Regulation of feed intake rumen microbiology and fermentation nutrient absorption and splanchnic metabolism endogenous regulatory and pregnancy lactation tissue growth host resistance against parasites and pathogens.

Ruminant Physiology: Digestion, Metabolism, Growth and Reproduction

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 microl 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%).

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Plasma leptin determination in ruminants: effect of nutritional status and body fatness on plasma leptin concentration assessed by a specific RIA in sheep

The influences of body condition score (BCS) at calving and postpartum nutrition on endocrine and ovarian functions, and reproductive performance, were determined by randomly allocating thin (mean BCS = 4.4 +/- 0.1) or moderate condition (mean BCS = 5.1 +/- 0.1) Angus x Hereford primiparous cows to receive one of two nutritional treatments after calving. Cows were fed to gain either 0.45 kg/d (M, n = 17) or 0.90 kg/d (H, n = 17) for the first 71 +/- 3 d postpartum. All cows were then fed the M diet until 21 d after the first estrus. A replication (yr 2; M, n = 25; H, n = 23) was also used to evaluate reproductive characteristics. Concentrations of IGF-I, leptin, insulin, glucose, NEFA, and thyroxine were quantified in plasma samples collected weekly during treatment and during 7 wk before the first estrus. Estrous behavior was detected by radiotelemetry, and luteal activity was determined based on concentrations of progesterone in plasma. All cows were bred by AI between 14 and 20 h after onset of estrus, and pregnancy was assessed at 35 to 55 d after AI by ultrasonography. Cows that calved with a BCS of 4 or 5 had similar endocrine function and reproductive performance at the first estrus. During treatment, H cows gained BW and increased BCS (P < 0.01), and had greater (P < 0.05) concentrations of IGF-I, leptin, insulin, glucose, and thyroxine in plasma than M cows. However, during the 7 wk before the first estrus, plasma concentrations of IGF-I, leptin, insulin, glucose, NEFA, and thyroxine were not affected by time. Cows previously on the H treatment had a shorter (P < 0.01) interval to first postpartum estrus and ovulation, and a larger dominant follicle (P < 0.01) at first estrus, than M cows, but duration of estrus and the number of mounts received were not influenced by nutrient intake. Pregnancy rate at the first estrus was greater (P < 0.03) for H (76%, n = 38) than for M (58%, n = 33) cows. Increased nutrient intake after calving stimulated secretion of anabolic hormones, promoted fat deposition, shortened the postpartum interval to estrus, and increased pregnancy rate at the first estrus. Concentrations of IGF-I and leptin in plasma were constant during 7 wk before the first estrus, indicating that acute changes in these hormones are not associated with the resumption of ovarian function in primiparous beef cows.

Influence of body condition at calving and postpartum nutrition on endocrine function and reproductive performance of primiparous beef cows

Leptin in ruminants. Gene expression in adipose tissue and mammary gland, and regulation of plasma concentration

An ovine-specific RIA, shown to be reli- able 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 Eigh- teen 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 < 005) 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 =+ 095) and underfed (r =+ 091) cows Underfeeding caused a significant decrease in plasma leptin levels from 80 ± 31 to 61 ± 23 ng/mL (P < 001) Nine adult Holstein cows initially fed at 130% of MER (control) were un- derfed 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 59 ± 04 to 38 ± 02 ng/mL (P < 001) by underfeeding and increased to reach 88 ± 10 ng/mL (P < 001) after refeeding It was positively related to plasma glucose (r =+ 052, P < 001) and negatively related to plasma NEFA (r =− 067, P < 0001) Plasma leptin measured 4 h after meal distribution was positively related to feeding level and to plasma 3-OH-butyrate (r =+ 061, P < 0005) and negatively related to plasma NEFA (r =− 056, P < 001) Differences between pre- and post- prandial leptin concentrations showed a decrease after meal intake in control and well-fed cows (−7 and −19%, P < 001, respectively) and an increase in underfed cows (+12%, P < 001) Leptin response to meal intake was positively related to glucose response (r =+ 066, P < 0001) and negatively related to 3-OH-butyrate re- sponse (r =− 078,P < 0001) 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 rumi- nant leptin determination is necessary to better under- stand 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

Plasma leptin concentration in adult cattle: effects of breed, adiposity, feeding level, and meal intake.

The expression of mRNA of leptin, the product of the obese gene, in bovine adipose tissue was analyzed by a lysate RNase protection assay. The mRNA level was significantly decreased by food deprivation for two days and partially recovered after 3 hr of refeeding, indicating that obese gene expression in the ruminant was regulated by feeding.

Toru Tsuchiya

Papers

Decrease of the Obese Gene Expression in Bovine Subcutaneous Adipose Tissue by Fasting