The effect of guanidino-acetic acid supplementation on Holstein heifer calf growth and blood parameters
The dairy industry in South Africa places a significant focus on production, as seen in the ongoing increase in total milk output, even though the number of cows and dairy farmers has decreased. This situation creates an urgent need to enhance calf-rearing practices to ensure a steady supply of healthy, fast-growing, and fertile replacement heifers to satisfy industry demands. Guanidino-acetic acid (GAA), a direct precursor to creatine, is vital for the body's energy storage system. Supplementing GAA has been proposed as a possible approach to improve creatine production and promote better growth performance in production animals, with a recent focus on dairy calves.
The present study determined the potential benefit of adding GAA to the milk replacer (MR) of pre-weaned Holstein heifer calves on subsequent growth and health. The effects on certain blood parameters were investigated to establish if the GAA inclusion had any effect in the calf on a physiological level. Thirty-one Holstein heifer calves with average live weight of 37.15 ± 4.83 kg (SE), were randomly assigned to one of three treatment groups: Control (CON) – 0 g GAA/kg LW, Lower inclusion (LI) – 0.02 g GAA/kg LW, and Higher inclusion (HI) – 0.03 g GAA/kg LW per day in the MR. The calves were reared in individual pens and weaned at 77 days of age. Supplementing MR with GAA did not have any positive effects on overall weight gain of calves, average daily gain, or feed conversion ratio. The treatment groups did not differ in terms of starter feed intake and total dry matter intake over the 11-week study period. Allometric growth-related parameters (wither height, heart girth circumference, and body length) did not differ among the treatment groups, which is reflected in no effect of GAA supplementation on weaning weight.
Plasma insulin-like growth factor (IGF-1) and total serum protein (TSP) concentrations were also comparable across the groups, with minor differences in β-hydroxybutyrate (BHBA) levels that were likely unrelated to GAA supplementation, indicating no adverse health effects. The supplementation of MR with GAA resulted in increased GAA blood levels, and a tendency for blood creatine level to increase for both experimental groups in comparison to the control, despite no influence on creatinine levels. Methionine levels did not differ among the treatment groups, and GAA supplementation did not influence amino acid availability. The GAA supplementation did not result in an arginine-sparing effect. Previous studies have demonstrated that GAA supplementation can enhance growth and performance in poultry, swine, weaned ruminants, and beef calves, which was not observed in this study where Holstein heifer calves were used. It can be concluded that the GAA inclusion levels used in this study and that were based on endogenous creatine supply and -requirement, were too conservative to elicit a growth response. It is recommended that follow-up research include larger animal numbers, and a higher level of GAA supplementation.