Feed mixture, its structure and method of administration to maximize growth

Feed is a critical factor in chicken growth and there are several important ways to achieve optimal flock growth through optimal feeding.

Early feeding

Broiler chickens are very efficient in utilizing nutrients from feed for growth, therefore any feed intervention has a significant impact on growth performance. Early nutritional support through the addition of pre-starter diets is an effective method. Pre-starters can be added in trays during transportation and are usually used until day 4 of fattening.

The use of pre-starters with lower levels of calcium (4 g/kg) from 0 to 4 days of age resulted in positive effects on body weight maintained to market age (+ 2.54%), heavier carcasses (+ 2.2%), and better uniformity about 3% when compared to chickens fed usual starter diets (Franco-Rosselló et al., 2022).

Early access to feed and water is crucial to support growth in broilers. Therefore, feed must be placed in feeders and scattered on paper as soon as the chickens arrive. Ideally, about 50% of the floor area should be covered with feed. Picking feed from the ground is a natural behavior and feed on the ground, combined with increased light intensity, is a good way to initiate growth in chickens.

Feed deprivation after hatching has a detrimental effect on the growth performance of chickens. It has been shown that for every 24 hours of feed deprivation after hatching, the body weight of chickens at the end of fattening decreases by about 3%. This is probably due to reduced feed intake, as feed intake decreases by the same values every 24 hours of feed deprivation (De jong et al., 2017). Availability of feed and water promptly after hatching determines the outcome of chicken growth.

Feeder space

The provision of sufficient feeder space is an important, influential factor in the feeding behavior of chickens. According to the guidelines of various breeding companies, the recommended values for feeder space during the fattening period range from 1.5 to 2.1 cm (Cobb, 2018), 1.7 cm (Aviagen, 2015) and 2.5 to 5.1 cm (Sasso, 2018).

A recent study compared three feeder space areas (2.3, 4.6 and 6.9 cm) on slow-growing chicken growth during fattening. The results demonstrated a direct correlation: in comparison to chickens with 2.3 cm and 4.6 cm, those with the highest feeder space (6.9 cm) were 6% and 4% heavier at 28 days of age, respectively. Increased feeder space positively correlates with an improved growth rate in chickens. Therefore, it can be recommended that chickens be provided with the maximum feasible quantity of feeder space (Purswell et al., 2021).

Feed structure

With the exception of nutritional composition of a given mixture, feed structure is the most important feed property. Chickens select their feed based on visual cues, as well as its reflectivity and taste. In spite of this, they possess a relatively low number of taste buds and use mechanoreceptors located in the chicken beak to decide whether to accept or reject a feed particle (Neves et al., 2014). Therefore, an optimal particle size positively influences the feed intake in chickens.

When feeding a mash diet, current literature  designates  the optimal particle size as between 6 and 9 mm, with the objective of maximizing chicken growth. However, a 15–20% increase in feed intake and growth was noted in chickens fed a pelleted diet when compared to those fed a mash diet (Naderinejad et al., 2016).

The length and diameter of pellets also play an important role in optimizing feed intake in broilers. The optimal pellet diameter for chicks up to seven days of age is up to 2 mm (Cerrate et al., 2008). Smaller pellets of up to 2 mm have a better quality and strength and therefore are less prone to crumbling during manipulation – a factor that can negatively impact feed intake (Cerrate et al., 2009).

In older broiler chickens, a diameter of 3 mm can be recommended for optimal chicken growth (Abdollahi and Ravindran, 2013a). A comparison of the effects of pellet length (3, 5 and 7 mm) in broiler chickens until 21 days of age demonstrated that smaller particles had a significant positive impact on broiler performance. Chickens fed shorter pellets (3 mm) exhibited 8–10% higher feed intake and 5–10% higher body weight gain from 7 to 21 days of age, in comparison to chickens fed longer pellets (5–7 mm) (Abdollahi and Ravindran, 2013b).

Given these findings, it can be recommended that the optimal pellet length and diameter for chicken feed intake and growth are 3 mm and 3 mm, respectively, from 7 days of age onwards.

Whole grains inclusion

One potential method for modifying the feed structure is to incorporate whole wheat grain into the feed mixture. This approach has been demonstrated to have positive effects on intestinal health, and it is therefore widely employed in poultry nutrition.

“However, scientific literature has shown no correlation, whether positive or negative, between the use of whole grain and growth performance.” There are two ways to incorporate whole grains into pelleted feed: pre-pelleting and post-pelleting. In the pre-pelleting method, whole grain is incorporated into a pellet as a replacement for a portion of the ground grain normally used. In contrast, post-pelleting incorporation involves mixing and pelleting other feed ingredients (referred to as pelleted concentrate), after which the whole grain is blended with the pelleted concentrate.

Abdollahi et al. (2018) conducted a comparative analysis of the inclusion of ground wheat grain and whole grain in the diet of broiler chickens at various stages of development, from 1 to 42 days of age. The results indicated that the inclusion of whole grain significantly decreased feed intake by 0.2-16% in broiler chickens. However, the same study also found that the improved function (gizzard development and stimulation of digestive enzymes) of the gastrointestinal tract from feeding whole grain can result in improved feed efficiency, consequently leading to enhanced chicken growth.

In order to achieve the positive impacts of whole grain inclusion, several rules must be followed. Firstly, the gastrointestinal tract of young chicks until 7 days of age is not yet ready for whole grain inclusion; therefore, inclusion after the first week of age is necessary. Secondly, a minimum of a week-long acclimatization period must be performed before full post-pelleting inclusion of whole grain. Finally, the rate of whole grain inclusion must be regulated to ensure that energy requirements do not increase as the gizzard begins processing the grain. Current evidence indicates that the optimal inclusion rate is approximately 15%. Compliance with these rules can result in a 14.3% improvement in feed efficiency (Svihus et al., 2010).

The incorporation of whole grains represents a promising approach to enhancing feed efficiency. However, given the observed reduction in feed intake, it can be postulated that the inclusion of whole grains does not fully optimize the growth of chickens.

Feeding program

It is generally recommended to feed chickens ad libitum to maximize their feed intake and growth. In optimal environmental conditions, it can be recommended to feed chickens ad libitum because constant access to feed is related to a 4–10% higher feed intake and consequently a 3–4% higher body weight gain compared to intermittent access to the feed (Sacranie et al., 2012; Svihus et al., 2010). The effect of the feeding regime on broiler feed intake is presented in Graph 1.

However, the birds are well developed to withstand periods of feed withdrawal thanks to crop protrusion, which serves as a feed reservoir for periods of no access to feed. In the case of heat stress, when increasing temperatures result in a decrease in feed intake and body weight gain in chickens, an intermittent feeding program may improve body weight gain. In general, it is recommended to feed chickens at night when temperatures are lower to support feed intake.

However, Erensoy et al. (2020) published an interesting study where broiler chickens were subjected to heat stress (30 °C) from 11:00 to 17:00. The first group had access to feed only at the same time from 11:00 to 17:00, while the second group was fed ad libitum. The results demonstrated that the first group exhibited a 3–4% higher feed intake, a 5% higher average weekly gain, and a 4% higher live body weight at six weeks of age compared to the ad libitum-fed group.

Consequently, intermittent feeding represents a viable approach to enhancing chicken growth during periods of high heat stress. However, under optimal conditions, ad libitum feeding remains the standard method for maximizing the growth of broiler chickens.

Graph 1 Feed intake comparison of ad libitum and intermittent feeding programs in 17-day-old broiler chickens during 18 hours of photostimulation (Svihus et al., 2010).  For intermittent feeding, feed was available only during the first hour of each given time period. Values represent grams of feed per chicken.

It can be concluded that the most effective method of feeding a flock in order to achieve optimal growth is to ensure that chicks are fed at an early age and that they have sufficient space to consume their food. The optimal structure of pelleted diets is also a crucial factor in achieving optimal feed intake and growth. Finally, ad libitum feeding has been proven to be a method of feed administration that supports optimal growth.

In closing, it is vital to mention that all of these findings and recommendations rely heavily on the accuracy and reliability of available bird weight data. Lacking such data severely limits the ability to effectively manage flocks in the ways mentioned above.

Cited sources

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