HEAT STRESS The importance of summer diets for poultry


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Annatachja De Grande obtained her PhD at the University of Ghent where she focused on the effects of dietary zinc source on growth and intestinal health in broilers. This article discusses the new insights presented by De Grande and other researchers in 2021. As she explains, “during heat stress, broilers have an increased need for several nutrients and trace minerals. This requires that poultry farmers and nutritionists adapt the formulation when a rise in temperature is expected. But at the same time, you don’t want to make the diet


unnecessarily expensive and only provide the extra nutrients when the animals really need them. In our trials we showed that strong anti- oxidants, such as zinc and vitamin E, should defi- nitely be part of a ‘summer diet’, as they have an important role in gut health and reducing oxida- tive damage in the muscle tissue. Using zinc as zinc amino acid complexes increases the availa- bility and uptake of the trace mineral, reflected in reduced drip loss, one of the most important parameters for meat quality and better growth and performance, due to better gut health and


better intestinal development after hatch with an increase in villi length, leading to better absorption of nutrients. These results have also been confirmed in previous studies and are important as this shows the benefits of modulating the gut at an early stage. This positive difference continued up to day 28 when the heat stress model was applied, reflected in a higher daily weight gain and daily feed intake and improved feed conver- sion ratio (FCR) over the whole period (Figure 2). This effect was not observed at a vitamin E level of 100 IU/kg, confirming the observation that a higher vitamin E inclusion rate is not necessary under these circumstances.


Early gut development Regardless of the vitamin E level, birds fed a diet supplement- ed with ZnAA had a greater villus length and villus length to crypt depth ratio in duodenum sections compared to birds fed a diet supplemented with ZnSO4


on days 10, 28 and 36.


The results seen at day 10 are particularly important because the gut is developing at this stage. An increase in villus length


Figure 2 – FCR (from 0-36 days) was optimum when ZnAA was used in combination with the lower dosage of vitamin E.


1.525 1.520 1.515 1.510 1.505 1.500 1.495 1.490 1.485


nutrient uptake in the gut. Surprisingly, these results were achieved in combination with a lower level of vitamin E, something we hadn’t really expected, but still very welcome in these times of high feed prices. It would be interesting to delve deeper into the complex interaction between zinc and vitamin E in the near future”.


results in an increase in intestinal surface which is directly proportional to digestive and absorptive efficiency and thus to feed conversion efficiency. This might partly explain the positive effects of ZnAA on performance parameters. A strong effect of zinc source was also observed for the infiltration of CD3 positive T-lymphocytes in duodenum sections at day 36, with a lower infiltration of CD3 positive T-lymphocytes for birds fed a diet supplemented with ZnAA compared to ZnSO4


.


A decreased infiltration of CD3 positive T-lymphocytes was already seen at day 10 using ZnAA and indicates decreased stimulation of the immune system of the intestinal tract. The study also looked at ovotransferrin, a marker for gut barrier failure in broiler chickens that can be used to assess the effi- cacy of additives or strategies that reduce intestinal damage. The lower the ovotransferrin level, the less gut health damage. For both vitamin E levels, the use of ZnAA resulted in a lower ovotransferrin concentration in the ileum content (μg/g), com- pared to ZnSO4


(at day 36). Further data showed that ZnAA


also performed better than the ZnSO4 in increasing breast meat yield by 3.1% and reducing 24 h drip loss by 25%.


50 IU VitE 100 IU VitE ZnSO4 24 ▶ POULTRY WORLD | No. 6, 2022 50 IU VitE 100 IU VitE ZnAA


Preparing the bird Performance and resilience against heat stress can be posi- tively influenced via supplementation of zinc in the form of ZnAA, as used in this trial, and a vitamin E level of 50 IU/kg early in life when the gut and its microbiome are develop- ing. Providing zinc in this form positively influences gut and microbiome development and hence promotes growth and, more importantly, prepares the bird for future challenges such as heat stress, while retaining breast meat quality and yield when heat stress occurs. Interestingly, under the con- ditions of this study, no positive effects on performance is observed when vitamin E was supplemented at 100 IU/kg in feed, therefore providing an economic benefit.


*Zinpro Availa Zn, part of the Zinpro Performance Minerals range.


PHOTO: GHENT UNIVERSITY


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