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)
4. Push energy intake early post-weaning
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
5. Post-weaning diet
5.1. Level of milk products
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.
5.2. Cooking cereals
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.