Metabolic and luteal sequelae to heightened dietary fat intake in undernourished, anestrous beef cows induced to ovulate

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.

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.

Effect of calcium salts of fatty acids and calcium salt of methionine hydroxy analogue on reproductive responses and milk production in Holstein-Friesian cows

The effects of a dietary supplement with calcium salts of fatty acids and methionine hydroxy analogue on reproductive performance, blood metabolites, milk production, milk composition, body weight and body condition score was studied in lactating dairy cows. Autumn-calving, Holstein-Friesian cows (no. = 162) were assigned 1 week post calving to one of two diets: (1) unsupplemented maize-silage-based complete diet while housed before turn-out to perennial ryegrass pasture and (2) the same diet with 400 g per cow per day of a supplement with calcium salts of long-chain fatty acids and methionine hydroxy analogue (Megalac Plus, Volac Ltd). Eleven cows were removed from the study following randomization for reasons not related to the experiment leaving 151 cows on dietary treatments. The diets were offered until the end of the 18-week breeding period. Cows receiving supplement had higher milk yield and milk lactose production and lower milk protein and milk fat proportion (P < 0·05). Body weight and body condition scores were not different between treatments in the first 20 weeks of lactation (P > 0·05). Overall reproductive performance was not different between dietary treatments (P > 0·05). However, first lactation animals (no. = 33) receiving the dietary lipid and methionine supplement tended to have increased conception rates to first and second service (P < 0·09) which resulted in a shorter calving-to-conception interval in those animals (P < 0·06). Services per conception (P < 0·08), services per cow served (P < 0·05) and services per conception for pregnant cows (P < 0·05) in first lactation animals was reduced in the supplemented group. Although plasma cholesterol concentrations were increased following lipid and methionine supplementation (P < 0·01), plasma progesterone concentrations on day 5 and day 8 after artificial insemination were not different between dietary treatments (P > 0·05). In conclusion, a dietary supplement of calcium salts of fatty acids and methionine hydroxy analogue increased milk yield, milk lactose production and blood cholesterol concentration but did not improve reproductive performance, except in first lactation cows.

A dietary supplement of calcium soaps of fatty acids enhances luteal function in sheep

The effect of a dietary supplement of calcium soaps of fatty acids on luteal steroidogenic activity was studied in sheep. Mature 3- to 5-year-old North Country Cheviot ewes were given either a pelleted control diet (C; grass, beet pulp, barley; no. = 15) providing daily, 29⋅8 g nitrogen and 13⋅7 MJ of metabolizable energy (ME) or the same diet with 5% (w/w) of the ingredients replaced with protected lipid (C + CaFA; calcium soaps of fatty acids, Megalac, Volac Etd; no. = 15) for 21 days. The latter diet provided daily 30⋅2 g nitrogen and 15⋅9 MJ ME. At the end of the feeding period the ewes were slaughtered and blood samples and ovaries were collected from individual animals. The numbers of large- (≤ 4 mm diameter) and small- to medium-sized (1 to 3 mm diameter) follicles were recorded and follicular fluids from both size groups were stored for later analyses following centrifugation. Each mature corpus luteum (CL) was isolated from its ovary and sliced to provide a pair of ca. 0⋅3 mm diameter sections. These sections (mean = 163 (s.e.12) mg) were cultured separately (4 h; 39°C; 5% CO2) in 3 ml Medium 199 in the absence or presence of 100 μIU LH. Dietary supplementation of calcium soaps of fatty acids increased progesterone concentrations in the plasma (P < 0⋅05) and follicular fluid (P < 0⋅01 and P < 0⋅05 for large and small to medium follicles, respectively); trigylcerides in plasma (P < 0⋅05); total cholesterol in plasma (P < 0⋅001) and follicular fluid (P < 0⋅001); HDL-cholesterol in plasma (P < 0⋅001) and follicular fluid (P < 0⋅01) and LDL-cholesterol in plasma (P < 0⋅01). Progesterone released by luteal tissue into the culture medium in vitro from ewes given protected lipid was higher than that from tissue of control ewes (P < 0⋅05) and supplementary LH in vitro stimulated progesterone secretion by luteal tissues from both groups (P < 0⋅05). In conclusion, a dietary supplement of calcium soaps of fatty acids altered the intra-follicular environment surrounding the oocyte and follicular cells and enhanced luteal function in sheep.

Effect of supplementation with corn oil on postpartum ovarian activity, pregnancy rate, and serum concentration of progesterone and lipid metabolites in F1 (Bos taurus x Bos indicus) cows

The aim was to evaluate the effect of corn oil supplementation during postpartum anoestrus on ovarian activity, pregnancy rate, progesterone (P(4)), and lipid metabolites (cholesterol, CHO; low and high density lipoproteins; LDL and HDL, respectively) concentrations in blood of F(1) (Bos taurus x Bos indicus) grazing cows. Cows were randomly assigned to an experimental group, fed with a supplement containing 4% corn oil on dry matter basis (OG, n = 11), and a control group with the same supplement without corn oil (CG, n = 12). Both supplements contained equivalent amounts of crude protein and metabolizable energy and were fed for 34 days continuously. All cows were induced to estrous 12 days after beginning of supplementation by using a synthetic progestagen and artificially inseminated 56 h after retiring the implants. Pregnancy diagnosis was performed by transrectal palpation 45 days after insemination, evaluating simultaneously ovarian activity. P(4) and lipid metabolites (CHO, HDL, LDL) concentrations were determined in blood samples collected at 3-day intervals, from the beginning of corn oil supplementation and up to 10 days after artificial insemination. Ovarian activity was affected by treatment (p < 0.05), finding ovarian structures in 72.7% of OG cows and in 50% of CG cows. Concentration of P(4) and CHO was higher for OG with respect to CG (2.52 +/- 0.65 vs 1.88 +/- 0.62 ng/ml and 117.79 +/- 11.57 vs 85.71 +/- 12.11 mg/dl, respectively), whereas pregnancy rate and blood concentrations of HDL and LDL were not affected by treatment (p > 0.05). Addition of corn oil to the supplement stimulated ovarian activity and increased serum concentrations of progesterone and cholesterol in grazing B. taurus x B. indicus cows with low body condition score showing postpartum anoestrus.

Effect of dried corn distillers grains plus solubles compared with soybean hulls, in late gestation heifer diets, on animal and reproductive performance

Dried distillers grains plus solubles (DDGS) contain fat and rumen undegradable intake protein, both of which have been shown to increase reproductive performance in heifers. The mechanisms leading to enhanced reproduction have not been fully defined. The objectives of this research were to evaluate effects of DDGS in late gestation heifer diets on animal and reproductive performance and on blood plasma concentrations of GH, IGF-I, and NEFA. Over 2 yr, 201 heifers were randomly allotted to 1 of 2 diets, which were similar in energy and adequate in rumen degradable intake protein and were fed from d 190 of gestation through calving. Diets were grass hay with DDGS or soybean hulls (SBH) and a supplement. Cow BW and BCS were measured from the beginning of treatment through weaning. Blood samples were collected prepartum on d 71 and 69 of the feeding period and weekly after calving for 4 and 6 wk (d 84 to 105 and d 76 to 111 relative to the feeding period) during yr 1 and 2, respectively. No treatment x year interactions were detected for any of the performance, hormonal, or reproductive dependent variables. Both treatments caused positive BW changes over the feeding period, but DDGS heifers had a greater (P < 0.01) positive BW change compared with SBH heifers. Initial and final BCS and BCS change were similar (P >/= 0.26) between DDGS and SBH treatments. Treatment did not influence (P >/= 0.12) BW or BCS change during the postpartum period. Calving ease, calf vigor, and calf birth weight, weaning weight, and ADG (birth to weaning) were similar (P >/= 0.41) between treatments. The proportion of cows that had initiated estrous cycles (P = 0.46) and the pregnancy distribution (P >/= 0.21) were similar between treatments. However, a greater (P = 0.058) percentage of DDGS cows became pregnant compared with SBH cows (94 and 84%). In both years, there were no effects of treatment (P >/= 0.17) or treatment x time (P >/= 0.52), but time influenced (P 0.10) for the duration of the sampling period. Concentrations of NEFA increased from calving through d 8 and gradually declined through d 20. Prepartum diets containing DDGS, a source of fat and UIP, benefited pregnancy rates in well-maintained, primiparous beef heifers.

Relationships between the conception rate of estrus synchronization using estradiol benzoate and CIDR (progesterone) and other parameters in holstein lactating dairy cows

The purpose of this study was to determine the relationships between conception rate and other parameters before estrus synchronization with a Controlled Internal Drug Release Device (CIDR) and estradiol benzoate (EB). In the estrus synchronization program, animals were injected with 2 mg EB and then received a CIDR. Seven days later, the CIDR was removed and the animals were given an injection of Prostaglandin F(2alpha). Twenty-four hours later, they received an injection of 1 mg EB, and they were artificially inseminated 24 h after that. This program was applied to 258 Holstein cows in Tohoku-machi (Aomori, Japan). Blood was collected at the beginning of the program, and the conception rate was determined about 40 days after insemination. The relationships among conception rate, blood biochemical values, age, body condition score and days in milk were statistically analyzed to determine better conditions for cow conception. The conception rate of the cows in the high progesterone group (more than 1 ng/ml, P(4)+) was significantly higher than that of the low progesterone group (less than 1 ng/ml, P(4)-; 47.9% vs. 28.6% P<0.01). In the P(4)- groups, the serum phospholipid level was significantly higher in the conception group than in the non-conception group, and the same tendency was seen in the P(4)+ groups. Blood urea nitrogen (BUN), albumin (Alb), and total cholesterol (TChol) were significantly higher in the conception group compared with the non-conception group, but no with P(4) was observed. We concluded that 1) the conception rate of the P(4)- group was remarkably low, that 2) the low conception rate and low P(4) level was related to a low PL level and that 3) BUN, Alb and TChol were higher in the conception group, although no relation with P(4) was found.

Chronic administration of recombinant ovine leptin in growing beef heifers: Effects on secretion of LH, metabolic hormones, and timing of puberty1

Serum concentrations of leptin increase linearly from approximately 16 wk before until the week of pubertal ovulation in beef heifers. To test the hypothesis that exogenous leptin can hasten the onset of puberty in heifers, we examined the effects of chronic administration of recombinant ovine leptin (oleptin) on timing of puberty, pulsatile and GnRH-mediated release of LH, and plasma concentrations of GH, IGF-I, and insulin. Fourteen fall-born, prepubertal heifers (Brahman x Hereford, 12 to 13 mo; 304.7+/-4.12 kg) were used. Heifers were stratified by age and BW and assigned randomly to one of two groups (seven animals per group): 1) Control; heifers received s.c. injections of saline twice daily (0700 and 1900) for 40 d; and 2) Leptin; heifers received s.c. injections of oleptin (19.2 microg/kg) twice daily at 0700 and 1900 for 40 d. Blood samples were collected at 10-min intervals for 5 h on. d 0, 5, 10, 20, 30, and 40, and twice daily, just before each treatment injection, throughout the study. On d 41, heifers received i.v. injections of GnRH at 0 (0.0011 microg/kg) and 90 min (0.22 microg/kg), with additional sampling for 5.5 h to examine releasable pools of LH. Diets promoted a gain of 0.32+/-0.09 kg/d, which did not differ between groups. Plasma concentrations of leptin increased markedly in leptin-treated heifers and were greater (P < 0.001) than controls throughout (27.8+/-0.8 vs. 4.9+/-0.12 ng/mL). None of the heifers reached puberty during the experiment, but did so within 45 d of its termination. Mean concentrations of plasma LH, GH, IGF-I, and insulin were not affected by treatment, nor was there an overall effect on the frequency of LH pulses. However, a treatment x day interaction (P = 0.02) revealed that the frequency of LH pulses (pulses/ 5 h) was greater (P = 0.03) in controls (3.6+/-0.36) than in leptin-treated heifers (1.7+/- 0.28) on d 10. Characteristics of GnRH-induced release of LH were not affected by treatment. In summary, chronically administered leptin failed to induce puberty or alter endocrine characteristics in beef heifers nearing the time of expected puberty.

Leptin attenuates the acute effects of centrally administered neuropeptide Y on somatotropin but not gonadotropin secretion in ovariectomized cows

We tested the hypothesis that recombinant ovine leptin would attenuate the acute effects of neuropeptide Y (NPY) on secretion of GH and gonadotropins (LH and FSH) in cows. Ovariectomized cows (n=6) fitted with third ventricle guide cannulas were assigned randomly to each of three groups in a Latin square arrangement: (1) control; saline treatment only, (2) NPY; saline followed by NPY, and (3) L-NPY; leptin pretreatment followed by NPY. Treatments were: s.c. injection of saline or leptin (30 microg/kg BW) at time 0, i.v. injection of saline or leptin (30 microg/kg BW) at 70 min, and intracerebroventricular (i.c.v.) injection of saline or NPY (500 microg) at 90 min. Plasma leptin was elevated (P<0.01) at least four-fold throughout the experiment in the L-NPY group. Mean plasma concentrations of LH declined within 1 h and were lower (P<0.03) than controls in both the NPY and L-NPY groups beginning 2 h after NPY injection. An acute increase in plasma concentrations of GH was observed within 1 h after NPY in the NPY group and mean values were greater (P<0.01) than controls. However, in the L-NPY group, leptin pretreatment attenuated the NPY effect on GH. Treatments had no effect on FSH secretion. Results confirm suppressive and stimulatory effects of NPY on LH and GH secretion, respectively, and indicate that leptin can attenuate the acute effects of NPY on GH secretion in cattle.

Leptin Prevents Fasting-Mediated Reductions in Pulsatile Secretion of Luteinizing Hormone and Enhances Its Gonadotropin-Releasing Hormone-Mediated Release in Heifers1

We tested the hypothesis that leptin could prevent fasting-mediated reductions in pulsatile secretion and modify GnRH-mediated release of LH in heifers approaching puberty. Thirteen crossbred, prepubertal heifers (13.5-16 mo; 280-350 kg) exhibiting frequencies of pulses of LH between 0.67 and 1 pulse/h, were assigned randomly to two groups: 1). control (n = 6), fasted for 72 h with s.c. injections of saline at 12-h intervals, and 2). leptin (n = 7), fasted for 72 h with s.c. injections of oleptin (19.2 microg/kg) at 12-h intervals. Blood samples were collected intensively for 6 h on Days 0 and 3. This was followed on Day 3 with sequential administration of physiological (0.0011 microg/kg, i.v.) and pharmacological (0.22 microg/kg, i.v.) doses of GnRH and additional blood sampling. Leptin treatment increased (P = 0.0003) plasma concentrations of leptin 5-6-fold compared to controls. Fasting caused a marked decline (P = 0.01) between Days 0 and 3 in the frequency of LH pulses in controls; however, this effect was prevented in the leptin group, with pulse frequency increasing (P < 0.008) from Day 0 to 3. Leptin treatment increased GnRH-induced release of LH at both low (P = 0.04) and high (P = 0.02) doses. Plasma insulin and insulin-like growth factor-1 were reduced by fasting and unaffected by leptin. Leptin increased mean concentrations of growth hormone. Results indicate, for the first time, that exogenous leptin can prevent fasting-mediated reductions in the frequency of LH pulses and modify GnRH-mediated release of LH in intact, prepubertal heifers.

Divergent effects of leptin on luteinizing hormone and insulin secretion are dose dependent

We have shown recently that fasting permits leptin to modulate both luteinizing hormone (LH) and insulin secretion in cows. In rodents, leptin causes divergent effects on LH and insulin release that are dose dependent. To test the hypothesis that leptin effects on LH and insulin secretion in fasted cows are dose related, we examined the effects of various doses of recombinant ovine leptin (oleptin) in mature cows. Twenty ovariectomized beef cows, each bearing an estradiol implant to maintain basal estradiol concentrations, were used. All cows were fasted for 60 hr with free access to water and were assigned randomly to one of four groups (n = 5/group): 1) saline control; 2) leptin, 0.2 microg/kg; 3) leptin, 2.0 microg/kg; and 4) leptin, 20 microg/kg body wt. Blood samples were collected at 10-min intervals for 6 hr on Days 0 and 2, with saline or oleptin injected intravenously immediately after the first intensive sample on Day 2 (54 hr). Leptin caused a dose-related increase (P < 0.001) in mean concentrations of circulating LH. Stimulation of LH release by leptin was significant at the lowest (141% of control) and middle (122% of control) doses used, but no increase was observed for the highest dose. Increased mean concentrations of LH appeared to result from an augmentation of basal secretion, as pulse characteristics were not affected. After 54 hr of fasting, plasma insulin concentrations were lowered (P < 0.01) in all treatment groups compared to Day 0. After leptin injections, plasma insulin concentrations increased (P < 0.01) and reached highest concentrations during the first hour of sampling. However, this increase was sustained for several hours only in the intermediate (2.0 microg/kg) dose group. Collectively, our results show that leptin has potent positive effects on both LH and insulin secretion in fasted cows, but the anterior pituitary and endocrine pancreas appear to become downregulated in the presence of excess ligand.

Age at puberty, total fat and conjugated linoleic acid content of carcass, and circulating metabolic hormones in beef heifers fed a diet high in linoleic acid beginning at four months of age

In the current study, we hypothesized that diets high in linoleic acid would increase conjugated linoleic acid (CLA) tissue content, reduce adiposity and leptin production, and result in an increase in the age at puberty in heifers. Heifers were weaned and blocked by body weight (heavy, n = 10, and light, n = 10) and allocated randomly within block to receive isocaloric and isonitrogenous diets with either added fat (HF, n = 10) or no added fat (C, n = 10) from 4 mo of age until post-pubertal slaughter. Whole sunflower seed (55% oil; 70% linoleic acid) was used as the fat source in HF diets and provided 5% added fat from the start of the study until heifers weighed 250 +/- 8 kg, at which time added fat was increased to 7% of dry matter until slaughter. Body weights were recorded weekly, and blood samples were collected weekly for total cholesterol and hormone analyses. Puberty was confirmed based on serum concentrations of progesterone and ultrasonographic confirmation of corpora lutea. Heifers were slaughtered at 325 +/- 10 d of age, and longissimus muscle between the 9th and 11th rib was collected and analyzed to estimate carcass composition. Subcutaneous and kidney, pelvic, and heart fat were collected at slaughter for fatty acid analyses. The HF heavy group tended (P < 0.10) to reach puberty later than all other groups, and one HF light heifer did not reach puberty during the study. Linoleic acid and cis-9, trans-11 CLA tissue contents were higher (P < 0.03) in HF heifers than controls, but neither total carcass fat nor percentage of dry matter differed by dietary group, although the percentage of protein tended (P < 0.10) to be lower in HF heifers. Mean serum concentrations of leptin did not differ due to diet; however, leptin increased (P < 0.01) linearly as puberty approached. Circulating concentrations of growth hormone and insulin-like growth factor I increased or remained relatively constant between wk 2 to 10 of feeding, and then declined (P < 0.01) until the onset of puberty. Serum IGF-I was lower (P < 0.01) in heifers receiving the HF diet. Mean serum concentrations of insulin and total cholesterol increased (P < 0.01) with time in both groups, but only total cholesterol was increased by the HF diet (P < 0.05). Results indicate that diets high in linoleic acid fed to growing beef heifers beginning early in life have little or no effect on total carcass fat, circulating leptin, or age at puberty despite measurable increases in CLA accumulation.

Effects of palm oil on lipid peroxidation, reduced glutathione, glutathione peroxidase, and vitamin A levels in the corpus uteri, cornu uteri and corpus luteum of young and adult female sheep

The aim of the current study was to determine whether a rumen protected palm oil based diet affect malondialdehyde (MDA), glutathione peroxidase (GSH-Px), reduced glutathione (rGSH) and vitamin A levels in the tissues of cornu uteri, corpus uteri and corpus luteum over the barley based isoenergetic and isonitrogenous diet, and whether the response is different between ewes and ewe-lambs. During the breeding season, half of Morkaraman ewes (2-4-year-old, n = 10) and ewe-lambs (7-8-months-old, n = 10) was offered a barley based diet and the other half was offered a protected palm oil based diet for 42 +/- 0.7 days. At the end of the experiment all animals were slaughtered and measurements carried out in the tissues collected. In all animals tested, cornu uteri had the highest MDA levels followed by corpus uteri and corpus luteum (P < 0.01) but no differences were between the tissues observed in GSH-Px and rGSH levels (P > 0.05). Vitamin A levels were, however, higher in corpus luteum than in cornu uteri and corpus uteri (P < 0.05). Corpus uteri MDA levels were not different (P > 0.05) but rGSH levels were higher for the palm oil fed groups (P < 0.05). GSH-Px and rGSH levels were higher for ewe-lambs than ewes (P < 0.05). In conclusion, it appears that MDA, rGSH, GSH-Px, and vitamin A work in a different fashion for corpus uteri, cornu uteri and corpus luteum, and for ewes and ewe-lambs. Dietary palm oil did not significantly affect the parameters studied except higher rGSH levels in corpus uteri. Levels of antioxidatively active substances, such as rGSH and GSH-Px were lower in ewes compared with those in ewe-lambs.

Central infusion of recombinant ovine leptin normalizes plasma insulin and stimulates a novel hypersecretion of luteinizing hormone after short-term fasting in mature beef cows

The present studies tested the hypotheses that short-term fasting would reduce leptin gene expression and circulating concentrations of leptin and insulin in mature, ovariectomized, estradiol-implanted cows and that intracerebroventricular infusions of recombinant ovine leptin (oleptin) would attenuate reductions in insulin concentration and stimulate LH secretion. Ovariectomized cows were assigned to either control (normal fed; n = 6) or fasted (60 h of fasting; n = 7) groups and infused with 200 microg recombinant oleptin three times at hourly intervals on Day 2 (n = 6 per group). Fasting decreased plasma concentrations of insulin (P < 0.01) and leptin (P < 0.04) but, as expected, did not reduce plasma concentrations of glucose or any LH secretion variable. Central infusion of leptin on Day 2 increased (P < 0.01) plasma concentrations of leptin in both control and fasted groups. Concomitantly, leptin treatment increased plasma insulin (P < 0.01) and LH (P < 0.03) concentrations in fasted but not in control cows. Increases in overall mean and baseline concentrations of LH after leptin treatment were the result of an augmentation of the size of LH pulses. The effects of fasting on leptin gene expression and the potential diurnal effects on circulating leptin were examined in a group of cows (n = 12) not treated with leptin. Fasting for 60 h reduced (P < 0.001) leptin gene expression by 30%, and no diurnal effects on circulating leptin were observed. These results indicate that although short-term fasting does not reduce the frequency or amplitude of LH pulses or the concentration of LH in mature cows, this nutritional perturbation clearly sensitizes both the hypothalamic-pituitary axis and endocrine pancreas to exogenous leptin, which in these experiments resulted in heightened secretion of both LH and insulin.

Induction of ovulation in postpartum suckled beef cows: a review

Prolonged postpartum acyclicity in suckled beef cows reduces the calf crop, and causes economic loss to beef cattle producers. Once anterior pituitary LH stores have been replenished between Days 15 and 30 post partum in suckled beef cows, methods to initiate cyclicity include non-hormonal methods such as weaning of calves (either complete, temporary or partial), or exposure to bulls, and hormonal methods such as administration of GnRH (either single injection, intermittent injections, or continuous infusion), gonadotropins (eCG, FSH, hCG), and steroids (estrogens, anti-estrogens, and progestogens). Weaning is costly, reduces growth rate of weaned calves, and short cycles are common after weaning-induced ovulation. Exposure of cows to bulls is not practical and its effect is not predictable. Repeated injections of GnRH, or a single injection of hCG are not always effective; ovulation is always followed by a short cycle, and usually a return to acyclicity. Estrogens and anti-estrogens do not consistently shorten postpartum anestrus. Exogenous progestogens include intravaginal devices, such as controlled-internal drug release (CIDR) or progesterone-releasing intravaginal device (PRID), norgestomet implants, and the feed-additive melengestrol acetate (MGA). Administration of exogenous progestogens is more practical than, and offers more advantages over, other treatments to shorten postpartum acyclicity in suckled beef cows. Mimicking the short cycle after Week 3 post partum, by maintaining circulating progesterone at subluteal concentrations or circulating progestin at intermediate concentrations, extends the life-span and allows terminal maturation of the postpartum dominant follicle as in cyclic cows, by initiating endogenous GnRH and LH pulses. This is followed by an LH surge, ovulation and normal cycles. The benefit from using exogenous progestogens after Week 3 post partum in suckled beef cows is that ovulation is induced, cyclicity is initiated, the resulting CL has a normal life-span and function, and there is no need to change management, such as weaning of calves. We present a model for the induction of ovulation and initiation of cyclicity using exogenous progestogens after Week 3 post partum in suckled beef cows.

Leptin gene expression, circulating leptin, and luteinizing hormone pulsatility are acutely responsive to short-term fasting in prepubertal heifers: relationships to circulating insulin and insulin-like growth factor I(1)

In the present study, we tested the hypothesis that short-term fasting would reduce leptin gene expression, circulating leptin, and LH pulsatility in prepubertal heifers in association with a decrease in circulating concentrations of insulin and insulin-like growth factor I (IGF-I). Twelve prepubertal crossbred heifers (mean +/- SD = 315 +/- 5 kg body weight) were assigned randomly to one of two treatments in two replicates: 1) control; normal feed consumption (n = 6) and 2) fasted; 48 h of total feed restriction (n = 6). Blood samples were collected at 15-min intervals for 8 h on Days 0 and 2 of the experiment and twice on Day 1. Subcutaneous fat samples were collected before treatment onset (Day -1) and at the end of the intensive blood sampling on Day 2. Acute feed restriction markedly reduced leptin mRNA in adipose tissue (P < 0.01) and circulating concentrations of leptin (P < 0.05), IGF-I (P < 0.01), and insulin (P = 0.05) as compared with controls on Day 2. Moreover, the treatment x day interaction (P < 0.076) and within-day contrasts (expressed as a percentage of Day 0 values) revealed that the mean frequency of LH pulses in the fasted group was lower (P < 0.06) than in controls on Day 2. Neither mean concentrations of growth hormone (GH) nor GH secretory dynamics were affected by acute feed restriction. Fasting-mediated decreases in leptin gene expression and circulating leptin, in association with reductions in secretion of IGF-I, insulin, and LH, provide a basis for investigating leptin as a hormone signaling energy status to the central reproductive axis in cattle.

Effect of calf isolation on follicular wave dynamics, gonadotropin and metabolic hormone changes, and interval to first ovulation in beef cows fed either of two energy levels postpartum

The effects of postpartum energy intake, restricted suckling, and cow-calf isolation on concentrations of LH, FSH, growth hormone, and insulin-like growth factor-I (IGF-I) and on postpartum anestrous interval were determined by randomly allocating beef cows with a mean body condition score of 2.3 +/- 0.1 to receive either 80 MJ metabolizable energy (low-energy diet [L]; n = 51) or 120 MJ metabolizable energy (high-energy diet [H]; n = 52) per cow per day from calving. At 30 days postpartum, cows within diet were randomized to 1) have continued full access to their calves from birth to weaning (ad libitum suckling: ADLIB), 2) be suckled once-daily with their calves penned adjacent (restricted suckling, adjacent: RESADJ), 3) be isolated from all calves except for a once-daily suckling period (restricted suckling, isolated: RESISO). The mean postpartum interval was similar (p > 0.10) for L and H cows (62 and 63 days, respectively). RESADJ cows had a shorter (p < 0.05) postpartum interval than ADLIB cows, and RESISO cows had a shorter interval (p < 0.05) than RESADJ cows, with all effects independent (p > 0.10) of diet. FSH secretion pattern was not affected by diet, suckling treatment, sequential follicle wave number, or follicle wave retrospectively realigned to emergence of first ovulatory wave. Within 5 days of suckling restriction and calf isolation, the number of LH pulses increased from 0.18 to 0.48 pulses per hour (p < 0.05). Both mean LH and the mean number of LH pulses increased linearly (p < 0.01) during the six follicle waves up to the first ovulatory wave. From 80 days before, until the time of, first ovulation, growth hormone decreased (p < 0.05) while IGF-I increased (p < 0.05), irrespective of treatment. The results indicate that the "suckling effect" in beef cows is the major factor affecting the duration of the postpartum interval and suggests that the maternal bond is more important than suckling in regulating LH pulse frequency, the key endocrine factor determining whether or not a dominant follicles ovulates. Removal of the suckling effect resulted in a rapid increase in LH pulse frequency, which was not dependent on level of postpartum nutrition, at least within the nutritional limits of this study. Mean concentrations of FSH, unlike LH, did not vary with follicle wave number, suggesting that lack of FSH is not a major factor delaying the resumption of ovulation in postpartum beef cows.

Metabolic hormone secretion and FSH-induced superovulatory responses of beef heifers fed dietary fat supplements containing predominantly saturated or polyunsaturated fatty acids

Ovulatory responses following FSH treatment were examined in beef heifers fed dietary fat supplements expected to produce differential effects on serum insulin concentrations and follicular recruitment patterns. Twenty-one heifers (n = 7/group) exhibiting regular estrous cycles were assigned randomly to either a control diet or to 1 of 2 fat-supplemented diets consisting of soybean oil (polyunsaturated fatty acids) or animal tallow (saturated fatty acids). The diets were formulated to be isoenergetic and isonitrogenous, and were fed until ovariectomy between experimental Days 35 and 45. Experimental Day 1 was defined for each heifer as the first day all of the treatment diet was consumed. After 20 d of diet consumption, estrous cycles were synchronized with prostaglandin F(2alpha) (PGF(2alpha)), and ovarian follicle populations were monitored via transrectal ultrasound for 4 d. Four days after estrus, the dominant follicle was aspirated and heifers were treated with FSH-P to induce superovulation. Ovulation rate was determined at ovariectomy 5 d after the superovulatory estrus (experimental Days 35 to 45). Both soybean oil and animal tallow diets increased (P < 0.05) the number of medium-sized follicles and increased (P < 0.02) serum concentrations of GH relative to the control diet. The soybean oil diet also increased (P < 0.001) serum concentrations of insulin on Days 14, 28, and 5 d after the superovulatory estrus. However, the number of ovulations following FSH treatment did not differ due to diet. Procedures employed in the current study were ineffective in recruiting the increased number of medium-sized follicles into the superovulatory pool.