Effect of maternal nutrition on brown adipose tissue and its prolactin receptor status in the fetal lamb

High linoleic acid safflower seed supplementation for gestating ewes: Effects on ewe performance, lamb survival, and brown fat stores1

Objectives of this study were to determine whether feeding high-linoleic safflower seed to gestating ewes increases cold tolerance and survival in lambs, and whether brown adipose tissue (BAT) stores in lambs are affected by prepartum safflower seed supplementation. In Trial 1, 234 gestating ewes (122 in yr 1 and 112 in yr 2; 75.5 and 81.2 +/- 0.6 kg initial BW for yr 1 and 2, respectively) were allotted randomly to one of two dietary treatments (four pens*treatment(-1)*yr(-1)). Ewes were fed alfalfa-based diets containing (DM basis) either 2.8 (LF) or 5.7% (HF) dietary fat beginning 55 (yr 1) and 42 (yr 2) +/- 1 d prepartum. In Trial 2, 40 Rambouillet cross ewes gestating twins (82.9 +/- 1.7 kg BW) were used in 2 yr (20/yr) and were fed diets containing (DM basis) either 1.9 (LF) or 4.9% (HF) dietary fat beginning 53.4 +/- 1.4 d prepartum. The basal diet was 37.5% each of grass and alfalfa hays and 25% corn silage (DM basis). Cracked safflower seeds (18% CP, 32% fat, 25.6% linoleic acid; DM basis) were used as the supplement in HF, whereas safflower meal and corn were used as the supplement in LF for both trials. At parturition, one lamb from each ewe was selected randomly for slaughter. Perirenal (PR) and pericardial (PC) BAT was excised and weighed, and the carcass was frozen for compositional analysis. In Trial 1, more lambs from HF 0.03; 15.4 vs. 5.8 +/- 2.8%), and dams survived (P = 0.03; 88.4 vs. 78.3 +/- 2.9%), fewer died due to starvation (P = there was a tendency for fewer to die due to pneumonia (P = 0.07; 0.0 vs. 1.7 +/- 0.6%). Ewes fed HF tended to wean more lambs per ewe (P = 0.09; 1.4 vs. 1.2 +/- 0.06) but had similar lamb weight weaned per ewe (P = 0.51; 23.1 +/- 1.22 kg). In Trial 2, prepartum ewe plasma NEFA and glucose concentrations increased with advancing gestation (P < 0.001). Lamb rectal temperature tended (P = 0.08) to be higher in LF lambs and tended (P = 0.06) to increase following parturition. Perirenal BAT weight did not differ among treatments (33.01 +/- 1.66 g; P = 0.28; 0.62 +/- 0.30% BW; P = 0.60). Lambs from LF dams tended (P = 0.08) to have greater PC BAT weight; however, the effect was not significant when expressed as a percentage of BW (0.13 +/- 0.007; P = 0.98). High-linoleic safflower seeds fed during the last 45 d of gestation may be beneficial in improving lamb survivability. Our data do not indicate this response was a result of increased BAT stores. More research is necessary to determine mechanisms that enhance lamb survival when high-linoleic saf-flower seed is fed during gestation.

Cellular localization and changes in expression of prolactin receptor isoforms in sheep ovary throughout the estrous cycle

The actions of prolactin (PRL) on target cells depend on the type of prolactin receptor (PRLr) predominantly expressed, particularly whether the long PRLr isoform is expressed. The aims of this study were to determine the cellular localization and the changes in expression of long and short PRLr isoforms in sheep ovary throughout the estrous cycle. Long and short PRLrs were localized mostly in the same ovarian cells. Maximum signal intensity, particularly for long PRLrs, was found in stromal cells surrounding primordial and primary follicles, and, for both PRLrs, in granulosa cells of preantral follicles and in luteal cells. Moderate signal intensity for PRLrs was found in theca cells of preantral to ovulatory follicles, and in granulosa cells of antral follicles up to the gonadotropin-dependent stage. Decreasing immunoreactivity to PRLrs was found in granulosa cells of gonadotropin-dependent to ovulatory follicles. For long PRLrs in particular, no signal was found in mural granulosa cells of gonadotropin-dependent follicles; for both isoforms, no signal was found in most granulosa cells of ovulatory follicles. In primordial to gonadotropin-dependent follicles, cellular localization of PRLr was similar on days 0, 10 and 15 of the cycle. Oocytes consistently showed positive immunostaining for PRLrs. Comparative RT-PCR analysis of long and short PRLr expression showed that the short isoform is evenly expressed throughout the estrous cycle, whereas the expression of the long form increases at the time of estrus and decreases at mid-luteal phase and at the onset of the follicular phase. Expression of long PRLrs was greater than that of short PRLrs on day 0 of cycle; expression of both isoforms was similar on day 10 and on day 15, long PRLrs expression was lower than that of short PRLrs. Our results indicate that in sheep ovary, the maximum responsiveness to PRL might occur during the preovulatory phase of the estrous cycle.

Nutritional Manipulation of Fetal Adipose Tissue Deposition and Uncoupling Protein 1 Messenger RNA Abundance in the Sheep: Differential Effects of Timing and Duration

A range of epidemiological and experimental studies have indicated that suboptimal nutrition at different stages of gestation is associated with an increased prevalence of adult hypertension, cardiovascular disease, and obesity. The timing of prenatal nutrient restriction is important in determining postnatal outcomes-including obesity. The present study, aimed to determine the extent to which fetal adiposity and expression of the key thermogenic protein, uncoupling protein (UCP)1, are altered by restriction of maternal nutrient intake imposed during four different periods, starting from before conception. Maternal nutrient intake was restricted from 60 days before until 8 days after mating (periconceptional nutrient restriction; R-C), from 60 days before mating and throughout gestation (R-R), from 8 days gestation until term (C-R), or from 115 days gestation until term. Fetal perirenal adipose tissue (PAT) was sampled near to term at approximately 143 days. UCP1 mRNA, but not protein, abundance in PAT was increased in fetuses in the R-R group (C-C 63 +/- 18; R-C 83 +/- 43; C-R 103 +/- 38; R-R 167 +/- 50 arbitrary units (P < 0.05)). In contrast, the abundance of UCP1 mRNA, but not protein, in fetal PAT was decreased when maternal nutrition was restricted from 115 days gestation. The major effect of maternal nutrient restriction on adipose tissue deposition occurred in the C-R group, in which the proportion of fetal fat was doubled, whereas maternal nutrient restriction from 115 days gestation reduced fetal fat deposition. In conclusion, there are differential effects of maternal and therefore fetal nutrient restriction on UCP1 mRNA expression and fetal fat mass and these effects are dependent on the timing and duration of nutrient restriction.

Maternal nutrient restriction during placental growth, programming of fetal adiposity and juvenile blood pressure control

Epidemiological and experimental studies have demonstrated that maternal undernutrition during pregnancy is associated with abnormal placental growth. In sheep, maternal nutrient restriction over the period of rapid placental growth (30-80 days) restricts placentome growth. Then following adequate nutrition up to term (147 days), placental mass is greater in association with a higher total abundance of the predominant placental glucose transporter-1. The resulting lambs are larger at birth, have heavier kidneys with an increased expression of the glucocorticoid-responsive type 1 angiotensin II receptor. Near to term, these fetuses possess more adipose tissue, the endocrine sensitivity of which is markedly enhanced. For example, the abundance of mRNA for 11beta-hydroxysteroid dehydrogenase type 1, which catalyses the conversion of cortisone to bio-active cortisol is increased. This is associated with a higher abundance of both leptin and glucocorticoid receptor mRNA. At 6 months of age, the juvenile offspring of nutrient restricted ewes have lower resting blood pressure that was positively correlated with plasma cortisol concentration, suggesting their blood pressure could be more strongly driven by circulating cortisol. These offspring also exhibited a greater pressor response to vasoconstrictor challenges, but showed no difference in vasodilatory response. At this age, the kidney weight was similar between groups, but the abundance of cytochrome c in kidney mitochondria was enhanced in lambs born to nutrient restricted ewes that could indicate increased mitochondrial activity. Reduced maternal nutrition during the period of rapid placental growth may therefore contribute to hypertension in later life through physiological and vascular adaptations during fetal life.

Ewe-lamb bonding behaviours at birth are affected by maternal undernutrition in pregnancy

Maternal undernutrition in pregnancy results in low birth-weights and impaired postnatal survival in sheep. Largely anecdotal evidence suggests that the expression of appropriate maternal and neonate behaviours may also be disrupted by undernutrition. In the present study, we investigated the effect of a moderate (35 %) reduction in ewe nutritional intake in pregnancy on the expression of ewe-lamb bonding behaviours in primiparous Scottish Blackface ewes. Low-intake (L) ewes had significantly higher plasma progesterone than high-intake (H) ewes from mid-gestation onwards (e.g. plasma progesterone at 20 weeks (ng/ml): H 15.72, L 22.38, sed 1.80, P<0.001), and a lower oestradiol: progesterone value than H ewes at delivery (H 0.46, L 0.35, sed 0.05, P<0.05). Lamb birth-weight was reduced in the L lambs compared with H lambs (mean body weight (kg): H 3.31, L 3.00, sed 0.14, P<0.05), but the incidence of malpresentation at delivery was greater in L lambs. L ewes spent significantly less time licking their lambs than H ewes after delivery (time grooming in 2 h after birth (%): H 56.12, L 48.17, sed 2.639, P<0.01) and were more aggressive towards the lambs. Lamb behaviours were not directly affected by maternal nutritional treatment, but lamb birth-weight had a significant effect on neonatal developmental progress. Low-birth-weight lambs were slower than heavier lambs to stand and sucked less frequently. In tests of maternal attachment to the lamb, H ewes received higher scores than L ewes at both 24 h after birth (ewes receiving high scores (%): H 41.3, L 21.4, P<0.05) and at 3 d postnatal. We conclude that even a moderate level of undernutrition impairs the attachment between ewes and lambs by affecting maternal behaviours expressed at birth. In addition, the results suggest that levels of nutrition resulting in a decrease in birth weight will affect neonatal lamb behavioural progress.

Fetal leptin is a signal of fat mass independent of maternal nutrition in ewes fed at or above maintenance energy requirements

In adults, circulating leptin concentrations are dependent on body fat content and on current nutritional status. However, the relationships among maternal nutrient intake, fetal adiposity, and circulating leptin concentrations before birth are unknown. We investigated the effects of an increase in nutrient intake in the pregnant ewe on fetal adiposity and plasma leptin concentrations during late gestation. Between 115 and 139-141 days gestation (term = 147 +/- 3 days gestation), ewes were fed a diet calculated to provide either maintenance (control, n = 6) or approximately 155% of maintenance requirements (well-fed, n = 8). The fetal fat depots (perirenal and interscapular) were dissected, and the relative proportion of unilocular and multilocular adipocytes in each depot was determined. Maternal plasma glucose and leptin concentrations were significantly increased in well-fed ewes. Fetal plasma glucose concentrations were also higher in the well-fed group (115-139 days gestation: control, 1.65 +/- 0.14 mmol/L; well-fed, 2.00 +/- 0.14 mmol/L; F = 5.76, P < 0.04). There was no effect of increasing maternal feed intake on total fat mass, the relative mass of unilocular fat, or fetal plasma leptin concentrations (115-139 days gestation: control, 5.2 +/- 0.8 ng/ml; well-fed, 4.7 +/- 0.7 ng/ml). However, in both the control and well-fed groups fetal plasma leptin concentrations (y) were positively correlated with the relative mass of unilocular fat (x): y = 1.51x + 1.70; (R = 0.76, P < 0.01). Thus, fetal leptin may play a role as a signal of unilocular fat mass in the fetus when maternal nutrient intake is at or above maintenance requirements.