ABSTRACT
Current equine threonine requirement estimates do not account for probable use of threonine to maintain
gut health and mucin synthesis. The objective of this study was to determine if threonine
supplementation (+Thr) would increase whole-body protein synthesis (WBPS) in weanling colts (Study
1) and adult mares (Study 2). Both studies used a crossover design, where each of six animals was studied
twice while receiving the isonitrogenous diets. The basal diets contained lower threonine levels (Basal)
than the threonine (+Thr) supplemented diets. Threonine intakes in mg/kg BW/day were as follows: 79
(Basal) and 162 (+Thr) for Study 1 and 58 (Basal) and 119 (+Thr) for Study 2, in comparison to the NRC
estimated requirements of 81 and 33 mg/kg BW/day for weanling and mature horses, respectively.
Following 5 days of adaptation, blood samples were taken before and 90 min after the morning concentrate
meal. The next day, whole-body phenylalanine kinetics were determined using a 2 h primed,
constant infusion of [13C]sodium bicarbonate followed by a 4 h primed, constant infusion of [1- 13C]phenylalanine. Most plasma amino acid (AA) concentrations were elevated post-feeding (P < 0.01).
Lysine and valine plasma concentrations were lower (P < 0.10), while methionine, threonine, and glycine
plasma concentrations were greater (P < 0.10) 90 min post concentrate meal feeding with +Thr in both
studies. Phenylalanine flux, intake, oxidation and non-oxidative disposal were similar between treatments
(P > 0.05). These findings suggest that supplementation of a single AA can affect the metabolism
of several AAs and threonine was not a limiting AA in these diets.
© 2015 Elsevi