Animal and Bioscience Department, Teagasc, Dunsany, Co. Meath, C15 PW93, Ireland; School of Agriculture and Food Science, University College Dublin, Belfield, Dublin 4, Dublin, D04 F6X4, Ireland.
Laboratory of Animal Reproduction, Department of Biological Sciences, University of Limerick, Limerick, V94 T9PX, Ireland.
J Dairy Sci. 2018 Apr;101(4):3447-3459. doi: 10.3168/jds.2017-13719. Epub 2018 Feb 7.
The aim of this study was to examine the effect of plane of nutrition (1) during the first 6 mo of life and (2) from 6 mo of age to puberty on early growth characteristics, age at puberty, and postpubertal semen production in Holstein-Friesian bulls. Holstein-Friesian bull calves (n = 83) with a mean (standard deviation) age and body weight of 17 (4.4) d and 52 (6.2) kg, respectively, were assigned to a high (Hi) or low (Lo) plane of nutrition for the first 6 mo of life. The Hi and Lo calves received 1,200 and 450 g of milk replacer, respectively; Hi calves were fed concentrate ad libitum and Lo were fed a maximum of 1 kg concentrate daily, and concentrate allowances remained the same after weaning. At 24 wk of age, bulls were reassigned within treatment to either remain on the same diet or to switch to the opposite diet until puberty, resulting in 4 treatment groups: Hi-Hi, Hi-Lo, Lo-Lo, and Lo-Hi. After puberty, all bulls were fed a moderate plane of nutrition until 60 wk of age; thereafter, the diet was ad libitum concentrates until slaughter at 72 wk of age. Bulls were weighed weekly before weaning and every 2 wk after weaning. Scrotal circumference (SC) was measured every 2 wk, beginning at 15 wk of age. Beginning at a SC of 24 cm, electro-ejaculation was carried out every 2 wk to establish the onset of puberty. Semen collection continued monthly after puberty. Thermal images of the scrotum were taken monthly from 28 to 36 wk of age. Scrotal skin thickness (SST) was measured monthly (from 16 wk of age to puberty) using a digital calipers. Bulls on the Hi diet had a higher scrotal temperature and SST at each time point than those on the Lo diet. Average daily gain (ADG) was greatest in Hi-Hi bulls, with Hi-Lo and Lo-Hi having similar ADG but both being greater than Lo-Lo. Bulls on the Hi diet pre-6 mo of age were younger at puberty, regardless of diet offered post-6 mo of age. Bulls offered a Hi diet post-6 mo were heavier at puberty. Neither scrotal temperature nor dietary treatment affected postpubertal semen production variables. In conclusion, a high plane of nutrition during the first 6 mo of age hastened the onset of puberty and the availability of saleable semen, regardless of plane of nutrition post-6 mo of age.
本研究旨在探讨（1）生命最初 6 个月和（2）从 6 个月到青春期的营养水平对荷斯坦-弗里森公牛早期生长特征、青春期年龄和青春期后精液产生的影响。具有平均（标准差）年龄和体重 17（4.4）天和 52（6.2）kg 的荷斯坦-弗里森公牛犊牛（n=83）被分配到生命最初 6 个月的高（Hi）或低（Lo）营养水平。Hi 和 Lo 小牛分别接受 1200 和 450g 代乳粉；Hi 小牛自由采食浓缩物，而 Lo 小牛每天最多喂食 1kg 浓缩物，断奶后浓缩物的摄入量保持不变。在 24 周龄时，根据处理内的分配，公牛被重新分配，要么继续接受相同的饮食，要么切换到相反的饮食，直到青春期，从而产生 4 种处理组：Hi-Hi、Hi-Lo、Lo-Lo 和 Lo-Hi。青春期后，所有公牛都以中等营养水平喂养，直到 60 周龄；此后，直到 72 周龄屠宰时，饮食为自由采食浓缩物。公牛在断奶前每周称重，断奶后每两周称重一次。从 15 周龄开始，每两周测量一次阴囊周长（SC）。当 SC 达到 24cm 时，每隔两周进行一次电刺激射精，以确定青春期的开始。青春期后，每月进行一次精液采集。从 28 到 36 周龄，每月拍摄阴囊的热图像。每月使用数字卡尺测量阴囊皮肤厚度（SST）（从 16 周龄到青春期）。接受 Hi 饮食的公牛在每个时间点的阴囊温度和 SST 都高于接受 Lo 饮食的公牛。Hi-Hi 公牛的平均日增重（ADG）最大，Hi-Lo 和 Lo-Hi 的 ADG 相似，但均高于 Lo-Lo。6 个月前接受 Hi 饮食的公牛在青春期时更年轻，无论 6 个月后提供何种饮食。6 个月后接受 Hi 饮食的公牛在青春期时体重更重。阴囊温度或饮食处理都没有影响青春期后的精液产生变量。总之，生命最初 6 个月的高营养水平加速了青春期的开始和可销售精液的获得，而不管 6 个月后营养水平如何。
