Effects of long-term exogenous bovine somatotropin on glucose metabolism and the utilization of glucose by the mammary gland in different stages of lactation of crossbred Holstein cattle

The effects of long-term administration of recombinant bovine somatotropin (rbST) on glucose turnover and the utilization of glucose in the mammary gland using a continuous infusion of [3-³H]glucose and [U-¹⁴C]glucose in lactating crossbred Holstein Friesian(HF) cattle were investigated. Glucose turnover of rbST-treated animals was significantly higher than those of control animals ( P  < 0.05) in mid lactation, while plasma glucose concentrations were not affected. The utilization of glucose of non-mammary tissues of rbST-treated animals significantly increased ( P  < 0.05) as lactation advanced. The glucose taken up by the mammary gland in early lactation increased flux through the lactose synthesis and the pentose cycle pathway with significant increases in NADPH formation for fatty acid synthesis during rbST administration. The utilization of glucose carbon incorporation into milk appeared to increase in milk citrate and milk triacylglycerol but not for milk lactose as lactation advances in rbST-treated animals. The stimulant effect for milk yield by rbST treatment was transiently and significantly increased in early lactation and was decreased in late lactation even though there was a high level of udder blood flow. These findings demonstrate that the regulation of biosynthetic capacity within the mammary gland would be influenced more by local than by systemic factors. The proportion of glucose would be metabolized less for lactose synthesis, but metabolized more via the Embden-Meyerhof pathway and the tricarboxylic acid cycle as lactation advances.     

Effects of long-term administration of recombinant bovine somatotropin on the plasminogen–plasmin system and milk composition of crossbred Holstein cattle

Experiments were performed to examine the effects of long‐term treatment with recombinant bovine somatotropin (rbST) on milk plasmin–plasminogen and milk composition by one injection of 500 mg of rbST in every 14 days throughout lactation in crossbred Holstein cattle. The animals receiving rbST gave a greater milk yield and rate of blood flow to the udder during early lactation than the control group. The milk lactose concentration remained constant while the milk protein concentration increased as lactation advanced in both groups. The level of milk fat in rbST‐treated animals was significantly greater than in controls in the early lactation period (P < 0.05). The milk sodium and chloride concentrations of the rbST‐treated animals significantly decreased in early lactation as compared with the control animals. The sodium : potassium ratio of the rbST‐treated animals was significantly lower than those of control animals in the early lactation (P < 0.05) and it markedly increased in late lactation. As lactation advanced, the concentration of plasmin in the milk gradually increased, while the milk plasminogen concentration significantly increased in both groups. The plasminogen : plasmin ratio decreased in the control animals while it increased in the rbST‐treated animals as lactation advanced. These findings demonstrate that rbST is involved the activity of the plasmin–plasminogen system but is not involved in maintaining tissue integrity in the mammary gland during late lactation in crossbred dairy cattle.     

Effects of misty‐fan cooling and supplemental rbST on rumen function and milk production of crossbred Holstein cattle during early,mid and late lactation in a tropical environment

Two groups of five crossbred 87.5% Holstein cattle were housed in normal shade only (NS) as non‐cooled cows and in shaded housing with misty‐fan cooling (MF) as cooled cows. The cows were treated with recombinant bovine somatotropin (rbST) in early, mid and late lactation with three consecutive injections of rbST in every 14 days. Ambient temperatures and the temperature humidity index in the NS barn were significantly higher than those of the MF barn, whereas relative humidity in MF was higher than that of NS barn. The DMI of cooled cows were higher than those of non‐cooled cows, and cooled cows exhibited more response to rbST treatment. Exogenous rbST significantly increased milk yield throughout lactation. The rbST‐treated cows had higher total ruminal fermentation products as volatile fatty acid and ammonia nitrogen than the non‐rbST treated cows and associated changes were greater in cooled animals in all stages of lactation. Exogenous rbST increased the concentrations of milk urea nitrogen in both groups. These results suggest that the changes in ruminal fermentation with greater production of total VFA and NH₃N in response to rbST in crossbred cows whether under misty‐fan cooling or not, is in part through an increase in feed intake, thereby making more substrate available to the mammary gland for milk synthesis.     

The effect of beta and kappa casein genes on milk yield and milk composition in different percentages of Holstein in crossbred dairy cattle

The objective of this study was to compare the genotype, and composite genotype frequency, and the association between beta and kappa casein genes and milk yield (MY), percentage of fat (%Fat), protein (%Prot), and solids non‐fat (%SNF) between two groups of crossbred Holstein: G1 ≤ 87.5% Holstein = 89 cows and G2 > 87.5% Holstein = 142 cows. Five genotypes of beta casein gene were observed. A1A2 and A1B were the most and rarest frequency, respectively, in both groups. Five genotypes of kappa casein gene were found. The highest and the lowest frequency were AA, and BB and BE, respectively, in both groups. Composite genotype A1A2AA was the most frequent in both groups. Linkage disequilibrium (LD) between two genes was detected. Significant differences of frequencies between both groups of both genes were not found. The association of the genes and the traits was different between G1 and G2. Negative effects on the traits were found in both groups. In addition, the stronger effect of the beta casein gene was observed in most of the traits. The conclusions were that different %Holstein caused different significant effects of these genes. A study of the association of these genes within each percentage of Holstein is strongly recommended.     

Effects of supplemental recombinant bovine somatotropin and mist-fan cooling on the renal tubular handling of sodium in different stages of lactation in crossbred Holstein cattle

The effect of supplementary administration of recombinant bovine somatotrophin (rbST) on the renal tubular handling of sodium in crossbred 87.5% Holstein cattle housed in normal shade (NS) or mist-fan cooled (MF) barns was evaluated. The cows were injected with 500 mg rbST at three different stages of lactation. The MF barn housed cows showed a slightly decreased ambient temperature and temperature humidity index, but an increased relative humidity. Rectal temperature and respiration rates were significantly lower in cooled cows. The rbST treated cows, housed in NS or MF barns, showed markedly increased milk yields, total body water, extracellular fluid and plasma volume levels, along with a reduced rate of urine flow and urinary excretion of sodium, potassium and chloride ions and osmolar clearance, in all three stages of lactation. Renal tubular sodium and water reabsorption were increased after rbST administration without any alteration in the renal hemodynamics. Lithium clearance data suggested that the site of response is in the proximal nephron segment, which may be mediated via increases in the plasma levels of aldosterone and IGF-1, but not vasopressin, during rbST administration.     

影响江苏某牛场荷斯坦牛日产奶量和乳成分因素分析

[目的]探究江苏某牛场荷斯坦牛日产奶量和乳成分的影响因素。[方法]试验采集了该规模化牛场2018—2020年139 703条测定数据,并利用多因素方差模型对其进行系统的分析。[结果]不同胎次、测定季节、产犊季节、泌乳月对荷斯坦牛日产奶量、乳脂率、乳蛋白率、体细胞评分、乳尿素氮均有极显著影响(P<0.01)。产奶量与乳脂率、乳蛋白率、体细胞评分均存在极显著负相关。[结论]综上结果,在生产中,应结合胎次、季节、产犊时间、泌乳等多种因素,灵活调整牛群结构、生产规划和饲养管理,以实现提高产奶量和乳品质的目的。     

On the alterations in serum concentration of somatotropin and insuline-like growth factor 1 in lactating cows after the treatment with a little studied recombinant bovine somatotropin

A study was performed to delineate bST and IGF-1 variation, over a whole lactation, in cows treated with a nowadays widely commercialised but little studied sustained release formulation of recombinant bST. Total bST levels were found to be exceptionally high in the first days after administration, but decreased rapidly in the second week after injection. The increase in the IGF-1 serum concentration was significant for almost the entire biweekly cycle. Based on this study, the peaks of ST (often above 100 ng/ml) are considered particularly unlikely to be found in non-treated bovines, even under pathological conditions, especially when detected in a number of animals within a herd. Notwithstanding the great heterogeneity of results on this topic, these data suggest that tests against fraud involving the use of rbST in dairy products may be regarded as a feasible possibility.     

营养水平对杂交肉牛FABP3基因表达及IMF的影响

为研究营养水平对杂交肉牛心脏型脂肪酸结合蛋白（FABP3）基因表达及肌内脂肪含量（IMF）的影响,以西门塔尔、利木赞和夏洛莱杂交肉牛为研究对象,利用实时荧光定量PCR技术,分别测定高、中、低营养水平的3种杂交肉牛背部脂肪中FABP3mRNA表达水平,并测定其背最长肌IMF。结果：（1）高营养组中夏洛莱牛IMF高于同营养组其他2种肉牛,其背部脂肪中FABP3mRNA水平也显著高于另外2种杂交肉牛（P〈0.01）;中营养组中西门塔尔和利木赞牛IMF均高于同营养组的夏洛莱牛,但FABP3mRNA的水平无显著差异（P〉0.05）;低营养组中夏洛莱牛IMF和FABP3mRNA水平均显著低于另外2种肉牛（P〈0.01）;（2）夏洛莱杂交肉牛背部脂肪中FABP3mRNA水平与IMF具有显著的相关性（P〈0.05）,而西门塔尔和利木赞牛中FABP3mRNA水平与IMF无显著相关性（P〉0.05）。该结果表明提高营养水平影响FABP3mRNA表达并在一定程度上影响IMF,但影响显著与否存在品种差异,在肉牛育种和牛肉生产中应当同时考虑营养因素和遗传因素。     

Effects of administering exogenous bovine somatotropin to beef heifers during the first trimester on conceptus development as well as steroid- and eicosanoid-metabolizing enzymes

The aim of this study was to evaluate the effect of bovine somatotropin (bST) on fetal and placental development during the first third of gestation in beef heifers. Angus heifers (n = 97) were randomly assigned to either receive a 500-mg injection of bST (BST) biweekly on days 0, 15, 29, 43, and 57 of gestation or not receive bST (CTL) throughout the experiment. Body weight (BW) was assessed on days −9, −3, 0, 15, 22, 29, 43, 50, 57, 64, and 77, while blood samples were collected on days 0, 22, 50, and 64. Pregnancy status was determined via transrectal ultrasonography on days 29 and 64. A subset of pregnant heifers (BST, n = 7; CTL, n = 5) were harvested on day 84, and complete gravid reproductive tracts and liver tissue were collected for analysis. Cytochrome P450 1A (CYP1A), 2C (CYP2C), 3A (CYP3A), and uridine 5′-diphospho-glucuronosyltransferase (UGT) activities were determined. Mean change in BW and average daily gain of heifers between fixed-time artificial insemination (day 0) and day 77 did not differ between treatments (P ≥ 0.05). Mean concentrations of insulin-like growth factor 1 (IGF-1) were greater (P < 0.001) in BST (347 ± 27.7 ng/mL) compared with CTL (135 ± 32.8 ng/mL) heifers. Mean placental weight, fetal membrane weight, uterine weight, and ovarian and corpus luteum (CL) weights, as well as fetal morphometric data, did not differ (P ≥ 0.05) between treatments. However, BST heifers had greater (P = 0.03) quantities of combined fetal fluid compared with CTL (521.6 ± 22.9 vs. 429.6 ± 27.14 g, respectively). Tendencies were observed for BST heifers to have reproductive tracts with fewer placentomes (P = 0.08) and fetuses with greater umbilical diameters (P = 0.09) compared with CTL. The activity of CYP1A did not differ (P ≥ 0.05) within the maternal and fetal liver, caruncle, cotyledon, or CL tissue samples between treatments. Furthermore, CYP3A activity was only observed in maternal liver samples and was not different between treatments (P ≥ 0.05). Interestingly, CYP2C activity was greater (P = 0.01) in the liver of BST vs. CTL heifers, and UGT activity was greater (P = 0.02) in the CL from BST heifers compared with CTL. In conclusion, the administration of bST during the first third of gestation increased plasma concentrations of IGF-1, which resulted in an increase in fetal fluid, decrease in placentome number, and greater umbilical diameter, but failed to alter fetal development.     

Effects of malic acid on feed intake, milk yield, milk components and metabolites in early lactation Holstein dairy cows

The objective of this study was to evaluate the effects of malic acid (MA) on feed intake, milk yield and composition, blood metabolites and energy balance in early lactation Holstein dairy cows from 1 to 63 day in milk (DIM). Twenty-eight multiparous Holstein dairy cows, blocked by lactation number, previous 305-d mature equivalent milk production, and expected calving date, were arranged into four groups in a randomized block design. Treatments were: control (without MA), LMA, MMA and HMA with 70, 140 and 210 g malic acid per cow per day, respectively. The supplement of food grade MA (99.8% of MA) was hand-mixed into the top one-third of the daily ration. Cows were fed ad libitum a total mixed ration consisting of equal proportion of forage and concentrate. Milk yield increased (P = 0.04), but feed intake and milk components were not affected (P > 0.05) by MA supplementation. The energy balance, expressed as the difference between energy input and output, tended to be higher (P = 0.08) for MA supplemented cows during the 63-DIM period MA and supplemented cows showed a trend (P = 0.07) toward less loss of BW during the 63-day period, especially during the first 21-day of lactation. Concentrations of plasma glucose and serum insulin were higher for cows fed LMA, MMA, and HMA relative to control and linearly (P < 0.01) increased with increasing MA supplementation. Concentrations of non-esterified fatty acids (NEFA), beta-hydroxybutyrate (BHBA) and urine ketones were lower for MA-supplemented cows at 7, 14 and 21 DIM of lactation and linearly (P < 0.01) decreased with increasing MA supplementation. Although feed intake was not affected, milk yield increased, MA-supplemented cows experienced higher concentrations of plasma glucose and serum insulin, lower concentrations of plasma BHBA and NEFA, and lower concentrations of urine ketones, suggesting that nutrient digestibilities and energy availability may have been improved.     

Effects of growth and dietary crude protein level until first insemination on milk production during first lactation in Holstein heifers

To decrease the age at first calving in Holsteins, the effects of average daily body weight gain (ADG) and crude protein (CP) level until first insemination on growth performance and milk production were examined. The MM group had a target ADG of 0.75 kg and received a diet with a CP level of 14%. The HM and HH groups had a target ADG of 1 kg; both these groups received a diet with CP levels 14% and 16%, respectively. The ADG in the HM and HH groups was 1.1 kg, whereas in the MM group it was 0.97 kg (P < 0.01). The HM and HH groups showed no differences in withers height at body weight 350 kg. The ages at first calving in MM, HM and HH groups were 23.1, 21.0 and 21.8 months, respectively. The HM and HH groups had lower milk yield at day 305 than the MM group (P < 0.01). These results suggest that growth performance until first insemination should be maintained at an ADG of 0.97 kg or less with a CP level of approximately 14%, to shorten time until first insemination and prevent the decrease of milk yield.     

Effects of first breeding age on the production and reproduction of Holstein heifers up to the third lactation

The effects of early initiation of first service for dairy heifers on their fertility and productivity up to the third lactation were examined under constant raising and management conditions. Eight Holstein heifers in their early breeding regimens and eight Holstein heifers in their late breeding regimens were initiated to be bred at 12 and 15 months of age, respectively, and were first calved at 21.5 and 25.1 months of age, respectively, with bodyweights of 563 and 638 kg after calving, respectively. Early first breeding resulted in a lower bodyweight and a lower body condition score, but it did not affect the fertility or milk production during the first lactation of heifers as cows. The calving intervals of cows to the second and third calving were similar in early and late bred heifers. Although the early bred heifers had a significantly lower fat‐corrected milk yield at the second lactation than that of the late bred heifers, early breeding did not impair the productivity indicated by the mean milk yield per day from birth to the end of the third lactation with a shorter production period.     

Comparative study on the regulation of body fluids and mammary circulation at different stages of lactation in crossbred Holstein cattle feeding on different types of roughage

The present study was carried out to evaluate the effect of prolonged feeding of urea‐treated rice straw, compared with feeding of hay, on the regulation of body fluids, milk yield and mammary circulation at early lactation (30 days postpartum), mid‐lactation (120 days postpartum) and late lactation (210 days postpartum) in crossbred Holstein Friesians. Sixteen first lactating crossbred Holstein Friesians (HF), consisting of eight animals of two breed types, 87.5%HF and 50%HF, were selected and each breed was randomly allocated into two groups. Each group, consisting of four animals from the same breed, was fed either 5% urea‐treated rice straw or pangola hay (Digitaria decumbens) as the source of roughage in combination with a similar concentrate throughout the experiments. During the course of lactation there were no significant differences in body weight, heart rate, mean arterial blood pressure, plasma osmolality, plasma volume and blood volume among groups of 87.5%HF animals and 50%HF animals fed either hay or urea‐treated rice straw. Water turnover rate, total body water space and total body water as a percentage of body weight of 50%HF animals were significantly higher than those of 87.5%HF animals fed either hay or urea‐treated rice straw. The packed cell volume was significantly higher in all lactating periods of both groups of 50%HF animals in comparison with 87.5%HF animals. The ratio of DM intake to milk production for 87.5%HF animals fed either hay or urea‐treated rice straw was significantly lower than that of 50%HF animals in early lactation. The udder blood flow and milk secretion of 87.5%HF were significantly higher in early lactation and markedly declined when lactation advanced in comparison with those of 50%HF animals fed either hay or urea‐treated rice straw. The ratio of mammary blood flow to milk yield for all groups was in a similar range during early lactation although it significantly increased in mid‐ and late lactation for both groups of 87.5%HF animals. From these results it can be concluded that both 50%HF and 87.5%HF animals feeding on urea‐treated rice straw as a roughage source do not show any undernutritional effects in comparison with those fed with hay during the course of lactation. The physiological response differences between breeds are that 87.5%HF animals, which have a genetic makeup closer to the exotic bos taurus breed and a high milk yield, show a poor adjustment to the tropical environment and poorer lactation persistency in comparison with 50%HF animals.     

免疫牛乳中乳铁蛋白的水平研究

应用ELISA法测定免疫牛乳中乳铁蛋白的水平,探讨除特异性抗体外,免疫乳治疗和预防感染性疾病的机制。结果表明,与非免疫牛比较,免疫牛的初乳中乳铁蛋白含量明显增高(P<0.05),提示特异性疫苗的接种对宿主合成乳铁蛋白等抗感染物质有促进作用。     

Effect of interaction between leucine and acetate on the milk protein synthesis in bovine mammary epithelial cells

The interaction between Leucine (Leu) and acetate affecting milk protein synthesis in the bovine mammary epithelial cells (BMECs), and underlying the molecular mechanisms are not well understood. The objectives of this study were to investigate the effect of Leu, acetate, and their interaction on the expression of genes involved in milk protein synthesis, and JACK2/STAT5, mTOR and AMP‐activated protein kinase (AMPK) signaling pathway. The study was a 2 × 6 factorial arrangement with treatments: Leu concentration (0.45 and 1.8 mM) and acetate concentration (0, 4, 6, 8, 10, and 12 mM). The results showed that 1.8 mM Leu or 8–10 mM acetate had positive effect on ATP content, the expression of casein genes, JACK2/STAT5 and phosphorylation of mTOR pathway, but reduced AMPK phosphorylation. Leu at 1.8mM had a positive effect on the up‐regulation of acetate on ATP content, the expression of CSN1S1, CSN2, CSN3, and JACK2, the expression and phosphorylation of eukaryotic initiation factor 4E, p70 ribosomal protein S6 kinase‐1, and mTOR, but reducing AMPK phosphorylation. The results suggest that acetate, Leu, and their interaction have effect on milk protein synthesis through the JACK2/STAT5, mTOR, and AMPK pathway. Acetate addition up‐regulated the effect of Leu on milk protein synthesis, and Leu facilitated the up‐regulation of acetate on milk protein synthesis through these pathways.     

日粮精粗比对思南杂交肉牛体尺性状和血液常规指标的影响

为研究日粮不同精粗比对思南杂交肉牛体尺性状与血液生化指标的影响,试验选择体重相近的12头思南杂交肉牛随机分为A、B、C、D共4个组,每组3个重复,每个重复1头牛,A、B、C、D组精粗比分别为3:7、4:6、5:5、6:4.结果表明:(1)提高思南杂交肉牛日粮精粗比可以促进体高、体斜长、胸围和管围的增长,并且各组后60天...     

恩诺沙星及其代谢产物在奶山羊的药动学及乳中药物浓度

本试验研究单剂量静脉注射、肌肉注射和乳房灌注恩诺沙星（2.5mg/kg)在健康奶山羊的药动学及乳中药物浓度。采用HPLC法测定血浆和乳中恩诺沙星及其代谢产物环丙沙星的浓度，用统计矩原理处理血浆中药物浓度－时间数据，计算非房室模型的药动学参数。静脉注射、肌肉注射和乳房灌注恩诺沙星的t1/2β分别为1.32、1．55、0．99h;AUC为1．06、3．04、2．66mghL^-1；恩诺沙星的代谢分数为35．01％、44．06％、45．73％；环丙沙星的t1/2β为1．81、2．94、2．32h。乳中的药物浓度高于同期血中药物浓度，且乳中环丙沙星浓度高于恩诺沙星浓度并维持更长的时间。     

Effects of white,yellow, and blue colored LEDs on milk production,milk composition,and physiological responses in dairy cattle

Light emitting diode (LED) is more energy efficient than incandescent or fluorescent light. This study was to evaluate effects of different colored LEDs on milk production, milk composition, and physiology of Holstein cow. According to milk production and parity, cows (n = 186) were allotted to four treatments: control (natural daylight), white, yellow, and blue LED groups. Of these, 40 cows that had passed 57 day‐in‐milk were used. Yellow and blue LED groups demonstrated greater rates of decline in milk production than control and white LED groups. At the finish point, milk fat, protein, and lactose contents were the lowest in the blue LED group, whereas milk–urea–nitrogen levels were the highest in the yellow and blue LED groups. Extended exposure to blue LED light lowered antioxidant enzyme activity and insulin‐like growth factor‐1 levels. Prolactin concentrations were higher in the white and blue LED groups than in the control. Cortisol level was the highest in the blue LED group among the groups. Nonesterified fatty acid levels in the yellow and blue LED groups decreased to the greatest extent compared to the start point. These results suggest that blue LED light can decrease milk production and generate more stress than white and yellow LED lights.     

Impact of bovine somatotropin administration beginning at day 70 of lactation on serum metabolites, milk constituents, and production in cows previously exposed to exogenous somatotropin.

Metabolic and production responses are reported for 72 cows treated with bovine somatotropin (BST) for 30 days starting at day 70 of lactation. Of these 72 cows, 48 had been exposed in the preceding lactation to long-term treatment with BST at 3 dosages and 24 (controls) had not been given BST. Approximately half of the cows in each group were parity-2 cows, the rest were older. Comparisons between groups were made separately for parity-2, and older cows. Analyses, using pretreatment values of each variable as a covariate, indicated that older cows, but not parity-2 cows, significantly (P less than 0.05) increased milk production during treatment. Parity-2 cows, however, had a significantly higher milk fat percentage than controls following treatment. Cows treated with 51.6 or 86 mg BST/d in both parity groups had significantly higher serum-free fatty acids than controls. Estimated net energy balances were significantly lower for older treated cows, but did not significantly differ from controls for parity-2 treated cows. Older cows in the 86 mg of BST/d group tended to have higher concentrations of blood glucose than did older control-group cows. Treatment with BST did not significantly increase serum ketone concentrations in any group of animals, and none of the cows developed clinical ketosis during this period. Estimated net energy balance (ENEB) during treatment was a significant (P less than 0.05) covariate for free fatty acid concentrations in older cows and for milk fat percentage in parity-2 cows. Covariate adjusted analyses, using ENEB during treatment as a covariate, indicated that lipolytic stimuli already acting may be enhanced by treatment with BST, but a negative energy balance was not a necessary precondition for free fatty acid concentrations to increase following somatotropin treatment. Similarly, milk fat percentages for parity-2 treated cows were significantly (P less than 0.05) higher during treatment than controls when ENEB during treatment was used as a covariate. Increased milk fat concentrations in parity-2 treated cows were not associated with significant increases in the ratio of C18:C4-10 milk fatty acids, indicating that increased milk fat resulted from either an increase in incorporation of C18 fatty acids into milk fat coupled with an increase in de novo mammary synthesis of C4-10 milk fatty acids or an increase in C12-16 fatty acids that may arise either from increased tissue mobilization, from diet, or from de novo mammary synthesis.     

新疆地区荷斯坦牛乳中体细胞评分对产奶量与乳成分的影响

为了探究牛乳中体细胞评分（SCS）对日产奶量（DMY）和乳成分之间的关系,了解奶牛乳房的健康状况,本研究使用新疆昌吉地区规模化牛场共2 338头荷斯坦牛的33 290条DHI记录和生产性能数据,将DHI记录中的体细胞数（SCC）转化为SCS后分析SCS对DMY与乳成分的影响。运用SAS 9.2软件对产奶量和乳成分进行最小二乘方差分析及多重比较,并对SCS与产奶量和乳成分进行相关性分析,其固定效应主要包括SCS、场、年份、季节及胎次效应。结果表明：SCS、场效应、年份效应、季节效应和胎次效应均对DMY与乳成分有极显著影响（P<0.01）。随着SCS的增加,DMY和乳糖率（MLP）呈下降趋势,当SCS为0水平,且SCC为9×10³~17×10³个/mL时,DMY和MLP极显著高于其他SCS水平（P<0.01）;MFP和MPP呈上升趋势,当SCS为9水平,且SCC为4 529×10³~4 904×10³个/mL时,MFP和MPP最高。相关性分析结果显示,SCS与DMY、MLP呈极显著负相关（P<0.01）;SCS与MFP、MPP呈极显著正相关（P<0.01）。因此,通过分析SCS对产奶量和乳成分间的关系,可为规模化牧场奶牛日常管理提供科学依据,预防和降低患乳房炎的风险。