Macrina A L, Kauf A C W, Pape-Zambito D A, Kensinger R S
Department of Animal Science, The Pennsylvania State University, University Park 16802.
Department of Animal Science, The Pennsylvania State University, University Park 16802.
J Dairy Sci. 2014 Mar;97(3):1446-53. doi: 10.3168/jds.2013-7241. Epub 2014 Jan 17.
Milk production in heifers induced into lactation is lower than that of postpartum primiparous cows. A method to improve milk production in induced lactations may provide opportunities for increased profitability as well as increase our understanding of the mechanisms that regulate mammary gland development and colostrum composition. The present study was conducted to determine if dexamethasone administration at the onset of milking or age at lactation induction would affect milk production in heifers induced into lactation. Holstein heifers at 14 [n=20; 354 ± 38 kg of body weight (BW)] and 18 mo of age (n=20; 456 ± 30 kg of BW) were assigned randomly to dexamethasone (DEX) or control (CON) treatment groups in a 2 × 2 factorial arrangement with age and dexamethasone treatment as the 2 factors. Heifers were induced into lactation with daily subcutaneous injections of estradiol-17β and progesterone (0.075 and 0.25 mg/kg of BW per d, respectively) on experimental d 1 to 7. They also received bovine somatotropin (bST) every 14 d beginning on experimental d 1. Milking began on experiment d 18 (lactation d 1). Dexamethasone (10mg) was administered on lactation d 1 and 2 following the morning milking; CON heifers did not receive dexamethasone. Milk yield from d2 to 15 of lactation of heifers receiving DEX (7.8 kg/d) was greater than that of CON heifers (6.0 kg/d) but was similar thereafter through 305 d of lactation (18.2 kg/d). Milk production to d 11 was similar for 14- and 18-mo-old heifers but was greater for 18- (18.9 kg/d) than for 14-mo-old animals (17.4 kg/d) through 305 d in milk. Milk fat percentage increased initially and was greater in DEX (4.51%) compared with CON (3.53%) heifers until 21 d in milk. Milk protein and lactose concentrations were not affected by DEX treatment. Age at induction did not affect milk fat, protein, or lactose percentages. Mean milk IgG concentration declined from 107.4 mg/mL on d 1 to 5.0mg/mL on d 7 of lactation, tended to be greater for 18- compared with 14-mo-old heifers, and was not different due to DEX treatment. Administration of DEX to heifers induced into lactation increased initial milk production during the first 2 wk of lactation but this effect did not persist through 305 DIM. Treatment with DEX appeared to stimulate mammary cell differentiation but did not change the rate of decline of milk IgG concentrations. Higher milk yield in 18-mo-old heifers may be due to greater mammary epithelium, higher body mass, or both.
诱导泌乳的小母牛产奶量低于产后初产母牛。一种提高诱导泌乳产奶量的方法可能会增加盈利机会，同时增进我们对调节乳腺发育和初乳成分机制的理解。本研究旨在确定在挤奶开始时或诱导泌乳的年龄给予地塞米松是否会影响诱导泌乳的小母牛的产奶量。将14月龄（n = 20；体重354 ± 38千克）和18月龄（n = 20；体重456 ± 30千克）的荷斯坦小母牛随机分配到地塞米松（DEX）或对照（CON）处理组，采用2×2析因设计，年龄和地塞米松处理为两个因素。在实验第1至7天，通过每天皮下注射雌二醇-17β和孕酮（分别为0.075和0.25毫克/千克体重）诱导小母牛泌乳。从实验第1天开始，每14天给它们注射一次牛生长激素（bST）。挤奶于实验第18天（泌乳第1天）开始。在泌乳第1天和第2天早晨挤奶后给予地塞米松（10毫克）；CON组小母牛不接受地塞米松。接受DEX处理的小母牛在泌乳第2至15天的产奶量（7.8千克/天）高于CON组小母牛（6.0千克/天），但此后直至泌乳305天（18.2千克/天）两者相似。14月龄和18月龄小母牛至第11天的产奶量相似，但在整个305天的泌乳期内，18月龄小母牛（18.9千克/天）的产奶量高于14月龄小母牛（17.4千克/天）。乳脂率最初升高，在泌乳至21天期间，DEX组小母牛（4.51%）的乳脂率高于CON组（3.53%）。乳蛋白和乳糖浓度不受DEX处理影响。诱导泌乳时的年龄不影响乳脂、乳蛋白或乳糖百分比。平均乳IgG浓度从泌乳第1天的107.4毫克/毫升降至第7天的5.0毫克/毫升，18月龄小母牛的乳IgG浓度往往高于14月龄小母牛，且不受DEX处理影响。给诱导泌乳的小母牛施用DEX可提高泌乳前2周的初始产奶量，但这种效果在305天的干物质摄入量期间并未持续。DEX处理似乎刺激了乳腺细胞分化，但并未改变乳IgG浓度的下降速率。18月龄小母牛产奶量较高可能是由于乳腺上皮更多、体重更大或两者兼而有之。
