The effect of guanidinoacetic acid supplementation in milk replacer on heifer calves’ growth and blood parameters
It has been shown that increasing preweaning average daily gain (ADG) could contribute to up to 22% increase in first lactation milk yield, indicating that a higher weaning weight (WW) could result in an increase in milk yield over the first lactation. This has led to a wide range of research with the focus on increasing WW, thereby securing higher production within the first lactation. Approaches have included feeding higher levels of milk replacer or whole milk, increasing the protein and/or fat content of milk replacer and optimising starter feed composition and intake.
Increasing WW could also be achieved by focusing more directly on muscle development. One of the ways in which this could be achieved is to enhance creatine supply to the calf. Creatine plays a critical role in muscle activity, since it is responsible for storing high-energy phosphate bonds in muscle. Creatine can be supplied through the diet or synthesized endogenously. Dietary sources of creatine are only found in products of animal origin, therefore livestock that are consuming plant-based diets rely only on de novo synthesis of creatine. Creatine also does not withstand heat treatment and is therefore not regularly present in animal feeds since it will be destroyed during the processing of animal protein products.
Guanidinoacetic acid (GAA) is the direct endogenous precursor of creatine in all vertebrates and is more stable and less expensive than creatine. Creatine is synthesized in the liver from GAA by methylation by S-adenosylmethionine. Methionine is used in the production of creatine and is often limiting for cattle. When supplementing GAA, it is important to feed methionine accordingly since the GAA is an obligate consumer and may cause a methionine deficiency. Guanidinoacetic acid is produced in the kidneys; however, its production depends on the supply of arginine and glycine. Simultaneously, the production of GAA decreases the availability of arginine and glycine. As methionine, arginine and glycine all play an important role in either producing GAA or producing creatine from GAA it is essential to ensure adequate supply to prevent any limitations.
The supplementation of GAA in broiler diets has been shown to decrease the effect of heat stress, improve feed conversion ratio (FCR) and increase breast meat yield. The success of GAA supplementation in broiler diets has led to research on the use of GAA in other animal species, such as cattle. Post-ruminal GAA supplementation to beef steers has shown a sparing effect on arginine and increased the level of creatine. Rumen degradation of GAA has been established to be between 47 to 49% and the implications of supplying GAA in the diet of ruminants needs to be considered.
Research on the effect of GAA on dairy calves is currently very limited. A calf transitions from a pseudo-monogastric animal to a functioning ruminant, meaning that that the rumen is not completely developed at birth and the rumen epithelium and microbial population need to be established. The rumen portion of the stomach chambers only reaches full capacity by 12 – 16 weeks of age after stimulation by starter feeds. Prior to 12 weeks of age, colostrum and MR will bypass the rumen, reticulum and omasum through the oesophageal groove and flow directly into the abomasum. The addition of GAA to a MR will therefore not be degraded in the rumen and will instead be absorbed from the small intestines, from where it can then be used for the synthesis of creatine.
The aim of this study is to determine whether the WW of dairy calves can be increased through the supplementation of GAA in MR.
The objectives of this study include the following:
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To determine the effect of two rates of GAA supplementation on growth parameters of pre-weaned dairy calves.
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To determine whether the supplementation of GAA can increase the WW of pre-weaned dairy calves.
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To determine the effect of two rates of GAA supplementation on blood parameters associated with growth and calf health.