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

Effect of postpartum body condition score change on the pregnancy outcomes of lactating Jersey cows inseminated at first service with sexed Jersey or conventional beef semen after a synchronized estrus versus a synchronized ovulation

Our objective was to compare insemination rate and pregnancies per artificial insemination (P/AI) of lactating Jersey cows inseminated at first service with sexed Jersey or conventional beef semen after submission to a Double-Ovsynch protocol for timed artificial insemination (TAI) versus a protocol to synchronize estrus at similar days in milk (DIM). Secondary objectives were to determine the effect of protocol synchrony and postpartum body condition score (BCS) change on P/AI. Lactating Jersey cows (n = 1,272) were allocated by odd versus even ear tag number, which was randomly allocated within the herd, within parity and semen type for submission to a Double-Ovsynch protocol (DO; n = 707) or a protocol to synchronize estrus (ED; n = 565). All ED cows detected in estrus were inseminated (EDAI; n = 424), with undetected cows receiving TAI after an Ovsynch protocol (EDTAI; n = 141). There was a treatment by parity interaction on insemination rate with 100% of DO cows receiving TAI, but a tendency for fewer primiparous ED cows to be detected in estrus and AI than multiparous cows (69.5% ± 0.04% vs. 77.1% ± 0.02%, respectively). For cows inseminated with sexed Jersey or conventional beef semen, DO cows tended to have and had more P/AI than EDAI cows (sexed, 49.2% ± 0.03% vs. 43.6% ± 0.03%; beef, 64.2% ± 0.04% vs. 56.3% ± 0.05%, respectively) and had more P/AI than EDAI+EDTAI cows (sexed, 49.1% ± 0.03% vs. 40.6% ± 0.03%; beef, 65.5% ± 0.04% vs. 56.2% ± 0.04%, respectively). Overall, 29.1% of DO cows expressed estrus with 5.0% and 24.2% of cows detected in estrus ≥24 h before and at TAI, respectively, and there was no difference in P/AI 61 ± 4 d after AI based on expression of estrus at TAI. The synchronization rate was greater for DO than EDAI cows (92.1% ± 0.01% vs. 79.2% ± 0.02%, respectively); however, synchronized DO cows had more P/AI than synchronized EDAI cows (55.0% ± 0.02% vs. 49.2% ± 0.03%, respectively). There was an interaction between BCS change from 7 to 39 ± 2 DIM and treatment on P/AI 61 ± 4 d after AI with no difference between DO and EDAI cows that lost = 0.25 (49.8% ± 0.04% vs. 51.0% ± 0.05%, respectively) or maintained or gained (55.6% ± 0.04% vs. 50.8% ± 0.05%, respectively) BCS, but within cows that lost ≥0.5 BCS, DO cows had more P/AI than EDAI cows (54.1% ± 0.04% vs. 36.1% ± 0.04%, respectively). In conclusion, submission of lactating Jersey cows to a Double-Ovsynch protocol for first insemination increased insemination rate and fertility to first insemination compared with AI after a detected estrus regardless of semen type and expression of estrus, particularly for cows with excessive postpartum BCS loss.

Effect of reduced water intake on ovarian reserve, leptin immunoexpression and impact of leptin on the in vitro culture of sheep secondary follicles

This study evaluated the effect of reduced water intake on survival, apoptosis and immunoexpression of leptin in sheep preantral follicles, activation of primordial follicles, serum levels of leptin, estradiol (E2) and progesterone (P4), and in vitro maturation (IVM) of oocytes antral follicles, as well evaluated the effects of leptin on in vitro culture of secondary follicles isolated these animals. Ewes (n = 32) were divided into four groups: water ad libitum (Control - 100%), 80%; 60% and 40% of ad libitum intake. Blood was collected to determine, leptin, E2 and P4, before and after experiment. After the slaughter, ovarian cortex was used to histological and immunohistochemistry analysis and oocytes IVM. Moreover, isolated secondary follicles were cultured in vitro for 12 days in control medium (α-MEM+) or α-MEM+ with 10 or 25 ng/mL leptin. The reduction of water intake caused a linear decreasing effect on the percentages of normal preantral follicles, especially of primordial (P < 0.05), increased the apoptosis (P < 0.05) and decreased leptin expression in preantral follicles. The treatment with 60% of water intake showed greater total growth rate of isolated secondary follicles cultured with 25 ng/L leptin (P < 0.05), compared to those cultured in α-MEM+ . In conclusion, reduced water intake impaired the number of normal sheep preantral follicles, especially of primordial follicles, increased apoptosis and decreased leptin expression in preantral follicles. Moreover, secondary follicles from of ewes that receive 60% water intake increased follicular growth after in vitro culture with 25 ng/mL leptin.

The Effect of Leptin on the Blood Hormonal Profile (Cortisol, Insulin, Thyroid Hormones) of the Ewe in Acute Inflammation in Two Different Photoperiodical Conditions

As a day animal with sensitivity to inflammation similar to that of humans, the sheep may highly outperform the rodent model in inflammation studies. Additionally, seasonality makes sheep an interesting model in endocrinology research. Although there are studies concerning inflammation’s influence on leptin secretion and vice versa, a ewe model, with its possible ‘long-day leptin resistance’, is still not examined enough. The present study aimed to examine whether leptin may modulate an acute inflammation influence on plasma hormones in two photoperiodical conditions. The experiment was conducted on 48 ewes divided into four groups (control, lipopolysaccharide (LPS), leptin, LPS + leptin) during short and long days. Blood sampling started 1 hour before and continued 3 h after LPS/saline administration for further hormonal analysis. The results showed that the photoperiod is one of the main factors influencing the basal concentrations of several hormones with higher values of leptin, insulin and thyroid hormones during long days. Additionally, the acute inflammation effect on cortisol, insulin and thyroid hormones was photoperiod-dependent. The endotoxemia may also exert an influence on leptin concentration regardless of season. The effects of leptin alone on hormone blood concentrations are rather limited; however, leptin can modulate the LPS influence on insulin or thyroxine in a photoperiod-dependent way.

Blood thyroid hormones, insulin and leptin, metabolites and enzymes in transition dairy ewes, as affected by dietary linseed and physiological stage

This study investigated the effects of dietary linseed and physiological state on blood concentrations of some metabolic hormones and indicators, in transition dairy ewes. From 21 d before lambing to 60 d post-partum, ewes were provided with one of three isoenergetic and iso‑nitrogenous pelleted concentrates, without (CTR, n = 21), or with 100 (EL-10, n = 22) or 200 g/kg (EL-20, n = 22) of extruded linseed. Animals were fed alfalfa hay ad libitum and had access to mixed pasture. Plasma thyroid hormones and insulin concentrations were not affected by diet and significantly changed by time. The last week of pregnancy T3 (2.27 ± 0.15 ng/mL) and T4 (102.63 ± 2.85 ng/mL) were lower than at 4 weeks before lambing (T3: 3.27 ± 0.27 ng/mL; T4: 125.89 ± 2.63 ng/mL). After lambing, T3 rose to be highest at 4 and 8 weeks of lactation (3.41 ± 0.22). Mean insulin peaked 2 weeks after lambing (0.31 ± 0.02 ng/mL) vs. late pregnancy (0.22 ± 0.01 ng/mL) and progressing lactation (0.18 ± 0.01 ng/mL). Plasma Leptin concentration (2.43 ± 0.03 ng/mL) was not affected by diet nor time. All the blood metabolites and enzymes investigated showed significant time x treatment interaction. Differences of several haematological parameters were found in EL vs. CTR (cholesterol, triglycerides, total protein, bilirubin, ALP, ALT), however, in most cases the values were fairly within the reference physiological ranges. Metabolic hormones are confirmed to be mainly linked to the different physiological states, energy intake and variations of energy balance, without clear effects by different sources of energy and quality of dietary lipids.

Symposium review: Adipose tissue endocrinology in the periparturient period of dairy cows

The involvement of adipose tissue (AT) in metabolism is not limited to energy storage but turned out to be much more complex. We now know that in addition to lipid metabolism, AT is important in glucose homeostasis and AA metabolism and also has a role in inflammatory processes. With the discovery of leptin in 1994, the concept of AT being able to secrete messenger molecules collectively termed as adipokines, and acting in an endo-, para-, and autocrine manner emerged. Moreover, based on its asset of receptors, many stimuli from other tissues reaching AT via the bloodstream can also elicit distinct responses and thus integrate AT as a control element in the regulatory circuits of the whole body's functions. The protein secretome of human differentiated adipocytes was described to comprise more than 400 different proteins. However, in dairy cows, the characterization of the physiological time course of adipokines in AT during the transition from pregnancy to lactation is largely limited to the mRNA level; for the protein level, the analytical methods are limited and available assays often lack sound validation. In addition to proteinaceous adipokines, small compounds such as steroids can also be secreted from AT. Due to the lipophilic nature of steroids, they are stored in AT, but during the past years, AT became also known as being able to metabolize and even to generate steroid hormones de novo. In high-yielding dairy cows, AT is substantially mobilized due to increased energy requirements related to lactation. As to whether the steroidogenic system in AT is affected and may change during the common loss of body fat is largely unknown. Moreover, most research about AT in transition dairy cows is based on subcutaneous AT, whereas other depots have scarcely been investigated. This contribution aims to review the changes in adipokine mRNA and-where available-protein expression with time relative to calving in high-yielding dairy cows at different conditions, including parity, body condition, diet, specific feed supplements, and health disorders. In addition, the review provides insights into steroidogenic pathways in dairy cows AT, and addresses differences between fat depots where possible.

Exogenous leptin promotes reproductive behavior during aphagia in red-sided garter snakes (Thamnophis sirtalis parietalis)

Despite the established dichotomy between investment in either reproduction or self-maintenance, a hormonal mechanism that influences an organism's decision to prioritize these behaviors remains elusive. The protein hormone leptin is a likely candidate because it is secreted from adipocytes in proportion to the amount of stored fat in numerous species. Although the majority of studies suggest that leptin stimulates reproduction, the actions of leptin can be context-dependent. Leptin increases sexual behavior in fed individuals, but inhibits sexual behavior in food-restricted individuals. We investigated if exogenous leptin influences sexual behavior in red-sided garter snakes (Thamnophis sirtalis parietalis) experiencing a predictable bout of aphagia during the mating season. We tested two doses of recombinant murine leptin injected for three days. Males were subjected to three mating trials, one on each day of injections, while females were subjected to one mating trial on the last day of injections. Leptin affects male and female snakes similarly by increasing both appetitive (i.e., mating behavior score) and consummatory (i.e., number of copulations, proportion of individuals copulated) sex behavior. We found no evidence to suggest that leptin influenced latency to copulate or duration of copulation. Because leptin promotes reproductive behavior in non-feeding garter snakes, these findings do not align with research on food-restricted mammals. Further investigations into how leptin affects sexual behavior in snakes exposed to food-restriction manipulations would clarify if the role of leptin is evolutionarily divergent.

Transcript Abundances of the Prolactin Receptor, the Leptin Receptor and their Major Suppressor in the Sheep Mammary Gland During Pregnancy and Lactation

This study aimed to expand the knowledge of the interactions between prolactin (PRL) and leptin in the ovine mammary gland during pregnancy and lactation; we examined the mRNA expression of prolactin receptor (PRLR), the long form of the leptin receptor (LRb) and suppressor of cytokine signaling (SOCS)-3 in mammary gland biopsies collected on days 60, 90 and 120 of pregnancy and on days 30, 60 and 90 of lactation (n = 6 for each time point), along with the plasma PRL and leptin concentrations. The PRL concentrations were stable throughout pregnancy and increased during lactation. The plasma leptin concentrations were comparable among nonpregnant, early-pregnant, late-pregnant and lactating ewes, but this metric peaked during mid-pregnancy. Expression of PRLR and SOCS-3 in the mammary gland fluctuated during the transition from pregnancy to lactation, and differences in LRb expression occurred during the late stages of lactation. The LRb transcript abundance was approximately 31 times higher in ewes on day 60 of lactation than in early-lactating ewes. Expression of SOCS-3 mRNA in biopsies gradually decreased over the course of pregnancy and reached a minimum value during late pregnancy. After lambing, the transcript level of SOCS-3 increased and peaked on day 60 of lactation. During pregnancy, the plasma PRL concentration positively correlated with the abundances of PRLR (r = 0.971, P<0.01) and SOCS-3 (r = 0.818, P<0.05). Positive correlations were also observed between the transcript abundances of SOCS-3 and LRb (r = 0.854, P<0.05). The variations observed in the plasma PRL and leptin concentrations and the changes in expression of key leptin and PRL signal transduction pathway components, such as PRLR, LRb and SOCS-3, indicate that the efficacies of both hormone actions are modulated in a multilevel manner throughout pregnancy and lactation. These interactions may regulate the ability of the mammary gland to respond to current energy requirements and challenges, thus affecting milk yield and lactation duration.

Photoperiod Affects Leptin Action on the Choroid Plexus in Ewes Challenged with Lipopolysaccharide-Study on the mRNA Level

The ovine choroid plexus (ChP) expresses the long isoform of the leptin receptor, which makes this structure a potential target for leptin action. In sheep, leptin concentration in plasma is higher during long days (LD) than short days (SD). This study evaluates the influence a of photoperiod on leptin impact on the gene expression of Toll-like receptor 4 (TLR4), proinflammatory cytokines (IL1B, IL6), their receptors (IL1R1, IL1R2, ILRN, IL6R, IL6ST) and inflammasome components necessary for pro-IL-1β activation (NLRP3, PYCARD, CASP1), chemokine (CCL2), leptin receptor isoforms (LEPRa, LEPRb) and a suppressor of cytokine signalling (SOCS3) in the ChP of ewes treated or not with lipopolysaccharide (LPS). Studies were conducted on adult female sheep divided into four groups (n = 6 in each): control, leptin (20 μg/kg), LPS (400 ng/kg), and LPS and leptin injected under SD and LD photoperiods. The leptin alone did not affect the gene expression but in co-treatment with LPS increased (p < 0.05) IL1B but only during SD, and SOCS3, IL1R2, IL1RN, IL6ST and CCL2 only during LD, and decreased (p < 0.05) the IL1R1 expression only during SD photoperiod. This indicates that the immunomodulatory action of leptin on the ChP is manifested only under the LPS challenge and is photoperiodically dependent.

Anagliptin suppresses diet-induced obesity through enhancing leptin sensitivity and ameliorating hyperphagia in high-fat high-sucrose diet fed mice

Obesity is a major risk factors for type 2 diabetes, and weight loss is beneficial to diabetic patients who are obese or overweight. Dipeptidyl peptidase-4 (DPP-4) inhibitors are anti-diabetic drugs. Although it has been known that the effect of most of the DPP-4 inhibitors on body weight is neutral, several studies suggested that some DPP-4 inhibitors suppressed body weight. Nonetheless, the mechanisms underlying DPP-4 inhibitor-induced weight loss are not fully understood. In this study, the mice fed high-fat high sucrose diet (HFHSD) containing a DPP4 inhibitor, anagliptin, showed reduced food intake and body weight compared to the mice fed non-treated HFHSD, but oxygen consumption and respiratory exchange ratio (RER) were not altered. Sequential administration of leptin suppressed food intake and body weight more apparently in anagliptin treated HFHSD fed mice than non-treated HFHSD fed mice. Oxygen consumption and RER were comparable between anagliptin treated and non-treated mice after leptin administration. The number of phospho STAT3 expressed cells in the arcuate nucleus after leptin administration was increased in anagliptin treated mice compared to non-treated mice. These data suggested that anagliptin ameliorated leptin resistance induced by HFHSD and thereby decreased food intake and body weight. These effects of anagliptin could be beneficial to the treatment of obese diabetic patients.

Effects of central and peripheral administration of an acute-phase protein, α-1-acid-glycoprotein, on feed intake and rectal temperature in sheep

In rodents, an acute-phase protein, α-1-acid-glycoprotein (AGP), was shown to provide a link between inflammation and suppression of feed intake by acting as a leptin receptor agonist. The objective of this study was to determine the effects of AGP on feed intake and rectal temperature in sheep. Ewes were ovariectomized, implanted with a cannula into a lateral ventricle of the brain, and kept indoors in individual pens. Feed intake and rectal temperature were determined for sheep in all experiments. In the first experiment, ewes (n = 4) received 1 of 4 treatments [0 (control), 0.012 (low), 0.06 (medium), or 0.30 (high) mg/kg BW AGP] into the lateral ventricle (ICV). All sheep received all treatments in a Latin square design balanced for carryover effects with 10 d between treatments. In the second experiment, ewes (n = 10) received 1 of 2 treatments (0 and 3 mg/kg BW of AGP) intravenously (IV) in a completely randomized design. In the third experiment, ewes (n = 19) received peripheral treatments (IV) of an antipyretic [0 (control) or 2.2 mg/kg BW flunixin meglumine (FLU)] 30 min before receiving central AGP [0 (control) or 0.3 mg/kg BW of AGP] in a completely randomized design. All data were analyzed using a mixed model analysis of variance and tested for effects of treatment, time, and the interaction of treatment and time. Cumulative 48-h feed intake after administration of treatments was also determined. In the first experiment, there was no effect of ICV treatment (P = 0.37) on feed intake rate or on cumulative feed intake (P = 0.31). There was an effect of ICV treatment (P = 0.002) on rectal temperatures, which were greater (P < 0.05) after the high dose of centrally administered AGP. In the second experiment, there was no effect of AGP administration IV on feed intake rate (P = 0.98), on cumulative feed intake (P = 0.41) or on rectal temperature (P = 0.71). In the third experiment, there was an effect of central AGP treatment (P < 0.0001) and an interaction of central AGP and time (P < 0.0001) on rectal temperature, whereas FLU had no effect (P = 0.93), demonstrating that AGP increased rectal temperatures regardless of antipyretic treatment. These results indicate that central AGP increases rectal temperature in sheep by pathways that do not involve prostaglandins. Further research is needed to determine whether AGP may be an important integrator of energy balance and inflammation.

Technical note: Effects of pegylation and route of administration on leptin kinetics in newborn lambs1

Chronic energy insufficiency resulting from inadequate feed intake or increased nutrient demand reduces plasma leptin in ruminants. Treatment of energy-deficient ruminants with exogenous leptin has identified some physiological consequences of reduced plasma leptin, but their full complement remains unknown. Additional leptin-dependent responses could be identified by using strategies that interfere with leptin signaling such as administration of leptin mutants that act as competitive antagonists. The effectiveness of these antagonists depends on their fold excess over endogenous leptin, and this condition can be achieved under in vivo conditions by extending the half-life (t1/2) of the antagonist by addition of a polyethylene glycol (PEG) molecule (pegylation). Use of this approach in ruminants, however, is limited by the lack of information on the t1/2 of native and pegylated leptin and on the most effective route of administration. To answer these questions, newborn lambs (n = 3) were injected with an intravenous (i.v.) bolus of 150 µg of human leptin followed by blood sampling over the next 12 h. Analysis of the semilog plasma leptin concentration over time yielded a t1/2 of 43 ± 4.9 min; an i.v. bolus of 276 µg of bovine leptin yielded a comparable t1/2 (P > 0.05). Next, newborn lambs (n = 4) received a single dose of 229 μg/kg of metabolic body weight (BW0.75) of pegylated super human leptin antagonist (PEG-SHLA) via the i.v. or subcutaneous (s.c.) route. Plasma PEG-SHLA concentration reached a peak of 1,528 ± 78 ng/mL after 1 min and a nadir of 71 ± 9 ng/mL after 24 h with the i.v. route versus a peak of 423 ± 43 ng/mL after 300 min and a nadir of 146 ± 22 ng/mL after 24 h for the s.c. route; the t1/2 of PEG-SHLA was 394 ± 29 min for the i.v. route and 433 ± 58 min for the s.c. route. Finally, plasma concentration of PEG-SHLA was modeled when given either i.v. or s.c. at a dose of 229 μg/kg BW0.75 every 12 h. Once a steady state was reached, peak and lowest concentrations PEG-SHLA over the 12-h windows were 2,269 and 403 ng/mL for the i.v. route and 814 and 555 ng/mL for the s.c. route. Weighted PEG-SHLA concentrations over the 12-h period were 1,455 and 713 ng/mL for the i.v. and s.c. route, translating into 364- and 178-fold excess over endogenous plasma leptin. These data confirm the effectiveness of pegylation in extending the t1/2 of leptin antagonists in newborn lambs and in increasing their circulation in fold excess over endogenous leptin.

Hypothalamic-Pituitary and Adipose Tissue Responses to the Effect of Resistin in Sheep: The Integration of Leptin and Resistin Signaling Involving a Suppressor of Cytokine Signaling 3 and the Long Form of the Leptin Receptor

We hypothesized that resistin is engaged in the development of leptin central insensitivity/resistance in sheep, which is a unique animal model to explore reversible leptin resistance. Thirty Polish Longwool ewes, which were ovariectomized with estrogen replacement, were used. Treatments consisted of the intravenous injection of control (saline) or recombinant bovine resistin (rbresistin): control (Control; n = 10), a low dose of rbresistin (R1; 1.0 μg/kg body weight (BW); n = 10), and a high dose of rbresistin (R2; 10.0 μg/kg BW; n = 10). The studies were performed during short-day (SD) and long-day (LD) photoperiods. Leptin and resistin concentrations were determined. Expression levels of a suppressor of cytokine signaling (SOCS)-3 and the long form of the leptin receptor (LeptRb) were determined in selected brain regions, including in the anterior pituitary (AP), hypothalamic arcuate nucleus (ARC), preoptic area (POA), and ventro- and dorsomedial nuclei (VMH/DMH). The results indicate that resistin induced a consistent decrease in LeptRb (except in POA) and an increase in SOCS-3 expression during the LD photoperiod in all selected brain regions. In conclusion, the results demonstrate that the action of resistin appears to be strongly associated with photoperiod-driven changes in the leptin signaling pathway, which may underlie the phenomenon of central leptin resistance.

Supplementation with eicosapentaenoic and docosahexaenoic acids in late gestation in ewes changes adipose tissue gene expression in the ewe and growth and plasma concentration of ghrelin in the offspring1

Omega-3 long chain fatty acids have a positive impact on production. When consumed during late gestation, it might have fetal programming effects on the fetus, which will have lifelong impacts on development and production. The objectives of the present study were to evaluate the effect of increasing doses of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in the diet of ewes in the last third of gestation on their body weight (BW), subcutaneous adipose tissue relative mRNA abundance of genes associated with adipose tissue metabolism, and growth performance and plasma metabolites and hormones of their offspring during the finishing phase. Ewes (n = 72) were blocked by BW and allotted to pens (8 per treatment) with 3 ewes per pen. Ewes were supplemented with an EPA and DHA source (Strata G113) at concentrations of 0, 1, or 2% of dry matter intake during the last 50 d of gestation. At lambing, all ewes were penned together and offered the same diet. After weaning at 60 d of age, lambs were blocked by BW and sex and fed for 56 d. All lambs were fed the same pellet diet (61.09% ground corn, 24.08% soy hulls, 11.09% soybean meal, 1.48% Ca salt of palm oil, and 2.26% mixed mineral vitamin), and were weighed every 14 d until the end of the trial. Blood samples were collected on the weight sampling days. Dry matter intake and refusals were weighed daily. Data were analyzed as a randomized complete block design with repeated measurements (SAS 9.4). Polynomial contrast (linear-L and quadratic-Q) was used for mean separation. There were no differences in ewe body condition score, milk production, milk fat, or milk protein, but there was a trend for increased (L, P = 0.06) lactose concentration, and also differences in DGAT1 (L, P = 0.04), Δ5-desaturase (Q, P = 0.06) and Δ6-desaturase (Q, P = 0.07), PPARα (Q, P = 0.03), ELOVL2 and 5 (Q, P < 0.07), FABP4 (Q, P = 0.04), FATP1 (Q, P = 0.06), leptin (Q, P = 0.02), and resistin (L, P = 0.05). Feeding pregnant ewes an increased amount of EPA and DHA in late gestation increased final BW (L, P = 0.01), ADG (L, P = 0.04; Q, P = 0.01), DMI (Q, P ≤ 0.01), plasma glucose concentration (L, P = 0.04), and trended to decrease ghrelin concentrations (L, P = 0.07) in offspring during the finishing period. Dam supplementation did not affect G:F, nor plasma NEFA concentration (P ≥ 0.53) of lambs. Therefore, increasing supplementation of EPA and DHA in pregnant ewes has an impact on offspring performance, increasing DMI, ADG, and BW.

Effects of leptin on the follicular development and mitochondrial activity of ovine isolated early antral follicles cultured in vitro

This study evaluated the effect of leptin on the in vitro culture of isolated sheep early antral follicles. Early antral follicles (300-450 μm) were isolated and cultured for 12 days in tissue culture medium 199 (TCM 199) supplemented with glutamine, hypoxanthine, transferrin, insulin, selenium, ascorbic acid, bovine serum albumin (BSA) and recombinant follicle stimulating hormone (rFSH) (TCM 199⁺: control medium) or TCM 199⁺ supplemented with 2 or 10 ng/mL leptin. After culture, oocytes were subjected to in vitro maturation (IVM). The parameters analyzed were morphology, extrusion rate, follicular diameter, growth and fully-grown oocytes (oocytes ≥110 μm) rates. After IVM, reactive oxygen species (ROS) levels, mitochondrial activity, meiotic stages and meiotic resumption rates were also analyzed. After 12 days of culture, the concentration of 2 ng/mL of leptin showed a higher percentage of morphologically normal follicles, fully-grown oocytes (≥110 μm), active mitochondria and meiotic resumption compared to the control medium (TCM 199⁺; P < 0.05) but did not differ when compared to leptin concentration of 10 ng/mL (P > 0.05). After culturing, no significant differences existed among treatments in terms of the follicle diameter and ROS levels. In conclusion, the addition of 2 ng/mL leptin to the base culture medium is capable of improving follicular survival, oocyte growth, mitochondrial activity and meiotic resumption after the in vitro culture of isolated sheep early antral follicles.

Downregulation of LRb in VMH/DMH during the second half of gestation and upregulation of SOCS-3 in ARC in late-pregnant ewes - Implications for leptin resistance

To investigate factors involved in pregnancy-induced regulation of tissue sensitivity to leptin, we determined leptin concentrations and expression levels of the long form of the leptin receptor (LRb) and suppressor of cytokine signalling (SOCS)-3 in the ventro- and dorsomedial nuclei (VMH/DMH), arcuate nucleus (ARC), median eminence (ME) and anterior pituitary (AP) in 15 Polish Longwool ewes euthanized at 30, 60, 90 and 120 days of pregnancy and before gestation (n = 3 per group). Leptin concentrations increased during the first half of pregnancy, peaked on day 60, and then declined. In the VMH/DMH, LRb mRNA levels decreased from day 60 of pregnancy; in the ARC, LRb mRNA levels remained stable before and throughout pregnancy. LRb expression in the ME was lower in the first two months of pregnancy than before pregnancy (P < 0.01) and peaked at day 90. In the AP, LRb mRNA levels were higher during mid-pregnancy (P < 0.05) than before pregnancy. SOCS-3 expression in the VMH/DMH was higher throughout gestation (P < 0.05) than before pregnancy but was undetectable at day 120. SOCS-3 transcript levels were higher in the ARC (P < 0.05) in late-pregnancy (at day 120) than in non-pregnant ewes. SOCS-3 mRNA levels in the ME were lower at days 30 and 60 (P < 0.05) than at day 120 or before pregnancy. In the AP, SOCS-3 transcription was stable throughout gestation except at day 120, when it increased (P < 0.05). The changes in plasma leptin concentrations during pregnancy, hypothalamic LRb downregulation in the VMH/DMH during the second half of gestation and SOCS-3 upregulation in the ARC in late-pregnant ewes identified here may be essential components of the mechanisms driving ovine leptin insensitivity.

The effects of leptin on plasma concentrations of prolactin, growth hormone, and melatonin vary depending on the stage of pregnancy in sheep

The effects of hyperleptinemia and leptin resistance during gestation are unclear. Leptin, an important neuroendocrine regulator, has anorexic effects, but its interactions with other metabolic hormones during pregnancy are unclear. We examined potential roles of leptin in regulating prolactin (PRL), GH, and melatonin plasma concentrations during pregnancy in Polish Longwool ewes. Twelve estrus-synchronized ewes carrying twins after mating were randomly assigned to receive i.v. injections of saline or recombinant ovine leptin (2.5 or 5.0 µg/kg BW). Blood samples were collected (15-min intervals over 4 h) immediately before the first injection at dusk and kept under red light. Treatments were repeated at 2-wk intervals, starting before mating and continuing from days 30 to 135 of gestation. Concentrations of plasma PRL, GH, and melatonin were determined using a validated RIA. The effects of leptin on hormone plasma concentrations varied depending on pregnancy stage and leptin dose. PRL plasma concentrations were affected at most stages of pregnancy and before gestation. In non-, very early- (day 30), and late- (day 120 and 135) pregnant ewes, exogenous leptin stimulated PRL (P < 0.001) plasma concentrations, while during the second month of gestation, it decreased PRL concentrations (P < 0.01). Leptin affected GH plasma concentrations (P < 0.05) only during the first 2 mo of pregnancy, with no effects during the second part of gestation or before pregnancy. In early-pregnant ewes (day 30 and 45), leptin decreased melatonin plasma concentrations (P < 0.05), but at day 60, leptin stimulated melatonin plasma concentrations at low (P < 0.01) and high doses (P < 0.05), with no effects in ewes after 105 d of gestation. These data indicate specific pregnancy-induced endocrine adaptations to changes in energy homeostasis, supporting the hypothesis that leptin affects PRL, GH, and melatonin release during gestation.

Regulation of GnRH pulsatility in ewes

Early work in ewes provided a wealth of information on the physiological regulation of pulsatile gonadotropin-releasing hormone (GnRH) secretion by internal and external inputs. Identification of the neural systems involved, however, was limited by the lack of information on neural mechanisms underlying generation of GnRH pulses. Over the last decade, considerable evidence supported the hypothesis that a group of neurons in the arcuate nucleus that contain kisspeptin, neurokinin B and dynorphin (KNDy neurons) are responsible for synchronizing secretion of GnRH during each pulse in ewes. In this review, we describe our current understanding of the neural systems mediating the actions of ovarian steroids and three external inputs on GnRH pulsatility in light of the hypothesis that KNDy neurons play a key role in GnRH pulse generation. In breeding season adults, estradiol (E₂) and progesterone decrease GnRH pulse amplitude and frequency, respectively, by actions on KNDy neurons, with E₂ decreasing kisspeptin and progesterone increasing dynorphin release onto GnRH neurons. In pre-pubertal lambs, E₂ inhibits GnRH pulse frequency by decreasing kisspeptin and increasing dynorphin release, actions that wane as the lamb matures to allow increased pulsatile GnRH secretion at puberty. Less is known about mediators of undernutrition and stress, although some evidence implicates kisspeptin and dynorphin, respectively, in the inhibition of GnRH pulse frequency by these factors. During the anoestrus, inhibitory photoperiod acting via melatonin activates A15 dopaminergic neurons that innervate KNDy neurons; E₂ increases dopamine release from these neurons to inhibit KNDy neurons and suppress the frequency of kisspeptin and GnRH release.

Interaction of dietary energy source and body weight gain during the juvenile period on metabolic endocrine status and age at puberty in beef heifers

Using a previously established model for nutritional acceleration of puberty, beef heifers ( = 48; 1/2 Angus × 1/4 Hereford × 1/4 Brahman) were used in a replicated 2 × 2 factorial design to examine the effects of diet type (high forage [HF] vs. high concentrate [HC]) and rate of BW gain (low gain [LG], 0.45 kg/d, vs. high gain [HG], 0.91 kg/d) on key metabolic hormones and age at puberty. After weaning at 14 ± 1 wk of age, heifers were assigned randomly to be fed HC-HG, HC-LG, HF-HG, or HF-LG ( = 12/group) beginning at 4 mo of age for 14 wk. Heifers were then switched to a common growth diet until puberty. Average daily gain was greater ( < 0.04) during the dietary treatment phase in HG heifers (0.81 ± 0.06 kg/d) than in LG heifers (0.43 ± 0.06 kg/d), and there was no diet type × rate of gain interaction. Puberty was achieved at a younger age (54.5 ± 1.8 wk) in both HG groups than in LG groups (60.2 ± 1.9 wk; < 0.04), but dietary energy source (HC vs. HF) did not influence this variable. Moreover, mean BW at puberty did not differ by diet type or rate of gain during the dietary treatment phase. Nonetheless, heifers fed HC-HG exhibited a striking increase ( < 0.0001) in serum leptin beginning at 26 ± 1 wk of age and remained elevated ( < 0.01) throughout the remainder of the experimental feeding phase compared to all other treatments. However, serum leptin in HC-HG dropped precipitously when heifers were switched to the common growth diet and did not differ from that of other groups thereafter. Overall mean concentrations of serum glucose were greater ( < 0.006) in HG heifers than in LG during the dietary treatment phase, with serum insulin also greater ( < 0.04) in HG than in LG only during weeks 20, 22, and 30. Mean serum IGF-1 was not affected by dietary type or rate of BW gain. We speculate that failure of the marked increase in serum leptin observed in HC-HG heifers during the dietary treatment phase to further accelerate puberty compared to HF-HG occurred because of its abrupt decline at the onset of the common growth phase, thus attenuating the temporal cue for activation of the reproductive neuroendocrine system.

The effect of feeding intensity during the dry period on plasma leptin and time to return to cyclicity in dairy cows

Much evidence has accumulated showing that female reproductive functions are disrupted when changes in nutritional status take place in both over- and undernutrition. The peptide hormone leptin is considered a possible link between nutrition and reproduction. One objective with the present study was to investigate how different levels of feed intake during the dry period, thereby creating differences in body condition at parturition, affected the plasma leptin concentration and the reproductive function after parturition.

Plasma leptin in transition dairy cows. Effects of body fatness, ambient temperature and dietary factors

In ruminants plasma leptin is increased with increasing body fatness. Leptin acts on hypothalamus to decrease food intake and increase energy expenditure. It is possible that leptin has a key role in transition from pregnancy to lactation of dairy cows. The objective of the present work was to investigate the pattern of plasma leptin concentration, as well as its relationship with other hormones and metabolites and dairy cow performance.

Adipose triglyceride lipase protein abundance and translocation to the lipid droplet increase during leptin-induced lipolysis in bovine adipocytes

Proper regulation of lipid metabolism is critical for preventing the development of metabolic diseases. It is clear that leptin plays a critical role in the regulation of energy homeostasis by regulating energy intake. However, leptin can also regulate energy homeostasis by inducing lipolysis in adipocytes, but it is unclear how the major lipases are involved in leptin-stimulated lipolysis. Therefore, the objectives of this study were to determine if (1) leptin acts directly to induce lipolysis in bovine adipocytes, (2) the potential lipases involved in leptin-induced lipolysis in bovine adipocytes, and (3) increases translocation of adipose triglyceride lipase (ATGL) and hormone sensitive lipase (HSL) during leptin-stimulated lipolysis in bovine stromal vascular cell-derived adipocytes. As hypothesized, leptin induced a lipolytic response (P = 0.02) in isolated adipocytes which was accompanied by an increase in phosphorylation of signal transducer and activator of transcription (STAT)3 (P = 0.03), a well-documented secondary messenger of leptin, and ATGL protein abundance (P < 0.01). Protein abundance of STAT3, perilipin, HSL, and phosphorylation of HSL by PKA and AMPK were not altered during leptin-stimulated lipolysis (P > 0.05). Immunostaining techniques were employed to determine the location of HSL and ATGL. Both lipases translocated to the lipid droplet after 2 h of exposure to isoproterenol (P < 0.02). However, only ATGL was translocated to the lipid droplet during leptin-stimulated lipolysis (P = 0.04), indicating ATGL may be the active lipase in leptin-stimulated lipolysis. In summary, leptin stimulates lipolysis in bovine adipocytes. The lack of phosphorylated HSL and translocation of HSL to the lipid droplet during leptin-stimulated lipolysis suggest minimal activity by PKA. Interestingly, leptin-stimulated lipolysis is accompanied by an increase in ATGL protein abundance and translocation to the lipid droplet, indicating its involvement in leptin-stimulated lipolysis either due to an increase in protein abundance or through a novel lipolytic cascade.

Circulating leptin and its muscle gene expression in Nellore cattle with divergent feed efficiency

Background

Leptin has a strong relation to important traits in animal production, such as carcass composition, feed intake, and reproduction. It is mainly produced by adipose cells and acts predominantly in the hypothalamus. In this study, circulating leptin and its gene expression in muscle were evaluated in two groups of young Nellore bulls with divergent feed efficiency. Individual dry matter intake (DMI) and average daily gain (ADG) of 98 Nellore bulls were evaluated in feedlot for 70 d to determinate the residual feed intake (RFI) and select 20 animals for the high feed efficient (LRFI) and 20 for the low feed efficient (HRFI) groups. Blood samples were collected on d 56 and at slaughter (80 d) to determine circulating plasma leptin. Samples of Longissimus dorsi were taken at slaughter for leptin gene expression levels.

Results

DMI and RFI were different between groups and LRFI animals showed less back fat and rump fat thickness, as well as less pelvic and kidney fat weight. Circulating leptin increased over time in all animals. Plasma leptin was greater in LRFI on 56 d and at slaughter (P = 0.0049). Gene expression of leptin were greater in LRFI animals (P = 0.0022) in accordance with the plasma levels. The animals of the LRFI group were leaner, ate less, and had more circulating leptin and its gene expression.

Conclusion

These findings demonstrated that leptin plays its physiological role in young Nellore bulls, probably controlling food intake because feed efficient animals have more leptin and lower residual feed intake.

Tissue cell stress response to obesity and its interaction with late gestation diet

Intrauterine growth restriction in late pregnancy can contribute to adverse long-term metabolic health in the offspring. In the present study we used an animal (sheep) model of maternal dietary manipulation in late pregnancy, combined with exposure of the offspring to a low-activity, obesogenic environment after weaning, to characterise the effects on glucose homeostasis. Dizygotic twin-pregnant sheep were either fed to 60% of requirements (nutrient restriction (R)) or fed ad libitum (~140% of requirements (A)) from 110 days gestation until term (~147 days). After weaning (~3 months of age), the offspring were kept in either a standard (in order to remain lean) or low-activity, obesogenic environment. R mothers gained less weight and produced smaller offspring. As adults, obese offspring were heavier and fatter with reduced glucose tolerance, regardless of maternal diet. Molecular markers of stress and autophagy in liver and adipose tissue were increased with obesity, with gene expression of hepatic glucose-related protein 78 (Grp78) and omental activation transcription factor 6 (Atf6), Grp78 and ER stress degradation enhancer molecule 1 (Edem1) only being increased in R offspring. In conclusion, the adverse effect of juvenile-onset obesity on insulin-responsive tissues can be amplified by previous exposure to a suboptimal nutritional environment in utero, thereby contributing to earlier onset of insulin resistance.

Identifying factors contributing to slow growth in pigs

Pigs that grow slower than their contemporaries can cause complications for animal welfare and profitability. This study was conducted to investigate factors that may contribute to slow growth of pigs. Pigs ( = 440) farrowed by 65 sows were monitored from birth to market. Pigs were categorized as slow, average, and fast growers based on market weight adjusted to 170 d of age (slow growers were <105 kg, average growers were between 105 and 125 kg, and fast growers were >125 kg). Blood samples were collected from 48 focal pigs at 9 and 21 wk of age and analyzed for hormone and free AA concentrations. Data were analyzed using the Mixed and Logistic procedures of SAS. Slow-growing pigs accounted for 10% of pigs marketed, average growers accounted for 49% of pigs marketed, and fast growers accounted for 41% of pigs marketed. Compared with fast growers, slow growers were lighter at birth ( < 0.01), at weaning ( < 0.01), and at nursery exit ( < 0.01) and had less backfat ( < 0.01) and smaller loin muscle area ( < 0.01) at marketing at 21 wk of age. Slow growers had lower plasma concentrations of IGF-1 ( = 0.03) and insulin ( < 0.001) during the nursery period and lower concentrations of leptin ( < 0.001) and insulin ( < 0.001) during the finishing period compared with average and fast growers. Serum concentrations of several essential, nonessential, and total free AA were less for slow growers during both the nursery and finishing periods compared with average and fast growers. Gilts were more likely to become slow growers than barrows (odds ratio = 2.17, 95% confidence interval = 1.19 to 3.96, = 0.01). Litter size and parity of the pigs' dam were not associated with slow growth. These results suggest that low concentrations of IGF-1, insulin, leptin, and AA may contribute to or be associated with slow growth in pigs.

Feeding distillers dried grains in replacement of forage in limit-fed dairy heifer rations: Effects on metabolic profile and onset of puberty

The objective of this study was to determine the effect of increasing the inclusion rate of distillers dried grains (DDGS) in replacement of forage in limit-fed diets on the metabolic profile and onset of puberty in dairy heifers. A 16-wk randomized complete block design study was conducted using 48 Holstein heifers (199 ± 2 d of age) with 3 treatments. Treatments were (1) 30% DDGS (30DG), (2) 40% DDGS (40DG), and (3) 50% DDGS (50DG), with the remainder of the diet consisting of grass hay and 1.5% mineral mix. Heifers were housed in groups of 6 and individually limit-fed using Calan gates at 2.65, 2.50, and 2.35% of body weight (BW) on a dry matter (DM) basis for 30DG, 40DG, and 50DG, respectively. Jugular blood samples were collected during wk 0, 4, 8, 12, and 16 for metabolite and metabolic hormone analysis. Additional samples were taken during wk 16 for plasma fatty acid analysis. When heifers weighed 200 kg, coccygeal vein blood samples were taken twice per week for progesterone analysis to estimate onset of puberty. Blood samples continued until cycling was confirmed via ultrasound for the presence of a corpus luteum. A quadratic response and a linear tendency in the proportion of total fatty acids as linoleic acid were observed. Linear and quadratic responses for plasma concentrations of linoleic acid and arachidonic acid occurred. Overall results for fatty acid analysis demonstrated that total fatty acid and polyunsaturated fatty acids concentration in the blood were linearly increased, with a quadratic response for polyunsaturated fatty acids with 30DG and 50DG having the greatest concentrations. No interactions of treatment by week were observed for any of the metabolites and metabolic hormones measured. Glucose, insulin, insulin-like growth factor-1, leptin, and triglycerides were similar across treatments. A linear response of plasma urea nitrogen and a quadratic response tendency for cholesterol concentration were observed. Age and BW at puberty were similar across treatments. Limit-feeding heifers with greater inclusion rates of DDGS maintained energy status without the accumulation of excess adipose tissue as indicated by leptin. Treatments had no detrimental effects on age or BW at puberty.

Histidine deficiency has a negative effect on lactational performance of dairy cows

A 10-wk randomized complete block design experiment with 24 Holstein cows was conducted to investigate the long-term effects of feeding a His-deficient diet on lactational performance of dairy cows. Cows were blocked by days in milk, milk yield, and parity, and randomly assigned to 1 of the following 2 treatments: (1) His-adequate diet [HAD; providing +166 g/d over metabolizable protein (MP) requirements, according to the National Research Council (2001) and digestible His (dHis) supply of 68 g/d, or 2.5% of MP requirements] and (2) His-deficient diet (HDD; +37 g/d over MP requirements and dHis supply of 49 g/d, or 1.9% of MP requirements). Both HAD and HDD were supplemented with rumen-protected (RP) Met and Lys supplying digestible Met and digestible Lys at 2.4 and 2.4% and 7.2 and 7.1% of MP requirements, respectively. At the end of the 10-wk experiment, HDD was supplemented with RPHis (HDD+RPHis; total dHis supply of 61 g/d, or 2.4% of MP requirements) for an additional 9 d. Dry matter intake (DMI; 25.4 and 27.1 kg/d, standard error of the mean = 0.41), yields of milk (37.6 and 40.5 kg/d, standard error of the mean = 0.62), protein and lactose, energy-corrected milk, and milk and plasma urea-N were decreased by HDD compared with HAD. Feed and energy-corrected milk feed efficiencies, milk fat, protein and lactose concentrations, body weight, and body condition score of the cows were not affected by treatment. Apparent total-tract digestibility of dry and organic matter, crude protein, and neutral detergent fiber, and excretion of urinary N and urea-N were decreased by HDD compared with HAD. Concentration of plasma leptin tended to be decreased for HDD compared with HAD. Plasma concentrations of EAA (His, Leu, Lys, Val) and carnosine decreased and total EAA tended to be decreased in cows fed HDD compared with HAD. Muscle concentrations of free His, Leu, and Val decreased and Gly and β-alanine tended to be increased by HDD compared with HAD. Cows fed HDD had a lower blood hemoglobin concentration than cows fed HAD. At the end of the 10-wk study, the 9-d supplementation of HDD with RPHis (i.e., HDD+RPHis) increased DMI and plasma His, and tended to increase energy-corrected milk yield and plasma carnosine, compared with HDD. In conclusion, feeding a diet deficient in dHis supplying adequate MP, digestible Met, and digestible Lys affected negatively lactational performance of dairy cows. These results confirm our previous findings that low dietary His supply can impair DMI, yields of milk and milk protein, and blood hemoglobin in dairy cows.

Effects of grain level on lamb performance, ruminal metabolism and leptin mRNA expression in perirenal adipose tissue

The effects of four different grain composition diets of finishing lambs on lamb performance, dry matter (DM) digestibility, rumen fermentation and leptin mRNA expression were evaluated. Thirty-two Pelibuey lambs (25.35 ± 4.73 kg bodyweight) were used in a completely randomised experiment in which lambs were fed diets that contained 30%, 45%, 60% or 75% grain (DM basis). The results indicated that increasing the grain level improved the average daily weight gain, hot carcass weight, DM digestibility and feed conversion linearly (P < 0.01); however, feed intake was not affected. Ruminal pH decreased linearly as the grain content was increased (P < 0.01). Ruminal propionate concentration increased and acetate concentration declined with increased grain content (P < 0.01). Leptin mRNA expression in perirenal adipose tissue increased linearly (P < 0.05) as grain content increased. Based on these results, we conclude that increasing grain level in the diets of finishing feedlot lambs improved weight gain and feed efficiency; however, because weight gain and feed efficiency were similar at the higher grain levels, our data suggest including 60% grain in lamb finishing rations.

The effect of supplementing rumen undegradable unsaturated fatty acids on marbling in early-weaned steers

The objective of this study was to determine if supplementation with a rumen undegradable unsaturated fatty acids (FA) source improved marbling deposition in early-weaned steers. All steers (Angus, = 23; Angus × Hereford, = 24) were weaned at 150 ± 5 d of age. Steers were blocked by BW and breed and then randomly assigned to either control (CON; average 1.5 kg of corn gluten feed [CGF], = 23) or isocaloric supplementation containing a rumen undegradable fat source (RUF; 200 g of Megalac-R added to an average of 1.06 kg of CGF, = 24) offered 5 d/wk for 110 d. All steers had ad libitum access to pastures throughout treatment and received supplements individually. Steer BW and blood samples were collected at 0, 55, and 110 d of supplementation, and real-time ultrasound measurements were collected at d 110. Following treatment, steers were transported to Oklahoma State University for finishing and subsequent harvesting at a commercial plant. All data were analyzed using the PROC MIXED procedure of SAS either as repeated measures or ANOVA depending on parameters. There were no significant changes in BW from the beginning of treatment to harvest due to treatment. Ultrasound data showed that RUF steers tended ( = 0.08) to have more i.m. fat than CON at d 110. Serum concentrations of FA showed a treatment × day interaction ( < 0.02) for 16:0, 18:0, 18:1-9, 18:2, 20:4, and total FA. These specific FA concentrations slightly increased in CON steers, but there was a more pronounced increase in the concentration of these FA across the supplementation period in RUF steers. Serum triglyceride and cholesterol concentrations were increased ( < 0.01) on d 55 and 110 in RUF steers compared with those in CON steers. Serum leptin concentration in RUF steers was greater ( < 0.01) than CON steers at d 110. After harvest, RUF carcasses had greater ( = 0.01) marbling scores than those of CON carcasses. All other carcass measures were similar between treatments. The percentage of total lipids was increased ( = 0.011) in steaks from RUF compared to CON. There was a decrease ( < 0.05) in adipocyte diameter in i.m. fat depot of RUF steers compared to CON. There was also a tendency ( = 0.06) for RUF steers to have a greater percentage of 20 to 30 μm adipocytes in their i.m. depot than CON steers. This study indicates that supplementation of unsaturated FA can positively impact marbling deposition in early-weaned steers without impacting other carcass measures.

The relationships between body fatness, leptin, testosterone, and reproductive performance in ram lambs as affected by level and frequency of feeding

This study was carried out using 24 Najdi ram lambs of approximately 6.5 months old to evaluate the effects of feed restriction and frequency of feeding on hormone concentrations of leptin and testosterone, sexual behavior, and semen traits. Ram lambs were allotted equally into three feeding groups. The first group was used as a control and fed ad libitum. The second and third groups were restricted fed at 0.85 ad libitum and fed either once (R1M) or twice daily (R2M). Sexual behavior and semen evaluation were assessed during the sixth, seventh, and eighth weeks of the study. Blood samples were drawn at 1-hour pre-feeding on days 41, 48, and 55 of the study for the determination of serum leptin and testosterone concentrations. All lambs were slaughtered after 8 weeks of experimentation. Results showed that the restricted-fed groups had lower (P < 0.01) values for slaughter body weight, average daily gain, dry matter intake, internal fat, tail fat, body fat thickness, body wall thickness, and testes weight than the ad libitum group; these corresponding traits did not differ between both restricted-fed treatments. Leptin and testosterone concentrations in restricted-fed rams were (P < 0.01) lower and higher, respectively, than in the ad libitum rams; there were no differences between R1M and R2M groups. The restricted-fed rams had lower (P < 0.01) ejaculation latency time compared with control, whereas the percentage of sexually active rams and sexual desire score were not affected by feeding restriction or frequency of feeding. Sperm motility, progressive motility, and percentage of sperm moving at rapid speed were higher (P < 0.01) in feed-restricted rams than in the ad libitum rams. R1M rams had higher (P < 0.01) value for straightness and lower (P < 0.01) value for curvilinear velocity in comparison with the ad libitum group. Testosterone was correlated positively (P < 0.05) with sperm motility and progressive motility and negatively (P < 0.04) with fat measurements, leptin, and ejaculation latency time. In conclusion, moderate intake restriction can optimize body fatness and testosterone concentrations in rams, which helped to improve some reproductive traits.

The relationships between leptin and vitamin A levels in plasma of fattening cattle supplemented with vitamin A

The objective of this study was to examine the effect of dietary vitamin A (retinol) on leptin in cattle. The relationship between plasma leptin and insulin was also examined. The experiment studies 16 9-month-old steers over the following 20-month fattening period. Four treatment diets were given to four steers in each of four groups. Cattle in treatment A were given a diet high in vitamin A (9000 to 10500 µg/day) throughout the experiment. Cattle in treatment B were given a diet low in vitamin A (300 to 4500 µg/day) for 0 to 10 months, after that they were given the high vitamin A diet during the period 10 to 20 months. Cattle in treatment C were given the low vitamin A diet for 0 to 14 months, after that they were given the high vitamin A diet for the period 14 to 20 months. Cattle in treatment D were given the low vitamin A diet throughout the experiment. Plasma samples were collected at 2-month intervals during the experiment to determine the plasma leptin, insulin and vitamin A concentrations. Plasma leptin concentration significantly increased over the fattening period (P< 0·001) but did not differ between the treatments (P> 0·05). Plasma leptin concentration was positively correlated with insulin concentration (r = 0·44,P< 0·001), although it was not correlated with plasma vitamin A concentration (r = –0·01,P> 0·05). It was concluded that dietary vitamin A in cattle does not affect plasma leptin concentration.

Plasma leptin concentration in pre- and post-weaning lambs

Leptin has an important rôle in the control of appetite and energy expenditure. Several studies have reported the effects of leptin in ruminants. However, little is known about changes in circulating leptin concentrations in neonates of ruminant species, or the effects of weaning on plasma leptin concentrations. The main objectives of this experiment were: to examine plasma leptin concentrations in lambs, in the period from just after birth through to weaning; to examine the effect of weaning on plasma leptin concentrations, and to compare leptin concentrations measured using a ‘multi-species’ leptin radio-immunoassay (RIA) kit and a specific ovine RIA in lambs during the 6-month period after weaning. In a previous paper, we reported leptin concentrations using a commercial RIA during the post-weaning period. However, we were not able to measure plasma leptin concentrations from just after birth to weaning as they were apparently below the level of sensitivity of the assay. In the present study, five crossbred lambs were removed from their dams within 2 days after birth, and bottle-fed on milk replacer at a level sufficient to meet a 1•2 times maintenance metabolizable energy intake. Lambs were weaned 45 days after birth, and housed individually in pens. The lambs were offered timothy hay, rolled barley and soya-bean meal to meet a 200 g daily gain during the post-weaning period. During the pre-weaning period, blood samples were collected within 5 h of birth and thereafter at 09:00 h; every day from 2 to 6 days of age; at 2-day intervals from 6 to 14 days of age; and at 3-day intervals from 14 to 45 days of age. During the post-weaning period, blood samples were collected before and 3 and 6 h after the morning meal at the ages of 0•5, 1, 2, 3, 4, 5 and 6 months. Plasma leptin concentrations slightly increased (P < 0•05) just after birth and then remained constant until 45 days old (P > 0•05). Additionally, plasma leptin concentration was not significantly changed following weaning. During the post-weaning period, plasma leptin concentrations were compared using two RIA systems. The correlation between plasma leptin concentrations measured by the ‘multi-species’ leptin RIA kit and specific ovine RIA was poor (r = 0•41). These findings are consistent with other reports and suggest that the ‘multi-species’ leptin RIA kit is not suitable for estimating leptin plasma concentrations in ruminants.

The relationships between leptin and insulin in blood plasma of growing lambs

The present study was designed to examine the pattern of changes in plasma leptin concentration during the early stage of young ruminants. Five crossbred lambs weaned at 45 days were housed individually in pens. The lambs were offered timothy hay, rolled barley and soya-bean meal to meet a 200 g daily gain, and were given free access to water and mineral block. Blood samples were collected just before the morning feeding and at 30-min intervals for 6 h after the morning feeding beginning at 0·5 months after weaning and thereafter monthly for the next 6 months. Plasma leptin level increased dramatically from 0·5 to 3 months after weaning. Thereafter, it dropped to a similar level to that at 2 months after weaning and remained at that level. Moreover, plasma leptin level was not affected by feeding, and no variation throughout the day of sampling was observed. Plasma insulin levels showed similarity to changes in plasma leptin levels. Plasma insulin levels were positively correlated (r = 0·63) with plasma leptin levels. This study shows that plasma leptin level dramatically increases after weaning. Additionally, it suggests that insulin contributes to the increase of leptin with growth in lambs.

Effects of oral meloxicam administration to beef cattle receiving lipopolysaccharide administration or vaccination against respiratory pathogens

This study evaluated the effects of oral meloxicam administration on metabolic, inflammatory, and acute-phase responses of beef cattle receiving a lipopolysaccharide (LPS) challenge (Exp. 1; d -1 to 6) or vaccinated against respiratory pathogens (Exp. 2; d 7 to 21). Twenty-one Angus steers ( = 11) and heifers ( = 10) were housed in individual pens on d -15 and were offered free-choice water, mineral-vitamin mix, and hay until d 21. In Exp. 1, cattle were ranked on d -1 by sex and BW and assigned to 1) oral meloxicam administration (1 mg/kg BW daily) from day -1 to 6 (MEL8), 2) oral meloxicam administration (1 mg/kg BW) on d 0 and oral lactose monohydrate administration (1 mg/kg BW) on d -1 and from d 1 to 6 (MEL1), or 3) oral lactose monohydrate administration (1 mg/kg BW daily) from d -1 to 6 (CON). On d 0, cattle received an intravenous LPS bolus (0.5 μg/kg BW) concurrently with treatment administration. Rectal temperature (RTEMP) was assessed, and blood samples were collected at -2, 0, 2, 4, 6, 8, 12, 16, 24, 36, 48, 60, 72, 96, 120, and 144 h relative to LPS administration. No treatment effects were detected ( ≥ 0.36) for RTEMP, concentrations of serum tumor necrosis factor α (TNFα), plasma haptoglobin, cortisol, insulin, and leptin, as well as blood mRNA expression of α and cyclooxygenase-2, although all variables increased ( < 0.01) across treatments after LPS administration. In Exp. 2, cattle received the same treatments that they were assigned to in Exp. 1 from d 7 to d 13 and were vaccinated against respiratory pathogens concurrently with treatment administration on d 8. Blood samples were collected, and RTEMP was assessed as in Exp. 1 in addition to 168, 240, and 336 h relative to vaccination. No treatment effects were detected ( ≥ 0.26) for RTEMP, the same plasma and serum variables evaluated in Exp. 1, and serum concentrations of antibodies against or serum titers against bovine respiratory syncytial virus, bovine herpesvirus-1, bovine viral diarrhea virus-1, and parainfluenza-3 virus. All variables increased ( < 0.01) across treatments after vaccination, except for serum TNFα and titers against bovine viral diarrhea virus-1 ( ≥ 0.40). Collectively, this study found no evidence that oral meloxicam administration, at the doses and intervals utilized herein, mitigated the metabolic, inflammatory, and acute-phase reactions elicited by LPS administration or vaccination against respiratory pathogens.

Relationship of leptin concentrations with feed intake, growth, and efficiency in finishing beef steers

The objective of this experiment was to determine the association of serum leptin concentrations with production measures including DMI, ADG, and G:F as well as carcass characteristics in genetically diverse finishing beef steers. Three cohorts of steers ( = 473 total) were individually fed a finishing ration for 92, 64, and 84 d for cohort 1, 2, and 3, respectively. Serum was collected on d 42, 22, and 19 of the experiment for cohort 1, 2, and 3, respectively. Leptin concentrations were positively correlated to DMI ( = 0.21, < 0.01) but negatively correlated to grams DMI per kilogram initial BW ( = -0.21, < 0.01). Leptin concentrations were also negatively correlated to ADG and G:F ( < 0.01). Leptin concentrations were positively correlated to 12th-rib fat thickness, yield grade, and marbling score ( < 0.01) and negatively correlated to LM area ( < 0.01). Using a mixed model analysis (SAS 9.3; SAS Inst. Inc., Cary, NC) to account for breed effects, leptin concentrations were positively associated with DMI ( = 0.01) and accounted for 1.10% of the variance. However, if initial BW and yield grade were included as covariates to account for body size and fatness, leptin was negatively associated with DMI ( = 0.02) and accounted for 0.54% of the variance. Regardless of covariates included in the model, leptin was negatively associated with ADG ( < 0.01) and G:F ( < 0.01) and accounted for 2.62 and 7.87% of the variance for ADG and G:F, respectively. Leptin concentrations were also positively associated with 12th-rib fat thickness, yield grade, and marbling score ( < 0.01) and accounted for 14.74, 12.74, and 6.99% of the variance for 12th-rib fat, yield grade, and marbling score, respectively. Leptin concentrations could be a useful physiological marker for growth and feed efficiency of finishing beef cattle. Genetic influences on the biology of leptin also need to be considered when using leptin as physiological marker for production measures.

Effects of vaccination against respiratory pathogens on feed intake, metabolic, and inflammatory responses in beef heifers

The objective of this study was to evaluate intake, metabolic, inflammatory, and acute-phase responses in beef heifers vaccinated against pathogens that cause bovine respiratory disease (BRD). Eighteen weaned Angus heifers (initial BW 257 ± 3 kg; initial age 245 ± 2 d) were ranked by BW and allocated to 2 groups, which were assigned to 2 experiments of 7 d and the following treatments on d 1 of each experiment: 1) revaccinated against infectious bovine rhinotracheitis virus, parainfluenza-3 virus, bovine respiratory syncytial virus, bovine viral diarrhea Types 1 and 2 viruses, and (VAC; 2 mL [s.c.]) and 2) receiving a 2-mL s.c. injection of 0.9% sterile saline (CON). The group receiving VAC in Exp. 1 was assigned to CON in Exp. 2 and vice versa. Heifers were weaned 21 d before Exp. 1, when they all received the first dose of the aforementioned vaccine. Heifers were maintained in individual pens and offered free-choice mixed alfalfa-grass hay and 3.5 kg/d (DM basis) of a corn-based supplement throughout the study. During Exp. 1, hay and concentrate intake were evaluated daily. During Exp. 2, blood samples were collected before (-2 and 0 h) and at 2, 4, 6, 8, 12, 16, 24, 36, 48, 60, 72, 96, 120, 144, and 168 h after treatment administration. In Exp. 1, treatment × day interactions were detected ( < 0.01) for forage intake and total DMI; these parameters were reduced ( ≤ 0.05) in VAC heifers compared with CON heifers on d 1 and 2 by an average of 1.7 and 0.8 kg (DM basis), respectively. In Exp. 2, mean serum tumor necrosis factor α (TNFα) concentration was greater ( = 0.05) in VAC heifers compared with CON heifers and treatment × hour interactions were detected for all plasma variables ( ≤ 0.02), whereas a similar tendency was detected ( = 0.09) for blood α mRNA expression. Haptoglobin concentrations were greater ( ≤ 0.05) in VAC heifers compared with CON heifers from 16 to 120 h. Blood α mRNA expression was greater ( = 0.05) in VAC heifers compared with CON heifers at 12 h. Cortisol concentrations were greater ( ≤ 0.05) in VAC heifers compared with CON heifers from 2 to 16 h. Insulin concentration was greater ( = 0.02) in VAC heifers compared with CON heifers at 2 h. Leptin concentrations were greater ( ≤ 0.05) in VAC heifers compared with CON heifers from 6 to 16 h. In conclusion, vaccinating beef heifers against BRD pathogens decreased forage intake and total DMI during the 2 d following vaccination in Exp. 1, which can be associated with transient metabolic, inflammatory, and acute-phase responses elicited by vaccination in Exp. 2.

Leptin concentrations in finishing beef steers and heifers and their association with dry matter intake, average daily gain, feed efficiency, and body composition

The objective of this experiment was to determine the association of circulating plasma leptin concentrations with production and body composition measures of finishing beef steers and heifers and to determine if multiple sampling time points improve the associations of plasma leptin concentrations with production and body composition traits. Individual dry matter intake (DMI) and ADG were determined for 84 d using steers and heifers (n = 127 steers and n = 109 heifers). Blood was collected on day 0, day 42, and day 83 for determination of plasma leptin concentrations. Leptin concentrations were greater in heifers than those in steers on day 0 (P < 0.001 for sex by day interaction), and leptin concentrations increased in both sexes but were not different from each other on day 83. Leptin concentrations at all 3 time points and the mean were shown to be positively associated with DMI (P ≤ 0.006), whereas the mean leptin concentration explaining 8.3% of the variance of DMI. Concentrations of leptin at day 42, day 83, and the mean of all 3 time points were positively associated with ADG (P ≤ 0.011). Mean leptin concentration was negatively associated with gain:feed ratio and positively associated with residual feed intake (RFI), indicating that more efficient cattle had lower leptin concentrations. However, leptin concentrations explained very little of the variation in residual feed intake (≤ 3.2% of the variance). Leptin concentrations were positively associated with body fat measured by ultrasonography at the 12th rib and over the rump (P < 0.001), with the mean leptin concentration explaining 21.9% and 12.7% of the variance in 12th rib and rump fat thickness, respectively. The same trend was observed with carcass composition where leptin concentrations were positively associated with 12th rib fat thickness, USDA-calculated yield grade (YG), and marbling score (P ≤ 0.006) and mean leptin concentration explained 16.8, 18.2, and 4.6% of the variance for 12th rib fat thickness, yield grade, and marbling score, respectively. Given these and previous results, it appears that leptin physiology could be a candidate for mechanisms that contribute to feed intake and feed efficiency variation in beef cattle.