Peripartal calcium homoeostasis of multiparous dairy cows fed rumen‐protected rice bran or a lowered dietary cation/anion balance diet before calving

Milk fever is one of the most important metabolic diseases in dairy cattle. Reducing the dietary cation/anion balance (DCAD) with anionic salts is a common prevention strategy. However, many small European farms cannot use total mixed rations (TMR) in the close‐up period. Including anionic salts in compound feeds can result in feed refusals and moderate inclusions to preserve feed palatability results in insufficient DCAD reduction. Rumen‐protected rice bran induces the adaptation of Ca metabolism in dairy cows by a reduction of Ca intake and by a reduction of the availability of dietary Ca. In the presence of a negative control, rumen‐protected rice bran (2.8 kg/day) was compared with a lowered DCAD diet (from 269 to 4 meq/kg DM) in their effect to prevent milk fever. In a randomized block design, 45 multiparous Holstein cows joined the trial sequentially from 21 days before the expected calving date and were observed until the 8th week of lactation. Feed and nutrient intakes were recorded, and Ca, P, Mg in serum and urine, urine pH, serum NEFA and milk production in early lactation were compared. Feeding rumen‐protected rice bran before calving improved the recovery of calcaemia after calving and had a positive effect on DMI after calving. The moderately low DCAD diet did not positively influence serum Ca at calving. Calcaemia recovered even later than in control, and cows showed reduced DMI post‐calving and higher NEFA levels in the first 36 h after calving. This moderate reduction of DCAD did not provide an intermediate prevention level indicating that DCAD needs to be reduced to the recommended levels to prevent milk fever. Rumen‐protected rice bran may be a suitable feed to reduce hypocalcaemia post‐partum and can be included in pre‐calving compound feeds representing a palatable alternative to anionic salts.     

Milk fever in dairy cows: a review of pathophysiology and control principles

The periparturient or transition period of 4 weeks before and 4 weeks after calving is characterised by a greatly increased risk of disease. Hypocalcaemia around calving is a risk factor for many of these diseases and is an indirect risk factor for increased culling. The incidence of clinical hypocalcaemia (milk fever) in the field generally ranges from 0-10%, but may exceed 25% of cows calving. In research trials conducted on milk fever the incidence has approached 80% of cows calving. Homeostasis of calcium (Ca) is regulated by calcitonin, parathyroid hormone and 1,25(OH)(2) vitamin D(3). Age increases the risk of milk fever by approximately 9% per lactation. Control of milk fever has revolved around stimulation of homeostatic mechanisms through feeding a pre-calving diet low in Ca. More recently, the role of the dietary cation anion difference (DCAD) in the prevention of Ca disorders has been examined, both by field research and meta-analysis. The most appropriate form of the DCAD equation has been contentious, but recent meta-analyses have shown that the equation (Na(+)+K(+))-(Cl(-)+S(2-)) is most effective for predicting milk fever risk. Decreased risk of milk fever is linear with DCAD, whereas the effect of DCAD on urinary pH is curvilinear. A pivotal role of providing dietary magnesium (Mg) before calving has been confirmed by meta-analysis, and a quadratic effect of Ca on milk fever risk was found with a peak occurring with dietary levels of 1.1-1.3% of dry matter. Risks of milk fever increase with increased dietary phosphorus (P) fed pre-calving and with increasing days of exposure to a pre-calving diet. Meta-analysis has revealed that the important roles of dietary Ca, Mg and P, as well as the duration of exposure to the pre-calving diet in milk fever control strategies are independent of DCAD. Studies on the effect of exposure to well designed pre-calving diets have shown that substantial improvements in production, reproduction and animal health can be made but further examination of the influence of the period of exposure to different diets is warranted.     

Impact of dietary plane of energy during the dry period on lipoprotein parameters in the transition period in dairy cattle

The high energy demands of dairy cows during the transition period from late gestation into early lactation can place them at an increased risk for the development of metabolic and infectious diseases. Modification of the dry period diet has been investigated as a preventive means to minimize the detrimental aspects of metabolic shifts during the transition period. Studies investigating the impact of dry period diet on lipid parameters during the transition period have largely focused on markers of lipolysis and ketogenesis. Total cholesterol declines during the periparturient period and increases in early lactation. The impact total energy in the dry period diet has on the ability of the cow to maintain total serum cholesterol, as well as its natural high‐density lipoprotein‐rich status, during this metabolically challenging window is not clear. The impact of lipoproteins on inflammation and immune function may have a clinical impact on the cow's ability to ward off production‐related diseases. In this study, we hypothesized that the provision of adequate, but not excessive, total metabolizable energy, would better allow the cow to maintain total cholesterol and a higher relative proportion of HDL throughout the transition period. Cows were allocated to one of three dry period dietary treatment groups following a randomized block design. Total serum triglycerides, cholesterol and lipoprotein fractions were measured on a weekly basis from approximately 7 weeks pre‐calving to 6 weeks post‐calving. The cows on the high energy diet maintained total serum cholesterol as compared to the cows provided a lower energy diet, but there was no significant increase in the LDL fraction of lipoproteins between diet treatment groups.     

不同DCAD值对崂山奶山羊尿液pH值及血气指标的影响

为了探讨不同日粮阴阳离子差值(DCAD)对崂山奶山羊尿液pH值及血气指标的影响,试验选取健康崂山奶山羊4只,采用4×4拉丁方试验设计,在保证日粮营养水平一致的条件下,调整各试验组日粮DCAD值分别为0、50、100、200 mEq/kgDM。试验结果表明,尿液pH值与日粮阴阳离子差值呈显著正相关,相关系数为0.899 7;DCAD水平能够显著影响血液血气指标(P0.05)。     

Effects of increasing days of exposure to prepartum transition diets on reproduction and health in dairy cows

Objective To evaluate the effect of the number of days exposure to a prepartum transition diet on reproduction and health in dairy cows. Design A prospective cohort study. Procedures We enrolled 1008 dairy cows from three herds to examine the effects on reproduction and health of increased days exposure to prepartum transition diets that included ryegrass pasture, ryegrass silage, cereal hay, grain, by-products, oilseed meals, BioChlor®, rumen modifiers, minerals and vitamins. Diets provided 9.9 MJ metabolisable energy per kg dry matter (DM), a metabolisable protein balance of 286 g/day and a dietary cation anion difference of −150 meq/kg DM. Statistical models controlled for herd, calving day, age and gestation period. Results In two of the three herds increased days exposure to prepartum transition diets increased the hazards of submission for breeding, conception and clinical mastitis, and decreased the hazard of cow removal. The odds of pregnancy by 6 and 21 weeks after the mating start date tended to increase with increasing days of exposure to prepartum transition diets. Conclusions Increasing exposure to a prepartum transition diet improved the calving to conception interval, tended to improve the odds of pregnancy and reduced the risk of culling of cattle, but increased the hazard of clinical mastitis.     

Clinical acidosis in a Gippsland dairy herd

OBJECTIVE: To report on spontaneous clinical and subclinical acidosis in a large dairy herd, to evaluate the diets and feeding strategies involved, and to report on measures of rumen function in the cows affected. DESIGN: A Gippsland dairy herd was sampled as part of a wider randomised cross-sectional study that examined the prevalence, risk factors for, and effects of, acidosis on rumen function of dairy cattle. Three herds on the farm were involved in the study: the transition herd (cows 3 weeks prior to calving), the very fresh lactating herd (1 < days in milk < 10, herd 1) and the fresh lactating herd (10 < days in milk < 120, herd 2) including a small lame herd fed separately. The transition cows were fed 2 kg dry matter triticale per cow per day and hay with an estimated total dry matter intake of 4.8 kg per cow per day. The lactating cow diet included 6.75 kg dry matter triticale per cow per day with total concentrate fed being 8.1 kg dry matter per cow per day in the milking parlour. Silage, lucerne cubes, hay and pasture (herd 2 only) was also fed to the lactating cows with the estimated total dry matter intake for cows in herds 1 and 2 being 13.7 kg and 20.8 kg per cow per day respectively. Three primiparous and five multiparous cows in early lactation (< 100 days in milk) were randomly selected from each of two lactating herds: herds 1 and 2. Rumen fluid was sampled from each cow by both rumenocentesis and stomach tube. The rumenocentesis samples were tested for pH at the time of sampling. Stomach tube samples were frozen and subsequently tested for volatile fatty acid, ammonia, and D- and L-lactate concentration. RESULTS: In the very fresh herd, there was a high prevalence of severe lameness and scouring, coupled with a mean rumen pH 5.67, low mean total volatile fatty acid concentration 71.0 mM and high mean concentrations of L- and D-lactate, (7.71 mM and 7.31 mM), respectively. Cows in the fresh herd had moderate signs of scouring and lameness. A lame herd comprising approximately 50 cows separated from the fresh herd was also present on the farm. The mean rumen pH of the fresh herd was 5.74 and mean rumen concentrations of volatile fatty acids, ammonia, L- and D-lactate were within ranges considered normal. CONCLUSIONS: The transition diet failed to supply sufficient energy and protein for maintenance of cows of this live weight in late gestation. The diet fed to the very fresh herd was low in effective fibre and contained an excessive content of non-structural carbohydrate in the form of processed, rapidly fermentable grain. The sudden change from the transition diet to the diet fed to the very fresh herd probably also precipitated the outbreak of acidosis. This case report provides unique detail, including information on diets and rumen parameters, of an outbreak of acidosis in a pasture-fed herd.     

疾病对奶牛繁殖性能的影响及其研究进展Ⅲ:营养代谢性疾病

现代规模化、集约化奶牛养殖生产模式下,不断供给高营养水平日粮是维持后备牛快速生长发育和泌乳母牛高泌乳性能的物质基础。然而,在遗传品质到达"瓶颈期"后,尽管随着日粮营养浓度的不断提高和干物质采食量（DMI）的增加,奶牛单产水平可以继续维持在一定的高水平状态,但是高产奶牛的营养代谢性疾病的发病率也呈现快速增长趋势,特别是围产期能量负平衡（negative energy balance,NEB）引起的酮病,高精日粮引发的酸中毒、高蛋白质日粮引起的血液中尿素氮升高等营养代谢性疾病,负调控奶牛繁殖性能,造成奶牛产后发情不明显,配种率和受胎率下降等,直接影响奶牛生产群的更新速度、优质牛群泌乳性能正常发挥以及奶牛养殖的经济效益。作者详细介绍了近年来国内外不同营养代谢性疾病对奶牛繁殖性能影响的相关研究资料,重点分析了酮病、低血钙、瘤胃酸中毒等围产期高发的营养代谢性疾病影响奶牛繁殖性能的分子机制,并对营养代谢性疾病与高产奶牛繁殖性能今后研究的方向提出了展望和思考,以期为提高中国规模化牧场高产奶牛群繁殖效率和母牛围产期营养管理水平提供一定的借鉴和理论依据。     

Effects of Diseases on Reproductive Performance in Dairy Cattle Ⅲ: Nutritional Metabolic Diseases

Under the modern large-scale and intensive dairy farming production mode,the continuous supply of feed with high nutrition level is the material basis for maintaining the rapid growth and development of reserve cows and the high lactation performance of lactating cows.However,after the genetic quality reaches the "bottleneck period",although the milk yield of dairy cow can continue to maintain a certain high level with the continuous improvement of the nutrient concentration of feed and the increase of dry matter intake (DMI),the incidence of nutritional metabolic diseases of high-yield dairy cows also shows a rapid growth trend,especially ketosis caused by the negative energy balance in perinatal period,acidosis caused by high-precision diet and the increase of blood urea nitrogen caused by high-protein diet,negatively regulate the reproductive performance of dairy cows,resulting in inconspicuous postpartum estrus,decreased mating rate and conception rate of dairy cows,which directly affect the update speed of dairy cows production groups,the normal performance of high-quality cattle and the economic benefits of dairy farming.In this paper,the author introduced in detail the relevant research on the current situation and its mechanism influence of different nutritional metabolic diseases on the reproductive performance of dairy cows in recent years,and focused on analyzing the molecular mechanism of nutritional and metabolic diseases with high perinatal incidence such as ketosis,low blood calcium and moderate gastric acid,and put forward the prospect and thinking on the future research direction of nutritional and metabolic diseases and reproductive performance of high-yielding dairy cows,in order to provide some reference and theoretical basis for improving the reproductive efficiency of high-yielding dairy cows in large-scale pastures in China and the perinatal nutrition management level of dairy cows.     

日粮添加包被氯化铵对围产期奶牛健康的影响

本试验旨在探讨在围产前期日粮中添加包被氯化铵(美宝安)对奶牛健康的影响.试验采用分阶段环比比较,根据奶牛尿液pH值和产后瘫痪情况调整日粮DCAD值:不添加美宝安、仅饲喂基础日粮,此期有62头围产牛,为试验前阶段;日粮添加180g美宝安,此期有30头围产牛,为试验开始阶段(DCAD1);日粮添加180g美宝安+70gCa...     

Glycerol use in dairy diets: A systemic review

There is an increasing interest in the production of biodiesel as bio-renewable fuel source, with numerous biofuel byproducts becoming available. The annual productions of biodiesel and crude glycerol were 34.5 and 3.8 billion liters, respectively, in 2016 and that of biodiesel is expected to reach 41 billion liters in 2019. Glycerol is a sugar alcohol without a color or odor, but with a sweet taste and high solubility index in water. Experiments support the use of glycerol at low levels ranging from 5% to 8% of the diet dry matter as a transition cow therapy. Administration of glycerol increases serum glucose and decreases ketone bodies. Glycerol is very rapidly fermented in the rumen to propionate and butyrate, at the expense of acetate, resulting in a decreased milk fat. Because glycerol is highly fermented in the rumen, it requires an adaptation period at the beginning of feeding. Administration of glycerol in the diet of lactating animals was paralleled with a decreased or an unaffected feed intake in most experiments. Improved ruminal environment to enhance nutrient digestibility was observed in many experiments; however, others observed reduced digestion of dietary fiber with feeding glycerol. Enhanced, lowered, or unaffected milk production and composition were observed with the administration of glycerol in lactating animal diets; however, in most cases, glycerol decreased milk fat content. The inconsistencies between results of experiments are due to the level and the purity of glycerol, diets, production stage of the animals, and other factors. Therefore, further research should be conducted to establish the efficacy of different levels, purity and administration periods of glycerol, and production stage of dairy animals fed glycerol-based or supplemented diets.     

Influence of varying levels of dietary cation anion difference on ruminal characteristics,nitrogen metabolism and in situ digestion kinetics in buffalo bulls

This study was conducted to examine the influence of varying dietary cation anion difference (DCAD) on nutrient intake, digestibility, ruminal characteristics, blood acid base status and in situ digestion kinetics in Nili Ravi buffalo bulls. Four iso‐nitrogenous and iso‐caloric diets having ?110, +110, +220 and +330 mEq/kg dry matter (DM) DCAD were formulated which were represented by A (anionic), LC (low cationic), MC (medium cationic) and HC (high cationic), respectively. These diets were used in four ruminally cannulated Nili Ravi buffalo bulls in a 4 × 4 Latin Square Design. Improved nutrient intake was recorded at high DCAD levels while digestibility remained unaffected. Ruminal ammonia nitrogen, rumen pH, acetate and acetate : propionate ratio were higher in buffalo bulls fed MC and HC diets than those fed A and LC diets. Blood pH and HCO₃^‐ also tended to increase as DCAD level was increased in the diet. Serum Ca and Cl concentrations were higher in bulls fed A and LC diets whereas serum Mg, P and S remained unaffected. Urine pH increased with increasing DCAD level. Nitrogen intake and blood urea nitrogen concentrations were also higher in bulls fed MC and HC diets. There was a consistent increase in ruminal DM and neutral detergent fiber degradability, rate of disappearance and extent of digestion at high DCAD levels in the diet. However, lag time decreased at high DCAD level. This study indicated that buffalo bulls fed MC and HC diets improved feed intake, ruminal characteristics and digestion kinetics.     

奶牛中性洗涤纤维营养研究进展

本文对奶牛中性洗涤纤维(NDF)和物理有效中性洗涤纤维(peNDF)营养调控进行了较全面的综述。日粮中NDF能够通过影响奶牛采食、咀嚼和反刍,调节瘤胃中有机酸、pH和微生物的数量等途径对瘤胃发酵进行调控;peNDF的营养调控作用也主要体现在奶牛的采食和消化过程中。日粮中适宜浓度的NDF和peNDF是维持奶牛健康和生产性能的重要因素。     

过瘤胃胆碱在围产期奶牛的应用研究进展

奶牛养殖过程中,围产期被认为是最重要的时期之一,在该时期奶牛从干奶状态转为泌乳状态,生理上所受的应激造成奶牛泌乳早期采食量降低,易发生能量负平衡.此外,奶牛生产性能和繁殖性能也会降低,并常常伴有一些围产期疾病的发生,如脂肪肝、酮症、乳房炎等.胆碱能影响奶牛的生产与繁殖性能,参与奶牛的脂肪代谢,可降低脂肪肝发生率,提高免疫性能.对围产期奶牛饲喂过瘤胃保护胆碱(rumen protected choline,RPC),可改善奶牛机体代谢,增加小肠胆碱供应,进而提高奶产量、改善乳成分、缓解脂肪肝、减少围产期疾病的发生.本文综述了RPC对围产期奶牛干物质采食量、生产性能、乳成分以及健康状况的影响,旨在为围产期奶牛的养殖提供理论参考依据.     

Calcium homeostasis, acid–base balance, and health status in periparturient Holstein cows fed diets with low cation–anion difference

Forty multiparous Holstein dry cows on d 21 prepartum were randomly allocated to four blocks of 10 cows to examine the effects of reducing the dietary cation–anion difference (DCAD) on calcium homeostasis, acid–base balance, health status, and subsequent lactation performance. The reduced DCADs (Na + K − Cl − S, mEq/kg DM) of + 150,+ 50, − 50, and − 150 were obtained by addition of anionic salts. Reducing DCAD resulted in mild metabolic acidosis as indicated by the sharp decline in urinary pH, and minor reductions in blood pH and HCO₃⁻ concentration. Greater plasma calcium concentration was observed in cows fed diets of − 50 and − 150 DCAD (P < 0.05) than those on + 50 and + 150 DCAD diets. The nadir of plasma calcium level on the day of calving was lower (P < 0.05) than the highest level on d 14 prepartum (8.33 vs. 9.30 mg/dL). Composite colostrum calcium concentration was decreased (P < 0.05) with time on d 1 relative to d 2 postpartum (0.212 vs. 0.174%), and feeding of diet − 150 DCAD induced higher (P < 0.05) composite colostrum calcium content than other three DCAD diets. No case of milk fever occurred for any diets, but feeding the two negative DCAD diets reduced (P < 0.05) retained placenta incidence compared with diet of + 150 DCAD. Dry matter intake, milk yield and compositions of fat, protein, and lactose were non-significantly affected (P > 0.05) by dietary treatments. In conclusion, urinary pH is an effective indicator of extracellular fluid acid–base balance, and feeding negative DCAD in late gestation period is beneficial for dairy cows in blood calcium homeostasis and improvement of health status.     

奶牛低淀粉型日粮研究进展

低淀粉型日粮的应用不仅可以满足高产奶牛生产阶段的能量需要,而且可以保证奶牛瘤胃健康,避免瘤胃酸中毒。常用低淀粉型饲料有优质牧草、中性洗涤可溶性纤维源饲料以及可溶性糖三大部分。饲喂低淀粉型日粮可以有效缓解挥发性脂肪酸的产生,避免瘤胃pH降低,并促进了奶牛的采食以及养分消化,提高乳品质。本文从低淀粉型日粮的实现手段,以及瘤胃发酵参数和生产性能方面阐述低淀粉型日粮在奶牛生产中的必要性,确立今后的研究重点应该在各种原料替代谷物原料的最适比例及组合效应方面,从而完善奶牛低淀粉型日粮配制技术。     

Nutrient intake, acid base status and growth performance of growing male buffalo calves fed varying level of dietary cation anion difference

Influence of + 110, + 220 and + 330 mEq/kg of dry matter (DM) dietary cation anion difference (DCAD) on growth performance of growing male buffalo calves was examined in a randomized complete block design. Three DCAD diets were randomly allotted to three groups, ten calves in each group. A linear increase in nutrient intake was recorded with increased DCAD level. However, digestibilities of nutrients remained unaltered across all diets. Calves fed + 330 DCAD diet had higher nitrogen balance than those fed + 110 DCAD diet. Blood pH and serum HCO₃ increased with increased DCAD level. Serum chloride was high in calves fed + 110 DCAD diet, while serum (Na + K) − (Cl + S) increased linearly with increased DCAD level. Serum calcium increased with decreased DCAD level while serum magnesium and phosphorus remained unaffected. Ca balance remained unaltered by calves fed varying level of DCAD. Urine pH increased with increased DCAD level. Calves fed + 220 and + 330 DCAD diets gained more weight than those fed + 110 DCAD diet. In conclusion, increased DCAD level not only increased dry matter intake but also weight gain in growing buffalo calves.     

短期添加高水平亚麻籽对奶牛生产性能、牛奶脂肪酸组成和瘤胃发酵的影响

本试验旨在研究短期添加高水平亚麻籽对奶牛生产性能、牛奶脂肪酸组成和瘤胃发酵的影响。选取健康、体重相近的荷斯坦牛奶牛30头,随机分为3组,每组10头。分别饲喂牧场基础饲粮（CK组）、添加3 000 g/d （13.01% DM）完整亚麻籽饲粮（WF组）和添加3 000 g/d （13.01% DM）粉碎亚麻籽饲粮（GF组）。试验周期为7周,第1周为环境适应期,第2~6周为饲粮适应期,第7周为试验期,记录试验期日采食量和产奶量,于试验最后1天采集奶样和瘤胃液样品,利用气相色谱-质谱联用（GC-MS）测定乳和瘤胃液中脂肪酸组成。结果表明：①与CK组相比,添加3 000 g/d亚麻籽对奶牛干物质采食量和产奶量均无显著影响（P>0.05）,GF组乳脂率和乳蛋白率较CK组有降低的趋势（0.05<P<0.1）。②WF和GF组乳中α-亚麻酸（ALA）和ω-3多不饱和脂肪酸（ω-3 PUFA）的产量较CK组均显著提高（P<0.05）,且GF组ALA和ω-3 PUFA的产量显著高于WF组（P<0.05）。③WF组瘤胃pH显著低于CK和GF组（P<0.05）,氨态氮（NH₃-N）浓度显著高于CK和GF组（P<0.05）。综上所述,饲粮中短期添加高水平完整亚麻籽和粉碎亚麻籽均不影响奶牛干物质采食量和产奶量,但提高了乳中ALA含量,GF组提高效果较WF组更明显。添加高水平粉碎亚麻籽有降低乳蛋白率和乳脂率的趋势,高水平完整亚麻籽影响了奶牛瘤胃内环境。在实际生产中,应控制亚麻籽的添加量及其饲喂形式,在提高乳中ALA含量的同时,减少亚麻籽对瘤胃发酵的影响。     

Transition cow: interaction with fertility

In recent years a progressive worsening of fertility indices in dairy cow herds has been observed. Several factors (genetic, dietary and management) seem to be more related to poor fertility than milk yield level. The degree and the length of the energy deficit during the transition period are inversely related to reproductive indices (e.g. conception rate is <30% for BCS decreases over one unit). A serious energy deficit reduces (or suppresses) pulsatile secretion of gonadotrophins (ovarian dysfunction and/or smaller follicles): IGF-I and insulin plasma levels (slower follicle growth and higher embryonic mortality); and progesterone production from the corpus luteum (higher rate of embryonic abortions). The diet influences fertility in several ways. Excess of rumen degradable proteins, apart from negative energy balance, negatively affects reproductive activity. Conversely, some nutrients (i.e. some polyunsaturated fatty acids or some amino acids) seem to show positive effects on fertility. Finally, the relationship between health status, often compromised during the transition period, and fertility efficiency is discussed. The release of cytokines seems to be related directly and indirectly (mainly by the change in usual hepatic metabolism to the malfunction of reproductive apparatus. Quick recovery of reproductive activity requires the adoption of strategies around calving to cover the higher environmental and nutritive requirements and to prevent disorders of any kind.     

Stimulating effects of a diet negative in dietary cation–anion difference on calcium absorption from the rumen in sheep

The concept of feeding anionic salts in late gestation is widely used to prevent milk fever in dairy cows. While the effects of these diets on renal Ca excretion and tissue responsiveness towards parathyroid hormone have clearly been demonstrated, data on a potential impact on gastrointestinal Ca absorption are conflicting. Therefore, the aim of this study was to investigate the influence of feeding a diet negative in dietary cation–anion difference (DCAD) on ruminal mineral concentrations, fermentation products, electrophysiological properties of rumen epithelia and Ca flux rates. For this purpose, sheep were kept for 3 weeks on diets that were either positive or negative in DCAD. The induction of a compensated hyperchloremic metabolic acidosis could be demonstrated by increased plasma Cl and enhanced concentrations of ionised Ca, while plasma concentrations of and base excess were decreased with the low DCAD diet. Neither transmural potential differences nor fermentation products were affected, but ruminal concentrations of Cl and Mg as well as the relation of ionised to total Ca were increased. Ussing chamber experiments revealed alterations of electrophysiological parameters and an increase in the electroneutral component of Ca flux rates from the mucosal to the serosal side of rumen epithelium. As plasma calcitriol concentrations were not affected, it can be concluded that the administration of anionic salts results in a vitamin D‐independent stimulation of ruminal Ca transport.     

Transition Cow: Interaction with Fertility

In recent years a progressive worsening of fertility indices in dairy cow herds has been observed. Several factors (genetic, dietary and management) seem to be more related to poor fertility than milk yield level. The degree and the length of the energy deficit during the transition period are inversely related to reproductive indices (e.g. conception rate is < 30% for BCS decreases over one unit). A serious energy deficit reduces (or suppresses) pulsatile secretion of gonadotrophins (ovarian dysfunction and/or smaller follicles); IGF-1 and insulin plasma levels (slower follicle growth and higher embryonic mortality); and progesterone production from the corpus luteum (higher rate of embryonic abortions). The diet influences fertility in several ways. Excess of rumen degradable proteins, apart from negative energy balance, negatively affects reproductive activity. Conversely, some nutrients (i.e. some polyunsaturated fatty acids or some amino acids) seem to show positive effects on fertility. Finally, the relationship between health status, often compromised during the transition period, and fertility efficiency is discussed. The release of cytokines seems to be related directly and indirectly (mainly by the change in usual hepatic metabolism) to the malfunction of reproductive apparatus. Quick recovery of reproductive activity requires the adoption of strategies around calving to cover the higher environmental and nutritive requirements and to prevent disorders of any kind.