Effects of clinical mastitis on reproductive and milk performance of Holstein cows in Morocco

The aim of this study was to determine the influence of clinical mastitis and time of first mastitis occurrence on reproductive and milk performance of Holstein cows. Data were collected in a dairy farm from 2008 to 2012 on 1725 cows, among which 464 cows with mastitis. To determine the influence of clinical mastitis on reproductive and milk performance, models included fixed effects of parity, calving season, calving year, and group (cows with and with no mastitis). To determine the effect of time of 1st mastitis occurrence on reproductive performance, the mastitic cows group was further reclassified into three groups: prior to 60 days, between 60 and 90 days and greater than 90 days postpartum. For milk performance, the mastitic cows group was divided into two groups: before and after peak milk yield. Clinical mastitis had significant effects on calving to first AI interval, milk yield, and fat yield, but a non-significant effect on days open, number of inseminations per conception, and milk fat percentage. Mastitic cows had a calving to first AI interval 6.1 days longer and 549.6 kg milk and 20.4 kg fat per 305 days of lactation lower than those with no mastitis. Time of 1st mastitis occurrence did not have any significant effect on reproductive performance. Further, milk and fat yields of cows diseased before peak milk yield were 506 kg and 23.9 kg, respectively, lower than those of cows affected after peak milk yield. Extra attention needs to be paid to mastitis during the early postpartum period.

     

不同能量和蛋白水平日粮对西农萨能奶山羊泌乳性能的影响

为筛选西农萨能奶山羊泌乳期全价料最适能量和蛋白水平,选取体重(50.56±0.76)kg、胎次(2～3)、产奶量(2.12±0.10)kg/d相近和分娩日期与体况一致,并处于泌乳高峰期的健康西农萨能奶山羊36只,随机分为6组,每组6只。采用3×2因子随机区组试验设计6种日粮,NE水平为12.64、13.08和13.52MJ/d,CP水平为16.13%和17.82%。试验期84d,共分4个阶段,每阶段21d。结果表明:日粮NE和CP水平对奶山羊DMI和血液生化指标没有显著影响,但存在交互作用,NE 13.52MJ/d和CP16.13%处理组的DMI最高。随日粮NE和CP水平升高泌乳量增加,其中CP提高可显著增加泌乳量(P=0.041);而乳脂肪、乳蛋白、乳糖、干物质和非脂乳固体等乳成分指标则降低,其中CP提高可显著降低乳蛋白(P=0.013)和非脂乳固体(P=0.031);日粮NE和CP水平对奶山羊泌乳性能的影响存在交互作用,NE 13.52MJ/d和CP17.82%时泌乳量最高,而NE 13.08MJ/d和CP16.13%时乳品质最好。综合各项指标并考虑生产实际,得出西农萨能奶山羊泌乳期日粮适宜的NE和CP水平分别为13.08MJ/d和CP16.13%。     

Disposition of ampicillin trihydrate in plasma,uterine tissue,lochial fluid,and milk of postpartum dairy cattle

The objective of this study was to determine the disposition of ampicillin in plasma, uterine tissue, lochial fluid, and milk of postpartum dairy cattle. Ampicillin trihydrate was administered by intramuscular (i.m.) injection at a dose of 11 mg/kg of body weight every 24 h (n = 6, total of 3 doses) or every 12 h (n = 6, total of 5 doses) for 3 days. Concentrations of ampicillin were measured in plasma, uterine tissue, lochial fluid, and milk using HPLC with ultraviolet absorption. Quantifiable ampicillin concentrations were found in plasma, milk, and lochial fluid of all cattle within 30 min, 4 h, and 4 h of administration of ampicillin trihydrate, respectively. There was no significant effect of dosing interval (every 12 vs. every 24 h) and no significant interactions between dosing interval and sampling site on the pharmacokinetic variable measured or calculated. Median peak ampicillin concentration at steady‐state was significantly higher in lochial fluid (5.27 μg/mL after q 24 h dosing) than other body fluids or tissues and significantly higher in plasma (3.11 μg/mL) compared to milk (0.49 μg/mL) or endometrial tissue (1.55 μg/mL). Ampicillin trihydrate administered once daily by the i.m. route at the label dose of 11 mg/kg of body weight achieves therapeutic concentrations in the milk, lochial fluid, and endometrial tissue of healthy postpartum dairy cattle.     

饲粮磷水平对崂山奶山羊泌乳性能和血清生化指标的影响

本试验旨在研究饲粮磷水平对崂山奶山羊泌乳性能和血清生化指标的影响。选择体重(56.55±1.17)kg、产奶量(2.20±0.07)kg/d、泌乳中期的2胎健康崂山奶山羊30只,采用单因素随机分组设计,随机分成3组,每组10只,每只羊为1个重复。各组饲喂能量和蛋白质水平基本一致,磷水平分别为0.26%、0.36%及0.46%的饲粮。预试期15 d,正试期60 d。结果表明:1)饲粮磷水平对干物质采食量均无显著影响(P0.05)。2)0.36%组产奶量全期平均值较高,极显著高于0.26%组、0.46%组(P0.01),0.26%组与0.46%组差异不显著(P0.05);干物质采食量/产奶量、干物质采食量/4%标准乳产量均以0.36%组较低,极显著低于0.46%组(P0.01)。3)饲粮磷水平对乳脂率、乳蛋白率、乳糖率、乳非脂固形物率、乳磷含量、乳钙含量均无显著影响(P0.05)。4)饲粮磷水平对血清中钙、磷、尿素氮含量及碱性磷酸酶活性均无显著影响(P0.05)。由此可见,泌乳期崂山奶山羊饲粮磷水平以0.36%为宜。     

营养强化低脂羊奶粉对幼龄动物生长发育及血脂的影响

[目的]研究营养强化低脂羊奶粉对幼龄动物生长发育及脂肪含量的影响。[方法]给予幼龄SD大鼠营养强化低脂羊奶粉,试验周期42天。测定动物生长发育指标（体重、体长）、食物利用率、甘油三酯、胆固醇,及体内脂肪和股骨骨密度。[结果]营养强化低脂羊奶粉组与空白组比较,生长发育指标（体重、体长）无不良影响,股骨骨密度明显升高（P<0.01）,营养强化低脂羊奶粉对体脂无明显影响。[结论]营养强化低脂羊奶粉可促进幼龄SD大鼠骨骼生长,对血脂含量及体脂率无影响。     

Changes in lying behavior after abrupt cessation of milking and regrouping at dry-off in freestall-housed cows: A case study

The objectives of this case study were to evaluate differences between primiparous and multiparous cows in milk production over the last 10 days before abrupt cessation of routine milking to end lactation and to assess the effect of parity and milk production on changes in lying behavior around the routine on-farm practice of abrupt cessation of milking and regrouping in 1 freestall herd in Ontario (Canada). Lying behavior and milk production were monitored in 33 primiparous and 75 multiparous cows. Cows were dried-off abruptly (i.e., no longer milked) after the afternoon milking, regrouped with dry cows, and switched to high-forage diet. At the time of dry-off, cows were producing more than 20 kg/day on average. However, there was great variability across cows, with some cows producing over 35 kg/day on the day before dry-off. After removing 3 outliers, there was no difference between parities in the slope of the milk decrease over the last 10 days before dry-off. There was a negative association between the milk produced on the day before dry-off and lying time on the day of dry-off (coefficient estimate = −11.6 ± 4.7 minute/day) in primiparous cows only. Multiparous cows increased their daily lying time after dry-off; this increase leveled off 2 days after dry-off (lying time [minute/day] = 750.6 + 47.8 day − 9.9 day²). In contrast, primiparous cows decreased their daily lying time on the day of dry-off; however, daily lying time then increased until day 3 after dry-off (lying time [minute/day] = 641.6 − 11.9 day + 19.9 day²). Overall, the frequency of lying bouts increased on the day of dry-off, decreasing over the next days (lying bouts/day = 9.7 + 0.5 day − 0.3 day²). Although average lying bout duration decreased on the day of dry-off and increased over the subsequent days for all cows, the initial decrease was greater in primiparous cows (lying bout duration [minute] = 82.5 − 0.7 day + 1.8 day² and 68.0 − 3.2 day + 3.6 day² for multiparous and primiparous cows, respectively). The lying behavior diurnal patterns illustrated a decrease in lying time associated with each milking session on the 2 days before dry-off. Interestingly, similar patterns persisted after dry-off, although the magnitude of the decrease in lying time associated with each omitted milking was lower. Given that lying is a high-priority behavior in dairy cattle, these results suggest that the welfare of cows around the routine on-farm practice of abrupt cessation of milking and regrouping at dry-off, particularly after their first lactation, may be compromised.     

Research on the preparation,uniformity and stability of mixed standard substance for rapid detection of goat milk composition

Taking fresh goat milk as raw material after filtering, centrifuging, hollow fiber ultrafiltration, allocating formula, value detection and preparation processing, a set of 10 goat milk mixed standard substances was prepared on the basis of one‐factor‐at‐a‐time using a uniform design method, and its accuracy, uniformity and stability were evaluated by paired t‐test and F‐test of one‐way analysis of variance. The results showed that three milk composition contents of these standard products were independent of each other, and the preparation using the quasi‐level design method, and without emulsifier was the best program. Compared with detection value by cow milk standards for calibration fast analyzer, the calibration by goat milk mixed standard was more applicable to rapid detection of goat milk composition, detection value was more accurate and the deviation showed less error. Single factor analysis of variance showed that the uniformity and stability of the mixed standard substance were better; it could be stored for 15 days at 4°C. The uniformity and stability of the in‐units and inter‐units could meet the requirements of the preparation of national standard products.     

羊奶及其制品稳定性的研究进展

对羊奶的热稳定性、酒精稳定性、凝乳特性及羊奶制品(羊奶粉、羊奶酸奶)稳定性的影响因素进行综述.研究表明:温度、pH值、离子浓度等对羊奶的稳定性都有显著的影响.温度在120～140℃范围内时,随着加热温度的升高,羊奶的热稳定性明显降低;30～80℃范围内,酒精稳定性随温度的升高而降低.pH6.7时,羊乳的热稳定性最好,pH6.4～7.2时,随pH值升高,羊乳的酒精稳定性增强.无机盐离子Ca2+对羊奶热稳定性和酒精稳定性的影响作用相似,稳定性均随Ca2+浓度的增大而降低.对于羊奶制品,降低水分活度可以提高其贮藏稳定性,乳清蛋白和酪蛋白含量的增加会降低酸奶贮藏期间的滴定酸度、黏度及持水性.另外,发酵酸奶所用稳定剂的不同、贮藏温度的不同也会影响制品的稳定性.     

The Diurnal Variation of Urea in Cow’s Milk and how Milk Fat Content,Storage and Preservation Affects Analysis by a Flow Injection Technique

Six Swedish Red and White dairy cows, producing 20-39 kg of 4% fat-corrected milk were given a ration balanced in energy and protein. They had access to feed from 05.15 to 09.00 and from 13.00 to 16.30 and were milked at 06.15 and 15.30. The milk was analysed for urea with a FIA technique.There was a significant diurnal variation in milk urea. The highest values were found 3–5 h after the beginning of the morning feeding and the lowest values (down to 60% of the max. values) during late night. Within 1 h after the start of the morning feeding the urea values had increased significantly, but they had decreased within the same time after the start of the afternoon feeding. Since there was a pronounced diurnal variation in the milk fat content, the urea concentration was also recalculated to concentration in the water phase of the milk. It was higher in that phase, but the pattern of the diurnal variation was not changed significantly. However, analyses on milk with a very high fat content may give misleading results.There were no important differences in the milk urea concentration of different udder quarters. When calculated as concentration in the water phase of the milk, no differences in urea concentration were found between the beginning and the end of milking. The analytical method had a good precision (coefficient of variation max. 3%). The milk urea concentration was not changed significantly after storage during 10 days at 4°C when no preservative was added; but after 17 days the milk had turned sour and the urea value had increased. When a preservative (bronopole) was added the urea concentration remained unchanged during 17 days. Deepfreezing did not influence the urea concentration.     

Effect of water restriction on milk yield and quality in Lacaune breed ewes

The effect of water restriction on body weight, body condition score, milk yield, and milk composition and rheological characteristics in intensively reared Lacaune ewes was evaluated. After 7 days of adaptation, the trial lasted 28 days. Thirty lactating ewes (48 ± 5 months of age; mean value ± standard deviation) at the beginning of third lactation month were divided into three groups (n = 10), corresponding to the following water restriction treatment: a group control received no drinking water restriction (W100), and two groups received water to the extent of 80% and 60% of W100 daily consumption (W80 and W60 group respectively). The effects of water restriction were assessed at the beginning of experiment (D0), at D14 and D28. The W60 group resulted in a significant decrease in body weight, body condition score, milk yield and feed consumption of hay due to the experimental treatment; whereas a marked increase in both W60 and W80 groups of milk lactose, urea, sodium, sodium chloride content and titratable acidity was observed. Rheological parameters of milk, rennet coagulation time and curd‐firming time were positively affected by water restriction treatments, with a decrease in both experimental groups of the time required for the formation of a stable and firm curd. Results highlight the importance of water consumption in dairy sheep. The scarce availability of water, significantly affecting ewes milk production, is worthy of particular attention in arid area where water stress‐resistant breeds should be considered. This study underlines that milk yield, being closely linked to the availability of water of the breeding habitat due to its high water content (about 81%), could be reached in area where water is not a limiting factor without reducing the genetic expression of the animals. Less severe water restrictions, such as 20% of daily voluntary water intake, produce no detrimental effect on milk yield.     

Closantel plasma and milk disposition in dairy goats: assessment of drug residues in cheese and ricotta

Closantel (CLS) is currently used in programs for the strategic control of gastrointestinal nematodes. CLS is extralabel used in different dairy goat production systems. From available data in dairy cows, it can be concluded that residues of CLS persist in milk. The current work evaluated the concentration profiles of CLS in plasma and milk from lactating orally treated dairy goats to assess the residues pattern in dairy products such as cheese and ricotta. Six (6) female Saanen dairy goats were treated orally with CLS administered at 10 mg/kg. Blood and milk samples were collected between 0 and 36 days post‐treatment. The whole milk production was collected at 1, 4, 7, and 10 days post‐treatment to produce soft cheese and ricotta. CLS concentrations in plasma, milk, cheese, whey, and ricotta were determined by HPLC. The concentrations of CLS measured in plasma were higher than those measured in milk at all sampling times. However, the calculated withdrawal time for CLS in milk was between 39 and 43 days postadministration to dairy goats. CLS residual concentrations in cheese (between 0.93 and 1.8 μg/g) were higher than those measured in the milk used for its production. CLS concentrations in ricotta were sixfold higher than those in the milk and 20‐fold higher than those in the whey used for its production. The persistent and high residual concentrations of CLS in the milk and in the cheese and ricotta should be seriously considered before issuing any recommendation on the extralabel use of CLS in dairy goat farms.     

乳头封闭剂和不同干奶药品对预防奶牛产后乳房炎的研究

奶牛乳腺健康直接关系到奶牛生产性能,和牧场效益息息相关。如何有效预防奶牛乳房炎的发生,是牧场的重中之重。干奶期是奶牛乳腺机能恢复健康的一个重要阶段,对预防奶牛产后乳房炎的发生有着重要意义。本文利用长达1 年的时间,对635 头奶牛进行分组试验,并追踪观察其产后90 天内乳房炎的发生情况和产奶量情况。通过数据分析发现,奶牛干奶期联合使用抗生素和乳头封闭剂对奶牛进行干奶,比单独使用抗生素干奶,产后7 天的体细胞阳性率降低了28.58%;产后60 天临床乳房炎发病率降低了35.40%,产后90天降低了41.32%;各组之间的产奶量并无显著差异（P>0.05）。     

Comparison of Milk Fat Globule Membrane Proteins in Milk Samples of Dairy Cow and Goat

In order to compare the difference of milk fat globule membrane（MFGM）proteins between dairy cow and goat milk,30 milk samples were collected in a dairy farm and a goat farm from Anhui area,respectively.Extracted proteins from the MFGM-enriched fractions were identified and quantified by LC/MS approach.The results showed that 284 and 334 proteins of MFGM from dairy cow and goat were identified,the biological processes of MFGM proteins were similar between dairy cow and goat which were mainly related to biological regulation,localization,transport,signal transduction and response to stimulus.Meanwhile,there were some differences in molecular functions,and protein binding and nucleotide binding were the most prevalent molecular functions in dairy cow MFGM proteins,while protein binding and structural molecule activity were the most prevalent molecular functions in goat MFGM proteins.And structural molecule activity was the main molecular functions among the difference proteins.Pathway analysis revealed that tight junction,axon guidance,antigen processing and presentation,complement and coagulation cascades were enrichment in dairy cow MFGM proteins,and regulation of actin cytoskeleton was enrichment in goat MFGM proteins.Those results revealed the protein expression pattern difference between MFGM protein of dairy cow and goat milk,and provide reference data for further exploring the molecular mechanism of synthetic milk fat globule.     

牛奶和山羊奶中乳脂球膜蛋白的比较研究

试验旨在分析牛奶与山羊奶中乳脂肪球膜（milk fat globule membrane,MFGM）蛋白组成及潜在的生物学功能。采集牛奶和山羊奶各30份,离心分离牛奶和山羊奶中脂肪,提取MFGM蛋白,液相色谱串联质谱分析结合数据库搜索鉴定,比较了奶牛和山羊MFGM蛋白的差异,分析了MFGM蛋白参与的生物过程、分子功能及相关代谢通路。结果显示,奶牛和山羊MFGM中分别鉴定了284和334个蛋白,奶牛和山羊中蛋白参与的生物学过程的模式非常相似,主要涉及生物调控、定位、转运、信号转导和应激反应等。分子功能方面二者存在一定的差异,奶牛MFGM蛋白主要涉及蛋白结合和核苷酸结合,而山羊MFGM蛋白主要涉及蛋白结合和结构分子活性。奶牛和山羊中差异表达的MFGM蛋白主要涉及结构分子活性。通路分析发现,奶牛和山羊MFGM蛋白涉及的生物学通路稍有差异,其中紧密接头、轴突导向、抗原加工与递呈、补体和凝血级联反应通路在奶牛MFGM蛋白中得到富集,而调节肌动蛋白细胞骨架通路在山羊奶中得到富集。研究结果展示了奶牛和山羊MFGM蛋白的表达模式及差异,为进一步探索两种奶畜乳腺合成脂肪球的分子机制的异同提供科学依据。     

和田多胎红羊泌乳规律初步研究

本研究旨在探明和田多胎红羊泌乳规律,提高双羔成活率。选取6只产双羔和田多胎红羊母羊为试验动物,检测其产后1~28 d泌乳量、乳成分变化规律;测量产后第1天母羊乳房体尺指标,并与泌乳量进行相关性分析。结果显示,和田多胎红羊产后1~28 d总泌乳量为29.87 kg,平均每日泌乳量为1.07 kg,泌乳量在第1~3天上升速度最快,在第21天达到峰值1.23 kg,泌乳曲线方程为：y=537t^0.477e^-0.033t;乳脂、非脂乳固体、密度、乳糖、固形物、蛋白质指标在和田多胎红羊母羊产后1~3 d快速下降,7~28 d趋于稳定,且6项指标第1天与第7、14、21、28天均差异极显著（P<0.01）;和田多胎红羊母羊产后第1天与第14、21、28天的泌乳量之间相关性不显著（P>0.05）,产后第2天与第28天的泌乳量相关性不显著（P>0.05）,其他均显著相关（P<0.05）;母羊产后第1、2、3、7天泌乳量与乳房宽呈显著相关（P<0.05）,母羊产后第14、21、28天泌乳量与乳房体尺指标相关性不显著（P>0.05）。以上研究结果为和田多胎红羊新类群种质特性、选育、饲料配制、羔羊早期断奶等提供理论依据。     

Lack of effects of an equine chorionic gonadotropin (eCG) administration between days 9 and 15 postpartum on reproductive performance in a Holstein dairy herd

Recently, it has been demonstrated that administration of equine chorionic gonadotropin (eCG) in the postpartum period in dairy cows can enhance follicle growth, reduce the interval from calving to first ovulation and increase plasma estradiol concentrations, and, thus, could enhance reproductive performance in a dairy herd when administered on day 6 postpartum. The aim of this study was to investigate the effects of a single dose of eCG between days 9 and 15 postpartum on parameters of reproductive performance in dairy cows. German Holstein cows (n = 1937; primiparous cows: n = 748; pluriparous cows: n = 1189) in a commercial dairy farm were randomly assigned to three experimental groups. Animals within the group eCG received a single dose of 600 IU eCG intramuscularly (i.m.) between days 9 and 15 postpartum followed by an i.m. administration of 500 μg cloprostenol after 14 days. Those of treatment group PG received cloprostenol only between days 23 and 29 postpartum. Cows of the control group remained untreated. Starting on day 49 postpartum, cows were subjected to a Presynch‐Ovsynch protocol and inseminated artificially. The impact of application time (days postpartum) of eCG on the intervals calving to first service and calving to conception was statistically not significant. Outcomes of reproductive performance (i.e. first service conception rate, proportion of pregnant cows until 100 and 150 days in milk [DIM], number of inseminations until 150 DIM, calving to first service interval and calving to conception interval) did not differ significantly between treatment group eCG and group PG compared to control group. Regarding postpartum eCG administration, significant interactions between treatment and parity, season, milk yield, and early puerperal disorders, respectively, could not be shown. In conclusion, an eCG treatment of dairy cows between days 9 and 15 postpartum to increase reproductive performance cannot be recommended under the given circumstances.     

Effects of wheat protein in milk replacers on abomasal emptying rate in calves

Diarrhoea is a condition with tremendous impact on calf health. Infectious agents play a dominant role; however, non‐infective factors may also contribute to pathogenesis of diarrhoea. One factor, the abomasal emptying rate, is mainly influenced by the composition of feed. The aim of the study was to assess the influence of different protein sources in milk replacers on abomasal emptying rate and clinical parameters. The effect of increasing age of the calves on abomasal emptying was also evaluated. The study compared abomasal emptying rates and clinical parameters in calves, which were fed either milk replacer containing only whey protein or one which partially contained wheat protein. Abomasal emptying rate was estimated by ultrasonography. Ten calves were used in the study over 18 days, and each calf was fed 3 periods of 3 days length using different milk replacers in an alternating crossover design. The abomasum was emptied significantly faster when the wheat protein containing milk replacer was fed (half‐emptying time wheat protein 49.1 ± 4.1 min, half‐emptying time milk protein 59.1 ± 7.4 min); however, clinical parameters and weight gain did not differ between the feeding regimes. Age did not significantly influence abomasal emptying rate. As milk replacers containing wheat proteins increased abomasal emptying rate, they may have a higher potential to initiate diarrhoea, especially if high volumes are fed. Thus, the feeding regimes are likely to be even more important when such milk replacers are used.     

饲粮中添加黄花蒿乙醇提取物对奶牛产奶性能及乳脂中共轭亚油酸含量的影响

本文旨在研究饲粮中添加黄花蒿乙醇提取物对奶牛产奶性能及乳脂中共轭亚油酸(CLA)含量的影响。试验选取体重(600±29)kg、胎次2~3胎、泌乳期(158±3)d及泌乳量(22.8±1.8)kg/d的泌乳期荷斯坦奶牛15头,采用完全随机区组设计分为3组,每组5头,进行为期40 d的饲养试验,其中1~9 d为预试期,10~40 d为正试期。对照组饲喂基础饲粮,试验1组和试验2组分别在基础饲粮中添加96和160 g/(d·头)的黄花蒿乙醇提取物。结果表明:整个试验期间,2个试验组的产奶量(第24、31和40天)、乳脂率、乳脂产量、乳蛋白率、乳蛋白产量、非脂固形物含量以及乳脂中的饱和脂肪酸、单不饱和脂肪酸、多不饱和脂肪酸、短链脂肪酸、中链脂肪酸和长链脂肪酸含量与对照组相比均无显著差异(P0.05);2个试验组的乳脂中CLA含量分别比对照组提高了30.7%和38.6%,其中试验2组与对照组差异显著(P0.05)。由此得出,饲粮中添加适量的黄花蒿乙醇提取物对奶牛产奶性能没有明显影响,但可以提高其乳脂中CLA含量,从而优化乳脂中脂肪酸的比例。     

Effects of first postpartum progesterone rise,metabolites, milk yield,and body condition score on the subsequent ovarian activity and fertility in lactating Holstein dairy cows

Seventy multiparous healthy lactating Holstein cows (fat-corrected milk yield = 7,561.8 kg) were monitored from 14 days before to 70 days after calving. Transrectal ultrasound scanning was performed twice weekly from 7 to 65 days postpartum. Blood samples were also collected twice weekly to measure serum P₄ and biweekly to detect serum β-hydroxybutyrate (βHB) and nonesterified fatty acid (NEFA) concentrations. Body condition score (BCS) was taken biweekly after calving. Based on the serum P₄ profile of 59 cows (11 cows were excluded due to the occurrence of postpartum diseases) studied, 27 (45.8%) had normal ovarian activity, while 21 (35.6%), six (10.1%), three (5.1%), and two (3.4%) had delayed ovulation (DOV), prolonged luteal phase (PLP), short luteal phase (SLP), and cessation of ovarian activity, respectively. Cows with PLP had an earlier ovulation compared to that of cows with normal ovarian activity (23.16 ± 4.02 vs 31.9 ± 8.35 days; P < 0.05). PLP cows also had a greater mean ± standard deviation peak milk yield (44.2 ± 5.8 vs 37.2 ± 5.7 kg/day, 75 days postpartum; P < 0.05) than cows with normal postpartum ovarian activity. The PLP group also had greater milk production in the previous lactation period. Logistic regression analysis indicated that cows with P₄ concentration ≥1 ng/ml on day 24 after calving were more at risk for PLP by 1.1 for each 1 kg increase in mean peak milk yield during 75 days after calving. BCS was lower in cows with DOV compared to that of cows with normal ovarian activity at any time after calving (P < 0.05). Serum βHB concentrations in DOV cows were significantly higher than that of normal cows on day 42 after calving (0.69 ± 0.29 vs 0.54 ± 0.12 mmol/L, P < 0.05). No significant difference was found in the mean concentrations of NEFA between cows in different groups at any time after calving (P > 0.05). The concentrations of P₄ on days 28 and 31 were negatively correlated with βHB concentration on day 42 after calving in cows with normal ovarian activity (R = −0.44, P = 0.02). In conclusion, these findings suggest that early ovulation and hence early postpartum P₄ rise in addition to the high milk production could partly be responsible for the occurrence of PLP in dairy cows.