Introduction

Feeding to ensure healthy pigs is a goal of all swine nutritionists and nursery pig managers. While several factors can influence pig health, this paper will address the following aspects;

1. Influence of weaning age and weight
2. Matching formulation to nursery pig maturity
3. Maximizing feed intake
4. Growth promotion nutrient levels

Influence of Weaning Age and Weight

Recent Kansas State University research (Main et al., 2004; 2005) has shown that increasing weaning age through 21 days linearly increases growth rate and reduces mortality from weaning to market. In these studies, wean-to-finish growth performance and productivity (as measured by average daily gain [ADG], mortality, off-test weight per day of age and weight sold per pig weaned) improved as weaning age increased from 12 to 21 days of age. Linear improvements in growth and mortality rate largely occurred in the initial 42-day post-weaning period, with some ongoing growth improvements in finishing performance. Financial performance improved linearly as weaning age increased up to 21.5 days. Data were then modelled to determine the linear rates of improvement observed as weaning age increased from 15 to 21.5 days (Table 2). Each day increase in weaning age increased initial weight (taken prior to weaning) by 256±4 g and weight sold to slaughter 1.80±0.15 kg per pig weaned. In the financial analysis, income over cost increased $0.94±0.07 per wean age day in the limited finishing space scenario and $0.53±0.06 per wean age day in the non-limited space scenario. These studies suggest increasing weaning age up to 21.5 d can be an effective production strategy to improve wean-to-finish growth performance in a multi-site production system.

Match Dietary Nutrient Levels and Ingredients with Weight and Age of the Nursery Pig

The rapidly changing and unique biology of the young pig must be considered in selecting sources and levels of amino acids, carbohydrates and fat. The main considerations for the young pig should be their:

1. high level of body protein deposition
2. low level of feed intake
3. high lactase and low amylase, maltase and sucrase digestive enzyme activities at birth (see Figure 1), and
4. limited ability to utilise dietary fat.

Figure 1. Digestive development
(adapted from Manners et al. (1972) [1] and Kitts et al. (1956) [2])

The newly weaned pig has a tremendous capacity for protein deposition in relation to the level of feed intake. Thus, diets must be formulated with high levels of amino acids. The reduction of disease exposure will improve health status and increase the amino acid requirements of the young pig by increasing the level of protein deposition.

Because feed intake is limited, a highly digestible carbohydrate source is advantageous, both to stimulate feed intake and supply a relatively high net energy value. The high lactase enzyme levels at birth and high digestibility of lactose make crystalline lactose or one of several lactose sources, e.g. dried whey, deproteinised whey, whey permeate etc., an excellent carbohydrate source for young pigs. As long as the diet contains a basal level of lactose, several other carbohydrate sources can be used for the remainder of the diet while achieving acceptable performance. When using a cereal grain as a main carbohydrate source – corn, sorghum, wheat, barley or oat products – finely grinding these ingredients (600 to 750 microns) is important to improve digestibility and pellet quality. An important point in formulating diets for very young pigs (less than 10 days of age) is their limited ability to digest sucrose at birth. Thus, sugar should not be used in diets for pigs less than 10 days of age.

The low feed intake of young pigs often leads nutritionists to feed high levels of fat to increase the energy density of the diet. Unfortunately, fat utilisation from the diet is limited in the pig before approximately 35 days of age. Poor utilisation of dietary fat is not well understood and may be due to a combination of factors including low digestibility during the initial period from changing fatty acid type compared to milk fat after weaning. Also, newly weaned pigs have limited ability to catabolise fat from body stores. However, added dietary fat is extremely important from a feed manufacturing standpoint because it helps lubricate the pellet mill die and thus, improves pellet quality of starter diets that contain high levels of milk products.

The bottom line is that fat utilisation increases with age and fat should be used strategically in the first diets after weaning as an aid in pelleting rather than as a main energy source. As the pig’s digestive enzyme systems mature and fat metabolism improves, fat can serve as an increasingly important energy source in dietary phases 3 (15 to 25 lb) and 4 (25 to 50 lb).

Soybean meal delay type hypersensitivity

An allergenic hypersensitivity to specific proteins contained in soybean meal has been implicated as a primary factor in a post-weaning performance lag often observed in weaned pigs. These findings stimulated research efforts in the early 1990’s to determine the performance and economic impact associated with using various levels and types of soy proteins in wean pig diets. Utilising readily available sources of soy protein (without significantly impacting performance) can offer significant cost savings opportunities.

The pathogenesis of soybean meal hypersensitivity response occurs three to four days after exposure to adequate soy antigens. This transient hypersensitivity results in digestive abnormalities that include disorders of digestive movement and inflammatory responses in the intestinal mucosa. Villi are sloughed from the small intestinal mucosa and absorptive capabilities are reduced. Increased susceptibility to enterotoxins and bacterial infection also occurs during this hypersensitive time period. Although the exact mechanisms are not known, these changes are thought to be the result of antigen-antibody complexes that initiate the pig’s own immune system to produce cytokines and complement. The cytokines and complement are thought to cause directly the damage to the intestinal mucosa. Most importantly, these changes result in reduced growth performance. Recovery occurs after 7 to 10 days when oral immune tolerance begins to develop and eventually, the intestinal mucosa returns to normal with little evidence of long term damage.

Research efforts completed at Kansas State University demonstrated that delayed exposure to soy protein only delays the hypersensitivity response (Table 1). Pigs fed an all-milk diet for the first 14 days post-weaning had greater growth performance in this time period compared to those fed an all-soy protein-based diet. However, when all the pigs were switched to a common diet containing soybean meal (days 14 to 35), pigs previously fed the all-milk protein based diet had decreased daily gain and feed efficiency (Table 1.) In addition, the overall ADG (days 0 to 35) of the milk-fed pigs was decreased.

This work indicates that the hypersensitivity was not eliminated. This delayed response lead to an overall decrease in performance. Additional studies have been conducted with graded levels of soybean meal and diets of varying complexity.

Table 1. Effect of exposure to soybean protein after weaning on starter pig performance

These studies have lead to the development of our current recommendations for management of the soybean DTH response. The authors currently recommend that diets fed immediately after weaning contain 10 to 20 per cent soy protein. The health status and/or environment of the weaned pigs will likely have an impact on the level of complicating challenges associated with the hypersensitive period. Therefore, customisation of farm- or system-specific programmes may be appropriate. Ideally, this exposure to soy protein and induction of tolerance would occur prior to weaning. However, successfully providing exposure during the lactation period has not been practical under commercial conditions.

Additional work with further refined soy products has demonstrated some advantages to using moist extruded products. However, these products do not appear to be cost-effective relative to high quality soybean meal. Recent development of several small-scale moist extruded soy processing plants throughout the Midwest may provide a readily available further processed soy protein for use in nursery diets.

Exposing young pigs to increasing levels of soybean meal in each diet will allow them to overcome the hypersensitivity to soy protein more quickly, without causing a long-term reduction in performance. The early exposure permits inclusion of soybean meal at higher levels in subsequent diets without reducing growth performance. The negative effects of the transient hypersensitivity can be minimised by carefully selecting high quality complementary protein and carbohydrate sources. This approach has consistently proven to be more economical than delaying exposure to soybean meal.

Ingredient quality

With increasing weaning age, some pigs may be fed only a limited amount of a Phase 1 or Phase 2 diets that contain higher levels of specialty protein and lactose sources. However, this does not dismiss the importance of using high quality, highly digestible sources of these products in diets in which they are included. While older weaned pigs have a more advanced digestive tract to digest protein products, they cannot utilise poorly processed or heat-damaged ingredients any better than a younger, lighter pig. The use of high quality ingredients, such as spray-dried blood meal and lactose sources, from a reputable source can ensure that ingredient quality is not a limiting nutritional factor in diets.

Importance of Feed Intake

Newly weaned pigs cannot consume enough feed to meet their energy needs for protein deposition. They are in a highly energy-dependent state. Thus, any increase in energy intake results in improvements in growth rate and lean deposition. Comprehension of this concept will lead to an understanding of the varying response to diet complexity in different situations.

Feed intake (and, thus, energy intake) is highly dependent on environmental factors. If feed intake is compromised due to health status, environment, management or other factors, diets that contain a variety of specialty ingredients (commonly called complex diets) can help serve as an aid to increase consumption. Lactose, spray-dried animal plasma and other palatable ingredients typically used in complex diets will increase feed intake of early weaned pigs. However, if feed intake is excellent due to improved environment and minimal disease exposure, the dependency on complex diets fed to nursery pigs can be reduced.

Key points in understanding the interaction of diet complexity and feed intake are: (1) feed intake drives growth performance in early weaned pigs, (2) complex diets improve feed intake primarily for the first few weeks after weaning and (3) diet complexity can and should be reduced rapidly as impact on feed intake declines with age and to control feed cost per unit of gain effectively.

Studies have shown that increased feed intake in the post-weaning period will increase nursery growth rate but that this weight advantage is maintained and in some instances increased in the finishing phase compared with pigs with poor feed intake after weaning. Studies also show that increased feed intake will dramatically reduce the risk of enteric disease in the nursery phase.

Growth Promotion Nutrient Levels

Post-weaning diarrhea associated with haemolytic E. coli are a common, and potentially emerging problem in early weaned pigs. Utilising zinc fortification in excess (3000 ppm zinc oxide) of the nutrient requirement (100 ppm has been reported to promote daily gain in healthy wean pigs nursery diets with 3000 ppm zinc oxide post-weaning has also been observed to have beneficial effects in helping control post-weaning E. coli-associated challenges under field conditions.

Another recent study demonstrated that pigs supplemented with zinc oxide at 3000 ppm had a reduced translocation of bacteria to the ileal-mesenteric lymph node. The potential mechanism for this finding, as well as the other beneficial effects demonstrated above is not clearly understood. Zinc has been demonstrated to have an effect on cells undergoing rapid turnover, as it is needed for DNA and protein synthesis. Zinc also seems to play a role in stabilising cell membranes and modify membrane functions. Therefore, zinc’s beneficial impact may be in part due to a direct supportive or protective role of intestinal epithelial cells.

Managing post-weaning E. coli challenges is increasingly becoming more complex. These challenges need an ongoing effort for improved prevention or intervention techniques. Using excess supplemental zinc early in the nursery phase is one option available to help minimise these challenges and promote growth. The environmental concerns associated with feeding zinc are significant. This concern re-emphasises the desire to restrict the 3000 ppm zinc oxide inclusion in the first two weeks after weaning.

Further Reading

-

You can view other papers presented at Swine Profitability Conference 2009 by clicking here.