The production performance and financial outcomes associated with weaner diet complexity for pigs of different weight classes at weaning were examined in this experiment. A total of 720 weaner pigs (360 entire males and 360 females) were selected at weaning (27 ± 3 d) and allocated to pens of 10 based on individual weaning weight (light weaning weight: pigs below 6.5 kg; medium weaning weight: 6.5 to 8 kg; heavy weaning weight: above 8.5 kg). Pens were then allocated in a 3 × 2 × 2 factorial arrangement of treatments with the respective factors being weaning weight (heavy, medium and light; H, M and L, respectively), weaner diet complexity (high complexity/cost, HC; low complexity/cost, LC), and gender (male and female). Common diets were fed to both treatment groups during the final 4 weeks of the weaner period (a period of 39 days). In the first 6 d after weaning, pigs offered the HC diets gained weight faster and used feed more efficiently than those offered the LC diets (P = 0.031). Pigs fed a HC diet after weaning tended to be heavier at the sale live weight of 123 d of age compared with pigs fed the LC diet (P = 0.056). There were no other main effects of the feeding program on growth performance through to slaughter. Weaning weight had a profound influence on lifetime growth performance and weight at 123 d of age, with H pigs at weaning increasing their weight advantage over the M and L pigs (101.3, 97.1, 89.6 kg respectively, P < 0.001). Cost-benefit analyses suggested there was a minimal benefit in terms of cost per unit live weight gain over lifetime when pigs were offered a HC feeding program to L, with a lower feed cost/kg gain. The results from this investigation confirm the impact of weaning weight on lifetime growth performance, and suggest that a HC feeding program should be focused on L weaner pigs (i.e., weaning weight less than 6.5 kg at 27 d of age) in order to maximise financial returns.

The β-agonist ractopamine is a dietary ingredient that improves growth and increases the lean mass with little change in fat mass in gilts and barrows. Limited data in boars indicate that dietary ractopamine may increase lean tissue and decrease fat deposition, whereas there are no data for immunocastrated boars. The aims of this investigation were 1) to assess whether the growth performance of all sexes could be maintained over 31 d by using a step-up dietary ractopamine feeding program of 5 mg/kg of ractopamine for the first 14 d, then increasing the dose to 10 mg/kg for a further 17 d, and 2) to determine if dietary ractopamine would increase lean mass in all sexes and decrease fat mass in boars and immunocastrated boars. The study involved 286 pigs randomized and proportionally allocated by breed into 24 groups of 11 or 12 pigs at 17 wk of age, with equal groups of boars, immunocastrated boars, and gilts. Dietary ractopamine decreased (P = 0.005) ADFI during the first 2 wk, particularly in the intact and immunocastrated boars, with the reduction in ADFI being maintained in the immunocastrated boars after the increment in dietary ractopamine. Daily BW gain was not altered by dietary ractopamine during the first 2 wk, but was increased (P < 0.001) after the increment in dietary ractopamine. Dietary ractopamine decreased (P ≤ 0.033) feed conversion ratio in all sexes with the response being greater after the increase in dietary ractopamine. Carcass weight was increased (P < 0.001) by dietary ractopamine in all sexes, whereas back fat tended (P = 0.076) to be reduced in the immunocastrated boars. Dietary ractopamine increased (P = 0.018) lean tissue mass by 4.0, 4.8, and 6.5 kg in the intact boars, gilts, and immunocastrated boars, respectively. In the entire and immunocastrated boars, the increase in lean tissue was accompanied with a decrease (P = 0.004) in fat mass. There was little effect of dietary ractopamine on fat mass in gilts. However, carcass percent fat was decreased (P = 0.004) and percent lean increased (P = 0.006) in all sexes. Immunocastration caused a decrease in lean tissue mass and an increase in fat mass and an increase in ADFI in the last one-half of the study. Dietary ractopamine may decrease fat mass in intact and immunocastrated boars and offers an excellent means of maximizing the effects of immunocastration and minimizing the increase in fat mass sometimes observed in immunocastrated boars. Copyright © 2009. American Society of Animal Science .

The influences of creep feed composition and piglet weaning age on apparent creep feed disappearance and post-weaning performance were examined. A total of 24 gilts and 72 multiparous sows were selected at farrowing, and their litters allocated to a 2 by 2 factorial arrangement of treatments with the factors being weaning age (22 or 29 days of age) and the composition of the creep feed [simple (diet based predominately on cereals and animal and vegetable protein sources) or complex (diet based predominately on cereals, animal protein sources and 300 g/kg whey powder)]. Creep feed was offered to all litters from 9 days of age to weaning. While creep feed disappearance did not affect pre-weaning growth performance, there was a greater disappearance of the simple creep feed than the complex creep feed from 9 days of age to weaning (776 versus 461 g/litter, respectively, P = 0.004). Apparent creep feed intake from individual piglets in a subset of litters was assessed at three time points (16 and 19 days of age and at weaning), allowing the characterisation of individual pigs as good, moderate, small or non-eaters. There was no difference between treatment groups (?2 = 6.27, P = 0.71) in the characterisation of apparent creep feed disappearance by individual piglets, however piglets offered the simple creep diet before weaning consumed more feed (P = 0.004) and gained weight faster (P = 0.007) during the first 5 days after weaning than those animals offered the complex creep diet. Feed intake from weaning to 49 days of age also tended to be greater in pigs offered the simple creep diet before weaning (P = 0.053), with this difference reflected in daily gain from weaning to 49 days of age (P = 0.051). Despite these differences, creep feed composition did not influence lifetime growth performance or carcass composition. Pigs weaned at 22 days of age were heavier midway through the weaner period (49 days of age) than pigs weaned at 29 days of age (15.2 versus 14.3 kg, respectively, P = 0.009), and tended to grow faster from birth to slaughter (616 versus 610 g/day, respectively, P = 0.079). These data suggest that the provision of a complex creep diet during lactation may not improve lifetime growth performance above that of a less expensive creep diet. Weaning age may however influence lifetime performance, with weaning at 29 days of age tending to reduce rate of gain from birth to slaughter.

The backfat of pig carcasses is greater in spring than summer in Australia. The unexplained seasonal variation in carcass backfat creates complications for pig producers in supplying consistent lean carcasses. As a novel explanation, we hypothesised that the increased carcass fatness in spring was due to a greater percentage of born-light progeny from sows that were mated in summer and experienced hot conditions during early gestation. The first part of our experiment compared the birth weight of piglets born to the sows mated in summer (February, the Southern Hemisphere) with those born to sows mated in autumn (May; the Southern Hemisphere), and the second part of the experiment compared the growth performance and carcass fatness of the progeny that were stratified as born-light (0.7–1.1 kg) and born-normal (1.3–1.7 kg) from the sows mated in these two seasons. The results showed that the sows mated in summer experienced hotter conditions during early gestation as evidenced by an increased respiration rate and rectal temperature, compared with those mated in autumn. The sows mated in summer had a greater proportion of piglets that were born ≤1.1 kg (24.2% vs. 15.8%, p < 0.001), lower average piglet birth weight (1.39 kg vs. 1.52 kg, p < 0.001), lower total litter weights (18.9 kg vs. 19.5 kg, p = 0.044) and lower average placental weight (0.26 vs. 0.31 kg, p = 0.011) than those mated in autumn, although litter sizes were similar. Feed intake and growth rate of progeny from 14 weeks of age to slaughter (101 kg live weight) were greater for the born-normal than born-light pigs within the progeny from sows mated in autumn, but there was no difference between the born-light and normal progeny from sows mated in summer, as evidenced by the interaction between piglet birth weight and sow mating season (Both p < 0.05). Only the born-light piglets from the sows mated in summer had a greater backfat thickness and loin fat% than the progeny from the sows mated in autumn, as evidenced by a trend of interaction between piglet birth weight and sow mating season (Both p < 0.10). In conclusion, the increased proportion of born-light piglets (0.7–1.1 kg range) from the sows mated in summer contributed to the increased carcass fatness observed in spring.

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.

Five hundred and ten multiparous sows were allocated at 66 days after mating to one of 6 dietary treatments that were imposed for the subsequent 35 days. The dietary treatments were 5 feeding levels of 2.2, 2.6, 3.0, 3.4, and 3.8 kg/day of a gestation diet containing 12.9 MJ DE/kg, 127 g crude protein/kg, and 5.6 g lysine/kg, plus a protein intake treatment where sows received 2.8 kg/day of a lactation diet containing 13.8 MJ DE/kg, 168 g crude protein/kg, and 8.3 g lysine/kg. After the treatment period, all sows were offered the lactation diet at the common feeding level of 3.0 kg/day and after farrowing, all sows were offered this diet ad libitum throughout lactation. Increasing feeding levels between Day 66 and Day 101 of pregnancy increased (P < 0.001) liveweight gain prior to farrowing but increased (P < 0.001) liveweight loss during lactation. The majority of the extra maternal energy intake during mid to late gestation was deposited as maternal gain. These linear weight responses during lactation were explained by the significant inverse relationship between voluntary daily feed intake in lactation (FI) and average daily digestible energy intake in the previous gestation (DE): AR05195_E1.gif Neither increasing the feeding level during mid to late gestation nor increasing the protein content of the diet had any significant effect on litter birth weight, average piglet birth weight, or the standard deviation of individual piglet birth weight within the litter. In addition, there were no significant effects of gestation feeding treatments on litter size weaned or weaning weight. Furthermore, neither increasing the feeding level during mid to late gestation nor increasing the protein content of the gestation diet had any significant effect on subsequent fertility or litter size. In conclusion, when average individual piglet birth weight is already well in excess of 1.5 kg, there is no significant response to feed intake levels between 2.2 and 3.8 kg/day when offered between Day 66 and Day 101 of gestation.