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.

     

Effects of feeding rumen-protected choline on incidence of diseases and reproduction of dairy cows

The objectives of this study were to determine the effects of feeding rumen-protected choline (RPC) to dairy cows on the incidence of disease in early lactation, and on their fertility as measured by return to ovarian cyclicity and pregnancies per insemination (P/AI). In the first experiment, 369 cows were fed 15 g/day of RPC between 25 days pre-calving and 80 days post calving. In the second experiment, 578 primigravid cows were fed 15 g/day of RPC for the last 21 days of gestation only. In both experiments, P/AI were evaluated for the first and second inseminations, and health disorders were monitored daily until 90 days after calving. Return to cyclicity was evaluated in experiment 1 only, on days 51 and 61 post calving. In the first experiment, feeding RPC reduced the incidence of clinical ketosis, mastitis, and morbidity, and the number of cases of mastitis per cow. Feeding RPC did not influence cyclicity and P/AI. In the second experiment, cows fed RPC tended to have greater morbidity than controls because of an increased incidence of metritis and fever, although the incidence of retained fetal membranes was lower. The P/AI for first and second inseminations were similar between treatments. Supplementing the diets of dairy cattle with RPC from before until after calving improved the health of early lactation cows. However, in primigravid cows feeding RPC before calving only had mixed effects on health. Feeding RPC had no beneficial effects on reproduction in either experiment.     

Risk factors for repeat-breeder syndrome in New South Wales dairy cows

A retrospective case-control study involving 1041 cow lactations from 10 commercial dairy herds in Australia determined relationships between biographic, production, reproductive and disease factors and repeat-breeder syndrome (RBS) (conception to greater than two inseminations). The study population was stratified into primiparous- and multiparous-cow sub-groups and logistic regression was used. Effects of herd were examined by including this variable alternatively as a fixed and a random effect. In the primiparous-cow fixed-effect model, the risk of RBS was increased with post-calving metritis, stillbirth, and with increasing days taken to reach peak milk yield, and reduced following dystocia. An inverted U-shaped relationship with total milk-solids percentage at the time of first service was detected. In the multiparous-cow fixed-effect model, the risk of RBS was increased in cows with chronic metritis, cystic ovarian disease (COD), in cows of parity >5 and in cows that were sub-fertile in the previous lactation. Increasing days to first recorded heat (DFH) reduced risk of RBS and a non-linear relationship with average 120-day milk-protein percentage was found. When herd was fitted as a random effect, stillbirth and 120-day average milk-protein percentage were no longer significant in the primiparous and multiparous models, respectively. The study emphasises the need to control appropriately for the clustering effect of herd and supports the need to minimise periparturient disease and improve nutrient balance to achieve optimal fertility in dairy herds.     

Improved knowledge about conception rates influences the decision to stop insemination in dairy cows

The conception rate in dairy cows is dependent on a number of cow factors such as days in milk and insemination number. Unfortunately, some of these factors were not accounted for in optimal insemination and replacement decision models. By using wrong estimates of the conception rate, the calculated optimal insemination and replacement policy might differ from the real optimal insemination and replacement policy. The objective of this study was to evaluate different sets of conception rates with an increasing level of accuracy to determine the insemination policy. An existing dynamic program for optimal insemination and replacement was used to compare three different scenarios in the estimation of conception rates, based on the reproductive performance of Dutch dairy cattle: (i) constant conception rate throughout lactation, (ii) conception rate dependent on parity and months in milk, and (iii) conception rate dependent on parity, months in milk and insemination number. The time step of the model was 30.4 days (1 month). The discounted future cash flow of culling a cow at each time step (replace a heifer immediately) was compared with keeping that cow under optimal future decisions. The difference between immediate culling and optimal decisions is defined as the retention pay-off. The insemination value was calculated as the difference between the future cash flow between immediate insemination of a cow and waiting one time-step. The results show that the difference in the insemination values and the optimal time to stop insemination depend on parity, lactation stage and the relative milk yield. In older cows with equal milk yields and at the same months in milk, the insemination value was lower than in younger cows. Within a parity, the insemination value was higher for cows with a higher milk yield. On individual cow level, using more accurate conception rate as input in the optimal insemination and replacement model might reduce miscalculation of the economic consequences for at least of €20-€38 per cow per year. Basing insemination decisions on less accurate input of the probabilities of conception, however, did not have an economic consequence at the herd level. In conclusion, using the appropriate conception rate as input in the optimal insemination and replacement model would increase the precise decision for the optimal time to stop insemination and hence improve the reproductive management efficacy.     

荷斯坦牛泌乳前期体况评分及其对泌乳性能和离群寿命的影响

为了探究荷斯坦牛泌乳前期体况评分（body condition score,BCS）的影响因素及BCS对生产性能和离群寿命的影响,本研究收集江苏省某大型牛场2018年1月至2020年12月共7 811头荷斯坦牛泌乳前期BCS、生产性能测定（dairy herd improvement,DHI）结果及淘汰记录,利用多因素方差分析法在分析奶牛泌乳前期BCS变化及影响因素基础上,重点分析泌乳前期BCS及其变化对泌乳性能和离群寿命的影响,利用Cox回归对泌乳前期不同BCS的荷斯坦牛生存曲线进行绘制,并对不同BCS荷斯坦牛的淘汰原因进行卡方检验。结果表明,全群泌乳前期BCS均值为（2.95 ±0.32）。胎次、产犊季节和泌乳天数对泌乳前期BCS有极显著影响（P<0.01）,1胎牛和夏季产犊的母牛泌乳前期BCS均最高;5~30、31~60、61~100 d BCS呈显著下降。泌乳前期BCS对产奶量、乳脂率、乳蛋白率、体细胞评分等均有极显著影响（P<0.01）。产奶量和高峰奶量随BCS的增加呈极显著下降（P<0.01）。泌乳前期BCS与产奶量、高峰奶量呈极显著负相关（P<0.01）,与乳蛋白率呈极显著正相关（P<0.01）。泌乳前期BCS的变化对SCS和高峰奶量均有显著影响（P<0.05）。泌乳前期BCS对离群胎次和淘汰月龄有极显著影响（P<0.01）。生存分析表明,BCS为2.75的牛只生存概率最大。2胎和4胎母牛、冬季产犊的母牛不同BCS淘汰比例均呈极显著差异（P<0.01）;低产淘汰的牛只泌乳前期BCS淘汰分布具有极显著差异（P<0.01）。在本研究牛群中,当泌乳前期BCS为2.75时,牛只生产性能较佳且淘汰风险最低,本研究为规模化牛场荷斯坦牛泌乳前期的饲养管理提供了参考。     

Neospora caninum infection does not affect the fertility of dairy cows in herds with high incidence of Neospora-associated abortions

This present study, was designed to establish whether Neospora caninum infection affects the fertility of high-producing dairy cows, and was based on yearly serological screening for neosporosis and on the confirmation of N. caninum infection in aborted foetuses. Assessment was made of 7518 artificial inseminations (AI) (applied to parous cows) performed in three herds. Of these inseminations, 2540 (33.8%) resulted in pregnancy; 34% of which corresponded to seronegative cows (2226 of 6556 AI performed in seronegative cows) and 32.6% to seropositive animals (314 of 962). Abortion occurred in 97 (30.1%) of the 314 pregnancies recorded in dams seropositive for N. caninum, while only 93 (4.2%) of the 2226 pregnancies in seronegative animals ended in abortion. Logistic regression analysis indicated no significant effects of N. caninum antibody titre, days in milk and milk production at insemination on fertility. Factors found to affect fertility were herd, season of insemination, lactation and insemination number, semen-providing bull and AI technician. Our results indicate that N. caninum infection does not affect the fertility of high-producing dairy cows.     

Genetic and Environmental Correlations Among Female Fertility Traits and Milk Production in Different Parities of Swedish Red and White Dairy Cattle

The main objective of this study was to estimate genetic correlations between fertility and production traits in first, second and third lactations as well as between fertility traits measured in the same way at different ages. The fertility traits studied were: number of inseminations per service period, number of treatments for reproductive disturbances, interval between first and last inseminations, interval between calving and first insemination, and interval between calving and last insemination. Early milk production was measured as the average of the energy-corrected milk yield at the second and third monthly testdays in a lactation. The number of records was approximately 450 000, 350 000, 180 000 and 75 000 in the heifer period, first, second, and third lactations, respectively. A linear, trivariate model that included the effects of herd-year, year, month, age and sire of the cow was applied. To reduce the effect of ongoing selection, 305-days kg protein production in first lactation was included as a variate in all of the analyses. Correlations between the herd-year effects indicated that factors of herd-year level conducive to increased production had a tendency to increase the number of inseminations as well as the number of reproductive treatments, although there was an earlier start and termination of the insemination period. Genetic correlations between fertility traits and production were in the range of 0.2-0.4, all of them unfavourable and higher at later parities. The genetic correlations between fertility traits in the heifer period and the same traits in first lactation were 0.7. Genetic correlations between the first and second lactation varied between 0.7 and 0.9, and between the second and third lactation they were all 0.9 or higher. In conclusion, fertility and production traits need to be selected for simultaneously if fertility is going to be maintained along further genetic improvement on production, and such selection should include fertility results from lactating cows.     

Studies on the replacement policies in dairy cattle. III. Influence of variation in reproduction and production

The optimum policy of insemination and replacement of dairy cows was determined by the dynamic programming technique. The model used in the previous study was extended to allow variation in time of conception. From 2 to 7 months after calving three alternatives were considered for an open cow namely (a) inseminating the cow, with a calculated probability of success, (b) leaving her open, and (c) replacing her immediately. When it was profitable to leave a cow open, the optimum time for replacement during the lactation period was determined.The minimum production level for insemination to be the optimum choice depended on the stage of lactation and the parity of the cow. In the optimum situation the average calving interval was 371 days, while 13% of the cows had an interval of 14 months or longer.The optimum policy was greatly affected by changes in the replacement heifer price. Changes in the probability of conception and persistency of milk production had significant but smaller effects. In herds with a smaller decline in production after the peak, insemination should be continued for longer than in herds with a larger decline.The relation between production and calving interval that resulted from the optimum policy was determined. When a measure of milk production was used that was not affected by gestation, the average correlation was 0.09. The correlation increased to 0.35 when the total 305-day production was used.     

Relationship between antibodies against Mycobacterium avium subsp. paratuberculosis in milk and shape of lactation curves

To analyze how infection with Mycobacterium avium subsp. paratuberculosis (MAP) affects the shape of lactation curves, a three-level hierarchical test-day model was set up with fat-corrected test-day milk yield (FCTM) as response. Milk samples from 6955 cows in 108 Danish dairy herds were tested with ELISA to detect antibodies against MAP. Optical densities (ODs) recorded on a continuous scale were standardized according to parity and stage of lactation. In addition to standardized ODs (stOD), seven fixed covariates, quadratic terms and first-order interactions were included in the model. Cow and cow nested in herd were included as random effects. Cows of first, second and higher parities were analyzed separately. The lactation curves after peak yield were significantly less persistent in young infected cows, where an increase of one stOD unit was associated with a depression of the milk yield per day through day 305 of 3.7 kg FCTM in first parity and 2.7 kg FCTM in second parity. In second-parity cows, the lactation curve also was both depressed through the entire lactation and more steep after 60 days in milk (DIM). In third and older parities, a significant effect of the quadratic term of stOD indicated exponentially increased losses with increased ODs.     

产犊季节、胎次及牛场对荷斯坦牛泌乳性能的影响

[目的]研究产犊季节、胎次及不同牛场对奶牛泌乳性能的影响情况,以期为提高奶牛的泌乳性能及牛奶质量提供可靠的理论依据。[方法]收集3个千头以上奶牛场共8 872次相关信息,用多因素方差分析法分析产犊季节、胎次和牛场对泌乳天数、305d校正奶量、305d脂肪产量、305d蛋白产量和全泌乳期产奶量5个泌乳性能的影响进行分析。[结果]不同产犊季节、胎次和牛场都极显著影响奶牛的5项泌乳性能(P<0.01)。夏季和秋季产犊奶牛的泌乳性能较为理想。夏季产犊奶牛的泌乳天数和全泌乳期产奶量最高,其他三个泌乳性能都位居第二;秋季产犊奶牛的305d校正奶量、脂肪产量和蛋白产量都显著高于其他三个季节(P<0.05),泌乳天数和全泌乳期产奶量也仅次于夏季。头胎牛的各项泌乳性能都显著高于其他胎次的奶牛(P<0.05),其次为2胎产犊奶牛。随着胎次的增加,泌乳性能的各项指标都有不同程度的降低。除了泌乳天数之外,A牛场的各项泌乳性能都最佳,且显著高于B、C两个奶牛场(P<0.05)。[结论]在饲养条件良好的情况下,本研究中三个牛场的奶牛适宜在夏、秋两个季节产犊,此时泌乳性能较好;此外,头胎产犊奶牛的泌乳性能在各胎次中最高。     

Relationship between the lactation curve and udder disease incidence in different lactation stages in first‐lactation Holstein cows

We examined the relationships between the shape of the first parity lactation curve and udder disease incidence at different stages of lactation in 538 Holstein cows. Data used were first‐parity daily milk yields and treatment records. Each cow was classified according to whether or not it had had udder disease at least once over the whole lactation period or in one of three stages within the lactation period. We then examined the differences in the shapes of the lactation curves between the disease incidence and non‐incidence group in each stage. Cows that had high rates of increase in milk yield and high milk yields in early lactation were predisposed to udder disease afterwards. Cows with high milk production over a long period but with low lactation persistency were predisposed to udder disease after the peak of lactation. There was no difference in total milk yield between incidence and non‐incidence groups in all stages, suggesting that, for a comparable level of lactation, cows without udder diseases have flatter lactation curves.     

产犊季节对北京地区荷斯坦奶牛Wood泌乳曲线参数的影响探究

本研究通过对北京地区1998-2016年28个场区的奶牛生产性能测定（DHI）数据进行分析,旨在比较不同产犊季节对1~3胎奶牛泌乳曲线相关参数的影响。使用Wood模型对1~3胎不同产犊季节群体和个体泌乳曲线进行拟合,并获得相应胎次下不同产犊季节奶牛泌乳曲线参数a、b、c （分别代表泌乳潜力、产奶量上升至顶峰速率、产奶量达到顶峰后下降速率）、泌乳曲线二级参数Per、PY （分别代表泌乳持续力、泌乳峰值）及305 d产奶量（305MY）。群体和个体水平的曲线拟合采用SAS 9.2中NLIN模块进行,采用混合线性模型分析不同产犊季节对各胎次奶牛泌乳曲线参数的影响。结果显示：产犊季节对Wood泌乳曲线的泌乳潜力、达到峰值的上升速率、达到峰值后的下降速率、泌乳峰值及305MY均有显著影响（P<0.05）,对于泌乳持续力没有显著影响（P>0.05）。夏季产犊牛泌乳曲线整体低于其他产犊季节,且胎次越高趋势越明显,1胎牛受到的影响较小;从胎次上分析,头胎牛泌乳持续力极显著高于经产牛（P<0.01）;头胎牛夏季产犊305MY比其他产犊季节的低274.33~490.17 kg,经产牛夏季产犊305MY比其他产犊季节的低440.76~930.68 kg。以上结果提示,北京地区牛场应注重做好经产牛和头胎牛的防暑降温工作,注意调整配种时间,避免夏季产犊牛过多,造成损失。     

The ovarian response and fertility in cows with acidosis induced by acetic acid]

The effects of acetic acid administered at an amount of 300 to 600 g (5 to 10 mol) to the rumen of breeding cows, were investigated on ovulation, conception and progesterone levels in the blood and milk of cows with cloprostenol-induced (Oestrophan Spofa) oestrus at a dose of 500 micrograms i.m. In the group of 15 cows exposed to the acetic acid load five cows got in calf after the first insemination (33.3%), and 12 cows (80.0%) after all inseminations in 37.6 days after cloprostenol administration, with the insemination index 1.67 (Tab. I). In the control group (five cows) four cows (80.0%) got in calf after the first insemination, in total all five breeding cows got in calf in 20.6 days after cloprostenol administration, with the insemination index 1.2. In the experimental group of 15 cows a clinical examination of ovaries on day 7 after insemination revealed ovulation disorders in eight cows, that means in 53.3% of the animals (Tab. II). No ovulation disorders were observed in the control group of five cows. Progesterone levels in the blood showed high variability (Tab. III). In the group of cows administered acetic acid they were by more than a half lower (1.49; 0.67; 1.53 per ml) on days 7, 14 and 21 after insemination in comparison with the control group (3.35; 2.5; 3.38 ng per ml). The average progesterone levels in milk (Tab. IV) were 1.27 and 1.53 on day 7, 6.74 and 7.27 on day 14 and 3.52 and 11.85 ng per ml on day 21, respectively, the higher values apply to the control. It was not possible to evaluate reliably from the progesterone levels in the blood and milk if ovulation took place and if the corpus luteum was developing (Tab. V and VI). The clinical control of ovaries on days 7 and 8 after oestrus and insemination was more reliable to determine the ovulation disorders than the progesterone determination in the blood and milk of cows.     

Neospora caninum Infection Does Not Affect the Fertility of Dairy Cows in Herds with High Incidence of Neospora‐associated Abortions

This present study, was designed to establish whether Neospora caninum infection affects the fertility of high‐producing dairy cows, and was based on yearly serological screening for neosporosis and on the confirmation of N. caninum infection in aborted foetuses. Assessment was made of 7518 artificial inseminations (AI) (applied to parous cows) performed in three herds. Of these inseminations, 2540 (33.8%) resulted in pregnancy; 34% of which corresponded to seronegative cows (2226 of 6556 AI performed in seronegative cows) and 32.6% to seropositive animals (314 of 962). Abortion occurred in 97 (30.1%) of the 314 pregnancies recorded in dams seropositive for N. caninum, while only 93 (4.2%) of the 2226 pregnancies in seronegative animals ended in abortion. Logistic regression analysis indicated no significant effects of N. caninum antibody titre, days in milk and milk production at insemination on fertility. Factors found to affect fertility were herd, season of insemination, lactation and insemination number, semen‐providing bull and AI technician. Our results indicate that N. caninum infection does not affect the fertility of high‐producing dairy cows.     

影响荷斯坦牛产奶量差的因素分析

产奶量差是奶牛个体同一胎次前后2个泌乳月产奶量的差值,可准确反映产奶量变化情况。为探究影响荷斯坦牛产奶量差的因素,本研究收集整理了江苏省某大型奶牛场2015-2018年55 193头次荷斯坦牛生产性能测定记录,并利用最小二乘法分析胎次、测定年度、产犊季节、泌乳月4个因素对荷斯坦牛产奶量差的影响。结果显示:胎次、测定年度、产犊季节、泌乳月及其交互作用对产奶量和产奶量差均有极显著影响(P<0.01)。其中,不同胎次、测定年度和产犊季节的荷斯坦牛总产奶量在第2个泌乳月增加最快,产奶量差为8.79kg;头胎第6泌乳月、二胎第7泌乳月和三胎及以上第6泌乳月产奶量下降最大,产奶量差分别为-2.86kg、-4.59kg和-6.13kg;2015-2018年4个测定年度中,第10、第6、第7、第6泌乳月产奶量降低最大,产奶量差分别为-2.26kg、-4.98kg、-4.44kg和-3.56kg;春季产犊的荷斯坦牛第4泌乳月、夏季产犊的荷斯坦牛第12泌乳月、秋季产犊的荷斯坦牛第9泌乳月、冬季产犊的荷斯坦牛第6或第7泌乳月产奶量下降最大,产奶量差分别是-4.34kg、-4.71kg、-5.36kg和-5.40kg。此外,产奶量差与泌乳持续力呈极显著正相关(P<0.01),与产犊间隔呈显著正相关(P<0.05),与泌乳天数、高峰奶、乳脂率、蛋白率、305d产奶量呈极显著负相关(P<0.01)。因此,产奶量差作为衡量奶牛产奶量变化的指标之一,可为牧场进行科学饲养管理提供参考。     

中国荷斯坦奶牛不同地区、泌乳天数及胎次的产奶量校正系数研究

本研究通过对规模化牧场测定日数据进行分析,旨在估计不同地区305 d校正产奶量对应泌乳天数(DIM)的校正系数与胎次校正系数。利用Wood(不完全伽玛)模型对来自不同温度带9个参考群11 749头荷斯坦奶牛2010－2020年间的683 160条测定日产奶量拟合泌乳曲线,估计泌乳曲线参数,计算头胎牛和经产牛1~305 d泌乳天数对应的校正系数,分别分析参考群和验证群305 d校正产奶量和305 d实际累积奶量的差异;利用SAS 9.2中混合线性模型对1~6胎至少有前5个胎记录的牛估计305 d奶量的胎次效应值,并计算1~6胎各胎次的乘法校正系数;比较传统系数和新系数校正结果的差异。结果表明:①参考群头胎牛和经产牛中,泌乳曲线方程的拟合度R²范围分别为0.4593~0.4913和0.5796~0.6341,泌乳高峰日分别为79~85和53 d,泌乳高峰奶量分别为33.1~34.4和46.0~48.6 kg;②对于参考群,头胎牛和经产牛校正系数分别在泌乳≥90 d和泌乳≥30 d基本趋于一致,头胎牛和经产牛泌乳≥60 d的305 d校正产奶量均趋近于305 d实际累积奶量,奶量差值分别在100和200 kg以内;③对于验证群的305 d校正产奶量,头胎牛泌乳≥150 d和经产牛泌乳≥180 d的泌乳天数校正系数适用性更佳,305 d校正产奶量与305 d实际累积奶量比值高于79%;④1~6胎的胎次校正系数分别为1.2121、1.0380、1.0063、1.0000、1.0220和1.0290;⑤与传统系数相比,新泌乳天数校正系数校正效果更好,头胎牛和经产牛新系数校正的305 d奶量较305 d实际累积奶量相差分别在900和700 kg以内;利用新胎次校正系数,2~4胎产奶量可较为准确地校正到5胎成年当量。本研究结果表明,定期更新305 d校正产奶量的泌乳天数与胎次校正系数,便于准确地将不同泌乳天数、不同胎次状态下泌乳牛的产奶量调整到同一基准上,从而更好地比较奶牛个体泌乳性能的高低,为牧场管理提供参考依据。     

The effect of strain of Holstein-Friesian, feeding system and parity on lactation curves characteristics of spring-calving dairy cows

The purpose of the present study was to investigate the influence of strain of Holstein-Friesian (HF) cow and feeding system (FS) on the lactation curve characteristics of spring-calving cows. The Wilmink model was used to analyse the lactation curves. The three strains of HF cows compared were high production North American (HP), high durability North American (HD) and high Breeding Worth New Zealand (NZ). The three FS compared were a high milk output from pasture feed system (MP), a high concentrate feed system (HC) and a high stocking rate feed system (HS). A repeated measures model with a factorial arrangement of treatments was used to determine the influence of strain of HF, FS, parity and their interactions on the shape of the lactation curve. The curve was described based on yield at calving, the degree of ascendancy between calving and peak yield, and the persistency after peak yield. Analysis of the residuals indicated a good fit of the Wilmink curve to the data set. Strain of HF, FS, parity and the interaction of strain of HF with FS had significant effects on lactation curve characteristics. In all three FS, the HP strain achieved the highest milk production post-claving and peak yield, with the lowest persistency of lactation. In the HC system, milk production post-claving and at peak yield were higher for all three strains. Offering higher levels of concentrate supplementation to the HP strain on a pasture-based system improved their persistency of lactation. The highest persistency of lactation was achieved with NZ strain. The highest milk production post-claving and at peak and lowest persistency was achieved with third parity cows. The existence of strain by feed system interactions for lactation curve parameters clearly exhibits that the optimum system of production varies with strain of HF.     

中国荷斯坦牛干奶期长度的群体特征及其与生产性能的关系

本研究旨在探究北京地区中国荷斯坦牛干奶期长度（DPL）的变化规律及其变异对奶牛各项生产性能的影响，包括产奶性能、繁殖性能、初乳品质和乳房健康。收集了北京地区34个牧场出生于2009—2018年136 231头中国荷斯坦牛的干奶日期、生产性能记录、繁殖性能记录等。通过整理试验牛群的干奶记录，揭示了北京地区中国荷斯坦牛1胎和2胎DPL的群体规律，利用固定模型分析了胎次、产犊季节、场-产犊年和初产月龄对DPL的影响；此外，利用固定模型分析了DPL的变异对日产奶量、乳脂率、乳蛋白率、首末次配种间隔（interval from first to last insemination，IFL）、产犊至首次配种间隔（interval from calving to first insemination，ICF）和初乳品质的影响，利用Logistic回归过程分析了DPL的变异对首次配种受胎率（conception rate of first insemination，CR）、首次配种56 d不返情率（56-days non-return rate of first insemination，NRR56）、难产率和乳房健康的影响。研究结果显示，北京地区中国荷斯坦牛DPL平均为58.81 d，胎次、产犊季节、场-产犊年和初产月龄均对DPL有显著影响（P<0.05）。DPL的变异对日产奶量、乳蛋白率、ICF、CR、NRR56、难产率和乳房健康有显著影响（P<0.05）。干奶期短的奶牛测定日平均乳蛋白率、CR和NRR56更高；DPL适中的奶牛测定日平均产奶量更高、乳房健康水平更好、ICF更短、难产率更低。本研究在国内利用大规模牛群数据揭示了中国荷斯坦牛DPL的群体规律，可为中国规模化奶牛场提升管理水平提供参考。     

An epidemiological study of hyperketonaemia in Swedish dairy cows; Determinants and the relation to fertility

In a study based on 3078 Swedish dairy cows from 126 herds, milk acetone was measured at the first 3 monthly production tests after calving. The values were assessed together with data from the official milk recording system, artificial insemination records and the computerised recording system for veterinary treatments. Milk acetone concentrations above 0.40 mmol 1^?1 were considered to indicate hyperketonaemia. The prevalence of hyperketonaemia was 8.9, 4.7 and 1.1%, respectively, at the first 3 monthly production tests. A significant influence on milk acetone was found for herd mean production, breed, herd, lactation number, cow, week of lactation, season and the interaction between lactation number and week of lactation. The highest individual milk yield and highest individual acetone value were significantly positively correlated. Test-day milk yield and milk acetone on the same day were significantly negatively correlated. The recorded incidence of clinical ketosis and ovarian cysts increased with increasing highest milk acetone concentration. Significant correlations were found between the prevalence of hyperketonaemia and herd means of the intervals from calving to first and last service. No significant correlations were found between milk acetone and fertility traits when calculated on an individual cow basis.     

Effect of parity number on the dry matter intake of dairy cows during the first week after calving

We investigated the effect of parity number on the dry matter intake (DMI) of cows during the first week after calving. Eighty‐three cows were evaluated from 14 days before to 7 days after calving. DMI and milk yield were measured for 7 days after calving, and the calving score was measured. Blood samples were collected throughout the experiment. The average DMI during the first week after calving was reduced in the first‐lactation heifers and high‐parity number cows. A quadratic relationship between the parity number and the DMI was observed. The first‐lactation heifers had lower prepartum serum total protein (TP) concentration and milk yield, higher prepartum serum nonesterified fatty acid (NEFA) concentration and calving score than the multiparous cows. The recovery rate of serum calcium (Ca) after calving was slow in the cows in the parity 6. The DMI was positively affected by the serum Ca concentration after calving, milk yield, and prepartum serum TP concentration and was negatively affected by the calving score and prepartum serum NEFA concentration. We conclude that the DMI immediately after calving tends to be lower in first‐lactation heifers and high‐parity number cows, but factors that reduce the DMI differ according to parity number.