Genetic and seasonal variations of Trypanosoma theileri and the association of Trypanosoma theileri infection with dairy cattle productivity in Northern Japan.

Trypanosoma theileri is considered a non- or low-pathogenic trypanosome that generally causes latent infection in apparently healthy cattle; however, T. theileri propagates in the bloodstream and may cause clinical disease in pregnant animals or co-infection with bovine leukemia virus or Theileria orientalis. In the current study, a monthly survey of T. theileri infection over one year was carried out in a research dairy farm in Hokkaido, Japan to determine the 1) seasonal variations in the prevalence, 2) genetic characterization of T. theileri, and 3) associations of milk and blood parameters in dairy cattle with T. theileri infection, including data of metabolic profile tests and dairy herd performance tests, using linear mixed models. We found that 1) the prevalence of T. theileri infection was significantly higher in summer and winter than in other seasons; 2) T. theileri possibly showed genetic diversity in Eastern Hokkaido; and 3) T. theileri infection was associated with significantly lower levels of blood urea nitrogen, milk protein, and solids-not-fat, which are caused by a low rumen fermentation level. This is the first study to report the negative impact of T. theileri infection in dairy cattle, and our study indicates that control of T. theileri infection can improve the productivity of dairy cattle.

Development of CpGP15 recombinant antigen of Cryptosporidium parvum for detection of the specific antibodies in cattle.

The infection of neonatal calves with Cryptosporidium parvum can have a huge economic impact because diarrhea caused by the parasite sometimes results in death. A serodiagnostic system will be helpful in the diagnosis of C. parvum infection. CpP23 is commonly used as an antigen for enzyme-linked immunosorbent assay (ELISA); however, some positive sera show low reactivities, as shown in this study. Herein, we focused on three other antigens, CpGP15, CpP2 and CpGP60, in addition to CpP23, to detect C. parvum-specific antibodies in cattle sera. CpP23 and CpGP15 showed substantial ability to discriminate between positive (n = 10) and negative (n = 10) control cattle sera. Unlike our previous report, both the sensitivity and the specificity were 100% when the two antigens were employed for the ELISA. The newly developed ELISA was applied to a total of 344 sera obtained from 9 cattle farms. Two farms among them had suffered from C. parvum infections before, and were regarded as the C. parvum-positive farms. The positive rates of antibodies against CpP23 and CpGP15 in the C. parvum-positive farms were 42.7% and 49.8%, respectively, whereas the positive rate for either of the antigens was 63.0% in the farms. In contrast, 14.3% and 9.8% were positive for CpP23 and CpGP15 in the C. parvum-negative farms, respectively, whereas 18.8% was positive for either of the antigens. This study revealed that the ELISAs employing both of CpP23 and CpGP15 can avoid false-negative results and are useful for monitoring of the C. parvum infection in cattle farms.

Associations of the first occurrence of pathogen-specific clinical mastitis with milk yield and milk composition in dairy cows.

The aim of this study was to estimate the associations of the first occurrence of pathogen-specific clinical mastitis (CM) with milk yield and milk composition (somatic cell count (SCC), lactose, fat, protein content in milk and milk urea nitrogen (MUN)). We studied 3149 dairy cows in 31 Hokkaido dairy farms in Japan. Five pathogen groups were studied: Streptococcus spp.; Staphylococcus aureus (S. aureus); coagulase-negative staphylococci (CNS); coliforms; and fungi. Test-day milk data and clinical records were collected from June 2011 until February 2014. Mixed models with an autoregressive correlation structure were fitted to quantify the effects of CM and several other control variables (herd, calving season, parity, week of lactation, and other diseases). Primipara (first lactation) and multipara (second and later lactations) were analysed separately. All pathogens, particularly S. aureus and fungi, were associated with significant milk losses in multipara. In this study, S. aureus and CNS infections were not associated with significant milk loss in primipara. All pathogens, in particular S. aureus and fungi, significantly increased SCC in both parity groups. All pathogens, especially CNS (in primipara) and S. aureus (in multipara), decreased lactose content. All pathogen groups except for fungi were associated with significant changes in fat, protein and MUN. Some pathogens such as Streptococcus spp. and coliforms seemed to be associated with long-term fat, protein and MUN changes. These findings provide estimates that could be used to calculate precise costs of CM, and also provide better indicators of pathogen-specific mastitis.

Relationship of vaginal discharge characteristics evaluated by Metricheck device to metabolic status in postpartum dairy cows.

The relationship between vaginal discharge characteristics and metabolic status has been studied in postpartum dairy cows. Vaginal discharges at 2-6 weeks postpartum were scored weekly on a 1 (clear) to 5 (purulent material with stench) scale using the Metricheck device and classified into three groups as follows: Endometritis group (n = 19), greater than or equal to score 4 until 3 weeks postpartum; Delayed involution group (n = 9), score 2 or 3 after having score 1; Healthy group (n = 23), cows except those belonging to the Delayed involution and Endometritis groups. The uterus and cervix were assessed using ultrasonography. Blood samples were collected twice weekly from 1 to 6 weeks postpartum from all cows and were additionally obtained for 13,14-dihydro-15-keto-prostaglandin F2α (PGFM) measurements from multiparous cows. Cows with delayed involution had delayed onset of luteal activity (p < 0.05) and higher serum urea nitrogen (BUN) concentrations (p < 0.01) than healthy animals. Cows with endometritis had more peripartum diseases (p < 0.05), lower milk yield (p < 0.05), longer cervix diameter (p < 0.05), and lower serum albumin (p < 0.01), total cholesterol (p < 0.01), and magnesium (p < 0.01) concentrations, and higher aspartate aminotransferase levels (p < 0.05) than healthy cows. Plasma PGFM concentrations tended to be higher in the Delayed involution group (p = 0.083) and lower in the Endometritis group (p = 0.085) than in the Healthy group. In summary, delayed involution was shown to be associated with higher BUN concentration, and endometritis may have been caused by peripartum diseases and hepatic dysfunction.

Impact of metritis on the generation of reactive oxygen species by circulating phagocytes and plasma lipopolysaccharide concentration in peripartum dairy cows.

This study examined the relationship between postpartum metritis, reactive oxygen species (ROS) generation, and plasma lipopolysaccharide (LPS) concentration in peripartum dairy cows. Blood was collected twice weekly from 2 weeks prepartum through 6 weeks postpartum. Whole blood chemiluminescence (WBCL) was measured using the luminol-enhanced zymosan-stimulated chemiluminescence assay. Cows were examined for uterine health disorders and classified into two groups, healthy (n = 11) and metritis (n = 5). Metritis had a significant effect on WBCL, with cows with metritis having a higher WBCL. Plasma LPS concentrations in cows with metritis were significantly higher than in healthy cows. To examine the effect of LPS on WBCL, blood was sampled in healthy peripartum cows (1 to 2 weeks prepartum, n = 8; 0 to 3 weeks postpartum, n = 11; and 4 to 8 weeks postpartum, n = 8) and incubated with LPS. At 1 endotoxin units/mL of LPS, similar to the plasma LPS concentration in cows with metritis, the WBCL increased in cows at 0 to 3 weeks postpartum. Results indicate that the increase in ROS generation and plasma LPS concentration are associated with metritis, and LPS may be responsible for enhanced ROS generation in early postpartum dairy cows.

Feed-derived volatile basic nitrogen increases reactive oxygen species production of blood leukocytes in lactating dairy cows.

The present study investigated over 9 months the changes of fermentative quality of total mixed rations (TMR) containing grass silage (GS) as a major component, associated with changes in the volatile basic nitrogen (VBN) levels in an experimental dairy farm. Effects of VBN levels in TMR on metabolic parameters, reactive oxygen species (ROS) production by blood polymorphonuclear leukocytes (PMNs) and conception rates for dairy cows were analyzed. According to VBN levels in TMR during survey periods, three distinct phases were identified; phase A with low VBN; phase B with high VBN; and phase C with mid-VBN. Metabolic parameters in blood were all within normal range. However, during phases B and C, nitrogen metabolic indices such as blood urea nitrogen and milk urea nitrogen showed higher levels compared to those in phase A, and a simultaneous increase in ROS production by blood PMNs and the load on hepatic function in metabolic parameters was observed in the cows with a lower conception rate. This suggests that feeding TMR with elevated VBN levels due to poor fermented GS results in stimulation of ROS production by PMNs by ammonia, and negatively affects metabolism and reproductive performance in lactating dairy cow.

Influence of hepatic load from far-off dry period to early postpartum period on the first postpartum ovulation and accompanying subsequent fertility in dairy cows.

The aim of the present study was to investigate nutritional and metabolic parameters during the dry and early postpartum periods of ovulatory and anovulatory cows, as well as their postpartum reproductive performance. Blood samples from 20 multiparous Holstein cows were collected once a week from the far-off dry period to 3 weeks postpartum. Early postpartum (0-3 weeks) ovulation was confirmed using plasma progesterone concentration profiles, and cows were considered ovulatory if they had resumed luteal activity by this point (n = 9), whereas cows that had not were considered anovulatory (n = 11). Data from the ovulatory and anovulatory cows were analyzed separately for the far-off dry period (7-4 weeks prepartum), the close-up dry period (3-1 weeks prepartum), and the early postpartum period (0-3 weeks). Serum gamma-glutamyl transpeptidase activity (far-off, P = 0.065; close-up, P = 0.051; and early postpartum, P = 0.030) and aspartate aminotransferase (close-up, P = 0.050 and early postpartum, P = 0.087) activities were higher in anovulatory than in ovulatory cows. The days open period was longer (P = 0.019) in anovulatory than in ovulatory cows, and the number of artificial inseminations per conception (P = 0.025) was greater. In conclusion, we found that continuously high gamma-glutamyl transpeptidase activities in serum, which may be induced by liver disorders, prevent subsequent ovulation and affect subsequent fertility, even if cows obtain sufficient ovulation-related energy and ß-carotene.

Relationship between the degree of insulin resistance during late gestation and postpartum performance in dairy cows and factors that affect growth and metabolic status of their calves.

This study aimed to investigate the effects of insulin resistance (IR) during the close-up dry period on the metabolic status and performance of dairy cows as well as to determine the effects on body weight (BW) and metabolic status of their calves. An insulin tolerance test (ITT) was conducted by administering 0.05 IU/kg BW of insulin to 34 multiparous Holstein cows at 3 weeks prepartum. Blood samples were collected at 0, 30, 45 and 60 min after insulin injection, and cows were divided into two groups based on the time required for glucose to reach the minimum levels [non-IR (NIR), 45 min (n=28); and IR, 60 min (n=6)]. Blood or milk sampling and body condition score (BCS) estimation were performed twice weekly during the experimental period. Blood samples from calves were collected immediately after birth. Cows with IR showed lower BCS (P<0.05) and serum urea nitrogen (P<0.05) and glucose concentration (P=0.05) before calving, and lower serum non-esterified fatty acid concentration (P<0.05) and milk yield (P<0.05) and earlier resumption of luteal activity (P<0.05) after calving; their calves showed lower BW (P<0.05) and plasma insulin-like growth factor-I concentration (P<0.001) and higher plasma insulin concentration (P<0.05). In conclusion, IR at 3 weeks prepartum in dairy cows is related to postpartum metabolic status and performance along with growth and metabolic status of their calves.

Association of rumen fill score and energy status during the close-up dry period with conception at first artificial insemination in dairy cows.

Recent studies have shown significant associations between prepartum energy status and postpartum fertility in dairy cows; therefore, the assessment of energy status by blood metabolites and metabolic hormones and suitable improvement of management during the prepartum period may enhance reproductive performance. Rumen fill score (RFS) is associated with feed intake; however, it is unknown whether RFS is also related to blood parameters. Therefore, this study investigated the relationship between RFS and energy status during the prepartum period, and their associations with conception at first artificial insemination (AI) after parturition. In 42 multiparous Holstein cows, RFS assessment and blood sampling were carried out twice a week during 3 weeks of the peripartum period. Ovarian cycles until AI were evaluated by measuring milk progesterone levels. Before calving, positive correlations were observed between RFS and total cholesterol, and RFS did not change in pregnant cows at first AI after parturition, whereas in non-pregnant cows, RFS decreased gradually as the calving day approached. After calving, non-pregnant cows showed lower energy status compared with pregnant cows, and some non-pregnant cows showed anovulation and cessation of estrous cycle. In conclusion, RFS during the close-up dry period is related to real-time energy status, and is associated with postpartum energy status and conception at first AI in dairy cows. © 2016 Japanese Society of Animal Science.

The effect of a continuous supply of betaine on the degradation of betaine in the rumen of dairy cows.

We investigated the degradation of betaine in the rumen by a continuous supply of betaine to dairy cows. After 24 h of betaine incubation using rumen fluid from dairy cows, more than 80% of the betaine remained undegraded. Furthermore, the continuous supply of betaine for about 70 d did not influence the in vitro degradation of betaine.

Effects of exogenous oxytocin on uterine blood flow in puerperal dairy cows: the impact of days after parturition and retained fetal membranes.

The objective of this study was to examine whether an oxytocin challenge test (OCT), evaluated by measuring the changes in uterine blood flow using transrectal colour Doppler ultrasonography, is a suitable non-invasive method to determine uterine contractility in puerperal dairy cows. The changes in uterine blood flow during uterine contractions induced by oxytocin were evaluated on days 2 and 5 postpartum (pp). Twelve clinically healthy Holstein cows were randomly assigned into two groups: (1) oxytocin group (n=7), 50 IU oxytocin injected IM and (2) control group (n=5), 5 mL saline injected IM. Blood flow volume (BFV) and pulsatility index (PI) in the uterine arteries were determined before and after injection for 120 min on days 2 and 5 pp. BFV declined and PI increased rapidly after oxytocin injection on day 2 (P<0.05), whereas oxytocin on day 5 pp did not cause changes in blood flow parameters. The result confirmed that uterine responsiveness to oxytocin decreases with time postpartum in healthy cows. The same OCT was applied in cows with retained fetal membranes (n=6) on day 2 pp, however uterine blood flow showed no change after oxytocin injection. The results showed that an OCT on day 2 pp may be a useful method for investigating the uterine contractile response to oxytocin (reflected as the decrease of uterine blood flow) and the potential pathophysiology of uterine involution in cows.

Tissue distribution of Neospora caninum in experimentally infected cattle.

Histopathology and quantitative PCR (qPCR) were used to determine the tissue distribution of Neospora caninum in calves at 80 days postinfection. Our findings revealed that the most appropriate brain areas for researching N. caninum pathogenesis were the amygdala and hippocampus for qPCR and the corpus striatum and diencephalon for histopathology.

Cloning, monoclonal antibody production, and bodily distribution pattern of a bovine lipocalin.

A bovine lipocalin, previously identified as a putative odorant-binding protein in bovine colostrum (bcOBP), was cloned and expressed, and its monoclonal antibody was established. bcOBP was constantly secreted into milk on day of parturition until at least 10 d postpartum at a concentration of 181±39 µg/L. Besides milk, bcOBP occurred in the nasal mucus, saliva, amniotic fluid, vaginal discharge, and blood plasma. Despite its low concentration, the distribution pattern and the finding that bcOBP harbored a characteristic sequence motif, CxxxC, which is conserved among insect and mammal pheromone binding proteins, suggest that bcOBP functions as a pheromone carrier. The presence of bcOBP in the plasma at varied concentrations depending on the lactation period does not exclude the possibility that bcOBP is secreted into milk from the blood. Cross-reactivity of the monoclonal antibody indicated presence of proteins homologous to bcOBP in the colostrum of farm animals of Cetartiodactyla.

Nutritional factors that regulate ovulation of the dominant follicle during the first follicular wave postpartum in high-producing dairy cows.

During recent decades, milk production per cow has increased drastically due to improved management, nutrition, and genetic selection; however, the reproductive performance of high-producing dairy cows has been declining. One of the factors responsible for this low reproductive performance is negative energy balance (NEB). NEB affects the onset of first ovulation in early postpartum cows. It is generally accepted that early first ovulation positively relates to the resumption of normal ovarian function, first service, and conception rate in dairy cows. Hence, delayed first ovulation has a negative impact on subsequent fertility. The metabolic condition of cows in NEB shifts to catabolic metabolism, which in turn causes increased plasma growth hormone and non-esterified fatty acid concentrations and decreased plasma insulin-like growth factor-1, insulin, and glucose concentrations. On the other hand, plasma ß-carotene concentrations decrease throughout the dry period and reach their nadir in about the first week postpartum, and this change reflects energy balance during the peripartum period. ß-Carotene plays a role independently of vitamin A in the reproductive performance of dairy cows, and the positive relationship between supplemental ß-carotene and reproductive function has been demonstrated in many studies during the past decades. However, ß-carotene content in corn silage, which is a popular main feed in high-producing dairy cows, is very low. This review describes nutritional factors related to ovulation during the first follicular wave postpartum in dairy cows.

Upregulation of interferon-stimulated genes and interleukin-10 in peripheral blood immune cells during early pregnancy in dairy cows.

In cows, interferon-tau (IFNT) regulates maternal recognition around days 15-19 after artificial insemination (AI). The present study hypothesized that if key target genes of IFNT are clearly upregulated in earlier stages of pregnancy, these genes could be use as indices of future pregnancy in cows. Therefore, we determined the expression of these genes in peripheral blood mononuclear leukocytes (PBMCs) and polymorphonuclear granulocytes (PMNs) during the maternal recognition period (MRP). Twenty multiparous Holstein cows were subjected to AI on day 0 and categorized into the following groups: pregnancy (Preg, n = 9), embryonic death (ED, n = 5) and non-pregnancy (NP, n = 6). Progesterone levels in the Preg group were higher than those in the NP group on days 12-21. ISG15 and OAS-1 (IFN-stimulated genes: ISGs) mRNA in PBMCs on day 8 was higher in the Preg group than in the NP group, and these mRNAs in PMNs was higher in the Preg group on day 5 than in the NP and ED groups. Interleukin-10 (IL-10, Th2 cytokine) mRNA expression increased on day 8 in the PBMCs of pregnant cows. Tumor necrosis factor α (TNFα, Th1 cytokine) mRNA expression was stable in all groups. In an in vitro cell culture experiment, IFNT stimulated mRNA expression of ISGs in both PBMCs and PMNs. IFNT stimulated IL-10 mRNA expression in PBMCs, whereas IFNT increased TNFα mRNA levels in PBMCs in vitro. The results suggest that ISGs and IL-10 could be responsive to IFNT before the MRP in peripheral blood immune cells and may be useful target genes for reliable indices of pregnancy before the MRP.

Slow recovery of blood glucose in the insulin tolerance test during the prepartum transition period negatively impacts the nutritional status and reproductive performance postpartum of dairy cows.

In peripartum dairy cows, insulin resistance (IR) increases to adjust the direction of energy to lactation after calving. To investigate the effect of prepartum IR on postpartum reproductive performance, the insulin tolerance test (ITT) was applied to 15 cows at 3 weeks (Pre21) and 10 days (Pre10) before the predicted calving date. Blood glucose area under the curve (AUC(glu)) within 120 min after administration of 0.05 IU/kg-BW insulin was calculated. The occurrence of first ovulation, days to first artificial insemination (AI) and first AI conception rate were recorded. Nutritional status postpartum was evaluated by blood chemical analysis. Based on AUC(glu) changes from Pre21 to Pre10, cows were classified into either the AUC-up group (AUC(glu) increase, n=5) or the AUC-down group (AUC(glu) decrease, n=10). There was no difference in the decrease in blood glucose at 30 min after insulin injection between groups, although glucose recovery from 30 to 60 min during the ITT was slow at Pre10 in the AUC-up group. The AUC-up group had a higher number of days to first AI and high glucose, total protein, globulin, γ-glutamyltransferase, triacylglycerol levels and a low albumin-globulin ratio at the 14th day postpartum. The present study infers that prepartum slow glucose recovery rather than insulin sensitivity might increase the potential for subclinical health problems postpartum and thus suppress reproductive performance. During the prepartum transition period, glucose dynamics in the ITT can be considered as a new indicator for the postpartum metabolic status and reproductive performance of dairy cows.

Effect of temperature on survival of pathogenic bacteria in biogas plants.

The paper deals with the hygienic advantages of sanitation to treat dairy manure in full-scale biogas plants. The slurry samples were collected from two thermophilic biogas plants (55°C) and two mesophilic biogas plants (38°C) in Hokkaido Japan. A detectable number of Coli-aerogenes group and Enterococcus in the slurries after anaerobic digestion (AD) could not be found in either thermophilic biogas plants. However, in both mesophilic biogas plants the viable numbers of Coli-aerogenes group and Enterococcus were detected in the slurries even after anaerobic digestion. The mean decimation reduction time (T(90) ) values of the Coli-aerogenes group and Enterococcus in the slurries during mesophilic digestion were 13.3 days and 16.7 days, respectively.

Relationships between the first ovulation postpartum and polymorphism in genes relating to function of immunity, metabolism and reproduction in high-producing dairy cows.

The decrease in fertility and conception rates of high-producing dairy cows is one of the major negative impacts for today's producers. The recovery of ovarian activity postpartum is affected by the status of immunity, metabolism and reproduction and plays a critical role in subsequent fertility after parturition in the cow. In the present study we investigated the relationships between polymorphisms in genes relating to the above functions and the first postpartum ovulation as a marker of the recovery of ovarian function in the cow. In immune function related-factors, the occurrence of first postpartum ovulation within 3 weeks in the C/C genotypes of tumor necrosis factor α (TNFα) exon (55.4%) and the A/G genotypes of TNFα promoter (55.4%) was significantly higher than that in T/T genotypes of TNFα exon (14.3%) and A/A genotypes of TNFα promoter (14.3%). Moreover, anovulatory cows with the T/T genotype of TNFα exon and the A/A genotype of TNFα promoter tended to have a prolonged days open compared with those of the other genotypes of TNFα polymorphisms. In metabolic function-related factors, ovulatory and anovulatory cows had a different distribution for alleles of the growth hormone receptor, but there were no significant differences in genotype and allele frequency of insulin-like growth factor-I polymorphism. No significant relationships were found between ovarian function after parturition and polymorphisms for reproduction-related genes. In conclusion, polymorphisms of TNFα gene both in exon and promoter regions have a strong association with the early first ovulation within 3 weeks after parturition in the high-producing dairy cow. Taken together, polymorphisms of TNFα gene could be strongly related to early first ovulation after parturition, thus being an effective tool of selection for improving reproductive performance in the high-producing dairy cow.

Generation of IFN-gamma-producing cells that recognize the major piroplasm surface protein in Theileria orientalis-infected bovines.

Theileriosis is a tick-borne protozoan disease caused by Theileria species. The Theileria species are classified into two groups depending on the cell type in which they proliferate and the clinical symptoms. The first group consists of lymphoproliferative Theileria species (T. parva and T. annulata), which mainly proliferate in lymphocytes, causing uncontrolled lymphocyte proliferation. The other group consists of a nonlymphoproliferative Theileria species (T. orientalis, also known as T. sergenti) that proliferates in erythrocytes and causes hemolytic anemia. Based on reports of generation of antigen-specific CD4(+) and CD8(+) T cells in lymphoproliferative theileriosis, we investigated whether T cells specific to the T. orientalis antigen are present in the nonlymphoproliferative form of the disease. In this study, we developed a new assay based on an enzyme-linked immunospot (ELISpot) to detect interferon-gamma (IFN-gamma)- and interleukin-10 (IL-10)-secreting cells in a series of cryogenically preserved bovine peripheral blood mononuclear cells (PBMCs). We first determined that IFN-gamma- and IL-10-secreting T cells were present in PBMCs by stimulating them with phytohemagglutinin L (PHA-L=red kidney bean lectin L, known as T cell stimulator), and then determined whether T. orientalis-specific T cells are present in T. orientalis-infected bovines. Peptides derived from T. orientalis major piroplasm surface protein (MPSP) were used as a T. orientalis-specific stimulator in the ELISpot assay, and peptides from glycoprotein B (gB) of the bovine herpes virus-1 (BHV-1) were used as a BHV-1-specific stimulator as a control for monitoring the immune response. Compared with results obtained using the BHV-1 (gB peptides)-specific IFN-gamma ELISpot assay to assess BHV-1-immunized Holsteins, prominent T. orientalis MPSP peptide-specific IFN-gamma and IL-10 positive spots were detected in T. orientalis-infected Holsteins but weak positive responses were exhibited by T. orientalis-infected Angus and Japanese Black cattle. As far as we are aware, this is the first report to show direct evidence of the presence of T. orientalis-specific T cells in T. orientalis-infected bovines using an antigen-specific ELISpot assay system and that T. orientalis-specific, IFN-gamma- and IL-10-producing T cells are produced in T. orientalis-infected Holsteins.

The absence of corpus luteum formation alters the endocrine profile and affects follicular development during the first follicular wave in cattle.

We previously established a bovine experimental model showing that the corpus luteum (CL) does not appear following aspiration of the preovulatory follicle before the onset of LH surge. Using this model, the present study aimed to determine the profile of follicular development and the endocrinological environment in the absence of CL with variable nadir circulating progesterone (P(4)) concentrations during the oestrous cycle in cattle. Luteolysis was induced in heifers and cows and they were assigned either to have the dominant follicle aspirated (CL-absent) or ovulation induced (CL-present). Ultrasound scanning to observe the diameter of each follicle and blood collection was performed from the day of follicular aspiration or ovulation and continued for 6 days. The CL-absent cattle maintained nadir circulating P(4) throughout the experimental period and showed a similar diameter between the largest and second largest follicle, resulting in co-dominant follicles. Oestradiol (E(2)) concentrations were greater in the CL-absent cows than in the CL-present cows at day -1, day 1 and day 2 from follicular deviation. The CL-absent cows had a higher basal concentration, area under the curve (AUC), pulse amplitude and pulse frequency of LH than the CL-present cows. After follicular deviation, the CL-absent cows showed a greater basal concentration, AUC and pulse amplitude of growth hormone (GH) than the CL-present cows. These results suggest that the absence of CL accompanying nadir circulating P(4) induces an enhancement of LH pulses, which involves the growth of the co-dominant follicles. Our results also suggest that circulating levels of P(4) and E(2) affect pulsatile GH secretion in cattle.