Effect of progressive cachectic parasitism and growth hormone treatment on hepatic 5'-deiodinase activity in calves

Thyroid status is compromised in a variety of acute and chronic infections. Conversion of thyroxine (T₄) into the metabolically active hormone, triiodothyronine (T₃), is catalyzed by 5′-deiodinase (5′D) mainly in extrathyroidal tissues. The objective of this study was to examine the effect of protozoan parasitic infection (Sarcocystis cruzi) on hepatic 5′D (type I) activity and plasma concentrations of T₃ and T₄ in placebo- or bovine GH (bGH)-injected calves. Holstein bull calves (127.5±2.0 kg BW) were assigned to control (C, ad libitum fed), infected (I, 250,000 S. cruzi sporocysts per os, ad libitum fed), and pair-fed (PF, non-infected, fed to intake of I treatment) groups placebo-injected, and three similar groups injected daily with pituitary-derived bGH (USDA-B-1, 0.1 mg/kg, i.m.) designated as C_GH, I_GH and PF_GH. GH injections were initiated on day 20 post-infection (PI), 3–4 days prior to the onset of clinical signs of the acute phase response (APR), and were continued to day 56 PI at which time calves were euthanized for liver collection. Blood samples were collected on day 0, 28, and 55 PI. Alterations in nutritional intake did not affect type I 5′D in liver. Treatment with bGH increased (P<0.05) 5′D activity in C (24.6%) and PF (25.5%) but not in I calves. Compared to PF calves, infection with S. cruzi reduced 5′D activity 25% (P<0.05) and 47.8% (P<0.01) in placebo- and bGH-injected calves, respectively. Neither nutrition nor bGH treatment significantly affected plasma concentrations of T₄ and T₃ on day 28 and 55 PI. However, plasma thyroid hormones were reduced by infection. On day 28 PI, the average plasma concentrations of T₃ and T₄ were reduced in infected calves (I and I_GH) 36.4% (P<0.01) and 29.4% (P<0.05), respectively, compared to pair-fed calves (PF and PF_GH). On day 55 PI, plasma T₃ still remained lower (23.7%, P<0.01 versus PF) in infected calves while plasma T₄ returned to control values. The data suggest that parasitic infection in growing calves inhibits both thyroidal secretion and extrathyroidal T₄ to T₃ conversion during the APR. After recovery from the APR, thyroidal secretion returns to normal but basal and bGH-stimulated generation of T₃ in liver remains impaired.     

Total and free iodothyronine levels of growing Thoroughbred foals: Effects of weaning and gender

The aim of this study was investigate the effect of growing associated with different gender on circulating total and free iodothyronine concentrations during the first 13 mo of age in foals. In addition, we investigated the evolution of circulating concentrations of thyroid hormones during the first 3 d of weaning. Blood was collected from 13 clinically healthy Thoroughbred foals every month. All foals were weaned at the 4 mo and blood samples were taken also at 24, 48 and 72 h after weaning. The results obtained showed growing effects for tri-iodothyronine (T₃), thyroxine (T₄), free tri-iodothyronine (fT₃) and free thyroxine (fT₄) values (P < .001).

Serum T₃ concentrations averaged respectively 2.89 and 0.29 nmol/L at 7 and 9 mo. Serum T₄ concentrations averaged respectively 100.17 and 21.77 nmol/L at 1 and at 10 mo. Serum fT₃ concentrations averaged respectively 6.96 and 1.50 pmol/L at 1 and 4 mo. Serum fT₄ concentrations averaged respectively 31.40 and 4.93 pmol/L at 1 and 9 mo. Significant correlations between T₃, T₄, fT₃ and fT₄ with body weight (BW) and between T₃, T₄ and fT₄ with age were observed.

Weaning effects (P < .001) were shown for T₃ and fT₄ levels. No differences (P > .05) in T₄ and fT₃ levels were observed over the 3-day period. Gender effects (P < .001) were shown for T₃, T₄, fT₃, and fT₄ levels. Significant correlations between T₄ and fT₄ with BW and age were observed in colts and fillies. T₃ concentrations were correlated with age only in colts and fT₃ with BW only in colts. The results obtained seem to lend support to the recognized effects of growing and weaning in modulating the thyroid function of Thoroughbred foals. In fact, significant and differentiated effects of growing and weaning on total and free iodothyronine levels have been demonstrated.     

Prolactin signaling in porcine adrenocortical cells: involvement of protein kinases

Prolactin (PRL) was found to have a stimulatory effect on adrenal steroidogenesis in vivo and in vitro in several species including pigs. PRL signal transduction pathways, however, in adrenocortical cells are poorly recognized. Therefore, the goal of this paper is to ascertain the involvement of protein kinase C (PKC) and tyrosine kinases in PRL signaling in porcine adrenal cortex. Adrenals were harvested from locally slaughtered mature gilts. Cortical cells were dispersed by sequential treatment with collagenase. The cells were seeded into 24-well culture plates at a density of 3×10⁵/mL. Cells were incubated with or without PRL (500 ng/mL), ACTH (5 nM—a positive control), tyrosine kinase inhibitor—genistein (1; 2.5 or 5 μM), PKC inhibitor—sphingosine (20–1000 nM) and PKC activators—diacylglycerol (DiC8; 10–100 μM) and phorbol ester (PMA; 1–1000 nM). All incubations were performed for 8 h (95% air and 5% CO₂, 37°C). PRL and ACTH (P<0.05) increased cortisol and androstenedione (A₄) secretion. DiC8 and PMA mimicked the stimulatory effect of PRL. Sphingosine (P<0.05) suppressed basal and PRL-stimulated steroid secretion. Genistein inhibited (P<0.05) PRL-stimulated cortisol secretion and enhanced (P<0.05) basal and PRL-stimulated A₄ secretion. Moreover, PKC activation was assessed by measuring the specific association of [³H]phorbol dibutyrate ([³H]PDBu) with adrenocortical cells after treatment with PRL or ionomycin (a positive control). PRL (within 2–3 min) and ionomycin (within 2–5 min) increased (P<0.05) specific binding of [³H]PDBu to the porcine adrenocortical cells. In addition, PRL did not augment the cortisol and A₄ secretion by PKC-deficient adrenocortical cells. In conclusion, presented results support the hypothesis that PKC and tyrosine kinases are involved in PRL signaling in adrenocortical cells in pigs. Moreover, activation of PKC is associated with the increased secretion of cortisol and A₄.     

Seasonal and pulsatile dynamics of thyrotropin and leptin in mares maintained under a constant energy balance

The objective of this study was to determine if seasonal and/or pulsatile variations occur in plasma concentrations of thyrotropin (TSH) and leptin in mares while maintaining a constant energy balance. Blood samples were collected every 20 min during a 24 h period in winter and again in summer from six Quarter Horse type mares. Plasma concentrations of TSH, leptin, and T₄ were determined by radioimmunoassay. No differences were observed in body weight between winter (388.1 ± 12.5 kg) and summer (406.2 ± 12.5 kg; P = 0.11). Plasma concentrations of TSH were greater in the summer (2.80 ± 0.07 ng/ml) when compared to winter (0.97 ± 0.07 ng/ml; P < 0.001). Pulse frequency of TSH was not different between winter (6.17 ± 0.78 pulses/24 h) and summer (5.33 ± 0.78 pulses/24 h; P = 0.49). Mean TSH pulse amplitude, pulse area, and area under the curve were all greater in summer compared to winter (3.11 ± 0.10 ng/ml versus 1.20 ± 0.10 ng/ml, 24.86 ± 0.10 ng/ml min versus 13.46 ± 1.90 ng/ml min, 3936 ± 72.93 ng/ml versus 1284 ± 72.93 ng/ml, respectively; P < 0.01). Mean concentrations of leptin were greater in summer (2.48 ± 0.17 ng/ml) compared to winter (0.65 ± 0.17 ng/ml; P < 0.001). Pulsatile secretion patterns of leptin were not observed in any horses during experimentation. Mean concentrations of T₄ were greater in winter (20.3 ± 0.4 ng/ml) compared to summer (18.2 ± 0.4 ng/ml; P < 0.001). These seasonal differences between winter and summer provide evidence of possible seasonal regulation of TSH and leptin.     

Influence of daily injections of porcine somatotropin on growth, puberty, and reproduction in gilts

To determine whether recombinant porcine somatotropin (rpST) alters reproduction, 40 crossbred gilts weighing 59.1 +/- .5 kg at 125 +/- 1 d of age were assigned randomly to an experiment arranged as a 2 x 2 factorial. Eight gilts were given daily injections of diluent until they reached 104 kg BW (DW), and eight received diluent injections until puberty (DP). Twelve gilts were given rpST (4 mg/d) until 104 kg BW (PW) and 12 were given rpST injections until puberty (PP). All gilts were individually fed on an ad libitum basis an 18% CP corn-soybean meal diet (1.2% lysine and 3.1 Mcal/kg of ME). Beginning at 5 mo of age, gilts were exposed 20 min daily to mature boars. Serum concentrations of progesterone were measured weekly from 5 to 8 mo of age to verify age of puberty. Gilts observed in pubertal estrus were mated to two different boars 10 h apart. At 47 +/- 1 d of gestation, gilts were slaughtered to assess fetal development. After 60 d of treatment, serum LH and FSH profiles were determined in blood samples drawn at 20-min intervals for 4 h from eight diluent- and eight rpST-treated gilts fitted with indwelling jugular catheters. By 28 d, feed intake, feed/gain, and blood urea nitrogen were decreased (P less than .005) by rpST. Treatments did not affect (P greater than .05) the proportion of gilts attaining first ovulation (DW = 6/6; DP = 10/10; PW = 7/9; PP = 14/14) or conception rate (DW = 5/6; DP = 7/10; PW = 4/6; PP = 11/12).(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of dietary yeast and protected methionine on performance and trace minerals status of growing Awassi lambs

Eighteen growing Awassi lambs were used in this study to determine the effect of supplementing two levels of yeast and methionine (cyc-methionine) on the trace elements bioavailability, growth rate, and general performance. The lambs were divided to three groups. The dietary treatments were the control diet (C), control diet plus 2 g cyc-methionine/lamb/day (T₁) and control diet plus 4 g cyc-methionine/lamb/day (T₂).

Lambs fed 2 g/day of cyc-methionine (T₁) showed a significantly higher (P < 0.05) copper, zinc, and cobalt concentrations in liver and meat tissues, but not the same trend in kidney. No significant (P > 0.05) effect of time and time × treatment interaction on copper, zinc, cobalt, and manganese concentrations in blood serum, but cobalt and manganese concentration showed significant (P < 0.05) change by time. Moreover, a significantly (P < 0.05) higher total body gain, average daily gain, dressing percentage, and lower feed conversion were detected in lambs from T₁ compared with the control and T₂ groups.

Feeding 2 g of cyc-methionine to growing lambs increased the net profit by $6.017/lamb and only $3.52/lamb fed 4 g cyc-methionine/day when compared with the control group.

In conclusion, feeding growing Awassi lambs yeast and methionine in a form of cyc-methionine, with a low level of 2 g/day, improve the bioavailability of copper, zinc, and cobalt by growing lambs and their growth performance.     

The effects of recombinant porcine somatotropin on reproductive function in gilts treated during the finishing phase.

The objective of this study was to determine the effects of recombinant porcine somatotropin (rpST) treatment during the finishing phase on subsequent reproductive function in crossbred gilts. Forty gilts weighing 50 kg and housed in a swine finishing facility were randomly assigned to control or rpST treatment. Four control and four rpST-treated gilts were allotted per pen. Twenty rpST-treated gilts received 6 mg of rpST.gilt-1.d-1 in 1 ml of buffered carrier and 20 control gilts received 1 ml of buffered carrier.gilt-1.d-1. Injections were administered daily at 1400 in the extensor muscle of the neck. All gilts received an 18% CP diet containing 1.2% lysine. Treatment was terminated when the average weight in each pen reached 110 kg. Gilts treated with rpST gained more weight (P less than .05) than control gilts (59.8 +/- 1.0 vs 53.5 +/- 1.0 kg). Age at puberty was not different (rpST, 182.2 +/- 3.3; control 181.4 +/- 3.1 d). Prior treatment with rpST did not significantly affect length of estrus (rpST, 1.9 +/- .1; control, 1.8 +/- .1 d) or estrous cycle length (rpST, 20.6 +/- .4; control, 20.4 +/- .4 d). Ovulation rates at second estrus were similar for rpST gilts (15.1 +/- .5) and control gilts (14.4 +/- .5). More embryos (P = .10) were recovered on d 9 to 12 of gestation from rpST-treated gilts than from control gilts (13.1 +/- .9 vs 10.7 +/- .9).(ABSTRACT TRUNCATED AT 250 WORDS)     

The correlation between passage rate of digesta and dry matter digestibility in various stages of swine

The relationship between passage rate of digesta (PRD) and apparent faecal dry matter digestibility (DMD) was investigated in five trials. In trial 1, 2, and 3, 36 weanling (16.9 ± 3.0 kg), 24 growing (51.3 ± 8.8 kg), and 23 finishing (104.8 ± 5.2 kg) barrows were housed in metabolic crates. The beginning and end of 5-day collection periods were marked by the addition of 0.5% indigo carmine to the feed for total faeces collection and PRD determination by observing the time required for the marker to appear. In trial 4 and 5, 21 gestating gilts (215.0 ± 15.0 kg), and 19 lactating sows were individually penned. Addition of 0.5% chromic oxide to the feed enabled indirect determination of DMD and PRD. The PRD, which ranged from 12 to 80 h, was positively correlated with DMD in weanling (R² = 0.483, P < 0.001), growing (R² = 0.425, P < 0.01), and finishing (R² = 0.553, P < 0.001) pigs. Body weight and DMD were not significantly correlated in weanling (R² = 0.001, P = 0.893), growing (R² = 0.000, P = 0.995), or finishing (R² = 0.092, P = 0.156) pigs. A positive correlation between PRD, which ranged from 27 to 102 h, and DMD occurred in gestating gilts (R² = 0.231, P < 0.05), but not in lactating sows (R² = 0.014, P = 0.633). The results indicate that longer retention times of digesta improve DMD in swine. Also the results indicate the importance of PRD as a potential independent variable in digestibility assessments.     

Endotoxin challenge increases xanthine oxidase activity in cattle: effect of growth hormone and vitamin E treatment

In addition to its basic role in the metabolism of purine nucleotides, xanthine oxidoreductase (XOR) is involved in the generation of oxygen-derived free radicals and production and metabolic fate of nitric oxide (NO). Growth hormone (GH) and Vitamin E (E) have been shown previously to modify immune response to infection. Our objective was to determine in heifers the effect of endotoxin challenge (LPS; 3.0 μg/kg BW, i.v. bolus, Escherichia coli 055:B5) on xanthine oxidase (XO) activity in plasma and liver and the modification of this response by daily treatment with recombinant GH (0.1 mg/kg BW, i.m., for 12 days) or GH+E (E: mixed tocopherol, 1000 IU/heifer, i.m., for 5 days). In experiment 1, 16 heifers (348.7±6.1 kg) were assigned to control (C, daily placebo injections), GH, or GH+E treatments and were challenged with two consecutive LPS injections (LPS1 and LPS2, 48 h apart). After LPS1, plasma XO activity increased 290% (P<0.001) at 3 h, reached peak (430%) at 24 h and returned to basal level by 48 h after LPS2. XO responses (area under the time×activity curve, AUC) were greater after LPS1 than LPS2 (P<0.001). Total plasma XO responses to LPS (AUC, LPS1+LPS2) were augmented 55% (P<0.05) over C with GH treatment but diminished to C responses in GH+E. There was a linear relationship (r²=0.605, P<0.001) between total response in plasma XO activity and plasma nitrate+nitrite concentration. In experiment 2, 24 heifers (346±6 kg) were assigned to C or GH treatments and liver biopsy samples were obtained at 0, 3, 6, and 24 h after a single LPS challenge. Hepatic XO activities increased 63.3% (P<0.05) 6 h after single LPS challenge and remained elevated at 24 h (100.1%, P<0.01) but were not affected by GH treatment. Results indicate that LPS-induced increases in plasma XO activity could be amplified by previous GH treatment but attenuated by E administration. The data also suggest that E may be effective in controlling some mediators of immune response associated with increased production of NO via the effect on XO activity and its production of superoxide anion as well as uric acid.     

Acute and chronic hormone and metabolite changes in lambs fed the beta-agonist, cimaterol

The objective of this study was to determine if acute and chronic changes in circulating metabolic hormone and metabolite concentrations are associated with β-agonist-induced nutrient repartitioning in young growing lambs. Two groups of 12 Dorset and Dorset-Finn cross ram lambs weighing 36 or 33 kg live weight were assigned to 3- or 6-week treatment intervals, respectively, to achieve similar slaughter weights. Six lambs within each treatment interval were fed ad libitum a complete mixed high-concentrate diet containing either 0 or 10 ppm cimaterol. During the first 12 hr of cimaterol administration plasma somatotropin (ST), thyroxine (T₄), and triiodothyronine (T₃) concentrations were not altered by treatment, but plasma insulin, glucose, non-esterified fatty acids (NEFA) and glycerol concentrations were elevated 2 hr after ingestion. These acute responses suggest direct stimulation of glycogenolysis and lipolysis by cimaterol, which is characteristic of β-adrenergic alteration of carbohydrate and lipid metabolism. Chronic administration of cimaterol significantly decreased insulin concentrations by 36% and 52% at 3 and 6 weeks, respectively, while glucose concentrations remained unchanged. Serum IGF-I concentrations were not significantly altered by cimaterol. T₄ levels were reduced 22.1% after 3 weeks of cimaterol treatment. Although plasma NEFA concentrations were chronically elevated 56% to 65% in lambs fed cimaterol, plasma glycerol concentrations remained at baseline levels. The relative changes in plasma NEFA and glycerol concentrations are consistent with a decreased rate of lipogenesis, rather than an increase in lipolysis.     

体外产气法评价生薯条加工副产品-稻草混贮与全株玉米青贮组合效应的研究

旨在探究生薯条加工副产品-稻草混贮（以下简称“薯稻混贮”）与全株玉米青贮间的组合效应。“薯稻混贮”是按照1∶2混合（混贮后的干物质含量为35%）、添加青贮添加剂、用搅拌机混匀、打捆裹包机裹包、发酵60 d制成。根据“薯稻混贮”与全株玉米青贮的不同比例分为7个组合，分别为T₀组（0∶100）、T₂₀组（20∶80）、T₄₀组（40∶60）、T₅₀组（50∶50）、T₆₀组（60∶40）、T₈₀组（80∶20）、T₁₀₀组（100∶0），每个组合3个重复。通过体外产气法，测定各组合发酵48 h干物质降解率（DMD）、pH、氨态氮（NH₃-N）浓度、微生物蛋白（MCP）产量以及挥发性脂肪酸（VFA）浓度等指标，测定各组合在发酵2、4、6、8、10、12、24、36和48 h的产气量（GP）。并计算每个单项组合效应指数（SFAEI）及综合效应指数（MFAEI）。结果表明：1）GP和DMD随“薯稻混贮”比例增加显著或极显著降低（P<0.05或P<0.01）。SFAEI中T₅₀和T₈₀组的GP和DMD最低，GP和DMD最高值均出现在T₂₀组。2）不同组合发酵后的pH值为6.46~6.59，其中T₈₀组pH最高，显著或极显著高于除T₁₀₀组外的其他组别（P<0.05或P<0.01），SFAEI在T₈₀组最高。3）各组合间NH₃-N浓度、MCP产量无显著差异（P>0.05），但均以T₄₀组最高，而SFAEI分别以T₄₀和T₈₀组最高。4）乙酸、丙酸、戊酸和TVFA浓度均以T₀组最高，T₁₀₀组最低，且两组间差异极显著（P<0.01）；丁酸也以T₀组浓度最高，但以T₈₀组浓度最低。SFAEI指标中，乙、丙、丁酸分别以T₈₀、T₂₀和T₆₀组最高。通过MFAEI指数评定得出，两种饲料组合均产生正组合效应，其中T₄₀组（40∶60）最优，其次是T₅₀组（50∶50）。     

Effect of recombinant porcine somatotropin on fetal and placental growth in gilts with reduced uterine capacity

Crowded uterine conditions were induced by unilateral hysterectomy-ovariectomy (UHO) in 42 gilts to determine the effect of recombinant porcine somatotropin on fetal and placental growth. Gilts were randomly assigned across three replicates to one of three treatments: Control (C; n = 14), daily injections of 1 mL saline from d 0 to 64 of gestation, Early (E; n = 12), 5 mg of rpST/d from d 0 to 30, followed by 1 mL saline from d 31 to 64, and Late (L; n = 16), 1 mL saline/d from d 0 to 29, followed by 5 mg of rpST/d from d 30 to 64 of gestation. Blood was collected from each gilt via jugular venipuncture at d 0 and every 15 d thereafter. Gilts were hysterectomized on d 65 of gestation. Length of placental attachment and fetal crown-rump length were measured. Placentas and fetuses were weighed. Placental length, wet weight, and dry weight were recorded. Treatment with rpST (either E or L) increased (P < 0.0001) maternal plasma IGF-I concentrations relative to controls. Treatment with rpST did not affect placental wet weight or placental DNA content. However, E and L treatments increased the percentage of placental protein (P = 0.01) and placental dry matter (P = 0.10) and increased contact area of uterine-placental interface (P = 0.01). Despite changes in placental composition and morphology, weights of fetuses collected from L-treated gilts did not differ from controls, whereas weights of fetuses collected from E-treated gilts tended to be less than controls (P < 0.06). Administration of rpST increased maternal IGF-I concentrations and placental surface area but failed to increase fetal growth in the UHO model. Therefore, mechanisms that are independent of maternal IGF-I or placental contact area may control early fetal growth under crowded uterine conditions.     

Mammary uptake and excretion of prostanoids in relation to mammary blood flow and milk yield during pregnancy-lactation and somatotropin treatment in dairy goats

Mammary arterious − venous differences (A − V) and excretion into milk of four prostanoids were related to changes in milk yield and milk vein blood velocity (MBV) in goats at different stages of pregnancy and lactation, and during somatotropin (ST) treatment in mid-lactation. Arterial concentrations and mammary A − V for the vasodilators prostacyclin (PGI₂) and prostaglandin (PG) E₂ (measured as 6-keto-PGF₁ and bicyclic PGE₂, respectively) decreased from late pregnancy to lactation. A − V were negatively correlated to MBV (r = −0.32 to −0.34). Arterial concentrations of the vasoconstrictors PGF₂ and TXA₂ (measured as TXB₂) changed similarly, but no A − V across the mammary gland were found. The vasodilator to vasoconstrictor ratio in plasma was around 1:1, and in skimmed milk around 0.29–0.49 due to significantly higher TXB₂ levels in milk compared to plasma. Close linear correlations were established between milk yield and excretion of TXB₂ into milk (r = 0.80, P < 0.001), and between MBV and PGE₂ excretion into milk (r = 0.69, P < 0.001). ST treatment stimulated MBV and mammary prostanoid supply, and decreased prostanoid concentration in milk vein plasma. The high arterial levels of prostaglandins during pregnancy most likely reflected uterine synthesis. Our results support a role for PGI₂ and PGE₂ in local mammary blood flow regulation during lactation. Increased mammary uptake of these two prostanoids may be involved in the mammary blood flow response to ST. TXA₂ may be synthesized by mammary epithelial as well as vascular cells, and TXA₂ may be an important factor in regulation of mammary function.     

Postnatal changes in circulating concentrations of growth hormone, somatomedin C and thyroid hormones in pigs

Plasma concentrations of growth hormone (GH), somatomedin (SmC), thyroxine (T₄) and triiodothyronine (T₃) were determined from birth to post weaning in pigs (Yorkshires). Plasma samples were obtained from the smallest, median and largest piglet from 11 litters. No differences in the circulating concentrations of any of the hormones were observed between piglets of different sizes. However, there were changes in circulating concentrations of hormones during postnatal development. Plasma concentrations of GH decreased between 2 and 8 to 10 days of age. A progressive increase in the circulating concentrations of SmC was observed with concentrations rising (3.83-fold between 2 days and 40 days of age). Plasma concentrations of T₄ and T₃ were maximal at 23 and 16 days of age, respectively.     

饲粮钙磷水平对伊犁马初乳成分、乳脂脂肪酸组成、产后血液钙磷及激素的影响

旨在研究妊娠后期饲喂不同钙磷水平饲粮对产后伊犁马初乳成分、乳脂脂肪酸组成、血液钙磷及钙磷代谢激素、繁殖及生长代谢激素等生理生化指标的影响，为明确伊犁马在妊娠后期对钙磷的适宜需要量提供参考。本试验选取健康、无亲缘关系、12~13周岁、体重为（380±32）kg、胎次为4~5胎、处于第10妊娠月左右的伊犁马25匹，随机分为5组，每组5个重复。各组饲粮钙饲喂水平分别为36.00、39.00、42.00、45.00和48.00 g·d^-1，磷饲喂水平分别为26.30、28.30、30.30、32.30和34.30 g·d^-1。试验预试期10 d，正试期从第11天至母马分娩后第2天结束。母马分娩后12 h内采集初乳用于测定乳成分和乳脂脂肪酸含量，空腹血液用于测定Ca、P、甲状旁腺素（PTH）、降钙素（CT）、骨钙素（OC）、胎盘催乳素（PL）、垂体催乳素（PRL）、雌酮（E₁）、雌二醇（E₂）、血清孕酮（PROG）、甲状腺素（T₄）、三碘甲状腺原氨酸（T₃）、生长激素（GH）、胰岛素样生长因子-Ⅰ（IGF-1）等激素浓度。结果表明：1）饲粮钙磷水平对初乳中钙、磷、乳脂率、乳糖率均无显著影响，组间乳蛋白率、总固形物、体细胞数、乳脂中饱和脂肪酸（SFA）和不饱和脂肪酸（UFA）比例存在显著差异（P<0.05）。随着饲粮钙、磷水平的增加，乳磷浓度、乳蛋白率和UFA比例呈显著线性增加（P<0.05），总固形物呈显著二次增加（P<0.05），而乳糖率、SFA及肉豆蔻酸比例呈显著线性降低（P<0.05）。2）饲粮钙磷水平显著影响血液中OC和PROG浓度（P<0.05），随着饲粮钙磷水平的增加，血液中离子钙、CT和OC浓度呈显著的线性降低（P<0.05），而PTH和PROG水平呈显著的线性升高（P<0.05）。饲粮钙、磷水平对PL、PRL、E₁、E₂等生殖激素以及T₃、T₄、GH和IGF-1等生长代谢激素浓度均无显著影响。由此可见，在本试验条件下，饲粮钙磷通过提高初乳中乳蛋白率和总固形物来改变乳脂中饱和脂肪酸含量和不饱和脂肪酸比例影响初乳成分；通过降低血液中OC浓度影响钙磷代谢；通过提高血液中PROG浓度影响繁殖状况。     

Effect of exogenous thyrotropin-releasing hormone (TRH) administration on plasma levels of triiodothyronine (T3), thyroxine (T4) and growth hormone (GH) in chronically catheterized suckling piglets.

The purpose of the present study was to determine experimental conditions to stimulate secretion of thyroid hormones (T₃ and T₄) with thyrotropin-releasing hormone (TRH) injections in suckling piglets during the first weeks of postnatal life. Three consecutive experiments were conducted. Four 10–20 d old piglets were i.m. injected with 0, 20, 100, 500 μg (experiment 1) or 0, 4, 20, 100 μg TRH/kg BW (experiment 2) according to a 4 × 4 latin square design involving different litters in each experiment. Blood samples were taken −15, −1, 15, 30, 45, 60, 90, 120 180 and 300 min after TRH injection in experiment 1, and −.25, −.08, .25, .5, 1, 2, 4, 6, 8, 12, 24, 30, 36, 48, 60 and 72 hr after TRH injection in experiment 2. T₃ and T₄ levels were significantly (P<.01) increased as soon as 30 and 45 min after TRH injection, respectively. Maximal levels of T₃ and T₄ were obtained 2 and 4 hr after the injection of 100 μg TRH. T₃ and T₄ returned to basal levels within 6 and 8 hr post injection, respectively. Plasma pGH levels were significantly (P<.001) increased 15 min after TRH injection in piglets injected with 500 μg. In experiment 3, 100 μg TRH/kg BW were injected i.m. either daily or every other day from .0 to 23 days of age. Results showed that T₄ response to TRH did not decrease after repeated injections. These results indicate that daily i.m. injections of 100 μg TRH/kg BW can be used to increase thyroid hormone levels for at least 13 d in the young suckling piglet.     

Influence of gonadotropins on insulin- and insulin-like growth factor-I (IGF-I)-induced steroid production by bovine granulosa cells

To determine the effect of gonadotropins on insulin- and insulin-like growth factor (IGF-I)-induced bovine granulosa cell functions, granulosa cells from bovine ovarian follicles were cultured for 2 days in the presence of 10% fetal calf serum (FCS), and then cultured for an additional 2 days in serum-free medium with added hormones. In the presence of 0 or 1 ng/mL of insulin or IGF-I, FSH had little or no effect (P>0.05) on estradiol production by granulosa cells from both small (1–5 mm) and large (≥8 mm) follicles. However, in the presence of ≥3 ng/mL of insulin, FSH increased (P<0.05) estradiol production by granulosa cells from small and large follicles such that the estimated dose (ED₅₀) of insulin necessary to stimulate 50% of the maximum estradiol production was decreased by 2- to 3-fold from 22 to 28 ng/mL in the absence of FSH to 7–14 ng/mL in the presence of FSH. Similarly, in the presence of ≥3 ng/mL of IGF-I, FSH increased (P<0.05) estradiol production by granulosa cells from small and large follicles such that the ED₅₀ of IGF-I for estradiol production was decreased by 4- to 5-fold from 25 to 36 ng/mL in the absence of FSH to 5–6 ng/mL in the presence of FSH. In the presence of FSH, the maximal effect of insulin on estradiol production was much greater than that of IGF-I (137- versus 12-fold increase) and were not additive; when combined, 100 ng/mL of IGF-I completely blocked the stimulatory effect of 100 ng/mL of insulin. In the absence of FSH, the maximal effect of insulin and IGF-I on estradiol production was similar. Concomitant treatment with 30 ng/mL of LH reduced (P<0.05) insulin-stimulated estradiol production by 52% on day 1 and 19% on day 2 of treatment. Insulin, IGF-I and FSH also increased (P<0.05) granulosa cell numbers and progesterone production but their maximal effects were less (i.e., <4-fold increase) than their effects on estradiol production. In conclusion, insulin and IGF-I synergize with FSH to directly regulate ovarian follicular function in cattle, particularly granulosa cell aromatase activity.     

Hormonal changes following an acute stress in control and somatostatin-immunized pigs

Sixteen Yorkshire pigs (49 ± 2 kg BW at 17 weeks) were immunized against somatostatin (SRIF; 4 males, 4 females) or its conjugated protein, bovine serum albumin (BSA; controls; 4 males, 4 females). Immunizations were done at 10, 12 and 14 weeks of age. Jugular vein cannulae were surgically inserted at 17 weeks of age. Five d later, half of each sex from the control and SRIF-immunized groups were stressed. The other half were subjected to the same stress 48 hr later. On both days, remaining animals were used as unstressed controls. The stress consisted of 5 min of snare restraint. Blood samples were collected from all pigs on both days at −20, −15, −10, −5, 0 (beginning of stress), 2, 6, 10, 15, 20, 30, 40, 60, 90, 120, 150, 180 and 240 min. Samples were radioimmunoassayed for cortisol, growth hormone (GH), prolactin (Prl), insulin, triiodothyronine (T₃), thyroxine (T₄) and insulin-like growth factor I (IGF-I). Mean antibody titers against SRIF (1:150 dilution) at 15 weeks were 0.49 ± .09% and 54.5 ± 4.9% for control and SRIF immunized pigs, respectively. Gender and immunization against SRIF had no effect on any of the variables measured (P>0.05), except for T₃ levels which were greater in females than in males (P<0.05). The stress by time of sampling interaction was significant (P<0.01) for all hormones measured. Cortisol values almost tripled within 15 min of stress, reaching concentrations above 100 ng/mL. Maximal increases were seen at 2 min for T₄ (14%), at 6 min for T₃ (36%), at 15 min for Prl (46%) and at 10 min for insulin (141%). An increase of 129% in GH concentration was present at 20 min in stressed pigs; however, an increase of 97% was also seen at 120 min in control pigs. Concentrations of IGF-I decreased (21%) by 60 min in the stressed pigs and remained depressed for up to 150 min. Stress associated with snare restraint, therefore, induces major changes in the concentrations of a series of hormones in growing pigs. On the other hand, immunization against SRIF did not alter any of the hormonal profiles measured. Since snare restraint is widely used to handle pigs during jugular puncture, any study of hormonal secretion in this species should be carried out under carefully controlled conditions in terms of blood sampling technique.     

Effect of constant-release melatonin implants and prolonged exposure to a long day photoperiod on prolactin secretion and hair growth in mouflon (Ovis gmelini musimon)

The aims of this study were to examine whether mouflons exposed to constant long and short day photoperiods are able to exhibit an annual cycle of hair growth and moult, and prolactin (PRL) secretion. Mouflon ewes were assigned to three groups of treatment. Ewes were maintained, either under natural photoperiod (control, n=9), or received a series of subcutaneous melatonin implants from December to April (n=8), or were exposed to a constant long day photoperiod (16-h light:8-h dark; 16L:8D) during 18 months (n=7). Blood was collected weekly to determine PRL concentrations, and hair samples were clipped weekly from the base of the neck to measure the length of predominant hair. Under constant long days and with melatonin implants, mouflons expressed an annual rhythm of PRL secretion, even though these treatments modified the times of rise or falling of PRL concentrations throughout the year. Hair growth initiation was almost coincident with the summer solstice in both control and melatonin-implanted mouflons but occurred two months earlier in long day hold mouflons (P<0.001). Long day hold mouflons had a lower hair growth rate than control and melatonin-implanted mouflons (P<0.001), and at the end of the experiment, a shorter hair length (3.4±0.24 cm; P<0.01) than control (4.3±0.17 cm), and melatonin-implanted mouflons (4.2±0.12 cm). Our data support the conclusion that in mouflon, an endogenous circannual rhythm of PRL secretion exists, and that the seasonal cycle of hair growth and moult appears to depend, at least in part, on circulating levels of PRL.     

The C bicarbonate dilution technique to determine energy expenditure in young bulls validated by indirect calorimetry

We explored the applicability of the ¹³C bicarbonate dilution technique for determination of energy expenditure (EE) in young bulls in comparison to whole body indirect calorimetry (IC). Twelve bulls of a F2 German Holstein x Charolais cross (4.5 months, 332 ± 16 kg BM) received a diet providing 1000 kJ ME d^− 1 kg BM^− 0.75 and 4.3 g crude protein d^− 1 kg BM^− 0.75. Bulls were housed in respiration chambers and received an intravenous bolus of NaH¹³CO₃ (A: 3 μmol kg BM^− 1 (n = 2), B: 7 μmol kg BM^− 1 (n = 4), C: 17.5 μmol kg BM^− 1 (n = 6), 99 at.% ¹³C) into the jugular vein to measure EE. Simultaneously, EE was determined by IC. After the ¹³C administration blood samples and breath gas were collected from the animals in the respiration chamber during a 24-h period (7.00–7.00 h). The recovery of ¹³C in breath CO₂ (% of ¹³C dose) was irrespective of NaH¹³CO₃ dose (A: 69.7 ± 2.7%, B: 70.5 ± 4.5%, C: 75.0 ± 4.9%; P > 0.05). Only small amounts of ¹³C were excreted in urine (3.4 ± 2.6%) and feces (2.0 ± 1.3%). The EE determined by the ¹³C bicarbonate method using breath and blood ¹³C recovery rates as correction factors was not different from that measured by IC (816 ± 81 [blood] or 827 ± 101 [breath] vs. 820 ± 90 kJ d^− 1 kg BM^− 0.75). Bland–Altman analysis showed a 95% confidence interval for EE of ± 99 and ± 109 kJ d^− 1 kg BM^− 0.75 based on blood and breath ¹³C recovery, respectively. In conclusion, the ¹³C bicarbonate dilution method is appropriate to obtain reliable estimates of EE in young bulls using blood CO₂ or breath CO₂ under standardized experimental conditions, i.e. in the fasting state.