NUTRITION ▶▶▶
Limiting the impact of diet change for broilers
In order to match nutrient requirements with bird age it is necessary to change dietary specifications throughout the production cycle. Although requirements change slowly over time, we can only practically accommodate this transition with rather abrupt changes to the diet formulation. Luckily, birds easily adapt.
BY STEVE LEESON, PROFESSOR EMERITUS, UNIVERSITY OF GUELPH O
ur current strains of broilers show outstanding ge- netic potential in terms of growth rate fuelled by ever increasing feed intake. This genetic potential is necessarily underpinned by evermore sophisti-
cated environmental control and providing diets that match requirements to age and level of performance. For broilers, depending on market age, we usually impose two or three diet changes. It is generally recognised that with high- er sustained genetic potential, we now have bird strains that are perhaps more sensitive to any given diet change. An alter- native view is that any adverse response may have always oc- curred but has only more recently been measured with the in- troduction of more sophisticated monitoring systems. In broilers there is often very transient feed refusal or feed wast- age when the pelleted grower diet is first introduced. There is surprisingly little information available on how broilers re- spond to these abrupt diet changes that are necessary as part of modern lifecycle feeding regimes. As with many situations in life, the bird likes consistency in its environment, including in its feed, and takes time to adjust to any new situation.
Two factors There are likely two general factors that impact transient change to feed intake in response to diet change; firstly, the physical characteristics of the diet and secondly, its nutrient and any anti-nutrient content. With a change in feed formula- tion comes a change in the nutrient composition, as well as a change in the ingredient composition. Additionally, and per- haps of more importance to the young broiler, these changes are also associated with a major change in feed texture. For broilers any response to feed change is very transitory, as will be discussed later. Research suggests that this transition is ex-
18 ▶ POULTRY WORLD | No. 1, 2021
ceptionally short-lived and is much less dramatic than sug- gested by our casual management observations. It is difficult to accept that any nutrient change in the feed could have an immediate and short-lived impact on feed intake. While die- tary nutrient composition is definitely involved in long-term feed intake regulation (>24h), it is more likely that changes in the physical characteristics of the feed are the main reason behind an alteration in the very short-term feed intake. Such physical characteristics are feed texture, feed colour, feed taste and feed density/hardness. Table 1 indicates the possible relevance of these feed characteristics. The physical nature of the feed, namely, the combination of texture and hardness, are the overwhelming factors impact- ing feed intake at the time of diet change, as clearly seen in the transition from crumbs to pellets in young broilers. Changes in ingredient composition and nutrient profile are intimately linked, and together can represent an important additional novel change during this transition. Feed colour and taste are of lesser importance but this maybe because we don’t yet fully understand their significance to the bird.
Feed colour and taste It seems unlikely that change in feed colour or taste could have a major impact on transitory feed intake. The bird has more taste buds than originally documented, so it’s a myth that the bird has no sense of taste. Broilers seem to have more taste buds than layer strains. They respond measurably to ‘bitter’ tastes but much less to a ‘sweet’ taste, hence the myth about stimulating early feed intake of chicks with sugar, etc. There are numerous reports of compounds that birds find unpalatable which was the basis for developing varieties of sorghum that wild birds are reluctant to eat. The active com- pound in bird-resistant sorghum is closely related to cin- namaldehyde, a compound we have shown to have a nega- tive linear effect on feed intake in broilers. Similarly, we have shown that broilers reduce their intake when feed is artificial- ly flavoured with ‘mushroom’ which is possibly an evolution- ary defence mechanism against the ingestion of mycotoxins. There are no reports of any flavours that stimulate feed intake which mitigates against the development of any unique flavours to aid in the diet transition process. It is also a myth that birds are colour-blind and so feed colour may be of more significance than is generally assumed. Birds have red, blue and green cones in their eyes, as do most
PHOTO: JAN WILLEM SCHOUTEN
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