Abstract
The effects of feed processing, pea cultivar and their interaction on the nutritional value of field pea (Pisum sativum L.) for poultry were evaluated in regard to its apparent metabolizable energy (AMEn), apparent protein digestibility (APD), and rate and extent of starch digestion. Amino acid sparing as affected by the rate of starch digestion was studied in laying hens and broiler chickens. Also, the effects of feeding a slowly digested starch (SDS) from pea on performance and metabolism of broiler-breeder pullets were investigated. The first objective of this research was to evaluate the effects of screen-hole size, cold pelleting, and pre-pelleting conditioning temperature on nutrient digestibility of pea. There was no interaction between dietary treatments on all studied parameters. Small hammer-mill screen-hole size (3.2-mm) increased AMEn, APD, and extent of starch digestion values compared with coarse screen-hole size (6.4-mm). The AMEn and extent of protein digestion were not affected by cold pelleting, but the site of protein digestion was affected. In contrast, cold pelleting increased the rate and extent of starch digestion. Pre-pelleting conditioning temperature affected AMEn of pea in a quadratic fashion but had no positive effect on starch digestibility. The 70°C of pre-pelleting conditioning temperature maximized pea AMEn. Increasing pre-pelleting conditioning temperature decreased APD in a linear fashion. The second objective of this research was to study the effects of feed processing, pea cultivar and their interaction on AMEn, APD, and rate and extent of starch digestion. In vitro and in vivo experiments were conducted. An in vitro procedure simulating the gastric and small intestine conditions of chickens was developed to predict the rate and extent of starch digestion as affected by pea cultivar and sieve-hole size (0.5-, 1.0-, 2.0-mm). The rate and extent of starch digestion of cereal grain samples (barley, corn, and wheat) was also compared to pea starch. No interactions were found between pea cultivar and sieve-hole size on the kinetics of starch digestion. Pea cultivar affected the rate and extent of starch digestion. The small sieve-hole size in the in vitro assay resulted in a higher rate and extent of starch digestion. Pea starch was slowly digested in comparison with cereal grains. The in vivo experiment confirmed that fine grinding and pelleting improves AMEn and APD. Cultivar effects on AMEn and APD were observed, but no interaction was found between pea cultivar and feed processing. The third objective of this research was to investigate whether feeding SDS from pea would have sparing effect on amino acid utilization in chickens. In the first experiment, the effects of three levels of pea inclusion 0, 150, 300 g/kg on the response of laying hens to three levels of lysine intake (700, 780, and 860 mg per day) were evaluated using performance and production criteria. This experiment revealed that pea inclusion up to 300 g/kg in laying hen diets was well tolerated by laying hens and improved energy retention as indicated by increased body weight and egg weight. However, this experiment did not confirm the hypothesis that SDS from pea spared amino acids for laying hens. The second experiment investigated the interaction between SDS derived from pea and amino acid levels on the performance and carcass quality of broiler chickens. Six levels of pea inclusion (0, 150, 300, 450, 600, and 750 g/kg) and two levels of amino acids (100 and 85% of Ross Ơ Ross 308 requirement) were examined in a broiler trial (0 - 35 d). The maximum level of pea inclusion recommended in diets increased with broiler age, but the effect of SDS from pea on amino acid sparing could not be confirmed. In the third experiment, the effects of feeding SDS from pea on growth performance and metabolism of broiler breeder pullets were investigated. Body weight and uniformity of pullets fed pea-based diet were similar to that of a wheat-based diet. Target body weight and uniformity of pullets were not affected by feeding a diet containing 890 g/kg of pea. Mean blood glucose levels and relative liver weight were markedly lower in broiler pullets fed pea-based diet compared with those fed a wheat-based diet. In conclusion, feed processing independently had a significant effect on the availability of pea nutrients. Pea is a good source of both energy and protein and that it can be partially or completely included to replace wheat and soybean meal in poultry diets. However, the effect of SDS on amino acid sparing could not be confirmed. Further research is needed to examine other feed processing techniques, pea cultivars, level of inclusion, and to understand other metabolism responses to feeding SDS from pea.