Gestation In Dairy Cows Research Articles

Transcriptome changes associated with elongation of bovine conceptuses II: Differentially expressed transcripts in the endometrium on day 17 after insemination

The objective was to characterize endometrial transcriptome on d 17 of gestation in dairy cows according to conceptus length. Nonlactating Holstein cows (n = 48) were euthanized 17 d after AI and the uterine horn ipsilateral to the CL was flushed with saline solution. Recovered conceptuses were classified as small (1.2 to 6.9 cm; n = 9), medium (10.5 to 16.0 cm; n = 9), or large (18.0 to 26.4 cm; n = 10). Samples of intercaruncular endometrium dissected from the caudal, intermediate, and cranial portions of the uterine horn ipsilateral to the pregnancy were pooled for analyses. Total mRNA was extracted from endometrial tissue and subjected to transcriptome analyses using the Affymetrix Gene Chip Bovine array. Data were normalized using the GCRMA method and analyzed by robust regression using the Linear Models for Microarray library within Bioconductor in R. Transcripts with P ≤ 0.05 after adjustment for false discovery rate and fold change ≥1.5 were considered differentially expressed. Functional analyses were conducted using the Ingenuity Pathway Analysis platform. Comparisons between endometria of cows carrying large vs. small (LvsS), large vs. medium (LvsM), and medium vs. small (MvsS) conceptuses yielded a total of 235, 21, and 94 differentially expressed transcripts, respectively. Top canonical pathways included the antigen presentation pathway and Th1/Th2 activation pathways, both for LvsS and MvsS. Interferon-α and -γ were identified as activated upstream regulators, primarily based on differently expressed transcripts such as IDO1, ISG20, WARS, LGALS9, IFI44, and PSMB9 (LvsS and MvsS). For LvsS, regulator analyses revealed predicted activation of FOXO1, IFN, NFACTC2, IL-12, IL-6, and IL-18, whereas it depicted inhibition of IL10RA and ZBTB1. Changes in these regulators were associated with a downstream activation of leukocytes, as well as quantity and expansion of T lymphocytes. Canonical pathways associated with the comparison LvsM included cell cycle G2/M DNA damage checkpoint regulation, cell cycle control of chromosomal replication. Moreover, tretinoin was predicted, as activated in upstream analysis for the same comparison. In conclusion, most of the differently expressed transcripts in the endometrium on d 17 of gestation were identified between cows carrying small conceptuses compared with counterparts carrying medium and large conceptuses and were involved with pathways associated with modulation of the immune response.

Embryonic losses between the early diagnosis and the confirmation of gestation in dairy cows from different farms for one year

Objective: To determine embryonic losses between the early diagnosis and the confirmation of gestation in dairy cows from different barns for one year. Design/Methodology/Approach: A total of 3,413 confined Holstein cows from three different dairy barns in the Mexican Altiplano (highlands) were studied. Cows were milked three times a day with an average daily production of 36.5 ± 1.5 L. Gestation diagnosis was performed by ultrasonography at 34 ± 7 d after the artificial insemination, while gestation was confirmed at 60 ± 5 d. Average pregnancy loss was determined and embryonic losses were compared taking into account barn and month. Results: The overall average of embryonic losses was 18.8%. Neither the month factor nor the month × barn interaction affected the percentage of embryonic losses (p<0.05). Differences per barn (p<0.05) were observed and barns 1, 2, and 3 recorded losses percentages of 4 ± 1.6 %, 11.4 ± 1.6 %, and 22.9 ± 1.6%, respectively. Study Limitations/Implications: Detailed differences between barns were not studied, since cow management was similar in all three of them. Embryonic losses must be recorded, given their significant impact on the barn. Findings/Conclusions: There is a high variability among barns regarding embryonic losses between the early diagnosis and the confirmation of gestation. This situation may be the result of management differences, since the breed and environmental conditions were the same in all three barns.

Meta-analysis of the incidence of pregnancy losses in dairy cows at different stages to 90 days of gestation

Pregnancy losses are a biological challenge and economically important in dairy herds. A meta-analysis was conducted to quantify losses in 4 periods from 19 to 90 d of pregnancy corresponding to the physiological development of gestation in dairy cows. A total of 19,723 diagnostic records from 46 studies were included. Pregnancy losses averaged 27%, 13%, 7%, and 2% in the early embryonic (19 to 32 d), late embryonic (30 to 45 d), early fetal (45 to 60 d), and later fetal (60 to 90 d) stages. These results provide a formal synthesis of the incidence of pregnancy losses in dairy cows.

Effects of Intramuscular Injections of Vitamins AD3E and C in Combination on Fertility, Immunity, and Proteomic and Transcriptomic Analyses of Dairy Cows during Early Gestation.

This research aimed to investigate the effects of the intramuscular injection of vitamins AD3E and C in combination immediately before the estrus synchronization program (the Ovsynch program) on conception and pregnancy rates, blood parameters, serum biochemical properties, immune systems, antioxidant parameters, and proteomic and transcriptomic analyses during early gestation in dairy cows. Forty nonlactating multiparous cows were randomly assigned to one of four treatments: (1) C: control with normal saline injection; (2) VAD3E: a single intramuscular injection (I/M) of vitamin AD3E; (3) VAD3EC: injection of both vitamins AD3E and C; (4) VC: a single dose of vitamin C. Blood and serum samples were taken immediately at day 0 (before AI), day 7, and day 14 (after AI for 5 days) from the coccygeal vein. Generally, injections of AD3E and C in combination had no effect on the rate of conception or pregnancy. However, they improved hematological parameters and immune and antioxidant activities. Serum samples were analyzed using LC-MS/MS, and 8190 proteins were identified. Five proteins were successfully validated using the quantitative real-time reverse transcription PCR (qRT-PCR) method. This study found that lymphocyte-specific protein 1 (LSP1, A0A3Q1M894) could be used as a protein biomarker for cows administrated with vitamins AD3E and C.

Impact of heat stress on embryonic development during first 16\xa0days of gestation in dairy cows

Objective was to elucidate the effects of heat stress (HS) on embryo development during first 16 gestational days (GD) and circulating hormone concentrations on GD-16 in lactating Holstein cows. Cows in HS and control (CON) groups were exposed to temperature humidity index (THI) of ≥ 73 and < 73, respectively, for 3 weeks before the experiment. GD-7 (67 vs 49%) and GD-16 (52 vs. 31%) conception rates following single insemination were greater (P < 0.01) for CON compared with HS cows. Control cows produced more GD-7 transferrable embryos following superovulation compared with HS cows (84.8 vs 53.1%; P < 0.001). Mean (± SEM) length (45.2 ± 10.6 vs. 59.2 ± 9.1 mm) and weight (31.4 ± 4.3 vs. 42.4 ± 6.2 mg) of GD-16 conceptus were greater for CON compared with HS cows (P < 0.05). Control cows yielded more filamentous conceptus (≥ 25 mm) compared with HS cows (71 vs 45%; P < 0.05). Progesterone (2.09-fold) was higher, and cortisol (1.86-fold), prolactin (1.60-fold), substance-P (1.55-fold), Isoprostane-8 (1.34-fold) and prostaglandin F metabolites (1.97-fold) were lower in CON compared with HS cows (P < 0.05). Progesterone positively, and substance-P, isoprostane-8 and the THI negatively were associated with GD-16 conceptus length (P < 0.05). In conclusion, altered hormones concentrations in heat-stressed cows plausibly resulted in lower GD-7 and GD-16 conception rates, fewer GD-7 transferable embryos, and stunted GD-16 conceptus elongation.

Evaluation of serum analytes in pregnant and non-pregnant dairy cows as indicators of pregnancy

This study was conducted to reveal the dynamics of haematological indicators in pregnant and non-pregnant dairy cows. Sixty multiparous healthy dairy cows were divided into four groups based on the length of time they had been pregnant, namely first, second and third trimesters, and non-pregnant (n=15 each). Blood was collected from each animal, and serum was harvested and stored at -20 °C for biochemical profiling. Concentrations of serum total oxidants (TOC), ceruloplasmin oxidase (CpO) and triiodothyronine (T3) were higher (P &lt;0.05) during the third trimester compared with non-pregnant cows. Serum arylesterase (Ary) concentration was lower (P &lt;0.05) during the second and the third trimesters compared with the non-pregnant cows. The concentration of serum total homocysteine (tHcy) was higher (P &lt;0.05) the third trimester compared with the first and the second trimesters. The concentrations of serum total antioxidants (TAC), paraoxonase 1 (PON1), thyroxine (T4), aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were not different in the pregnant and the non-pregnant cows. Thus, TOC, Ary, CpO, tHcy and T3 could be taken as biological markers to assess the progression of pregnancy and to develop management tools to improve health status during late gestation in dairy cows&#x0D; Keywords: ceruloplasmin, hepatic enzymes, late gestation, triiodothyronine

Insulin resistance: Relationship between indices during late gestation in dairy cows and effects on newborn metabolism.

To investigate the relationship between insulin resistance indices ["Revised quantitative insulin sensitivity check index" (RQUICKI; RQ), "Revised quantitative insulin sensitivity check index - β-hydroxybutyrate" (RQUICKIBHB ; RQBHB ), and "Homeostasis model assessment-insulin resistance" (HOMA-IR; HR)], and metabolic parameters in dams during late gestation, and their newborn calves. Blood was sampled twice weekly during the experimental period in 30 dry Holstein cows. In calves, blood sampling and body weight measurements were performed immediately after birth, and in 1-week-old male calves, liver and muscle biopsy samples were obtained for determining metabolic factor mRNA levels. RQ and RQBHB were negatively correlated with insulin, nonesterified fatty acid, BHB, and albumin and were positively correlated with leptin levels in blood during late gestation (p<.05). RQ, rather than RQBHB , reflected metabolism of dams, while stronger positive correlations were present between HR and blood insulin concentrations than other parameters, and calves of dams with high HR had low body weight, and high liver and muscle expression of growth hormone and insulin receptor mRNA (p<.05). RQ and HR of dams during late gestation could serve as indicators of dam metabolism and predictors of metabolism in newborn calves respectively.

141 Metabolic ramifications of heat stress during late pregnancy and early gestation in dairy cows.

141 Metabolic ramifications of heat stress during late pregnancy and early gestation in dairy cows.

Placentome Nutrient Transporters and Mammalian Target of Rapamycin Signaling Proteins Are Altered by the Methionine Supply during Late Gestation in Dairy Cows and Are Associated with Newborn Birth Weight

Background: To our knowledge, most research demonstrating a link between maternal nutrition and both fetal growth and offspring development after birth has been performed with nonruminants. Whether such relationships exist in large ruminants is largely unknown.Objective: We aimed to investigate whether increasing the methionine supply during late pregnancy would alter uteroplacental tissue nutrient transporters and mammalian target of rapamycin (mTOR) and their relation with newborn body weight.Methods: Multiparous Holstein cows were used in a randomized complete block design experiment. During the last 28 d of pregnancy, cows were fed a control diet or the control diet plus ethylcellulose rumen-protected methionine (0.9 g/kg dry matter intake) (Mepron; Evonik Nutrition & Care GmbH) to achieve a 2.8:1 ratio of lysine to methionine in the metabolizable protein reaching the small intestine. We collected placentome samples at parturition and used them to assess mRNA and protein expression and the phosphorylation status of mTOR pathway proteins.Results: Newborn body weight was greater in the methionine group than in the control group (44.1 kg and 41.8 kg, respectively; P ≤ 0.05). Increasing the methionine supply also resulted in greater feed intake (15.8 kg/d and 14.6 kg/d), plasma methionine (11.9 μM and 15.3 μM), and plasma insulin (1.16 μg/L and 0.81 μg/L) in cows during late pregnancy. As a result, mRNA expression of genes involved in neutral amino acid transport [solute carrier (SLC) family members SLC3A2, SLC7A5, SLC38A1, and SLC38A10], glucose transport [SLC2A1, SLC2A3, and SLC2A4], and the mTOR pathway [mechanistic target of rapamycin and ribosomal protein S6 kinase B1] were upregulated (P ≤ 0.07) in methionine-supplemented cows. Among 6 proteins in the mTOR pathway, increasing the methionine supply led to greater (P ≤ 0.09) protein expression of α serine-threonine kinase (AKT), phosphorylated (p)-AKT, p-eukaryotic elongation factor 2, and the p-mTOR:mTOR ratio.Conclusion: Supplemental methionine during late gestation increases feed intake and newborn body weight in dairy cows, and this effect may be mediated by alterations in the uteroplacental transport of nondispensable and dispensable amino acids and glucose at least in part through changes in gene transcription and mTOR signaling.

Accuracy of diagnosing double corpora lutea and twin pregnancy by measuring serum progesterone and bovine pregnancy-associated glycoprotein 1 in the first trimester of gestation in dairy cows

Progesterone (P4) and bovine pregnancy-associated glycoprotein 1 (bPAG-1) concentrations during gestation are dependent on the number of CL and fetuses, respectively. The objective of this present study was to measure and evaluate the usefulness of measuring the P4 and bPAG-1 concentrations in cases of single versus twin pregnancies and one versus two CL at the first 4 months of gestation. We hypothesized that both the number of the CL and the number of fetus might have an effect on P4 and pregnancy protein concentrations, and we can set up clinically useful threshold levels to predict twin gestations. Eighty-four Holstein-Friesian dairy cows were enrolled in this prospective observational clinical trial. Blood was collected at time point 1: between Days 29 and 42, time point 2: between Days 57 and 70, time point 3: between Days 85 and 98, and time point 4: between Days 113 and 126 of gestation, and bPAG-1 and P4 concentrations were measured. Binary logistic regression analyzing serum P4 concentrations differed at time point 2 compared with baseline level, but the area under the curve (AUC) had low sensitivity. The bPAG-1 concentrations were statistically different at each time point of gestation. The AUC cutoff values of serum bPAG-1 concentrations were sufficiently sensitive to differentiate between twin gestations from singleton ones. At time points 3 (cutoff value of 3.4 ng/mL) and 4 (cutoff value of 56.5 ng/mL), statistically significant differences with low sensitivity, high specificity, and a high AUC were found. On the basis of these results, the diagnosis of twin pregnancy using pregnancy protein measurements is clinically insufficient before Day 85 of gestation; however, the ability to confirm the early twin pregnancy diagnosis with bPAG-1 measurements appears to be promising. To achieve high sensitivity, further studies are required.

Use of Ultrasonography to Age Pregnancy in Early Gestation in Dairy Cows

Using ultrasonography for diagnosis and aging of pregnancy is becoming more widespread among bovine practitioners because it can be done earlier than by traditional methods, and because it can be used to monitor fetal development and determine fetal age and sex. This 3-page fact sheet presents a detailed measurement of the amniotic vesicle from 27 to 34 days after breeding so a more precise aging of early pregnancies can be performed. Written by Klibs N.A. Galvão and published by the UF Department of Veterinary Medicine-Large Animal Clinical Sciences, May 2012. VM184/VM184: Use of Ultrasonography to Age Pregnancy in Early Gestation in Dairy Cows (ufl.edu)

Effects of plane of nutrition and 2,4-thiazolidinedione on insulin responses and adipose tissue gene expression in dairy cattle during late gestation

Specific mechanisms by which dry period dietary energy affects transition cow metabolism have been intensively investigated but those of thiazolidinedione (TZD) administration have not. We hypothesized that effects of both are mediated via changes in insulin, glucose, or fatty acid metabolism. The objective of this experiment was to determine the effects of the insulin-sensitizing agent TZD and dietary energy level on glucose and fatty acid metabolism during late gestation in dairy cows. Multiparous Holstein cows (n=32) approximately 50 d before expected calving date were dried-off and assigned to 1 of 2 dietary energy levels for 3 wk (high: 1.52Mcal/kg of NEL, or low: 1.34Mcal/kg of NEL) and treated daily during the final 14 d with 4.0mg of TZD/kg of body weight (BW) or saline in a completely randomized design. Cows fed the low energy diet had lower dry matter intake (12.8 vs. 16.1kg/d) and higher plasma nonesterified fatty acid (NEFA) concentrations (103.3 vs. 82.4μEq/L) compared with cows fed the high energy diet. Cows administered TZD had higher plasma glucose concentrations (62.5 vs. 59.6mg/dL) than saline controls and cows fed the high energy diet had higher plasma insulin concentrations (35.1 vs. 25.3μU/mL) compared with those fed the low energy diet. After 2 wk of TZD treatment, all cows were subjected to an intravenous glucose tolerance test (GTT; 0.25g of dextrose/kg of BW) followed 110min later by an insulin challenge (IC; 1.0μg of insulin/kg of BW). Differences in plasma glucose response to GTT were minimal based on diet; however, cows fed the low energy diet had more negative NEFA areas under the curve (AUC; −4,838 vs. −2,137μEq/L × min over 90min) and greater rates of NEFA decrease (1.35 vs. 0.63%/min) during GTT, suggesting differential responses of tissue glucose and fatty acid metabolism in response to dietary energy level. During IC, the TZD-treated cows tended to have more negative glucose AUC (−45.0 vs. −12.1mg/dL × min over 15min) than controls, suggesting that TZD-treated cows had greater responses to insulin. Limited interactions were observed between dietary and TZD treatments in all response variables measured. Adipose tissue biopsies performed on the final day of treatment suggested higher expression of peroxisome proliferator-activated receptor-γ (0.71 vs. 0.50 relative expression) and lipoprotein lipase (0.71 vs. 0.40 relative expression) in cows fed the high energy diet as measured by quantitative real-time PCR. These results indicate that energy level and insulin-sensitizing agents affect glucose and lipid metabolism during the dry period.

Dinâmica de anticorpos durante a gestação em vacas naturalmente infectadas com Neospora caninum de quatro rebanhos leiteiros no Brasil

Neospora caninum é descrito como uma importante causa de abortamento em bovinos por todo o mundo. O objetivo do presente estudo foi caracterizar o padrão da dinâmica de anticorpos durante a gestação em vacas leiteiras infectadas naturalmente por N. caninum. Doze vacas gestantes infectadas naturalmente com N. caninum foram selecionadas de quatro rebanhos leiteiros do Brasil e amostras de sangue foram mensalmente colhidas da concepção até o parto das vacas. Soros foram testados para anticorpos contra N. caninum pela reação de imunofluorescência indireta (RIFI). Durante a gestação, todas as vacas permaneceram clinicamente normais e geraram bezerros saudáveis. As vacas permaneceram soropositivas durante o estudo e títulos de anticorpos anti-N. caninum variaram de 100 a 12.800; somente o animal 234 apresentou um resultado negativo no primeiro mês de gestação. Diferenças significativas dos títulos da RIFI para N. caninum foram encontradas entre os meses de 1 a 9 de gestação pelo Teste de Friedman (P&lt;0,001). As análises estatísticas mostraram um aumento dos títulos de anticorpos anti-N. caninum no segundo e terceiro trimestre de gestação em relação ao primeiro trimestre. Altos títulos de anticorpos foram observados em algumas vacas após o mês cinco de gestação. Este estudo mostrou variação dos níveis de anticorpos em vacas soropositivas durante diferentes períodos gestacionais. Altos títulos foram observados durante o segundo e terceiro trimestre e o aumento dos títulos de anticorpos após o quinto mês de gestação não foi associado a abortamentos.

Specific anti- Neospora caninum IgG1 and IgG2 antibody responses during gestation in naturally infected cattle and their relationship with gamma interferon production

Gamma interferon (IFN-γ) production has been attributed a protective role against abortion in Neospora-infected dairy cows. This study investigate possible relationships between plasma levels of the N. caninum-specific immunoglobulin (Ig) isotypes IgG1 and IgG2 and IFN-γ production throughout gestation in dairy cows naturally infected with the parasite. Data were obtained from 31 pregnant Neospora-seropositive animals. Blood samples were collected on gestation days 40, 90, 120, 150, 180 and 210 or until abortion. Ten pregnancies ended in abortion. One of the 11 cows producing IFN-γ suffered abortion (9.1% of the cows producing IFN-γ). Non-aborting cows producing IFN-γ ( n = 10) showed a significantly higher IgG2/IgG1 antibody ratio throughout the gestation period than cows not producing IFN-γ ( n = 11). A significant negative effect of IFN-γ production on IgG1 antibodies was also observed, while IFN-γ production did not affect IgG2 antibody levels. In contrast, higher levels of IgG2 antibodies compared to IgG1 antibodies were observed over the whole of gestation in aborting animals, both in those not producing IFN-γ and in the single aborting cow that produced the cytokine. Our findings indicate that a Th1 immune response, in which IgG2 antibodies prevail, could be protective against N. caninum abortion, but only in the presence of IFN-γ production. On their own, elevated IgG2 antibody titres appear to be insufficient to protect dams chronically infected with N. caninum against abortion.

Crystallization and the number of neutrophils increase in the cervical mucus as parturition approaches in dairy cows

The aim of the present study was to determine changes in the crystallization and cytology of cervical mucus in late gestation in dairy cows. Eleven 7-month pregnant Holstein cows with a sound reproductive history were used in this study. Samples of cervical mucus were collected on 53±3, 38±3, 23±3, 12±2, 8±1, 5±1 and 2±1 days before parturition for cytology and examination of crystals. Coccygeal blood samples were also collected after each cervical mucus sampling for determination of plasma estrogen and progesterone concentrations. A sample of nasal secretions was also collected after each blood sampling for examination of crystals. The thin cervical smears were Giemsa stained for cytological examination and the thick smears of cervical and nasal mucus were also evaluated for crystallization. The results of the present study showed an increased (p<0.05) percentage of neutrophils and typical crystals in the cervical mucus as parturition approached. This coincided with the gradual rise of the plasma estrogen concentrations and the gradual decline of the plasma progesterone concentrations in the last 2 weeks before the onset of parturition. Further, a significant positive correlation was observed in the changes of the crystallization pattern between nasal and cervical mucus samples (p<0.05; r=+0.86). In conclusion, crystallization and increased neutrophils in the cervical mucus in late gestation could be related to impending parturition in dairy cows.

Changes in Plasma Estrogen Concentrations during the First Trimester of Gestation in Dairy Cows: Comparison with the Origin of Embryos and Fetal Number

The objectives of this study were to determine the profiles of plasma estrogen concentrations during the first trimester of gestation and to correlate them with the origin of the embryos and fetal number. Pregnancies were induced either by artificial insemination (AI) on the day of estrus (day 0) or by transfer of 1 or 2 blastocysts produced in vitro (IVF-ET) on day 7. Five singleton-bearing cows impregnated by AI, and 6 singleton and 6 twin pregnancies induced by IVF-ET were used in the experiment. Blood was collected by jugular venipuncture at 2 to 5-day intervals until day 100. The concentrations of plasma estrone, estradiol-17β and estrone sulfate were measured by using a radioimmunoassay. Concentrations of all the estrogens fluctuated at low levels until day 50 in all the groups. Thereafter, the concentration of estrone sulfate gradually increased, whereas those of estrone and estradiol-17β remained at basal levels until day 80. The concentration of estrone sulfate after day 50 was affected by the day of gestation and the number of fetuses. After day 80, the concentration of estrone sulfate increased drastically, coinciding with the increases in the estrone and estradiol-17β concentrations. The rate of increase in the concentration of estrone sulfate during days 80 to 100 was the highest among all the estrogens. In the singleton pregnancies, the concentrations of estrone and estrone sulfate between days 80 and 100 were higher in the artificially inseminated cows than in the IVF-ET cows. In the pregnancies induced by IVF-ET, estrone sulfate levels were higher in the twin-bearing cows than in the singleton-bearing cows during days 50 to 80 and 80 to 100. These results suggest that the concentrations of estrogens in bovine peripheral blood plasma could be applied for monitoring fetoplacental development in the first trimester of gestation.

Chiral inversion of (R)-ketoprofen: influence of age and differing physiological status in dairy cattle.

The chiral inversion of ketoprofen has been previously demonstrated in cattle, but no studies have been performed on different ages and metabolic situations in the animals. The aim of this work was to study any modifications of the stereoconversion of ketoprofen that occur by reason of age, lactation or gestation in dairy cows. Holando Argentino cattle were divided into three groups: 8 cows in early lactation, 8 pregnant cows and 8 newborn calves. Four animals from each group received the enantiomer R-(-)-ketoprofen by intravenous administration; the other four animals received the S-(+) enantiomer, all at doses of 0.5 mg/kg. Blood samples were collected at standardized times after dosing and assayed for ketoprofen by high-performance reversed-phase liquid chromatography (HPLC). The percentage inversion of R-(-)-ketoprofen to S-(+)-ketoprofen was 50.5% (SD +/- 2.4) in the preruminants, 33.3% (SD +/- 1.7) in cows in early lactation and 26.0% (SD +/- 5.1) in cows in gestation. These results indicate a differing enantioselective metabolic behaviour for one compound in one species under different physiological situations.

Lactation and gestation in dairy cows: flexibility avoids nutritional extremes.

The modern dairy cow has been selectively bred to produce large amounts of milk. Partly as a result, food consumption is considerably less than milk energy output in early lactation. It is only at 2 months or more postpartum that intake increases to the point where positive energy balance is regained, the initial production being achieved by a substantial mobilisation of body reserves. These reserves are laid down before parturition, but it is certainly not the case that the pregnant cow will accumulate adipose tissue recklessly; in the last third of pregnancy well-fed cows in good body condition exhibit reduced, not increased, appetite. There is a fine balancing act to perform. Excessive body condition at parturition quickly leads to metabolic problems such as ketosis, but cows who subsequently become too thin have increased risk of metabolic diseases such as mastitis and lameness. The biological mechanisms regulating output of milk are reasonably well understood, those controlling appetite less well so, and there has been little attempt at systematic integration of the two. The transition from pregnancy to lactation represents a major challenge to homeostasis, made more complicated in multiparous cows by the fact that much of gestation is concurrent with lactation. Herein lies the potential for nutritionally-entrained flexibility. In the wild, concurrent pregnancy and lactation only occur when nutritional conditions are favourable. If conditions are poor, rebreeding will be delayed and lactation will continue, at an energetically-sustainable level, for much longer than its 'normal' duration. In this way the twin energetic burdens of pregnancy and lactation are separated, and extremes are avoided. Given the increasing public concern about stresses suffered by intensively-managed dairy cows, this case may be one where commercial dairying could learn useful lessons from nature.

Serum Folates in Gestating and Lactating Dairy Cows

In Experiment 1, 70 cows were distributed in five groups of 14 animals each. Each group represented one physiological stage: parturition, 2 mo postpartum, 3 mo of gestation, 6 mo of gestation, and drying off at approximately 2 mo before parturition. Plasma volume, concentration of serum folates, and total serum folates were measured at each stage. In Experiment 2, four doses of folic acid (40, 80, 160, and 320mg) were administered by intramuscular injection to four groups of 5 cows in late gestation and four groups of 5 cows in early lactation. Serum folates in all cows and milk folates in lactating cows were determined before injection of folic acid and on d 1, 2, 4, 8, and 16 after injection. In Experiment 1, plasma volume did not differ between physiological stages, but total serum folates increased from parturition to reach a peak value 2 mo later; thereafter, serum folates decreased from 3 mo of gestation to parturition. In Experiment 2, during late gestation, serum folates increased after injection of folic acid and reached the highest concentration with the dose of 160mg. However, during early lactation, injection of folic acid had no effect on concentrations of serum or milk folates. Therefore, total serum folates decreased by 40% from 2 mo postpartum (around mating) to parturition. Moreover, at the end of gestation, serum folates can be increased by an intramuscular injection of folic acid. This may be an indication of an increased need for folic acid during gestation of dairy cows.

Factors Associated with the Duration of Gestation in Dairy Cattle

The duration of gestation in dairy cows is of importance to the dairy husbandman from a management standpoint, for it is desirable that dairy cows be in a no~l-lactating state during the last 6 to 8 wk. of each pregnancy. Thus, it is possible to prepare the cow physically for parturit ion and her next lactation. Dairy cattle breed associations also require that a living calf be produced within a maximum time limit after the completion of certain types of official production records. The purpose of this requirement is to assist in verifying the duration of pregnancy during the Official testing period. Recently the Brown Swiss Cattle Breeders' Association has extended the calving requirements following the completion of an official record to conform with the abnormally long gestation period found to exist in the Brown Swiss breed. Likewise, the Holstein-Friesian Association has reduced the gestation length used in the verification of applications for registration. This decision was based on the preliminary results of this study and data from similar investigations. In addition to these very practical applications, the possibility of various environmental and genetic factors influencing the duration of gestation is intriguing and may lead to fundamentally important discoveries. The commonly accepted opinion at the beginning of the nineteenth century was that normal gestations for dairy cattle averaged 270 days (33). Systematic investigations soon revealed this figure to be less than that normally observed. In 1817, Tessier (8) is reported to have found that 575 gestations averaged 282.2 days. Then, in 1840, the Earl of Spencer (33) is reported to have made ade tailed study of Durham gestatimm. His results showed the average length of 764 gestations to be 283.3 days. The range for calves born alive, reported by Spencer, was from 220 to 313 days. However, no calves born earlier than 242 days lived. Over half a century ago, Fleming-(18) reported the average gestation of cattle to be 283 days. Of the 1,062 observations included in his summary, 15 gestations were less than 241 days and 32 greater than 301 days.