| The muscle fiber hyperplasia and type transition are regulated by maternal nutrition during gestation and lactation, which are closely related to the subsequent performance and meat quality of pigs at market. In addition, ?-hydroxy-?-methylbutyrate (HMB) is a metabolite of leucine, which is widely used to repair and resist the atrophy of the muscle. It has been established that the birth and weaning weights of pigs were increased by feeding HMB to sows during late gestation. However, whether HMB could regulate muscle fiber development of the offspring is not yet fully understood. Therefore, we firstly investigated the effects of dietary HMB supplementation to sows during gestation or lactation on the muscle fiber development of the offspring. Subsequently, we explored the effects of dietary HMB supplementation to sows or piglets on growth performance, meat quality and muscle fiber development of pigs and the possible mechanism.The main contents and results are presented as follows.Experiment 1. Effects of dietary HMB supplementation on reproductive performance of pregnant sows and the growth, pork quality and muscle fiber development of the offspring.The aim of the study was to determine the effects of dietary HMB supplementation to sows during day 35 of gestation to parturition on reproductive performance, and muscle fiber development, growth performance, and pork quality of the offspring. On the day 35 of gestation, a total of 20 sows (Landrace × Yorkshire, at third parity) with similar body weight (BW,205.6±3.7 kg) were blocked and randomly assigned to 1 of 2 dietary treatments. Dietary treatments included a basal diet group or the same diet supplemented with 4 g/day ?-hydroxy-?-methylbutyrate calcium (HMB-Ca) from day 35 of gestation to parturition. After parturition, a total of 20 male piglets from control (CON) and HMB groups were slaughtered and collected the longissimus dorsi (LD) and semitendinosus (ST). The piglets were weaned on the day 28 after birth. After weaning, a total of 48 mixed sex pigs (24(?)+24?) were selected according to maternal treatments and moved to 12 pens (each pen comprising 2 barrows and 2 gilts)where the pigs remained to the day 180 of age. In the whole experimental period, all the pigs had free access to water and were fed the same grower, early and late finisher diets for weaning (days 28 to 66), growing (days 67 to 108) and finishing period I (days 109 to 150) and ? (days 151 to 180). At 180 days of age, a total of 12 fattening pigs (6 barrows and 6 gilts) approaching to the average weight were selected according to maternal treatment and slaughtered after overnight fasting to collect LD samples and determine the related carcass and meat quality of the offspring. The results are presented as follows:(1) No differences were observed in the numbers of total piglets, piglets born alive and weaning pigs between treatments (P> 0.10). The evident effect was observed on the litter birth weight (P< 0.05) by dietary HMB treatment to sows during gestation. In addition, piglets in the HMB group had an decreased tendency on the relative rate of low birth BW (BW< 1.0 kg) piglets (11.69 vs 5.26%, P=0.05) than those in the CON group, meanwhile, maternal HMB consumption during gestation increased the relative weights of LD and ST of the offspring at birth (P< 0.05). However, sows in the HMB group exhibited a lower feed intake than their CON counterparts throughout lactation (5.9 vs 5.3kg, P< 0.01).(2) The ADFI of pigs during postnatal days 28 to 180 was not different (P> 0.10) between dietary treatment groups. However, pigs from sows fed HMB diet during gestation showed superior ADG and lower Feed/Gain (F/G) (P< 0.05) than did pigs from sows fed the CON diet during postnatal days 109 to 150.(3) Maternal HMB treatment during gestation led to decreases in the contents of cooking loss (P< 0.05) and drip loss (P< 0.05) in the LD of pigs. In addition, a higher a* value in the LD was discovered (P< 0.05) in pigs from sows fed HMB diet than that in the pigs from sows fed the CON diet.(4) Sows fed HMB diet during gestation had higher plasma glucose content at days 1 and 28 of lactation than sows fed the CON diet (P< 0.05). In addition, a higher content of fat in the milk was observed in pigs from sows during days 14 and 28 of lactation in the HMB group than those in the CON group (P< 0.05).(5) Piglets from sows fed the HMB diet showed increased protein content and creatine kinase (CK) activity in the LD and ST compared with those from sows fed the CON diet (P<0.01).(6) Pigs from sows fed HMB diet had higher mRNA expressions of myogenic differentiation factor (MyoD), muscle regulatory factor 4 (MRF-4), insulin-like growth factor-? (JGF-?) and insulin-like growth factor-? (IGF-?) in the LD and ST muscle (P< 0.05) compared with those from the CON sows, and the lower mean cross-sectional area and fast-mysosin heavy chain (Fast-MyHC) protein expression in the LD were observed in pigs from sows fed HMB diet than those from sows fed CON diet (P< 0.05). In addition, maternal HMB supplementation increased total number of muscle fibers of the offspring (P< 0.05).Collectively, this results indicated that supplementing sow diets with HMB during day 35 of gestation to parturition significantly increased litter birth weight and reduced the relative rate of lower birth weight piglets. In addition, maternal HMB treatment during gestation could improve pork quality by increasing muscle fiber number in the muscle of the offspring, which was related to higher mRNA expression of myogenic factors including Pax7 and MyoD in the muscle.Experiment 2. Effects of dietary HMB supplementation on reproductive performance of lactating sows and growth performance, pork quality and muscle fiber development of the offspring.The study was to investigate the effects of dietary HMB supplementation on reproductive performance and muscle fiber development, growth performance, and pork quality of the offspring. At day 110 of gestation, a total of 20 Landrace × Yorkshire (the third parity) pregnant sows with similar body weight (252.9±3.6 kg) were moved to farrowing room and randomly assigned to CON (n=10) or HMB groups (n=10). Dietary treatments included a basal diet group or the same diet supplemented with 2 g/kg HMB-Ca during days 1 to 28 of lactation. The piglets were weaned on the day 28 after birth. After weaning, a total of 12 male weaning piglets from CON and HMB groups were slaughtered and collected samples of LD and ST. In addition, a total of 48 mixed sex pigs (24(?)+24(?)) according to maternal treatments were selected and moved to 12 pens (each pen comprising 2 barrows and 2 gilts) where the pigs remained to the day 180 of age. In the whole experimental period, all the pigs had free access to water and the grower, early and late finisher diets formulated for weaning (days 28 to 66), growing (days 67 to 108) and finishing period ? (days 109 to 150) and ? (days 151 to 180). At 180 days of age, a total of f 12 fattening pigs (6 barrows and 6 gilts) which were close to the average live BW according to maternal treatment were selected and slaughtered after overnight fasting to collect LD samples and determine the related carcass and meat quality of the offspring. The main results are presented as follows:(1) No significant effects were observed on growth performance and the relative weights of LD and ST of piglets between dietary groups (P>0.10). However, piglets in the HMB group had an increased tendency (P=0.089) in the relative weights of the small intestine than those in the CON group. In addition, dietary HMB supplementation significantly decreased the ADFI of sows during lactation (-10%, P<0.01).(2) The ADFI of pigs during postnatal days 28 to 180 was not different between dietary treatments (P>0.10).However, pigs from sows fed HMB diet during lactation exhibited higher final weight (+6.0%, P<0.05),ADG (+6.4%, P<0.05),and had a decreased tendency in F/G (-3.5%, P=0.069) than did pigs from sows fed the CON diet during postnatal days 28 to 180.(3) Maternal HMB treatment during lactation led to increases in the carcass weight (+7.7%, P< 0.01) of the fattening pigs, and an increased tendency in the lean meat percentage (+5.1%, P=0.067) was observed in the pigs from sows fed HMB diet than that in pigs from sows fed the CON diet during lactation. Moreover, pigs in the HMB group had higher pH24 value in the LD (P<0.05) than did pigs in the CON group.(4) Sows fed HMB diet had higher HMB level in the milk during the day 28 of lactation (P<0.01), which led to increases in the HMB content of LD for the offspring at day 28 after birth (P<0.05).Furthermore, lactating sows fed HMB diet had higher content of milk fat during days 14 and 28 of lactation relative to those fed the CON diet (P<0.05).(5) Maternal HMB treatment during lactation increased plasma glucose (P<0.05), leucine (P<0.05),and essential amino acid (EAA) concentration of piglets (P<0.05), and had an increased tendency in plasma insulin level (P=0.078) of the offspring at weaning.(6) The higher mRNA expression of mTOR and Sox6 were discovered in the LD of weaning pigs in the HMB group than that in the CON group (P< 0.05), meanwhile, the increased expression of MyHC-?b mRNA and Fast-MyHC protein were observed in the LD of weaning and fattening pigs from sows fed HMB diet compared with those from sows fed the CON diet (P< 0.05). In addition, pigs from sows fed HMB diet had higher loin muscle area and type II fiber cross-sectional area (CSA) than those from sows fed the CON diet (P< 0.05). However, the total number of muscle fibers did not differ in the LD of offspring from sows between HMB and CON groups.In a word, maternal HMB (2 g/kg) treatment during lactation could improve fat and HMB levels in the milk and enhance the transfer of HMB from maternal milk to skeletal muscle of piglets, which contributed to type conversion of Fast-MyHC in the muscle of weaning pigs. In addition, maternal HMB treatment during lactation increased growth performance and carcass quality of fattening pigs by increasing the muscle fiber CSA, which was related to higher mRNA expression of transcription factor of Sox6 in the muscle.Experiment 3. Effects of dietary HMB supplementation during the early postnatal period on the growth performance and muscle fiber development of piglets, and its underlying mechanism.In order to evaluate further the effects of inclusion of HMB in maternal milk on muscle fiber development of pigs, we designed the experiment 3, which was to explore the effects of dietary HMB supplementation to piglets during the early postnatal period on the muscle fiber development and the possible mechanism.The study also evaluated the effects of dietary HMB supplementation during the early postnatal period on the growth performance and muscle fiber development of piglets. At day 7 after birth, a total of 12 pairs of IUGR (BW,1.85 ± 0.36 kg) and NBW (BW,2.51 ± 0.39 kg) male piglets, which were from parities 2 and 3 of 24 sows, were weaned and assigned according to BW, to groups fed the basal diets supplemented with 0 or 0.08% HMB-Ca. There were four treatment groups (birth weight/diet, n=6 per group) according to the 2 × 2 factional design. All piglets were fed with liquid diets every 3 h by bottle feeding during 7 to 28 days after birth and had free access to water. At day 29 of age, all piglets were euthanized and collected the LD, and the right half of the carcass was further manually separated into muscle tissue, subcutaneous adipose tissue (SCAT), skin and bones. The main results are shown as follows:(1) Piglets in the HMB group also showed an increased ADG (+14%, P< 0.10) and a decreased F/G (-7%, P< 0.01) during days 7 to 28 after birth in comparison to that of the CON pigs. In addition, dietary HMB treatment increased (P< 0.05) the relative ratio of skeletal muscle by 3.1% and 4.4% for IUGR and NBW piglets, respectively, compared with that of the piglets fed the CON diet.(2) Piglets supplemented with HMB diet had an increased HMB concentration in their LD (P< 0.01) relative to that of piglets fed the CON diet. Meanwhile, piglets in the HMB group also had elevated plasma insulin, leucine, BCAA, EAA and NEAA content (P< 0.05) relative to that of their CON counterparts.(3) Both the CK (P< 0.05) and LDH activity (P< 0.05) of the LD were greatly increased in piglets fed HMB diet compared with that in piglets fed the CON diet. Furthermore, the mean type ? fiber CSA of piglets in the HMB group was significantly increased (P< 0.01) relative to those of pigs in the CON group.(4) Piglets fed HMB diet had significantly higher MyHC ?b, IGF-1, mTOR, MRF-4 and Sox6 mRNA levels in the LD (P< 0.05) than did pigs fed the CON diet. In addition, the Fast-MyHC protein content was significantly higher in the LD of piglets fed HMB diet than that in the LD of piglets fed the CON diet (P< 0.05).This study suggested that dietary supplementation of HMB during days 7 to 28 after birth increased the type ? muscle fiber CSA and growth performance for IUGR and NBW piglets, which was correlated with the improved skeletal muscle growth resulted largely from the activation of the mTOR signaling pathway and promotion in the type conversion of Fast-MyHC in the muscle by feeding HMB to piglets.In conclusion, our research demonstrated supplementing sow diets with HMB from day 35 of gestation to parturition improved litter weight and skeletal muscle growth of piglets, and increased muscle fiber number of piglets, which contributed to the improved pork quality of the offspring at market, but reduced he feed intake of sows during lactation. On the other hand, maternal HMB supplementation during lactation improved fat and HMB levels in the milk and promoted type ? muscle fiber type twitch and muscle protein synthesis of piglets at weaning, and the increased type ? muscle fiber cross-sectional area led to the improved performance and carcass quality of the offspring at market, but decreased feed intake of sows during lactation. In addition, dietary supplementation of HMB during the early postnatal period could increase performance and skeletal muscle growth of IUGR and NBW piglets by accelerating fast-twitch glycolytic fiber conversion. Finally, this study indicated also that maternal supplementation of HMB contributed to muscle fiber hyperplasia by increasing the expression of myogenic factors including Pax7 and MyoD, and the fast-twitch glycolytic fiber conversion by enhancing the Sox6 transcription factor expression in the muscle of the offspring. |
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