Bridging the post-weaning piglet growth gap: the NuPro® experience in the Asia Pacific region

The piglet at weaning is faced with numerous stressors that include separation from the sow and litter mates, being moved to a different shed and environmental conditions, and changes in feed type and feeder. In response to these stressors, the weaned piglet’s growth rate is reduced. This ‘post-wean growth check’ results in growth performance of the weaned piglet that is significantly below genetic potential. This growth deficit is commonly referred to as the ‘post-wean growth gap.’

A significant amount of research has been devoted to the numerous factors responsible for this drop in performance and the interventions that alleviate the post-wean piglet growth gap (reviews by Black et al., 2001; Pluske et al., 1997; Le Dividich and Herpin, 1994); however, it continues to be a major problem in just about every type of pig production system in the Asia Pacific region.

In this paper we examine some of the effects of piglet post-wean growth check on overall growth performance and profitability. In the latter part of this paper we highlight recent research investigating the use of NuPro®, a functional nutrient source, and its impact on post-wean growth check and wean-to-slaughter growth performance and profitability.


Post-wean piglet growth gap in the Asia Pacific region

The rate of growth and the feed conversion ratio of pigs raised under commercial environments are inferior compared with their genetic potential or growth under ideal conditions. Campbell and Taverner (1985) measured growth rates in excess of 1110 g/ day for entire male pigs when grown from 45 to 90 kg live weight in a research environment, yet the growth rate of an identical strain and sex of pigs grew at less than 800 g/day over the same weight range in a commercial environment. Commercially grown pigs were also fatter when fed the same amount of feed compared with their counterparts grown under ideal conditions (Williams, 1998), indicating that they were not depositing body protein to their genetic potential.

Numerous inter-related factors influence the post-wean piglet growth-gap, among which are weaning age and weight, group size, stocking rate, air quality and cleanliness of the weaner environment, disease and microbial load, climate, pig temperament, pig response to stressors, feed quality and feed presentation, water quality and supply. The impact of the post-wean growth gap of commercially grown pigs has been estimated to decrease the profitability of pig enterprises by as much as 25% (Black et al., 1994). Understanding and overcoming the factors that cause this post-wean growth gap therefore represent a significant opportunity for pig production enterprises in the Asia Pacific.

The modern piglet has the genetic potential to reach a bodyweight of 30 kg at 70 days of age, and 120 kg at 170 days of age (Close, 2002). The feed intake and growth rates required to achieve these liveweights in the post-weaning period are outlined in Table 1. Piglet weight at weaning and growth rate immediately post-weaning have a major influence on whether the pig can achieve these targets. For example, an increase of 0.1 kg in the weight of the piglet at weaning can result in that animal reaching the target slaughter weight one day earlier, whilst an increase in the post-wean growth rate by just 5-10 g/day also represents approximately one day less to slaughter (Varley, 2004).






Table 2 highlights the wean-to-slaughter growth performance of pig production systems in the Asia Pacific region. These data were collated during the Premier Pig Program™ (Close and Turnley, 2004) workshops held in the region during 2006. The growth gap for a number of countries in the Asia Pacific region varies widely with a low of 11 days compared with a high of 31 days. Based on feed costs alone, the estimated cost of the post-wean growth gap per pig ranges from US$6.05 to approximately US$17.00. Whilst these data are based on estimates only, they do highlight the significant increase in production costs associated with the post-wean growth gap.







Role of nutrition in reducing the post-wean growth gap

Structural and functional changes in the small intestine such as villous atrophy and crypt hyperplasia cause a decrease in digestive and absorptive capacity in the weaned pig and are key contributors to the growth check in weaned piglets and the post-wean growth gap observed in commercial pig herds. Mediators of intestinal structure and function post-weaning have been widely reviewed and have been shown to reduce the impact of the post-wean growth gap (Cranwell, 1995; Pluske et al., 1997). Mediators and related considerations include enteropathogens, transient hypersensitivity to dietary antigens, the withdrawal of milk-borne growth-promoting factors, and food intake and other dietary exogenous growth factors.

Voluntary food intake in the post-weaning period is very low and variable. Bark et al. (1986) concluded that during the post-weaning period, pigs often fail to consume sufficient food to meet the energy requirement for maintenance. Le Dividich and Herpin (1994) summarized several data sets and concluded that the metabolisable energy (ME) requirement for maintenance is not met until the fifth day post-weaning, with preweaning ME intake not being attained until the end of the second week post-weaning.

Additionally, the presence of food in the intestinal lumen is one of the most potent stimuli of intestinal cellular proliferation in the baby pig (Diamond and Karasov, 1983). The absence of nutrients from the gut lumen, such as that which occurs post-weaning, has marked effects on the rate of cell differentiation and cell turnover, resulting in a significant growth check. Hence it is crucial that the food intake and its consequent physical presence in the gastrointestinal tract be maintained to promote the structural and functional integrity of the intestinal mucosa, thereby maintaining growth performance and minimizing the post-wean growth gap.

Similarly, the inclusion of functional nutrients in piglet diets can enhance the structure and function of the piglet gut, thereby increasing nutrient absorption and improving growth performance. The provision of oral glutamine to the baby pig, for example, has been shown to support mucosal growth thereby maintaining villous integrity and the structure and function of the small intestine. Pluske et al. (1996) reported a linear increase in crypt depth with increasing glutamine intake in pigs fed ewes’ whole milk for five days post-weaning.


Nucleotides and NuPro®

Nucleotides and their related products are yet another example of functional nutrients that play key roles in many biological processes in the human baby (Carver, 2003). Numerous human and animal studies suggest that dietary nucleotides play a role in the development of the gastrointestinal and immune systems that collectively reduce the growth check that occurs in almost all baby mammals post-weaning (Rutz et al., 2006). NuPro® (Alltech Inc.) is manufactured from the cell contents of a specific strain of the yeast Saccharomyces cerevisae. It is a rich source of highly digestible amino acids with a crude protein content of approximately 45%.

However, it is the other components of NuPro® that make it more than just a high quality source of amino acids and enhance its functional properties. These include (i) glutamate, which gives the product a distinct flavour and consequently improves palatability of the feed resulting in improved feed intake; (ii) inositol, a vitamin that is a fundamental component of cell membranes and is necessary for the proper function of nerves, brain and muscles in the body; and (iii) nucleotides, which are important for immunity and gut health.

The initial series of studies exploring the potential of NuPro® to replace plasma proteins in pig diets has been previously summarized (Tibbetts, 2002). The university and field studies conducted have shown equal or better performance when uniformly balanced diets were fed. Among the findings was that although plasma proteins derived from cattle or pigs are very effective intake enhancers in most trials, performance in terms of growth and feed efficiency did not always follow the improved intake, especially if piglets were disease-challenged. Mahan et al. (2001) demonstrated that peptide protein products in combination with yeast extract could completely replace plasma protein if diets were correctly formulated. In addition, in diets not containing blood plasma, NuPro® has been shown to improve feed intake against controls and other animal protein sources (Maribo, 2001).


EXPERIENCE WITH NUPRO® IN THE ASIA PACIFIC REGION

Feed intake, growth rate and liveweight gain

As discussed earlier, feed intake in the post-weaned piglet is both low and variable resulting in a growth check that can affect the growth performance in the wean-to-finisher period. Low feed intake continues to be a major factor in all growth phases in the Asia Pacific region with ambient temperature perhaps being the biggest limiting factor.

The inclusion of NuPro® in piglet diets in both research and commercial studies has been shown to significantly increase feed intake of the weaned piglet (Figure 1). Research and commercial studies in the Asia Pacific region (Australia, China, Philippines and Taiwan) indicate that the feed intake in piglets was increased on average by 15%, compared with research studies conducted in the US and Europe, which reported feed intake increases between 7 and 12%.






The improved feed intake highlighted in the post-wean piglet had a positive impact on average daily gain (ADG) when NuPro® was included in the piglet diets. Figure 2 reports the average daily gain increase in piglets fed NuPro® (2-4%) in commercial studies conducted in the Asia Pacific region. The NuPro® commercial studies conducted in this region (Australia, China, Philippines) indicate a 14% average increase in growth rate (range of 6-21%). This increase is comparable to increases of 12 and 6% observed under research conditions in the US and Europe.






The improved feed intake and growth rate (Figures 1 and 2) highlighted in the postwean piglet had a positive effect on the liveweight gain of piglets at the end of the NuPro® supplementation period. Figure 3 shows that the increase in liveweight gain was approximately 8% and was comparable to the increase reported by Carlson et al. (2005).






Reducing the growth gap

Carlson et al. (2005) conducted an experiment comparing the effect of NuPro® (5%) or plasma (5%) with a control diet (vegetable protein only) in weaner piglets. As expected, the piglets fed the plasma and NuPro® diets had significantly higher feed intake, ADG, and liveweight at the end of the supplementation period (28 days).

After the 28-day supplementation period with NuPro® or plasma, all treatment groups were fed a standard grower and finisher diet and their subsequent growth performance was monitored. Piglets fed NuPro® had significantly higher ADG and body weight compared with pigs fed the control and plasma diets. The improvements in liveweight between the NuPro® and control pigs, and the NuPro® and plasma pigs at the end of the experiment were 7.2 kg and 10.1 kg, respectively. These improvements in liveweight represent approximately 5-7 days less to slaughter and a significant reduction in the post-wean growth gap.

Moore et al. (2006) reported a study investigating the effects of 2% NuPro® supplementation in sow lactation diets on the subsequent growth performance of their piglets. There were no differences in the average weaning weight, piglet average daily gain or litter growth rate between the control and NuPro® groups; however, piglets from sows fed a diet containing NuPro® during lactation grew faster by approximately 40 g/day compared with the control pigs for three months post-weaning. Thus, the number of days for the NuPro® pigs to reach the required slaughter weight was reduced (135 vs 139 days) compared with the control pigs.


Reducing growth performance variation

Some variation in growth performance and final liveweight at slaughter is unavoidable due to the inherent variation that exists within a herd due to age ranges of pigs entering the grow-out systems, or growth ranges due to sex differences and differing genetic potential. Generally, the coefficient of variation for all-in-all-out (AIAO) pig production systems range from 15-20% (Brumm, pers. comm.). The economic impact of this variation is calculated by Payne et al. (1999) using the AUSPIG model. As an example, Payne et al. (1999) reported that a growth rate distribution of 20% high, 60% medium and 20% low would reduce overall profitability by US$ 0.57/pig sold compared with 100% medium growth rate. Hence it is important to ensure that the variation in pig production systems is kept to a minimum.

A major cause of variation in all production systems is the performance and marketing of ‘slow-growing’ pigs or what is commonly referred to as the ‘tail.’ A commercial study conducted in Western Australia reported that slow-growing piglets fed NuPro® in the creep and weaner diet had significantly improved growth rate and liveweight gain compared with slow-growing pigs fed a control diet. The weight variation was reduced from 19 to 15%, which would increase the eventual percentage of pigs that could be sold in the top grade.


Conclusion

The piglet at weaning is faced with numerous stressors that include separation from the sow and litter mates, changes in location, environment, feeds and feeders. These stressors cause a post-wean growth gap that reduces the profitability of pig production systems.

NuPro® supplementation in sow lactation and piglet creep and weaner diets has been shown to be a viable option to enhance the growth performance of the post-wean piglet, reduce the growth gap and increase profitability.


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