Influence of dietary lysine level on whole-body protein turnover, plasma IGF-I, GH and insulin concentration in growing pigs

Four growing pigs (initial liveweight 25.9 ± 0.54 kg, final liveweight 43.0 ± 1.06 kg) were used to study the effect of dietary lysine level on nutrient digestibility, whole-body protein turnover, plasma insulin-like growth factor-I (IGF-I), growth hormone (GH), insulin, glucose, and urea nitrogen (PUN). Four diets, containing 7.0 g (L1), 9.5 g (L2), 12.0 g (L3) and 14.5 g (L4) lysine per kg diet respectively, were formulated as experimental treatments. The animals and diets were allocated in a 4 × 4 Latin square design. Nitrogen (N) metabolism and whole-body protein turnover were measured by classical method and single-dose ¹⁵N end-product method, respectively. The blood samples were taken at the end of each experimental period. Results showed that N retention (NR) and N biological value (NBV) were significantly increased from L1 to L4 (P < 0.05). However, differences in NR and NBV between L2, L3 and L4 were not significant (P > 0.05). There was no significant difference on dry matter (DM) digestibility, organic matter (OM) digestibility and N digestibility between different treatments (P > 0.05). Whole-body protein synthesis, protein degradation and protein accretion increased markedly from L1 to L2 (P < 0.05), but did not increase further from L2 to L4. Whole-body protein accretion (y, g/kg W^0.75/d) increased with dietary lysine (x, g/kg) in a quadratic manner: y = − 0.09x² + 2.12x − 5.14 (r² = 0.96, n = 4, P < 0.05).The results also showed that differences in plasma IGF-I, GH, glucose and PUN concentration between different treatments were not significant (P > 0.05). Plasma insulin concentration (y, μIU/ml) was increased with dietary lysine (x, g/kg) in a quadratic manner: y = 0.23x² − 4.10x + 32.25 (r² = 0.99, n = 4, P < 0.05), but it was not found that plasma insulin concentration was related to NR. A significant correlation was found between NR (y, g/d) and plasma IGF-I (x, ng/ml): y = − 3.1 × 10^− 3x² + 1.31x − 122.28 (r² = 0.99, n = 4, P < 0.05).It was concluded that dietary lysine level had a significant influence on NR and whole-body protein turnover but not on plasma IGF-I and GH concentration. Plasma IGF-I may be an important factor controlling N metabolism of growing pigs. Further research was needed to study the mechanism.     

Influences of lipopolysaccharide-induced immune challenge on performance and whole-body protein turnover in weanling pigs

The objective of this study is to characterize the influence of immune stress induced by lipopolysaccharide (LPS) on protein utilization and turnover for early-weaned pigs. A total of 15, crossbred weanling pigs (initial body weight 10.15 ± 0.39 kg) were assigned to one of three treatments. Pigs were injected with LPS and fed ad libitum (LPS-challenge), or injected with endotoxin-free physiological salt solution (PSS) and fed ad libitum (control), or injected with PSS and fed the same amount of feed as LPS-challenged pigs (pair-feed). All pigs received a 4-d nitrogen balance trial. On d 1 and 3 of the trial, LPS-challenged pigs were injected intramuscularly with 200 μg/kg BW of LPS dissolved in 1 ml PSS. Pigs in other treatments were injected with 1 ml PSS. ¹⁵N-Glycine (5 mg/kg BW) was gastrically infused after the second injection. Feces and urine were collected daily to determine the N output throughout the duration of the trial. Lymphocyte blastogenesis (LB) and serum immunoglobulins (IgA, IgG, IgM) were also detected to illustrate the LPS-induced immune responses. Results indicated that the injection of LPS significantly (P < 0.01) elevated the LB and resulted in lower average daily gain (ADG), feed intake (ADFI) and efficiency of feed utilization than control pigs. Pair-fed pigs had higher performance than LPS-challenged pig but poorer than control pigs. Injection of LPS also resulted in significantly (P < 0.01) lower nitrogen intake and efficiency of utilization than controls, and more fecal N excretion than Pair-fed pigs (3.19 ± 0.85 vs. 2.19 ± 0.67 g/d, P < 0.05). The whole-body nitrogen flux (4.34 ± 0.19 vs. 11.35 ± 0.12 g N/kg BW^0.75/d) and N accretion (5.57 ± 0.59 vs. 10.17 ± 1.12 g Pr/kg BW^0.75/d) were acutely (P < 0.01) reduced as the feed intake decreased, but there was no significant difference between LPS-challenged and pair-fed pigs. Injection of LPS markedly (P < 0.05) increased the protein degradation (16.76 ± 1.09 vs. 14.53 ± 1.24 g N/kg BW^0.75/d). It is concluded that LPS-induced immune challenge depresses growth performance and feed utilization efficiency by enhancing protein degradation rate and decreasing protein utilization for body protein retention.     

A genetic upper limit to whole-body protein deposition in a strain of growing pigs

The genetic upper limit to daily whole-body protein deposition (Pdmax) is an important constraint on pig growth. The Pdmax was determined for a specified pig genotype using N balance and serial slaughter techniques. A traditional N-balance study, involving 36 and 90 kg of BW Large White x (Landrace x Large White) entire male pigs, was first conducted to demonstrate that a highly digestible, nutrient-dense diet (1.54% Lys; 18 MJ of DE/kg, air-dried basis) was able to support the attainment of Pdmax within the constraints of pig appetite. Animals were allocated to set levels of feed intake [set proportions of ad libitum DE intake (DEi), 50 to 100%]. Nitrogen retention increased linearly with DEi up to 25.3 and 35.2 MJ of DE/d for the 36 and 90 kg of BW pigs, respectively, then showed a departure (P < 0.05) from linearity. For DEi of the experimental diet above the latter intakes, which were approximately 80% of a determined ad libitum DEi, the pigs deposited protein at a rate approaching Pdmax. When a linear plateau response model (accepted a priori) was fitted, Pdmax values of 189.9 g/d at a DEi breakpoint of 28.3 MJ of DE/d at 36 kg of BW and 186.4 g/d at a DEi breakpoint of 37.3 MJ of DE/d at 90 kg of BW were found. In the serial slaughter study, 18 female and 18 entire male pigs were allocated to 5 slaughter BW (25, 45, 65, 85, and 110 kg) such that there were 5, 3, 3, 3, and 4 animals of each sex at each slaughter weight, respectively. Animals were fed the experimental diet ad libitum, and whole-body protein was determined at slaughter. Growth data were analyzed by differentiating and combining continuous mathematical functions for BW and body composition. The ad libitum DEi were 27.4 and 50.7 MJ/d at 36 and 90 kg of BW for the entire males and were assumed, based on the N-balance results, sufficiently high to allow expression of Pdmax. There was an effect (P < 0.05) of sex on Pdmax vs. time (days on trial). Over the BW range of 25 to 85 kg, Pdmax was constant for the entire male and female pigs at 170 and 147 g/d, respectively. Above 85 kg of BW, Pdmax was no longer constant for either sex.     

Differences in whole-body protein turnover between Iberian and Landrace pigs fed adequate or lysine-deficient diets

The capacity for protein deposition in Iberian pigs is lower than in modern (e.g., Landrace) pig breeds, and the reasons for this remain unknown. The hypothesis tested in this work is that under similar nutritional and physiological conditions, whole-body protein turnover as well as the protein synthesis to protein deposition ratio differs between Iberian and Landrace breeds, resulting in dissimilar protein deposition rates. As a main objective, these variables were compared at different protein and Lys intakes in growing gilts. The study examined the effect of Lys deficiency because this is the prevalent condition during the fattening period of the Iberian pig in the Mediterranean forest, where the main feed source is oak acorn, which provides approximately one-third of the available Lys present in an ideal protein. Three diets were tested within each breed: 2 diets with an optimal essential AA pattern, containing 12 or 16% CP as-fed, or a Lys-deficient diet (35% of the recommended Lys content). This diet was supplied at 12% CP for the Iberian and 16% CP for the Landrace pigs, respectively. The contrasts made were breed x dietary protein concentration and breed x AA pattern (adequate vs. inadequate Lys content). Cumulative urinary (15)N excretion over 60 h after receiving an oral dose of [(15)N]-glycine was used to calculate N flux. Mean BW for Landrace and Iberian pigs were 25.8 +/- 0.55 kg and 30.8 +/- 0.74 kg, respectively. Protein deposition (g of N/(kg(0.75).d) was lower in the Iberian than in the Landrace gilts (4 to 16%; P = 0.002) and increased with dietary protein content. In contrast, protein synthesis and degradation [g of N/(kg(0.75).d)] were greater for the Landrace breed (16 to 18 and 23%, respectively, for the 2 dietary protein contents studied; P < 0.05), but no breed differences were detected in fractional protein synthesis and degradation rates. The ratio of protein synthesis:protein deposition (S/PD) did not change with dietary protein concentration or breed and achieved a mean value of 5.4. Irrespective of breed, Lys deficiency had a strong negative effect on N balance (P < 0.001) and increased the ratio of S/PD (P = 0.012). The greater rates of protein deposition, synthesis, and degradation in Landrace pigs than in Iberian pigs fed optimal AA-pattern diets were then attributed to differences in body protein mass. Consequently, these results validate the hypothesis of unequal synthesis and degradation, but not of unequal S/PD, between breeds.     

Influence of threonine intake on whole-body protein deposition and threonine utilization in growing pigs fed purified diets.

The relationship between available threonine (Thr) intake and whole-body protein deposition (PD) was established using the serial slaughter method in 36 individually housed growing gilts between 39 and 77 kg live BW. Pigs were prescreened for their maximum PD (PDmax), based on a N balance starting at 25 kg BW while they consumed semi-ad libitum a nonlimiting diet. Pigs were fed combinations of a casein and cornstarch-based diet that was confirmed to be first-limiting in Thr and a protein-free diet starting at approximately 30 kg BW. Casein-bound Thr was provided at 60, 70, 80, 90, 100, or 120% of estimated Thr requirements for PDmax. Energy intake was kept constant across treatments and exceeded requirements for PDmax. Pigs were fed three equal meals per day; feeding levels were adjusted weekly based on BW. Pigs were killed at either 39 kg BW (n = 2 per treatment) or 77 kg BW (n = 4 per treatment) for determining chemical body composition. Composition of 39-kg BW pigs was not different across treatments (P > 0.10); therefore, an overall mean initial body composition was used to estimate body protein content at the initial BW. Across treatments, mean daily ME intake was 25.3 (SE 0.08) MJ/d and did not differ (P > 0.10) among treatments. Average daily true ileal digestible Thr intake varied between 5.33 and 9.66 g/d, representing means for pigs on the lowest and the highest Thr intakes, respectively. Mean PD was 93, 102, 118, 124, 139, and 133 (SE 4.2) g/d for pigs on the six respective treatments. Dietary Thr intake did not influence (P > 0.10) Thr content of body protein at the final BW or the partitioning of body protein between carcass, viscera, and blood. The efficiency of Thr utilization for PD was lowest (P < 0.05) at the highest Thr intake level and highest (P < 0.05) at the lowest Thr intake level. It was similar (P > 0.10) at the four intermediate Thr intake levels, in which the relationship between true ileal digestible Thr intake and PD was linear. Based on these four treatments, calculated Thr disappearance, which is closely associated with inevitable Thr catabolism, was 23.5 (SE 0.55)% of available Thr intake. This value is consistent with an efficiency of using available Thr intake above maintenance Thr requirements (54 mg/kg BW0.75) for Thr retention with PD of 73.4 (SE 1.11)%. Based on N balances conducted at approximately 40 and 75 kg BW, the marginal efficiency of Thr utilization was not influenced by BW.     

Strain differences in whole-body protein turnover in the chicken embryo.

1. Whether or not there is a strain difference in embryonic whole-body protein turnover rates was tested using the chicken embryos of Rhode Island Red carrying a sex-linked dwarf gene (dwarf), White Leghorn (layer), and White Cornish X White Plymouth Rock (broiler) strains on day 12 of incubation. 2. Whole-body protein synthesis was estimated by injecting L-[15N]-phenylalanine either intraperitoneally or intravenously on day 12 of incubation in order to investigate the effect of the route of isotope administration. The results showed that the values for fractional and absolute synthesis rates were approximately 13% higher by intravenous injection than by intraperitoneal injection. 3. Whole-body protein turnover, both in terms of fractional and absolute rates, was significantly faster in dwarf than in broiler embryos, with intermediate values in layer embryos, although no growth differences were observed on day 12. 4. Difference in egg weight, measured before incubation, did not affect protein turnover. 5. It was concluded that the strain difference manifested in whole-body protein turnover of the chicken embryo would probably be a reflection of differences in genetic background.     

Influence of dietary protein intake on whole-body protein turnover in chicks

1. Experiments were conducted to investigate whether or not varying dietary protein intake affects whole-body protein turnover rates in young chicks. 2. Seven-d-old single comb White Leghorn male chicks were fed on diets with protein concentrations of 0, 100, 200 or 400 g/kg diet under conditions of ad libitum or equalised feeding. At the end of the experiments, the rate of protein synthesis and protein degradation in the whole body were measured in vivo. 3. The results showed that both fractional and absolute rates of protein synthesis increased with increasing dietary protein up to 200 g/kg; above this concentration they remained almost constant when feeding was ad libitum. 4. Similar responses were found with equalized feeding except that a significant reduction in protein synthesis was found when dietary protein was increased from 200 to 400 g/kg diet. 5. Less sensitive and almost parallel changes in protein degradation rates were found. 6. It was concluded that adaptation to varied dietary protein intake occurred primarily through changes in protein synthesis, accompanied by parallel alterations in protein degradation in the whole body.     

Whole-body protein turnover and nitrogen balance in growing pigs supplied with an antibiotic feed additive (Avilamycin)

Introduction   Antibiotic feed additives like Avilamycin (Maxus^®) exert a well-documented stimulatory effect on growth rate and feed efficiency in pig production (reviewed by, e.g., R oth and K irchgessner 1990; K amphues and M eyer 1992). The benefits to production performance seem to originate mainly from an enhanced gain of body protein as has been demonstrated in nitrogen balance trials with piglets and fattening pigs (R oth and K irchgessner 1993a,b; W indisch et al. 1998). However, the primary mode of action of antibiotic feed additives is not clarified completely. The growth-stimulating effect is assumed to originate from an enhanced absorptive capacity of the digestive tract for essential nutrients due to an improved microbial ecosystem in the gut (reviewed by, e.g., G reife and B erschauer 1988). However, metabolic effects may contribute to the higher protein accretion capacity also, as for example a reduced immune defense stress at the small intestine for example (discussed by, e.g., S chole et al. 1985). In order to elucidate possible metabolic effects of antibiotic feed additives it was the aim of the present study to combine a nitrogen balance experiment on Avilamycin-treated growing pigs with measurements on whole-body protein turnover.     

Growth hormone concentrations in plasma of healthy pigs and pigs with atrophic rhinitis.

Plasma concentrations of porcine growth hormone (PGH) were similar in healthy pigs and those with atrophic rhinitis (AR), therefore, observed reduced growth rates and feed efficiency in naturally infected pigs with AR were not attributed to low concentrations of plasma PGH. Also, pituitary glands in both groups of pigs were responsive to growth hormone-releasing hormone (GHRH) challenge by increasing PGH secretion. Administration of clonidine hydrochloride to pigs naturally infected with AR failed to elicit any significant change (5.3 +/- 1.4 ng/ml) in the plasma concentration of PGH within a 45-minute bleeding interval. The pretreatment concentrations of PGH were similar in specific-pathogen-free toxin-treated and specific-pathogen-free control groups, but they increased significantly in toxin-treated pigs (20.7 +/- 8.2 ng/ml) within 15 minutes after GHRH injection. Porcine growth hormone release in toxin-treated pigs was variable; however, all pigs did not respond to GHRH administration: 3 responded with an increase in PGH release (35.6 +/- 10.6 ng/ml), 2 did not respond (6.7 +/- 0.5 ng/ml), and 1 had a decrease in PGH release (3.9 ng/ml). Therefore, the observed reduced growth rates reported in the literature may be attributed to factors at the target level of PGH action, such as insufficient or down-regulation of PGH receptors, changes or impaired ability in the PGH receptor-binding characteristics, and inability of PGH receptor complex to transduce signal. Toxins are known to modulate signal transduction pathways. It has been speculated that serotype-D Pasteurella multocida toxin may influence growth by its effect on signal transduction from PGH receptor complex on the cell membrane to the interior of the cell.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of dietary protein on whole-body protein turnover and endocrine function in young-adult and aging dogs.

Thirty-six adult female Beagles averaging 2 (young-adult) or 8 (geriatric) yr of age were used to assess the effects of graded levels of dietary protein (16, 24, or 32%) on endocrine-controlled regulation of whole-body protein turnover. Rates of whole-body protein synthesis (WBPS) and whole-body protein degradation (WBPD) were estimated using orally administered 15N-glycine and total excreta collection. Although N balance was similar for all dogs, N flux through the metabolic pool increased linearly (P < 0.05) as protein intake increased. Rates of WBPS, WBPD, or the difference between them were not influenced by age (P > 0.10). A quadratic increase (P < 0.05) in WBPS and WBPD was observed in response to dietary protein. Serum insulin-like growth factor-I (IGF-I), IGF-I-binding protein 3, and total IGF-I-binding proteins were higher (P < 0.05) in geriatric dogs than in young-adult dogs regardless of protein intake. These results indicate that dietary protein in excess of 16% may not be required to maintain N balance in young-adult and aging dogs despite the linear increase in N flux through the metabolic pool. Furthermore, age-induced changes in endocrine functionality may differ between dogs and other species.     

Injection of porcine growth hormone releasing hormone gene plasmid in skeletal muscle increases piglets' growth and whole body protein turnover

The aim of the current study was to investigate the effects of a porcine growth hormone releasing hormone (pGHRH) gene plasmid injection in piglets on growth performance and whole body protein turnover. Sixty male Canadian Landrace × Chinese Taihu piglets were assigned to an intramuscular injection of 0 (control), 0.25, 0.5, 1 and 2 mg. All pigs were fed with the same diet (crude protein: 239.8 g/kg, digestible energy: 14.28 MJ/kg) at ad libitum intake. Protein turnover was determined on the 22nd day with a three-pool model by using a single-dosage, end-product analysis method with ¹⁵ N-glycine as a tracer. Injection of the pGHRH gene plasmid increased the piglets' growth rate, altered feed intake and decreased feed conversion ratio. It increased plasma growth hormone releasing hormone (GHRH), growth hormone (GH), insulin-like growth factor-I (IGF-I) and somatostatin but reduced serum urea and triglyceride. It reduced the urinary nitrogen excretion and led to higher nitrogen retention as well as the efficiencies of nitrogen retention and digestible N utilization. It increased the rates of protein synthesis, protein breakdown and net protein gain. Excretion of endogenous urinary nitrogen was reduced and nitrogen reutilization rate was improved. Conclusions: Injection of the pGHRH gene plasmid in skeletal muscle stimulated GHRH, GH and IGF-I excretion in piglets. Protein deposition was increased by an increase in protein synthesis and a smaller increase in protein breakdown, which was accompanied by reducing amino acid oxidation and increasing nitrogen reutilization.     

Comparative protein and amino acid digestibilities in growing pigs and sows.

An experiment was conducted to compare apparent total tract protein digestibilities and apparent ileal digestibilities of protein and amino acids in growing pigs and adult pregnant and lactating sows. Twelve growing pigs and 12 sows were used and surgically fitted with simple T-cannulas at the distal ileum. Six experimental diets based on corn, barley, wheat, soybean meal, canola meal, or meat and bone meal were formulated, and each diet was fed to growing pigs, gestating sows, and lactating sows for 7 d. Chromium oxide was included in all diets as an indigestible marker (.25%) for calculating nutrient digestibilities. Fecal material was collected on d 5 of each feeding period by grab sampling, and ileal samples were collected for 12 h/d during the last 2 d of each feeding period. Apparent fecal protein digestibilities for all feed ingredients were higher (P < .05) in gestating and lactating sows compared to growing pigs, but no differences between the two groups of sows were observed (P > .05). At the distal ileum, no differences (P > .05) in protein digestibilities were detected between sows and growing pigs regardless of feed ingredient. For all feed ingredients tested, lactating sows had apparent ileal digestibilities of most amino acids that were two to six percentage units higher than those obtained in growing pigs, but not all of the differences were significant. Gestating sows had digestibilities of most amino acids that were intermediate between those of growing pigs and lactating sows. The combined results from the six feed ingredients showed that lactating sows had higher (P < .05) digestibilities of all indispensable amino acids except arginine, and gestating sows had higher (P < .05) digestibilities of five of the indispensable amino acids than did growing pigs. The results of this experiment indicate that apparent fecal protein and apparent ileal amino acid digestibilities obtained in growing pigs are not always representative of digestibilities in either gestating or lactating sows.     

Some effects of protein deficiency in young growing pigs. I. The serum protein system

No significant differences between the serum protein concentrations of the totally starved pigs and control animals given a milk protein supplemented diet were found. Serum lipid levels rose in the totally starved group. During the first 42 days of the experimental period sharp falls in serum protein concentrations were noted in the protein deprived pigs. The losses were greatest in the albumin and two β-globulin fractions, γ-globulin levels rose but at a much slower rate than in the control group. In the pigs which were refed a protein containing diet during the second 42 day period, the concentrations of all the serum protein fractions except for γ-globulin had reached control levels by the end of the investigation. The pigs which continued with the protein free diet showed further losses of albumin, a reduction in some α-globulin fractions and a cessation of net γ-globulin synthesis. The trends observed by measurements of protein bound carbohydrate were similar to those obtained from polypeptide determinations indicating quantitative rather than qualitative changes in the serum proteins. The reduction in the serum lipid concentrations of the pigs undergoing protein starvation was largely accounted for by losses of α- and β-lipoproteins. The protein deprived pigs maintained their initial body weight, while a continuous fall in weight was found in the totally starved group and a continuous increase in the control pigs.     

Interaction of dietary protein content and exogenous porcine growth hormone administration on protein and lipid accretion rates in growing pigs

Sixty-six intact male pigs were used to investigate the relationships between exogenous porcine growth (pGH) administration (0, excipient-treated, and .09 mg recombinant pGH.kg-1.d-1) and dietary protein content (8.3, 11.4, 14.5, 17.6, 20.7 and 23.8%) on protein and lipid accretion rates over the live weight range of 30 to 60 kg. Feed intakes were restricted (1.84 kg.pig-1.d-1) and pGH was administered daily by i.m. injection. Rate of protein deposition increased with increasing dietary protein up to 17.6 and 20.7%, respectively, for control and pGH-treated pigs; both growth and protein deposition were enhanced by pGH on the four higher protein diets but remained unaffected by pGH administration to pigs given the two lowest protein diets. Plasma IGF-I concentration was elevated by pGH administration in pigs given the four higher protein diets but unaffected by pGH with the two lowest protein diets. Rate of fat deposition was depressed on all dietary protein treatments by pGH administration; carcass fat content of control and pGH-treated pigs declined with each increase in dietary protein up to 17.6 and 23.8%, respectively. The results demonstrate that pGH acts independently on protein and lipid metabolism.     

Whole body protein turnover of growing rats in response to different dietary proteins--soy protein or casein.

Whole body protein turnover was studied in growing rats fed restrictively on isoenergetic (GE 17.6 MJ/kg DM) and isonitrogenous (104 g CP/kg DM) diets based on soy protein isolate or casein supplemented with D,L-methionine. During each of the three separate experiments six male Fischer rats per group were housed individually in metabolic cages at 24 degrees C. Prefeeding of both dietary groups up to similar body weights at the start of the main experimental periods (105-134 g) lasted up to 16 d for casein-fed rats and up to 30 d for the soy protein-fed rats. Following the energy and nitrogen balance periods whole-body protein synthesis was estimated by the end-product method using a single tracer dose of a mixture of 15N-labelled amino acids. Fractional protein accretion rate [% of the protein pool accreted per day] was significantly lower in soy protein-rats than in casein-fed rats in all three experiments whereas fractional synthesis rate was not significantly lower. Therefore, protein breakdown subsequently calculated as the difference between synthesis and accretion showed a tendency towards higher values in this group. In soy protein-fed rats also a tendency towards higher excretion of 3-methylhistidine as a marker of myofibrillar protein breakdown was observed. It is concluded that increase in lean tissue growth resulting from improved protein quality is brought about by changes of both rates, by small increase of protein synthesis and by reduced rate of body protein breakdown.     

Serum growth hormone release during a 60-hour period in growing pigs

Growth hormone (GH) profiles were measured during a 60-hour period in four release was not affected by feeding when measured at 2, 4 and 8 hr before and after castrated male and five female, 20-week-old Yorkshire pigs. During this period, GH feeding time. A photoperiod of 12 hr light and 12 hr darkness produced a decrease (P<.05) in baseline mean GH levels from 4.0 to 3.5 ng/ml during periods of darkness. This effect was observed in both genders. Females and castrated males exhibited (P>.05) similar baseline GH levels and identical numbers of GH peaks during feeding and photoperiod studies. However, during these periods, the amplitude of the GH peaks and areas under the GH curves were greater (P<.05) in females. These results indicate that: 1) feeding did not influence GH secretion; 2) darkness produced a decrease in the baseline GH levels in both sexes; and 3) females secreted more GH than castrated males of the same age.     

Growth performance and whole-body composition of pigs experimentally infected with Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae (Mh) is the primary infectious pathogen responsible for enzootic pneumonia in pigs. Although Mh is thought to impair growth performance, whole-body composition, and fat and protein accretion in pigs with pneumonia have not been reported and the mechanism through which Mh reduces growth is unknown. The objectives of this study were to evaluate the effects of Mh on growth performance, whole-body composition, and protein and fat accretion in nursery pigs and to determine whether Mh infection increases the expression of interleukin (IL)-1beta, IL-6, and tumor necrosis factor-alpha (TNF-alpha). Sixty-four 2-wk-old Mh-free pigs were used (two trials) in a randomized complete block design. In each trial, two pigs were housed in each of 16 disease-containment chambers. At 4 wk of age, pigs were inoculated intratracheally with 3 mL of Mh broth (P5722-3, 10(7) cfu/mL) or sterile Friis culture medium. Clinical signs of disease and feed intake were monitored daily and body weight was determined weekly for 4 wk. Whole-body composition was determined from pigs killed 0, 14, and 28 d after inoculation, and the comparative slaughter technique was used to estimate protein and fat accretion. At death, gross lung lesions were quantified, and lung tissue was collected to verify the presence or absence of Mh, and to determine cytokine mRNA levels. Control pigs displayed no overt signs of infection and were Mh-negative and free of pulmonary lesions. Pigs inoculated with Mh showed pneumonic coughing (P < 0.005), were Mh-positive, and had pulmonary lesions that affected 4.5% (P < 0.01) and 14.1% (P < 0.001) of total lung surface area at 14 and 28 d, respectively, after inoculation. Ribonuclease protection assays revealed increased IL-1beta (P < 0.04) and TNF-alpha (P < 0.06) mRNA in lung tissue collected from a lesion site compared with tissue collected 10 cm from a lesion site or from control pigs. Interestingly, Mh did not depress weight gain or feed efficiency during any week of the 28-d study (P > 0.10). Moreover, Mh did not affect whole-body fat or protein accretion (P > 0.10). Thus, in spite of inducing disease and expression of inflammatory cytokines, Mh alone did not affect growth performance and whole-body composition of nursery pigs during the 4-wk experiment. The ability of pigs to contend with Mh may have resulted from the absence of other pathogens that generally co-exist with Mh under commercial conditions.     

Assessment of factors regulating serum growth hormone binding protein in pigs.

These studies were conducted to examine the influence of several variables on the growth hormone binding protein (GHBP) activity in serum of pigs. Continuous long-term porcine somatotropin (pST) injections (daily for 6 to 7 wk) increased GHBP activity (P less than .05). However, periodic short-term pST injections (daily, every 2nd d, or every 4th d for 2 wk) did not cause a significant change in GHBP levels (P greater than .40). Although fasting seems to reduce liver GH receptors, no difference was observed between fed animals and animals fasted for 5 d (P greater than .30). Between 0 and 6 mo of age, boar and gilt serum GHBP activity were not significantly different from each other but increased with age in both sexes (P less than .0001). There was no significant correlation between serum GHBP and BW at 6 mo of age in this study (P greater than .30). In pregnant sows, GHBP concentrations were highest at the beginning (d 72) of the third trimester (P less than .05). Growth hormone receptor activity reported by other researchers and GHBP activity in this study seem to vary similarly except during fasting, which may indicate alternate regulation of either the GHBP or the GH receptor.