Relation between the level of free amino acids in milk and milk production

A negative relationship of glutamic acid content and milk yield over the first 100 days of lactation was found in a set of 20 cows. In some free amino acids, large differences exist between the cows with the higher milk yield and those with the lower milk yield, the largest difference being recorded in the content of glutamic acid (in favour of the cows with the lower milk output). The group of cows with the higher milk output per day or per first 100 days of lactation showed no dependence on any of the free amino acids in milk. The group of cows with the lower milk yield showed a significant negative relation of glutamic acid content to milk yield over the first 100 days of lactation and a significant to highly significant positive relation between serine, threonine and alanine contents on the one hand and daily milk yield on the other.     

Relation between biochemical parameters in the blood of cows and milk production

No differences in blood samples were found out when the biochemical parameters in arterial and venous blood of dairy cows were compared before and after milking. Negative correlation coefficient (r = -0.3460) approaching the significance level was determined by comparing the values for milk yield on the day of sampling (in ascending phase of lactation) and protein content in venous blood after milking, and significant negative correlation coefficient (r = -0.3813) for daily milk yield and gamma-globulin concentration in venous blood before milking. The relationship between butterfat content on the day of milking and the values of alkaline phosphatase can be characterized by significant up to highly significant negative correlation coefficients in all three blood samples (r = -0.3232 to -0.3908).     

Relation between the biochemical composition of the blood of cows and variations in milk production

A significantly lower alkaline phosphatase activity was recorded in the arterial blood of cows with higher milk efficiency. They also had higher sugar contents in their blood: highly significantly in arterial blood and significantly in venous blood after milking. As to the other blood components, the differences are low and insignificant. A significant positive relationship between the daily milk yield and the content of ash in blood (mainly in venous blood before milking), highly significant positive relationship between protein content in arterial blood and daily milk yield, and significant to highly significant negative relationship between the activity of alkaline phosphatase in arterial and venous blood before milking and the level of gamma-globulins in arterial blood were recorded in the group of cows with higher milk output. In the group of cows with lower milk production, significant to highly significant negative relationships were obtained between protein content in blood and the daily milk yield (in arterial and venous blood before milking).     

Association between anti-F. hepatica antibody levels in milk and production losses in dairy cows

This study was conducted to determine: (1) the associations between anti-Fasciola hepatica antibody levels in milk and some productive and reproductive parameters in dairy cattle, and (2) the threshold antibody level associated with loss of productivity, at both herd and individual level. Anti-F. hepatica antibodies were analysed by MM3-SERO ELISA in milk samples from the bulk tanks of 490 dairy farms and from 686 lactating cows. The results of general linear model analysis revealed a significant (P<0.05) negative association between the F. hepatica infection status at herd level, determined by analysis of specific antibodies in bulk tank milk, and the average herd milk production. Highly positive herds (MM3-SERO ELISA result>0.405) produced an average of 1.5 kg milk/cow per day less than the negative herds. At cow-level, the mixed model analysis also revealed a significant (P<0.05) association between anti-F. hepatica antibody levels and milk yield. A significant (P<0.05) average reduction of 2 kg milk/day was observed in cows with highly positive ELISA results (>0.762) in relation to cows with negative results. The results of the study led us to conclude that MM3-SERO ELISA is a powerful tool that can be successfully applied, if appropriate "economic thresholds" are established, to identify herds and cows suffering from milk production losses associated with natural infection by F. hepatica.     

不同精粗饲料对泌乳中期山羊氨基酸的代谢流向及乳蛋白含量的影响

 通过检测泌乳中期山羊血浆及乳中游离氨基酸含量的变化,探讨不同精粗比饲料对机体中氨基酸（ａｍｉｎｏａｃｉｄｓ,ＡＡ）的代谢流向及乳蛋白的影响。选用泌乳中期山羊７只,随机分为２组,分别饲喂精粗比４∶６（低精料组）和６∶４（高精料组）日粮,颈静脉血管瘘采血,手工挤奶取奶样。Ｂｒａｄｆｏｒｄ法测定乳中总蛋白质浓度,ＲＰ－ＨＰＬＣ检测山羊血浆和乳中游离氨基酸的含量。结果表明,２组山羊血浆中均分离出１４种游离氨基酸,乳中分离出８种游离氨基酸,不同精粗比饲料对血液或乳中游离氨基酸谱无明显影响。不同精粗比日粮情况下,除丙氨酸外,血液中游离氨基酸的含量均高于乳中同种氨基酸的含量;且血液中生酮氨基酸（Ｌｅｕ,Ｌｙｓ）、兼性氨基酸（Ｐｈｅ,Ｉｌｅ）和支链氨基酸（Ｌｅｕ,Ｉｌｅ和Ｖａｌ）含量显著或极显著高于乳中。高精料组除Ｇｌｙ和Ａｌａ外,其余氨基酸含量均低于低精料组;乳中总蛋白浓度略高于低精料组,但无统计学差异。表明血液中游离氨基酸为乳蛋白的合成提供了原料和能量保证。饲喂高精料日粮,血液中游离氨基酸含量较低,不利于乳蛋白含量和产量的提高。     

Interrelation between profile test indicators in the decreased milk acidity syndrome in cows

The internal environment of high-yielding dairy cows was investigated in relation to 36 variables of the blood metabolic profile, blood serum, milk and urine, with the incidence of reduced titration acidity milk syndrome. The levels of variables were confronted with references values. At the same time the statistical significance of differences of arithmetical means from the reference mean was calculated. Correlation analysis of all variables yielded 630 correlation coefficients. Certain correlations were represented in form of correlogrammes. It has been demonstrated that the reduced titration acidity milk syndrome with the lowest values of 1.9 ml 0.25N NaOH per 100 ml occurred after administration of the feed ration deficient both in digestible crude protein and starch units (nutritive ratio 1:7.5) which contained unsafe grass haylage with a high content of ammonia (232.9 mg per 100 g). A highly significant negative correlation was proved to exist between lactose concentration and pH value of milk (r = -0.913); the regression equation (lactose) is 36.997--4.7536 (pH).     

Ileal digestibility of amino acids in pigs fed barleys differing in protein content

The apparent digestibility of nitrogen and amino acids was measured by the ileal and faecal methods in pigs fed nine barleys differing in nitrogen content (from 1.73 to 2.16 per cent/DM). A positive (r = 0.87) and significant relationship was found between the apparent nitrogen digestibility at the end of the ileum and the crude protein content of barley. Generally, the higher the protein of the grain, the higher the ileal digestibilities of the amino acids. For most amino acids the faecal values were greater than the ileal ones. This being specially so for threonine, tryptophan, histidine and cystine belonging to the nutritionally important amino acid group. When the relationship between the amino acid and nitrogen digestibilities at the level of ileum is considered, the values were found to be similar to that of nitrogen in the case of tryptophan, higher for isoleucine, valine (both 2-3 units), cystine, histidine, leucine, methionine (all 5-6 units) and phenylalanine (10 units) and lower only for lysine and threonine (7-8 dig. units).     

颈静脉灌注不同模式的氨基酸混合物对泌乳奶牛乳蛋白合成的影响

本试验旨在比较颈静脉灌注酪蛋白模式和理想模式的氨基酸混合物对泌乳中期荷斯坦奶牛乳产量、乳成分以及乳腺对氨基酸摄取利用的影响。选择8头泌乳中期[泌乳天数:(82±11)d]荷斯坦奶牛作为试验动物,试验采用随机区组设计,将试验牛随机分为2组,分别颈静脉灌注160g/d酪蛋白模式(Casein组)和理想模式的氨基酸混合物(R组)。2个试验组分别以各自灌注前作为空白对照组(C1组为Casein组的空白对照组,C2组为R组的空白对照组)。预试期14d,灌注期5d。试验采用全混合日粮(TMR)饲喂,以玉米、豆粕、棉籽粕、玉米青贮、苜蓿干草和羊草为主要原料,参照NRC(2001)奶牛饲养标准配制。结果表明:灌注酪蛋白模式的氨基酸混合物后,乳蛋白产量和含量较灌注前呈上升趋势(乳蛋白产量上升7.14%,P=0.078;乳蛋白含量上升3.27%,P=0.072);并且,奶牛动脉血浆中异亮氨酸(Ile)、亮氨酸(Leu)、赖氨酸(Lys)和组氨酸(His)的浓度较灌注前有不同程度的上升(Ile的浓度提高31.5%,P=0.097;Leu的浓度提高65.9%,P=0.041;Lys的浓度提高36.9%,P=0.088;His的浓度提高40.1%,P=0.010),而苏氨酸(Thr)、缬氨酸(Val)、蛋氨酸(Met)、苯丙氨酸(Phe)和精氨酸(Arg)的浓度在数值上虽较灌注前高但无显著差异(P0.05)。灌注酪蛋白模式的氨基酸混合物后,奶牛乳腺对天冬氨酸(Asp)和半胱氨酸(Cys)的摄取率显著升高(Asp的摄取率提高95.2%,P=0.031;Cys的摄取率提高49.6%,P=0.031),而奶牛乳腺对甘氨酸(Gly)的摄取率显著降低(降低158.3%,P=0.041)。灌注理想模式的氨基酸混合物后,乳蛋白含量比灌注前有上升趋势(提高5.78%,P=0.064),而乳脂产量显著低于灌注前(降低8.57%,P=0.015);并且,奶牛动脉血浆中Arg的浓度有上升趋势(提高18.0%,P=0.093),而酪氨酸(Tyr)的浓度呈下降趋势(降低47.8%,P=0.074)。灌注理想模式的氨基酸混合物后,奶牛乳腺对谷氨酸(Glu)、Cys和Ile的摄取率显著上升(Glu的摄取率提高118.7%,P=0.015;Cys的摄取率提高77.4%,P=0.032;Ile的摄取率提高46.0%,P=0.012),而奶牛乳腺对Ser的摄取率呈下降趋势(降低56.2%,P=0.052)。灌注氨基酸混合物后,Casein组乳脂产量增量显著高于R组(P=0.012),且Casein组的乳产量增量(P=0.095)和乳糖产量增量(P=0.091)较R组有升高的趋势,而2组间其他指标增量无显著差异(P0.05)。由此得出,在本试验条件下,颈静脉灌注酪蛋白模式和理想模式的氨基酸混合物均可提高泌乳奶牛的乳蛋白含量,而灌注酪蛋白模式氨基酸混合物同时可以促进乳蛋白产量的升高,因此,颈静脉灌注酪蛋白模式氨基酸混合物的效果优于灌注理想模式氨基酸混合物。     

Level of free amino acids in the milk of cows in relation to values in arterial and venous blood

The levels of free amino acids in cow's milk vary greatly. The highest value of 164.484 mumol/l was recorded in glutamic acid, followed by glycine, alanine, lysine, and the lowest values were found in cystine, methionine, phenylalanine, tyrosine and isoleucine (5--10 mumol/l). The levels of free amino acids in milk and their order differ from the values and the order in blood. For a large proportion of free amino acids, significant to highly significant relations exist between the levels in arterial blood and venous blood before and after milking. On the other hand, significant positive correlations were found only between the level of cystine in arterial blood and in venous blood after milking, between threonine level in arterial blood and in venous blood before milking, and a highly significant negative correlation was recorded between the leucine level in venous blood before milking and the respective value in milk.     

Relationship between concentration of citrate and ketone bodies in cow's milk

The authors' hypothesis is that the members of the tricarboxylic acid cycle (TCA cycle) such as citrate decrease in association with increased ketone body formation. To prove this hypothesis the connection between ketone bodies and citrate formation of milk was studied. A fluorimetric method was used to determine citrate and a headspace sampling gas chromatographic (GC) method was developed for determination of ketone bodies. Under real conditions of milk sampling, transport and storage, preserved milk samples of 119 clinically healthy dairy cows obtained in the 48 hours after milking were investigated. A low level of acetoacetate (ACAC) was found in all samples. This fact can be explained by the spontaneous decarboxylation of acetoacetate during sample storage (previously decarboxylised acetoacetate = pdACAC) and, consequently, the majority of the amount of acetoacetate in the samples (AC + pdACAC) appeared in the measured acetone concentrations. Based on the measured acetone concentration of milk samples two groups were formed retrospectively: HA (high-acetone) group (n = 41) with an AC + pdACAC concentration of > 0.4 mmol/l and a LA (low-acetone) group (n = 78) with an AC + pdACAC level of < or = 0.4 mmol/l. In the milk of cows of Group HA a positive correlation (r = +0.623) and linear connection between acetone (AC + pdACAC) and beta-hydroxybutyrate (BOHB) levels was found [BOHB = 2.491 + 0.586 x (pdAC + ACAC)]. Furthermore, in this group a negative correlation between citrate and BOHB and AC + pdACAC was also established (r = -0.579). Focusing on the results of this group the authors found a significant drop of AC + pdACAC and citrate during the metabolically critical first 1-4 weeks of lactation. For this reason they suggest that simple, easy, automated methods (i.e. flow injection analysis, Fourier transformation infrared analysis) should be introduced for the simultaneous determination of acetone and citrate concentration in milk to make the evaluation of the energy status of high-producing dairy cows easier and more certain.     

Relation of the levels of mineral substances in the blood of cows, the quantity of milk and the fat content of the milk

No explicit relations to the milk yield on the day of sampling were found when studying the content of calcium, phosphorus, magnesium, potassium and sodium in the arterial and venous blood of cows before and after milking in the peak lactation period. However, there is a tendency of higher milk yields at higher phosphorus levels in the milk of the Black-Pied and higher-yielding cows. Some relations to milk fat content were found to be significant: a positive effect of phosphorus content in the blood of Slovak Spotted cows, a positive effect of calcium and magnesium content in the blood of more productive cows and a negative effect of magnesium content in the blood of less productive cows.     

过瘤胃氨基酸高能复合物对奶牛产奶量及乳成分的影响

为研究不同过瘤胃氨基酸高能复合物对奶牛产奶量及乳成分的影响,试验选择胎次(3～5胎)、产奶量、产犊日期相近,体重(600±20)kg健康荷斯坦泌乳高峰期奶牛24头,随机分为4组,每组6头。1组为对照组,饲喂牛场常规日粮;2、3、4组为试验组,分别在常规日粮基础上添加过瘤胃氨基酸高能复合物Ⅰ、Ⅱ、Ⅲ500 g/(d.头)。正式期60 d。结果表明:奶牛日粮中添加过瘤胃氨基酸高能复合物后,均可明显提高奶牛产奶量、乳脂率、乳蛋白率及乳中总干物质含量。尤其是复合物Ⅲ,添加效果最为理想,平均日产奶量、乳脂率、乳蛋白率及总干物质含量分别比对照组提高21.19%(P<0.05)、21.31%(P<0.05)、9.72%(P<0.05)和10.34%(P<0.05),平均日校正乳产量提高35.70%(P<0.05)。     

Effect of dietary fish oil on milk yield, fatty acids content and serum metabolic profile in dairy cows

The aim of the study was to evaluate the effects of dietary unprotected fish oil on milk yield, fatty acids content and serum metabolic profile in dairy cows. Forty lactating Polish Holstein-Friesian cows were assigned to two groups. The cows were fed a control basal diet (C group), or a basal diet containing 2% addition of fish oil on mineral carrier (FOM group) during a 8-week period. Supplementing FOM diet of dairy cows had no significant effect on milk fat, milk protein, milk lactose concentration and somatic cells count, but increased the milk yield (36.5 kg/d), (p < 0.05) compared with the control cows (34.28 kg/d). We observed an increase (p < 0.05) in body condition scoring between C and FOM groups. Additionally, higher levels of non-esterified fatty acids and β-hydroxybutyrate acid were noticed in FOM group after 8 weeks of the experiment; however, these serum parameters still were in the reference range. Concentration of insulin was higher (30.40 μU/ml; p < 0.01) in the FOM group compared with the control group (14.03 μU/ml). In the FOM group, significant increase (p < 0.01) in long-chain fatty acids, mainly cis-9, trans-11 CLA and n-3 fatty acids (eicosapentaenoic and docosahexaenoic acids) was observed. The obtained results demonstrated that addition of fish oil to cows' diet could profitably modify the fatty acids in cow's milk.     

Effects of phenylalanine and threonine oligopeptides on milk protein synthesis in cultured bovine mammary epithelial cells

This study was conducted to investigate the effects of phenylalanine (Phe) and threonine (Thr) oligopeptides on α_s1 casein gene expression and milk protein synthesis in bovine mammary epithelial cells. Primary mammary epithelial cells were obtained from Holstein dairy cows and incubated in Dulbecco's modified Eagle's medium‐F12 medium (DMEM/F12) containing lactogenic hormones (prolactin and glucocorticoids). Free Phe (117 μg/ml) was substituted partly with peptide‐bound Phe (phenylalanylphenylalanine, phenylalanyl threonine, threonyl‐phenylalanyl‐phenylalanine) in the experimental media. After incubation with experimental medium, cells were collected for gene expression analysis and medium was collected for milk protein or amino acid determination. The results showed that peptide‐bound Phe at 10% (11.7 μg/ml) significantly enhanced α_s1 casein gene expression and milk protein synthesis as compared with equivalent amount of free Phe. When 10% Phe was replaced by phenylalanylphenylalanine, the disappearance of most essential amino acids increased significantly, and gene expression of peptide transporter 2 and some amino acid transporters was significantly enhanced. These results indicate that the Phe and Thr oligopeptides are important for milk protein synthesis, and peptide‐bound amino acids could be utilised more efficiently in milk protein synthesis than the equivalent amount of free amino acids.     

Effects of continuous low dose infusion of lipopolysaccharide on inflammatory responses,milk production and milk quality in dairy cows

The objective of this study was to evaluate the effects of continuous low dose infusion of lipopolysaccharide (LPS) on inflammatory responses and milk production and quality in lactating dairy cows. Eight Holstein cows were assigned to two treatments in a cross‐over experimental design. Cows were infused intravenously either with saline solution or with saline solution containing LPS from Escherichia coli O111:B4 at a dose of 0.01 μg LPS/kg body weight for approximately 6 hr each day during a seven‐day trial. The clinical symptoms and milk production performance were observed. Milk samples were analysed for conventional components, fatty acids and amino acids. And jugular vein and mammary vein plasma samples were analysed for concentrations of cytokines and acute phase proteins. LPS infusion decreased feed intake and milk yield. An increase in body temperature was observed after LPS infusion. LPS infusion also increased plasma concentrations of interleukin‐1β, serum amyloid A, LPS‐binding protein, C‐reactive protein and haptoglobin. LPS infusion decreased the contents of some fatty acids, such as C17:1, C18:0, C18:1n9 (trans) and C18:2n6 (trans), and most amino acids except for methionine, threonine, histidine, cysteine, tyrosine and proline in the milk. The results indicated that a continued low dose infusion of LPS can induce an inflammatory response, decrease milk production and reduce milk quality.     

日粮宾州筛层级比例对泌乳牛产奶量、乳成分相关性关联分析与优化

[目的]对不同规模化牧场奶牛日粮宾州筛层级比例进行分析,研究其日粮宾州筛层级比例对泌乳早期奶牛产奶量、乳脂率、乳蛋白和尿素氮等乳成分的相关性,根据相关统计分析方法,结合日粮宾州筛的层级比例推荐范围,得出最优的日粮宾州筛层级比例。[方法]选择黑龙江省12个规模化牧场,对泌乳天数在0～100 d内的泌乳早期高产奶牛TMR日粮进行取样分析,对日粮宾州筛层级进行相关性分析、改进的灰色关联分析和通径分析,确定影响产奶量和乳成分的主要层级及其最优比例。[结果]日粮宾州筛第二层筛比例与泌乳前期奶牛产奶量和尿素氮呈正相关关系(相关系数为0.656,0.531,P<0.05),与乳脂率呈负相关关系,(相关系数为-0.448,P<0.05),日粮宾州筛第三层筛比例与乳蛋白率呈负相关关系(相关系数为-0.305,P<0.05)。[结论]当日粮宾州筛第二层级比例处于35%～40%范围内时,泌乳前期奶牛的产奶量和乳脂率可达相对最优水平;乳蛋白含量的最优区间为第三层筛日粮比例15%～20%的区间内。     

The usefulness of determining urea levels and the acidity of milk for evaluating protein nutrition in cows

Samples of blood, urine and milk were examined in 94 clinically healthy cows of 10 herds. The average milk samples and the feed ration used in these herds were also examined. The determination of urea concentration and milk acidity was evaluated as to its suitability for the assessment of the protein-glycide ratio and acid-base activity of feed ration. The determination of urea content in an average milk sample was found to be an expeditious procedure. The results of this examination can be used for the evaluation of the protein supply to cows with the same reliability as the determination of serum urea. The passage of urea from serum to milk was proportional. The correlation coefficient for the relation of both parameters was statistically highly significant (r = 0.940). According to the calculated equation of regression line (f2 = 0.734 + 0.669 X f1), the values from 2.94 to 4.10 mmol/l are approximately adequate to the reference range of serum urea from 3.30 to 5.00 mmol/l in milk used in Czechoslovakia. The acidity of milk was found to have a low sensitivity for being used with success for the determination of the acid-base activity of feed ration. The examination of the net acid-base urinary output cannot be replaced by the determination of milk acidity.     

山羊奶理化性状研究——Ⅳ.末乳主要理化性状及其变化和常乳中氨基酸组成与含量

本文分析研究了西农萨能奶山羊、英国萨能奶山羊和关中奶山羊末乳中脂肪、乳糖、蛋白质、总干物质、灰分及钙和磷的含量及其变化,同时也对3个被试品种羊奶中氨基酸含量进行了测定。研究结果表明末乳中 pH 值、灰分和蛋白质含量达到整个泌乳期最高水平,而酸度和乳糖含量则较低.蛋白质含量高于脂肪含量。3个品种间氨基酸含量基本相近。山羊奶里酪蛋白中谷氨酸与组氨酸的比值明显高于牛奶.这是山羊奶酪蛋白的特点之一。山羊奶中游离氨基酸含量明显高于牛奶。     

Levels of milk urea, plasma constituents and rumen liquid ammonia in relation to the feeding of dairy cows during early lactation

The study was undertaken to establish the relationships between milk and plasma urea levels and protein supply, using traditional and new measures of feed protein value. Samples of milk and plasma were taken before morning feeding twice weekly for the first 3 months post partum from 21 multiparous cows and 7 heifers. Samples of rumen fluid were collected every second week. The cows were distributed into 4 different feeding groups. Feeding regimens were factorial with respect to protein content of the concentrates (i.e. Low protein (Lp): 12.5% digestible crude protein (DCP) vs. High protein (Hp): 17.5% DCP) and concentrate allowances (i.e. Low energy (Le): substandard vs. High energy (He): standard). Silage was offered ad libitum. The within-animal coefficients of correlation between milk and plasma urea levels, and between milk urea levels and the levels of ammonia in the rumen fluid wer r = 0.88 (p less than 0.001) and r = 0.75 (p less than 0.001), respectively. Analysis of variance showed the following sources of urea variation to be significant: Protein balance in the rumen (PBV), intake of DCP, intake of amino acids absorbed in the intestine (AAT), intake of fattening feed units, and the individual animal factor. A similar tendency was found for the variation of ammonia in rumen fluid. The coefficients of determination (R2 model) were not increased by introducing protein balance (BADCP), the amount of PBV and AAT in the dry matter ingested, or the protein/energy ratio as alternative parameters of protein intake in the models. The levels of protein or energy intake did not significantly influence the levels of plasma albumin. The correlations between urea levels and other plasma indicators of metabolic status and liver function were generally low.     

Relation between milk production and biochemical indicators in high- and low-producing cows]

23 cows of the Holstein-Friesian breed during second lactation were used in the experiment. All animals were housed in one stable with tying. The blood was collected from each cow four times during first to third, fourth to sixth, seventh to ninth and above nine months of lactation. After 305 days of lactation, the milk cows were classified as with high (n = 14) and lower performance (n = 9), the limit value was 5000 kg of milk. The difference in milk production between groups was highly significant even during the period of the first 90 days (501 kg) and this difference increased for 305 days of lactation to 1538 kg (Tab. I); the dairy cows with high performance produced 6162 kg of milk per 305 days and that with the lower performance gave 4624 kg during the same period. Another significant differences occurred in the fat contents per kg and in the amount of milk converted on 4% fat content. During the first stage of lactation a slightly higher haemoglobine level was found in cows with high performance, the opposing results were obtained in another studies (Tab. II), the highest difference was recorded in the course of 7th to 9th month. The level of total protein was, except 7th to 9th month, always higher in cows of the first group. The difference was significant at the beginning of lactation. Insulin concentration (INS) exhibited identical tendency for the whole lactation--dairy cows with high milk production exhibited lower values, significant differences were recorded in the first observation at the beginning of lactation and in the period above 9 months. Similarly as in case of insulin, it is also in hormones of thyroid gland, the cows with high milk capacity had the lower values (Tab. III). The highest differences in triiodothyronine (T3) concentration were recorded in the second half of lactation, significance ranged from 7th to 9th month of lactation. In thyroxine content (T4), marked differences were recorded during the first and last observations, the difference was highly statistically significant during the seventh to ninth month of lactation. The levels of cyclic adenosine monophosphate (AMP) were higher for the whole experiment in animals with lower milk production. Tab. IV gives the correlation coefficient of different parameters between periods under study. Almost all parameters are in a close positive relation, the closest dependences were observed between second, third and fourth periods in hormones of thyreoidea. The most significances were recorded in adenosine monophosphate, thus confirming its stability of minimum variance between observations.(ABSTRACT TRUNCATED AT 400 WORDS)