Insulin secretion, body composition and pig performance are altered by feeding pattern Ronald E. Newman A , Jeffery A. Downing A , Peter C. Thomson A , Cherie L. Collins B , David J. Henman B and Stuart J. Wilkinson A,C A Faculty of Veterinary Science, University of Sydney, Camden, NSW 2570, Australia. B Rivalea Australia Pty Ltd, Corowa, NSW 2646, Australia. C Corresponding author. Email: stuart.wilkinson@sydney.edu.au Abstract. Three studies investigated the effect of feeding strategy on production performance and endocrine status of growing pigs. For Experiment 1, 20 entire male pigs (70.0  4.6 kg) were allocated randomly to individual pens in one of four climate-controlled rooms. Pigs were fed for 23 days either ad libitum or entrained to feed bi-phasically for two 90-min periods. For Experiment 2, 20 entire male pigs (41.2  3.5 kg) were housed as per Experiment 1. Pigs were fed for 49 days either ad libitum or fed bi-phasically for two 60-min periods. For Experiment 3, 100 female pigs (66.1  3.5 kg) were randomly allocated to individual pens within a commercial piggery and fed for 42 days either ad libitum or bi-phasically for two 60-min periods. Ear vein catheters were inserted into 10 pigs from each group and hourly blood samples were collected for 24 h in Experiments 1 and 2 and for 11 h in Experiment 3. Plasma insulin, non-esterified fatty acid and glucose concentrations were determined in Experiments 1 and 2, and glucose and insulin concentrations in Experiment 3. Feed intake and performance were recorded in all experiments and carcass composition was assessed by computed tomography for Experiment 2. There were no differences in final liveweight between the two treatment groups for all experiments. Pigs fed for two 90-min periods (Experiment 1) showed no difference in feed intake when compared with feeding ad libitum. Pigs in Experiment 2 fed for two 60-min intervals consumed 2.49 kg/pig.day compared with those fed ad libitum that consumed 2.68 kg/day (P = 0.057). In Experiment 3, pigs fed twice daily consumed 2.82 kg/pig.day compared with 2.91 kg/pig.day in ad libitum-fed pigs (P = 0.051). Bi-phasic fed pigs in Experiment 2 had improved (P < 0.05) feed conversion efficiency compared with pigs fed ad libitum. For all experiments, there was no difference in plasma glucose concentrations between the two treatments. In all three experiments, the circulating insulin concentrations for pigs fed ad libitum remained at a constant level throughout the sampling period. However, plasma insulin concentrations for the bi-phasic fed pigs significantly increased ~1 h after both feeding periods during all three experiments. Insulin secretion of pigs fed for two 90-min periods differed from that of pigs fed for two 60-min periods. Plasma insulin concentration increased five-fold following feeding for 60 min, compared with that in pigs fed for 90 min, which increased two-fold. Bi-phasic-fed pigs from Experiment 2 had reduced (P < 0.05) total carcass fat and significantly increased muscle when compared with pigs fed ad libitum. The data showed that feeding pigs at two succinct periods aligned insulin secretion to the time of feeding. Pigs fed for 60 min, unlike those fed for 90-min intervals, had reduced feed intake in comparison to those fed ad libitum. This may suggest that the duration of the feeding bout is important for this response and this may in turn influence both energy balance and the way energy is partitioned. Additional keywords: carcass composition, feed efficiency, feed intake, pigs. Received 27 March 2013, accepted 8 July 2013, published online 28 August 2013 Introduction Ad libitum feeding is the most common feeding pattern used in commercial pig production and a major management strategy used to optimise both pig performance and efficiency of feed utilisation. A principal objective for most pig producers is to increase lean gain while limiting fat tissue deposition (Quiniou et al. 1999). Feeding pattern has been shown to have effects not only on feed efficiency (Cohn et al. 1962; Scrimgeour et al. 2008) but also on carcass composition (Leveille 1970; Partridge et al. 1985; Persson et al. 2008). For optimal protein deposition in growing animals, a balanced supply of amino acids and energy is required (van den Borne et al. 2007). However, it is the metabolic hormones such as insulin that regulate metabolism, which has an important role in the metabolism of glucose, fats and proteins (Stockhorst et al. 2004). Metabolic hormone secretion patterns and concentrations, particularly growth hormone and insulin, are altered with differing feeding strategies, and this appears to have important consequences for performance (Steffens 1967; Scrimgeour et al. 2008). A recent study in pigs fed ad libitum identified CSIRO PUBLISHING Animal Production Science http://dx.doi.org/10.1071/AN13120 Journal compilation Ó CSIRO 2013 www.publish.csiro.au/journals/an