Effects of dietary concentrate to forage ratio on milk performance, milk amino acid composition and milk protein synthesis of lactating donkeys

Abstract

The purpose of this experiment was to compare the effects of the dietary concentrate-to-forage ratio on lactating donkey milk production performance, milk protein synthesis and milk amino acid composition by replacing part of low-quality roughage with alfalfa. The second objective was to investigate the possible mechanism by which the dietary concentrate-to-forage ratio affects donkey milk protein synthesis. These results will provide a theoretical basis for the rational preparation of feed and optimization of the amino acid composition of donkey milk. This experiment adopted a single-factor randomized trial design. Sixteen Dezhou donkeys with similar ages (6.73 ± 1.16 years), weights (250.84 ± 27.21 kg), parities (3.25 ± 1.12 foals) and lactation days (40 ± 4 days) were selected and evenly (n = 8 per group) divided into a low forage feed group (LF) and a high forage feed group (HF). The LF group was fed a diet with a concentrate to forage feed ratio of 40:60, and the HF group was fed a diet with a concentrate to forage feed ratio of 30:70. The energy and protein levels of the two diets were the same, and the test period lasted 8 weeks. Compared with the LF group, the concentrations of total protein, prolactin and hydrocortisone in the serum of donkeys in the HF group were increased (P < 0.05); the apparent digestibility of dry matter, neutral detergent fiber and energy digestibility and energy metabolic of the donkeys in the HF group were improved (P < 0.05); the concentrations of albumin, epidermal growth factor and urea phosphate tended to decrease (0.05 < P < 0.10); the concentrations of threonine (Thr), lysine (Lys), methionine, histidine, proline and limiting amino acids (LAAs) in the plasma and nitrogen metabolism of the donkeys in the HF group were increased (P < 0.05); milk yield, production and synthesis efficiency of milk protein and most amino acid (AA) production in milk (except serine and valine) were increased (P < 0.05); the proportions of Thr, Lys phenylalanine and LAA in donkey milk were increased (P < 0.05); the final body weight and the body weight gain of donkey foals in the HF group was improved. Under the condition of feeding the same energy and nitrogen levels, increasing the proportion of forage from 60% to 70% by replacing part of low-quality forage with alfalfa promoted the protein and energy metabolism, increased milk protein synthesis efficiency, milk production efficiency and milk production performance, improved the proportion of LAAs and optimized the AA composition of donkey milk.