2.2. Animals, Experimental Design, and Growth Performance

Animals were maintained according to the guidelines set by the Biological Studies Animal Care and Use Committee of Gansu Province, China (2005–12). Fifty male Hu lambs with an average age of three months and an average initial body weight (BW) of 17.5 ± 0.34 kg were randomly allocated to one of five treatment groups, each with ten lambs. All diets contained 30% corn (Zea mays L.) straw, 50% concentrate mixtures, and 20% common vetch stover or 20% alfalfa hay as the control (Table 1). The diets varied in the variety of common vetch stover added, with the treatments being the alfalfa control as above, or 20% stover of one of the common vetch varieties C333A, CLJ1, CLJ2, or CLJ3. The dried forage and concentrate components were combined as pelleted total mixed rations (TMR). The diets were formulated according to feeding standards for meat-producing sheep and goats [16]. Ingredients and chemical composition of the experimental diets are shown in Table 1.

Ingredients and chemical compositions (g/kg dry matter) of the experimental diet.

¹ Control, diet containing alfalfa hay; C333A, diet containing 333A stover; CLJ1, diet containing Lanjian No. 1 stover; CLJ2, diet containing Lanjian No. 2 stover; CLJ3, diet containing Lanjian No. 3 stover; ² Mineral and vitamin premix contained, g/kg: Fe 69.63, Cu 7.41, Mn 23.7, Zn 55, I 0.67, Se 0.3, Co 0.3, vitamin A 2500 IU, vitamin E 23 IU; ³ F:C ratio, proportion between the amounts of roughage and concentrate in diet.

The lambs were treated for internal parasites before commencement of the study. The experimental period lasted 67 days, with an adaptation period of 10 days, a 50-day fattening period, and a 7-day digestibility trial. Throughout the experimental period, all lambs were randomly assigned to individual pens (3.1 m × 1.0 m × 0.85 m) equipped with feeders and water buckets. The daily feed ration was offered ad libitum to the lambs in two parts at 08:30 and 16:30 h. During the fattening period, amounts of feed offered were recorded daily and the orts were weighed weekly, for each lamb individually, to estimate dry matter intake (DMI). A two-day-average BW of lambs, with weighing carried out before the morning feeding, was recorded individually at the beginning and at the end of the fattening period to determine average daily gain (ADG) and feed conversion ratio (FCR = DMI/ADG).