Effects of starter feeding and early weaning on developmental expressions of IGF-I gene in liver and IGF-IR gene in rumen of lambs from birth to eighty-four days of age.

The early weaning and starter feeding have significant effects on lamb growth and digestive tract development. However, it is not clear whether the expression of IGF-1/IGF-1R genes could be affected by feeding starter and weaning. Therefore, a total of 102 Hu male neonatal lambs were randomly divided into 3 groups: fed with starter at 42d + weaned at 56d (group A), fed with starter at 7d + weaned at 28d (group B) and fed with starter at 7d + weaned at 56d (group C), to explore the effects of starter feeding and weaning age on developmental expressions of IGF-I gene in liver and IGF-IR gene in rumen of Hu sheep. The results showed that IGF-I and IGF-IR genes were expressed extensively in various tissues of lambs, the expression of IGF-I was significantly higher in liver (p < 0.01), while the expression of IGF-IR was higher in rumen among gastrointestinal tissues. The mRNA level of IGF-I of group C was strikingly higher than that of group A at 28, 70, and 84d (p < 0.01) in liver, respectively. Rumen mRNA level of IGF-IR of group C was prominently higher than that of group A at 70d and 84d (p < 0.05), respectively. However, IGF-IR expression of group A was higher than that of group C at 14 and 42d (p < 0.05). The mRNA level of IGF-I of group B was significantly higher than that of group C at 42, 56, 70, and 84d (p < 0.01) in liver, while IGF-IR expression of group B was higher than that of group C at 70d (p < 0.01). In conclusion, early weaning and starter feeding affected liver IGF-I mRNA and rumen IGF-IR mRNA expression.

Polymorphisms in BMPRIB gene affect litter size in Chinese indigenous sheep breed.

The BMPRIB gene belongs to the TGF-ß superfamily and is considered to be a regulator of sheep reproductive performance. Single nucleotide polymorphisms (SNPs) of BMPRIB gene in the Small Tail Han, Hu, Mongolian, Oula, Gansu Alpine Fine-wool, Dorper and Australian White sheep were detected by Sanger sequencing. Five SNPs (rs427897187 G > A, rs418841713 A > G, rs159952533 T > C, rs429416173 C > A and rs403555643 A > G) of BMPRIB gene were identified. For rs427897187 G > A, further analysis revealed that genotype GG and GA had 0.26 (p < 0.05) and 0.33 (p < 0.05) litter size less than those with genotype AA in Oula sheep. For rs403555643 A > G, further analysis revealed that genotype GG and AG had 0.65 (p < 0.05) and 0.38 (p < 0.05) litter size more than those with genotype AA in Oula sheep, and genotype GG had 0.56 (p < 0.05) litter size more than those with genotype AA in Mongolian sheep. The results showed that rs427897187 G > A and rs403555643 A > G are potential molecular markers wich could improve litter size of Chinese indigenous sheep and be used in Chinese indigenous sheep breeding.

Transcriptome Analysis Identifies Candidate Genes and Pathways Associated With Feed Efficiency in Hu Sheep.

In the genetic improvement of livestock and poultry, residual feed intake (RFI) is an important economic trait. However, in sheep, the genetic regulatory mechanisms of RFI are unclear. In the present study, we measured the feed efficiency (FE)-related phenotypes of 137 male Hu lambs, and selected six lambs with very high (n = 3) and very low (n = 3) RFI values and analyzed their liver transcriptomes. A total of 101 differentially expressed genes were identified, of which 40 were upregulated and 61 were downregulated in the low-RFI group compared with that in the high-RFI group. The downregulated genes were mainly concentrated in immune function pathways, while the upregulated genes were mainly involved in energy metabolism pathways. Two differentially expressed genes, ADRA2A (encoding adrenoceptor alpha 2A) and RYR2 (ryanodine receptor 2), were selected as candidate genes for FE and subjected to single nucleotide polymorphism scanning and association analysis. Two synonymous mutations, ADRA2A g.1429 C > A and RYR2 g.1117 A > C, were detected, which were both significantly associated with the feed conversion rate. These findings provide a deeper understanding of the molecular mechanisms regulating FE, and reveal key genes and genetic variants that could be used to genetically improve FE in sheep.

Molecular Characterization and Expression of SPP1, LAP3 and LCORL and Their Association with Growth Traits in Sheep.

The SPP1, LAP3, and LCORL are located on chromosome 6 of sheep and a domain of 36.15-38.56 Mb, which plays an essential role in tissue and embryonic growth. In this study, we cloned the complete coding sequences of SPP1 and partial coding regions of LAP3 and LCORL from Hu sheep (Gansu Province, China) and analyzed their genomic structures. The RT-qPCR showed that the three genes were expressed widely in the different tissues of Hu sheep. The SPP1 expression was significantly higher in the kidney (p < 0.01) and LAP3 expression was significantly higher in the spleen, lung, kidney, and duodenum than in the other tissues (heart, liver, rumen, muscle, fat, and ovary; p < 0.05). The LCORL was preferentially expressed in the spleen, duodenum, and lung (p < 0.05). In addition, the nucleotide substitution NM_001009224.1:c.132A>C was found in SPP1; an association analysis showed that it was associated with birth weight and yearling weight (p < 0.05), and NM_001009224.1:c.132C was the dominant allele. Two mutations XM_012179698.3:c.232C>G and XM_012179698.3:c.1154C>T were identified in LAP3. The nucleotide substitution XM_012179698.3:c.232C>G was confirmed to be associated with birth weight, 1-month weight, 3-month weight (p < 0.05), and 2-month weight (p < 0.01). The nucleotide substitution XM_012179698.3:c.1154C>T was associated with birth weight (p < 0.01), 1-month weight, and 2-month weight (p < 0.05). The LAP3 gene XM_012179698.3:c.232C>G mutation with the C allele has higher body weight than other sheep, and CC genotype individuals show higher birth weight, 1-month weight, and weaning weight than the GG genotype individuals (p < 0.05). Our results support the conclusion that the mutations on ovine SPP1 and LAP3 successfully track functional alleles that affect growth in sheep, and these genes could be used as candidate genes for improving the growth traits of sheep during breeding.

Association of residual feed intake with growth and slaughtering performance, blood metabolism, and body composition in growing lambs.

The aim of this study was to determine the association of residual feed intake (RFI) with growth performance, blood metabolic parameters, and body composition factors in growing lambs. Individual body weight (BW) and dry matter intake (DMI) were determined in 137 male Hu lambs that were given a pellet feed four times a day for 50 d. RFI did not show a correlation with metabolic BW (MBW) or average daily gain (ADG), but it showed a positive correlation with DMI and feed conversation ratio (FCR). Organ weight and intestine length had a large influence on RFI in lambs. The low-RFI lambs have smaller rumen and longer duodenum indicating the less feed intake and more sufficient absorption rate of low-RFI lambs. The smaller organs like liver, lung and kidney in low-RFI lambs may be related to lower energy consumption and slower metabolic rate. The observed bigger testis was in low-RFI lambs was another cause of the improved feed efficiency. Finally, the plasma concentrations of thyroxine (T4) and adrenocorticotropic hormone (ACTH) were lower in the ELow-RFI group than in the EHigh-RFI group. This study provides new insight into the biological processes underlying variations in feed efficiency in growing lambs.

Supplementation with dietary linseed oil during peri-puberty stimulates steroidogenesis and testis development in rams.

Omega-3 polyunsaturated fatty acids (ω-3 PUFAs), such as α-linolenic acid (ALA), eicosapentaenoic acid, and docosahexaenoic acid, are involved in male reproductive function. In this study, we investigated the effects of linseed oil (LO) as a source of ALA on the steroidogenesis and changes of testicular histology in rams. Sixteen 3-month old rams during peri-puberty were randomly assigned into two groups. Eight rams were assigned as the control group, and the other received LO (4% dry matter of total diet) as the LO treatment group. After an 81-day feeding trial, the rams were slaughtered and investigated. Results revealed that compared with control group, diet containing LO did not affect body weight (36.87 ± 0.53 kg vs. 37.65 ± 0.64 kg, respectively; P = 0.361), average daily gain (227.47 ± 5.82 g vs. 237.95 ± 9.22 g, respectively; P = 0.353) and epididymis weight (40.77 ± 4.41 g vs. 45.53 ± 4.01 g, respectively; P = 0.398), however, it up-regulated PUFAs metabolism and steroidogenesis-related genes mRNA expression (P < 0.05), and increased plasma estradiol concentration (14.88 ± 0.67 pg/mL vs. 19.50 ± 1.27 pg/mL, respectively; P < 0.05). Therefore, LO stimulated seminiferous tubule development and increased the number of Sertoli cells (19.17 ± 2.14 vs. 27.2 ± 2.39, respectively; P < 0.01), germ-cell layers, as well as testis weight (148.65 ± 22.66 g vs. 249.96 ± 30.63 g, respectively; P < 0.05). All these results suggested that LO can improve testis development during peri-puberty by regulating steroidogenesis in rams' testes.

Rumen Bacteria Communities and Performances of Fattening Lambs with a Lower or Greater Subacute Ruminal Acidosis Risk.

Several ruminal cellulolytic bacteria species are sensitive to pH and could therefore be used as biomarkers to determine the risk of sub-acute ruminal acidosis (SARA) in finishing lambs. This study compared a 2-4 h post feeding ruminal pH measurement to abundances of the ruminal pH-sensitive bacteria to evaluate the risk of SARA in a herd of 120 finishing lambs. The lambs were reared in individual units for 50 days. Ruminal fluid was collected by use of an orogastric tube on day 51 2-4 h after feeding. Although the lambs were fed an identical diet, they responded differently in the abundances of four ruminal pH sensitive cellulolytic bacteria (Ruminococcus albus, Ruminococcus flavefaciens and Fibrobacter succinogenes and Butyrivibrio fibrisolvens). Lambs with the most or the least cellulolytic bacteria were then classified as either lower SARA risk (LSR, n = 10) or higher SARA risk group (HSR, n = 10), respectively. Data showed that the ruminal pH and VFA profiles were uncorrelated with the number of cellulolytic bacteria (P > 0.050). Lambs with the HSR showed lower ruminal pH (P = 0.013) and acetate to propionate ratio (P = 0.018), higher concentrations of lactate (P = 0.035) and proportion of propionate (P = 0.033) compared to those with the LSR. The DMI and ADG did not differ in LSR and HSR lambs (P > 0.050). A diversity analysis revealed significantly lower diversity in HSR lambs than in LSR (Simpson index, P = 0.004). The relative abundances of the phyla Bacteroidetes, Fibrobacteres, Verruomicrobia, and Proteobacteria were higher in LSR lambs than in HSR (P < 0.050). The abundances of several phyla including Firmicutes, Tenericutes and Actinobacteria were higher in the HSR than in the LSR group (P < 0.050). The bacterial communities of the LSR and HSR clustered separately in rumen based on the Unifrac distances, indicating distinct bacteria communities at OTU level between the LSR and HSR lambs. Overall, there was no correlation between 2 and 4 h post-feeding ruminal pH and the abundance of pH-sensitive bacteria and the amount of these bacteria could be used as a potential biomarker of SARA in lamb herd.

Effects of early feeding on the host rumen transcriptome and bacterial diversity in lambs.

Early consumption of starter feed promotes rumen development in lambs. We examined rumen development in lambs fed starter feed for 5 weeks using histological and biochemical analyses and by performing high-throughput sequencing in rumen tissues. Additionally, rumen contents of starter feed-fed lambs were compared to those of breast milk-fed controls. Our physiological and biochemical findings revealed that early starter consumption facilitated rumen development, changed the pattern of ruminal fermentation, and increased the amylase and carboxymethylcellulase activities of rumen micro-organisms. RNA-seq analysis revealed 225 differentially expressed genes between the rumens of breast milk- and starter feed-fed lambs. These DEGs were involved in many metabolic pathways, particularly lipid and carbohydrate metabolism, and included HMGCL and HMGCS2. Sequencing analysis of 16S rRNA genes revealed that ruminal bacterial communities were more diverse in breast milk-than in starter feed-fed lambs, and each group had a distinct microbiota. We conclude that early starter feeding is beneficial to rumen development and physiological function in lambs. The underlying mechanism may involve the stimulation of ruminal ketogenesis and butanoate metabolism via HMGCL and HMGCS2 combined with changes in the fermentation type induced by ruminal microbiota. Overall, this study provides insights into the molecular mechanisms of rumen development in sheep.