Milk-derived products are commonly applied in feed formulation in order to facilitate the transition of young pigs to the weaning event. The weaning of piglets from the sow is associated with stressors of social, environmental and nutritional nature. The latter refers to the abrupt change from a diet based on milk, which is rich in fat and lactose, to plant-based diets with starch as a major energy source. This generally results in gastrointestinal disturbances that are also associated with poor performance. The inclusion of good quality, highly digestible protein sources facilitates the transition of weaned pigs to this event, favouring the development of the digestive system (Grinstead et al., 2000). Fats and oils are also relevant energy-yielding nutrients, although, the addition of fat to the diet of weaned pigs has resulted in variable responses (Pettigrew and Moser, 1991). This variability is mostly related to the disparity in chemical structure and composition of added fats, which can affect their digestion. It is known that sow milk contains high levels of fat (40% on a DM basis), which is considered 95% digestible by the suckling piglet. Furthermore, processing conditions and technological treatments may help to improve the digestibility of diets for weaned pigs, hence resulting in improved growth performance and health status during the post weaning period.
Reducing fat globule size
A number of factors affect the utilisation of dietary fat by weaning piglets (Reis de Souza et al., 1995). Among these are physical factors, such as size of fat globules, methods of fat incorporation into the diet, as well as other fat processing technologies, such as spray-drying. Spray-drying is a commonly used method for drying aliquid feed, causing the encapsulation of fat by protein and lactose. In addition, a smaller size of the fat droplets can be achieved by homogenisation and spray-drying (Figure 1). Small size fat globules may help to stimulate
good fat digestion, which is beneficial to meet the specific nutritional requirements of young piglets (Xing et al., 2004). Schothorst Feed
Research B.V. (Lelystad, the Netherlands) examined, in cooperation with Sloten B.V. (Deventer, the Netherlands), the influence of technological treatment and composition of homogenised mixtures of milk protein and vegetable oils on the performance and health of weaned pigs. Experiment 1 (2001) was conducted in order to determine the influence of spray-drying a homogenised mixture of delactosed whey and vegetable oils on the performance and feed utilisation of weaned pigs in comparison with the
inclusion of the same ingredients as single ingredients in a diet without technological treatment. This experiment was comprised of four treatments in a 2 x 2 factorial design with net energy (9.9 or 11.0 MJ/ kg) and technological treatment (free mixed or spraydried fat) as the main effects. Piglets were weaned at approximately 26 days of age and an average body weight (BW) of 8.4 kg. Animal performance was determined over a 4-week post weaning period. This study showed that increasing the energy content of the diet, by adding a higher amount of fat-rich ingredients,
improved the feed conversion ratio (FCR) of weaned pigs (Table 1).
Spray-drying increased the feed intake of pigs after weaning, which could be associated with the reduced fat globule size. These results suggest that spray-drying could be an effective technique to increase feed intake of weaned pigs irrespective of the net energy content of the diet.
Influence of the degree of fat saturation
The ability of the weaned pig to digest fat is also related to the source of dietary fat. The degree of saturation of the fat fraction in the diet, as represented by the ratio of unsaturated:saturated (U:S-ratio) fats, influences fat digestion and consequently the utilisation of fat as an energy source for growth (Wiseman et al., 1998). This study (Experiment 2, 2005) investigated the influence of spray-drying and dietary U:S-ratio on the performance of weaned pigs. Three dietary treatments were considered (Table 2), in which the target high or low U:S-ratio was reached by altering the proportion of vegetable oils in the diet. Similar to the previous
experiment, these ingredients were added free or in a homogenised spraydried mixture. The inclusion level of the spray-dried dairy fat concentrate was 20%. This was added at the expense of whey powder, soybean concentrate, wheat gluten and soybean oil. Piglets were weaned at approximately 27 days (average BW: 8.4 kg). Animal performance was also determined over a 4-week post
weaning period. Results from this experiment showed a clear improvement on the FCR by the dietary inclusion of spray-dried fats. It is generally accepted that a high U:S-ratio facilitates the digestion of fats (Wiseman et al., 1998). Numerical differences showed that spray-drying of a high U:S-ratio diet improved the growth of weaned pigs compared to the low U:S-ratio diet (380 g/d vs 359 g/d). Nonetheless, results from this study illustrate that fat digestibility seems to be enhanced by the technological treatment applied, irrespective of the U:S-ratio.
Efficacy of Nuklospray®
In the last study (Experiment 3, 2006) the efficacy of Nuklospray® (Sloten B.V.,Deventer, the Netherlands) was tested. This product consists of a spray-dried mixture of high quality liquid whey with homogenised vegetable fats. Dietary treatments were provided in two phases (1+2 and 3+4 weeks post weaning), with an inclusion level of Nuklospray® of 20% and 10% respectively.
This product was included in the diet at the expense of sweet whey powder, wheat protein, potato protein and soybean oil. As with the previous studies, 27 days-old weaned piglets were used (average BW, 8.5 kg) in a 4-week experimental period. The addition of Nuklospray® showed a positive influence on the growth rate and FCR of weaned pigs during the first two weeks after weaning. Furthermore, daily gain was significantly improved with dietary Nuklospray® inclusion, mainly due to a higher feed intake (Table 3)
Spray-drying is a beneficial technological treatment to improve the utilisation of homogenised mixtures of milk products and vegetable oils as high quality feed ingredients for weaned pigs. The results from these studies indicate that inclusion of spray-dried ingredients may improve growth performance in weaned piglets due to an increased feed intake and/or more efficient feed utilisation. The smaller fat globule size, as a consequence of homogenisation and spray-drying, may improve fat digestion. This seems to allow the use of fat with low U:S-ratios without detrimental effects on growth performance. Thus, it can be concluded that spray-drying facilitates the nutritional adaptation of pigs to the weaning event.
References are available on request from the authors