Effects of guanidinoacetic acid and betaine on growth performance, energy and nitrogen metabolism, and rumen microbial protein synthesis in lambs

Abstract

In this study, we investigated the effects of guanidinoacetic acid (GAA) and betaine (BT) on growth performance, nutrient digestion, energy-nitrogen metabolism, and microbial protein synthesis in lambs. Forty-eight 3-month-old Dorper × Thin-tailed Han first crossbred generation ram lambs with similar body weight (22.03 ± 1.3 kg; mean ± SD) were randomly divided into 4 groups. According to the 2 × 2 factorial arrangement, lambs in each of the 4 groups were fed basal diets, or basal diets supplemented with 0.9 g GAA/kg dietary dry matter (DM), 5 g BT/day, or 5 g BT/day + 0.9 g GAA/kg dietary DM. Before the formal trial, all lambs were allowed to adapt to the facilities as well as the basal diet for 15 days. This study lasted for 71 days including a 60-day period for feeding trial and an 11-day period for digestion and metabolism trials. The results showed that supplementation with GAA or BT increased the average daily gain (ADG) and feed efficiency (FE). However, no further increase in ADG or FE was observed with the combination of GAA and BT compared to that induced by addition of GAA or BT alone. Moreover, the addition of GAA or BT improved the apparent digestibility of dry matter (DM) and neutral detergent fiber (NDF), while GAA increased acid detergent fiber (ADF). GAA or BT supplementation decreased ruminal pH but increased the concentration of total volatile fatty acids (T-VFA), propionate, and valerate. Ruminal ammonia N content was not influenced by GAA or BT supplementation. Addition of GAA or BT resulted in an increase in microbial protein (MCP) synthesis. Additionally, supplementation with GAA or BT promoted digestible nitrogen (N), retained N, digestible energy and apparent digestibility of gross energy, and reduced fecal N. Supplementation with GAA decreased urinary N and increased metabolizable energy. The addition of GAA or BT increased total protein and creatine levels in serum, but the addition of BT alone decreased blood homocysteine (Hcy) levels. GAA elevated blood insulin-like growth factors-1 (IGF-1). These results demonstrate that supplementation with GAA or BT improves growth performance, nutrient digestibility, and energy-nitrogen metabolism, but the addition of BT and GAA in combination does not further improve the growth of lambs.