不同去勢年齡對國內肉用山羊生長性能之影響

去勢是肉用動物常見之飼養管理方法，在臺灣去勢可減少羊肉腥羶味，為多數消費者所喜愛。山羊脂肪分布和綿羊不同，山羊脂肪大多累積於腹腔內臟周邊；綿羊則多累積於皮下及肌肉間。本試驗旨在探討不同品種（純種阿爾拜因、努比亞雜交）及去勢年齡（3~4及6~7月齡）對山羊之生長、飼料換肉率及經濟效益之影響，提供肉羊飼養者參考，以提升其產品品質與經濟效益。本試驗選用兩種國內市場常見品種，試驗一為16隻阿爾拜因公羊（初始體重19.78 ± 0.73 kg），依體重逢機分成兩組分別於4月齡及7月齡去勢；試驗二為18隻努比亞雜交公羊（初始體重15.15 ± 0.51 kg），依體重逢機分成兩組分別於3月齡及6月齡去勢。羊隻於試驗期間每兩週秤重一次，每日記錄採食量。結果顯示，於生長期之平均日增重與飼料效率以努比亞雜交公羊顯著高於阿爾拜因公羊（P < 0.05）；於肥育期，平均日增重、每日平均乾物質採食量及飼料轉換率亦以努比亞雜交閹公羊顯著優於阿爾拜因閹公羊（P < 0.05），然而，超音波測定結果顯示，於生長期之背脂厚度、背最長肌面積、深度及寬度均以努比亞雜交閹公羊顯著高於阿爾拜因閹公羊（P < 0.05）；於肥育期，努比亞雜交閹公羊之背最長肌面積與深度有高於阿爾拜因閹公羊之趨勢（P = 0.05）。去勢年齡對生長期之終體重、總增重、平均日增重、總採食量及飼料效率皆無顯著差異（P > 0.05），然超音波測定於生長期均呈現晚去勢組之背最長肌深度有顯著高於早去勢組（P < 0.05）；於肥育期則顯示，去勢年齡對兩品種羊之生長性能皆無顯著影響（P > 0.05），此外，去勢年齡對肥育後之背脂厚度、背最長肌面積、深度及寬度均無顯著影響（P > 0.05）。本試驗結果顯示，農民飼養生長性能較佳之努比亞雜交閹公羊，可縮短飼養期且有較佳之經濟效益。去勢年齡並不影響生長性能，因此，去勢時間可由農民考量各場飼養管理自行決定。

關鍵字

去勢；山羊；生長性能；超音波

並列摘要

Castration of meat animals is a commonly used method in feeding and management system. Castration can reduce the gamey taste of mutton, and it is accepted by most Taiwanese consumers. The distribution of fat in goats is different from that in sheep. As for goat most fat deposits around the viscera; while for sheep fat accumulates mostly under the skin and between the muscles. Therefore, the trial aims to investigate the effects of different breed (purebred of Alpine and Nubian goat hybrid) and castrated age (3~4 months age and 6~7 months age) on growth, feed conversion ratio and economic benefits, so as to provide reference for meat goat farmers in order to improve their product quality and economic benefits. In this experiment, two common breeds of domestic goat were selected. In experiment one, 16 Alpine male goats (initial weight 19.78 ± 0.73 kg) were divided into two groups according to body weight. Castration is being done at the age of 4 months and 7 months, respectively. In experiment two, 18 Nubian crossbred male goats (initial weight 15.15 ± 0.51 kg) were divided into two groups according to body weight. Castration was done at the age of 3 months and 6 months, respectively. Goats were weighted every two weeks during the experimental period, and daily food intake was recorded. The results showed that during growth period the average daily gain and feed conversion ratio of Nubian crossbred male goats were significantly better than those of Alpine male goats（P < 0.05）; During fattening period, the average daily gain, the average feed intake and the feed conversion ratio of the Nubian crossbred wethers were significantly better than those of Alpine wethers（P < 0.05）. However, the result of ultrasonic measurements showed that during growth period the backfat thickness, longissimus dorsi area, longissimus dorsi depth and longissimus dorsi width of Nubian crossbred wethers were significantly higher than Alpine wethers （P < 0.05）; In the fattening period, the longissimus dorsi area and depth of the Nubian crossbred wethers were higher than that of the Alpine wethers（P = 0.05）. The results of growth performance at different castration ages showed that there was no significant difference in final body weight, total weight gain, average daily gain, total feed intake and feed conversion ratio the goats during growth period（P > 0.05）. However, the result of ultrasonic measurements showed that there was a significantly higher in depth of the longissimus dorsi muscle in the late castration groups between the two breed（P < 0.05）; In the fattening period, there was no significant difference in growth performance between experiment 1 and experiment 2（P > 0.05）. In addition, there was no significant difference in back fat thickness, longissimus dorsi depth and longissimus dorsi width between early stage or late stage of castration（P > 0.05）. The results of experiment showed that farmers tend to raise Nubian crossbred wethers with better growth performance and it can reduce the feeding period, thus with better economic benefit. The difference of castration age doesn’t affect the growth performance. Therefore, the timing of castration could be determined by the convenience of the owner's management.