Duncan D. S. Mackenzie

Dietary fat regulates mammary stearoyl CoA desaturase expression and activity in lactating mice

Mice in mid lactation (n=6 per group) were fed a control diet (1.19% fat), or diets containing safflower oil (25% w/w) or olive oil (25% w/w) for 7d. Mammary and liver stearoyl CoA desaturase (SCD) mRNA levels and mammary SCD activities were higher in lactating mice fed the control diet than in those fed the oil-supplemented diets. Further, mammary SCD mRNA was directly related to mammary SCD activity. Milk fat composition was influenced by dietary fat composition. The olive oil diet, high in 18:1, led to high levels of this fatty acid in milk and the safflower oil diet, high in 18:2, resulted in a milk fat with high levels of 18:2. These results show that there is regulation of SCD at the transcriptional level, associated with changes in enzyme activity and in milk fat composition.

Quantitative fatty acid signature analysis on New Zealand sea lions: model sensitivity and diet estimates

Abstract We used quantitative fatty acid signature analysis (QFASA) to predict the long-term diet of New Zealand (NZ) sea lions (Phocarctos hookeri) incidentally caught in the NZ arrow squid (Nototodarus spp.) fishery. The QFASA model used fatty acid (FA) profiles based on 82 blubber samples of NZ sea lions bycaught between 2000 and 2006. First, the model was optimized by a series of simulations for which 1 model parameter—6 different sets of calibration coefficients (CCs) from different pinniped species and feeding regime, 2 sets of FAs, and the consideration of individual prey values, or mean prey values—varied each time. The best-fit parameters were those giving the lowest Kullback–Liebler distance values. Second, these parameters were used in a model to estimate the diet of NZ sea lions. QFASA was highly sensitive to the set of CCs applied. Across years the most important prey estimated with the best-fit CCs were southern arrow squid (Nototodarus sloani, 18–28% mass), hoki (Macruronus novaezelandiae, 10–27% mass), rattails (Macrouridae, 7–27% mass), and possibly scampi (Metanephrops challengeri, 1–19% mass). Despite the uncertainty on the accuracy of the match between the best-fit CCs used and the true FA metabolism of NZ sea lions, the variation of prey estimated among years was highly consistent with the trends of commercial catches during the same period, providing some confidence in the present QFASA predictions. The most important estimated prey were demersal species living mainly at depths >200 m that NZ sea lions encounter on the slopes of the Auckland Islands shelf. Our study emphasized the importance of these areas for bycaught NZ sea lions over the 1st half of the lactation period.

Ontogeny and epithelial-stromal interactions regulate IGF expression in the ovine mammary gland.

Although the insulin-like growth factors (IGF-I and -II) have been implicated in the stimulation of mammogenesis, little is known of their regulation in the mammary gland. In this study we removed epithelial tissue from one of the two mammary glands of 1-week-old ewe lambs and examined IGF-I and -II mRNA expression during postnatal development in both the intact mammary gland and in the gland cleared of epithelial tissue. Expression of IGF-I mRNA was highest at 6 and 10 weeks of age, coincident with the prepubertal phase of rapid mammary growth, then declined and remained low until expression increased during late pregnancy. IGF-I mRNA was more abundant in the mammary fat pad adjacent to parenchyma (MFP) than in the contralateral fat pad that had been surgically cleared of epithelium (CFP). The level of IGF-II mRNA in parenchyma was highest at 1-23 weeks of age due to an increase in the abundance of specific mRNAs. Expression was lower in the fat pads, with generally higher levels in the intact MFP than the CFP, and in these tissues IGF-II expression was shown to increase with age between 6 and 23 weeks. We also investigated the influence of the ovary and estrogen on the expression of IGFs. While IGF-I mRNA abundance was unaffected by ovariectomy, exogenous estrogen resulted in higher levels of expression in the MFP of ovariectomized ewes and tended to increase its level in the parenchyma of intact ewes. Ovariectomy increased IGF-II mRNA within mammary parenchyma whereas estrogen suppressed levels in both the parenchyma and MFP. These findings demonstrate that IGF-I and -II mRNAs are expressed locally within the developing ovine mammary gland and are regulated by stage of ontogeny, ovarian hormones, and epithelial stromal interaction.

The proliferation of mouse mammary epithelial cells in response to specific mitogens is modulated by the mammary fat pad in vitro.

SummaryThe ability of the murine mammary fat pad to directly stimulate the growth of mammary epithelial cells and to modulate the effects of various mammogenic agents has been investigated in a newly described, hormone- and serum-free coculture system. COMMA-1D mouse mammary epithelial cells were cultured for 5 or 7 d with various supplements in the absence or presence of epithelium-free mammary fat pad explants from virgin female BALB/c mice. Cocultured fat pad stimulated increases in the DNA content of COMMA-1D cultures by two- to threefold or six-to eightfold after 5 or 7 d, respectively. The mitogenic effect was additive to that of 10% fetal calf serum and could not be attributed to the release of prostaglandin E2 or synthesis of prostaglandins by epithelial cells. In addition, bovine serum albumin attenuated (P<0.05) the mitogenic effect of cocultured mammary fat pad. Added alone, insulinlike growth factor-I, epidermal growth factor, and insulin increased (P<0.05) total DNA of COMMA-1D cultures by 2.5-, 3.7-, and 2.3-fold, respectively. Cocultured mammary fat pad markedly interacted (P<0.01) with these mitogens to yield final DNA values that were 21.2-, 13.3-, and 22.1-fold greater than in basal medium only. Associated with this proliferation was the formation of numerous domes above the COMMA-1D monolayer. There was no proliferative response to growth hormone or prolactin in the absence or presence of cocultured fat pad (P>0.05). Whereas hydrocortisone did not alter cell number, it attenuated (P<0.05) the mitogenic effect of cocultured mammary fat pad. These results indicate that the murine mammary fat pad is not only a direct source of mitogenic activity, but also modulates the response of mammary epithelial cells to certain mammogens.

Proximate composition, energy content, and fatty acid composition of marine species from Campbell Plateau, New Zealand

Abstract Campbell Plateau is an important fishing ground for the main commercial New Zealand species. Yet, studies on trophic interactions between species and their nutritional values are limited. The objectives of this study were to determine the proximate composition and energy contents of selected commercial and non‐commercial marine species from Campbell Plateau and their fatty acid (FA) composition, and to evaluate the degree to which species can be differentiated by their FA compositions. We analysed 43 fish specimens from 5 different species (Macruronus novaezelandiae, Lepidorhynchus denticulatus, Pseudophycis backus, Hemerocoetes spp. and Squalus acanthias), 17 cephalopod specimens from 2 species (Nototodarus sloani and Enteroctopus zealandicus), and 6 Metanephrops challengeri (crustacean). The variation of energy contents between fish species was not significant, but their lipid and protein contents varied significantly. FA signatures distinguished the species analysed and, at a broader scale, the type of habitat. Within‐specie s variability was important for benthic species. In general, the diet inference from FA trophic markers was consistent with reported diets from stomach contents.

The bone-muscle ratio of fetal lambs is affected more by maternal nutrition during pregnancy than by maternal size

Bone formation and loss are related to the strain imposed on bone by muscle forces. Bone mineral content (BMC) and lean mass (LM) of fetal lambs was determined at day 140 of pregnancy in 8 groups of ewes, which were of either large or small body size, on either high (ad libitum) or maintenance pasture intake from day 21 of pregnancy, or carrying either singletons or twins. BMC and LM (using DXA scanning) of fetal hindquarters/spine were corrected to leg length. BMC and LM were less in twin than singleton groups (P < 0.001). Large ewes on high intake produced single fetuses with a (group mean) BMC/LM ratio that was higher (P < 0.002) than that in fetuses of large ewes with singletons on maintenance intake or twins on either high or maintenance intakes, the ratios of which were not different. In single fetuses from small ewes on high intake, the BMC/LM ratio was higher than those from small ewes with singletons on maintenance intake or twins on either high or maintenance intakes, the ratios of which were not different. The ratio was not different in singleton fetuses of ewes on high intake, whether they were large or small. Different fetal environments resulted in a given amount of muscle being associated with a higher or lower bone mass. Dietary intake during pregnancy was more important than maternal size in affecting the ratio. We conclude that intrauterine environmental factors may be important in determining bone mass postnatally, and possibly later in life.

Paracrine action of keratinocyte growth factor (KGF) during ruminant mammogenesis.

Keratinocyte growth factor (KGF) is a stroma-derived mitogen mediating epithelial-stromal interactions. We investigated the role of KGF during epithelial-stromal interactions accompanying ruminant mammogenesis. Target-specificity of KGF was demonstrated in that KGF-stimulated proliferation of bovine mammary epithelial, but not ovine mammary stromal cells. Consistent with a paracrine function, 4.6, 2.4, 1.5 and 0.9 kb mRNA transcripts were expressed by bovine stromal, but not epithelial cells. Within the ovine mammary gland, 2.4 and 1.5 kb KGF mRNAs were expressed in the fat pad while only the 2.4 kb transcript was transcribed in parenchyma. The abundance of KGF mRNA was greater in the extra-parenchymal fat pad than in the contralateral epithelium-free fat pad prior to puberty, and was less in parenchyma than in the intact or epithelium-free fat pads. Ovariectomy tended to increase KGF transcription while estrogen reduced expression. Of several tissues, mammary parenchyma expressed a 2.4 kb mRNA while adipose tissues expressed a 1.5 kb transcript. These results demonstrate local and systemic regulation of KGF transcription and support a paracrine role for KGF during ruminant mammogenesis.

Interannual and individual variation in milk composition of New Zealand sea lions (Phocarctos hookeri)

Abstract In this study 308 milk samples were collected and analyzed from 181 individual female New Zealand sea lions (NZ sea lions; Phocarctos hookeri) breeding on Enderby Island (Auckland Islands). Samples were collected from the 1st part of early lactation (January and February) over a period of 7 years (1997, 1999–2003, and 2005). The effect of year, month, and maternal characteristics (body mass, body condition index [BCI], and age class) on the composition of milk was evaluated using a mixed model for repeated measures. The gross composition (± SD) of the milk was lipid (21.3% ± 8.1%), protein (9.4% ± 2.4%), water (67.9% ± 8.8%), ash (0.48% ± 0.06%), and energy content (10.3 ± 3.2 kJ/g). Overall, the quality of milk of the NZ sea lions in this study was relatively lower in solids and fats than that of other pinnipeds and, in particular, other sea lion species. There were significant effects of year and month on the concentration of lipids in milk, and of year and maternal age class on maternal body mass and BCI. There were significant relationships between various maternal characteristics and milk composition. Thus, the concentration of milk lipids was significantly correlated with maternal BCI, body mass, and pup age. Given that NZ sea lions are a nationally critical species in decline, the relationship between the temporal (yearly and monthly) variations in milk composition, maternal body mass, reproductive success, and changes in food supply in relation to natural perturbations or fisheries resource competition warrants further investigation to disentangle this relationship and implement appropriate management initiatives.

Comparison of methods for the analysis of New Zealand sea lion, Phocarctos hookeri, milk.

Abstract The milk composition of New Zealand sea lion, Phocarctos hookeri, was determined using standard analytical methods, a MilkoScan™ FT 120 and an accelerated solvent extractor (ASE) for fat concentration. The results for fat, protein and total solid concentrations between the different analytical methods were assessed using different measures of statistical fitness including coefficient of determination, concordance correlation coefficient, mean prediction error, and intraclass correlation coefficient. The repeatability and reliability of the results obtained with the calibrated MilkoScan™ FT 120 were comparable with those obtained using standard methods, the Roese‐Gottlieb method for fat, Kjeldahl method for protein and gravimetric method for total solids. The MilkoScan™ FT 120s are fast and cost‐effective and are widely used in dairy laboratories around the world, which should make them readily accessible to ecologists/biologists studying the milk composition of non‐domestic animals.