Effects of compensatory growth on milk protein gene expression and mammary differentiation

Nutritional Regulation of Mammary Gland Development and Milk Synthesis in Animal Models and Dairy Species

In mammals, milk is essential for the growth, development, and health. Milk quantity and quality are dependent on mammary development, strongly influenced by nutrition. This review provides an overview of the data on nutritional regulations of mammary development and gene expression involved in milk component synthesis. Mammary development is described related to rodents, rabbits, and pigs, common models in mammary biology. Molecular mechanisms of the nutritional regulation of milk synthesis are reported in ruminants regarding the importance of ruminant milk in human health. The effects of dietary quantitative and qualitative alterations are described considering the dietary composition and in regard to the periods of nutritional susceptibly. During lactation, the effects of lipid supplementation and feed restriction or deprivation are discussed regarding gene expression involved in milk biosynthesis, in ruminants. Moreover, nutrigenomic studies underline the role of the mammary structure and the potential influence of microRNAs. Knowledge from three lactating and three dairy livestock species contribute to understanding the variety of phenotypes reported in this review and highlight (1) the importance of critical physiological stages, such as puberty gestation and early lactation and (2) the relative importance of the various nutrients besides the total energetic value and their interaction.

Growth targets and rearing strategies for replacement heifers in pasture-based systems: a review

Dairy heifer growth and liveweight at first calving are regarded as important management variables affecting profitability and animal welfare. However, the appropriateness of heifer growth rate targets for different farming systems is not clear. Retrospective assessments of the association between heifer liveweight and subsequent productivity indicate significant benefits in milk production and, even, reproduction from increasing liveweight at breeding and first calving. However, prospective interventionist experiments do not concur, with very variable effects of liveweight at breeding on milk production and with only limited evidence of a positive effect of first-calving liveweight on first-lactation milk yield. In addition, any benefit in the first lactation is not evident in subsequent lactations in the limited number of long-term studies reported. Pre-weaning nutrition and average daily weight gain are areas of increasing interest, with lifelong increases in milk production resulting from accelerated growth rates during the first 8 weeks of life, indicating a possible significant return from a short-term investment. This could be one reason for the inconsistent effects of heifer liveweight at breeding and first lactation on milk production. Although the effect of pre-weaning average daily gain on heifer liveweight is short-lived, a recent meta-analysis indicated that pre-weaning average daily gain explains 22% of the variation in first-lactation milk production. Whether these differences in animal physiology have relevance in grazing systems, wherein heifers and cows do not consume sufficient nutrients to reach their potential, requires investigation. Despite considerable extension efforts over successive decades, current evidence indicates that failure to provide the new-born calf with sufficient high-quality colostrum is common. To understand the reasons for suboptimal colostrum feeding requires social research, with appropriate extension strategies developed to elicit practice change. Although there can be little doubt regarding the importance of heifer rearing to the profitability and sustainability of the farming business, the collective literature points to a failure of retrospective analyses in determining the cause of poor heifer performance. In reality, it is likely to be a combination of factors. The objective of this review is to investigate the effect of liveweight gain at various stages of the growth cycle of the heifer on the milk-production capacity of the lactating animal.

Effects of rice straw versus wheat straw as ingredients in a total mixed ration on intake, digestibility and growth of Holstein heifers

Rice straw (RS) has generally not been considered as an ingredient in dairy heifer or cow rations in the developed world, at least partly due to its tough physical character. However, recent research aimed at developing harvesting methods that increase mixability and reduce animal-sorting problems has identified straw-preparation methods with substantially improved physical properties. A ‘slicer’ baler method was used to prepare RS for use in two feeding studies, so as to determine effects of RS versus wheat straw (WS) as ingredients in a total mixed ration (TMR) on dairy heifer performance. The WS-TMR-fed heifers in Experiment 1 had substantially higher frame growth than did RS-TMR-fed heifers, and maintained body condition score, while RS heifers lost body condition score. A main reason for reduced performance with the RS-TMR-fed heifers was at least partly due to reduced DM intake, which may have been due to slower-degrading fibre and/or a higher dietary cation–anion difference (DCAD) of the RS-TMR. However, the large treatment differences may also have been due to compensatory growth in WS-TMR-fed heifers as all heifers had been fed the RS-TMR before initiation of the study. The WS-TMR-fed heifers in Experiment 2 had the same frame growth, but somewhat higher BCS accumulation, than did RS-TMR-fed heifers, which may have been due to the lower straw-inclusion levels in the diets, smaller treatment differences in DCAD versus Experiment 1 and/or a lack of compensatory growth, since all heifers had been fed a higher-energy diet before the study. However, after a further 28-day period, when all calves were fed the WS-TMR, measures of skeletal growth and BCS had converged. Overall, results support a lower nutritional value of RS than WS, while demonstrating the practical utility of using energy restriction–realimentation regimes to increase heifer growth efficiency.

Role of compensatory mammary growth in epigenetic control of gene expression

To better understand the role of nutrition in regulating mammary gland development and lactation, we designed a novel stair-step compensatory nutrition regimen that is a unique combination of dietary energy restriction and realimentation (refeeding) phases; the basic concept of this regimen is to exploit the biological nature of the compensatory growth phenomenon in concert with one or more hormone-sensitive allometric phases of mammary development (i.e., peripuberty through gestation). Nutritionally induced compensatory growth during different developmental stages before first parturition positively affects mammary development and life-long lactation performance. This permanent enhancement of mammary gland growth and lactation potential strongly suggests a possible mechanistic link between nutritionally induced compensatory growth, epigenetic control of mammary gene expression, and metabolic imprinting. We hypothesize that compensatory-directed metabolic imprinting once set during late pregnancy prior to the first parturition persistently maintains and exerts its adaptive response on mammogenesis and galactopoiesis (i.e., maintenance and/or enhancement of milk secretion). The ability to influence heritable genes regulating milk synthesis may be used to improve the quality and quantity of milk (e.g., infant health, the secretion of certain immunoglobulins or growth factors) as well as the longevity of lactation.

A compensatory nutrition regimen during gestation stimulates mammary development and lactation potential in rats

The proper nutritional status during the hormone-sensitive growth phases preceding first parturition can affect mammary development and subsequent lactation performance. We developed a compensatory nutrition regimen (CNR), which is designed to stimulate mammary growth by exploiting the biological characteristics of the energy restriction and compensatory growth phenomenon. In the present study, we examined the effect of compensatory growth induced only once during late gestation upon mammary development and subsequent lactation potential over 2 lactation cycles. Female rats were mated and randomly assigned to either the control or the CNR group. Control rats were offered the control diet (AIN-93G) throughout the experiment. CNR rats were subjected to 40% energy restriction during the first 10 d of gestation followed by free access to the control diet for the remainder of the experiment. Dams on the CNR produced 14% more milk than control dams (P = 0.12). Mammary cell proliferation rates were approximately 46% (P < 0.05) and 27% (P = 0.07) higher in the CNR group than in the control during late gestation and early lactation of the first lactation cycle, respectively. Caspase-3 enzyme activity was decreased 15% (P < 0.05) and 22% (P = 0.11) in mammary tissues from the CNR group compared with that from the controls during the first and second lactation cycles, respectively. These results indicate that compensatory growth induced only once during late gestation increases mammary cell proliferation and differentiation and decreases regression of mammary cells throughout consecutive lactation cycles.

Nutritionally directed compensatory growth enhances heifer development and lactation potential

The objectives of this study were 1) to examine the interactive influence of a compensatory nutrition regimen and lasalocid supplementation on dairy heifer growth performance and 2) to document the extent to which compensatory growth sustains lactation potential over the first two lactation cycles. Twelve Holstein heifers, weighing an average of 160 kg (about 6 mo of age) were randomly assigned to treatments arranged in a 2 x 2 factorial design. Treatment variables were two dietary regimens (control and stair-step compensatory nutrition) and two levels of lasalocid (0 and 200 mg/d). The control heifers were fed a diet containing 12% crude protein (CP) and 2.35 Mcal of metabolizable energy (ME) per kilogram of dry matter. The stair-step compensatory nutrition heifers were subjected to a phased nutrition regimen and reared according to an alternating 3-2-4-3-4-2-mo schedule. The first stair-step (prepubertal phase) consisted of energy restriction [17% CP and 2.35 Mcal/kg of ME] for 3 mo followed by realimentation (12% CP and 3.05 Mcal/kg of ME) for 2 mo. The second step (puberty and breeding) consisted of energy restriction for 4 mo followed by realimentation for 3 mo. The third step (gestation period) was energy restriction for 4 mo concluding with realimentation for 2 mo. Dry matter intake of heifers during the restriction phase was limited to 70% of the control intake. Heifers were given ad libitum access to a high energy density diet during realimentation to allow compensatory development. Stair-step heifers supplemented with lasalocid had the highest efficiency of growth (body weight gain/dry matter intake), suggesting synergistic metabolism of lasalocid with compensatory growth action. Compensatory growth induced during the last trimester enhanced metabolic status by increasing circulating insulin and decreasing triglyceride levels. Heifers on the stair-step regimen had a significant increase in milk yield during the first (21%) and second (15%) lactation cycles. These results support our thesis that compensatory growth induced during an allometric growth phase improves mammary development and energy and protein metabolic status of dairy heifers.

Nutritionally-directed compensatory growth enhances mammary development and lactation potential in rats

A nutritionally-regulated compensatory growth regimen imposed during a growing period from prepuberty to gestation can significantly affect mammary development and subsequent lactation performance. The objectives of this study were as follows: 1) to determine whether a compensatory nutrition regimen enhances lactation potential for the first and second lactation cycles and 2) to determine the extent to which a compensatory nutrition regimen modulates cell proliferation, differentiation, and apoptosis and expression of genes in mammary tissues of female rats. Female Sprague-Dawley rats (n = 122, 35 d of age) were randomly assigned either to the control group, with free access to diet, or to a stair-step compensatory nutrition feeding regimen, with an alternating 2-2-3-3-wk schedule. The regimen began with an energy-restricted diet (40% restriction) for 2 wk, followed by the control diet for 2 wk; this step was then repeated at 3-wk intervals. Pups of dams from the compensatory nutrition regimen group gained more during mid-lactation than did control group pups. Mammary tissues were obtained from early (d 2) and late (d 19) lactating rats. Mammary tissue from the compensatory nutrition group exhibited increased cell proliferation and greater gamma-glutamyltranspeptidase and ornithine decarboxylase gene expressions than did tissue from the control group during early lactation of both cycles. Mammary tissue from the compensatory nutrition group also had fewer apoptotic cells than tissue from the control group during late lactation of the first lactation cycle. These results suggest that the compensatory nutrition regimen imposed during the peripubertal developmental phase stimulated mammary growth and enhanced lactation performance by affecting the expression of genes that regulate the cell cycle.

Compensatory nutrition-directed mammary cell proliferation and lactation in rats

The proper use of a time-dependent and controlled nutrition regimen during the hormone-sensitive growth phase before first parturition can significantly affect mammary growth and subsequent lactation performance. The objective of the present study was to determine if a compensatory nutrition regimen improves lactation performance by affecting proliferation and apoptosis of mammary epithelial cells. Forty female rats (7 weeks of age, average weight 148 g) were assigned to either (1) control, free access to diet or (2) stair-step compensatory nutrition regimen, an alternating 3-4-week schedule beginning with an energy-restricted diet (31.2% restriction) for 3 weeks, followed by the control diet for 4 weeks. Estimated milk yield was greater (P < 0.05) on day 15 of lactation in the compensatory nutrition group than in the control group. Mammary cell proliferation values were 1.4- and 2.7-fold greater in mammary tissue from the compensatory group during pregnant and early lactating stages respectively, compared with those from the control group. Ornithine decarboxylase (EC 4.1.17) mRNA was 24% higher (P < 0.05) in mammary tissues of rats from the compensatory nutrition group during pregnancy than in those from the control group. These results indicate that the compensatory nutrition regimen imposed during the peripubertal growth phase stimulated mammary epithelial cell proliferation and improved lactation performance.

Nutritionally directed compensatory growth and effects on lactation potential of developing heifers

Our objective was to determine the extent to which a stair-step compensatory nutrition regimen regulated the growth and subsequent lactation performance of developing beef heifers. Forty crossbred beef (Angus x Gelbvieh) heifer calves were assigned to either a control or stair-step compensatory nutrition regimen. Heifers fed the stair-step compensatory nutrition regimen were fed according to an alternating schedule beginning with a high energy diet (130% of the metabolizable energy recommended by the National Research Council) for 2 mo, followed by an energy restricted diet (70% of the recommended metabolizable energy) for 3 mo, and concluding with the high energy diet again for 2 mo. Thereafter, all heifers received the control diet. The average daily gain of heifers fed the stair-step compensatory nutrition regimen was 2-fold higher than that of control heifers during the final high energy phase. The RNA and protein contents in the mammary tissues of heifers fed the experimental regimen in early lactation were greater than those of control heifers. Lipid content was significantly reduced in the mammary tissues of heifers fed the experimental regimen. The expression of beta-casein in the mammary tissues of heifers fed the experimental regimen was higher than that of the control heifers. Heifers fed the stair-step regimen yielded 6% more milk than did those fed the control regimen. Total protein and casein in milk of heifers fed the experimental regimen were higher than those in milk of control heifers. These results indicate that the stair-step compensatory nutrition regimen enhanced mammary development and subsequent lactation performance.

Induction of the endogenous whey acidic protein (Wap) gene and a Wap-myc hybrid gene in primary murine mammary organoids

In rodents, the whey acidic protein (Wap) is the major whey protein expressed in mammary glands in response to lactogenic hormones. The regulation of the Wap gene differs from that of other milk protein genes, with one consequence being that little or no Wap expression is detectable in cell culture. Here we describe the efficient in vitro induction of the Wap gene in mammary organoids isolated from midpregnant mice. Mammary organoids were isolated as intact epithelial subcomponents which retained the glandular microarchitecture. If organoids were cultured in contact with a monolayer of 3T3-L1 adipocytes, significant levels of Wap mRNA were induced upon hormonal stimulation, with the highest level of Wap mRNA being induced by a combination of hydrocortisone, prolactin, and insulin. Dissociation of the three-dimensional organization abrogated Wap inducibility. Organoids cultured on plastic or hydrated type I collagen did not transcribe Wap mRNA even after hormonal stimulation. Addition of hormones was required to maintain low levels of Wap mRNA in organoids cultured on reconstituted basement membrane, however, Wap mRNA was not induced. Organoid-adipocyte interactions as well as cell-cell interactions inherent in the structure of organoids promote hormone-dependent Wap mRNA expression. In order to study the Wap promoter region in vitro, we cocultured organoids from transgenic mice harboring a chimeric Wap-myc gene with 3T3-L1 adipocytes. Lactogenic hormones induced the Wap-myc transgene in vitro. The kinetics of induction were similar for both the transgene and the endogenous Wap gene indicating that the 2.5-kb regulatory Wap region present in the hybrid gene contains the sequence elements required for hormone-induced gene expression in vitro.