不同放牧制度和强度下奶牛生产性能的研究──2.放牧对奶牛产奶量及体增重的影响

本文作者在湖南南山牧场首次研究了不同放牧制度(分区轮牧和连续放牧)和放牧强度(0.467,0.667和0.867ha/头)下在多年生黑麦草/白三叶人工草地上放牧的黑白花奶牛产奶量、乳比重及体重的变化。结果表明:轮牧制奶牛的产奶量显著高于连续放牧制(1632.5vs.1462.3kg/头)。不同放牧强度下,奶牛的产奶量以中等放牧强度最高,轻牧次之,重牧最低,分别为1724.5、1571.1和1331.2kgh头。放牧期间两种放牧制间奶牛平均日增重差异不显著,以轮牧制较高(0.224vs.0.205kg/头·天);三种放牧强度间奶牛的平均日增重差异也不显著,由大到小依次为B3>B2>B1,分别为0.242、0.225和0.176kg/头·天。不同放牧处理对牛奶比重影响不大。这说明在本试验条件下,放牧制度和放牧强度对奶牛平均日增重增加影响不显著,但对奶牛的产奶量有显著的影响。     

不同放牧制度和强度下奶牛生产性能的研究──1.放牧对牧草采食量及营养摄入量的影响

本文作者在湖南南山牧场研究了两种放牧制度（分区轮牧和连续放牧）和三种放牧强度（0．467，0．667和0．867ha／头）对处于泌乳中后期的黑白花奶牛在多年生黑麦草／由三叶人工草地上的放牧来食量、采食植物组成、营养摄入量的影响。结果表明：轮牧制奶牛的采食量低于连续放牧制，但其口粮组成中黑麦草和白三叶的比例高于连续放牧，故粗蛋白质、总能、钙和磷的日摄入量也低于轮牧制奶牛。随放牧强度的增加，奶牛的来食量、以及粗蛋白质、酸性洗涤纤维、总能、钙和磷的摄入量均有所增加，但三种放牧强度间差异并不显著。放牧强度越大，家畜日粮组成中黑麦草和白三叶的比例越大，而枯草和杂草所占比例越小。这说明在南山试验条件下，放牧制度和放牧强度对奶牛的采食量及各种营养物质的日摄入量有一定影响。     

不同放牧处理对泌乳奶牛血液生化指标的影响

在中国农业大学沽源草地试验站研究了两种放牧制度与放牧强度对在多年生禾草/紫花苜蓿混播人工草地上放牧奶牛血液生化指标的影响。结果表明:放牧促进了奶牛营养状况的改善,血清中游离脂肪酸和尿素氮含量明显降低,而Ca、P、血糖、甘油三酯、碱性磷酸酶、总蛋白和白蛋白等含量则均有所提高,不同放牧处理对奶牛血液代谢有一定的影响,轻度轮牧对奶牛机体代谢的促进作用高于中度轮牧和连续放牧。     

奶牛放牧对北方农牧交错带人工草地植被的影响

研究了不同处理奶牛放牧对混播人工草地植被的影响。结果表明,牧草现存量随着放牧强度的增加而降低,轻牧比中牧高7.28%,且轮牧高于连续放牧1.99%,轮牧对紫花苜蓿和无芒雀麦的再生有利。随放牧强度增加,紫花苜蓿和无芒雀麦重要值下降,蓝茎冰草和新麦草增加。放牧对牧草的茎叶比有显著影响,放牧后4种牧草的茎叶比均有下降,连续放牧高于轮牧。根系主要集中在土壤表层0~10 cm,约占0~30 cm总量的70%,且其生物量也以轮牧制较高,随放牧强度的增加而下降。     

自然生产条件下热应激周期变化揭示泌乳中期奶牛出现“热应激乳蛋白降低征”

本试验在连续3年时间里测定了上海地区热应激周期变化对泌乳中期奶牛生产性能和牛奶品质的影响。通过实地测定并计算分析,绘制了上海地区热应激周期变化图谱,揭示了整个热应激周期中不同热应激程度的分布状况。研究对比了自然生产环境下无热应激与中度热应激对奶牛生产性能和牛奶品质的影响,发现中度热应激极显著降低了奶牛采食量、产奶量、乳脂校正乳产量、能量校正乳产量、乳脂率、乳蛋白含量、总固体含量(P<0.01),而且显著增加了乳中尿素氮含量(P<0.05)。在热应激周期变化研究中发现,中度热应激显著升高泌乳奶牛的直肠温度和呼吸频率(P<0.05),而且呼吸频率比直肠温度对热应激变化的反应更快、更敏感。热应激周期变化对奶牛干物质采食量、产奶量的影响取决于热应激程度,2012年整个热应激周期的热应激程度比较低,热应激周期变化对奶牛干物质采食量、产奶量无显著影响(P>0.05),但是2013年热应激程度更加严重,热应激周期变化对奶牛干物质采食量、产奶量产生了极显著影响(P<0.01)。在牛奶品质中,受热应激影响最大的是乳蛋白合成量(P<0.01)。2012年和2013年2个热应激周期变化对其他乳成分含量没有显著影响(P>0.05),但是两年的热应激周期变化都导致乳蛋白含量显著下降(P<0.05)和乳中尿素氮含量显著升高(P<0.05)。尤其值得注意的是,2012年热应激周期变化并没有导致奶牛采食量下降(P>0.05),而且产奶量也没有显著性差异(P>0.05),但是仍然出现了乳蛋白含量下降和乳中尿素氮含量升高(P<0.05)。这表明热应激周期变化改变了泌乳中期奶牛氮代谢的途径,发生了氮营养重分配(repartitioning)现象,而且这种现象不依赖于采食量和产奶量,可以称之为“热应激乳蛋白降低征”(heat-stressed milk protein decrease syndrome,HS-MPD)。     

不同程度热应激对泌乳中期奶牛产奶量和乳成分的影响

选取36头临床健康、头胎、泌乳中期奶牛,通过实时监控外界温湿度指数,结合奶牛呼吸、心率、肛温等生理指标,确定奶牛热应激状态,并测定奶牛产奶量和乳成分。结果,与无热应激相比,中度热应激使奶牛日均产奶量降低16.33%,轻度热应激对此影响不明显。中度热应激奶牛乳脂率较轻度热应激显著降低,但与无热应激组相比差别不显著。轻度热应激使奶牛乳蛋白水平极显著降低,但随热应激程度加深,乳蛋白水平有升高趋势。试验结果表明:不同程度热应激对泌乳中期奶牛产奶量和乳成分有不同影响。     

日粮添加甘油对奶牛泌乳性能的影响

选用36头经产奶牛,根据泌乳期、上一泌乳期305d产奶量和预产期,采用随机区组设计分为4组,研究甘油（0、100、200和300g／d）对泌乳早期奶牛采食量、产奶量、乳成分和饲料转化效率的影响。结果表明：日粮添加甘油对奶牛的采食量、产奶量、乳蛋白率、乳糖率和乳干物质率无显著影响,200g/d组和300g／d组饲料转化效率显著高于对照组（P〈0．05）,300g／d组乳脂率显著低于对照组和100g/d组（P〈0.05）。根据试验结果,添加甘油明显改善了泌乳早期奶牛能量平衡,甘油适宜添加量为200g／d。     

日粮添加甘油对奶牛泌乳的影响

选用36头经产奶牛.根据泌乳期、上一泌乳期305d产奶量和预产期.采用随机区组设计分为4组,研究甘油(0、100、200和300g/d)对泌乳早期奶牛采食量、产奶量、乳成分和饲料转化效率的影响.结果表明:日粮添加甘油对奶牛的采食量、产奶量、乳蛋白率、乳糖率和乳干物质率无显著影响,200g/d组和300g/d组饲料转化效率显著高于对照组(P<0.05),300g/d组乳脂率显著低于对照组和100g/d组(P<0.05).根据试验结果,添加甘油明显改善了泌乳早期奶牛能量平衡,甘油适宜添加量为200g/d.     

干乳期和泌乳期奶牛饲喂湿玉米麸饲料对其产奶量的影响

美国内布拉斯加大学的Kononoff其体况分比饲喂对照日粮的奶牛显著提高。在泌乳教授等利用36头初产和40头经产荷期,奶牛的体况分没有显著差异。与对照组相比,添加斯坦奶牛进行试验,观测饲喂湿玉米麸WCGF的泌乳期奶牛虽然会消耗更多的饲料,但其产饲料(WCGF)在305d内对奶牛产奶量、奶量也较高,在WCGF-L和WCGF-DL这两组处理干物质采食量(DMI)、体况评分(BCS)以中,DMI和实际产奶量无显著差异,这表明产前日粮及健康状况的影响。试验处理包括:①不会影响奶牛的泌乳性能。日粮中添加WCGF使牛对照组(27头):日粮中不添加WCGF;奶中的乳…     

不同程度热应激与奶牛产奶量关联性分析

选取泌乳中期奶牛63只作为观察对象,分为A、B、C三组(各21只),A组进行轻度热应激,B组进行中度热应激,C组未进行热应激,观察三组奶牛产奶量和乳成分变化。结果:与无热应激相比,中度热应激使奶牛日均产奶量降低,轻度热应激影响不大;中度热应激使奶牛乳脂率明显降低;轻度热应激差异不大。此结果表明:不同程度热应激会使得泌乳中期奶牛产奶量和乳成分出现差异。     

Feed intake, lactation performance, blood metabolites and fertility in early lactation dairy cows grazing a timothy pasture

The present study was conducted to investigate feed intake, milk yield, milk composition, blood metabolites and fertility in early lactation dairy cows grazing a timothy pasture. Fourteen multiparous Holstein cows that calved between 20 May and 19 July were used over a 3‐year period. The stocking rate was 3.6–4.3 cow/ha. Concentrates were fed separately at 9.5–11.5 kg/day per cow (dry matter basis) from 1 to 13 weeks postparturition. Herbage intake was estimated using chromium oxide as an indigestible marker. The mean contents of crude protein, total digestible nutrients and neutral detergent fiber of pasture during the 3‐year study period were 22.3%, 71.8% and 51.7%, and those of total diet were 18.9%, 77.3% and 40.3%, respectively. The mean herbage dry matter intake was 13.0 kg/day from 2 to 13 weeks postparturition during the study, total dry matter intake was 23.7 kg/day, the total digestible nutrients sufficiency rate was 105%, milk yield was 39.7 kg/day, and milk fat percentage was 3.30%. The decrease in bodyweight postparturition was slight. Urea nitrogen concentrations in serum were below 18.3 mg/dL. The mean days to first estrus and days open were 36 and 104 days, respectively. These results indicate that energy deficiency, decrease in bodyweight and fertility in early lactation barely occur when high producing dairy cows are fed enough grazing grass and suitable concentrates.     

Effects of grazing adaptation on herbage intake,milk production,and body weight change in lactating dairy cows after turning out to pasture in early spring

The present study investigated the effects of adaptation to grazing in early spring on the herbage intake, milk production, and body weight changes in lactating dairy cows. The experiment included 12 Holstein lactating cows during early spring. Six cows were allowed to gradually adapt to grazing (ADP) over 10 days. They were allowed to graze on a pasture for 4 h during the first week and for 19 h during the remaining 3 days (adaptation period). During the 10-day period, the remaining six cows were housed in a barn (CON). Cows in both groups received adequate silage, hay, and concentrate during the adaptation period. Subsequently, cows in both groups were allowed to graze together for 19 h for 4 weeks (experimental period). No cow received supplements during the experimental period. In the first week of the experimental period, the ADP cows showed a higher herbage intake than the CON cows. During the subsequent weeks, there were no differences in herbage intake between the two groups. At the start of the experimental period, milk production and body weight of the ADP cows were higher than those of the CON cows, and this difference lasted until the end of the experiment.     

Effect of using Acacia mearnsii tannin extract as a feed additive on nutritional variables and productive performance in dairy cows grazing a temperate pasture

This study was carried out to evaluate the impact of including Acacia mearnsii tannin extract (TA) as a feed additive on nutrition and productive performance of dairy cows grazing a high‐quality temperate pasture and receiving supplementation with a concentrate feedstuff. Fourteen multiparous Holstein cows were assigned to either of the following treatments: concentrate without or with 20 g TA/kg dry matter (DM). Concentrate intake accounted for 32% of the total DM intake. Tannin addition increased the herbage DM intake by 22% (p < .05). There was no effect of TA inclusion on milk yield, milk composition, milk nitrogen (N) excretion, milk and plasma urea‐N concentration, urinary excretion of total N, urea‐N, and purine derivatives. However, TA inclusion increased the N intake and retention, total N excretion in manure, fecal N to urine N ratio, and decreased the dietary N efficiency for milk production and the percentage of ingested N excreted in urine (p < .05). In conclusion, supplementing dairy cows grazing a high‐quality temperate pasture with a concentrate containing 20 g TA/kg DM showed the potential of decreasing the proportion of ingested N excreted in urine without affecting the productive performance.     

Effects of Turnout to Pasture and Dietary Fat Supplementation on Milk Fat Composition and Conjugated Linoleic Acid in Dairy Cows

Turnout to pasture involves considerable changes in the feed intake and metabolism of dairy cows. The aim of this study was to investigate how these changes affect milk production and milk fat composition, in cows selected for high (HFI) or low (LFI) milk fat content producing the same yield of 4% fat-corrected milk. Furthermore, two different concentrates, with high or low inclusion of soya oil, were studied. The experiment was conducted with 44 multiparous mid-lactating cows over a 4 week period. Samples of milk and blood were obtained before turnout to pasture, during transition to pasture and when cows were adapted to pasture. Milk yield decreased with 3.6 kg energy-corrected milk (ECM) on average during the first 5 days after turnout to pasture. This decrease, together with a drop in plasma insulin and increased plasma non-esterified fatty acids (NEFA), indicated nutritional insufficiency at turnout to pasture. Milk fat composition changed towards more long-chain fatty acids (LCFA) and fewer de novo synthesized fatty acids. This was probably caused by an increased supply of LCFA of feed and body origin to the udder. LFI cows showed higher levels of conjugated linoleic acid at pasture than HFI cows.     

Effects of pre-feeding of a corn silage-based supplement on the feed intake, milk production and nitrogen utilization of grazing dairy cows

Four Holstein cows were used to determine the effect of timing of the feeding of a corn silage (CS)‐based supplement on the feed intake, milk production and nitrogen utilization of grazing dairy cows. The cows were fed the supplement 2 h before grazing (pre‐grazing) or immediately after grazing (post‐grazing). Cows were grazed for 5 h per day under a rotational grazing system. There was no difference in the herbage and total feed intake between treatments. The milk protein yield for pre‐grazing tended to be higher than that for post‐grazing, whereas the milk yield did not differ between treatments. The total nitrogen intake for pre‐grazing tended to be higher than that for post‐grazing (P = 0.06). There was no difference in the urinary nitrogen output between treatments, whereas the proportion of urinary nitrogen output : total nitrogen intake for pre‐grazing tended to be lower than that for post‐grazing (P = 0.06). The milk nitrogen output and nitrogen retention for pre‐grazing tended to be higher than that for post‐grazing (milk nitrogen, P = 0.06; nitrogen retention, P = 0.05). Nitrogen utilization of grazing dairy cows was improved by feeding a CS‐based supplement before grazing.     

Dry matter intake and milk production of grazing dairy cows supplemented with corn silage or a total mixed ration offered ad libitum in a subtropical area

This study aimed to evaluate the feeding choice, dry matter (DM) intake, and milk production of dairy cows that strip grazed on a mixed perennial species pasture receiving different supplementation strategies. The treatments were without supplementation (WS) or with supplementation of either corn silage (CS) or a total mixed ration (TMR) based on CS and concentrates, in a subtropical area. The supplements were provided ad libitum after the afternoon milking. Twelve Holstein × Jersey cows in mid-lactation (133 ± 43 days in milk) were divided into six groups (two cows/group) and distributed in accordance with a replicated 3 × 3 Latin square design, with three 21 day periods (15 adaptation days and 6 evaluation days). The total DM intake, milk production, milk fat, and milk protein production were greater in the TMR treatment than in the WS and CS treatments and were similar between the WS and CS treatments. The herbage DM intake and proportion of time spent grazing were greater in the CS treatment than in the TMR treatment. CS supplementation did not affect the total DM intake or milk production/cow, whereas TMR supplementation greatly improved the total DM intake and milk production of the dairy cows grazing on mixed perennial species.     

Herbage intake and ruminal digestion of dairy cows grazed on perennial ryegrass pasture either in the morning or evening

This study aimed to clarify diurnal fluctuations of herbage intake, ruminal fermentation of herbage carbohydrates and proteins, and digesta particulate weight in the rumen of grazing dairy cows. Six ruminally cannulated, non‐lactating dairy cows were grazed on perennial ryegrass/white clover pasture either in the morning (04.00 to 08.00 hours) or the evening (16.00 to 20.00 hours). Cows grazed in the evening spent more time (P < 0.01) and consumed more herbage (P < 0.01) compared with cows grazed in the morning. Higher (P < 0.05) daily mean concentrations of total volatile fatty acid, propionate and n‐butyrate in rumen fluid were observed for cows grazed in the evening compared with cows grazed in the morning. Although cows grazed in the evening ingested more crude protein compared with cows grazed in the morning, no significant difference in NH₃‐N concentration in rumen fluid was observed between them. The ratio of purine‐derivative concentration to creatinine concentrations was higher (P < 0.01) in the urine of cows grazed in the evening than in cows grazed in the morning. These results clearly indicated that evening grazing was advantageous for dairy cows compared with morning grazing, in terms of ruminal fermentable energy intake and nitrogen utilization efficiency.