A specific leptin RIA was developed to assess concentrations of leptin in ovine plasma, and was shown to be efficient with bovine and caprine plasma. A specific, high-affinity antibody was generated against recombinant ovine leptin which, when used in a competitive leptin RIA, provided valid estimates of linearity (r=+0·989-0·998), recovery (102%), repeatability (13%) and limit of sensitivity (0·83 ng/ml for 100 µl sample size). Serial dilutions of five ovine, bovine or caprine plasma samples showed good linearity and parallelism with the recombinant ovine leptin standard curve. A comparison of this RIA was made with a commercial 'multi-species' RIA kit using 56 ovine plasma samples. Major differences were found in assay sensitivity. Non-lactating, non-pregnant, ovariectomized ewes were fed a ration for 65 days which provided 90 9% (control; n=12) or 39 2% of maintenance energy requirements (underfed; n=16) in order to analyse the respective effects of body fatness (estimated by either an in vivo dilution technique or body condition scoring) and of nutritional status on plasma leptin concentration. There was a significant positive correlation between body fatness or body condition score and plasma leptin levels (r=+0·68, P<0·001 or r=+0·72, P<0·001 respectively). When concentrations of leptin were assessed over time, underfed ewes exhibited a dramatic reduction in plasma leptin values ( 56%, P<0·001). These data provide strong evidence that, in sheep, the variations in plasma concentrations of leptin are related to variations in body fatness (35%) and, to a lesser extent, in nutritional status (17%).

An ovine-specific RIA, shown to be reliable for bovine leptin determination, was used to study the effects of breed, body fatness, feeding level, and meal intake on plasma leptin level in adult cattle. Eighteen fat Charolais, fat Holstein, and lean Holstein adult cows were either well-fed (130% of maintenance energy requirements [MER]) or underfed (60% of MER) for 3 wk. The breed tended to have a small effect on plasma leptin level, which was decreased by 70% (P < 0.05) in lean compared to fat Holstein cows. A strong curvilinear relationship was found between mean adipocyte volume and plasma leptin concentrations in well-fed (r = +0.95) and underfed (r = +0.91) cows. Underfeeding caused a significant decrease in plasma leptin levels from 8.0+/-3.1 to 6.1+/-2.3 ng/mL (P < 0.01). Nine adult Holstein cows initially fed at 130% of MER (control) were underfed to 21% of MER for 7 d, and five of them were refed to 237% of MER for 21 d. Plasma leptin measured 1 h before meal distribution was decreased from 5.9+/-0.4 to 3.8+/-0.2 ng/mL (P < 0.01) by underfeeding and increased to reach 8.8+/-1.0 ng/mL (P < 0.01) after refeeding. It was positively related to plasma glucose (r = +0.52, P < 0.01) and negatively related to plasma NEFA (r = -0.67, P < 0.001). Plasma leptin measured 4 h after meal distribution was positively related to feeding level and to plasma 3-OH-butyrate (r = +0.61, P < 0.005) and negatively related to plasma NEFA (r = -0.56, P < 0.01). Differences between pre- and postprandial leptin concentrations showed a decrease after meal intake in control and well-fed cows (-7 and -19%, P < 0.01, respectively) and an increase in underfed cows (+12%, P < 0.01). Leptin response to meal intake was positively related to glucose response (r = +0.66, P < 0.001) and negatively related to 3-OH-butyrate response (r = -0.78, P < 0.001). By using the "multispecies" commercial RIA, leptin concentrations were lower and we observed similar physiological responses, although less related to other hormones or metabolites. These data provide evidence, first, that a specific RIA for ruminant leptin determination is necessary to better understand leptin regulation, and second, that plasma leptin is strongly related to adipose cell size and positively related to feeding level in adult cattle, and that an effect of meal intake could be mediated by glucose and(or) ketone bodies.

Although healthy animals are born after nuclear transfer with somatic cells nuclei, the success of this procedure is generally poor (2%-10%) with high perinatal losses. Apparently normal surviving animals may have undiagnosed pathologies that could develop later in life. The gross pathology of 16 abnormal bovine fetuses produced by nuclear transfer (NT) and the clinical, endocrinologic (insulin-like growth factors I and II [IGF-I and IGF-II], IGF binding proteins, post-ACTH stimulation cortisol, leptin, glucose, and insulin levels), and biochemical characteristics of a group of 21 apparently normal cloned calves were compared with those of in vitro-produced (IVP) controls and controls resulting from artificial insemination. Oocytes used for NT or IVP were matured in vitro. NT to enucleated oocytes was performed using cultured adult or fetal skin cells. After culture, Day 7, grade 1-2 embryos were transferred (one per recipient). All placentas and fetuses from clones undergoing an abnormal pregnancy showed some degree of edema due to hydrops. Mean placentome number was lower and mean placentome weight was higher in clones than in controls (69.9 +/- 9.2 placentomes with a mean weight of 144.3 +/- 21.4 g in clones vs. 99 and 137 placentomes with a mean individual weight of 34.8 and 32.4 g in two IVP controls). Erythrocyte mean cell volume was higher at birth (P < 0.01), and body temperature and plasma leptin concentrations were higher and T4 levels were lower during the first 50 days and the first week (P < 0.05), respectively, in clones. Plasma IGF-II concentrations were higher at birth and lower at Day 15 in clones (P < 0.05). Therefore, apparently healthy cloned calves cannot be considered as physiologically normal animals until at least 50 days of age.

No abstract

No abstract

Thirty-two 1-yr-old nulliparous Prealpes du Sud ewes were randomly allocated in a 2 x 2 factorial design and induced to lactate by injection of estradiol (.5 mg x kg(-1) x d(-1)) and progesterone (1.25 mg x kg(-1) x d(-1)) for 7 d (d 1 to 7). On d 18, 19, and 20, ewes received 1 mg/kg of hydrocortisone acetate twice daily to induce lactogenesis. Experimental ewes (n = 16) received human growth hormone-releasing factor 1-29 NH2 (hGRF 1-29 NH2) treatment (four daily x 100 microg hGRF i.v.) from d 10 to d 20. The other 16 ewes were controls. Half of both groups was maintained at either 8.5 h (ShD) or 15.5 h light (LD), and half of each subgroup was slaughtered on d 21. The remaining ewes were milked during a 6-wk period. Mammary gland epithelial tissue DNA concentration and liver growth hormone (GH) binding were evaluated on tissues from slaughtered ewes. The estrogen-progesterone treatment induced mammary gland development and enhanced the plasma concentrations of prolactin (PRL), GH, and IGF-I between d 1 and 7; concentrations increased 1.5, 2.3, and 2.6 times, respectively (P = .002). Between d 10 and 20, hGRF treatment enhanced (P < .001) plasma concentrations of GH (5 +/- 1.4 ng/mL on d 7 vs 14.4 +/- 1.3 ng/mL on d 20) and IGF-I (722 +/- 42 ng/mL on d 7 vs 1,281 +/- 82 ng/mL on d 18). Mammary DNA concentration at d 21 was greater (P = .07) for hGRF-treated ewes (1.2 vs .95 mg/g fresh tissue). Milk yield was greater (P < .025) in the hGRF groups (246 +/- 25 g/d vs 128 +/- 40 g/d). The long photoperiod regimen enhanced these responses. These results suggest that mammogenesis and(or) early lactogenesis in ewes is in part controlled by GH.

No abstract

No abstract