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Accelerated growth programs during prepubertal periods have been promoted to advance the first calving of beef heifers. The objectives of the present study were to evaluate nutrition-induced changes on first lactation milk yield and composition and on gene expression of the mammary gland in Parda de Montaña primiparous cows. Female calves ( = 16) were involved in a 2 × 2 factorial experiment. In the preweaning period (PRE-W; 0-6 mo), female calves were either fed a creep feed supplement (Creep) or fed only their dam's milk (Control). In the postweaning period (POST-W; 6-15 mo), heifers received either a high-energy diet (91.7 MJ/d) or a moderate-energy diet (79.3 MJ/d). All the heifers were managed together from breeding (15 mo) to the end of their first lactation (32 mo). Animal performance; milk production and quantity during the first lactation; plasma glucose, IGF-I, and leptin concentrations; and RNA samples from the mammary gland at the end of the first lactation of the primiparous cows (32 mo) were analyzed. The BW and ADG of the primiparous cow during its first lactation were not different among treatments; however, creep feeding during PRE-W reduced milk production (0.01), milk CP, crude fat, lactose, nonfat solids, and casein content throughout lactation and increased somatic cell count in the third (0.05) and fourth month of lactation (0.10). The energy level during the POST-W had no effect on milk production and quality. Gene expression in the mammary gland was affected by the diet in the PRE-W and POST-W, with the PRE-W diet having the greatest impact. During the PRE-W, creep feeding resulted in upregulation of genes related to immune response and chemokine activity, suggesting that these animals might be in a compromised immune status. Therefore, this strategy would not be recommendable; meanwhile, increasing the energy level in the diet during the POST-W would be recommendable, because it had no deleterious effects on milk yield and composition.

The aim of this study was to investigate the effects of vitamin E (VE) supplementation and alfalfa grazing during fattening on fatty acid composition and mRNA expression of genes related to lipid metabolism in the LM of Rasa Aragonesa light lambs. After weaning, 48 lambs were kept indoors and fed a commercial concentrate and a VE supplemented concentrate (480 mg DL-α-tocopheryl acetate/kg DM) for 0 (control [CON]), 10 (VE10d), 20 (VE20d), and 30 d (VE30d) before slaughtering at 22 to 24 kg. Simultaneously, 8 unweaned lambs grazed in alfalfa (154 mg α-tocopherol/kg DM) paddocks with their dams and supplemented with the commercial concentrate (ALF). Immediately after slaughter, LM was sampled to determine gene expression. After 24 h of cooling at 4°C, LM was extracted to determine intramuscular fat (IMF) content and fatty acid composition. The IMF content did not differ with the dietary treatment ( = 0.212). Unweaned grazing alfalfa lambs had greater concentration of rumenic acid (C18:2 c9,t11; P0.001) and lower oleic acid (C18:1 c9; = 0.001) content and PUFA n-6:n-3 ratio (P0.001) but similar expression of genes implicated in lipid metabolism compared to the concentrate-fed lambs. Vitamin E supplementation did not modify muscle fatty acid composition; however, it increased the expression of FADS2 and ELOVL6, which are involved in desaturation of long-chain fatty acid and the elongation of SFA and MUFA. The results showed that a short period of VE supplementation, especially 10 (VE10d) and 20 d (VE20d), modified gene expression. Overall, the results showed that VE may be acting as a regulatory factor for transcriptional control of genes related to lipid metabolism in the muscle of Rasa Aragonesa light lambs (22-24 kg live weight and younger than 90 d old).

Meat intramuscular fat (IMF) contributes to meat quality and consumer acceptance. Molecular events that occur during IMF deposition and the identification of genes that are differentially expressed during this process are important to the design of an optimal nutrition plan for animals. In the present study, we examined the effect of the forage type (grazing vs. hay pasture) fed to ewes and the effect of lamb sex on the LM fatty acid (FA) profile and gene expression of suckling lambs (10 to 12 kg of BW at slaughter); ewes received pasture hay (PH) or grazed pasture (GRE). Forage type had a significant effect on IMF FA profile. Ewes grazing green forage (GRE) promoted the formation and deposition of vaccenic acid (C18:1n-7), CLA, and PUFA n-3 in LM from their suckling lambs (P0.05). We found that forage type affected the expression of the sterol regulatory element binding transcription factor 1 (SREBF1) gene in females. However, in males, it modulated stearoyl CoA desaturase (SCD) gene expression (P0.05). Moreover, our results showed that females, independent of the diet of the ewes (PH or GRE), are predisposed to develop fat and to upregulate the expression of key genes of transcriptional factors PPARA, CEBPB, SREBF1, and lipoprotein lipase (LPL) and SCD (P0.05). The data suggest that SREBF1, SCD, and most likely CEBPB gene expression in young suckling lambs is modulated by both lamb sex and forage type fed to ewes. Fatty acid indicators PUFA, n-6/n-3, CLA, and SFA are closely related to LPL, SCD, PPARA, and CEBPB gene expression depending on animal sex or the diet of ewes. This study suggests that grazing pasture affects FA composition promoting greater vaccenic, CLA, and total PUFA n-3 FA in female and male suckling lambs, and it is mediated through the regulation of lipogenic enzyme expression.