The present study was designed to describe the effects of early feed restriction of Merino lambs on feed efficiency during the fattening period by examining ruminal microbiota and fermentation parameters, gastrointestinal morphology, digestibility or liver proteome. In total, 24 male Merino lambs were randomly assigned to two experimental treatments (n=12 per treatment). Lambs of the first group (ad libitum (ADL)) were kept permanently with the dams, whereas the other 12 lambs (restricted (RES)) were milk restricted. When lambs reached a live BW (LBW) of 15 kg, all the animals were offered the same complete pelleted diet (35 g dry matter/kg LBW per day) until slaughter at a LBW of 27 kg. The RES lambs showed poorer feed efficiency during the fattening period when compared with the ADL group (feed to gain ratio, 3.69 v. 3.05, P<0.001). No differences were observed in ruminal microbiota, fermentation parameters or apparent digestibility. However, the proportion of the small intestine and the length of ileal villi were reduced in the RES lambs. In total, 26 spots/proteins were identified in the liver proteomic profile, with significant differences (P<0.05) between experimental treatments, suggesting a higher catabolism of proteins and a reduction in β-oxidation of fatty acids in RES lambs when compared with the ADL animals. In conclusion, early feed restriction of Merino lambs during the suckling period promotes long-term effects on the small intestine and the proteomic profile of the liver, which may influence the metabolic use of nutrients, thus negatively affecting feed efficiency during the fattening phase.

The objective of the study was to determine the effect of early feed restriction on carcass and meat quality traits in Merino lambs. Twenty-four male Merino lambs (4.81±0.256kg) were assigned to two groups (12 animals in each group). The first group (ad libitum, ADL) was kept permanently with the dams. The second group (restricted, RES) was milk-restricted. After weaning (15kg), daily feed intake of all lambs was identical, but a lower gain: feed ratio was recorded in the RES group (0.320 vs. 0.261; P<0.001). After animals were slaughtered (27kg), lower ultimate pH and reduced yellow colouration of subcutaneous fat was recorded in meat from the RES lambs when compared to ADL group, whereas a trend towards a significant increment of intramuscular fat content and no effect on meat quality traits was observed in the RES lambs. Early feed restriction may be useful to increase intramuscular fat accretion in Merino lambs during the fattening period.

Nutritional programming caused by feed restriction during the early life may counteract the profitability of the dairy sheep farm. However, most studies have been focused exclusively on the prenatal period, and scarce information regarding the effect of milk replacer (MR) restriction on feed efficiency [residual feed intake (RFI)] and progesterone patterns of replacement ewe lambs is available. Therefore, in the present study 40 Assaf female newborn lambs were penned individually and assigned randomly to 1 of 2 treatment groups (n = 20 per treatment). The first group of lambs was fed MR ad libitum (ADLB), whereas the second one (restricted, RES) only received approximately 62.5% of the MR intake measured in the ADLB group. All the lambs were weighed twice a week until they were 35 d old. Then 8 lambs from each group were killed and a morphological study of the gut was performed. Moreover, a piece of liver was cut to measure fat content and oxidative status. The rest of the ewe lambs (24) were weaned and offered a total mixed ration ad libitum to calculate the RFI during the replacement phase. Plasma samples were collected when ewe lambs were 8 mo old to perform a nontargeted metabolomic analysis on a hybrid quadrupole-time-of-flight mass spectrometer coupled to an ultra-high-performance liquid chromatographic system. Progesterone was also measured weekly on serum samples by sequential competitive immunoassay until the end of the experiment (9.5 mo old). The results observed indicate that moderated MR restriction promoted differences in the morphology of the gut of the 35-d-old lambs, but not in the apparent digestibility or feed efficiency traits (RFI) during the replacement phase. However, there was a trend toward reduced live body weight of the RES ewe lambs when they were 9.5 mo old. Moreover, progesterone patterns revealed that only 1 RES versus 4 ADLB ewe lambs had ovulated for the first time at the end of the experiment. This evidence suggests the existence of long-term effects caused by early feed restriction with negative consequences on live body weight and reproductive traits of replacement ewe lambs.

The increasing world population is driving demand for improved efficiency of feed resources of livestock. However, the molecular mechanisms behind various feed efficiency traits and their regulation by nutrition remain poorly understood. Here, we aimed to identify differentially expressed (DE) genes in the liver tissues of fattening Merino lambs and differences in metabolites accumulated in plasma to identify modified metabolic pathways as a consequence of milk restriction during the suckling period. Twenty-four male Merino lambs (4.81 ± 0.256 kg) were divided into 2 groups (n = 12 per dietary treatment). The first group (ad libitum, ADL) was kept permanently with the dams, whereas the other group (restricted, RES) was milk restricted. When they reached 15 kg of live body weight (LBW), all the animals were offered the same complete pelleted diet at the same level (35 g DM/kg LBW per day) to ensure no differences in dry matter intake. All the lambs were harvested when they reached 27 kg of LBW. For transcriptomic analysis, 4 liver samples from each group (8 samples in total) were selected for RNA sequencing (RNA-seq), and plasma samples from all animals (24 samples in total) were used to perform a nontargeted metabolomic analysis on a hybrid quadrupole-time-of-flight mass spectrometer coupled to an ultra-high performance liquid chromatographic system (UHPLC/QTOF-MS). Thirty-eight DE annotated genes were identified by RNA-seq, with 23 DE genes being down-regulated and 15 up-regulated in the liver of RES lambs relative to the ADL group (P < 0.10). Also, the metabolomic assay identified 38 differentially accumulated compounds (P < 0.10). In general, those genes and pathways involved in protein synthesis or protease inhibitors were down-regulated in the RES group, whereas those related to proteolytic degradation were up-regulated, thus suggesting a higher catabolism of proteins in these lambs. RES lambs showed over-expression of xenobiotic metabolism pathways, whereas those genes related to β-oxidation of fatty acids were down-regulated. According to the data obtained, early feed restriction during the suckling period of Merino lambs promoted long-term effects on both the hepatic transcriptomic profile and plasma metabolic profile, which might have modified fatty acids metabolism, catabolism of proteins, and detoxification of xenobiotics, thus reducing feed efficiency during the fattening period.

Undernutrition during the first stages of life may impair maturation of the immune system, harming the health status permanently. Thus, the aim of the present study was to define the impact of moderated milk replacer (MR) restriction during the artificial rearing period on the gut-associated lymphoid tissues of pre-weaned ewe lambs and long-term effects on biochemical profile and animal performance during the replacement period. Forty female Assaf lambs [average live body weight (LBW) 4.73 ± 0.116 kg] were penned individually. The first group of lambs (n=20) was fed MR ad libitum (ADL) whereas the second one (restricted, RES; n=20) only received approximately 62.5% of the MR intake measured in the ADL group. All the lambs were weighed twice a week until they were 35-days-old. Then, 8 lambs from each group (preweaned) were harvested and ileal samples collected. The rest of the lambs (12 ADL vs. 12 RES) were weaned progressively, and then offered a total mixed ration (TMR) ad libitum until the end of the experiment (7.5-months-old). The lower nutrient intake of RES pre-weaned lambs caused greater percentages for T lymphocytes (CD4 + , CD8 + , WC1 +) and an increased secretory immunoglobulin A (sIgA) production in the ileum compared to the ADL group (P<0.05). These results, together with the significant differences in the expression of toll-like receptors and cytokines at this level (e.g., interferon gamma was increased in the RES group; P<0.05) suggest the existence of pro-inflammatory conditions in the ileum of pre-weaned lambs promoted by early feed restriction. Moreover, the biochemical profile revealed that liver function (e.g., albumin, gamma glutamyl transpeptidase) was impaired during several months once the feed restriction period was finished, whereas the average daily gain during the replacement phase was reduced for the early feed restricted lambs (182 vs. 202 g/day for RES and ADL groups, respectively; P<0.05). Therefore it can be concluded that moderated MR restriction promoted both, pro-inflammatory conditions at ileal level in the pre-weaned lambs and an altered liver function which lasted several months after the end of feed restriction. Both circumstances might have impaired animal performance during the replacement phase of the ewe lambs.

Bacteria firmly attached to the gastrointestinal epithelium during the pre-weaning phase may show a significant impact on nutrient processing, immunity parameters, health and feed efficiency of lambs during post-weaning phases. Thus, the aim of this study was to describe the differences in the ileal epimural microbiota (e.g. total bacteria, Prevotella spp., Bifidobacterium spp. and Lactobacillus spp.) of fattening lambs promoted by early feed restriction during the suckling phase trying to elucidate some of the underlying mechanisms behind changes in feed efficiency during the fattening period. A total of 24 Merino lambs (average BW 4.81±0.256 kg) were used, 12 of them (ad libitum, ADL) kept permanently in individual pens with their mothers, whereas the other 12 lambs were separated from their dams for 9 h each day to be exposed to milk restriction (RES). After weaning (BW=15 kg) all the animals were penned individually, offered the same complete pelleted diet (35 g/kg BW per day) and slaughtered at a BW of 27 kg. During the fattening period, reduced gain : feed ratio (0.320 v. 0.261, P<0.001) was observed for the RES group. Moreover, increments of Prevotella spp. were detected in the ileal epimural microbiota of RES lambs (P<0.05). There were also higher numbers of infiltrated lymphocytes (T and B cells) in the ileal lamina propria (P<0.05), a higher M-cell labelling intensity in ileal Peyer's patches domes (P<0.05) and a trend towards a thickening of the submucosa layer when compared with the ADL group (P=0.057). Some other immunological parameters, such as an increased immunoglobulin A (IgA) production (pg IgA/µg total protein) and increments in CD45+ cells were also observed in the ileum of RES group (P<0.05), whereas transforming growth factor β and toll-like receptor gene expression was reduced (P<0.05). In conclusion, early feed restriction during the suckling phase promoted changes in ileal epimural microbiota and several immunity parameters that could be related to differences in feed efficiency traits during the fattening period of Merino lambs.

Lambs from intensive dairy sheep production systems are sold out either after weaning as milk-fed lambs or after a fattening characterized by high intakes of concentrate feeds (mainly cereals) which can lead to ruminal disorders. Therefore, it is essential to explore different feeding alternatives in order to reach a balance between economic or productive benefits and animal welfare. Twenty weaned male lambs (6 to 8 weeks age, 14.8 ± 0.16 kg body weight) were allocated randomly to one of two different groups (n=10 per group) to study the effect of feeding a complete pelleted diet (CPD) in which cereal grains were ground at two different sieve sizes (either 2-mm with 13.5% dry matter (DM) of the particles > 1.7 mm or 6-mm with 47.1% DM of particles > 1.7 mm) on DM intake, nutrient digestibility, ruminal microbiota and fermentation. Lambs were fed the corresponding CPD ad libitum and slaughtered when they reached 27 kg. DM intake was greater in the lambs fed 2-mm grains than in those fed 6mm grains (P<0.05). Feeding 2-mm grains in comparison to 6-mm grains resulted in darker colour of ruminal mucosa (100 vs. 127, from a scale where 0 is black and 256 white; SED=9.8; P=0.017) and thicker stratum corneum (45.3 vs. 30.9 µm; SED=3.67; P=0.001), suggesting more severe acidotic conditions in the rumen with the smaller cereal particle size. Analysis of microbial communities revealed that the presence of ruminal bacteria such as Prevotella and Quinella, were increased in the digesta of animals fed the 2-mm diet. These data were corroborated by the odd-and branched-chain fatty acid profile of ruminal contents, which would indicate a shift from cellulolytic to amylolytic bacteria in the rumen of lambs fed the 2-mm diet. In conclusion, feeding 6-mm in comparison to 2-mm ground cereal grains included in CPD formulated for growing lambs is an alternative strategy that may reduce ruminal acidosis through changes in the microbiota.

Simple SummaryInadequate nutrition of lambs during early life may compromise their health status during their whole lifetime. The aim of this study was to investigate the long-term effects of milk restriction during the suckling period on biochemical, immunological, hepatic, and ruminal parameters of fattening lambs. The results obtained reveal that early feed restriction during the suckling period of merino lambs promotes systemic metabolic disorders during the fattening phase that are not related to ruminal acidosis occurrence. This information may contribute to design strategies to enhance the health status of lambs undergoing milk restriction due to low milk production (e.g., udder problems) or lack of lamb vitality.AbstractEarly postnatal nutrition may have a significant subsequent impact on metabolic disorders during the entire lifespan of lambs. The aim of the present study was to describe the changes in biochemical, immunological, hepatic, and ruminal parameters of fattening lambs derived from early feed restriction during the suckling phase. Twenty-four merino lambs (average body weight, BW, 4.81 ± 0.256 kg) were used, 12 of them were milk-fed ad libitum (ADL) remaining permanently with their dams, whereas the other 12 lambs (restricted, RES) were subjected to milk restriction. After weaning, all the lambs were fed 35 g/kg BW per day of the same complete pelleted diet to ensure no differences between groups in dry matter intake (603 vs. 607 g/day for ADL and RES lambs, respectively, p = 0.703), and were slaughtered at a BW of 27 kg. Biochemical profiles revealed higher concentrations of ceruloplasmin and low-density lipoproteins, whereas insulin concentration was lower in the RES lambs compared to the ADL group. Liver thiobarbituric acid reactive substances were lower in the RES lambs. No significant differences in ruminal or blood immunological parameters were found. In conclusion, early feed restriction promoted metabolic disorders not related to ruminal acidosis occurrence, which can compromise the health status during the fattening period of merino lambs.