GAA supplementation and lactation
Considering the high energy demand of lactation and the potential of guanidinoacetic acid (GAA) addition on the increase in creatine supply for cows, the study investigated the effects of 0, 0.3, 0.6 and 0.9 g kg−1 DM of GAA supplementation on lactation performance, nutrient digestion and ruminal fermentation in dairy cows. The study used fourty mid-lactation multiparous Holstein cows and lasted for 100 days. Dry matter intake was not affected but milk and milk components yields and feed efficiency increased linearly with increasing GAA addition. The total-tract digestibility of dry matter, organic matter, neutral detergent fibre, acid detergent fibre and non-fibre carbohydrates increased linearly and that of crude protein increased quadratically with increasing GAA addition. When the addition level of GAA increased, ruminal pH, molar percentages of butyrate, isobutyrate and isovalerate and acetate-to-propionate ratio decreased linearly, total volatile fatty acids concentration and propionate molar percentage increased linearly, but acetate molar percentage and ammonia-N concentration were unaltered. The activities of fibrolytic enzymes, α-amylase and protease increased linearly. The populations of total bacteria, fungi, Ruminococcus albus, Fibrobacter succinogenes, R. flavefaciens, Ruminobacter amylophilus and Prevotella ruminicola increased linearly, but protozoa and methanogens decreased linearly with increasing GAA addition. As for the blood metabolites, concentrations of glucose, urea nitrogen and methionine were unchanged, total protein, albumin, creatine and homocysteine increased linearly but folate decreased linearly with increasing GAA supply. The current results indicated that supplementation of GAA improved milk performance and rumen fermentation in lactating dairy cows.
Liu YJ, Zhang J, Wang C et al. Effects of guanidinoacetic acid supplementation on lactation performance, nutrient digestion and rumen fermentation in Holstein dairy cows. J Sci Food Agricult (in press). doi: 10.1002/jsfa.12249