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This study was conducted to determine effects of pre-synchronization of ovulation timing among heifers and delayed fixed-time artificial insemination (TAI) with sex-sorted semen on proportion of heifers pregnant after TAI (PR/AI). Heifers were assigned to one of eight treatments: 1 and 2), 7-d CO-Synch + CIDR treatment regimen with administration of gonadotropin-releasing hormone and a CIDR insert on Day 0, prostaglandin F2α (PGF) at CIDR removal on Day 7, and TAI occurring 54 h later with conventionally processed (CTRL54-CNV) or sex-sorted semen (CTRL54-SEX); 3 and 4), same as CTRL54 but TAI delayed to 72 h with conventionally processed (CTRL72-CNV) or sex-sorted semen (CTRL72-SEX); 5 and 6), same as CTRL54 but additional administration of PGF on Day -7 and TAI with conventionally processed (PRE54-CNV) or sex-sorted semen (PRE54-SEX); 7 and 8), same as PRE54 treatments but TAI delayed to 72 h with conventionally processed (PRE72-CNV) or sex-sorted semen (PRE72-SEX). Proportion of heifers pregnant after TAI was greater (P ≤ 0.02) with conventionally processed semen compared with sex-sorted semen, yet PR/AI did not differ (P = 0.14) between heifers in PRE72-CNV and PRE72-SEX groups. There were greater PR/AI in the PRE72-SEX (P = 0.03) than CTRL54-SEX group (46.1 % and 36.9 %) and there was no difference (P = 0.31) in PR/AI between CTRL54-CNV and PRE72-SEX groups (50.4 % and 46.1 %). In conclusion, pre-synchronization of ovulation timing among heifers combined with delayed TAI resulted in increased PR/AI with sex-sorted semen compared with the 7-d CO-Synch+CIDR treatment regimen.

Kisspeptin, neurokinin B, and dynorphin are imperative for GnRH/LH pulsatility and reproductive cyclicity. Neurons co-expressing these neuropeptides, KNDy neurons, within the arcuate nucleus of the hypothalamus (ARC) are positioned to integrate energy balance signals from neuronal and glial cells. Energy balance mediates neurokinin B expression in the ARC and LH pulse amplitude. Dynorphin mediates progesterone negative feedback on GnRH neurons. The hypothesis that the number of KNDy-expressing neurons in the ARC of ewes during the luteal phase of the estrous cycle is influenced by energy balance was tested using ovary-intact, mature ewes fed to lose, maintain, or gain body weight. Fluorescent multiplex immunohistochemistry was employed to identify and quantify neurons expressing a single neuropeptide and co-expressing kisspeptin, neurokinin B, and dynorphin in the ARC. Kaminski et al. (1) reported previously that concentrations of insulin and leptin differed between ewes fed to achieve different body weights and that ewes fed to gain body weight had increased concentrations of progesterone in the luteal phase of the estrous cycle. Moreover, tanycyte density and cellular penetration into the ARC are increased in ewes fed to gain body weight (2). Number of neurons in the ARC expressing kisspeptin (14.9 ± 2.7 neurons, 20.9 ± 3.6 neurons, and 51.5 ± 3.3 neurons in ewes fed to lose, maintain, and gain body weight, respectively), neurokinin B (21.5 ± 3.2 neurons, 31.3 ± 4.3 neurons, and 56.0 ± 3.9 neurons in ewes fed to lose, maintain, and gain body weight, respectively), and dynorphin (10.1 ± 2.4 neurons, 14.9 ± 3.2 neurons, and 33.1 ± 2.9 neurons in ewes fed to lose, maintain, and gain body weight, respectively) protein was increased (P < 0.0001) in ewes fed to gain body weight. Number of KNDy neurons in the ARC expressing kisspeptin, neurokinin B, and dynorphin protein was decreased in ewes fed to lose body weight (1.0 ± 0.5 neurons; P = 0.01) and increased in ewes fed to gain body weight (6.7 ± 0.6 neurons; P = 0.0005) when compared to ewes fed to maintain body weight (3.3 ± 0.7 neurons). These findings suggest that expression of kisspeptin, neurokinin B, and dynorphin protein in the ARC during the luteal phase of the estrous cycle may be influenced by nutritionally-induced alterations in circulating concentrations of progesterone that drive changes in morphology and density of tanycytes. Moreover, these results demonstrate that changes in KNDy neurons within the ARC occur as an adaptation to energy balance, potentially regulated divergently by metabolic milieu. References: (1) Kaminski et al., Theriogenology. 2015 83:808-16. (2) Prezotto et al., Domestic Animal Endocrinology. 2020 Accepted.

The pubertal transition of gonadotropin secretion in pigs is metabolically gated. Kisspeptin (KISS1) and neurokinin B (NKB) are coexpressed in neurons within the arcuate nucleus of the hypothalamus (ARC) and are thought to play an important role in the integration of nutrition and metabolic state with the reproductive neuroendocrine axis. The hypothesis that circulating concentrations of luteinizing hormone (LH) and expression of KISS1 and tachykinin 3(TAC3, encodes NKB) in the ARC of female pigs are reduced with negative energy balance was tested using ovariectomized, prepubertal gilts fed to either gain or lose body weight. Restricted feeding of ovariectomized gilts caused a rapid and sustained metabolic response characterized by reduced concentrations of plasma urea nitrogen, insulin, leptin, and insulin-like growth factor-1 and elevated concentrations of free fatty acids. The secretory pattern of LH shifted from one of low amplitude to one of high amplitude, which caused overall circulating concentrations of LH to be greater in restricted gilts. Nutrient-restricted gilts had greater expression of follicle-stimulating hormone and gonadotropin-releasing hormone receptor, but not LH in the anterior pituitary gland. Expression of KISS1 in the ARC was not affected by dietary treatment, but expression of TAC3 was greater in restricted gilts. These data are consistent with the idea that hypothalamic expression of KISS1 is correlated with the number of LH pulse in pig, and further indicate that amplitude of LH pulses may be regulated by NKB in the gilt.

Three experiments were conducted to investigate the effects of the kisspeptin receptor agonist, 1-adamantanecarbonyl-RF-NH2 (RF9) on the secretion of gonadotropins, the role of estradiol-17β in modulating this response, and the metabolic half-life of RF9 in the mare. During the luteal phase of the estrous cycle (experiment 1), light horse mares were treated with sequential I.V. injections of RF9 (0.2 and 0.4 mg/kg) within a 1-hour interval to determine effects on coincident secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Dose-dependent increases (P

The blood–brain barrier regulates the transport of molecules that convey global energetic status to the feeding circuitry within the hypothalamus. Capillaries within the median eminence (ME) and tight junctions between tanycytes lining the third ventricle (3V) are critical components of this barrier. Herein, we tested the hypothesis that altering the plane of nutrition results in the structural reorganization of tanycytes, tight junctions, and capillary structure within the medial basal hypothalamus. Proopiomelanocortin (POMC) neuronal content within the arcuate nucleus of the hypothalamus (ARC) was also assessed to test whether reduced nutritional status improved access of nutrients to the ARC, while decreasing the access of nutrients of overfed animals. Multiparous, nongestating ewes were stratified by weight and randomly assigned to dietary treatments offered for 75 d: 200% of dietary recommendations (overfed), 100% of dietary recommendations (control), or 60% of dietary recommendations (underfed). The number of POMC-expressing neurons within the ARC was increased (P ≤ 0.002) in underfed ewes. Overfeeding increased (P ≤ 0.01) tanycyte cellular process penetration and density compared with control and underfeeding as assessed using vimentin immunostaining. Immunostaining of tight junctions along the wall of the 3V did not differ (P = 0.32) between treatments. No differences were observed in capillary density (P = 0.21) or classification (P ≥ 0.47) within the ME. These results implicate that changes within the satiety center and morphology of tanycytes within the ARC occur as an adaptation to nutrient availability.

Mechanisms governing the timing of puberty in pigs are poorly understood. A genome-wide association study for age at first estrus in pigs identified candidate genes including neuropeptide FF receptor 2 (NPFFR2), which is a putative receptor for RFamide-related peptides (RFRP). RFRP has been shown to negatively regulate secretion of reproductive hormones from hypothalamic and pituitary tissue of pigs in culture. Here, the porcine NPFFR2 gene was further screened and four potentially functional variants were identified to be associated with age at first estrus in pigs (1,288 gilts). The RFRP neurons in the porcine hypothalamus were localized in the paraventricular and dorsomedial nuclei with RFRP fibers in the lateral hypothalamic area. There were marked changes in expression of NPFF receptors in the anterior pituitary gland and hypothalamus of gilts beginning with the peripubertal period. The hypothesis that NPFF receptor function is related to secretion of luteinizing hormone (LH) in gilts was tested with various NPFF receptor ligands. The NPFF receptor antagonist RF9 stimulated a pulse-like release of LH in prepubertal gilts. The putative NPFF receptor agonist RFRP3 modestly suppressed LH pulses in ovariectomized (OVX) prepubertal gilts. A porcine-specific RFRP2 failed to have an effect on LH secretion in OVX prepubertal gilts despite its high degree of homology to avian gonadotropin-inhibitory hormone. Results indicate that an RFRP system is present in the pig and that NPFFR2 is important for pubertal onset in gilts. It is not clear if this regulation involves major control of LH secretion or another unknown mechanism.

Objectives were to determine the effects of advancing gestation, maternal nutrient restriction during early and mid-gestation, and realimentation on fetal liver and jejunal mass and energy use in both dams and fetuses. On day 30 of pregnancy, multiparous, non-lactating beef cows (initial BW=621±11.3 kg and body condition score=5.1±0.1) were assigned to one of the two dietary treatments: control (CON; 100% requirements; n=18) and restricted (R; 60% requirements; n=28). On day 85, cows were slaughtered (CON, n=6; R, n=6), and remaining cows continued on control (CC; n=12) and restricted (RR; n=12) diets, or were realimented to the control diet (RC; n=11). On day 140, cows were slaughtered (CC, n=6; RR, n=6; RC, n=5), remaining cows continued on the control diet (CCC, n=6; RCC, n=5), or were realimented to the control diet (RRC, n=6). On day 254, all remaining cows were slaughtered. Maternal liver O2 consumption linearly increased (P⩽0.04) and jejunal weight (g/kg) linearly decreased (P=0.04) as gestation advanced in CON groups. Fetal BW, and hepatic and small intestinal absolute mass, protein content and O2 consumption linearly increased (P⩽0.04) as pregnancy advanced in CON groups. However, mass and O2 consumption relative to BW linearly decreased (P⩽0.001) in the fetal liver in CON groups. When analyzing the effects of dietary treatment, at day 85, fetal jejunal O2 consumption (mol/min per kg BW) was lower (P=0.02) in the R group when compared with the CON group. At day 140, maternal hepatic weight (g) was lower (P=0.02) in RC and RR cows when compared with CC, and fetal jejunual O2 consumption (mmol/min per mg tissue and mmol/min per g protein) was greater (P⩽0.02) in RC when compared with RR. At day 254, maternal hepatic O2 consumption (absolute and relative to BW) was lower (P⩽0.04) in the RCC cows when compared with RRC. Fetal hepatic weight was lower (P=0.05) in the CCC group when compared with RCC and RRC. The changes in response to nutrient restriction and realimentation in both the dam and fetus may indicate an adaptation to a lower amount of available nutrients by altering tissue mass and metabolism.

Maternal nutrient restriction during gestation can exert long-term negative effects on offspring health and performance. Arginine supplementation may rescue some of the negative effects elicited by maternal nutrient restriction. We tested the hypothesis that maternal arginine supplementation during gestation would rescue deleterious effects of nutrient restriction on in vitro O2 consumption in the liver and jejunum and hypothalamic protein expression of proopiomelanocortin (POMC), neuropeptide Y (NPY), agouti-related peptide (AgRP), and neuronal nitric oxide synthase (nNOS), and the colocalization of nNOS and active phosphor-signal transducer and activator of transcription 3 (pSTAT3) in female offspring. Multiparous ewes were assigned to dietary treatment at 54 d of gestation: 100% of requirements (Con), 60% of control (Res), or Res plus rumen-protected arginine (Res-Arg; 180 mg/kg). At parturition, offspring were immediately removed from their dam and placed on a common diet. At 54 ± 4 d of age, female lambs (n = 6 per treatment) were weighed, the liver and jejunum were weighed, and samples were collected for in vitro measurement of O2 consumption. The hypothalamus was collected to determine protein expression of POMC, NPY, AgRP, and nNOS, and the colocalization of nNOS and pSTAT3 (n = 3, 4, and 4 for Con, Res, and Res-Arg, respectively). Hepatic consumption of O2 in vitro (mol/min/liver) was decreased (P = 0.04) in the Res and Res-Arg group compared with Con. Intensity of staining for NPY-containing fibers tended to decrease (P = 0.10) in Res and Res-Arg compared with Con. Number of POMC neuronal cells in the arcuate nucleus (ARC) of the hypothalamus decreased (P ≤ 0.03) in the Res group compared with Res-Arg. These observations demonstrate that maternal nutrient restriction decreases energy utilization in the liver and number of POMC cells in the ARC of offspring. Supplementation of arginine to the gestating ewe failed to influence hepatic use of energy in lambs from Res ewes. Numbers of POMC-containing cells were increased in the ARC in lambs from ewes restricted to 60% of nutritional requirements and supplemented with rumen-protected arginine, potentially influencing feeding behavior and hepatic energy metabolism.

To determine the effects of maternal nutrition on modifications of foetal development of the skeletal muscle and possible increase in the potential of skeletal muscle growth in cattle, gestating cows were either fed 190% NRC recommendations (overnourished; ON) or 100% NRC recommendation (control; CO). Interaction between maternal nutrition (MN) and the foetal sex (FS) was also investigated. Foetuses were necropsied at four different time points throughout gestation (139, 199, 241 and 268 days of gestation) to assess the mRNA expression of myogenic, adipogenic and fibrogenic markers in skeletal muscle. Phenotypic indicators of the development of skeletal muscle fibres, intramuscular lipogenesis and collagen development were also evaluated. Modifications in mRNA expression of skeletal muscle of foetuses were observed in function of MN and FS despite the lack of effect of MN and FS on foetal weight at necropsy. Maternal ON increased the mRNA expression of the myogenic marker Cadherin-associated protein, beta 1 (CTNNB1) and adipogenic markers Peroxissome proliferator-activated receptor gamma (PPARG) and Zinc finger protein 423 (ZNF423) at midgestation. However, no differences on foetal skeletal muscle development were observed between treatments at late gestation indicating that a compensatory development may have occurred on CO foetuses making the effect of MN on skeletal muscle development not significant at late gestation. Moreover, our data have shown an evidence of sexual dimorphism during foetal stage with a greater skeletal muscle development in male than in female foetuses. In conclusion, providing a higher nutritional level to pregnant cows changes the trajectory of the development of skeletal muscle during midgestation, but apparently does not change the potential of post-natal growth of muscle mass of the offspring, as no differences in skeletal muscle development were observed in late gestation.

Feeding a high-concentrate diet to heifers during the juvenile period, resulting in increased body weight (BW) gain and adiposity, leads to early-onset puberty. In this study, we tested the hypothesis that the increase in GnRH/LH release during nutritional acceleration of puberty is accompanied by reciprocal changes in circulating leptin and central release of neuropeptide Y (NPY). The heifers were weaned at 3.5 months of age and fed to gain either 0.5 (Low-gain; LG) or 1.0 kg/day (High-gain; HG) for 30 weeks. A subgroup of heifers was fitted surgically with third ventricle guide cannulas and was subjected to intensive cerebrospinal fluid (CSF) and blood sampling at 8 and 9 months of age. Mean BW was greater in HG than in LG heifers at week 6 of the experiment and remained greater thereafter. Starting at 9 months of age, the percentage of pubertal HG heifers was greater than that of LG heifers, although a replicate effect was observed. During the 6-h period in which CSF and blood were collected simultaneously, all LH pulses coincided with or shortly followed a GnRH pulse. At 8 months of age, the frequency of LH pulses was greater in the HG than in the LG group. Beginning at 6 months of age, concentrations of leptin were greater in HG than in LG heifers. At 9 months of age, concentrations of NPY in the CSF were lesser in HG heifers. These observations indicate that increased BW gain during juvenile development accelerates puberty in heifers, coincident with reciprocal changes in circulating concentrations of leptin and hypothalamic NPY release.

It was hypothesized that metabolic programming of processes underlying puberty can be shifted temporally through the use of a stair-step compensatory growth model such that puberty is optimally timed to occur at 11 to 12 mo of age. Forty crossbred beef heifers were weaned at approximately 3.5 mo of age and, after a 2-wk acclimation period, were assigned randomly to 1 of 4 nutritional groups: 1) low control (LC), restricted feed intake of a forage-based diet to promote BW gain of 0.5 kg/d until 14 mo of age, 2) high control (HC), controlled feed intake of a high-concentrate diet to promote BW gain of 1 kg/d until 14 mo of age, 3) stair-step 1 (SS-1), ad libitum feed intake of a high-concentrate diet until 6.5 mo of age followed by restricted access to a high-forage diet to promote BW gain of 0.35 kg/d until 9 mo of age, ad libitum feed intake of a high-concentrate diet until 11.5 mo of age, and restricted intake of a high-forage diet to promote BW gain of 0.35 kg/d until 14 mo of age, and 4) stair-step 2 (SS-2), reverse sequence of SS-1, beginning with restricted access to a high-forage diet. Body weight (every 2 wk) and circulating concentrations of leptin (monthly) were determined throughout the experiment. Concentrations of progesterone in blood samples collected twice weekly beginning at 8 mo of age were used to determine pubertal status. Body weight gain followed a pattern similar to that proposed in our experimental design. Circulating concentrations of leptin increased following distinct elevations in BW but decreased abruptly after feed intake restriction. Survival analysis indicated that the percentage of pubertal heifers in the LC group was lower (P < 0.05) than all other groups throughout the experiment. Although heifers in SS-1 were nutritionally restricted between 6.5 and 9 mo of age, the proportion pubertal by 12 mo of age did not differ (P = 0.36) from that of the HC group, with 80% and 70% pubertal in SS-1 and HC, respectively. In contrast, the proportion of heifers pubertal by 12 mo of age in the SS-2 group (40%) was lower (P < 0.05) than both HC and SS-1. However, by 14 mo of age, 90% of heifers in the SS-2 group had also attained puberty compared to only 40% of the LC group. In summary, these data provide evidence that changes in the nutritional and metabolic status during the early juvenile period can program the onset of puberty that occurs months later, allowing optimal timing of sexual maturation in replacement beef heifers.

Onset of the winter anovulatory period in mares is associated with a marked diminution in adenohypophyseal synthesis and release of LH. Native GnRH, unlike its synthetic agonists, stimulates the synthesis and secretion of LH in mares without pituitary refractoriness. Herein we tested the hypotheses that (1) the average Julian day of pregnancy can be accelerated by up to 2 months in winter anovulatory mares treated continuously with native GnRH beginning on February 1 and (2) mares will sustain luteal function and pregnancy after treatment withdrawal. Forty-two winter anovulatory mares were stratified by age, body condition score, and size of the largest follicle across two locations in a randomized design and assigned to one of three groups (n = 14 per group): (1) CONTROL: untreated, (2) GnRH-14: GnRH delivered subcutaneously in saline at a rate of 100 μg/h for 8 weeks (February 1-March 29) using four consecutive 14-day pumps (Alzet 2ML2), or (3) GnRH-28: GnRH delivered as in (2), but using two 28-day pumps (Alzet 2ML4). On development of a 35-mm follicle and expression of estrus, mares were bred the following day and treated with hCG. Pregnancies were confirmed using transrectal ultrasonography on Days 14, 24, 33, and 45, with blood samples collected to assess luteal function. Mares treated with GnRH (GnRH-14 and GnRH-28) did not differ reproductively in their responses and data were pooled for statistical comparisons. Mares treated with GnRH exhibited marked increases (P ≤ 0.04) in the frequency of development of a 35-mm follicle, submission rate for live cover and/or artificial insemination, ovulation, and pregnancy compared with control mares on treatment Day 56 (March 29). Interval to the first 35-mm follicle was 51.8 ± 4.9 and 19.3 ± 3.5 days (least square mean ± standard error of the mean) for control and GnRH-treated mares, respectively. Interval to pregnancy was 65.3 ± 6.7 and 28.6 ± 4.8 days (least square mean ± standard error of the mean) for control and GnRH-treated mares, respectively, excluding one GnRH-14 mare that failed to become pregnant over four cycles. By the end of the treatment period (March 29), only 21% of control mares were pregnant compared with 79% of GnRH-treated mares. Furthermore, mean serum concentrations of progesterone were similar to (GnRH-28; P = 0.26) or greater than (GnRH-14; P = 0.01) that of control mares from Day 0 to 46 postbreeding. Data illustrate that continuous administration of native GnRH is a highly efficient option for managing seasonal anovulation in mares and could be effectively used in the breeding industry if a user-friendly delivery option were available.

Em um delineamento quadrado latino 4 X 4 balanceado, foram utilizados quatro potros, filhos do mesmo garanhão, com idade entre 10 e 12 meses e 270 ± 9,80 kg. Foram analisados os efeitos dos níveis de 5, 10, 15 e 20% de óleo de soja no concentrado sobre a aceitabilidade e a digestibilidade dos nutrientes e sobre a concentração plasmática de colesterol total e suas frações nas lipoproteínas de densidade muito baixa (VLDL-C), densidade baixa (LDL-C) e densidade alta (HDL-C) e nos triglicérides totais. O aumento do nível de óleo na dieta afetou as digestibilidades da matéria orgânica, fibra em detergente neutro e fibra em detergente ácido, que apresentaram resposta quadrática, com diminuição após os valores de 10,7; 9,5 e 10,5%, respectivamente, de extrato etéreo na dieta. Os níveis de óleo de soja tiveram efeito linear sobre as concentrações plasmáticas de colesterol e LDL-C, que apresentaram diminuição de 0,65 mg/dL e 0,58 mg/dL, respectivamente, a cada 1% de aumento no extrato etéreo do concentrado. Níveis de óleo de soja superiores a 9,5% no concentrado afetam a digestibilidade da dieta, principalmente na parede celular, e diminuem as concentrações plasmáticas de colesterol e LDL-C.

Avaliou-se a substituição de milho triturado ou extrusado por sorgo triturado ou extrusado no concentrado utilizado em dietas para eqüinos. Utilizaram-se quatro éguas com peso médio de 450 kg e 24 meses de idade, sem raça definida, em um delineamento experimental quadrado latino 4 × 4, em esquema fatorial. Avaliaram-se a digestibilidade aparente total da dieta e dos nutrientes e o perfil metabólico dos animais considerando os valores plasmáticos de glicose e insulina pós-ingestão das dietas. As dietas contendo milho e sorgo extrusado proporcionaram coeficientes de digestibilidade total da matéria seca (MS), matéria orgânica (MO), proteína bruta (PB), fibra em detergente neutro (FDN) e fibra em detergente ácido (FDA) maiores que os obtidos com dietas contendo estes ingredientes triturados. Os coeficientes de digestibilidade aparente total do amido foram semelhantes entre as dietas. A resposta glicêmica e insulinêmica foi maior quando fornecidas as dietas extrusadas, logo, o processamento provocou alterações no metabolismo dos eqüinos. A total substituição do milho pelo sorgo em dietas para eqüinos é possível, uma vez que os coeficientes de digestibilidade dos nutrientes e os níveis plasmáticos de glicose e insulina não diferiram entre as formas de processamento do sorgo testadas. A forma de processamento do milho e do sorgo por extrusão aumenta os coeficientes de digestibilidade do amido e melhora o potencial energético da dieta.

Increased body weight (BW) gain during the juvenile period leads to early maturation of the reproductive neuroendocrine system. We investigated whether a nutritional regimen that advances the onset of puberty leads to alterations in the hypothalamic neuropeptide Y (NPY) circuitry that are permissive for enhanced gonadotropin-releasing hormone (GnRH) secretion. It was hypothesized that NPY mRNA and NPY projections to GnRH and kisspeptin neurons are reduced in heifers that gain BW at an accelerated rate, compared with a lower one, during the juvenile period. Heifers were weaned at approximately 4 mo of age and fed diets to promote relatively low (0.5 kg/day; low gain [LG]) or high (1.0 kg/day; high gain [HG]) rates of BW gain until 8.5 mo of age. Heifers that gained BW at a higher rate exhibited greater circulating concentrations of leptin and reduced overall NPY expression in the arcuate nucleus. The proportion of GnRH neurons in close apposition to NPY fibers and the magnitude of NPY projections to GnRH neurons located in the mediobasal hypothalamus were reduced in HG heifers. However, no differences in NPY projections to kisspeptin neurons in the arcuate nucleus were detected between HG and LG heifers. Results indicate that a reduction in NPY innervation of GnRH neurons, particularly at the level of the mediobasal hypothalamus, occurs in response to elevated BW gain during the juvenile period. This functional plasticity may facilitate early onset of puberty in heifers.

RFamide-related peptide 3 (RFRP3), the mammalian homologue of avian gonadotropin-inhibitory hormone, has been shown to negatively regulate the secretion of LH and may contribute to reproductive seasonality in some species. Herein, we examined the presence and potential role of the RFRP3-signaling system in regulating LH secretion in the mare during the breeding and nonbreeding seasons. Hypothalamic NPVF mRNA (the precursor mRNA for RFRP3) was detected at the level of the dorsomedial nucleus and paraventricular nucleus, but expression did not change with season. A greater number of RFRP3-expressing cells was observed throughout the rostral-caudal extension of the dorsomedial nucleus. Furthermore, adenohypophyseal expression of the RFRP3 receptor (NPFFR1) during the winter anovulatory season did not differ from that during either the follicular or luteal phases of the estrous cycle. When tested in primary adenohypophyseal cell culture or in vivo during both the breeding and nonbreeding seasons, neither equine nor ovine peptide sequences for RFRP3 suppressed basal or GnRH-mediated release of LH. However, infusion of RF9, an RFRP3 receptor-signaling antagonist, into seasonally anovulatory mares induced a robust increase in secretion of LH both before and following continuous treatment with GnRH. The results indicate that the cellular machinery associated with RFRP3 function is present in the equine hypothalamus and adenohypophysis. However, evidence for functionality of the RFRP3-signaling network was only obvious when an antagonist RF9 was employed. Because GnRH-induced release of LH was not affected by RF9, its actions may occur upstream from the gonadotrope to stimulate or disinhibit secretion of GnRH.

Maternal nutrition has been shown to impact fetal pancreatic endocrine development (Dahri et al., 1995). However, less is known about its effects on exocrine function. The objectives were to determine the effect of nutrient restriction and realimentation during gestation on maternal and fetal pancreatic mass and digestive enzymes.

The extensive use of grazing systems for beef cattle and the high variation in forage quality throughout the year has an important impact on production. Changes in forage quality and availability alter the nutritional and physiological status of cows during gestation. Nutrient restriction during this crucial time plays a large role on cow weight change and on fetal growth and development. The objectives were to determine how nutrient restriction and realimentation during gestation influences energy utilization and oxygen consumption of intestinal and liver tissues of the cow and the developing fetus.

Reproductive seasonality in the mare is characterized by a marked decline in adenohypophyseal synthesis and secretion of LH beginning near the autumnal equinox. Thus, ovarian cycles have ceased in most mares by the time of the winter solstice. Endogenous reproductive rhythms in seasonal species are entrained or synchronized as a result of periodic environmental cues. In the horse, this cue is primarily day length. Hence, supplemental lighting schemes have been used managerially for decades to modify the annual timing of reproduction in the mare. Although a full characterization of the cellular and molecular bases of seasonal rhythms has not been realized in any species, many of their synaptic and humoral signaling pathways have been defined. In the mare, neuroendocrine-related studies have focused primarily on the roles of GnRH and interneuronal signaling pathways that subserve the GnRH system in the regulatory cascade. Recent studies have considered the role of a newly discovered neuropeptide, RF-related peptide 3 that could function to inhibit GnRH secretion or gonadotrope responsiveness. Although results that used native peptide sequences have been negative in the mare and mixed in all mammalian females, new studies that used an RFRP3 antagonist (RF9) in sheep are encouraging. Importantly, despite continuing deficits in some fundamental areas, the knowledge required to control seasonal anovulation pharmacologically has been available for >20 yr. Specifically, the continuous infusion of native GnRH is both reliable and efficient for accelerating reproductive transition and is uniquely applicable to the horse. However, its practical exploitation continues to await the development of a commercially acceptable delivery vehicle.

Objetivou-se avaliar os efeitos da inclusão de gordura de origem animal ou vegetal e de óleo mineral sobre a aceitabilidade, a digestibilidade dos nutrientes e as concentrações plasmáticas de triglicérides e colesterol em equinos. Utilizaram-se quatro potros de 13 a 16 meses de idade recebendo dieta contendo feno de gramínea e concentrado, em delineamento quadrado latino, analisado por contrastes ortogonais. A aceitabilidade não foi influenciada pela quantidade nem pelo tipo de óleo adicionado às dietas. Os menores valores de digestibilidade de matéria seca (MS), matéria orgânica (MO) e extrato etéreo (EE) foram observados para as dietas acrescidas de óleo mineral (58,90; 60,29 e 32,02%) em comparação à dieta controle, cujos valores foram de 62,58; 64,41 e 77,72%. O coeficiente de digestibilidade do EE obtido com a dieta com óleo mineral foi menor (32,02%) que o obtido para as dietas com gordura animal (90,26%) e gordura vegetal (86,47%). A dieta com óleo mineral reduziu a concentração de HDL-C (68,75 mg/dL) em relação à dieta controle (76,00 mg/dL). A adição de fontes lipídicas e óleo mineral não influencia na aceitabilidade da dieta por equinos. O óleo vegetal não se diferencia da gordura animal quanto à digestibilidade dos nutrientes, no entanto, essas fontes de lipídios afetam a digestibilidade do extrato etéreo. A adição de óleo mineral reduz os níveis plasmáticos de HDL-C, ao passo que a adição de gordura animal e gordura vegetal não altera as concentrações plasmáticas de colesterol. The objective of this study was to assess the effects of including animals or vegetable fats and mineral on the acceptability, nutrient digestibility and triglyceride plasma concentrations and cholesterol in horses. Four foals aged 13 to 16 months were used receiving diet containing grass hay and concentrate. The experimental design was a Latin Square; using orthogonal contrasts. The acceptability was not influenced by the quantity nor the type of oil added to the diets. The smallest dry matter (DM) digestibility values, organic matter (OM) and ether extract (EE) were observed for the diets with the addition of mineral oil (58.90, 60.29 and 32.02%) compared to the control diet, whose values were 62.58, 64.41 and 77.71%. The EE digestibility coefficient obtained for the diets with animal fat (90.26%) and vegetable fat (86.47%). The diet with mineral oil reduced the HDL-C concentration (68.75 mg/dL) compared to the control diet (76.00 mg/dL). The adition of fat sources and mineral oil did not influence the acceptability of the diet by the horses. The vegetable oil did not differ from animal fat regarding nutrient digestibility, but these fat sources affected ether extract digestibility. The addition of mineral oil reduced the plastmatic HDL-C levels while the addition of animal fat and vegetable fat did not alter the cholesterol plasmatic concentrations.

Avaliou-se o efeito do processamento do feno de alfafa (Medicago sativa L.) e da adição de óleo de soja em dietas sobre a digestibilidade total de matéria seca, matéria orgânica, proteína bruta, extrato etéreo, fibra em detergente neutro e fibra em detergente ácido em eqüinos. Utilizaram-se quatro potros machos, sem raça definida, com aproximadamente 14 meses de idade e 197,25 kg, em delineamento quadrado latino (4 × 4) e em arranjo fatorial (2 × 2), composto de duas formas de fenação da alfafa (em cubos ou em ramas) e da adição ou não de óleo de soja em dietas contendo concentrado comercial na forma de péletes. A digestibilidade dos nutrientes foi determinada pelo método de coleta total de fezes durante três dias. A adição de óleo de soja refinado aumentou a digestibilidade total de matéria seca, matéria orgânica, extrato de etéreo e fibra em detergente neutro. A fenação da alfafa em cubos aumentou a digestibilidade total da proteína bruta, fibra em detergente neutro e da fibra em detergente ácido. A adição de óleo de soja nas dietas avaliadas foi um modo prático e seguro de aumentar a densidade calórica sem reduzir a digestibilidade dos macronutrientes orgânicos. O processamento da alfafa na forma de cubos melhorou a digestibilidade total da proteína bruta, fibra em detergente e fibra em detergente ácido da dieta em eqüinos.

The objective was to examine the effect of maternal nutrient restriction followed by realimentation during midgestation on uterine blood flow (BF). On Day 30 of pregnancy, lactating, multiparous Simmental beef cows were assigned randomly to treatments: control (CON; 100% National Research Council; n = 6) and nutrient restriction (RES; 60% of CON; n = 4) from Day 30 to 140 (period 1), and thereafter, realimented to CON until Day 198 of gestation (period 2). Uterine BF, pulsatility index (PI), and resistance index (RI) were obtained from both the ipsilateral and contralateral uterine arteries via Doppler ultrasonography. Generalized least square analysis was performed. Ipsilateral uterine BF in both groups increased quadratically (P < 0.01) during period 1 and linearly (P < 0.01) during period 2. There was a treatment (P = 0.05) effect during period 2; where RES cows had greater ipsilateral BF versus CON. Ipsilateral uterine PI and RI decreased linearly (P ≤ 0.01) during period 1 across treatments. Contralateral uterine BF in CON cows tended (P < 0.09) to be greater versus RES in both periods. Contralateral PI in both groups increased linearly (P ≤ 0.01) during period 1. Contralateral uterine RI was increased (P ≤ 0.05) in RES cows versus CON in both periods. There was no interaction or treatment effect (P ≥ 0.24) for total BF during either period. Nutrient restriction does not alter total uterine BF, but it may increase vascular resistance. However, up on realimentation, local conceptus-derived vasoactive factors appear to influence ipsilateral uterine BF.