The evaluation of the curd forming ability of milk replacers

Inadequate milk curd formation in the abomasum of newborn calves causes malnutrition and diarrhea. In order to define the factors of inadequate curd formation, we compared the curd forming ability among 9 kinds of milk replacers, bulk milk (raw milk), and skim milk both in vitro and in vivo . When rennet was added, the raw milk and one milk replacer formed firm curds. The rest of the milk replacers and skim milk did not form any curd. When a solution of HCl was added, raw milk, three milk replacers and skim milk formed the curd at pH 4.5, but the other milk replacers did not. When HCl was added following the rennet, raw milk, one milk replacer and skim milk formed the curd. In vivo , raw milk, two milk replacers and skim milk showed good curd formation whereas the other milk replacers showed poor curd formation inside the abomasums of the calves. This study showed that most of the milk replacers sold in Japan could not form the curd with rennet.     

Organic management of dietary rosemary extract in dairy sheep: effects on milk quality and clotting properties

The increasing demand for animals from organic breeding systems has increased interest in certain natural substances, called nutraceuticals, to stimulate the organic defenses of the animals. The aim of this trial was to study the effects of dietary rosemary extract in 36 ewes, from 57 to 154 days of lactation, divided into three groups: CTR (basal diet), ROXLD (600 mg extract/head/day) and ROXHD (1,200 mg extract/head/day). A significantly higher quantity of milk and quantitative daily production of protein, casein, fat, and lactose were observed in the milk of animals in the ROXHD group compared with milk from animals in the CTR and ROXLD groups. No significant differences were observed for somatic cell counts, considering that treated groups showed lower values compared with controls. A significant decrease in clotting time (r) and increase in curd firmness (a ₃₀ ) were observed in milk of both treated groups (ROXLD and ROXHD) compared with the CTR group. These results could be related to the significantly higher acidity values, pH and SH°, observed in the milk of animals from the treated groups. Dietary rosemary extract in dairy sheep enhanced milk yield, quality, and renneting properties due to its “natural, functional ingredients.”

     

A multiple-phenotype imputation procedure as a method for prediction of cheese-making efficiency in Spanish Assaf sheep

Sheep milk is mainly intended to manufacture a wide variety of high-quality cheeses. The ovine cheese industry would benefit from an improvement, through genetic selection, of traits related to the milk coagulation properties (MCPs) and cheese yield-related traits, broadly denoted as “cheese-making traits.” Considering that routine measurements of these traits needed for genetic selection are expensive and time-consuming, this study aimed to evaluate the accuracy of a cheese-making phenotype imputation method based on the information from official milk control records combined with the pH of the milk. For this study, we analyzed records of milk production traits, milk composition traits, and measurements of cheese-making traits available from a total of 1,145 dairy ewes of the Spanish Assaf sheep breed. Cheese-making traits included five related to the MCPs and two cheese yield-related traits. The milk and cheese-making phenotypes were adjusted for significant effects based on a general linear model. The adjusted phenotypes were used to define a multiple-phenotype imputation procedure for the cheese-making traits based on multivariate normality and Markov chain Monte Carlo sampling. Five of the seven cheese-making traits considered in this study achieved a prediction accuracy of 0.60 computed as the correlation between the adjusted phenotypes and the imputed phenotypes. Particularly the logarithm of curd-firming time since rennet addition (logK₂₀) (0.68), which has been previously suggested as a potential candidate trait to improve the cheese ability in this breed, and the logarithm of the ratio between the rennet clotting time and the curd firmness at 60 min (logRCT/A60) (0.65), which has been defined by other studies as an indicator trait of milk coagulation efficiency. This study represents a first step toward the possible use of the phenotype imputation of cheese-making traits to develop a practical methodology for the dairy sheep industry to impute cheese-making traits only based on the analysis of a milk sample without the need of pedigree information. This information could be also used in future planning of specific breeding programs considering the importance of the cheese-making efficiency in dairy sheep and highlights the potential of phenotype imputation to leverage sample size on expensive, hard-to-measure phenotypes.     

Genetic structure of milk protein polymorphisms and effects on milk production traits in a local dairy cattle

The milk protein genetic structure of the Reggiana dairy local cattle with remarkable milk quality properties was analysed and compared with the structure of Italian Friesian and Italian Brown cattle. A total of 1138 individual milk samples from the three breeds were typed by isoelectrofocusing. Polymorphism was found at the α_s1‐casein (CSN1S1), β‐casein (CSN2), κ‐casein (CSN3), and β‐lactoglobulin (LGB) loci. High frequencies were observed for some casein alleles in Reggiana (CSN1S1*C, 25%; CSN2*B: 28%) with considerable differences to those observed in a survey carried out 30 years before. A great variation among breeds was observed for casein haplotype frequencies and high linkage disequilibrium was detected at the three polymorphic casein loci CSN1S1‐CSN2‐CSN3. The prevalent haplotypes were CA²B (23%; Reggiana), BA²A (48%; Italian Friesian) and BA²B (51%; Italian Brown). Higher G_ST values between breeds were observed when haplotype frequencies were considered instead of gene frequencies. In the Reggiana cattle, the occurrence of two casein alleles at a rather high frequency (CSN1S1*C, CSN2*B) allowed to estimate the effects of rare casein haplotypes on milk traits. The CA²B haplotype was associated with a significantly higher milk protein and fat content and a significantly higher protein per cent was found also for the BA¹B haplotype.     

Effects of total replacement of corn silage with sorghum silage on milk yield,composition, and quality

Background: In the last years, difficulties occurring in corn cultivation(i.e., groundwater shortages, mycotoxin contamination) have been forcing dairy farmers to consider alternative silages. Some experiments conducted on lactating cows have proven that the total replacement of corn silage with sorghum silage did not reduce milk yield.However, this kind of substitution involves supplementing sorghum-based diets with grains, to compensate for the lower starch content of sorghum silage compared to corn silage. Change of silage type and inclusion of starch sources in the diet would influence rumen fermentations, with possible effects on milk composition(i.e., fatty acid profile) and coagulation properties. A worsening of milk coagulation properties would have a negative economic impact in Italy, where most of the milk produced is processed into cheese.This study was designed to compare milk composition and quality, with emphasis on fatty acid profile and coagulation properties, in dairy cows fed two diets based on corn or sorghum silage.Results: The sorghum diet reduced milk yield(P = 0.043) but not 4% fat corrected milk(P = 0.85). Feeding sorghum silage did not influence milk contents of protein(P = 0.07) and lactose(P = 0.65), and increased fat content(P = 0.024).No differences emerged for milk concentrations of saturated(P = 0.61) and monounsaturated fatty acids(P = 0.50),whereas polyunsaturated fatty acids were lower(P 0.001) for the sorghum diet. Concentrations of n-6(P 0.001) and n-3 fatty acids(P = 0.017) were lower in milk of cows fed the sorghum diet. Milk coagulation properties did not differ between the two diets, except the "a30"(the curd firmness, expressed in mm, 30 min after rennet addition), that was lower(P = 0.042) for the sorghum diet.Conclusions: Feeding a forage sorghum silage, properly supplemented with corn meal, as total replacement of corn silage maintained milk composition and did not influence negatively milk coagulation properties, which have a great economic relevance for the Italian dairy industry. Thus, silages obtained from forage sorghums could have a potential as substitute of corn silages in dairy cow diets.     

Effect of dietary net energy concentration on dry matter intake and energy partition in cows in mid‐lactation under heat stress

This study aimed to determine the net energy requirement of Holstein cows in mid‐lactation under heat stress. Twenty‐five multiparous Holstein cows were randomly allocated to five groups corresponding to five isonitrogenous total mixed rations, with net energy for lactation (NE_L) content of 6.15 (NE‐6.15), 6.36 (NE‐6.36), 6.64 (NE‐6.64), 6.95 (NE‐6.95), 7.36 (NE‐7.36) MJ/kg of dry matter (DM), respectively. Throughout the experimental period the average temperature humidity index at 07.00, 14.00 and 22.00 hours was 72.1, 88.7, and 77.6, respectively. DM intake decreased significantly with the elevated dietary NE_L concentration. Fat corrected milk increased quadratically, and milk fat content and milk energy (MJ/kg) reached the greatest in the NE‐6.95 group with increasing dietary NE_L content. Strong correlations were found between dietary NE_L content and: (i) DM intake; (ii) NE_L intake; (iii) milk energy (E_l); (iv) E_l/metabolizable energy intake (MEI); (v) E_l/NE_L intake, as well as between NE_L intake and fat corrected milk yield (FCM). The suitable net energy required for dairy cows producing 1 kg FCM ranged from 5.01 to 5.03 MJ, was concluded from the above‐stated regressions. Correlation between heat production (HP) and MEI could be expressed as: Log (HP) = ?0.4304 + 0.2963*MEI (n = 15, R² = 0.99, Root Mean Square Error (RMSE) = 0.18). Fasting HP was 0.3712 MJ/kg^0.75 when extrapolating MEI to zero.     

Ultrasonographic imaging of abomasal milk clotting and abomasal diameter in healthy and diarrheic calves

In case of diarrhea calves are treated with oral rehydration solutions (ORS), which are known to increase abomasal pH and inhibit milk clotting in vitro. Nevertheless, recent studies have shown that ORS with HCO₃^‐ ≤ 62 mmol/L do not interfere with abomasal milk clotting in healthy calves. However, in diarrheic calves, feeding ORS and milk simultaneously may disturb abomasal curd formation and exacerbate diarrhea due to faster abomasal passage of ingesta. Therefore, the aim of the present study was to ultrasonographically examine abomasal milk clotting and diameter after feeding milk and milk replacer (MR) with and without ORS to healthy and diarrheic calves. Abomasal curd formation and diameter in healthy and diarrheic calves were ultrasonographically imaged before and after feeding milk, MR and ORS prepared in milk or MR. Feeding mixtures of milk or MR with ORS did not cause any remarkable differences in the ultrasonographic images of abomasal content. Moreover, abomasal milk clotting was not disturbed due to diarrhea. Statistically significant differences of abomasal diameter after feeding between healthy and diarrheic calves indicated that abomasal emptying is delayed in diarrheic calves. Hence, further studies are needed to determine reasons for decelerated abomasal passage in calves suffering from diarrhea.     

Ultrasonography to investigate the effect of supplementing whole milk with complex carbohydrates and specific amino acids on curd retention in the abomasum of dairy calves

AIM: To determine whether the retention time of curd in the abomasum of calves was influenced by supplementing milk with a plant-derived carbohydrate and amino acid supplement, evaluated non-invasively using ultrasonography.

METHODS: Female dairy calves aged between 2–6 days of age were sourced from a commercial farm in March 2013. All calves were fed whole milk until weaning (4?L per day); 21 calves were supplemented with a probiotic until 18 days of age, and thereafter with a plant-derived complex carbohydrate and amino acid supplement until weaning, and 22 calves were just fed whole milk. Treatment groups were balanced for age, weight and breed. At 9–14, 24–29 and 52–57 days of age, the abomasum of each calf was examined using ultrasonography immediately before and after feeding, 1 and 2 hours after feeding, and then at 30 minute intervals until curd was no longer visible in the abomasum. Abomasal volume and curd size were recorded to assess retention time of curd in the abomasum.

RESULTS: At 9–14 days of age, mean retention time of curd in the abomasum was similar (4.6 hours) in both groups. At 24–29 days of age, when the supplemented calves had been receiving the supplement for approximately 10 days, mean curd retention time was longer by 1.4 (SE 0.28) hours in supplemented compared with unsupplemented calves (p<0.001). At 52–57 days of age, mean retention time was longer by 0.7 (SE 0.34) hours compared to unsupplemented calves (p=0.05).

CONCLUSION: Using ultrasonography, changes in abomasal content could be followed non-invasively over time and it was demonstrated that the plant-derived complex carbohydrate supplement increased the curd retention time in the abomasum. We speculate that the increased retention time enables an increased availability of nutrients following a more complete digestion of milk, thereby improving animal performance.     

预酸化对云南乳扇凝乳的影响

本研究利用热处理的酸乳清对牛乳进行预酸化处理,研究酸乳清对乳扇凝乳效果的影响,根据热烫拉伸工艺的需要,控制凝乳的pH值,分析不同的温度和pH值对凝乳效果的影响。结果表明:凝乳温度34℃、凝乳pH值5.2时,酪蛋白流失最少,凝乳效果最好。乳扇加工工艺中通过酸乳清对牛乳进行预酸化处理,可以解决凝乳过程中凝块pH值不固定的问题。     

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.     

Contributions of genetic and environmental components to changes in phenotypic variation between generations

We evaluate the extent to which changes in phenotypic variation among generations of populations kept in the same environment are due to changes in genetic (V_A) or in environmental (V_E) variance. Data were available on body weight of adult poultry on a total of 89186 birds (mainly females) from six generations of each of seven lines of layers. There was substantial heterogeneity of variation between generations, shown to be in both V_A and V_E components. Based on the Akaike information criterion (AIC), the best fit was with both components changing, and a better fit was obtained if V_A/V_E (i.e. heritability) or V_E, rather than V_A, was assumed constant. In analyses of quantitative genetic data spanning environmental groups, attention should be paid to whether and how the variance components change among groups before undertaking detailed variance partition that may be sensitive to such changes.     

Inheritance of the lace‐tailed laced plumage pattern of the sebright bantam

1. An investigation was conducted firstly among progeny from a cross between Blue Andalusian and Silver‐spangled Hamburgh bantams, and secondly between crosses of selected progeny of this mating with a Silver Sebright bantam in an effort to determine the genotype of the lace‐tailed laced plumage phenotype of the latter.

2. The genotype of the black‐laced blue and the spangled plumage phenotypes of the Andalusian and the Silver‐spangled Hamburgh had, respectively, been shown to depend on homozygosity of E, Co, db⁺, Ml and Pg, and of co⁺, Db, Ml and Pg together with a black down allele at the E‐locus presumed to be E, but also hypothesised to be E^R. The genes E and E^R are the extended black and birchen‐like allele at the E‐locus whilst Co, Db, Ml and Pg are, respectively, the eumelanin restrictors, Columbian and dark‐brown Columbian, the eumelanin extension melanotic and the pattern gene. The Sebright had been hypothesised to possess the E allele at the E‐locus, and to be homozy‐gous Co, Ml and Pg, a combination shown to be responsible for the black‐tailed laced phenotype of the Wyandotte.

3. Segregation in the F₂ generation varied from that expected if both parental genotypes were E/E, but gave close agreement if the Silver‐spangled Hamburgh was E^R/E^R.

4. A lace‐tailed laced segregant in the F₂ generation of the first mating, presumed to be homozygous E^R, Co, Db, Ml and Pg was mated to a Sebright. The F₁ generation failed to segregate at the 5 loci, thus suggesting the genotype of the lace‐tailed laced phenotype of the Sebright to be homozygous E^R, Co, Db, Ml and Pg. Segregation in the F₂ generation of a mating of the female F₁ with a Silver‐spangled Hamburgh male confirmed the genotype of the lace‐tailed lacing of the Sebright bantam, and demonstrated that of the Silver‐spangled Hamburgh to be homozygous E^R, co⁺, Db, Ml and Pg‐.     

Comparison of Methods Used to Detect Renibacterium salmoninarum,the Causative Agent of Bacterial Kidney Disease

Abstract

Various diagnostic methods used to detect Renibacterum salmoninarum, the causative agent of bacterial kidney disease (BKD), were compared. The most sensitive method was the enzyme immunoassay (the indirect dot blot assay), which could detect 10² bacterial cells per gram of kidney tissue. The minimum bacteria concentrations showing positive reactions to the indirect fluorescent antibody test (IFAT) and the coagglutination test were 10³ and 10⁴ cells/g kidney, respectively. The sensitivities of the Gram stain, immunodiffusion procedure, and latex agglutination test were low, and these methods could only be applied to fish with overt BKD symptoms. Altogether, 656 coho salmon Oncorhynchus kisutch were examined for R. salmoninarum antigen with the direct and indirect dot blot assays (DDBA and IDBA) and the IFAT. Among the fish sampled, positive reactions were obtained in 11.8% by the DDBA, 28.2% by the IDBA, and 12.9% by the IFAT.     

The hen's egg: Relationship of mean strain energy at shell fracture to shell compression speed,the nature of the compressing body and the location on the shell of the point of contact

1. The mean energy, E_f, required for fracture of an egg shell at its equator by a flat plate is known to depend on shell compression speed, v_m, for speeds in the range 20 μm/s to 2.lb5 mm/s; analysis of published data shows that E_f bears a linear relationship to log (v_m ) throughout the industrially important speed range from 20 μm/s to 1.lb1 m/s, increasing from 1.lb3 to 5.lb0 mJ.

2. At lower speeds down to 2 μm/s E_f is constant.

3. E_f is reduced if the flat plate is replaced by a sphere or cylinder; the greater its curvature, the smaller E_f.

4. E_f for the narrow pole is greater and for the broad pole smaller than that for the equator but these differences may be due in part to . systematic differences in shell thickness as well as curvature.     

Mechanism of blood coagulation in common carp (Cyprinus carpio)

In vitro, carp blood was anticoagulated by using MgSO₄ at a final concentration of 22.2 mmol L^?1 and sodium citrate at a final concentration of 11.8 mmol L^?1. The coagulation times for carp plasma diluted by ion‐free water (1:1), and that of carp plasma to which thrombocytes and small lymphocytes were added, were measured at 23 °C using standard methods, and then contrasted with the coagulation times for plasma obtained from chickens and rabbits. The shapes of the thrombocytes and small lymphocytes, which were either wet mounted or stained with hematoxylin and eosin, were observed under a light microscope. We found that: (i) the coagulation reaction of carp blood was significantly (P < 0.01) accelerated by the addition of ion‐free water; (ii) the three types of blood cells (thrombocytes, small lymphocytes and red blood cells) promoted plasma coagulation to a similar extent (P > 0.05); (iii) in carp Mg²⁺ plasma and K₂C₂O₄ plasma, the thrombocytes were usually morphologically normal, but many small lymphocytes were destroyed and became aggregated; (iv) in the citrate plasma, thrombocytes were often aggregated, but the small lymphocytes were usually morphologically normal; and (v) the coagulation time for chicken and rabbit plasma was significantly extended by adding ion‐free water.     

Allele frequencies of the extension locus encoding the melanocortin-1 receptor in Japanese and Korean cattle

In order to estimate the influence of the Extension (E) locus in cattle coat color, the melanocortin‐1 receptor (MC1R) gene in Japanese Black, Japanese Brown and Korean (Hanwoo) cattle were sequenced. The sequences of the coding region revealed three alleles (E^D, E⁺ and e), which were previously reported. Polymerase chain reaction‐restriction fragment length polymorphism was performed to investigate the gene frequencies of the three breeds. Japanese Black was almost composed of E^D and E⁺ individuals, E^D = 0.481 and E⁺ = 0.514, and no homozygous e/e, therefore that is consistent with the hypothesis that E^D and E⁺ induce black pigment synthesis. Allele frequencies between Japanese Brown and Hanwoo were obviously different; however, recessive red e allele frequency was 0.038 for Japanese Brown and 0.948 for Hanwoo, even though both breeds have quite similar coat colors (ranging from yellowish brown to dark brown including a red coat color). This result suggested that other genes are also associated with a coat color of red and brown in cattle.     

Gene expression of endothelin-1 and its receptors in the heart of broiler chickens with T(3)-induced pulmonary hypertension

To investigate the effect of T₃-induced pulmonary hypertension on endothelin (ET) production and genes expression of ET-1, ET_A and ET_B receptors (ET_AR and ET_BR) during rearing, semiquantitative RT-PCR and enzyme immunometric assay were performed in the heart ventricles and serum, respectively. The ET-1 and its receptor genes were expressed in the right and left ventricles of control and T₃-treated broilers at 12, 28 and 49 days of age. There were significant (P < 0.05) reductions of the relative amounts of ET-1 (in both ventricles) and ET_AR (in the right ventricle) mRNAs at 28 and 49 days of age, in T₃-treated broilers compared to controls. The relative amounts of ET_BR mRNA in the right and left ventricles did not significantly differ between control and T₃-treated broilers at any age. The serum level of ET was significantly (P < 0.05) increased in T₃-treated chickens at 28 and 49 days of age when compared with that of the control. It is concluded that ET-1, ET_AR and ET_BR genes are normally expressed in the heart ventricles of broilers. It is likely that increased serum level of ET and decreased ET-1/ET_AR genes expression in the ventricles are involved in the heart dysfunction of broiler chickens with developmental pulmonary hypertension.     

The influence of different forms and concentrations of nitrogen on total nonstructural carbohydrate allocation and growth in Digitaria eriantha

Abstract

Digitaria eriantha plants were grown under controlled conditions for a period of three months, during which time they were supplied with the following forms and concentrations of nitrogen: 50 mg/1 NO₃ ^?‐N, 200 mg/1 NO₃ ^?‐N, 200 mg/1 NH₄ ⁺‐N and a combined form containing both NO₃ ^?‐N and NH₄ ⁺‐N with a nitrogen concentration of 200 mg/1. Control plants received no nitrogen.

At monthly intervals both above and below ground components were assayed for soluble and insoluble carbohydrate contents. Dry mass and leaf areas were also measured.

The nitrogen treatments were found to influence the allocation of photosynthates into either soluble or insoluble carbohydrates. In above ground tissue, the soluble carbohydrate component decreased with time, while the insoluble component increased with time. In root tissue the reverse trends were observed. Both dry mass and leaf area development were enhanced in plants supplied with nitrogen in any form. It was suggested that growth of D. eriantha was influenced by carbohydrate fluctuations.     

Effects of flunixin meglumine and ketoprofen on mediator production in ex vivo and in vitro models of inflammation in healthy dairy cows

Donalisio, C., Barbero, R., Cuniberti, B., Vercelli, C., Casalone, M., Re, G. Effects of flunixin meglumine and ketoprofen on mediator production in ex vivo and in vitro models of inflammation in healthy dairy cows. J. vet. Pharmacol. Therap.  36 , 130–139. In this study, ex vivo assays were carried out in dairy cows to evaluate the anti‐inflammatory effects of two nonsteroidal anti‐inflammatory drugs: ketoprofen (KETO) and flunixin meglumine (FM). Twelve healthy Holstein dairy cattle were randomly allocated to two groups (n=6): group 1 received FM and group 2 received KETO at recommended therapeutic dosages. The anti‐inflammatory effects of both drugs were determined by measuring the production of coagulation‐induced thromboxane B₂ (TXB₂), lipopolysaccharides (LPS) (10 μg/mL)‐induced prostaglandin E₂ (PGE₂), and calcium ionophore (60 μm )‐induced leukotrien B₄ (LTB₄). Cytokine production was assessed by measuring tumor necrosis factor‐α (TNF‐α), interferon‐γ (IFN‐γ) and interleukin‐8 (CXCL8) concentrations after incubation in the presence of 10 μg/mL LPS. The IC₅₀ of FM and KETO was determined in vitro by determining the concentration of TXB₂ and PGE₂ in the presence of scalar drug concentrations (10^?9–10^?3 m ). Both FM and KETO inhibited the two COX isoforms in vitro, but showed a preference for COX‐1. FM and KETO showed similar anti‐inflammatory effects in the cow.     

北京及周边地区牛乳的凝固性分析

通过对北京和山东等地不同规模奶牛饲养场的牛乳凝固性的调查,分析奶牛年龄、胎次、泌乳期、季节和饲养方式等因素对牛乳凝固性的影响.结果表明:牛乳经发酵或凝乳酶作用后所形成的凝乳质量与牛乳的来源密切相关.随着奶牛年龄和胎次的增长,牛乳的凝乳质量呈现下降趋势,同时,产仔后泌乳中期的牛乳的凝乳质量较之前期和后期更低;全年中秋季和冬季凝乳质量较好.较大规模化的牛群饲养方式有利于牛乳品质及凝乳质量的提高.