Residual feed intake phenotype and gender affect the expression of key genes of the lipogenesis pathway in subcutaneous adipose tissue of beef cattle

Background: Feed accounts for up to 75% of costs in beef production systems,thus any improvement in feed efficiency(FE) will benefit the profitability of this enterprise.Residual feed intake(RFI) is a measure of FE that is independent of level of production.Adipose tissue(AT) is a major endocrine organ and the primary metabolic energy reservoir.It modulates a variety of processes related to FE such as lipid metabolism and glucose homeostasis and thus measures of inter-animal variation in adiposity are frequently included in the calculation of the RFI index.The aim of this study was to determine the effect of phenotypic RFI status and gender on the expression of key candidate genes related to processes involved in energy metabolism within AT.Dry matter intake(DMI) and average daily gain(ADG) were measured over a period of 70 d for 52 purebred Simmental heifers(n = 24) and bulls(n = 28) with an initial BW±SD of 372±39.6 kg and 387±50.6 kg,respectively.Residual feed intake was calculated and animals were ranked within gender by RFI into high(inefficient; n = 9 heifers and n = 8 bulls)and low(efficient; n = 9 heifers and n = 8 bulls) groups.Results: Average daily gain ±SD and daily DMI ±SD for heifers and bul s were 1.2±0.4 kg and 9.1±0.5 kg,and 1.8±0.3 kg and 9.5±1 kg respectively.High RFI heifers and bulls consumed 10% and 15% more(P < 0.05) than their low RFI counterparts,respectively.Heifers had a higher expression of all genes measured than bulls(P < 0.05).A gender × RFI interaction was detected for HMGCS2(P < 0.05) in which high RFI bulls tended to have lower expression of HMGCS2 than low RFI bulls(P < 0.1),whereas high RFI heifers had higher expression than low RFI heifers(P < 0.05) and high RFI bulls(P < 0.05).SLC2 A4 expression was consistently higher in subcutaneous AT of low RFI animals across gender.Conclusion: The findings of this study indicate that low RFI cattle exhibit upregulation of the molecular mechanisms governing glucose metabolism in adipose tissue,in particular,glucose clearance.The decreased expression of SLC2 A4 in the inefficient cattle may result in less efficient glucose metabolism in these animals.We conclude that SLC2 A4 may be a potential biomarker for RFI in cattle.

Effect of supplementation with n-3 polyunsaturated fatty acids and/or β-glucans on performance, feeding behaviour and immune status of Holstein Friesian bull calves during the pre-and post-weaning periods

Background: Previous research in both calves and other species has suggested n-3 polyunsaturated fatty acids(PUFA) and β-glucans may have positive effects on immune function. This experiment measured performance,behaviour, metabolite and immunological responses to pre-weaning supplementation of dairy bull calves with n-3 PUFA in the form of fish oil and β-glucans derived from seaweed extract. 44 Holstein Friesian bull calves, aged 13.7± 2.5 d and weighing 48.0 ± 5.8 kg were artificially reared using an electronic feeding system. Each calf was offered5 L(120 g/L) per day of milk replacer(MR) and assigned to one of four treatments included in the MR,(1) Control(CON);(2) 40 g n-3 PUFA per day(FO);(3) 1 g β-glucans per day(GL) and(4) 40 g n-3 PUFA per day & 1 g/d β-glucans(FOGL) in a 2 × 2 factorial design. Milk replacer and concentrate was offered from d 0–62(pre-weaning),while concentrate provision continued for a further 31 d post-weaning period. Individual daily feed intake and feeding behaviour was recorded throughout, while bodyweight and blood analyte data were collected at regular intervals.Results: Overall mean concentrate DMI from d 0–93 was 1.39, 1.27, 1.00 and 0.72 kg/d for CON, FO, GL and FOGL calves, respectively(SEM = 0.037;P < 0.0001). Calves supplemented with GL were significantly lighter(P < 0.0001) at both weaning(d 62) and turnout to pasture(d 93) than un-supplemented calves, with a similar effect(P < 0.0001)evident for calves receiving FO compared to un-supplemented contemporaries. Supplementation with GL reduced the number of unrewarded visits where milk was not consumed(P < 0.0001) while supplementation with FO increased mean drinking speed(P < 0.0001). Supplementation with GL resulted in greater concentrations of haptoglobin(P = 0.034), greater serum osmolality(P = 0.021) and lower lymphocyte levels(P = 0.027). In addition,cells from GL supplemented calves exhibited a lower response than un-supplemented contemporaries to both Phytohaemagglutinin A stimulated IFN-γ(P = 0.019) and Concanavalin A stimulated IFN-γ(P = 0.012) following in vitro challenges.Conclusions: Pre-weaning supplementation of bull calves with either n-3 PUFA or β-glucan resulted in reduced voluntary feed intake of concentrate and consequently poorer pre-weaning calf performance. There was no evidence for any beneficial effect of either supplementation strategy on calves’ immune responses.