Figure 3 - Relation between soluble dietary fibre (g/kg) and water to feed (W/F) ratio day 16-18. s_DF x W/F D16-18


1.50 1.70 1.90 2.10 2.30 2.50 2.70


20.0 25.0 s_DF


Figure 4 - Relation between insoluble dietary fibre (g/kg) and relative gizzard weight (g/kg BW).


i_DF x Gizzard weight (g/kg BW)


60


y = 0.0077x2 – 06875x + 34.681 R2 = 0.37


40


y = 0.0037x2 – 0.1732x + 4.1374 R2 = 0.64


30.0 35.0 20 0 25.0 45.0


65.0 i_DF


85.0 105.0


before it can be digested and absorbed. Due to the bile salt deconjugation by microbes, less dietary fat is emulsified, digested and absorbed, especially in the case of more saturated fats and oils as animal fat and palm oil in the diet. Coconut and palm kernel oil with shorter fatty acids (C12 and C14) or vegetable oils with more unsaturated fatty acids (C18:1, C18:2 and C18:3) are easier digested and absorbed. So, these fat sources are preferred in an AGP free poultry diet.


Fermentability of fibre sources More microbes in the gut also means more fermentation of carbohydrates and fibres. Fermentation of fibre sources can vary. Inert fibre sources as oat hulls, straw, wheat bran, rice hulls and sunflower hulls are less fermentable than more fermentable fibre sources as soybean hulls, citrus pulp, and sugar beet pulp. Poultry seems to prefer more inert or insoluble fibre instead of more fermentable or soluble fibre. SFR performed a desk study based on data from studies of Jiménez-Moreno et al. published between 2011 and 2019. Correlations were found between dietary ADF, body weight gain (BWG) and FCR parameters (Figure 1 and Figure 2). A minimum of 40 g/kg ADF can be recommended for broilers. Since an increase of


Figure 6 - Relation between dietary CP (%), FCR d21-35 and ADG (g/d) d21-35 (Belloir et al., 2015). FCR d21-35


ADG (g) d21-35


1.64 1.66 1.68 1.70 1.72 1.74


1.62 19% 18% 17% 16% 15% 80


100 102 104 106 108 110


19% 18% 17% 16% 15% ▶ ANTIBIOTIC REDUCTION | DECEMBER 2021


Figure 5- Relation between insoluble dietary fibre (g/kg) and gizzard pH.


i–DF x Gizzard pH 4.5


3.5 4


2.5 3


2


y = 0.0005x2 – 0.0804x + 6.5376 R2 = 0.26


25.0 45.0


65.0 i–DF


85.0 105.0


soluble dietary fibre (s_DF) resulted in a higher water to feed ratio (Figure 3), a maximum of 25 g/kg s_DF can be recommended. Finally, an increase of insoluble dietary fibre (i_DF) stimulated the relative gizzard weight (Figure 4) and reduced the gizzard pH (Figure 5). From these observations, a minimum of 65 g/kg i_DF can be recommended.


Protein digestion More microbes in the gut also results in more fermentation of undigested protein and production of toxic metabolites such as biogenic amines and ammonia. Intestinal mucus produc- tion and endogenous losses are increased as well. To counter- act this phenomenon, we need to use protein sources with a higher digestibility so that the dietary crude protein (CP) level can be lowered. Consequently, also more synthetic amino ac- ids will be used. This will help to reduce N excretion and inci- dence of wet litter as well. A study of Belloir et al. (2015) shows that CP level can be lowered down to 17% in broilers from day 21 onwards without affecting FCR (Figure 6).


Potential feed additives A lot of feed additives that can be used in animal feed (as a partial replacer of AGPs) are available nowadays, such as acidifiers (organic acids, SCFA, MCFA), amino acids,


W/F ratio


Gizzard pH


Gizzard weight


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