Larger litters are resulting in lighter and more variable birth and weaning weights in pigs which will make it even more difficult than before to achieve high intake and growth immediately post-weaning. To overcome the “growth lag” normally experienced at weaning, intake of feed and water should be targeted at levels achieved prior to weaning. Increasing weaning age particularly above 3 weeks will increase growth performance and improve piglet health and targeting increased piglet birth weight will increase post-weaning growth and lifetime performance. Post-weaning diets should contain milk by-products, the most important of which is dried whey, as a source of lactose. It is not necessary to cook cereals for inclusion in post-weaning diets but cereals should be well screened and clean. Acids, prebiotics and probiotics can be effective alternatives to antibiotics in weaned pig diets but the response from their use may not be as predictable as that from conventional antibiotic use. Good quality starter and link diets are necessary for weaned pigs; however, the levels used should be geared towards pig weaning weight, health and the optimization of lifetime growth. We have not found liquid feeding of weaned pigs to increase growth rate but rather to increase feed wastage and reduce piglet growth. However, feeding milk replacer for a short period after weaning can greatly increase piglet growth and gastrointestinal health.
Weaning is arguably the most stressful period in the pig’s life. At weaning the pig is removed from the sow where it has had access to ~20 small feeds of sow’s milk each day. It is removed to unfamiliar surroundings and mixed with strange pigs in pens where the only available food is predominantly vegetable in origin and generally fed in dry form. It is hardly surprising that with such social and nutritional stress the pig generally suffers a growth check in the immediate post-weaning period.
Irish sows now produce 1.7 more live born pigs per litter than they did 10 years ago and increases are likely to continue. However, large litters bring problems, with lighter piglets born and weaned, and greater within-litter variation in piglet birth and weaning weight. This is particularly important since birth weight has a huge influence on lifetime pig growth. We have always had a challenge to maintain pre-weaning growth rates in the early post-weaning period and this challenge is now even greater. Overcoming this post-weaning growth check will reduce mortality, increase lifetime growth and reduce the time needed to bring pigs to their target slaughter weight. Now is an opportune time to take stock of what we have learned about good post-weaning management and nutrition practices with this goal in mind.
Typically in Ireland pigs are weaned at ~26 days of age. Earlier weaning could increase sow productivity due to increased litters per sow per year. However, this can lead to greater health/mortality problems, and feed costs will increase as pigs are introduced to more expensive diets earlier. Leliveld et al. (2013) investigated the effect of weaning age (3, 4 and 5 weeks) on the growth performance of pigs up to 10 weeks of age. With each one week increase in weaning age, feed intake and growth rate increased and feed conversion improved in the first 2 weeks after weaning. When growth performance was measured to the same chronological age (10 weeks of age) feed intake and growth rate increased with each week increment in weaning age. Five week weaned pigs also had improved feed conversion efficiency compared to those weaned at 3 or 4 weeks (Table 1). Previously it was shown that each 1 day increase in weaning age contributes ~500 g of an increase in weight at 28 days post-weaning (Lawlor et al., 2003a). Older pigs adapt more rapidly to solid diets as their gastrointestinal tract is more developed.
Mortality between weaning and 10 weeks of age, and faecal E. coli counts at 10 days postweaning were higher in 3 week weaned pigs compared to those weaned at 4 weeks (Leliveld et al., 2013). Higher amounts of undigested feed are found in the gastrointestinal tract of early weaned pigs compared to those weaned later leading to the proliferation of pathogenic bacteria in the intestine and diarrhoea.
High feed intake and growth rate in the period immediately following weaning is essential if growth rates from weaning to sale are to be maximised. The key to achieving this is to wean heavier pigs. However, a heavy pig at weaning can originate because it was inherently heavier at birth or because, it received preferential management and nutrition during the suckling period. Increasing nutrition and management by creep feeding, offering milk replacer to suckling pigs and reducing litter size were effective in increasing weaning weight by 0.5kg per pig. However, boosting weaning weight in this manner did not influence post-weaning performance and the weight advantage created at weaning disappeared by 14 days postweaning (Lawlor et al., 2002a; Table 2).
Table 1. Effect of weaning age on growth performance (Leliveld et al., 2013)
表1.斷奶日齡對仔豬生長性能的影響(Leliveld等, 2013)
表1、斷奶日齡對生長性能的影響（leliveld等人，2013）
表2、斷奶前后的營養(yǎng)對斷奶后129天的生長性能的影響（實驗1；勞勒等，2002）
Table 2. Effect of pre- and post-weaning nutrition on pig performance to 129 days post-weaning (Experiment 1; Lawlor et al., 2002a).
Conversely, pigs that were heavier at weaning because they were heavier at birth had higher intake and daily gain in the first 4 weeks post-weaning and their weight advantage had increased by 60 % at 26 days post-weaning (Table 3). The differential in weight between heavy and light pigs at weaning (1.3 kg) could be traced back to a 170 g difference in birth weight between the two groups. Similar results are reported extensively and the benefit from a heavy weaning weight is evident up to slaughter weight. This work highlights the importance of achieving heavy birth weights. Pre-weaning management, although important cannot correct for low birth weights. The importance of birth weight in this regard is most likely because lighter pigs at birth have fewer muscle fibres which results in lower lean gain deposition rates and poorer FCE (Dwyer, et al., 1993). It is also important to note that, unless a high nutrient density diet is fed post-weaning, the benefits that arise from having a heavy pig at birth are lost (Lawlor et al., 2002a).