Hormonal control of mammogenesis and onset of lactation in cows--a review

The association between calf birth weight and the postcalving performance of its dairy dam in the absence of dystocia

The objective of the study was to quantify the association between the birth weight of a calf and the subsequent performance of its dairy dam in the absence of any recorded calving assistance. A total of 11,592 lactation records from 4,549 spring-calving dairy cows were used. The association between a series of quantitative cow performance metrics (dependent variable) and calf birth weight (independent variable) was determined using linear mixed models; logistic regression was used where the dependent variable was binary. Nuisance factors in the models were calf sex, heterosis coefficient of both the cow and calf, dry period length immediately before the birth of the calf, cow age at calving relative to the median cow age per parity, breed proportion of the cow, cow live weight between 100 and 200 d of lactation relative to the mean cow weight per parity, and contemporary group. Calf birth weight was included in the model as either a continuous or a categorical variable. Primiparous and multiparous cows were analyzed separately. Mean (SD) calf birth weight was 36.2 (6.8) kg. In primiparous cows, calf birth weight was associated with milk yield in the first 60 d of lactation, calving to first service interval, calving body weight (BW), and both nadir BW and body condition score (BCS). In multiparous cows, calf birth weight was associated with total milk, fat, and protein yield in the first 60 and 305 d of lactation, peak milk yield, total milk solids, both calving and nadir BW, and BCS loss from calving to nadir. Relative to primiparous cows that gave birth to calves weighing 34 to 37 kg (i.e., population mean), their contemporaries who gave birth to calves that weighed 15 to 29 kg produced 9.82 kg more milk in the first 60 d of lactation, had a 2-d shorter interval to first service, and were 8.08 kg and 5.51 kg lighter at calving and nadir BW, respectively; the former was also 0.05 units lower in BCS (5-point scale, 1 = emaciated and 5 = obese) at nadir. Relative to multiparous cows that gave birth to calves that were 34 to 37 kg birth weight, multiparous cows that gave birth to calves that were 15 to 29 kg yielded 59.63 kg, 2.44 kg, and 1.76 kg less milk, fat, and protein, respectively, in the first 60 d of lactation; produced 17.69 kg less milk solids throughout the 305-d lactation; and were also 10.49 kg lighter at nadir and lost 0.01 units more BCS to nadir. In a separate series of analyses, sire breed was added to the model as a fixed effect with and without calf birth weight. When calf birth weight was not adjusted for, 60-d milk yield for multiparous cows who gave birth to calves sired by a traditional beef breed (i.e., Angus, Hereford) produced 59.63 kg more milk than multiparous cows who gave birth to calves sired by a Holstein-Friesian. Hence, calf birth weight is associated with some subsequent dam performance measures; however, where associations do exist, the effect is biologically small.

INVITED REVIEW: Nutritional and management factors that influence colostrum production and composition in dairy cows

Colostrum is a rich source of nutritional and non-nutritional components and is recognized as essential to transfer passive immunity to newborn calves. Because of the individual and seasonal variability in colostrum yield and composition, maintaining an adequate supply of high-quality colostrum year-round remains a challenge for commercial dairy producers. In this narrative review, we described the individual, seasonal, and herd-level variability of colostrum production and summarized the association between individual animal factors such as parity, sex of the calf, calf birth weight, as well as indicators of the cow's metabolic status and the yield and composition of colostrum. Further, we reviewed the current knowledge on the influence of prepartum nutrition and management strategies on colostrum production. Research on the metabolizable energy and protein supplied in the prepartum diet as well as into the inclusion and source of vitamins, minerals, and feed additives suggests prepartum nutrition influences the yield, quality, and composition of colostrum. Furthermore, the prepartum environment and dry period length remain influential factors in the production of colostrum. However, additional research is needed to understand the mechanisms by which prepartum nutrition and management affects colostrum production. Lastly, time to colostrum harvest and oxytocin administration as well as the current knowledge on the effect of heat-treatment and colostrum storage strategies on colostral components were discussed. To conclude, we identify critical gaps in knowledge for future focus of investigation in colostrum research.

Parity predicts allonursing in a cooperative breeder

In some mammals that breed cooperatively, nonbreeding female helpers nurse offspring born to the breeding female in their group, a process known as allonursing. Previous laboratory studies have suggested that primiparous and multiparous females (those that have successfully given birth once or more, respectively) are more likely to contribute to allonursing than nulliparous females (those that have not given birth). In contrast, few field studies have been able to demonstrate whether breeding experience, or parity, affects the likelihood or duration of allonursing. In this study, we investigated whether the likelihood and duration of allonursing by subordinate female meerkats (Suricata suricatta) were associated with variations in their parity (number of pregnancies reaching a viable gestational age) and their immediate pregnancy status. Comparisons showed that nonpregnant nulliparous females were less likely to allonurse than nonpregnant primiparous and multiparous females, although parity was not related to variation in allonursing duration. Parity may enhance the expression of maternal behavior when exposed to foster pups, especially since mammary gland development has been shown to be directly associated with parity in other mammals.

Suppression of ovarian secretions before puberty strongly affects mammogenesis in the goat

The objective of this study was to provide insight into the biological mechanisms underlying mammary development and the role of the ovaries in prepubertal caprine mammogenesis using a serial ovariectomy approach. Young Alpine goats were ovariectomized (Ovx) or sham-operated (Int) at three periods before puberty (G1=1 month, G2=2 month and G3=3 months of age) and one after puberty (G7=7 months of age). The goats were slaughtered at 9 months of age and mammary glands were removed. Ovariectomy performed at 1, 2 and 3 months of age caused a 50% reduction in DNA concentration, in mammary tissue taken from the parenchyma-stroma border region. Morphological analysis of mammary tissue sections indicated that the parenchymal structures of Ovx goats were negatively affected by ovariectomy. Goats ovariectomized before 2 months of age (Ovx-1 and Ovx-2) showed a significant decrease in the percent of cells proliferating in mammary glands of 9-month old goats (proliferating cell nuclear antigen expression and antigen Ki67-positive cell number). Also, goats ovariectomized at 1 and 2 months of age had reduced matrix metalloprotease 2 activity at 9 months of age. E-cadherin was strongly decreased in goats ovariectomized before 2 months of age (80 and 85% in Ovx-1 and Ovx-2 goats, respectively). Quantitative PCR analysis of transcripts encoding for oestrogen (ERα) and progesterone receptors (PR) and immunodetection of ERα showed that ovariectomy at 1 and 2 months of age strongly inhibited the transcription of ERα and PR in the mammary gland. We conclude that ovariectomy before 3 months of age markedly impaired parenchymal development. These findings suggest that prepubertal mammogenesis in goats depends on the ovaries to initiate mammary epithelial cell proliferation and mammary gland remodelling.

Udder development, lactation and ascites in a ewe with an ovarian granulosa cell tumour

A 20-month-old sexually intact female mixed breed sheep was examined for lameness, unexpected udder development, lactation and anorexia. Tachycardia, tachypnoea, severe abdominal distension and vaginal prolapse were evident upon physical examination. A right hindlimb lameness was present at the walk. The udder was well-developed and milk, normal in appearance, was easily expressed from each teat. Ultrasonographic evaluation revealed a non-pregnant uterus, severe ascites and a large (12 cm diameter) abdominal mass. Although surgical treatment was discussed, the owners elected to euthanase the ewe. Necropsy examination confirmed the presence of severe ascites due to a ruptured ovarian tumour. The tumour was characterised as a granulosa cell tumour histologically. Unexpected udder development and lactation presumably occurred secondary to oestrogen and progesterone production by the tumour. To the authors' knowledge, this is the first report of udder development, lactation and ascites in a ewe secondary to an ovarian granulosa cell tumour.

Postpartum acyclicity in suckled beef cows: a review

Prolonged postpartum acyclicity in suckled beef cows is a source of economic loss to beef cattle producers. Duration of postpartum acyclicity is influenced by suckling status, nutritional status, calving season, age, and several other factors. Although uterine involution begins and ovarian follicular waves resume soon after parturition, dominant follicles of these waves fail to ovulate, due to a failure to undergo terminal maturation. As a result, postpartum anovulatory dominant follicles are smaller than the ovulatory follicles in cyclic cows. Failure of postpartum dominant follicles to undergo terminal maturation is due to absence of appropriate LH pulses, a prerequisite for follicular terminal maturation prior to ovulation. Absence of LH pulses early post partum is primarily due to depletion of anterior pituitary LH stores, although GnRH pulses are also absent during this period due to suckling. Following replenishment of LH stores between Days 15 and 30 post partum, absence of LH pulses is due to continued sensitivity of the hypothalamic GnRH pulse-generator to the negative feedback effect of ovarian estradiol-17beta, which results in absence of GnRH pulses. This negative feedback effect of estradiol-17beta is modulated by suckling which stimulates release of endogenous opioid peptides from the hypothalamus. As the postpartum interval increases, sensitivity of the GnRH pulse-generator to the negative feedback effect of ovarian estradiol-17beta decreases. This is followed by an increasing frequency of GnRH discharges and LH pulses, terminal follicular maturation, ovulation, and continued cyclicity. The first ovulation post partum is usually followed by a short cycle due to premature luteolysis because of premature release of PGF2alpha from the uterine endometrium, which is possibly intensified by the suckling-induced oxytocin release from the posterior pituitary. A model for the postpartum ovulatory acyclicity and for the resumption of cyclicity is presented.

Dietary fatty acids modulate hormone responses in lactating cows: mechanistic role for 5'-deiodinase activity in tissue

Supplemental dietary fat provides excess fatty acids (FA), which can alter circulating concentrations of several hormones. To test the effects of fatty acid isomer type and possible sites of regulation, we abomasally infused fat mixtures high in cis-C18:1 FA (iCIS), high in trans-C18:1 FA (iTRS) or no infusion (NI) and performed intravenous arginine (ARG) and intramuscular thyrotropin-releasing hormone (TRH) challenges. The experimental design was a replicated 3 x 3 Latin square. Challenges were conducted on Days 10 (ARG) and 12 (TRH) after initiation of fat infusion on each of three 4-wk experimental periods. Plasma concentrations of IGF-I were lower (P < 0.01) when cows received iCIS or iTRS compared with NI. Plasma insulin concentrations increased with ARG but responses were not affected by FA. Plasma growth hormone (GH) was unchanged after ARG. Peak plasma GH and thyroid-stimulating hormone (TSH) responses to TRH were blunted (P < 0.05 and P < 0.1, respectively), whereas thyroxine (T4) and triiodothyronine (T3) responses were augmented post-TRH (P < 0.01) when cows received either FA isomer. Prolactin responses to TRH were not different between infusion treatments, although basal plasma concentrations before TRH were higher in cows infused with iTRS (P < 0.05). To focus on fat regulation of the thyroid axis, we tested directly in vitro the ability of fatty acids dissolved with sodium taurocholate to affect Type-I 5'-deiodinase (5'D) activity in bovine liver homogenates. Homogenate 5'D was not affected by C2:0-C10:0 fatty acids, but decreased linearly (P < 0.01) with increasing concentrations of C12:0-C16:0 and C18:1 isomers. Cis C18:1 decreased 5'D more than the trans-isomer (P < 0.01), but the difference was only apparent at concentrations greater than 0.25 mM. The data suggest that various aspects of pituitary hormone regulation are differentially affected by FA composition. Fatty acid infusion may accentuate end organ responses in the thyroid axis and decrease IGF-I in the somatotropic axis. The data also suggest that FA isomer may alter patterns of extrathyroidal generation of thyroid hormones via direct influences on 5'D.

Dry cow nutrition. The key to improving fresh cow performance

Evidence supports the concept of the dry period being a critical component to lactation preparation rather than an insignificant rest period between lactations. Required nutrient amounts for the dry cow are the sum of maintenance, pregnancy, and reserve replenishment needs with additional requirements for growth during the first two pregnancies. Maintenance energy requirements can be dramatically increased by level of activity and adverse environmental conditions. A wide variety of feed ingredients can be successfully fed to dry cows as long as rations are appropriately formulated to meet energy, protein, mineral, and vitamin requirements. A early and close-up dry program best matches increasing pregnancy requirements and declining intake capacity with management capabilities. The early dry cow ration is formulated for high fiber/low energy density while the close-up ration contains higher energy density with less fiber. Both rations contain sufficient other nutrients based on determined intake. This two-group system provides maximal flexibility in managing for optimum body condition at calving. Environmental stresses and dramatic dietary changes should be minimized during the transition period from late gestation to lactation. A sound dry cow program results from integration of quality nutrition and cow management practices as described. A dry cow program that enacts these guidelines should result in reduced incidence of clinical mastitis, successfully complete pregnancy with a viable calf, maximize genetic potential for milk production, minimize incidence of health disorders, and allows cows to breed back within an economically optimum time interval. Overall, a sound dry cow program is a critical key to improved fresh cow performance.

Approaches to the manipulation of mammary involution

Mammary involution is a gradual process that occurs following cessation of milking. Regression of mammary secretory tissue accompanies dramatic changes in secretion composition during the transition from lactation to involution. Conversely, rapid differentiation of secretory tissue and copious accumulation of colostrum occur as parturition approaches. The duration of the nonlactating period, mammary gland health, and secretory cell response to hormones influence subsequent lactational performance in most species. Manipulation of the bovine mammary gland in an attempt to hasten involution has been studied. The primary objective of these studies was to determine if hastened involution would decrease new intramammary infections during the early nonlactating period. Results of these studies have also led to a more fundamental understanding of events that occur during physiological transition of the mammary gland. Adequate regression, proliferation, and differentiation of mammary secretory epithelium during the nonlactating period of ruminants appear to be essential for maximal milk production during lactation. Factors that interfere with these mechanisms can adversely affect mammary function during the impending lactation. A greater understanding of these processes may provide new approaches for increasing milk production in dairy cattle.

Teat stimulation-induced release of prolactin and basal concentrations of prolactin and growth hormone in pregnant dairy and beef heifers

The physiological bases for differences in milk production between breeds of cattle selected for beef or milk production are largely unknown. This study was conducted to determine concentrations of prolactin (PRL) and growth hormone (GH) in serum before and after teat stimulation in primiparous Hereford and Holstein heifers. Blood was collected from 6 beef and 9 dairy heifers at 115, 175, 230 and 250 d of gestation. Sampling times were -15, -10, -5, 0, 2, 4, 6, 8, 10, 12, 15, 20, 25 and 30 min relative to test stimulation. Mean areas under PRL response curves for beef and dairy heifers at 115, 175, 230 and 250 d of gestation were 427, 447, 556, 273 and 243, 189, 167, 343 ng/ml/30 min, respectively. Calculations of area (but not basal levels) excluded instances when no PRL response to test stimulation was obtained (22%). Neither stage of gestation nor breed affected PRL response. Basal PRL did not differ between breeds and was 1.8, 2.6, 2.4 and 9.2 ng/ml at 115, 175, 230 and 250 d of gestation. GH did not differ between breeds and was 6.6, 6.2, 5.5 and 7.4 ng/ml at 115, 175, 230 and 250 d. No difference between breeds was apparent with regard to PRL or GH secretion during first gestation.

Influence of recombinant deoxyribonucleic acid-derived bovine growth hormone on alpha-lactalbumin production by bovine mammary tissue maintained in athymic nude mice

Mammary tissue from five cows was cut into pieces approximately 3 mm2 x .2 mm and placed subcutaneously in athymic mice (10 to 12 pieces/mouse). After 30 d, all mice were injected for 10 d with 17 beta-estradiol (1 microgram), progesterone (1 mg), ovine prolactin (1 mg), and growth hormone (recombinant DNA-derived bovine) (1 mg). Four grafts were then removed from each mouse, mice were ovariectomized, and subsequently mice were injected daily for 7 d with hydrocortisone (.2 mg, all mice), growth hormone (0, .25, .5, or 1.0 mg), and 0 or .5 mg ovine prolactin (three mice/treatment per udder). alpha-Lactalbumin content of grafts was 36 +/- 9 micrograms/mg DNA after treatment with estradiol, progesterone, growth hormone, and prolactin but before hydrocortisone, prolactin, and growth hormone treatment. Hydrocortisone treatment increased alpha-lactalbumin to 147 micrograms/mg DNA. Growth hormone plus hydrocortisone treatment increased alpha-lactalbumin to 391, 451, and 480 micrograms/mg DNA for .25, .5, and 1.0 mg/d of growth hormone, respectively. Prolactin plus hydrocortisone treatment increased alpha-lactalbumin to 466 micrograms/mg DNA. With exogenous prolactin, growth hormone increased alpha-lactalbumin content of grafts to 581, 647, and 689 micrograms/mg DNA for .25, .5, and 1.0 mg/d of growth hormone, respectively. Histological examination of tissues indicated that the effect of growth hormone was not mediated through increased epithelial area. Data suggest that bovine mammary tissue is capable of organotypic differentiation in athymic mice.

Induction of lactation: histological and biochemical development of mammary tissue and milk yields of cows injected with estradiol-17 beta and progesterone for 21 days

Lactations were induced in nonpregnant, nonlactating dairy cows by subcutaneous injections of estradiol-17 beta and progesterone for 21 d (.10 and .25 mg/kg body weight/d) and dexamethasone (.028 mg/kg body weight/d) on d 31 to 34. Milking was initiated on d 35. Each cow was biopsied two or three times during the experiment with five to eight mammary tissue biopsies on d 0, 7, 14, 21, 28, 35, 49, and 130. Mammary tissue preinjection had abundant connective and adipose tissues with limited lobuloalveolar structures. Beginning on d 7, there was decreased stroma, increased epithelial cell area, increased lobuloalveolar architecture, plus the accumulation of intracellular and intraluminal secretions which were high in lipid droplets. From d 7 through 35, these changes were progressive although variable among cows. Changes in activities of enzymes and concentrations of ribonucleic acid and deoxyribonucleic acid were gradual during this time but essentially paralleled histological development. Tissue samples during lactation (d 49 and 130) showed increased histological and biochemical development; development was maximal for d 130 samples. Fourteen of 15 cows that lactated had mean daily yields of milk more than 5 kg and yields of milk of 12 cows with projected or actual 305-d lactations were 63.0% of that during their previous natural lactations. Reasons for less yields of milk and for varied patterns of tissue development were not identified nor explained by concentrations of several selected hormones in plasma.

Artificial induction of lactation in cattle: initiation of lactation and estrogen and progesterone concentrations in milk

Thirty heifers were given 11 subcutaneous injections of 5 mg estradiol benzoate and 200 mg progesterone every 3 d to develop their mammary glands. Three days later groups of animals were treated with 1) 20 mg dexamethasone twice, 2) 500 micrograms cloprostenol thrice, 3) dexamethasone and cloprostenol, 4) oxytocin 4 IU six times, or 5) no further injections. Two further groups of six heifers each (6 and 7) were treated in a manner similar to groups 1 and 3 except the dose of estrogen to develop their mammary glands was doubled to 10 mg/3 d. Six lactating first calf heifers were controls (8). The proportion of animals lactating, combined milk yield for each group (kg), and mean days lactated were 1) 5/6, 3831, 142; 2) 1/6, 912, 195; 3) 6/6, 4898, 194; 4) 3/6, 1066, 128; 5) 1/6, 293, 154; 6) 6/6, 6109, 130; 7) 6/6, 6265, 130; and 8) 6/6, 19, 190, 251. The lactogenic response to dexamethasone and oxytocin is similar to that in sheep, but the response to cloprostenol indicates a species difference. Intensive blood sampling before and after injection of hormones, intended to trigger lactogenesis, showed that plasma prolactin rose to peaks above 210 ng/ml in cows of groups 2, 3, and 4 and were unchanged from the base below 40 ng/ml in groups 1 and 5. Monitoring of steroids after induction treatment showed estradiol-17 beta ranged between 35 and 400 pg/ml and 20 to 80 pg/ml in mammary secretion and plasma and progesterone concentrations were less than at diestrus.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth and biochemical changes in mammary glands of ewes from 1 to 18 months of age

Growth and development of the mammary gland of ewe lambs was characterized by changes of various biochemical constituents. Mammary glands were removed from 49 ewe lambs ranging between 1 and 18 mo of age, weighed before and after trimming, and samples of the trimmed glands were fat extracted and dried. The dried fat-free tissues were weighed, ground, and analyzed for nucleic acids, nitrogen, sodium, potassium, and chloride contents. Fresh samples were used for glycogen determination. Trimmed weight of mammary glands increased rapidly after the 9th mo of age. The pattern was similar for nucleic acid content of mammary glands. Dry matter and fat contents of mammary glands increased up to the 9th mo, fat decreased thereafter, and dry matter remained constant. Protein content was low up to the 9th mo and increased thereafter. Sodium and glycogen content in mammary glands increased, but potassium decreased linearly from 1 to 18 mo of age. Allometric growth of mammary tissue started at about 3 mo of age, before onset of puberty at 8 mo of age, but intense mammary metabolic activity started only after the ewe attained puberty.

Lactogenic hormones: binding sites, mammary growth, secretory cell differentiation, and milk biosynthesis in ruminants

Roles of the lactogenic hormones prolactin and placental lactogen in mammary development in ruminants were reviewed. In contrast with other ruminants, failure to detect lactogenic activity in the serum of pregnant cows (in excess of that attributed to prolactin) suggests that placental lactogen may have little direct effect on mammary growth or lactogenesis. However, replacement and ablation experiments using ergocryptine provide definitive evidence that increased periparturient secretion of prolactin is necessary for maximal milk production in cattle. Quantitative microscopy indicates a relative failure of mammary cells in cows with inhibited secretion of prolactin to differentiate structurally. Prolactin induces synthesis and secretion of alpha-lactalbumin in prepartum bovine mammary tissue. Temporary disruption of mammary microtubules immediately prepartum in pregnant heifers reduced subsequent milk production, biosynthetic capacity, and cellular differentiation. For maximal milk production, mammary secretory cells apparently must respond to lactogenic hormone stimulation during the immediate periparturient period. Colchicine may desensitize the mammary epithelium to prolactin action. Membrane binding of radiolabeled human growth hormone to ruminant mammary gland provides a measure of lactogenic hormone binding sites. Specific binding to 600 micrograms of mammary membrane protein was 296% greater in lactating, compared with nonlactating, pregnant (65 days of gestation) ewes. Binding capacity (fmol/mg membrane protein) averaged 275 +/- 57 in mammary membranes from nonlactating, pregnant ewes (100 days gestation, n = 2) and 2,325 +/- 521 in mammary membranes from lactating ewes (n = 6, 14 to 21 days postpartum). Greater understanding of hormonal regulation of the ruminant mammary gland likely will result in development of techniques to produce milk more efficiently and perhaps capability to evaluate production potential of young animals.

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.

Radioimmunoassay of cortisol in peripheral blood plasma of buffaloes peripartum

Changes in the concentration of cortisol were observed in the jugular venous plasma of pregnant buffaloes on days 30, 15, 5, 2 and 1 prepartum, at partum, at regular 6-hr intervals up to 72 hr postpartum and on days 4, 6, 10, 18, 34 and 50 postpartum. A radioimmunoassay (RIA) procedure for cortisol standardized in the laboratory was used. Mean plasma cortisol levels showed little fluctuation (P<0.05) between days 30 and 2 prepartum with the values ranging from 1.28 +/- 0.23 to 1.46 +/- 0.13ng/ml. A small (but nonsignificant) rise in the hormone level was observed one day prepartum followed by a sharp increase to a high mean value of 3.78+/-0.36 ng/ml (P<0.05) at parturition. A sharp decline (P<0.05) to a low mean value was recorded within 6 hr postpartum followed by marked fluctuations in the hormone level up to 72 hr postpartum. The hormone levels subsequently varied narrowly between 1.74+/-0.39 and 2.01+/-0.27 ng/ml up to 50 days postpartum.

Influence of prepartum dietary crude protein on growth hormone, insulin, reproduction, and lactation of dairy cows

Effects of prepartum dietary crude protein on growth hormone, insulin in blood plasma, and subsequent reproduction and lactation were investigated in 30 Holsteins. Cows were fed either 80 or 100% of the crude protein recommended by National Research Council starting about 60 days precalving. Postcalving all animals were fed according to recommendations. Blood was sampled on days 220 (start of experiment), 250, 270, and 280 of gestation and on days 10 and 30 postpartum. Cows fed 80% crude protein prepartum showed decreased intake of dry matter and urea nitrogen in blood plasma prepartum, and yields of milk and total solids decreased by about 15%. Body weight changes through 30 days postpartum were not significantly different between treatments. There were no significant differences for growth hormone and insulin except growth hormone tended to be higher on day 270 of gestation for cows fed 80% crude protein. Insulin was negatively correlated with lactation number -5.1 to -5.6. Reproductive efficiency was similar between treatment groups. Lower crude protein intake during the dry period decreased dry matter intake and yields of milk and total solids.

Induction of lactation in nonpregnant cows by estradiol-17 beta and progesterone from an intravaginal sponge

An intravaginal sponge impregnated with 500 mg estradiol-17 beta and 1000 mg progesterone to induce lactation in nonpregnant dairy cattle was investigated. Sponge retention (greater than 95%) was achieved by its attachment to a nylon collar. Treatment with the sponge for 10 days resulted in lactogenesis in 25% of treated cows compared with an 89% success rate when an adjunct injection of dexamethasone esters (20 mg intramuscular) was given on day 6 or a 96% success rate when reserpine injections (2.5 mg intramuscular) were given on days 6, 8, and 10 10 after sponge insertion. Milking was begun 12 days after sponge insertion (2 days after removal). Peak milk yield was unaffected by adjunct treatments but was greater in spring (mean 11.5 kg/day) than in autumn treated cows (mean 3 and 6 kg/day) in 2 yr of trials. Concentration of estradiol-17 beta in plasma rose rapidly after sponge insertion to a peak similar to that in cows in late pregnancy. Measurement of estradiol-17 beta concentration in milk indicated less, even at first milking than in commercially distributed pasteurized milk. Milk fat and protein content were higher in milk from induced lactations compared with that from normally calving cows on the same day.

Factors associated with edema of the mammary gland in primigravid dairy heifers

The severity and anatomical extent of mammary edema (edema) of 73 primigravid Holstein heifers was scored, and certain hormones in peripheral blood plasma were quantified. The objective was to obtain by least-squares analysis of covariance independent estimates of the association of each hormone and other factors with edema scores around first calving. Mammary edema prepartum increased with age of heifer and gestation length, decreased as calf birthweight increased, but was unrelated to seasonal fluctuations in temperature and photoperiod. The increase in edema during the last week of pregnancy was accounted for by associations with prepartum concentrations of hormones in plasma. The independent estimates of hormonal relationships to edema score prepartum were positive for plasma estrone and estradiol-17 alpha and were negative for plasma estradiol-17 beta and progesterone. Plasma prolactin was not related to edema score. After parturition, estradiol-17 beta was the only independent variable associated (negatively) with edema. The results indicate a complicated interaction among the sex steroids of late pregnancy wherein some steroids may promote edema and other steroids may inhibit edema in heifers.

Induction of lactation: comparison of injections of estradiol-17 beta and progesterone for 7 or 21 days on prolactin response to thyrotropin releasing hormone and milk yield in dairy cattle

Subcutaneous injections of estradiol-17 beta and progesterone (.10 and .25 mg/kg of body weight) for 7 (group I) or 21 (II) days were used. Dexamethasone (.028 mg/kg of body weight per day) or adrenocorticotropin (200 IU per day) was injected into cows in each group on days 18 to 20 (I) or 32 to 34 (II). Additionally, 100 mug of thyrotropin releasing hormone was injected intravenously on days 1, 7, 17 (I) or 1, 7, and 31 (II). Milking was initiated on days 21 (I) or 35 (II). Overall 13 of 14 cows had mean daily yields of milk greater than 5 kg; 12 had 305-day lactations. Yields of milk in cows injected for 21 days were greater on day 1 and increased more rapidly until peak was reached at 10 wk; daily mean production throughout lactation was greater (14.3 versus 10.1 kg) than for cows injected for 7 days. Lactation curves pooled within cow within treatment differed. Concentrations of estradiol, estrone and progesterone increased during steroid injections and were 2- to 3-fold higher on day 21 in II than on day 7 (I or II), but concentrations of prolactin and total glucocorticoids in plasma did not differ during this time. The quantity of prolactin released in response to injection of thyrotropin releasing hormone was greater 10 days after steroid injections than before or during steroid injections. Preinjection concentrations of prolactin were correlated with magnitude of postinjection response to thyrotropin releasing hormone, but response was not correlated with concentrations of steroids in plasma on day of injection.

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.

Induction of lactation by two techniques: success rate, milk composition, estrogen and progesterone in serum and milk, and ovarian effects

Induction of lactation was attempted in 12 heifers and 12 cows with estradiol benzoate (.011 mg/kg body weight per day) subcutaneous for 10 days or that plus progesterone (.1 mg + .25 mg/kg body weight per day) for 7 days. Milking commenced on day 20 for those treated with the mixture and on day 11 for the others. Lactations were induced (minimum of 4.5 kg of milk/day) in five of six heifers and two of six cows by the mixture and in six of six heifers and three of six cows for estradiol benzoate. Milk production was 44% of herdmates in the 16 induced lactations. Cows on the single treatment had lower production than the other three groups. Ovarian status, cycling, cystic, or static, was affected adversely in 5 of 16 animals induced successfully. Two of the 16, both heifers, carried calves to term following induction. The transition to normal composition of milk was slower for single than double treatment. Lactose increased slowly to normal over the 1st wk of milking while protein decreased slowly. Estrogen and progesterone in milk of induced cows were approximately twice as concentrated as in normal postparturient cows, probably because milk production was halved.

Effects of processing milk on concentrations of glucocorticoids in milk

Concentrations of glucocorticoids were measured by protein binding in milk subjected to various processing methods. Raw whole milk was collected once per week for 3 wk from bulk milk tanks of each of 10 farms. Nine combinations of processing were tested: 1) none, 2) high-temperature short-time pasteurization of whole milk, 3) high-temperature short-time pasteurization and homogenization of whole milk, 4) bulk pasteurization of whole milk, 5) bulk pasteurization and homogenization of whole milk, 6) high-temperature short-time pasteurization of skim milk, 7) high-temperature short-time pasteurization and homogenization of skim milk, 8) bulk pasteurization of skim milk, and 9) bulk pasteurization and homogenization of skim milk. Mean concentrations of total glucocorticoids ranged from .46 to .65 ng/ml and were not different among either processing methods or whole versus skim milk classifications. No correlations were positive between percentage of fat and concentration of glucocorticoids in whole milk (-.22) or skim milk(-.09).

Glucocorticoids in mammary secretions and blood serum during reproduction and lactation and distributions of glucocorticoids, progesterone, and estrogens in fractions of milk

Concentrations of glucocorticoids were measured in milk and blood serum during the estrous cycle, prepartum, parturition, postpartum, and early and late lactation. Glucocorticoids in milk did not change during the estrous cycle, averaging .35 ng/ml whereas they averaged .50 ng/ml prepartum, 3.08 ng/ml at parturition, and .50 ng/ml 1 wk postpartum. Glucocorticoids in milk declined from .59 ng/ml to .25 ng/ml as lactation advanced from 1 to 10 mo. Concentrations of glucocorticoids in blood serum were approximately 8 to 10 ng/ml during all reproductive states. There was no positive relationship between percentage of milk fat and concentrations of glucocorticoids in milk. Cortisol was the predominant glucocorticoid in serum; in milk corticosterone concentrations exceeded those of cortisol. Glucocorticoids, being more polar, had higher affinity for the nonlipid portion of milk; in contrast, progesterone, estradiol 17beta, and estrone were located predominantly in the lipid fraction of milk.

Development of and fluid accumulation in mammary glands of freemartins administered estradiol, estrone, or testosterone

Eighteen Holstein freemartins acquired at 1 wk of age were assigned to a control and to four treatment groups, but only two of the groups received hormone the first 50 wk. Testosterone administered for the first 50 wk appeared to inhibit teat growth whereas estrone stimulated teat and udder length. At 50 wk of age, implants releasing daily approximately 12.9 microgram of testosterone, 2.9 microgram of estrone, or 2.6 microgram of estradiol-17beta per kg of body weight were implanted for 6 wk. One of three testosterone-treated and 9 of 11 estrogen-treated animals exhibited increased udder development associated with fluid accumulation. The 10 animals with fluid accumulation in the udders were milked once 39 days after implanting. The fluid contained 15.0% total solids, 4.1% fat, and 7.0% protein, values which are between those for normal milk and colostrum. These studies support the concept that administration of low concentrations of estrogens alone, released continuously from implants, were capable of stimulating fluid secretion in mammary glands of animals that had no detectable gonadal luteal tissue.