Maintaining Growth in pigs weaned from Large Litters

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)

 

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). 

Table 3. Effect of post-weaning diet on performance of heavy and light pigs from weaning to day 26 post-weaning (Experiment 2; Lawlor et al., 2002a)

It is vitally important to encourage piglets to maintain fluid intake post-weaning. It can take more than a week after weaning for the pig to restore its daily fluid intake to the equivalent of that on the day prior to weaning. According to Fowler and Gill (1989) a suckling pig has equivalent water consumption prior to weaning of ~680ml; however, water intake is only ~290ml in the first day post-weaning and averages ~442ml in the first week after weaning. It is only in the second week post-weaning that water intake averages ~770ml/pig. An adequate supply of fresh potable water is essential where the aim is to maximise post-weaning growth rates. Restricted water flow can reduce feed intake and consequently ADG by 15 %, respectively (Toplis and Tibble, 1994; Table 4). Drinker position is critical, as consumption can be inhibited if they are placed at the incorrect height, angle or position within the pen. Recommendations for the use of bite drinkers and bowls are shown in Table 5. Bowl drinkers are now more common because they waste 30 % less water and it is easier for pigs to find the water source. However, bowl drinkers should be cleaned at regular intervals to ensure a supply of clean water. Push type bowl drinkers have minimal water waste compared to nipple drinkers and float type bowls drinkers (Torrey et al., 2008). Whatever type of drinker is used for weaned pigs, it is important to use the same type also in the farrowing house. 

Table 4. Effect of water flow rate on post-weaning pig performance (Toplis and Tibble, 1994).

 Table 5. Recommendations on drinkers for weaner pigs (Pedersen, 1999)

Daily gain during the first week post-weaning has a positive relationship with pig weight at day 56 post-weaning and particularly so for light weaned pigs (Tokach et al., 1992). There is huge variation in pre-weaning growth rates of pigs. Edwards and Rooke (1999) reported a betweenfarm variation in post-weaning growth rates of 34 % and within-farm variation of 165 %, attributing most of this variation to differences in feed intake.

In Moorepark, average pre-weaning growth rates (birth to weaning at 26 days) of ~260 g/day have been seen (Lawlor, 2000). Maintaining this growth rate in the early post-weaning period is problematic and in practice, intake in the first few days after weaning is normally insufficient to cover even the maintenance requirement, much less to support pre-weaning rates of gain (Lawlor et al., 2002). As a consequence of this, there is often catabolism of fat as the pig strives to balance its energy requirement for maintenance. Another consequence is a reduction in villous height seen after weaning which affects nutrient digestion, thus prolonging the postweaning growth lag and affecting performance to slaughter.

Table 6 explores the average daily feed intake necessary for a range of weaning weights and a range of diets of differing energy density to maintain pre-weaning energy intake levels in the early post-weaning period. It is evident that, on a high health pig unit with good pre-weaning performance, if a starter diet of 16.5 MJDE/kg is provided then pigs would need to consume 420 to 464 g/day before pre-weaning energy intakes from milk are matched. This table also demonstrates that the necessary feed intake per pig is reduced when the energy density of the diet provided is increased. 

Table 6. Calculation of feed intake required post-weaning to match pre-weaning energy intake

Dairy products, though expensive, are very important constituents of diets for pigs in the early post-weaning period due to their effectiveness in improving growth rate and feed efficiency at this time (Lawlor et al., 2005a). The time taken to reach target slaughter weight (~97kg) was reduced by 5 days by feeding a high dairy product starter and link in the post-weaning period compared with a low dairy product starter (Table 8; Lawlor et al., 2003b). In addition to this, mortality, incidence of scour and veterinary interventions are all likely to be reduced while management is made easier when a high dairy product post-weaning diet is offered. However, economics (diet cost and pig price) will dictate the degree of complexity of the diet and its duration of feeding in the commercial situation (Lawlor et al., 2003b).

Including lactose as a carbohydrate source in the diet at levels even as high as 320 to 470 g/kg, increases post-weaning daily gain in weaned pigs. Dried whey contains 650 to 750 g/kg lactose and so it is the most widely used lactose source in starter diets. Crystalline lactose or de-proteinised whey can be used as lactose sources as long as they are of good quality. Skim milk powder is also commonly used in post-weaning diets but is not as critical in the diet as lactose and there is little benefit from substituting casein for soy protein sources for more than 2 weeks after weaning.

When cereals are included in diets for newly weaned pigs they have often been subjected to some form of heat processing. This is generally done to make the carbohydrate fraction of the cereal more available for enzyme digestion in the gut. This is particularly important in newly weaned pigs because of their initially low levels of starch-degrading enzymes. Increased starch availability is normally measured in the laboratory as an increase in the gelatinised starch content in a sample (Table 7).

Steam flaking is a relatively gentle heating process when compared with extrusion, expansion or micronization and is less likely to have negative consequences (formation of enzyme resistant starch and maillard reaction products, heat damage to amino acids). Steam flaking maize and wheat effectively increased the level of gelatinized starch in both maize and wheat (Table 7) but did not benefit post-weaning or lifetime pig performance. The response to inclusion of steam flaked maize and wheat in the post-weaning diet was not influenced by weaning age, weaning weight , level of dairy products in the diet (Lawlor et al., 2003a ;Table 8) or the sequence of feeding raw or uncooked cereals during the post-weaning period (Lawlor et al., 2003b). It is therefore difficult to justify the increased food cost associated with the process. Although we did not investigate the inclusion of barley in post-weaning diets, others found a 14% increase in average daily gain when the barley component of a post-weaning diet was extruded. This is most likely due to the higher fibre content in the barley. 

Table 7. Starch and gelatinised starch values for wheat and maize used in experimental diets (Lawlor et al. 2003b)

 Table 8. The effect of cooking maize and wheat (un-cooked or cooked) and level of dairy product (high or low) on pig performance from weaning to slaughter (Lawlor et al., 2003b)

 

Cereals are frequently thoroughly screened and cleaned in advance of any cooking process and these processes alone are beneficial in terms of reducing their microbial load and improving growth performance. Responses to cooking maize and wheat, in particular, are very variable in the literature and it is possible that where responses are seen that it may be due at least in part to a decontamination effect. Therefore, if raw cereals are to be used in post-weaning diets then quality well screened grains with a low microbial load should always be used.

Early weaned pigs produce insufficient levels of gastric acid which can result in a high stomach pH. As a result, the digestion of nutrients, especially protein is reduced. Moreover, high pH is favourable for the proliferation of diarrhoea-causing micro-organisms in the weaned pig. The use of organic acids has been suggested as a means of lowering gastric acidity in weaned pigs and has been reported to improve growth performance. The benefits that arise from feeding organic acids include an inhibitory effect on pathogenic bacteria, increased amino acid and energy digestibility and an increase in nitrogen retention. The response to organic acids was previously found to be greatest in diets with low levels of dairy products. Dairy products contain lactose which can be fermented to lactic acid thus reducing gut pH. In addition, milk proteins are much more easily digested than vegetable proteins in the immature gut. The response to diet acidification might be expected to be reduced when provided in post-weaning diets to pigs that were provided with creep feed prior to weaning as creep feeding of suckling pigs is thought to benefit post-weaning pig performance by stimulating gastric acid production and enzyme secretion.

Unexpectedly, Lawlor et al. (2005a) found that the response to a dietary acid was not influenced by the level of dairy product in the diet or whether pigs had or had not been creep fed while suckling the sow. Feed intake in one experiment was increased by ~32% in week 1 and by 11% over the first 3 weeks after weaning due to the dietary addition of fumaric acid. This increase in feed intake translated into a ~20% increase in growth rate in the first 3 weeks post-weaning. However, the response to diet acidification was not always consistent between experiments with a response to fumaric acid seen in 2 of the 3 experiments reported and the magnitude of the response varied greatly between the two experiments where a positive response was found. Similar results were found in later work (Lawlor et al., 2006). It was thought that microbial challenge during the post-weaning period has a major influence on the response to fumaric acid supplementation. 

Table 9. Effect of pre-weaning creep feeding on response of weaned pigs to dietary fumaric acid (Lawlor et al 2005a)

An alternative approach to diet acidification, which can yield similar benefits, is to formulate post-weaning diets to have a low acid binding capacity. Acid binding capacity can be defined as the amount of acid in milliequivalents (meq) of Hydrochloric acid required to lower the pH of 1kg of feed sample to (a) pH 4.0 (ABC-4) and (b) pH 3.0 (ABC-3) (Lawlor et al 2005b). The lower the acid-binding capacity of the feed, the lower the amount of gastric acid that is required to lower its pH and create an acidic environment in the stomach, which is beneficial to pig health and digestion. Lawlor et al. (2005b) published a data set of acid-binding capacity values for a wide range of feed ingredients. There is great variation between ingredients with regard to acid-binding capacity values. For this reason, complete post-weaning diets can be formulated to have a low acid-binding capacity by selection of ingredients from this dataset with low acid-binding capacity and by using the acid-binding capacity value for each ingredient in the diet formulation matrix. Such diets can be used when a high gastric pH is likely to be a problem (e.g., at weaning) and as an effective alternative to diet acidification. When such diets were formulated by reducing calcium and phosphorus content in the diet formulation, feed intake in the first week after weaning was increased by 17% (Lawlor et al., 2006). This is the time where we need to increase feed intake as it has such an influence on subsequent growth performance.

Probiotics are ‘live microorganisms which when administered in adequate amounts confer a health benefit on the host’ (FAO/WHO, 2001). They offer potential as an alternative to antibiotics for pigs, both as a means of controlling enteric pathogens and improving growth performance. Their possible modes of action include modulation of the immune system, competitive exclusion of pathogens in the gut and antimicrobial production. Prieto et al. (2014) evaluated the safety and efficacy of a marine-derived Bacillus pumilus strain for use as an infeed probiotic in newly weaned pigs. The B. pumilus used was pre-screened and selected for its ability to inhibit porcine pathogenic E. coli (Prieto et al., 2013). The Bacillus strain was administered to weaned pigs fed a non-medicated diet and compared to a negative control treatment without antibiotic or pharmacological levels of zinc oxide (non-medicated treatment) and a positive control treatment containing apramycin and pharmacological levels of zinc oxide (medicated treatment). The study herd was at the time experiencing oedema disease during the post-weaning period. The B. pumilus strain decreased ileal E. coli counts in a manner similar to the medicated treatment but without the reduction in growth performance (Table 10) and possible liver toxicity found with the medicated treatment (Prieto et al., 2014). 

Table 10. Effect of feeding non-medicated, medicated or B. pumilus treatments for 22 days on post-weaning pig growth performance^1,2 (Prieto et al., 2014)

 

Casey et al. (2007) investigated the effects of oral treatment of pigs with a mixture of five lactic acid bacteria probiotic strains, on both clinical and microbiological signs of Salmonella Typhimurium infection. Following probiotic administration for 6 days, animals were challenged orally with S. Typhimurium and monitored for 23 days post-infection. Animals treated with probiotic showed reduced incidence, severity, and duration of diarrhea, gained weight at a faster rate than control pigs, and had reduced fecal shedding of Salmonella

Prebiotics, like probiotics, are used as a strategy to influence the composition of the gastrointestinal microflora towards a more favorable balance, by reducing the amount of harmful/pathogenic species and promoting the growth of species thought to have beneficial effects on host health (O’Sullivan et al., 2010). A prebiotic is “a selectively fermented ingredient that allows specific changes, both in the composition and/or activity of the gastrointestinal microflora that confers benefits upon the host wellbeing and health”. Prebiotics are resistant to digestion in the upper gut (i.e. resistant to acid and enzymes), a selective substrate for the growth of beneficial bacteria and able to induce luminal or systemic effects that are beneficial to host health. To date only inulin, oligofructose, galactooligosaccharides and lactulose are considered true prebiotics; however, other potential sources of prebiotics such as seaweed-derived compounds are currently being explored (O’Sullivan et al., 2010). 

There is no disputing the necessity to feed nutrient-dense, milk product-rich diets in the postweaning period to ensure fast and efficient lifetime pig growth (Lawlor et al., 2002a; 2003b; 2005a). However, these diets are expensive and their overuse must be avoided. Feeding small quantities of these diets post-weaning may not maximize post-weaning performance but may be sufficient to optimize lifetime performance. Kavanagh (1995) found that pigs given 1 kg starter diet and 4 kg link diet were 2 kg lighter at 28 days post-weaning than pigs given 3 kg of starter and 8 kg link diet. However, by day 40 post-weaning this 2-kg weight advantage had been reduced to a 1-kg weight advantage and as pigs were not followed through to slaughter weight it is not known if full compensatory growth would have occurred by this time. Likewise, Lawlor et al. (2002a) compared two post-weaning dietary regimes: 1. 10kg starter followed by link to 27 days post-weaning and 2. 3kg starter followed by 10kg link followed by weaner diet to 27 days. In this experiment pig weight at day 27 was increased by 1.2kg and feed conversion efficiency was improved between weaning and day 27 post-weaning when the higher levels of starter and link were fed. However, the weight advantage was lost by day 50 post-weaning and pigs from both treatments reached target slaughter weight at the same age and had similar FCE from weaning to slaughter. This work also found that the benefit from feeding starter diet elapsed after day 10 post-weaning (Lawlor et al., 2002a).

In a more recent study Leliveld et al. (2013) fed four different allocation levels of starter and link diet (Table 11), and found that the allocation levels of starter and link diets immediately post-weaning had little influence on post-weaning growth performance. Moreover, Leliveld et al. (2013) found that weaning age (3, 4 or 5 weeks) did not affect the response to the level of starter and link diets fed. If growth performance was looked at alone this would suggest that there was no benefit from feeding more than 1kg starter and 3kg link diet. However, this should be treated with caution as mortality was higher in this study when low levels of starter and link were fed.

Bearing the above in mind it might be possible to feed allocations of starter and link as low as 1 and 3kg respectively to heavy weaned pigs in a high health situation. However, lighter weaned pigs, which are more likely in large litters, will likely benefit from a higher allocation of starter and link. In addition, if there are health problems on a unit then pigs will also likely benefit from a higher allocation of starter and link. 

Table 11. Effect of allocation of starter and link diets on growth performance (Leliveld et al., 2013)

Liquid feeding reportedly stimulates post-weaning feed intake and growth rate in pigs. A series of four experiments to examine the effect of liquid feeding of weaned pigs on postweaning growth performance and residual effects up to slaughter were conducted at Moorepark (Lawlor et al. 2002b). Table 12 summarises the results from one of these experiments. Surprisingly, feeding liquid feed to weaned pigs did not increase pig growth rate and in fact, in other experiments decreased it. It was also quite wasteful, leading to unacceptable feed efficiency. With fermented liquid feed, uncontrolled fermentation of the feed is highly unpredictable and the growth of undesirable bacteria, yeasts and moulds can cause problems. A starter culture was deliberately added to produce fermented liquid feed in this study; however, DM gain/feed was still decreased. It is concluded that there is no benefit from liquid feeding weaned pigs whether in fresh, acidified or fermented form. 

Table 12. Effect of liquid feeding on pig performance^a (LSM^b ± SEM; Lawlor et al. 2002b)

Feeding milk replacer in the immediate post-weaning period could be an effective strategy to increase feed intake and daily gain in the critical few days after weaning. Feeding a milk replacer plus starter diet for 4 days after weaning increased daily gain by 20-30% in the first week after weaning when compared with feeding the starter diet alone. The pigs also contained more protein and fat in their carcasses and had longer intestinal villi than pigs that were left on the sow, or pigs that were weaned directly onto starter diet (Zijlstra et al., 1996). Low post-weaning intakes are responsible for the reduction in villous height seen after weaning. This villous shortening accentuates the low growth rates normally observed in the first week after weaning. However, offering liquid milk diets at regular intervals during this period could help maintain gut integrity, and thereby help overcome the growth lag at this time (Pluske et al., 1995).

Feeding liquid milk post-weaning is not widely practiced due to economic and labour considerations. However, this is a strategy that could benefit immediate post-weaning feed intake and growth of, in particular, light weaned pigs. Extreme caution would be advised regarding hygiene for the system used to both deliver and feed the milk replacer to avoid associated health problems.