A study was conducted to evaluate the effects of supplemental protease and cereal grain type on nutrient digestibility (jejunum and ileum) and performance of broilers offered diets with reduced amino acid concentrations and supplemental xylanase and phytase. A total of 624 male broiler chicks (Ross 308) were randomly distributed into 48 floor pens (13 chicks/pen" 0.07 m2/bird) and offered one of six dietary treatments with eight replicates per treatment. Dietary treatments were either maize- or wheat-based with a positive control (PC) reference diet, a negative control diet without protease (NC" 60 g/kg lower amino acid density than PC), and an NC diet with protease. The reduction in amino acid density affected (P<0.05) nutrient digestibility by varying degrees depending on cereal grain source. At 14 d of age, cereal grain and protease showed a significant interaction (P<0.05) which affected jejunal and ileal starch digestibility, whereby protease increased digestibility in birds fed wheat-based diets but not in those fed maize-based diets. Cereal grain source affected (P<0.05) nitrogen (jejunum and ileum) and digestible energy (DE" ileum), where birds fed wheat-based diets had higher digestibility than those fed maize-based diets. At 28 d of age, birds fed wheat-based diets had a higher (P<0.01) jejunal and ileal nitrogen digestibility, whereas protease reduced ileal nitrogen digestion. Protease affected ileal starch digestion in birds fed wheat, but not maize-based diets, resulting in a significant cereal grain × protease interaction (P<0.05). Wheat-based diets had a higher DE than maize-based diets in both the jejunum and ileum. From 15 to 35 d of age, cereal grain source (P<0.05) affected performance, whereby broilers offered maize-based diets had better performance than those fed wheat-based diets.

An experiment was conducted to evaluate the effects of varying AME concentrations and protease supplementation on broiler performance and jejunal and ileal nutrient digestibility from 1 to 35 d of age. Ross £ Ross 308 male broilers (n = 1,008) were equally distributed into 48 floor pens and offered 1 of 6 dietary treatments (8 replicate pens/treatment). Dietary treatments consisted of a factorial arrangement with AME concentration (low-, moderate-, or highAME) and supplemental protease (without or with) as the main factors. Birds and feed were weighed on 1, 15, 29, and 35 d of age to determine body BW, BW gain (BWG), feed intake (FI) and feed conversion ratio (FCR). At 15 and 29 d of age, jejunal and ileal digesta contents were collected to determine nutrient digestibility. From 1 to 15 d of age, broilers offered moderateAME diets (P < 0.05) had 6.7, 7.1, 4.8% higher BW, BWG, FI, respectively, and a 2.1% lower FCR compared with those offered low-AME diets. Likewise, protease increased (P < 0.05) BW and BWG by 4.3 and 4.7%, respectively, and decreased (P < 0.05) FCR by 3.4%, compared with those offered the diets without protease. From 1 to 29 d of age, broilers offered high-AME diets had 2.9% lower (P < 0.05) FCR compared with those offered low-AME diets. Protease increased (P < 0.05) BW, BWG, and FI by 3.1, 3.2, and 4.2%, respectively, compared with the unsupplemented diets. From 1 to 35 d of age, broilers receiving high-AME diets had 2.9% lower (P < 0.05) FCR compared with those offered lowAME diets. Protease increased (P < 0.05) FCR by 1.0% compared with those offered unsupplemented diets. Jejunal (15 and 29 d of age) and ileal (29 d of age) starch digestibility and jejunal nitrogen digestibility (29 d of age) were lower (P < 0.05) in broilers offered high-AME diets compared with those offered low-AME diets. Both AME concentration and supplemental protease independently affected broiler performance, with responses being most apparent during early growth phases whereas digestibility measures were mainly influenced by AME concentration.

1. A study was conducted to assess the effects of supplemental protease (0 or 15,000 units/kg) and diet type (maize- or wheat-based) on apparent jejunal and ileal digestibility and apparent total tract metabolisability of nutrients in Cobb 500 mixed-sex broilers from 6 to 31 d of age.

2. Birds were randomly distributed into 56 metabolism cages (6 birds/cage" 14 replicates/treatment). At 22 d of age, jejunal and ileal digesta contents were collected and pooled from 4 birds/cage to determine apparent digestibility coefficients (DC) and digestible energy (DE). Feed intake was measured, and total excreta were collected from 8 to 11 and 18 to 21 d of age to determine apparent metabolisable energy (AME) and total tract nitrogen and starch metabolisability coefficients.

3. Broilers offered the maize-based diet with protease had greater (P < 0.05) jejunal nitrogen DC, starch DC, and DE (8.2, 6.5, and 14.9%, respectively) and ileal nitrogen DC and DE (5.1 and 6.8%, respectively) than those offered the maize-based diet without protease. Ileal starch DC was increased (P < 0.05) by 1.1% with protease supplementation.

4. Broilers offered maize-based diets had greater (P < 0.05) nitrogen (7.3%) and starch (0.6%) metabolisability coefficients and AME (4.7%) from 8 to 11 d of age, and nitrogen (4.3%) metabolisability coefficients and AME (2.0%) from 18 to 21 d of age compared with those offered wheat-based diets.

5. Thus, protease supplementation and diet type can affect digestive dynamics and nutrient utilisation in broilers.

Protease supplementation has been observed to increase crude protein and amino acid (AA) digestibility in broiler chickens. Positive effects on apparent metabolisable energy (AME) and net energy (NE) have also been observed. The magnitude of these improvements in AME are typically larger than the sum of energy contributed by the improvement in AA digestibility, which indicates that protease supplementation may have energy-sparing effects. A five-part study was conducted to explore the energy-sparing effects of protease supplementation in broiler diets. The primary objective of this project was to quantify these energy responses and establish a basic understanding of the mechanisms by which proteases influence energy metabolism in growing broilers. Moreover, protease supplementation has traditionally been examined as part of enzyme admixtures or in isolation within poultry diets, which may lead to nebulous results, as mono-component phytase and carbohydrase enzymes are typically included in commercial poultry diets. Therefore, the effects of monocomponent protease were considered in tandem with a mono-component phytase and xylanase enzymes, to enhance understanding of protease efficacy within commercial poultry diets. The first experiment evaluated the effects of supplemental protease and diet type (maize- or wheat -based) on jejunal and ileal digestibility and total tract metabolisability of nitrogen, starch, and energy in broilers from 6 to 31 d of age. The effect of protease was more pronounced in broilers offered the maize-based diet, with protease increasing nutrient digestibility in both the jejunum and ileum. Diet type affected nutrient utilisation and growth performance in a consistent manner, with broilers receiving maize-based diets having a higher nutrient utilisation, but less efficient FCR, compared with those receiving wheatbased diets. Protease supplementation in the wheat-based diet inconsistently affected individual AME. The second experiment further evaluated the effects of supplemental protease and cereal grain source (maize- or wheat-based) on nutrient digestibility and performance in broiler chicks fed diets with reduced amino acid concentrations. Protease inclusion improved ileal starch digestibility, but the efficacy appeared to be dependent on the source of cereal-grain used and formulation strategy. For example, cereal grain type led to a significant difference in performance, with broilers offered maize-based diets exhibiting better performance than those offered wheat-based diets. The third experiment assessed the effects of protease supplementation in an all plant-based protein maize-based diet formulated with reduced concentrations of digestible AA (dAA) on nutrient digestibility and net energy utilisation in broilers. Protease supplementation increased ileal N digestibility and NE of the diet. The fourth experiment evaluated the effects of varying AME concentrations (low-, moderate-, or high-AME) and protease supplementation (without or with) on broiler growth performance and jejunal and ileal digestibility of broilers during a 5-week production period. Both AME concentrations and supplemental protease independently affected broiler performance. Feeding adequate or higher-AME concentrations resulted in optimal early growth performance and cumulative FCR. Protease supplementation positively influenced broiler performance during the starter and grower phases. The minimal interactive and absent main effects of supplemental protease on nutrient digestibility, in conjunction with its positive effects on performance, indicated that benefits of supplemental protease extended beyond direct digestibility effects, to additional net effects. Finally, the fifth experiment evaluated the effects of supplemental protease (without or with) and dAA concentrations (standard or reduced) on broiler live performance and energy partitioning. Protease supplementation improved FCR and energy and N partitioning in broilers, and responses were more pronounced in broilers fed diets with reduced-dAA concentrations. Protease did not affect AME, but numerically increased NE and significantly reduced the heat increment of feed. These results demonstrated that diet type, AME and dAA concentrations can affect broiler live performance. Additionally, the inconsistent effects of protease on nutrient digestibility, in conjunction with the positive effects on live performance and energy partitioning, indicate that nutrient digestibility was not limiting in these experiments, and that the benefits of protease supplementation extend beyond direct digestibility to additional net effects. Moreover, protease supplementation reduced the heat increment of feed by 0.19 MJ/kg, suggesting that protease likely reduced maintenance energy requirements in growing broilers by altering digestive physiology. Additional mechanistic research investigating the specific sources of these energy-sparing effects is warranted to improve understanding and fully capitalize on these responses.