Hello there! This is my Research Digest #3.
Today, the article I wanted to share with you is titled 'The effect of total sulfur amino acid levels on growth performance, egg quality, and bone metabolism in laying hens subjected to high environmental temperature'
This is a work from Dr. Woo Kim's lab at University of Georgia in collaboration with CJ corporation, and it just came out as an Advance article on June 1 in Poultry Science.
Dr. Kim has done a lot of wonderful work on understanding mineral nutrition and bone health in poultry, and those results & bone pictures from MicroCT analysis are really cool to see!
Maintaining good skeletal health has always been a challenge in the poultry industry. Heat stress may negatively affect bone quality & egg production in laying hens due to reduced Ca intake; meanwhile, protein also constitute a major component of the structural bone matrix and dietary amino acids (such as Met) may affect Ca metabolism.
So the question asked in this study was - how would total sulfur amino acids (Met + Cys) level affect performance and bone quality in laying hens during heat stress?
What was done?
The experiment was a 2x3 factorial arrangement, and below is an illustration of what was done.
It was interesting that the authors raised all pullets under cyclic heat stress prior to the start of the study --- think they were hoping to see whether the birds may acclimate to the hot environment, but found out that the birds still prefer comfortable temperature even if they were raised hot (which I 100% agree with the birds 😜)
What was found?
- Growth Performance
Heat stress reduced egg production at all ages; 70% TSAA reduced performance (BW gain, feed intake, FCR, egg production, egg weight, etc.) regardless of heat stress, but birds fed 85% & 100% TSAA had normal performance as birds under control temperature at week 34 & 45.
- Bone quality
Heat stress or TSAA did not affect collagenous or non-collagenous protein content in the bone.
Heat stress did not affect bone mineral content or density. Interestingly, although TSAA level did not affect total bone mineral density (BMD) or mineral content (BMC), lower TSAA did reduce BMD in cortical and trabecular bone, while increase BMD (& BMC) in medullary bone.
Since medullary bone is the source of Ca for shell formation, a possible reason for this increase could be that birds fed lower TSAA had reduced egg production (see figure above), so less Ca was resorbed for egg shell formation, and thus mineralization of medullary bone was higher.
It is interesting to note that although Ca mainly comes from medullary bones, if that source becomes insufficient, bone resorption could occur in structural bones (cortical & trabecular bones) as well, which can lead to skeletal issues like bone fracture. Here, we see that birds fed higher TSAA had higher BMD in structural bones, suggesting that TSAA somehow could help minimize structural bone loss.
Take home message
Heat stress is never good for performance and egg quality in laying hens, no impact on bone quality though.
85% or 100% TSAA could mitigate the negative effects of heat stress & also improve BMD in structural bones.
Full article access 👇
Castro, F.L.S., Kim, H.Y., Hong, Y.G. and Kim, W.K., 2019. The effect of total sulfur amino acid levels on growth performance, egg quality, and bone metabolism in laying hens subjected to high environmental temperature. Poultry science.
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