cattle breeds, East Anatolian Red (EAR), South Anatolian Red (SAR), Turkish Grey (TG) and Anatolian Black (AB), Holstein and Brown Swiss (BS) breeds were genotyped for kappa‐casein (CSN3), bovine growth hormone (GH1) and prolactin (PRL) polymorphism by the polymerase chain reaction and restriction length polymorphism (PCR‐RFLP). The degree of genetic differentiation between populations F_ST was calculated as 0.053 and was found to be significant (P < 0.001). According to the genetic distance values (Nei), the highest genetic difference was found between SAR and EAR in four Turkish native cattle breeds and this difference was significant.     

Changes in concentrations of insulin-like growth factor 1, insulin and growth hormone in bovine mammary gland secretion ante and post partum

Concentrations of insulin-like growth factor 1 (IGF-1), insulin and growth hormone were measured in the secretion of the bovine mammary gland from day 70 ante partum until 6 d post partum. Highest levels were found during the last 2 weeks ante partum followed by a rapid decrease during the first milkings post partum. The association of IGF-1 with its binding proteins in milk was analysed and striking differences were found in the distribution of bound and free IGF-1. IGF-1 appeared mainly in the bound form (91%) at days 40-2 ante partum. Free IGF-1 preponderated in the first milkings post partum (73%) and changed again to about 85% in the bound form after day 4 post partum. A slightly acidic pH (6.3) of the secretion was correlated with high amounts of free IGF-1. Gel filtration experiments revealed a possible pH-dependent mechanism for the binding of IGF-1 to its binding proteins in milk.     

Effect of dry period management on mammary gland function and its endocrine regulation in dairy cows

The objective of this study was to evaluate the effect of shortening the dry period on the mammary gland and the hormonal regulation of its functions. Holstein cows (n = 18) were assigned to a short dry period (SDP; 35 d; n = 9) or a conventional dry period (CDP; 65 d; n = 9). All cows were fed the same diets, with the exception that, during the dry period, the SDP cows received only the pre-calving diet for 35 d, whereas the CDP cows were fed a high-fiber diet from 65 to 28 d before calving and then received the same pre-calving diet as the SDP cows. Mammary gland functional capacity was evaluated at 70 days in milk, and mammary biopsies were taken in early and midlactation. Dry period length averaged 64.3 ± 1.1 and 31.9 ± 1.0 d for the CDP and SDP cows, respectively. The SDP cows had a lower milk yield and a lower energy-corrected milk yield compared with the CDP cows. The SDP cows also had a lower dry matter intake from wk 5 to 20 of lactation and tended to have lower plasma concentrations of β-hydroxybutyrate from wk 1 to 4. Prepartum serum progesterone and estradiol concentrations were unaffected by the dry period management. Serum growth hormone concentrations and milking-induced prolactin release were similar in both groups. However, during the period when the CDP cows were dry but the SDP cows were still being milked (wk −9 to −6), serum prolactin concentrations were higher in the SDP cows than in the CDP cows. The SDP cows had a lower milk BSA content than the CDP cows after the dry period and similar milk lactose concentrations, suggesting that their mammary tight junctions were closed following parturition and, therefore, that the later stage of their lactogenesis was not impaired by SDP management. In early and midlactation, mammary cell apoptosis and proliferation rates as well as mammary expression of genes involved in the function of this tissue were unaffected by the dry period management strategy. For cows in their second lactation, mammary gland functional capacity at 70 d in milk tended to be lower in the SDP cows. In conclusion, even though SDP management decreased milk production during the subsequent lactation, it did not affect mammary cell activity. Although direct evidence is still lacking, decreased mammary cell growth during the dry period is likely responsible for this negative effect. The higher prolactin concentrations in lactating cows during late gestation could be involved in this effect. More research is needed to test these hypotheses.     

Stimulation of milk yield and feed intake by bovine placental lactogen in the dairy cow.

A 6 x 6 Latin square design was used to test the effects of recombinant bovine placental lactogen on milk yield, milk composition, feed intake, and blood hormone and metabolite levels in nonpregnant lactating cows. The six treatments (5, 10, 20, and 40 mg/d of placental lactogen, water as negative control, and 20 mg/d of bST as positive control) were administered by subcutaneous injection twice daily for 9 d. Blood samples were taken during the last 5 d of the treatment period. The three highest doses of placental lactogen increased milk yield, and there was a linear dose effect, although placental lactogen was less potent than bST. Milk concentrations of lactose, protein, and fat were not altered by any of the treatments. Dry matter intake was increased by two of the doses of placental lactogen, but not by bST. Blood urea N concentration was decreased in a dose-dependent manner by placental lactogen and was also decreased by bST. Similarly, serum insulin-like growth factor-I was increased in a dose-dependent manner by placental lactogen and was also increased by bST. Plasma concentrations of NEFA and glucose were increased by bST, but placental lactogen had little or no effect on either of these parameters. Thus, placental lactogen appears to act, in part, as a weak somatotropin agonist; however, it also appears to have specific activities, e.g., stimulating feed intake.     

Influence of amount fed on hormone concentrations and their relationship to mammary growth in heifers

Concentrations in blood serum of growth hormones, prolactin, insulin, and glucocorticoids were investigated in 22 pre- or postpubertal heifers fed restricted or ad libitum amounts of a ration. Gains for the respective feeding regimens were 613 and 1218 g daily. Growth hormone was elevated for prepubertal heifers on restricted feed, whereas there was no difference from feeding for postpubertal heifers. Concentrations of prolactin, insulin, and glucocorticoids were higher for heifers fed ad libitum than for those restricted. Mammary secretory tissue was positively correlated with blood serum concentrations of growth hormone, and extraparenchymal adipose tissue was negatively correlated with them. Prolactin was negatively related to mammary secretory tissue; however, this relationship disappeared after adjustment for concentrations of growth hormone, insulin, and glucocorticoids. Mammary tissue was not related to concentrations of insulin or glucocorticoids. The negative influence of excess feeding on mammary development of prepubertal heifers may be associated with a decrease in concentrations of growth hormone in blood.     

奶山羊乳腺中胰岛素样生长因子及其受体的表达与作用

为研究胰岛素样生长因子及胰岛素样生长因子受体在奶山羊乳腺组织青春期、妊娠期、泌乳期及退化期表达的差异及变化,探索其在奶山羊乳腺发育过程中的作用,根据奶山羊乳腺发育特点及生长阶段不同分为青春期、妊娠期、泌乳期及退化期,采用激光共聚焦显微镜检测胰岛素样生长因子在奶山羊乳腺各生长阶段的表达及定位,通过定量分析来比较胰岛素样生长因子在奶山羊乳腺各生长阶段表达的差异,描述其在奶山羊乳腺发育过程中的作用.结果显示:胰岛素样生长因子及胰岛素样生长因子受体在奶山羊乳腺法如各时期均有表达,表达水平与乳腺发育密切相关.