Effects of heat stress and β-carotene supplementation on postpartum reproductive performance in dairy cows

EXP.1 The objectives were to analyses the potential impact of heat stress in different regions, determine the monthly distribution of calving throughout the year and to investigate environmental sources of variation of days open (DO) in first lactation cows. The climate data were obtained from from the 25 official provincial meteorological stations covering the 33 provinces included in the study. Reproductive data were obtained from the bureau of Biotechnology in Livestock Production, Department of Livestock Development, Ministry of Agriculture and Cooperatives. These data contained information from 13,548 lactation records collected from years 2004 to 2006. The lower mean temperature-humidity index was observed in December (72) and the highest mean in April (80). THI differed significantly between regions (P<0.0001), and months (P<0.0001). Significant interactions between region and month (P<0.0001) was found on THI. THI values were different among regions (P<0.0001). The highest frequencies of calving were observed in September and October (13.1-14.91%) and the lowest frequencies were observed in February (4.14-5.12%). The average DO in the first lactation cows was 151.70 days. Significant effects of MOC (P<0.0001), region (P<0.0001) were found on DO. February calving cows had longest DO (219 ± 11 days) while cows calving in October and November had a significantly shorter mean DO (133 ± 7 and 133 ± 7 days). EXP. 2 The aims of this study were 1) to investigate the effect of heat stress on the resumption of ovarian activity and plasma non-esterified fatty acids (NEFA), insulin-like growth factor-1 (IGF-1) and cortisol concentrations in post partum first lactation dairy cows, and 2) to investigate the effect of heat stress on embryonic loss in first lactation dairy cows. This study was conducted in a commercial dairy farm. There were 68 first lactation cows included in the study. The proportion of normal ovarian cyclicity in mild stress (72 ≤ THI < 78) was higher than in severe stress (78 ≤ THI < 89) group (P<0.01). The interval from calving to first ovulation, interval from calving to first AI, days open and first service conception rate were not statistically different between MS and SS. BCS and body weight were unaffected by THI classification group. Plasma concentrations of NEFA, IGF-1 and cortisol, were not different between groups. Milk production was different (P=0.03) between MS and SS. Neither the number nor the different types of embryonic mortality were affected by heat stress. EXP. 3 The objective was to invesrtigate whether a supplement of β-carotne given during the dry period is able to 1) increase blood concentrations of β-carotene postpartum 2) improve ovarian function and progesterone production 3) enhance uterine involution and uterine health 4) improve milk production and milk composition 5) modify hormone and metabolic status in cow 6) increase colostral IgG content 7) modify hormone, metabolic status and enzyme activity in the neonatal calf. Forty high producing Holstein cows were included in the experiment. The β-carotene supplement was given individually to the cows (1g/d β-carotene) started at drying-off until calving. The results showed that supplementation of β-carotne during the dry period increased blood concentrations of β-carotene in cows (P<0.0001). On day 28 postpartum the percentage of neutrophils in the BC group was lower than in the C group (cervical smear; C: 21.0 ± 3.22% vs BC: 9.7 ± 3.14%, P<0.05 and uterine smear; C: 32.0 ± 3.86% vs BC: 20.9 ± 3.76%, P<0.05). Plasma concentrations of hydroxyproline in the BC group were higher than in the C group on day 21 postpartum (BC: 20.8 ± 1.33μmol/L vs. C: 15.0 ± 1.33μmol/L; P<0.01). The dietary supplement of β-carotene during the dry period had no effect on ovarian activity, progesterone production, cervix and uterine horn diameters, milk production and milk composition, hormone and metabolic status in cow, colostral IgG content, hormone, metabolic status and enzyme activity in the neonatal calf.试验1 本试验旨在分析不同区域热应激的潜在影响，明确全年产犊的月度分布规律，并探究头胎泌乳母牛空怀天数（days open, DO）的环境变异来源。气候数据取自覆盖本研究涉及33个省份的25个官方省级气象站。繁殖数据来自泰国农业与合作社部畜牧发展厅畜牧生产生物技术局，包含2004至2006年间收集的13548条泌乳记录。研究发现，温度湿度指数（Temperature-Humidity Index, THI）的平均值在12月最低（72），4月最高（80）。不同区域及月份的THI均存在极显著差异（P<0.0001），且区域与月份的交互效应对THI同样存在极显著影响（P<0.0001）。产犊频率最高的月份为9月和10月（13.1%~14.91%），最低为2月（4.14%~5.12%）。头胎泌乳母牛的平均空怀天数为151.70天。产犊月份（MOC）、区域对空怀天数均存在极显著影响（P<0.0001）。2月产犊的母牛空怀天数最长（219±11天），而10月、11月产犊的母牛平均空怀天数极显著更短（133±7天和133±7天）。 试验2 本研究旨在：1）探究热应激对产后头胎泌乳奶牛卵巢活动恢复及血浆非酯化脂肪酸（non-esterified fatty acids, NEFA）、胰岛素样生长因子-1（insulin-like growth factor-1, IGF-1）与皮质醇浓度的影响；2）探究热应激对头胎泌乳奶牛胚胎丢失的影响。本试验在商业化奶牛场开展，共纳入68头头胎泌乳母牛。轻度热应激组（72≤THI<78）的正常卵巢周期性比例显著高于重度热应激组（78≤THI<89）（P<0.01）。两组间的产犊至首次排卵间隔、产犊至首次人工授精（Artificial Insemination, AI）间隔、空怀天数及首次配种受胎率均无统计学差异。体况评分（Body Condition Score, BCS）与体重不受THI分组的影响。两组血浆NEFA、IGF-1及皮质醇浓度无显著差异。轻度与重度热应激组的产奶量存在显著差异（P=0.03）。热应激对胚胎死亡的数量及不同类型均无显著影响。 试验3 本试验旨在探究干奶期饲喂β-胡萝卜素补充剂能否实现以下目标：1）提升产后母牛血液β-胡萝卜素浓度；2）改善卵巢功能与孕酮生成；3）促进子宫复旧与子宫健康；4）提升产奶量与乳成分；5）调节母牛体内激素与代谢状态；6）提高初乳免疫球蛋白G（immunoglobulin G, IgG）含量；7）调节新生犊牛的激素、代谢状态及酶活性。本试验共纳入40头高产荷斯坦奶牛，从干奶期开始至产犊前，每日单独饲喂每头母牛1g β-胡萝卜素补充剂。试验结果显示，干奶期饲喂β-胡萝卜素补充剂可极显著提升母牛血液β-胡萝卜素浓度（P<0.0001）。产后第28天，β-胡萝卜素组（BC组）的中性粒细胞百分比在宫颈涂片检测中低于对照组（C组）（C组：21.0±3.22% vs BC组：9.7±3.14%，P<0.05），子宫涂片检测中同样低于对照组（C组：32.0±3.86% vs BC组：20.9±3.76%，P<0.05）。产后第21天，BC组血浆羟脯氨酸浓度高于C组（BC组：20.8±1.33μmol/L vs C组：15.0±1.33μmol/L，P<0.01）。干奶期饲喂β-胡萝卜素补充剂对母牛卵巢活动、孕酮生成、宫颈与子宫角直径、产奶量与乳成分、母牛体内激素与代谢状态、初乳IgG含量，以及新生犊牛的激素、代谢状态及酶活性均无显著影响。