Kyriazakis I, Oldham J D
Genetics and Behavioural Sciences Department, SAC Edinburgh.
Br J Nutr. 1993 May;69(3):617-29. doi: 10.1079/bjn19930064.
To test the proposition that sheep are able to select a diet that meets their crude protein (N x 6.25; CP) requirements, feeds L, A, B, C and H with the same energy content (11 MJ metabolizable energy/kg feed) but different CP contents (78, 109, 141, 172 and 235 g CP/kg fresh feed respectively) were formulated. In addition, feed U, which was feed L plus 21.4 g urea/kg (CP content 132 g/kg), was also made. The feeds were offered ad lib. either singly (n 4 per treatment) or as a choice between feed H and another feed (pairs LH, AH, BH, CH and UH; n 9 per feed pair) to individually penned Suffolk x Scottish mule wether lambs, over the live-weight range 25-45 kg. On the single feeds the rates of live-weight gain were 273, 326, 412, 418, 396 and 407 g/day (SE of difference (SED) 34; P < 0.01) and protein (excluding wool) gain were 27, 32, 44, 45, 41 and 39 g/d (SED 4; P < 0.001) for feeds L, A, B, C, H and U respectively. When sheep were given a choice between a feed below (L or A) and a feed above their CP requirements (H; as judged by the single-feeding treatments) the CP concentration selected was not different between the two pairs: 131 (SE 4) v. 133 (SE 4) g CP/kg feed for pairs LH and AH respectively. On the choices BH and CH (a choice between two feeds above requirements) the feed lower in CP was constantly preferred (874 (SE 33) and 910 (SE 33) g feed B and C respectively per kg total feed intake; CP selected was 157 and 178 g CP/kg respectively). However, this was not the case with the UH choice on which sheep consumed only 599 (SE 61) g feed U/kg total feed intake, resulting in a selection of a higher CP in their diet (173 g CP/kg). The live-weight gains of the animals given a choice between two feeds were 416, 387, 415, 410 and 383 g/d (SED 37) and protein gains were 45, 40, 46, 50 and 43 (SE 7) for pairs LH, AH, BH, CH and UH respectively, which were comparable with the best performance achieved on a single feed. The results suggest that sheep were able to select a diet that meets their CP requirements and avoid, at least to a certain extent, excess of protein intake.(ABSTRACT TRUNCATED AT 400 WORDS)
为验证绵羊能够选择满足其粗蛋白（氮×6.25；CP）需求的日粮这一命题，配制了能量含量相同（11兆焦代谢能/千克饲料）但CP含量不同（分别为78、109、141、172和235克CP/千克新鲜饲料）的饲料L、A、B、C和H。此外，还制备了饲料U，即饲料L加21.4克尿素/千克（CP含量132克/千克）。这些饲料自由采食，单独提供（每个处理4只）或作为饲料H与另一种饲料之间的选择（配对LH、AH、BH、CH和UH；每个饲料对9只），提供给体重在25 - 45千克的单独圈养的萨福克×苏格兰骡阉羔羊。对于单一饲料，饲料L、A‘ B、C、H和U的体重日增重分别为273、326、412、418、396和407克（差异标准误（SED）34；P < 0.01），蛋白质（不包括羊毛）日增重分别为27、32、44、45、41和39克/天（SED 4；P < 0.001）。当绵羊在低于（L或A）和高于其CP需求（H；根据单喂处理判断）的饲料之间进行选择时，两对选择中所选的CP浓度没有差异：LH和AH对分别为131（标准误4）和133（标准误4）克CP/千克饲料。在BH和CH选择（两种高于需求的饲料之间的选择）中，CP含量较低的饲料一直更受青睐（每千克总采食量中分别为874（标准误33）和910（标准误33）克饲料B和C；所选CP分别为157和178克CP/千克）。然而，UH选择并非如此，绵羊每千克总采食量仅消耗599（标准误61）克饲料U，导致其日粮中选择了更高的CP（173克CP/千克）。在两种饲料之间进行选择的动物的体重日增重分别为416、387、415、410和383克/天（SED 37），蛋白质增重分别为45、40、46,50和43（标准误7），分别对应LH、AH、BH、CH和UH对，这与单一饲料的最佳性能相当。结果表明，绵羊能够选择满足其CP需求的日粮，并至少在一定程度上避免蛋白质摄入过量。（摘要截断于400字）
