Fattening lambs with divergent residual feed intakes and weight gains: Unravelling mechanisms driving feed efficiency

Ruminal microbial metagenomes and host transcriptomes shed light on individual variability in the growth rate of lambs before weaning: the regulated mechanism and potential long-term effect on the host

Weaning weight is a reflection of management during the breastfeeding phase and will influence animal performance in subsequent phases, considered important indicators within production systems. The aims of this study were as follows: (i) to investigate variability in the growth rate among individual lambs from ewes rearing single or twin lambs fed with two different diets and (ii) to explore the molecular mechanisms regulating the growth rate and the potential long-term effects on the host. No significant change in lamb average daily gain (ADG) was observed in litter size and diet treatment, and there were large variations among individual lambs (ranging from 0.13 to 0.41 kg/day). Further analysis was conducted on serum amino acids, rumen fermentation characteristics, rumen metagenomics and transcriptome, and hepatic transcriptome of lambs with extremely high (HA; n = 6) and low (LA; n = 6) ADG. We observed significant increases in serum lysine, leucine, alanine, and phenylalanine in the HA group. The metagenome revealed that the HA group presented a higher rumen propionate molar proportion via increasing gene abundance in the succinate pathway for propionate synthesis. For the rumen transcriptome, higher expressed gene sets in the HA group were mainly related to rumen epithelial growth, including cytokine-cytokine receptor interaction, Jak-STAT signaling pathway, and adherens junction. For the liver transcriptome, the upregulated KEGG pathways in the HA group were primarily associated with fatty acid degradation, glyoxylate and dicarboxylate metabolism, cholesterol metabolism, and the immune system. This research suggests that preweaning lambs with high ADG may benefit from rumen development and enhanced liver metabolic and immune function.

IMPORTANCE

There is accumulating evidence indicating that the early-life rumen microbiome plays vital roles in rumen development and microbial fermentation, which subsequently affects the growth of young ruminants. The liver is also vital to regulate the metabolism and distribution of nutrients. Our results demonstrate that lambs with high average daily gain (ADG) enhanced microbial volatile fatty acid (VFA) metabolism toward rumen propionate and serum amino acid (AA) production to support host growth. The study highlights that high ADG in the preweaning period is beneficial for the rumen development and liver energy metabolism, leading to better growth later in life. Overall, this study explores the molecular mechanisms regulating the growth rate and the potential long-term effects of increased growth rate on the host metabolism, providing fundamental knowledge about nutrient manipulation in pre-weaning.

Weighted single-step genome-wide association study for direct and maternal genetic effects associated with birth and weaning weights in sheep

Body weight is an important economic trait for sheep meat production, and its genetic improvement is considered one of the main goals in the sheep breeding program. Identifying genomic regions that are associated with growth-related traits accelerates the process of animal breeding through marker-assisted selection, which leads to increased response to selection. In this study, we conducted a weighted single-step genome-wide association study (WssGWAS) to identify potential candidate genes for direct and maternal genetic effects associated with birth weight (BW) and weaning weight (WW) in Baluchi sheep. The data used in this research included 13,408 birth and 13,170 weaning records collected at Abbas-Abad Baluchi Sheep Breeding Station, Mashhad-Iran. Genotypic data of 94 lambs genotyped by Illumina 50K SNP BeadChip for 54,241 markers were used. The proportion of variance explained by genomic windows was calculated by summing the variance of SNPs within 1 megabase (Mb). The top 10 window genomic regions explaining the highest percentages of additive and maternal genetic variances were selected as candidate window genomic regions associated with body weights. Our findings showed that for BW, the top-ranked genomic regions (1 Mb windows) explained 4.30 and 4.92% of the direct additive and maternal genetic variances, respectively. The direct additive genetic variance explained by the genomic window regions varied from 0.31 on chromosome 1 to 0.59 on chromosome 8. The highest (0.84%) and lowest (0.32%) maternal genetic variances were explained by genomic windows on chromosome 10 and 17, respectively. For WW, the top 10 genomic regions explained 6.38 and 5.76% of the direct additive and maternal genetic variances, respectively. The highest and lowest contribution of direct additive genetic variances were 1.37% and 0.42%, respectively, both explained by genomic regions on chromosome 2. For maternal effects on WW, the highest (1.38%) and lowest (0.41%) genetic variances were explained by genomic windows on chromosome 2. Further investigation of these regions identified several possible candidate genes associated with body weight. Gene ontology analysis using the DAVID database identified several functional terms, such as translation repressor activity, nucleic acid binding, dehydroascorbic acid transporter activity, growth factor activity and SH2 domain binding.

Effects of propylene glycol used at different doses in Akkaraman lambs rations on metabolism-related parameters and liver gene and protein expression during different feeding periods

This study aimed to investigate the metabolic effects of propylene glycol (PG) over 60, 90, and 120 days in lambs. Seventy-two weaned male lambs were allocated into three groups: control (Con), PG1.5 (1.5 mL/kg live weight0.75 ), and PG3 (3 mL/kg live weight0.75 ). Blood samples were collected at the beginning and slaughter days. Biochemical parameters (glucose, triglycerides, ALT, AST, LDH, BUN, and insulin) and gene and protein levels of peroxisome proliferator activated receptor gamma (PPARγ), diacylglycerol o-acyltransferase 1 (DGAT1), carbohydrate responsive element binding protein (ChREBP), and sterol regulatory element binding transcription factor 1c (SREBP-1c) in the liver were determined. Glucose in PG1.5 was increased on Day 60, while significant differences were observed in biochemical parameters except for insulin on the 60, 90, and 120 days. Biochemical parameters such as ALT, AST, LDH, and BUN increased over time, while triglycerides decreased. DGAT1 gene and protein levels were lower, while SREBP-1c and PPARγ were higher in PG groups on Day 60. While SREBP-1c was lower in PG1.5, ChREBP was higher in PG3 on Day 90. PPARγ, DGAT1, and ChREBP were upregulated in PG3 on Day 120. Positive correlations were found between proteins. The long-term use of PG in lambs did not have detrimental effects on metabolism. The study provides valuable insights into the molecular mechanisms underlying the metabolic effects of PG in lambs, shedding light on its potential applications in lamb production.

Evaluation of the Links between Lamb Feed Efficiency and Rumen and Plasma Metabolomic Data

Feed efficiency is one of the keystones that could help make animal production less costly and more environmentally friendly. Residual feed intake (RFI) is a widely used criterion to measure feed efficiency by regressing intake on the main energy sinks. We investigated rumen and plasma metabolomic data on Romane male lambs that had been genetically selected for either feed efficiency (line rfi−) or inefficiency (line rfi+). These investigations were conducted both during the growth phase under a 100% concentrate diet and later on under a mixed diet to identify differential metabolite expression and to link it to biological phenomena that could explain differences in feed efficiency. Nuclear magnetic resonance (NMR) data were analyzed using partial least squares discriminant analysis (PLS-DA), and correlations between metabolites’ relative concentrations were estimated to identify relationships between them. High levels of plasma citrate and malate were associated with genetically efficient animals, while high levels of amino acids such as L-threonine, L-serine, and L-leucine as well as beta-hydroxyisovalerate were associated with genetically inefficient animals under both diets. The two divergent lines could not be discriminated using rumen metabolites. Based on phenotypic residual feed intake (RFI), efficient and inefficient animals were discriminated using plasma metabolites determined under a 100% concentrate diet, but no discrimination was observed with plasma metabolites under a mixed diet or with rumen metabolites regardless of diet. Plasma amino acids, citrate, and malate were the most discriminant metabolites, suggesting that protein turnover and the mitochondrial production of energy could be the main phenomena that differ between efficient and inefficient Romane lambs.

Dietary Administration of L-Carnitine During the Fattening Period of Early Feed Restricted Lambs Modifies Ruminal Fermentation but Does Not Improve Feed Efficiency

Early feed restriction of lambs may program animals to achieve reduced feed efficiency traits as a consequence of permanent mitochondrial dysfunction. The hypothesis at the background of the present study is that dietary administration of L-Carnitine (a compound that promotes the activation and transportation of fatty acids into the mitochondria) during the fattening period of early feed restricted lambs can: (a) improve the biochemical profile of early feed restricted lambs, (b) improve feed efficiency, (c) modulate the ruminal and intestinal microbiota, and (d) induce changes in the gastrointestinal mucosa, including the immune status. Twenty-two newborn male Merino lambs were raised under natural conditions but separated from the dams for 9 h daily to allow feed restriction during the suckling period. At weaning, lambs were assigned to a control group being fed ad libitum a complete pelleted diet during the fattening phase (CTRL, n = 11), whereas the second group (CARN, n = 11) received the same diet supplemented with 3 g of L-Carnitine/kg diet. The results revealed that even though L-Carnitine was absorbed, feed efficiency was not modified by dietary L-Carnitine during the fattening period (residual feed intake, p > 0.05), whereas ruminal fermentation was improved [total short-chain fatty acids (SCFAs), 113 vs. 154 mmol/l; p = 0.036]. Moreover, a trend toward increased concentration of butyrate in the ileal content (0.568 vs. 1.194 mmol/100 ml SCFA; p = 0.074) was observed. Other effects, such as reduced heart weight, lower levels of markers related to muscle metabolism or damage, improved renal function, and increased ureagenesis, were detected in the CARN group. Limited changes in the microbiota were also detected. These findings suggest that L-Carnitine may improve ruminal fermentation parameters and maintain both the balance of gut microbiota and the health of the animals. However, the improved ruminal fermentation and the consequent greater accumulation of intramuscular fat might have hidden the effects caused by the ability of dietary L-Carnitine to increase fatty acid oxidation at the mitochondrial level. This would explain the lack of effects of L-Carnitine supplementation on feed efficiency and points toward the need of testing lower doses, probably in the context of animals being fed in excess non-protein nitrogen.

The Role of Feed Restriction on DNA Methylation, Feed Efficiency, Metabolome, Biochemical Profile, and Progesterone Patterns in the Female Filial Generation (F1) Obtained From Early Feed Restricted Ewes (F0)

Deficient management of replacement animals in the farm during early developmental windows may promote adverse programming effects on reproductive traits and subsequent transmission to the next generation. In this sense, DNA methylation profiles allow researchers to decode epigenetic regulation mechanisms in mammals and identify novel candidate genes correlated with phenotype differences in both dams and offspring. Therefore, improving knowledge in the field of epigenetics and intergenerational effects caused by prenatal and postnatal early nutritional events (e.g., feed restriction) is crucial for refining strategies dedicated to animal breeding. In this study, we determined differences in the global blood methylation patterns, biochemical profile, and metabolome of ewe lambs (F1) born from either early feed restricted dams (F0-RES) or fed ad libitum (F0-ADL). Our data show that functional categories such as those related to cellular processes, phosphorylation, nervous system, immunity response, or reproductive function were enriched significantly in the F1-RES lambs due to differences in the methylation of genes in these categories. These F1-RES lambs did not show differences in feed efficiency during the replacement period but presented higher levels of insulin and triglycerides and reduced concentration of progesterone, whereas the metabolome profile demonstrated variations in the bile acid composition when compared with the F1-ADL lambs. Taken together, all these results suggest that intergenerational effects caused by early feed restriction of dams (F0) may persist in the F1 female lambs with negative consequences on genes involved in cellular processes and reproductive traits.

Interplay between feed efficiency indices, performance, rumen fermentation parameters, carcass characteristics and meat quality in Pelibuey lambs

Feed efficiency was measured in thirty Pelibuey noncastrated male lambs using the residual feed intake (RFI) and residual intake and gain (RIG). The lambs were fattened for 92 d and then slaughtered, with the aim of identifying the interplay between feed efficiency indices (FEIs) and performance, rumen fermentation parameters, carcass characteristics and meat quality traits from the 15 intermediate and most extreme lambs for each FEI. The mean values of the classes were -0.09, 0.00, and 0.09 kg DM/d for low, medium and high RFI, respectively. The RIG indicators were 2.6, -0.1, and -2.7, for high, medium and low, respectively. The lambs with high-RIG had a higher (P ≤ 0.05) average daily gain and improved feed conversion. Lambs with low-RFI and high-RIG had higher (P < 0.05) values of meat cooking loss. Efficient lambs had improved feed utilization without affecting the carcass characteristics or meat quality (except for cooking loss).