Effect of weaning at different ages on serum insulin-like growth factor I (IGF-I), IGF binding proteins and serum in vitro mitogenic activity in swine.

We investigated the effects of weaning or fasting of 21- or 35-d-old swine by monitoring serum mitogenic activity, circulating insulin-like growth factor I (IGF-I) and its binding proteins using L6 myoblast bioassays, RIA and ligand blotting techniques. Serum samples were collected from 21- or 35-d-old animals just before and 36 h after weaning or fasting. Sera from 21- and 35-d-old weaned animals were not significantly altered in their ability to promote myoblast proliferation, whereas sera from 21- and 35-d-old fasted animals caused 29 and 21% decreases (P less than .05) compared with preweaning. The mitogenic activity of control serum was inhibited by serum from fasted animals but not by preweaned or weaned sera. Serum IGF-I levels were decreased 65 to 70% (P less than .05) with weaning or fasting at both ages. Unoccupied binding sites on circulating IGF binding proteins in the 155 kDa range decreased 18 to 19% with weaning at both ages and decreased 40% (P less than .05) with fasting at 21 d but only 17% at 35 d. Ligand blotting revealed that the 43 and 39 kDa IGF binding protein bands decreased with weaning and fasting at both ages, whereas the 29-kDa band increased with weaning and fasting. These data indicate that serum IGF-I and specific IGF binding protein bands decrease during weaning or fasting at 21 and 35 d of age. However, serum mitogenic activity did not always follow serum IGF-I levels.     

Serum concentrations of IGF-I, estradiol-17beta, testosterone, and relative amounts of IGF binding proteins (IGFBP) in growing boars, barrows, and gilts

The purpose of this research was to determine whether serum concentrations of steroids, IGF-I, and relative amounts of serum IGF-binding proteins (IGFBP) differ in growing boars (n = 11), barrows (n = 11), and gilts (n = 12) from 70 to 140 d of age. Pigs of similar age and weight were housed in pens of three or four and given ad libitum access to a 17% CP corn-soy diet and water. Pigs were weighed and blood samples were collected every 14 d beginning at 70 d of age. Serum concentrations of IGF-I and steroids were determined by RIA and relative amounts of IGFBP were determined by ligand blot analysis. By 84 d of age and continuing through 140 d of age, mean serum concentrations of IGF-I were greater (P < .05) in boars than in barrows or gilts. Relative amounts of 46-kDa IGFBP3 and 28-kDa IGFBP-4 were similar (P > .05) among pigs at 70 d of age; however, boars and barrows had greater (P < .05) relative amounts of 24-kDa IGFBP-4 and 41-kDa IGFBP-3 than gilts. Relative amounts of IGFBP-2 were greater (P < .01) in barrows than in gilts or boars at 70 d of age. From 84 d of age through 140 d of age, relative amounts of both forms of IGFBP-3 and the 28-kDa IGFBP-4 were greater (P < .05) in boars than in gilts or barrows. Relative amounts of IGFBP2 were greater (P < .05) in barrows than in gilts or boars at 98 d of age, but by 140 d of age relative amounts were greater (P < .05) in boars and barrows than in gilts. Mean serum concentrations of estradiol-17beta were similar (P > .05) between gilts and boars at 70 d of age, but by 98 d of age, and continuing through 140 d of age, mean serum concentrations of estradiol-17beta were greater (P < .05) in boars than in gilts. Mean serum concentrations of testosterone in boars increased (P < .05) with increasing age and were greatest at 128 and 140 d of age. Serum concentrations of testosterone were negatively correlated (P < .01) with relative amounts of serum IGFBP-2 but positively correlated (P < .01) with serum concentrations of IGF-I and estradiol-17beta. Serum concentrations of estradiol-17beta were positively correlated (P < .01) with serum concentrations of IGF-I in boars. Changes in serum concentrations of IGF-I and relative amounts of IGFBP resulting from changes in serum concentrations of estradiol-17beta and testosterone may contribute to growth differences observed among sexes.     

Moderate doses of porcine somatotropin do not increase plasma insulin-like growth factor-I (IGF-I) or IGF binding protein-3.

The growth rate of the young pig is generally much less than its potential and may be constrained by endocrine status as well as by nutrient intake. The aim of this study was to determine whether porcine somatotropin (pST) could increase growth in the nursing pig. Fourteen sows nursing litters of 6 (n = 7) or 12 (n = 7) piglets were utilized to establish a high and low plane of nutrition for sucking pigs. On Day 4 of lactation, the median two male pigs from each litter were randomly allocated to one of two doses of pST (0 or 60 micrograms/kg/d) until weaning on Day 31. Pigs were bled on Days 4, 13, 22, and 31 of lactation and the plasma was analyzed for insulin-like growth factor (IGF)-I, IGF-II, and IGF binding protein-3 (IGFBP-3). Pigs were weaned into conventional accommodation and further weighed on Days 63, 91, and 119. Pigs from litters of 6 grew more quickly and weighed 2.2 kg (P = 0.01) and 3.5 kg (P = 0.04) more than pigs from litters of 12 at 31 and 63 d of age, respectively. There was no effect of pST on preweaning growth of sucking pigs (261 vs. 258 g/d, P = 0.68), although growth rate increased in the final 3 d before weaning at 31 d (241 vs. 294 g/d, P = 0.01). IGFBP-3 was greater (1.09 vs. 0.78 micrograms/ml, P < 0.001), whereas IGF-I tended to be greater (206 vs. 176 ng/ml, P = 0.14), in pigs from the small litters. There was no effect of pST on plasma IGF-I (182 vs. 195 ng/ml, P = 0.454) or IGFBP-3 (0.93 vs. 0.94 microgram/ml, P = 0.85) concentrations. Plasma IGF-I and IGFBP-3 were highly correlated with the growth rate of nursing pigs (R = 0.638 and 0.756, respectively). There were no effects of pST (340 vs. 328 ng/ml, P = 0.48) or litter size (336 vs. 333 ng/ml, P = 0.88) on IGF-II. In conclusion, pST had no little or no effect on growth performance or plasma IGF-I, IGF-II, or IGFBP-3 in sucking pigs on either a high or low plane of nutrition.     

Ontogenic maturation of the somatotropin/insulin-like growth factor axis

The ontogeny of the somatotropin/insulin-like growth factor system was examined in well-fed pigs under basal conditions and during a short-term challenge of porcine ST (pST). The study was conducted with two replicates of eight castrate male pigs from 3.8 kg BW (10 d of age) to 92 kg BW (129 d of age). Pigs were reared individually with ad libitum access to milk replacer through 23 d of age. Thereafter, pigs were fed a corn, soybean meal, and dry skim milk diet formulated to exceed nutrient requirements by approximately 30%. Pigs were randomly assigned to receive daily i.m. injections of either 0 (buffer) or 120 microg/kg BW of pST for a duration of 4 d starting at 10, 19, 33, 43, 63, 83, and 125 d of age. Blood was collected via jugular venipuncture on d 0 and 4 of the challenge. Circulating levels of IGF-I were not dramatically affected by age, but levels of IGF-II were low from 10 to 19 d of age and then increased through later stages of growth. Circulating concentrations of IGF binding protein (BP)-3 increased with age (P < .05), but levels of IGFBP-2, a 30-kDa IGFBP, and IGFBP-4 were unchanged (P > .10). The pST challenge reduced plasma urea nitrogen at all ages, but the magnitude of the response was less in younger pigs compared with the maximum response in pigs greater than 30 kg BW (63 d of age). The IGF-I response to the pST challenge also increased from approximately 30% in young pigs to a threefold increase in older pigs. Regardless of age, concentrations of IGF-II were minimally affected by the pST challenge. Circulating levels of IGFBP-3 increased and IGFBP-2 levels decreased in response to the pST challenge, and the magnitude increased with age. The high nutritional status of pigs in the early phases of growth diminished the postnatal changes in IGF-I and IGFBP-2, but not IGF-II or IGFBP-3. Overall, data demonstrate a developmental regulation of the ST/IGF system, with pST challenges altering circulating concentrations of IGF-I, IGFBP-3, and IGFBP-2 coincident with changes in amino acid metabolism.     

The ontogeny of serum insulin-like growth factor-I concentration in foals: Effects of dam parity,diet, and age at weaning

The effects of dam parity, age at weaning, and preweaning diet were examined in the ontogeny of serum insulin-like growth factor-I (IGF-I) concentrations in foals. Foals born to 13 primiparous and 19 multiparous draft-cross mares were weighed and bled near birth. About one-half of the foals in each group were weaned early (about 13 wk old); the remaining foals were weaned late (about 16 wk of age). Pooled values for serum IGF-I concentrations between birth and 17 wk of age were higher (P < 0.065) for foals born to multiparous (386 ng/ml) than to primiparous mares (237.5 ng/ml). Colts (378 ng/ml) had higher (P < 0.05) serum IGF-I concentrations than fillies (254.5 ng/ml), regardless of dam parity. Colts (173.5 kg) also tended (P = 0.12) to be heavier than fillies (159.2 kg). Weaning, whether at 13 or 16 wk of age, reduced (P < 0.05) growth rates and serum IGF-I concentrations. Serum IGF-I values recovered to preweaning values within 1–3 wk postweaning concurrent to an improved weight gain. Fifteen 1-d-old foals in a second study were fed milk replacer for 7 wk and were compared with five foals that nursed their mares for 8 wk. During the first 2 wk, replacer-fed foals (0.46 kg/d) did not gain as rapidly (P < 0.03) as mare-nursed foals (1.73 kg/d). The associated serum IGF-I values for replacer foals (139.4 ng/ml) were lower (P < 0.0001) than values for mare-nursed foals (317.4 ng/ml). Despite similarity in gains for both groups thereafter, serum IGF-I concentrations of replacer-fed foals were only 36 and 60% of values obtained for mare-nursed foals at 8 (weaning) and 18 wk of age, respectively. The intrinsic differences between mare-nursed and milk-replacer foals in serum IGF-I concentrations persisted to 1 yr of age despite similarities in dietary management and body weight of the foals. At 1 yr of age, the serum IGF-I concentration of mare-nursed foals (1,203 ng/ml) was 48% higher than that of replacer-fed foals (815 ng/ml). These data indicate that dam parity, sex of foal, and preweaning nutrition affect the ontogeny of serum IGF-I concentration in the foal. The chronic, persistent difference in serum IGF-I values created by the early nutritional management of growing animals has implications in the interpretation of longitudinal serum IGF-I studies in all species.     

Effects of restricted feeding, low-energy diet, and implantation of trenbolone acetate plus estradiol on growth, carcass traits, and circulating concentrations of insulin-like growth factor (IGF)-I and IGF-binding protein-3 in finishing barrows

Effects of restricted feeding (80% ad libitum), feeding a low-energy diet containing 84% DE (2.95 Mcal/kg) of the control diet, and implantation of Revalor H (140 mg trenbolone acetate plus 14 mg estradiol-17beta) on growth, carcass traits, and serum concentrations of insulin-like growth factor (IGF)-I and IGFbinding protein-3 (IGFBP-3) were studied in crossbred finishing barrows beginning from 59 +/- 0.9 kg of body weight. Blood samples were taken every 3 wk and the animals were slaughtered at approximately 105 kg body weight. Restricted feeding caused a decrease (P < 0.01) in ADG; feeding the low-energy diet was effective in reducing backfat thickness but decreased gain:feed; the implantation caused a decrease in ADG, feed intake, and backfat thickness and increased gain:feed. Overall pork quality based on pH, drip loss, and the lightness in color of longissimus muscle was not affected by any of the treatments. Serum IGF-I concentration increased following the implantation but did not change (P > 0.05) due to other treatments. Immunoreactive IGFBP-3 concentration was not changed by any of the treatments. Overall ADG was positively correlated with early-stage (d 21) IGF-I and IGFBP-3 concentrations only in unimplanted barrows, whereas backfat thickness was negatively correlated with d-42 IGF-I concentration in all but unimplanted barrows with ad libitum intake. A strong positive correlation (P < 0.01) between IGF-I and IGFBP-3 concentrations was apparent with increasing age of the animals. Results suggest that growth rate and backfat thickness are decreased by a moderate restriction of feed or energy intake with no accompanying changes in circulating IGF-I and IGFBP-3 concentrations and that the beneficial effect of Revalor H implantation on feed efficiency may be mediated, in part, by IGF-I. Moreover, both IGF-I and IGFBP-3 concentrations may be useful as growth indices in pigs.     

Administration of estradiol-17beta increases anterior pituitary IGF-I and relative amounts of serum and anterior pituitary IGF-binding proteins in barrows

Two experiments were conducted to determine whether 1) administration of estradiol-173 (E2) implants to barrows elevates serum concentrations of E2 to levels similar to those of adult boars and subsequently affects the anterior pituitary gland IGF system and 2) administration of E2 to barrows increases serum concentrations of E2, serum and anterior pituitary concentrations of IGF-I, and relative amounts of serum and anterior pituitary IGF-binding proteins (IGFBP), vs boars and unimplanted barrows. In Exp. 1, 20 crossbred barrows (150 +/- 6 d, 103 +/- 8 kg) were administered varying number of E2 implants (0, 2, 3, 4; n = 5/group) on d 1. Blood samples were collected weekly by jugular venipuncture, beginning on d 1. Pigs were killed on d 36 when a blood sample and anterior pituitary were collected. Serum concentrations of E2 were increased (P < 0.05) in pigs with 2,3, and 4 implants vs 0 implants, but no difference (P > 0.05) was detected in serum concentrations of E2 among pigs with 2, 3, and 4 implants. Orthogonal contrasts identified that three or four E2 implants were necessary to increase serum concentrations of E2 to that similar to boars. Serum and anterior pituitary concentrations of IGF-I were increased (P < 0.05) in pigs with 2, 3, and 4 implants vs 0 implants. Relative amounts of anterior pituitary IGFBP-2 and - 5 increased (P < 0.05) in response to administration of E2. In Exp. 2, three treatment groups were randomly allotted by litter; boars (n = 11), E2-implanted barrows (n = 9), and unimplanted barrows (n = 12). A blood sample was taken from all pigs on d 1 and every 14 d thereafter. Implanted pigs received four implants on d 1. Pigs were killed on d 91, when a blood sample and anterior pituitary were collected. Mean serum concentrations of E2 were greater (P < 0.05) in implanted pigs vs boars. Mean serum concentrations of IGF-I (ng/mL) were greater (P < 0.05) in boars (238.7 +/- 6.8) than in implanted barrows (170.2 +/- 8.9) and unimplanted (150.4 +/- 6.7) pigs and tended to be greater (P = 0.08) in implanted vs unimplanted pigs. Mean anterior pituitary concentrations of IGF-I (ng/mg tissue) were greater (P < 0.05) in implanted (773.6 +/- 57.0) pigs than boars (251.9 +/- 51.6) and unimplanted (185.6 +/- 49.4) pigs. Relative amounts of serum IGFBP-2 were greater (P < 0.05) in implanted pigs vs boars. Relative amounts of anterior pituitary IGFBP-2 and -5 were greater (P < 0.05) in boars than in implanted and unimplanted pigs. These data suggest that E2 may influence components of the porcine IGF system in the serum and anterior pituitary. Other gonadal factors present in boars may additionally affect the serum and anterior pituitary IGF system.     

Growth factor messenger RNA levels in muscle and liver of steroid-implanted and nonimplanted steers

Ribonuclease protection assays were used to measure steady-state semimembranosus muscle and/or hepatic levels of IGF-I, IGFBP-3, IGFBP-5, hepatocyte growth factor (HGF), and myostatin messenger RNA (mRNA) in steers implanted from 32 to 38 d with Revalor-S, a combined trenbolone acetate and estradiol implant. Insulin-like growth factor-ImRNA levels were 69% higher (P < 0.01, n = 7) in the livers of implanted steers than in the livers of nonimplanted steers. Similarly, IGF-I mRNA levels were 50% higher (P < 0.05, n = 7) in the semimembranosus muscles of implanted steers than in the same muscles from nonimplanted steers. Hepatic IGFBP-3 mRNA levels were 24% higher (P < 0.07, n = 7) in implanted steers than in nonimplanted steers. Hepatic HGF and IGFBP-5 mRNA levels did not differ between implanted and nonimplanted steers. Similarly, muscle IGFBP-3, IGFBP-5, HGF, and myostatin mRNA levels were not affected by treatment. Previous data from these same steers have shown that circulating IGF-I and IGFBP-3 concentrations were 30 to 40% higher (P < 0.01, n = 7) in implanted steers than in nonimplanted, control steers. Additionally, the number of actively proliferating satellite cells that could be isolated from the semimembranosus muscle was 45% higher (P < 0.01, n = 7) for implanted steers than for nonimplanted steers. Viewed together, these data suggest that increased muscle IGF-I levels stimulate increased satellite cell proliferation, resulting in the increased muscle growth observed in Revalor-S implanted steers.     

The ontogeny of the somatotropic axis in Hereford calves from birth to one year of age and its response to administration of exogenous bovine somatotropin

Administration of exogenous bovine ST (bST) increases growth rate, feed efficiency, and carcass quality in beef cattle. The magnitude of response to bST in beef cattle is variable and related to the age of the animal. Our objective was to determine the response of the somatotropic axis, in particular IGF-I, IGFBP-2, and IGFBP-3, to bST treatment from birth to 1 yr of age. Blood samples were collected before and after a single injection of bST (500 mg) every 50 d from birth to 1 yr of age in male and female Hereford calves. Body weights and serum concentrations of ST, IGF-I, IGFBP-2, and IGFBP-3 were determined. At birth, serum concentrations of ST, IGF-I, and IGFBP-3 increased (P < 0.05) following bST treatment. From 50 to 350 d of age, average concentrations of ST and IGF-I were greater (P < 0.05) in males, whereas IGFBP-2 concentrations were greater (P < 0.05) in females. No gender differences in IGFBP-3 concentrations were observed. Following bST treatment, IGF-I increased (P < 0.05) from 50 to 350 d of age, IGFBP-2 decreased (P < 0.05) from 50 to 200 d of age, and IGFBP-3 increased (P < 0.05) at 250 d of age. At 250 d of age, baseline concentrations of IGFBP-2 decreased (P < 0.05). Due to the positive response of IGFBP-3 and decreased baseline IGFBP-2 at 250 d of age, we conclude that this is an age at which the somatotropic axis is most responsive to exogenous bST, and it therefore may be an appropriate age to begin bST treatment in beef calves to realize the positive influence of bST on BW gain, feed efficiency, and carcass composition.     

Changes in circulating insulin-like growth factor-I, insulin-like growth factor binding proteins, and leptin in weaned pigs infected with Salmonella enterica serovar Typhimurium

One of the hallmarks of the pathophysiology of enteric disease in young pigs is reduced growth performance. This reduction in growth is associated with changes in the endocrine somatotropic growth axis. Our laboratory previously demonstrated that circulating insulin-like growth factor-I (IGF-I) was reduced in pigs infected with Salmonella enterica serovar Typhimurium (S. typhimurium) while circulating growth hormone remained unchanged. The objective of the current study was to determine if infection with S. typhimurium also was associated with changes in circulating IGF binding proteins (IGFBP). In addition, pigs experiencing active enteric disease have reduced feed intake. Because this inappetence may be related to systemic appetite reduction signals, we also evaluated circulating leptin in pigs undergoing active S. typhimurium-induced enteric disease. Crossbred pigs were penned in environmentally controlled rooms with free access to feed and water. Following an acclimation period, pigs were gavaged with 10(10) cfu of S. typhimurium (SAL; n=6) or were given a similar volume of sterile growth media (CON; n=6). Rectal temperatures and feed intakes were measured daily through 168 h to track the time course of the response to S. typhimurium infection. Samples of serum were obtained by jugular venipuncture at 0, 24, 48, 96 and 168 h after infection. Sera were frozen until evaluation for IGF-I by immunoradiometric assay (IRMA). In addition, sera were subjected to western ligand blotting utilizing 125I-IGF-I and 125I-IGF-II. Images were evaluated for total IGFBP and IGFBP-3 by densitometric analyses. Rectal temperature was increased in SAL pigs 24h post-infection (P<0.001) but not at other times. Feed intake was reduced in SAL pigs during the intervals 24-72 h (P<0.001) and 96-144 h (P<0.05) after infection. Serum IGF-I, expressed as a percentage of the 0 h concentration, was reduced in SAL pigs versus CON pigs at 48 h (28.1+/-18.7% versus 102.2+/-17.1%; P<0.01) and 96 h (20.0+/-18.7% versus 128.4+/-17.0%; P<0.0001) post-infection. Both total IGFBP and IGFBP-3, as estimated by ligand blotting, also were reduced in infected pigs at 48 h postchallenge (P<0.05). IGFBPs were similar between the two treatments at other sampling times. Concentrations of IGFBP-3 also were estimated utilizing an IRMA for human IGFBP-3. Serum IGFBP-3 was reduced in S. typhimurium-infected pigs at 24 h (P<0.01), 48 h (P<0.001), 96 h (P<0.001), and 168 h (P<0.05). Serum leptin levels were similar between SAL and CON pigs. The data suggest that swine enteric disease is associated with reduced circulating IGF-I and reductions in total IGFBP and IGFBP-3. However, serum leptin was not affected by enteric disease challenge.     

The influence of level of feeding on growth and serum insulin-like growth factor I and insulin-like growth factor-binding proteins in growing beef cattle supplemented with somatotropin

The objective of this study was to determine the effects of level of feeding on growth, feed efficiency (gain:feed; G:F), body composition (BC), and serum concentrations of somatotropin (ST), IGF-I, and IGF-binding proteins (BP) in growing beef cattle supplemented with bovine (b) ST. In each of two consecutive years, 40 growing beef cattle were blocked by weight (average BW: yr 1 = 316 kg, yr 2 = 305 kg) and used in a 2 x 2 factorial arrangement with main effects of bST (0 or 33 microg x kg BW(-1) x d(-1)) and level of feed intake (ad libitum [AL] or 0.75 AL). Relative to uninjected cattle, treatment with bST increased ADG 9.6% (1.14 vs 1.25 kg/d; P < 0.05) and increased G:F 8.1% (12.3 vs 13.3 gain [g]:feed [kg]; P < 0.05), whereas ADG in AL animals was 39% greater than that in 0.75 AL animals (1.39 vs 1.00 kg/d; P < 0.05). There was a tendency (P = 0.10) for a bST x level of feeding interaction, such that the increase in ADG with bST was greater in AL cattle than in 0.75 AL cattle (10.6 vs 7.8%; P = 0.10). Serum concentrations of ST were greater in 0.75 AL cattle than in AL cattle (13.0 vs 8.6 ng/mL; P < 0.05) and in bST-treated cattle than in uninjected cattle (16.3 vs 5.2 ng/mL; P < 0.05). Due to a bST x level of feeding interaction (P < 0.01), the magnitude of the increase in serum ST to exogenous bST was greater (P < 0.01) in 0.75 AL cattle than in AL cattle. Relative to uninjected cattle, treatment with bST increased (P < 0.05) serum concentrations of IGF-I and IGFBP-3 and reduced (P < 0.05) concentrations of IGFBP-2. Similarly, AL cattle had greater (P < 0.05) serum concentrations of IGF-I and IGFBP-3 and reduced (P < 0.05) IGFBP-2 compared with 0.75 AL cattle. In summary, treatment with bST increased growth rate and G:F and stimulated serum IGF-I and IGFBP-3 while reducing IGFBP-2. Feeding at 0.75 ad libitum intake reduced the magnitude of response for each of these variables. Thus, limit-feeding may reduce the effect of exogenous bST on growth rate by blunting bST-induced increases in IGF-I and IGFBP-3 and bST-induced decreases in IGFBP-2.     

Preweaning housing effects on behavior and physiological measures in pigs during the suckling and fattening periods

The effect of the preweaning housing system on the stress response of pigs before weaning and during fattening was studied in 33 litters of domestic pigs. Three preweaning housing systems were compared: barren crate (standard farrowing crate without straw), enriched crate (20% larger crate, with straw), and as a control, a farrowing pen (pen, 60% larger than the barren crate, with straw). At 25 d of age, pigs were tested with an isolation test and 1 d later with a human approach test (HumanT). Pigs were weaned at 28 d of age. At 3 and 6 mo of age, pigs were tested with an isolation-human approach test. The latency and frequency of squeal calls and locomotor activity were analyzed for all 3 tests, whereas physical contact with the human was also analyzed for the HumanT and isolation-human approach test. At 6 mo of age, the pigs were transported to a slaughterhouse. One day before transport, immediately after transport, and 1 h after transport, saliva samples were taken for cortisol analysis. The pH of the LM was also measured 45 min after slaughter. Preweaning housing system affected (P < 0.05) the probability of squeal vocalizations, the latency of locomotion, and the duration of locomotion during the HumanT. Pigs from the enriched pens vocalized less, had a longer latency to move, and performed less overall locomotion than pigs from the barren crates. Preweaning housing system did not affect behavior of fattening pigs. Cortisol concentrations before and after transport were not affected by preweaning housing system. An interaction of cortisol concentrations and housing systems was observed between the control sample and the sample taken immediately after transport in pigs from the barren crates (P < 0.05) compared with pigs from the enriched housing systems. Meat from pigs reared in the barren crate tended to have lower pH (P < 0.10) and that of pigs reared in enriched crates had lower pH (P < 0.05) than meat of pigs reared in enriched pens. No differences were observed between pigs from barren or enriched crates. Our results suggest that enrichment of the preweaning environment through enlarged space, provision of straw, and free movement for the sow had a positive effect on the coping behavior of pigs before weaning and prevented an increase in salivary cortisol concentration immediately after transport and a decrease in meat pH 45 min postmortem at the age of 6 mo. Minimal enrichment of the commercial farrowing crate did not affect behavior and physiological measures in pigs before and after weaning.     

Characterization of creep feed consumption and its subsequent effects on immune response, scouring index and performance of weanling pigs

Four trials were conducted to characterize the consumption of creep feed by nursing pigs and the effects of creep feeding (from 10 d to weaning at 28 d) on the immune response, scouring index and subsequent performance of weanling pigs. Pigs were fed a ground 20% CP corn-soybean meal-whey diet with 1.0% chromic oxide (control, 9 litters), this diet with 2.7% ovalbumin added as a dietary antigen (ovalbumin, 14 litters), or no creep feed (unexposed, 11 litters). At weaning, pigs within a litter were fed a 20% CP corn-soybean meal diet either with or without 2.7% ovalbumin. Creep-fed litters began eating at 11 d of age and disappearance of creep feed increased linearly until weaning (P less than .01). However, based on the chronic oxide coloring of the feces, total creep feed consumption was quite variable from pig to pig (13 to 194 g) and from litter to litter (107 to 1,550 g). Preweaning daily gain was similar between creep-fed and noncreep-fed litters; larger litters generally had lower daily gains (P less than .09) and less feed disappearance per pig (P less than .02). Weekly blood sampling showed that pigs fed the antigen diet had a higher (P less than .001) antibody titer to ovalbumin at 14, 21 and 28 d of age than did pigs fed the control diet or pigs unexposed to creep feed. At 56 and 63 d of age, all pigs given an ovalbumin injection at 49 d (1 ml containing 3 mg of ovalbumin) had responded (P less than .001) to injection, with the lowest titers for pigs fed the control creep diet and the highest titers for pigs fed the ovalbumin creep diet; titers were intermediate for pigs not fed creep. Regardless of preweaning or postweaning treatment, most pigs began scouring 4 to 5 d postweaning; scouring peaked at d 10 and returned to normal after d 15. Although the magnitude of difference was small, creep-fed pigs tended to scour more than pigs not fed creep (P less than .01). Postweaning performance was not influenced by preweaning treatments.     

Characterization of microbial populations and volatile fatty acid concentrations in the jejunum,ileum, and cecum of pigs weaned at 17 vs 24 days of age

In a series of five 17-d replicate trials, a total of 54 cannulated and 12 noncannulated pigs were used to determine the effects of weaning age (17 d or 24 d) on pH, dry matter percentage, aerobic and anaerobic microflora, lactate, and volatile fatty acid (VFA) concentrations in the jejunum, ileum, and cecum of weanling pigs. At -14 d of age, cannulated pigs were surgically fitted with T-cannulas in the jejunum (n = 20), ileum (n = 18), or cecum (n = 16). Upon weaning, cannulated pigs were individually caged in an environmentally controlled room with ad libitum access to a phase starter diet and water. Noncannulated pigs were killed at weaning and samples were collected from the jejunum, ileum, and cecum. Digesta and fecal swabs from cannulated pigs were collected twice weekly. The pH of cecal contents was lower (P < 0.05) and dry matter percentage was greater (P < 0.05) than those ofjejunal or ileal contents. Pigs weaned at 24 d of age had increased (P < 0.05) E. coli populations 3 d postweaning compared to preweaning populations, regardless of site of collection, whereas this increase was not observed in pigs weaned at 17 d of age. Unweaned pigs maintained higher (P < 0.05) lactobacilli populations compared to weaned pigs; however, populations declined (P < 0.05) in both groups by 3 d postweaning, with pigs weaned at 24 d of age having lactobacilli populations greater than pigs weaned at 17 d of age. Fecal populations of E. coli and lactobacilli declined (P < 0.05), whereas fecal bifidobacteria populations increased (P < 0.05) postweaning, regardless of weaning age. Concentrations of total fecal anaerobes declined (P < 0.05) in pigs weaned at 17 d of age but were maintained in pigs weaned at 24 d of age. Volatile fatty acid concentrations were greater (P < 0.05) in the cecum than in the jejunum or ileum, and acetic acid concentrations decreased (P < 0.05) postweaning regardless of weaning age. A tendency for L+ lactate concentrations to be greater (P < 0.07) in the ileum and jejunum vs the cecum was observed. Results indicate that weaning and weaning age have significant effects on microbial populations and VFA concentrations.     

Time course of changes in growth factor mRNA levels in muscle of steroid-implanted and nonimplanted steers

We used a muscle biopsy technique in conjunction with real-time PCR analysis to examine the time course of changes in muscle IGF-I, IGFBP-3, myostatin, and hepatocyte growth factor (HGF) mRNA in the longissimus muscles of Revalor-S-implanted and nonimplanted steers on d 0, 7, 12, and 26 after implantation (nine steers/treatment group). Administration of a Revalor-S implant increased (P < 0.01) ADG and improved (P < 0.05) feed efficiency, 36 and 34%, respectively, compared with steers that received no implant during the 26-d trial. Daily dry matter intake did not differ (P > 0.15) between nonimplanted and implanted steers. Steers receiving the Revalor-S implant had increased (P < 0.001) circulating IGF-I concentrations compared with nonimplanted steers. The longissimus muscles of steers receiving the Revalor-S implant contained increased (P < 0.001) IGF-I mRNA levels compared with longissimus muscles of nonimplanted steers over the 26-d duration of the study. Longissimus muscle IGF-I mRNA levels in implanted steers were increased (P < 0.003) relative to d-0 concentrations on d 7 and 12 (101% and 128%, respectively), and byd 26, longissimus muscle mRNA levels were more than three times (P < 0.0001) those in the longissimus muscles of the same steers on d 0. There was no treatment effect on the level of IGFBP-3, myostatin, or HGF mRNA in the longissimus muscle at any time point; however, levels of IGFBP-3, myostatin, and HGF mRNA increased with time on feed. Based on current and previous studies, we hypothesize that the increased IGF-I level in muscle of implanted steers by d 7 of implantation stimulates satellite cell proliferation and maintains a high number of proliferating satellite cells at a point in the growth curve where satellite cell numbers and activity are normally dropping off. This would prolong the period of rapid muscle growth, resulting in the observed increased rate and efficiency of muscle deposition in implanted steers.     

Insulin-like growth factor binding protein-3: its biological effect on bovine granulosa cells

This study was aimed at testing the hypothesis that insulin-like growth factor binding protein (IGFBP)-3 can modulate hormone-dependent differentiation of granulosa cells in vitro. Granulosa cells from small (1 to 5 mm) follicles were collected from cattle, cultured for 2 d in medium containing 10% fetal calf serum, washed, and then treated for an additional 2 d in serum-free medium with follicle-stimulating hormone (FSH) (50 ng/ml), recombinant human IGF-I (0, 1.3, 4.0, or 13.3 nM), or recombinant human IGFBP-3 (0 to 4.26 nM). In one series of experiments, IGFBP-3 (0.53 and 2.13 nM) inhibited (51% to 92% decreases; P < 0.05) progesterone and estradiol production induced by 1.3 nM of IGF-I, but did not influence (P > 0.10) granulosa cell numbers or steroidogenesis in the absence of IGF-I. Only 4.26 nM of IGFBP-3 inhibited (by 35%) the increase in granulosa cell numbers induced by 1.3 nM of IGF-I. In another series of experiments, 13.3 nM of IGF-I, but not 4.0 nM of IGF-I, was able to completely overcome the inhibitory effect of 4.26 nM of IGFBP-3 on estradiol production. The increase in cell numbers induced by 4.0 and 13.3 nM of IGF-I was attenuated (P < 0.001) by 4.26 nM of IGFBP-3. In a third series of experiments, IGFBP-3 inhibited 125I-IGF-I binding to granulosa cells. These results indicate that IGFBP-3 has a pronounced inhibitory effect on IGF-I action in cultured bovine granulosa cells, and that this inhibitory effect is likely attributable to IGFBP-3 binding/sequestering IGF-I. Thus, IGFBP-3 may play a significant role in regulating granulosa cell proliferation and steroidogenesis during follicular development in cattle.     

Effect of sodium butyrate on growth performance and response to lipopolysaccharide in weanling pigs

Two experiments were conducted to determine the effects of dietary sodium butyrate on growth performance and response to Escherichia coli lipopolysaccharide (LPS) in weanling pigs. In a 28-d experiment, 180 pigs (initial BW 6.3 kg) were fed 0, 0.05, 0.1, 0.2, or 0.4% sodium butyrate, or 110 mg/kg of dietary tylosin. There was no effect of dietary sodium butyrate or tylosin on overall G:F, but there was a linear trend (P < 0.07) toward decreased ADFI and ADG as levels of sodium butyrate increased. In a second 28-d experiment, 108 pigs (initial BW 6.3 kg) were assigned to 1 of 3 dietary treatments: 1) no antibiotics, 2) 0.2% sodium butyrate, or 3) 55 mg/kg of carbadox. On d 14, a subset of pigs from the no-antibiotic and butyrate treatment groups was challenged with E. coli LPS or injected with sterile saline in a 2 x 2 factorial arrangement (+/-LPS challenge; +/-dietary butyrate; n = 6 pigs/treatment group). Four hours after LPS challenge, blood samples were obtained, and samples of LM, liver, and ileum were collected for gene expression analysis. Serum samples were analyzed for IL-6, tumor necrosis factor alpha (TNFalpha), alpha(1)-acid glycoprotein, cortisol, IGF-I, insulin, and metabolites. The relative abundance of tissue cytokine and IGF-I mRNA was measured by real-time PCR. Feeding diets containing sodium butyrate or carbadox did not alter ADG or ADFI compared with pigs fed the control diet. From d 0 to 14, pigs fed diets containing 0.2% sodium butyrate had decreased (P < 0.05) ADG and tended (P < 0.06) to have decreased G:F compared with animals fed diets containing carbadox. Challenge with LPS increased (P < 0.05) serum cytokines and cortisol and decreased (P < 0.05) serum glucose and triglycerides. Injection with LPS increased (P < 0.05) the relative abundance of hepatic IL-6 and TNFalpha mRNA, increased (P < 0.05) LM TNFalpha mRNA content, and decreased (P < 0.05) IGF-I mRNA in LM. For serum cortisol, there was an interaction (P < 0.05) between dietary butyrate and LPS. The increase in serum cortisol attributable to LPS was greater (P < 0.05) in pigs fed butyrate than in pigs fed the control diet. There tended (P < 0.10) to be an interaction between LPS and diet and for butyrate to increase the relative abundance of IL-6 mRNA in LM. Carbadox did not alter cytokine or IGF-I mRNA or serum metabolites, but did decrease (P < 0.05) serum TNFalpha. These data indicate that dietary sodium butyrate does not enhance growth performance, but may regulate the response to inflammatory stimuli in weanling pigs.     

Alterations of serum insulin-like growth factor-I (IGF-I) and IGF-binding proteins (IGFBPs) in swine infected with the protozoan parasite Sarcocystis miescheriana.

The effects of a Sarcocystis miescheriana infection on insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding proteins (IGFBPs) were investigated to determine possible mechanisms of growth retardation in growing pigs. Sixteen pigs averaging 14 kg body weight were divided into 4 groups of 4 pigs each and infected either with 0.5, 1.0, or 3.0 × 10⁶ sporocysts of S. miescheriana. Four pigs were retained as non-infected controls; however, they became serologically positive during the course of the infection. Effects also were investigated in 2 groups of 3 pregnant sows. One group was infected with 0.5 × 10⁶ sporocysts and the other group was retained as uninfected controls. Body weights of infected growing pigs were depressed as compared to controls following the acute phase 15 d after infection (dai). Serum concentrations of IGF-I dropped significantly (p < 0.05) during the acute phase of infection in all infected groups of growing pigs. Conversely, the amounts of unsaturated serum IGFBPs were elevated significantly (p < 0.05) during the acute phase of infection. Specifically, serum concentrations of IGFBP-1, IGFBP-2, and IGFBP-4 were elevated at this time, as determined by ligand blot analysis. There was no association between growth factor alterations and tissue damage as measured by serum creatinine kinase and aspartate aminotransferase levels. The extent of effects in growing pigs was related to the amount of the original parasite inoculum.

During the acute phase of infection 2 of 3 pregnant sows aborted. The third sow went to term, but piglets were stillborn or died within 24 hr. Compared to uninfected controls, serum concentrations of IGF-I in infected pregnant sows were depressed during and after the acute phase of the infection. Levels of unsaturated serum IGFBPs in pregnant sows were not affected.

These data suggest that decreased IGF-I levels and/or elevated levels of specific forms of IGFBPs may be a mechanism by which growth is affected in feeder pigs infected with S. miescheriana.     

Cysteamine improves growth performance and gastric ghrelin expression in preweaning piglets

The aim of the present study was to investigate the effect of cysteamine on growth performance of preweaning piglets and gastric expression of ghrelin mRNA in vivo and in vitro. Twelve litters of newborn piglets were allocated randomly to control and treatment groups. From 15 d of age, piglets in the control group were fed basal creep diet, whereas the treatment group received basal diet supplemented with 120 mg cysteamine per kg of diet until weaning on 35 d of age. Body weight gain, creep feed consumption, and diarrhea rates were recorded, and gastric mucosal tissues were collected for quantifying mRNA expression. To evaluate the direct effect of cysteamine on gastric ghrelin expression, primary cultures of gastric mucosal cells isolated from 35-d-old piglets were exposed to cysteamine for 20 h at 0, 1, 10, and 100 μg/mL, respectively. Dietary cysteamine increased (P < 0.05) average daily creep feed consumption and BW gain in preweaning pigs, which was accompanied by reduction in diarrhea rates. At 35 d of age, piglets treated with cysteamine showed increased (P < 0.05) ghrelin and gastrin and decreased (P < 0.05) somatostatin mRNA expression in gastric mucosa. Moreover, dietary cysteamine treatment increased serum concentration of gastrin (P < 0.05). In vitro, cysteamine significantly increased ghrelin mRNA expression in gastric mucosal cells at the concentration of 10 μg/mL. In conclusion, dietary cysteamine is effective in improving the growth performance and health condition of preweaning piglets, which is associated with its stimulatory effects on gastric ghrelin mRNA expression both in vivo and in vitro.