Fatty-Acid composition of free-choice starter broiler diets

Fatty-Acid composition of free-choice starter broiler diets

Kessler AM^I; Lubisco DS^II; Vieira MM^II; Ribeiro AML^III; Penz Jr AM^III

^IUFRGS Professor

^IIEstudante Pós-Graduação, PPG-Zootecnia, UFRGS

^IIIUFRGS Professor

^{Mail Address}

ABSTRACT

Two experiments were carried out to evaluate the inclusion of vegetable oils with different fatty acid content in starter and pre-starter broiler diets. In Experiment I 480 1- to 9-day-old male Ross 308 broilers were fed diets containing corn oil (CO), acid corn oil (ACO), linseed oil (LO) or coconut fat (CoF). Chicks were distributed according to a factorial 2x2x2arrangement (2 free fatty acids - FFA ) x (2 n6:n3 ratios) x (2 medium-chain fatty acids levels - AGMC). Performance responses and dry matter (DMM), crude protein (CPM), and crude fat (CFM) metabolizability were evaluated. In Experiment II, 480 1- to 20-day-old male Ross 308 broilers were offered the free choice of 2 different diets: with no fat addition, or with 10% addition of the following fat sources: CO, LO, CoF, soybean soapstock (SBS), acid soybean oil (ASO), or acid cottonseed oil (ACtO). Performance responses and diet selection were evaluated. In experiment I, there were no significant effects of the diets on performance, DMM, or CPM; however, the inclusion of FFA depressed CFM. In experiment II, there was a marked preference of birds of the diets with fat inclusion, leading to the selection of diets with more than 3100 kcal/kg ME in the period of 1 to 20 days, independently of fat source. The broilers selected the high fat and energy diets since the first days of age, which resulted in better bird performance.

Keywords: Linseed oil, metabolizable energy, n6:n3 ratio, soybean oil, voluntary intake.

INTRODUCTION

The inclusion of fats in feeds positively influences broiler performance (Vieira et al., 2002; Pucci et al., 2003), and enhances feed palatability (NRC, 1994). The composition of the fatty acids added to diets affects body fat composition in broilers (Waldroup & Waldroup, 2005), and therefore body fat growth pattern can be modified by dietary fat (Crespo & Esteve-Garcia, 2002).

Birds fed diets with high saturated fatty acids from animal origin deposit relatively more mesenteric and abdominal fat as compared to other sites of the body (Crespo & Esteve-Garcia, 2002). The increase in the proportion of saturated fatty acids in broiler diets causes weight gain depression and worse feed conversion ratio, as well as reductions in fat and fatty acids digestibility and energy metabolizability (Zollitsch et al., 1997; Dänicke et al., 2000). On the other hand, diets with high polyunsaturated fatty acid content promote lower body fat deposition (Crespo & Esteve-Garcia, 2002).

The physiological capacity of birds during the first post-hatching days limits fat absorption (Carew et al., 1972), and the limited fat digestion seems to be caused by insufficient secretion of bile salts and lipase (Krogdahl et al., 1985). Fat digestibility in chicks is 6% lower than that of adult roosters (Freitas et al., 2005). In general, apparent fat metabolizability decreases as the proportion of dietary saturated fatty acids increases (Zollistsch et al., 1997).

Young broilers are capable of digesting and absorbing fats rich in polyunsaturated fatty acids, whereas fats with high saturated fatty acid content are poorly utilized (Wiseman, 1984). In addition, increasing saturation of fat sources and free fatty levels in the diet results in linear reductions in metabolizable energy (ME) in young broilers (Wiseman & Salvador, 1991). It is known that pre-starter broiler performance is positively influenced by feeds containing 3000 kcal ME/kg (Vieira et al., 2006); however, high ME values during this stage also promote an increase in carcass fat deposition (Zanusso et al., 1999).

This study aimed at studying the effects of the inclusion of vegetable oils with different fatty acid composition in pre-starter broiler diets on live performance and nutrient metabolizability, as well as to determine adequate dietary metabolizable energy level for the starter phase using free-choice feeding.

MATERIALS AND METHODS

Two experiments were carried out with male broilers in the pre-starter and starter phases.

Experiment I evaluated the inclusion of different types of vegetable oils and their mixtures in pre-starter diets. Experiment II evaluated bird preference for diets including or not different types of vegetable oils in the starter phase.

In experiment I, 480 1- to 9-day-old Ross broilers were housed in metal cages, kept in an environmentally-controlled room under a 24-h lighting program, and supplied water and feed ad libitum. The experimental diets were formulated to supply the recommended levels (Rostagno et al., 2005), and contained equal protein and energy levels, but different types and mixtures of vegetable oils. Eight diets were manufactured taking into consideration: (1) the presence or absence of free fatty acids (corn oil or acid corn oil, respectively), (2) two n6:n3 ratios (high: > 40:1 and low: < 5:1), and (3) two levels of medium-chain fatty acids (addition or not of coconut fat), as described in Table 1. Fatty acid profiles were calculated from the analyzed values of the four oil sources (corn, acid corn oil, linseed, and coconut), and ether extract levels of corn and soybean meals were estimated.

A completely randomized experimental design, with a 2 x 2 x 2 factorial arrangement (presence or absence of free fatty acids, high or low n6:n3 ratio, and inclusion or not of medium-chain fatty acids) was applied, with a total of 8 treatments of 5 replicates of 12 birds each.

In experiment I, performance (weight gain, feed intake, and feed conversion ratio) and dry matter (DMM), crude protein (CPM), and crude fat (CFM) metabolizability, which was determined by total excreta collection from 4 to 9 days of age, were evaluated.

In the second experiment, 480 male Ross 308 broilers were maintained in an environmentally-controlled room under a 24-h lighting program from 1 to 20 days of age. Seven starter diets containing different vegetable oils were compared. Birds were provided free choice between a diet with no fat inclusion and a diet containing 10% of the tested fat (Table 2). The side where the feeders were placed was changed daily to precent any possible behavioral bias.

The experimental diets were formulated to supply the recommended nutritional requirements (Rostagno et al., 2005), and were different only as to ME level and type of vegetable oil included (Table 3). The experimental diets were based on a single basal diet, to which the different oils and fats were added.

Performance parameters (weight gain, feed intake, and feed conversion ratio) and feed preference were evaluated. A completely randomized experimental design with 7 treatments of 5 replicates of one cage each (12 birds per cage) was applied in experiment II.

The statistical models of experiments I and II were analyzed by analysis of variance using the Generalized Least Square procedure of Statgraphics plus 4.1 software program (Manugistics, 1999). The means of the main factors were compared by the test of Tukey at 5% de probability.

RESULTS AND DISCUSSION

Table 4 shows bird performance results in experiment I. Feed intake increased when mediumchain fatty acids were included in the diet (p < 0.07), but was not affected by the other evaluated factors. There was no effect of the experimental treatments on weight gain or feed conversion ratio in experiment I, indicating the lack of influence of dietary fatty acid composition on the performance of broilers at this age. Similar results were found with the use of different fatty-acid profiles added to broiler diets (Crespo & Esteve-Garcia, 2002). On the other hand, Newman et al. (2002) observed that the dietary inclusion of polyunsaturated fatty acids (n-3 and n-6 sources) improved the feed conversion ratio of broilers; however, at an older age (3 weeks).

Table 5 shows dry matter (DMM), crude protein (CPM), and crude fat (CFM) metabolizability results for the period of 4 to 9 days. No significant differences were observed in DMM or CPM; however, CFM decreased when broilers were fed free fatty acids derived from acid corn oil. The action of free fatty acids on fat absorption was described by Wiseman & Salvador (1991), who observed that fat metabolizability decreased as FFA content increased in the diet of young broilers. This is explained by the fact that bile salt concentration in the intestine of broilers during the first week of life is not sufficient to allow efficient micella formation with the fatty acids (Katangole & March, 1980).

In experiment II, birds generally preferred the diets with fat addition since the first week of life (Table 6), except for those fed acid soybean oil or acid cottonseed oil. The birds seemed to prefer the diets containing soybean oil, corn oil, and coconut fat. This preference was maintained during the entire experimental period. The largest preference differences were observed between 1 to 4 days of age, when birds showed lower preference for the diets containing free fatty acids. During the following period (4 to 12 days), birds started to eat these diets twice as much as compared to the first period, reaching similar feed intakes as the birds fed the diets with the addition of the other oils. The preference for soybean oil, corn oil, and coconut fat during the total period resulted in higher crude fat and ME intake (Table 7).

In all free-choice treatments, during the period of 1 to 20 days of age, more than 50% of bird feed intake consisted of the fat-rich diets, leading to higher average crude fat and ME intake levels than those recommended for this rearing stage (less than 7% crude fat and AME lower than 3050 kcal/kg) (Rostagno et al., 2005).

It was observed that the birds did not adjust their feed intake as a function of the possibility of selection, as shown by the lack of significant differences in average feed intake among the different fat sources (Table 8). The chicks fed the low-energy diet (no oil inclusion) did not increase their feed intake to achieve the same calorie intake as the birds submitted to the free-choice treatments.

The capacity of digesting and absorbing lipids improves as broilers grow (Katangole & March, 1980). In the present study, weight gain started to be clearly influenced by dietary fat source after 4 days of age (Table 9). The lower energy intake caused by the lowenergy diet resulted in worse bird performance. The broilers fed the fat-supplemented diets presented higher weight gain as compared to those fed diets with The best numerical response in terms of weight gain no fat addition, independently of fat source, for the was observed when soybean oil, corn oil, and linseed total experimental period. The addition of fat to the oil were supplemented; however, means were not diets promoted higher weight gain, and consequent statistically different at 5% probability level. Other improvement in feed conversion ratio. These responses authors also did not detect differences in the were also verified by Pucci et al. (2003), who observed performance of broilers fed different oil sources that broiler performance improved as dietary fat levels (Crespo & Esteve-Garcia, 2002; Vieira et al., 2002). increased from 0 to 7.5%.

The best numerical response in terms of weight gain was observed when soybean oil, corn oil, and linseed oil were supplemented; however, means were not statistically different at 5% probability level. Other authors also did not detect differences in the performance of broilers fed different oil sources (Crespo & Esteve-Garcia, 2002; Vieira et al., 2002).

Dietary ME content positively influenced broiler weight gain, which was also observed by Oliveira et al. (2000) and Zanusso et al. (1999). Considering that the other nutrients supplied the birds' nutritional requirements, it can be inferred that weight gain increased due to the higher metabolizable energy intake resulting from the diets with oil addition as compared to the control diet with no oil. Therefore, the increase in weight gain verified in the present study can be related to a possible improvement in the energy:protein ratio in the feeds.

The better feed conversion results for the total experimental period (Table 10) were verified in birds fed the diets containing linseed oil and corn oil, but there were no differences in the period of 1 to 4 days of age. Better feed conversion during the period of 1 to 21 days of age when higher ME was fed to broilers was also observed by Zanusso et al. (1999), Oliveira et al. (2000), and Pucci et al. (2003).

The calorie ratios (kcal ME intake/kg weight gain) of the experimental treatments for each phase are presented in Table 11. The calorie ratio contrast between the dietary inclusion or not of oil was only significant for the period of 1 to 4 days of age (orthogonal contrast: T1x T2+T3+T4+T5+T6+T7; p<0.01). No relevant differences were observed among fat sources. This means that, during that period, broilers are not able to store large amounts of body fat when selecting higher energy diets. On the other hand, birds fed the control diet, i.e., with lower metabolizable energy level, gained less weight. The decrease in metabolizable energy intake as dietary ME is reduced was also found by Longo et al. (2006), who verified increasing energy requirements for weight gain (calorie ratio) as a function of bird age. Similarly, Mendes et al. (2004) observed that increasing dietary energy levels promoted a linear decrease in feed intake, and had a quadratic influence on the weight gain of 1- to 21day-old broilers.

Current practical tables work with low energy assumptions for the starter phases: 2960 kcal/kg from 1 to 7 days, and 3050 kcal/kg from 8 to 21 days (Rostagno et al., 2005). However, in the present study, independently of the type of vegetable oil added to the feeds, broilers selected diets containing much higher fat and energy levels than those recommended in the tables. The values of the basal diet, with no fat addition and 2843 kcal ME/kg, were the closest to those recommended by Rostagno et al. (2005). The birds selected the diets containing 3200 kcal/kg since the first days of age, with a more marked effect after 12 days of age, resulting in better performance results.

Based on the results of the present study, it can be concluded that diets containing different levels of free fatty acids, medium-chain fatty acids, and different n6:n3 ratios affected crude fat metabolizability, but did not influence the performance of 1- to 9-day-old broilers. Moreover, broilers selected diets containing high fat, and consequently high ME levels, at a very young age. The intake of pre-starter and starter diets containing high energy levels since the first days of age had a positive effect on the performance of broilers during this period.

Arrived: October/2008

Approved: March/2009

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Publication Dates

• Publication in this collection
  17 June 2009
• Date of issue
  Mar 2009

History

• Accepted
  Mar 2009
• Received
  Oct 2008