Serum progesterone and luteinizing hormone in dairy cattle fed varying levels of crude protein

Alleviative effect of melatonin on the decrease of uterine receptivity caused by blood ammonia through ROS/NF-κB pathway in dairy cow

High concentration of blood ammonia can affect the uterus receptivity and decrease fecundity in dairy cow. Melatonin can reduce reactive oxygen species (ROS) level and has antioxidant and anti-inflammatory effects. However, it is not clear whether melatonin can alleviate ammonia-induced apoptosis of endometrial epithelial cell (EEC) and reduced uterus receptivity. The bovine EEC were treated with ammonium chloride and/or melatonin. Cell viability, apoptosis, oxidative stress and mitochondrial membrane potential were measured and the expression of apoptosis-related genes (p53, Cyt-c, Bax, Bcl-2, caspase-8, caspase-9 and caspase-3), uterus receptivity related genes (VEGF, LIF and EGF) and inflammatory factors (TLR-4, IL-6 and NF-κB) were detected. In addition, the expression of VEGF was detected after adding NF-κB inhibitor (40 μM) and IL-6 (1 ng/mL and 50 ng/mL). The results showed that ammonia significantly increased intracellular ROS level, mRNA and protein expression of Bax, p53, Cyt-c, caspase-9, caspase-8, caspase-3, TLR-4, NF-κB and IL-6, promoted cell apoptosis, while decreased mitochondrial membrane potential, the mRNA and protein expression of VEGF and EGF. Interestingly, melatonin significantly mitigated ammonia-induced changes. However, melatonin could not alleviate ammonia-induced changes of IL-6 and VEGF when NF-κB signal pathway was inhibited. The addition of IL-6 significantly reduced mRNA and protein expression of VEGF. In conclusion, ammonia induced EEC apoptosis through ROS production and activation of mitochondrial apoptosis pathway, and induced inflammatory response through TLR4/NF-κB/IL-6 pathway. Melatonin alleviated EEC apoptosis by inhibiting ROS pathway, and reduced IL-6 expression by inhibiting TLR-4/NF-κB signal pathway, which eventually improved VEGF expression and uterus receptivity in dairy cows.

Heamatological parameters, endocrinological profiles, antioxidant and oxidative stress profiles of repeat breeding crossbred cows in Andaman and Nicobar Islands

The present study was carried out to assess the effect of repeat breeding syndrome (RBS) on heamatological, antioxidant, oxidative stress and endocrinological profiles in crossbred cows under tropical island ecosystem of Andaman and Nicobar Islands. Each of the twelve number of cows was selected (which were affected with repeat breeding syndrome) as Group 2 and normal cyclic breeding cows as Group 1. These cows were maintained under similar type of managemental conditions. Heamatological profiles, antioxidant and hormone profiles were estimated by automatic blood analyser and commercial diagnostic kits, respectively. The result revealed that the crossbred cows with RBS suffered severe anaemia. The RBS affected animals showed significantly lower level of antioxidant profiles and significantly higher malondialdehyde (MDA) than the unaffected animal groups. Similarly, endocrinological profiles revealed that the RBS affected animals had significantly higher level of cortisol, prolactin and lower level of 17 β-estradiol (E2), progesterone (P4), follicle stimulating hormone (FSH), luteinizing hormone (LH), thyroxine (T4) and insulin like growth factor-1 (IGF-1) than the unaffected crossbred cows. The study concluded that the RBS was due to anaemia, lack of antioxidants, overproduction of free radicals and disturbances of endocrinological profiles in crossbred cows of Andaman and Nicobar Islands.

Elevated blood urea nitrogen alters the transcriptome of equine embryos

High blood urea nitrogen (BUN) in cows and ewes has a negative effect on embryo development; however, no comparable studies have been published in mares. The aims of the present study were to evaluate the effects of high BUN on blastocoele fluid, systemic progesterone and Day 14 equine embryos. When a follicle with a mean (±s.e.m.) diameter of 25±3mm was detected, mares were administered urea (0.4g kg-1) with sweet feed and molasses (n=9) or sweet feed and molasses alone (control; n=10). Blood samples were collected every other day. Mares were subjected to AI and the day ovulation was detected was designated as Day 0. Embryos were collected on Day 14 (urea-treated, n=5 embryos; control, n=7 embryos). There was an increase in systemic BUN in the urea-treated group compared with control (P<0.05), with no difference in progesterone concentrations. There were no differences between the two groups in embryo recovery or embryo size. Urea concentrations in the blastocoele fluid tended to be higher in the urea-treated mares, with a strong correlation with plasma BUN. However, there was no difference in the osmolality or pH of the blastocoele fluid between the two groups. Differentially expressed genes in Day 14 embryos from urea-treated mares analysed by RNA sequencing were involved in neurological development, urea transport, vascular remodelling and adhesion. In conclusion, oral urea treatment in mares increased BUN and induced transcriptome changes in Day 14 equine embryos of genes important in normal embryo development.

Association of bulk tank milk urea nitrogen concentration with elevated individual cow values and investigation of sampling frequency for accurate assessment

Individual milk urea nitrogen (MUN) levels ≥ 19.63 mg/dL have been recently reported to significantly affect fertility. The objectives of the present study were to (a) predict the percentage of cows with elevated MUN within a herd using bulk tank (BTMUN) levels, in the absence of individual MUN records, and (b) establish a sampling frequency protocol for the assessment of actual BTMUN levels. A database of 17,687 monthly individual MUN and concurrent 229 monthly BTMUN records from 24 dairy herds was used. A ROC analysis was performed to determine the BTMUN threshold over which cows in the herd have elevated MUN concentrations that, based on literature, affect fertility. Moreover, a regression was run to predict the percentage of cows with elevated MUN within a herd from BTMUN values. A second database of 10,687 daily BTMUN records from 29 herds was used to identify an appropriate sampling frequency to assess the actual BTMUN levels. Eleven different sampling frequencies ranging from once to 8 times per month were assessed. A BTMUN value of 15.76 mg/dL was the optimum threshold over which cows with elevated MUN concentrations are included in a herd. The percentage of cows with elevated MUN values can be accurately predicted using BTMUN values (R² = 0.872; P < 0.001). A bulk tank sampling frequency of once per week seems appropriate for most herds in order to assess the actual BTMUN levels, in case daily BTMUN values are not available from milk processors.

Relationships between nutrition and fertility in dairy cattle

The reduced fertility that is becoming more evident in high yielding dairy cows may be related to many factors including changes in milk production, food intake and fluctuations in body condition. Metabolic and production markers have been studied as a way of predicting success to a particular artificial insemination. Successful conception to a particular service was not associated with milk production, body condition or plasma concentrations of several indicators of metabolic state around the time if insemination. This highlights the importance of time of information collection in fertility management programmes. Increased food intake may reduce systemic progesterone concentrations. This is more evident in sheep than cattle, but a positive relationship between systemic progesterone early post mating and establishment of pregnancy in cattle has been reported. However, progesterone concentrations in the ovarian vein and endometrium are not strongly correlated with systemic progesterone. Thus, the significance of modest changes in systemic progesterone in affecting oocyte and embryo development must be questioned. Blood urea concentrations can be altered by diet, and reduced pregnancy rates have been reported in cows with high urea concentrations. However, in other recent studies, no difference was reported in serum urea in cows that conceived and those that failed to conceive. Pregnancy rate was equally high in heifers when in-vitro produced embryos were transferred to heifers on high and low urea diets. When embryos were produced in sheep on high and low dietary urea, the effects on embryo development appear to occur early in the developmental process, suggesting a substantial effect on the development of the oocyte. The developmental capacity of oocytes and quality of embryos is reduced in cattle maintained on extremely high dietary intakes. Oocyte developmental capacity is reduced in cows of higher genetic merit and embryo quality can be substantially reduced in the early postpartum period. Collectively, these results suggest that high dietary intake or high metabolic load is deleterious to normal oocyte development and establishment of pregnancy. This highlights the importance of further studies on the effect of dietary intake on metabolic state and follicle, oocyte and embryo development. In a practical context, these results highlight the importance of nutritional management and avoiding changes in the amount or type of diet around the time of mating in high-production dairy cows.

Luteal function during the estrous cycle in arginine-treated ewes fed different planes of nutrition

Functions of corpus luteum (CL) are influenced by numerous factors including hormones, growth and angiogenic factors, nutritional plane and dietary supplements such as arginine (Arg), a semi-essential amino acid and precursor for proteins, polyamines and nitric oxide (NO). The aim of this study was to determine if Arg supplementation to ewes fed different planes of nutrition influences: (1) progesterone (P4) concentrations in serum and luteal tissue, (2) luteal vascularity, cell proliferation, endothelial NO synthase (eNOS) and receptor (R) soluble guanylate cyclase β protein and mRNA expression and (3) luteal mRNA expression for selected angiogenic factors during the estrous cycle. Ewes (n = 111) were categorized by weight and randomly assigned to one of three nutritional planes: maintenance control (C), overfed (2× C) and underfed (0.6× C) beginning 60 days prior to onset of estrus. After estrus synchronization, ewes from each nutritional plane were assigned randomly to one of two treatments: Arg or saline. Serum and CL were collected at the early, mid and late luteal phases. The results demonstrated that: (1) nutritional plane affected ovulation rates, luteal vascularity, cell proliferation andNOS3,GUCY1B3, vascular endothelial growth factor (VEGF) andVEGFR2mRNA expression, (2) Arg affected luteal vascularity, cell proliferation andNOS3,GUCY1B3,VEGFandVEGFR2mRNA expression and (3) luteal vascularity, cell proliferation and the VEGF and NO systems depend on the stage of the estrous cycle. These data indicate that plane of nutrition and/or Arg supplementation can alter vascularization and expression of selected angiogenic factors in luteal tissue during the estrous cycle in sheep.

Nutritional effects on ovulation, embryo development and the establishment of pregnancy in ruminants

The effects of high and low dietary dietary intake on reproduction in female cattle and sheep will be considered at the level of the pituitary gland, ovary and uterus. In sheep, increased dietary intake for a relatively short time will increase ovulation rate, by increasing gonadotropin secretion. Dietary intake can affect steroids such as progesterone and also intra-follicular concentrations of some growth factors such as IGF-1 and IGF-2. The effects of altered energy intake on gonadotropins and steroids in cattle are not as repeatable as those in sheep but follicular growth rates can be altered. High nutrition has a negative effect on oocyte quality, with animals onad-libitumhigh energy diets particularly at risk. Overfeeding can decrease embryo quality in both sheep and cattle and it appears that this results from changes primarily at the level of the follicle or oocyte. Restricted nutrition for a short time will enhance pregnancy rates in cattle; most of this benefit appears to occur if food is restricted before insemination. Thus feeding levels before mating are particularly important to subsequent reproductive success. High dietary crude protein may decrease pregnancy rate in lactating cows. In ewes and heifers supplementation with urea failed to have any effect on pregnancy rates when good quality embryos were transferred to recipient animals exposed to high dietary crude protein. In donor ewes there were adverse effects on early embryo development following urea treatment, suggesting that the mechanism affecting the reproductive process was primarily operating at the level of the oocyte. Collectively, these data identify the overall deleterious effects of high dietary intake and excess crude protein on fertility and highlight the importance of dietary intake before ovulation on the likelihood of establishing a viable pregnancy.

The Deep Correlation between Energy Metabolism and Reproduction: A View on the Effects of Nutrition for Women Fertility

In female mammals, mechanisms have been developed, throughout evolution, to integrate environmental, nutritional and hormonal cues in order to guarantee reproduction in favorable energetic conditions and to inhibit it in case of food scarcity. This metabolic strategy could be an advantage in nutritionally poor environments, but nowadays is affecting women's health. The unlimited availability of nutrients, in association with reduced energy expenditure, leads to alterations in many metabolic pathways and to impairments in the finely tuned inter-relation between energy metabolism and reproduction, thereby affecting female fertility. Many energetic states could influence female reproductive health being under- and over-weight, obesity and strenuous physical activity are all conditions that alter the profiles of specific hormones, such as insulin and adipokines, thus impairing women fertility. Furthermore, specific classes of nutrients might affect female fertility by acting on particular signaling pathways. Dietary fatty acids, carbohydrates, proteins and food-associated components (such as endocrine disruptors) have per se physiological activities and their unbalanced intake, both in quantitative and qualitative terms, might impair metabolic homeostasis and fertility in premenopausal women. Even though we are far from identifying a "fertility diet", lifestyle and dietary interventions might represent a promising and invaluable strategy to manage infertility in premenopausal women.

Milk Production and Fertility in Cattle

Evolutionary biology provides reasons for why the intensive selection for milk production reduces reproductive success rates. There is considerable exploitable genetic variation in reproductive performance in both dairy and beef cattle, and examination of national genetic trends demonstrates that genetic gain for both reproductive performance and milk production is possible in a well-structured breeding program. Reproductive failure is often postulated to be a consequence of the greater negative energy balance associated with the genetic selection for increased milk production. However, experimental results indicate that the majority of the decline in reproductive performance cannot be attributed to early lactation energy balance, per se; reproductive success will, therefore, not be greatly improved by nutritional interventions aimed at reducing the extent of negative energy balance. Modeling can aid in better pinpointing the key physiological components governing reproductive success and, also, the impact of individual improvements on overall fertility, helping to prioritize variables for inclusion in breeding programs.

Invited review: An evaluation of the likely effects of individualized feeding of concentrate supplements to pasture-based dairy cows

In pasture-based dairy systems, supplementary feeds are used to increase dry matter intake and milk production. Historically, supplementation involved the provision of the same amount of feed (usually a grain-based concentrate feed) to each cow in the herd during milking (i.e., flat-rate feeding). The increasing availability of computerized feeding and milk monitoring technology in milking parlors, however, has led to increased interest in the potential benefits of feeding individual cows (i.e., individualized or differential feeding) different amounts and types of supplements according to one or more parameters (e.g., breeding value for milk yield, current milk yield, days in milk, body condition score, reproduction status, parity). In this review, we consider the likely benefits of individualized supplementary feeding strategies for pasture-based dairy cows fed supplements in the bail during milking. A unique feature of our review compared with earlier publications is the focus on individualized feeding strategies under practical grazing management. Previous reviews focused primarily on research undertaken in situations where cows were offered ad libitum forage, whereas we consider the likely benefits of individualized supplementary feeding strategies under rotational grazing management, wherein pasture is often restricted to all or part of a herd. The review provides compelling evidence that between-cow differences in response to concentrate supplements support the concept of individualized supplementary feeding.

Effect of nutrition on plasma lipid profile and mRNA levels of ovarian genes involved in steroid hormone synthesis in Hu sheep during luteal phase

Ovarian steroid hormones regulate follicular growth and atresia. This study aims to determine whether key ovarian sterol-regulatory genes are differentially expressed in Hu sheep under different short-term nutritional regimens. Estrus was synchronized using intravaginal progestagen sponges. The ewes were assigned randomly to 3 groups. On d 6 to 12 of their estrous cycle, the control (CON) group received a maintenance diet (1.0×M), the supplemented (SUP) group received 1.5×M, and the restricted (R) group received 0.5×M. On d 7 to 12, blood samples were taken. The sheep were slaughtered at the end of the treatment, and their organs and ovaries were collected. The plasma concentrations of urea (P<0.01), total cholesterol (P<0.01), low-density lipoprotein cholesterol (P<0.01), NEFA (P<0.01), FSH (P<0.05), and estradiol (P<0.05) increased with decreasing dietary intake, whereas plasma triglyceride (P<0.01) and triiodothyronine (T3) concentrations decreased (P<0.05). The ewes in the R group had higher spleen weight and percentage of spleen to BW and lower liver and small intestine weights and percentage of liver/stomach to BW than the SUP group ewes (P<0.05). Nutritional restriction decreased the cytochrome p450 (CYP17A1) and estrogen receptor 1 (ESR1) mRNA expression (P<0.05) and increased the cytochrome p450 aromatase (CYP19A1) mRNA expression (P<0.05) in follicles>2.5 mm. Follicle size affected the mRNA expression of very low density lipoprotein receptor (VLDLR), estrogen receptor 2 (ESR2), FSH receptor (FSHR), CYP17A1, and CYP19A1 (P<0.05). In conclusion, we suggest that a potential mechanism by which short-term negative energy balance inhibits follicular growth may involve responses to disrupted reproductive hormone concentrations and influenced the intrafollicular expression of CYP17A1, CYP19A1, and ESR1. This result may be due to increased plasma urea and lipid concentrations.

Effects of high dietary crude protein on the characteristics of preovulatory follicles in dairy heifers

The objectives were to examine the effect of high dietary crude protein on characteristics of preovulatory follicles in dairy heifers. Eight Israeli-Holstein heifers, 4 fitted with rumen fistula and 4 intact, were assigned to 1 of 3 treatments in a replicated (n=2) 4 × 3 incomplete Latin square design with 39-d periods. Treatments were: low (6.0%; LP), moderate (13.0%; MP), and high (20.0%; HP) crude-protein diets, containing 1.27 Mcal NE(L)/kg dry matter. Diets were based on approximately 66% wheat straw and various proportions of ground corn grain and soybean meal. The estrous cycles of the heifers were synchronized, and 14 d after behavioral estrus, heifers received PGF(2 α) injections. After a further 40 h, at d 39 of each period, follicular fluid (FF) was aspirated from follicles of diameter >7 mm. The intake of the LP diet was 9% lower than that of MP and HP diets. Rumen ammonia and plasma urea nitrogen concentrations were highest in the HP and lowest in the LP, with intermediate levels in MP diets. No differences were found between treatments in plasma and FF concentrations of glucose and nonesterified fatty acids. High-protein diets increased urea concentrations very similarly in preovulatory FF and in plasma. No differences were observed between diets, in preovulatory follicle diameters and concentrations of androstenedione. However, higher estradiol and progesterone concentrations in FF were observed under the HP than under the MP diet, with no difference between diets in estrogen to progesterone ratio. It can be concluded that high concentrations of urea in plasma, caused by high dietary crude protein, penetrated into preovulatory follicles, but did not impair preovulatory characteristics. This lack of detrimental effects might be attributed to the use in this study of nonlactating heifers, which have fewer nutritional and physiological constraints and eliminate negative effects of potential interactions with high urea on dairy cows' reproductive systems.

Nutrition × reproduction interaction in pasture-based systems: is nutrition a factor in reproductive failure?

Dairy cow fertility has declined in recent decades, coincidental with large increases in milk production. Cows take longer to return to oestrus, display poorer signs of oestrus, have greater early embryo loss, and may have poorer conception rates. The problem is often considered to be nutritional, at least in part, and, therefore, can be corrected through dietary adjustment. Although acknowledged as highly digestible, high quality pastured forages tend to be low in non-structural carbohydrates (NSC), high in rumen degradable protein and the temporal supply may not be adequate for cow demand at key times; diet adjustment is often recommended to overcome these limitations. The interaction between nutrition and reproduction is poorly defined, however, and study results are often contradictory. Hypothesised limitations to pastured forages within a grazing system will be discussed, and the likely impact of nutritional adjustment on pre- and post-ovulatory reproductive processes examined. The effect of energy balance, carbohydrate type, protein and fat on reproductive outcomes will be considered. Nutrition is an important component of successful reproduction, but dietary adjustment to improve pregnancy rates is complicated, and merely offering pastured cows a supplement is unlikely to result in large effects. Conclusions indicate that care must be taken in interpreting associative analyses and in applying results from different farming systems.

Dietary manipulation of Bos indicus x heifers during gestation affects the reproductive development of their heifer calves

The effect of nutrition during the first and second trimesters of pregnancy in composite beef heifers on reproductive parameters of their female calves was determined in the present study. At artificial insemination, heifers were assigned to one of four treatment groups (i.e. HH, HL, LowH and LL) depending on the level of crude protein intake (H = high; L = low) for first and second trimesters of pregnancy. Gonadotrophin concentrations and ovarian parameters were measured in their female calves at 5 and 23 months of age. Crude protein intake was positively associated with dam plasma urea (P < 0.001). The density of healthy follicles in heifers at the time of death was negatively correlated with dam plasma urea at Day 179 (P = 0.009). Heifers from LowH dams had a smaller-sized prepubertal largest ovarian follicle (P = 0.03) and lower densities of primordial and primary follicles (P = 0.02) and healthy antral follicles (P = 0.009) when they were killed. There was a positive correlation between plasma FSH concentrations at 5 and 23 months of age (P = 0.02), as well as between the sizes of the largest ovarian follicles at 6 and 23 months of age (P = 0.01). In conclusion, the reproductive development of heifers may be affected by prenatal nutrition during early and mid-gestation.

Precalving factors affecting conception risk in Holstein dairy cows in tropical conditions

The objective of this study was to identify precalving nutritional risk factors that may affect variation in first service conception risk in 21 commercial Holstein dairy herds in a tropical environment (Reunion Island). The data set included 473 lactation records in 404 cows. A multivariate logistic-regression model including herd as a random effect was used to analyse the relationship between first service conception risk and energy status (body condition score, plasma glucose, insulin, cholesterol, non-esterified fatty acids and beta-hydroxybutyrate), nitrogen status (urea), hepatic function (gamma-glutamyltransferase, glutamate deshydrogenase, albumin), and mineral deficiencies (calcium, phosphorus, magnesium), adjusting systematically for factors such as breeding, season, parity, previous milk yield and fertility, calving to first service interval and type of oestrus (spontaneous versus induced). The overall mean conception risk was 0.27+/-0.02 (mean+/-S.E.M., n=473). First service conception risk was penalized by calving to 1st service interval shorter than 60 days, synchronized oestrus, previous 305-day milk yield >8000 kg (p<0.05), low blood glucose concentration in high-yielding cows (p<0.05) and combined high urea and beta-hydroxybutyrate concentrations (p<0.01). Precalving energy imbalance, revealed by low prepartum glucose concentration, was a strong nutritional predictor of low first service conception risk in high-yielding cows. Some precalving nutritional disorders potentially associated with consumption of spoiled silage which induces elevated circulating urea and beta-hydroxybutyrate have a delayed detrimental effect on conception, even if the true causes of this effect remain to be elucidated. As a conclusion, our findings should lead the breeders to pay more attention to the feeding of dry cows that is usually neglected in Reunion Island dairy farms.

Detrimental effects of high plasma urea nitrogen levels on viability of embryos from lactating dairy cows

High plasma urea nitrogen (PUN) concentrations are associated with decreased fertility in lactating dairy cows. Our objective was to evaluate the quality of embryos flushed from superovulated lactating cows having moderate or high PUN concentrations. Subsequent embryo survival was determined after transfer to recipient heifers with either low or high PUN. Lactating Holstein dairy cows (n = 23; 50-120 days in milk) were randomly assigned to one of two diets designed to result in moderate or high PUN concentrations (15.5 +/- 0.7 and 24.4 +/- 1.0 mg/dl, respectively; P < 0.001) and were fed for 30 days before embryo flushing and recovery. Embryos (n = 94) were evaluated morphologically, frozen and subsequently transferred into synchronized virgin heifers that were fed one of two diets designed to result in either low or high PUN concentrations (7.7 +/- 0.9 and 25.2 +/- 1.5 mg/dl, respectively; P < 0.001; 2 x 2 factorial design). The number, quality and stage of development of recovered embryos were similar for cows with moderate or high PUN. Transfer of embryos from moderate PUN donor cows resulted in a higher pregnancy rate (35%; P < 0.02) than the transfer of embryos from high PUN donor cows (11%). Pregnancy rate was not affected by either recipient diet or the interaction of donor and recipient diets (P > 0.05). These results indicate that high PUN concentrations in lactating dairy cows decrease embryo viability through effects exerted on the oocyte or embryo before recovery from the uterus 7 days after insemination.

Risk factors and the economic impact of ovarian cysts on reproductive performance of dairy cows in Korea

The objectives of this study were to determine the risk factors for development of postpartum ovarian cysts by evaluating several reproductive factors in individual cows, and to determine the economic impact of ovarian cysts on subsequent reproductive performance in dairy herds in Korea. The data, including cow parity, abnormal puerperium, endometritis, body condition score (BCS), and breeding status were collected from 634 cows in 9 dairy herds. We used logistic regression to evaluate the effects of these factors on ovarian cysts. A stepwise procedure, used to obtain the appropriate model with alpha=0.05, revealed that cow parity was the most important risk factor for ovarian cyst development within 8 weeks postpartum, while development of endometritis and BCS loss>or=1 from the dry period to 8 weeks postpartum were the most important risk factors for ovarian cyst development beyond 8 weeks postpartum. The occurrence of ovarian cysts beyond 8 weeks postpartum prolonged (P<0.01) the mean intervals from calving to first service (27 days) and conception (77 days), and increased (P<0.05) the culling rate (7.8%), while ovarian cyst development within 8 weeks postpartum did not affect (P>0.05) the mean intervals from calving to first service and conception or the culling rate. The economic loss resulting from the occurrence of ovarian cysts was estimated at approximately 823,996 won ($687) due to effects on the cost of nutrition, average growth of calves, labor and medical costs, and culling. These results suggest that cow parity is correlated with the development of ovarian cysts within 8 weeks postpartum, and endometritis and BCS loss>or=1 from the dry period to 8 weeks postpartum are correlated with the development of ovarian cysts after 8 weeks postpartum, which decreases reproductive performance and results in economic loss in dairy herds in Korea.

Effects of Urea Infusion on the Uterine Luminal Environment of Dairy Cows

Previous research indicates that high plasma urea nitrogen (PUN) concentrations are associated with decreased fertility in lactating dairy cows. The objective of this study was to monitor changes in the uterine environment during acute elevation of PUN. Lactating dairy cows (n = 8) were infused with saline or urea (0.01 g of urea/h per kg of body weight) through jugular vein catheters on d 7 after estrus. After 24 h, cows were switched to the opposite treatment for a second 24-h infusion period. Blood samples were collected every 2 h, and the pH within the lumen of the uterine horn ipsilateral to the corpus luteum was recorded every 6 h. At the end of each 24-h infusion period, 30 mL of sterile saline was flushed into the uterine lumen and immediately retrieved. Mean PUN concentration increased from 16.6 +/- 1.3 mg/dL during saline infusion to 22.6 +/- 1.3 mg/dL during urea infusion. Uterine pH decreased during urea infusion from 7.08 +/- 0.07 at 6 h to 6.88 +/- 0.08 at 18 h, but was unchanged during saline infusion (7.01 +/- 0.08 at 6 h to 7.06 +/- 0.07 at 18 h). Protein concentration, PGF(2alpha), and prostaglandin E(2) concentrations in uterine lavage samples were not different between treatments. The results of this study indicate that a short-term increase in PUN can exert direct effects on the uterine environment by decreasing uterine pH.

Relationship between milk urea concentration and the fertility of dairy cows

The relationship between milk urea concentration and the fertility of dairy cows was examined in two studies. The first examined the relationship between bulk milk urea concentration and overall herd fertility, using data collected from 250 herds in the UK. There was no relationship either between bulk milk urea concentration and fertility, or between changes in bulk milk urea concentration and fertility. The second study compared the relationship between the milk urea concentration five days after service, and the fertility of individual cows on 11 UK dairy farms. There was no significant difference between the milk urea concentration of the cows that became pregnant and those that did not.

Milk urea nitrogen and infertility in Florida Holstein cows

The objective of this study was to evaluate the association between milk urea nitrogen (MUN) and risk of nonpregnancy after first breeding in a commercial dairy herd in Florida. A total of 515 and 558 cows were classified as having high (17 to 25 mg/dl) or low MUN (6 to 16 mg/dl) within 30 d before first breeding; a total of 158 (30.6%) and 189 (33.8%) cows were diagnosed as pregnant, respectively. Logistic regression was used to evaluate the association between MUN and risk of nonpregnancy controlling for other variables associated with fertility (parity, calving season, breeding season). An interaction was found showing that cows with high MUN that were bred during the summer were 18 times (OR = 17.9; 95% CI = 10.0 to 31.7) at higher risk of nonpregnancy compared to cows with low MUN that were bred during the winter.

Evaluation of the effect of GnRH on follicular ovarian cysts in dairy cows using trans-rectal ultrasonography

The objectives of this study were to evaluate ovarian changes in cows with follicular ovarian cysts following treatment with either GnRH or saline. The parameters determined were the intervals from treatment to observation of a CL and from treatment to disappearance of the cyst, and the association between serum concentrations of LH, FSH and the LH/FSH ratio, before and after treatment, with the test intervals. Thirty-nine cows were identified as having follicular cysts. The GnRH treatment induced a significant increase in LH and the LH/FSH ratio. The gonadotropin response was not associated with the intervals from treatment to CL detection or to disappearance of the cyst. Survival curves for the intervals from treatment to CL detection and cyst disappearance indicate that treatment with GnRH or saline did not yield significantly different results for either parameter. The results question the efficacy of treating cystic ovarian disease with GnRH.

Review: effect of protein nutrition on ovarian and uterine physiology in dairy cattle

Milk production and dry matter intake of dairy cows are stimulated in response to increased intake of dietary protein, but, unfortunately, decreased fertility is often associated with this nutritional strategy. Ruminally degradable protein or ruminally undegradable protein in excess of requirement can contribute to reduced fertility in lactating cows. Dietary protein nutrition or utilization and the associated effects on ovarian or uterine physiology have been monitored with urea nitrogen in plasma or milk; concentrations above 19 mg/dl have been associated with altered uterine pH and reduced fertility in dairy cows. The uterine pH changed dynamically and inversely with plasma urea nitrogen, signaling possible changes in the uterine milieu. Mechanisms for reduced fertility include exacerbation of negative energy balance and reduced plasma progesterone concentrations when cows were fed rations that were high in ruminally degradable intake protein. Alternatively, changes in uterine secretions that are associated with high protein intake and elevated plasma urea nitrogen might be detrimental to embryos. Bovine endometrial cells in culture respond directly to increasing urea concentrations with alteration in pH gradient but respond most notably with increased secretion of prostaglandin F2 alpha (PGF2 alpha). Increased uterine luminal PGF2 alpha interferes with embryo development and survival in cows, thus providing a plausible link between elevated plasma urea nitrogen concentrations and decreased fertility. Poor fertility in high producing dairy cows reflects the combined effects of a uterine environment that is dependent on progesterone and rendered suboptimum by the antecedent effects of negative energy balance or postpartum health problems and that is further compromised by the effects of urea resulting from intake of high dietary protein.

Indications and implications for testing of milk urea in dairy cattle: A quantitative review. Part 2. Effect of dietary protein on reproductive performance

DIETARY PROTEIN AND DAIRY COW FERTILITY: Feeding more dietary protein has been negatively associated with dairy cow fertility in some but not all studies. We used meta-analysis to examine the relationship between dietary crude protein and conception rate. While a higher intake of dietary crude protein significantly lowered conception rate, the potential for feeding less degradable dietary protein to modify this relationship was not demonstrated. MILK UREA CONCENTRATIONS AND DAIRY COW FERTILITY: The use of milk urea as an indicator of dietary energy and protein intake and as an indicator of reproductive performance has been questioned. We found that changes in urea concentration in body fluids explained only 25% (p = 0.08) of the variance in conception rate after conducting a meta-analysis of available studies. INTERPRETATION OF MILK UREA CONCENTRATIONS: High intakes of dietary protein may induce adaptations in urea metabolism, and the negative relationship identified between high intakes of dietary protein and fertility for Northern Hemisphere dairy herds may not necessarily apply in Australasian dairy herds. Because of the potential for cows to adapt to high protein diets, the use of a single milk urea determination on a herd will have limited value as an indicator of nutritional status and little value as a predictor of fertility.

Protein degradability and calcium salts of long-chain fatty acids in the diets of lactating dairy cows: reproductive responses

Multiparous Holstein cows (n = 45) were assigned at calving to one of four diets arranged in a 2 x 2 factorial design. The two main factors were dietary concentration (dry matter basis) of 1) degradable intake protein (11.1 or 15.7%) and 2) supplemental fat (Ca salts of long-chain fatty acids; 0 or 2.2%). Soybean meal and urea were replaced with less degradable protein meals (corn gluten meal, meat and bone meal, fish meal, and blood meal). During the first 9 wk postpartum, cows fed diets containing the greater concentration of highly degradable protein demonstrated less follicular development on their ovaries, were delayed in their first luteal activity postpartum (25.2 vs. 38.6 d), accumulated less luteal tissue (< 15 vs. > 70 mm), and had lower plasma progesterone accumulated over time. The supplementation of Ca salts of long-chain fatty acids to the 15.7% degradable protein diet doubled the number of corpora lutea, reduced time to first rise in progesterone by 6 d, doubled the number of normal luteal phases, and restored the pattern of accumulated plasma progesterone concentrations to a pattern that was similar to that induced by other diets. Cows were synchronized to estrus and inseminated at approximately 65 d postpartum. Pregnancy rate was increased from 52.3 to 86.4% when fat was supplemented. Cows fed fat tended to have more corpora lutea and a larger corpus luteum and accumulated more plasma progesterone than did cows not fed fat. Diets containing excess degradable protein or Ca salts of long-chain fatty acids influenced ovarian structures and reproductive performance.

Dietary excesses of urea influence the viability and metabolism of preimplantation sheep embryos and may affect fetal growth among survivors

In the first of two experiments investigating the effect of dietary urea on the survival and metabolism of ovine embryos, 30 Border Leicester x Scottish Blackface ewes received a maintenance diet (milled hay, molasses, minerals, vitamins) with no urea (control, C; n = 10) or with added urea at 15 g (low urea, LU; n = 10) or 30 g (high urea, HU; n = 10) kg-1 feed for a 12 week period. The degraded nitrogen (N) status relative to estimated rumen microbial N requirements was -2, +9 and +20 g per day, respectively. One week after allocation to diets, progesterone priming (12 days) commenced. Ewes received 800 IU of equine chorionic gonadotrophin at progesterone withdrawal, were inseminated 52 h later (Day 0) and embryos were collected from five ewes per group at Day 4 and from five ewes at Day 11. If available, one embryo was returned to each ewe; the rest were cultured in vitro. There was no effect of treatment on progesterone, luteinizing hormone (LH), or time of oestrus onset C, LU and HU plasma urea (P < 0.001) and ammonia levels (C vs. HU, P < 0.01; LU vs. HU, P < 0.05) differed. Day 4 HU embryos were retarded relative to C and LU embryos. After 3 days of culture, 70%, 66% and 0% of C, LU and HU embryos, respectively, were viable. Mid-term pregnancy rates following transfer were 63%, 43% and 33%. Only one HU lamb (male) was born following embryo transfer, its birthweight (10.1 kg) exceeded that of its C (n = 3; 7.0, 7.0, 7.5 kg) and LU (n = 2; 7.3, 8.2 kg) counterparts (P < 0.025). In the second experiment, C2 (2.5 g urea kg-1; n = 5) and HU2 (30 g kg-1; n = 7) diets which provided similar intakes of degraded N relative to microbial requirements as those for C and HU ewes in Experiment 1 were fed to Border Leicester x Scottish Blackface ewes superovulated with 16 mg of porcine follicle-stimulating hormone. Urea and ammonia levels in utero-oviductal samples were elevated in HU2 ewes (P < 0.05). At collection (Day 3), HU2 embryos used more glucose (P < 0.01) and, following culture, some exhibited up to a 2.8-fold increase in metabolism. In conclusion, excess rumen degradable N in ewe diets elevates urea and ammonia in plasma and in utero, with an associated increase in embryo mortality. Nevertheless, metabolism appears to be up-regulated in some embryos and, among those that survive, fetal growth appears to be enhanced.

Effects of excess degradable protein on postpartum reproduction and energy balance in dairy cattle

The objectives of this study were to observe endocrine and reproductive responses of cows and heifers fed two diets (16 and 19% CP), which met undegradable protein requirements but differed in rumen degradable protein. Cows (n = 33) and heifers (n = 32) were randomly assigned within parity to diets at calving and remained on diets for 20 d after first breeding. Energy balance was determined twice weekly through the first luteal phase. Blood and milk samples were taken three times per week. Diet did not affect average daily energy balance, days to negative energy balance nadir, days to first ovulation, days to first service, or plasma glucose concentrations. First service conception rate was lower (31% vs. 48%) and plasma urea higher in animals fed the high protein diet. Days to energy balance nadir was correlated with days (r = .75) to first ovulation. Luteinizing hormone pulse frequency increased and pulse amplitude decreased in frequent samples (12-min intervals for 8 h) collected at 14 d postpartum versus sampling after the energy balance nadir. These data suggest that energy balance status plays an important role in determining the postpartum return of cyclic ovarian activity. Feeding excess CP as rumen degradable protein elevated plasma urea concentrations and decreased first service conception rate.

Effect of dietary protein and exogenous gonadotropin-releasing hormone on circulating progesterone concentrations and performance of Holstein cows

Sixty-three Holstein cows were used in a 2 x 2 factorial arrangement of treatments to determine the effects of dietary protein and exogenous gonadotropin-releasing hormone on performance postpartum and on circulating concentrations of progesterone. The experimental diets, 14 or 20% CP (dry basis), were fed from parturition to 14 wk postpartum. Blood serum urea N was elevated in the cows fed the 20% versus 14% CP diet. Feed intake was increased, but yield and composition of milk were not affected by the higher protein diet. Circulating concentrations of progesterone were lower in cows fed 20% than 14% protein on d 12 of both the synchronized and subsequent estrous cycles. Exogenous gonadotropin-releasing hormone administered on d 12 of the preceding estrous cycle did not increase the concentration of progesterone on d 12 of the subsequent estrous cycle. Luteal phase concentrations of progesterone were reduced by high dietary protein, but were not affected by gonadotropin-releasing hormone given on d 12 of the preceding cycle.

Effects of breed and wintering diet on growth, puberty and plasma concentrations of growth hormone and insulin-like growth factor 1 in heifers

Twenty-five Brangus (BR) and 15 Angus (AN) heifers were used to study the effects of breed and wintering diet on average daily gain (ADG), onset of puberty and plasma concentrations of growth hormone (GH) and insulin-like growth factor 1 (IGF-1). Wintering diets (fed for 107 days beginning November 15) consisted of the following: 1) native grass hay (NGH), 2) ammoniated NGH, 3) NGH plus cottonseed meal, 4) Diet 3 plus corn and 5) Diet 4 plus monensin. After wintering, heifers were transferred to ryegrass pasture for 70 days. Mean ADG during the wintering phase were -.20, -.10, .17, .29 and .39 kg for heifers fed Diets 1 through 5, respectively (P less than .01). ADG was greater (P less than .05) for BR than for AN heifers. Plasma concentrations of GH were higher (P less than .05) in heifers fed Diets 1 and 2 than in heifers fed Diets 3, 4 or 5. Plasma concentrations of IGF-1 were lowest in heifers fed Diet 1 and highest in heifers fed Diets 4 and 5. During ryegrass grazing, GH concentrations were similar for all groups. However, concentrations of IGF-1 were higher (P less than .05) in heifers fed Diets 3, 4 and 5 than in heifers fed Diets 1 and 2. Age at puberty (onset of cyclic progesterone concentrations) was greatest in heifers fed Diet 1 and lowest in heifers fed Diet 5. Weight at puberty was not affected (P greater than .10) by wintering diet but was greater (P less than .01) in BR than in AN heifers. Therefore, negative ADG appears to be associated with elevated plasma GH concentrations in heifers, and plasma IGF-1 concentration appears to be a more accurate indication of nutritional status than plasma concentrations of GH.

A farming systems study of abortion in dairy cattle on the Atherton Tableland. 4. Pasture composition and plasma progesterone concentrations of pregnant cows in affected herds

To provide more evidence for an apparent association between immature, high protein pasture diets and abortion in dairy cows on the Atherton Tableland in tropical north Queensland, pastures and cows on 4 farms were sampled on 5 occasions during a 7-month period. Pasture samples were analysed for dry matter (DM), protein, nitrate and fibre content. Plasma progesterone concentrations were determined in 18 to 20 pregnant cows. Fifty-four pasture samples (38 grass and 16 legume) were analysed and the distribution for 3 DM ranges was: 10% to 14.9% - 20 samples, 15% to 19.9% - 27 samples and 20% to 24.9% - 7 samples, while the distribution for 4 protein ranges was: 15% to 19% - 5 samples, 20% to 24% - 20 samples, 25% to 29% - 21 samples and 30% to 34% - 8 samples. Both pasture protein and DM content fluctuated with time. Pasture nitrate was low and insignificant while fibre (cell wall) levels appeared to be satisfactory for ruminant nutrition. Significant differences occurred between the mean plasma progesterone levels on 3 of the 4 farms. Raised levels in pregnant cows suggested the possibility of increased progesterone production in response to a previous low progesterone crisis or, alternatively, a decreased metabolic clearance rate of progesterone in pregnant cows on a declining plane of nutrition towards the end of the summer wet season. Progesterone data were not available from cows which previously aborted.(ABSTRACT TRUNCATED AT 250 WORDS)

Impact of protein nutrition on reproduction in dairy cows

In most but not all published studies, feeding diets with high concentrations of crude protein decreased reproductive efficiency. We were able to resolve some of the inconsistencies among published reports by considering the fate of consumed protein in the rumen and then using logistic regression analysis to identify factors affecting pregnancy. Our models showed that type and amount of protein fed explained much of the variation in conception rate. Age and dietary concentration of energy were identified as modifiers of the impact of protein on reproduction. Protein nutrition can affect reproduction through toxic effects of ammonia and its metabolites on gametes and early embryos, through deficiencies of amino acids, and by exacerbations of negative balances of energy. Alterations in the hypothalamic-hypophyseal-ovarian axis may be responsible for many of the effects of protein on reproduction.

Interactions of nutrition and reproduction

As dairy cattle achieve higher milk production, we are becoming aware of closer relationships between nutrition and fertility. An increasing body of evidence indicates that excessive protein intake in early lactation may be detrimental to postpartum fertility. In addition, protein solubility and degradability are important. Energy restriction in high producing cows may be detrimental to fertility through its effect on hypothalamic and ovarian function. Dairy producers are susceptible to advertisements advocating the addition of specific vitamins and minerals to the rations of high producing cows since inadequate or excessive quantities may be detrimental to fertility. This is particularly true for minerals. However, high producing cows do not usually receive grossly inadequate or excessive dietary sources of vitamins and minerals. Rather, they may be presented with a borderline intake of several vitamins and minerals, which together may be detrimental to fertility. Finally, new methods must be developed to provide a more sensitive indication of fertility. These are some of the research and educational needs of the dairy industry if it is to continue successfully increased milk production. Predictions of herd averages of 16,000 kg milk and individual records exceeding 30,000 kg have been made for the yr 2000.

Influence of protein intake and feeding strategy on reproductive performance of dairy cows

A study was conducted to determine the impact of dietary CP concentration (13 vs. 20%) and feeding strategy (total mixed ration vs. separate feeding of the forage and concentrate) on reproductive performance of 57 early lactation dairy cows. Cows were assigned to one of four treatments in a 2 x 2 factorial arrangement. Rations composed of 40% forage (50% grass-legume silage:50% corn silage) and 60% concentrate (DM basis) were fed from d 5 to 100 postpartum. Cows fed a total mixed ration had lower ruminal ammonia and plasma urea N concentrations compared with cows fed separately. Feeding strategy groups showed no differences in reproductive performance. Cows fed a 20% CP ration had higher CP intake, higher ruminal ammonia, and higher urea N concentration in plasma and vaginal mucus. There were no differences between low and high CP groups in days to first observed estrus (24 vs. 27), days to first service (55 vs. 59), days open (72 vs 82) or services per conception (1.5 vs. 1.8). Days to first estimated ovulation were longer (22 vs. 17) in the high vs. low CP groups, and there was an interaction between protein intake and lactation number. Cows managed with an intensive program for detection of estrus and for reproductive health did not show differences in reproductive efficiency when fed 13 or 20% CP rations.

Effects of nutrition on reproduction in dairy cows

It is clear that nutrition is closely related to reproduction in the dairy cow. In addition to classic nutrient deficiency and excess, dry cow body condition and postpartum energy balance have a major impact on fertility. Dry cow rations must be designed to prevent milk fever, dystocia, retained placenta, other calving problems, and metritis. Most importantly, milk yield and reproductive performance should be regularly monitored to detect nutritionally associated health and performance changes that precede impairment of reproductive function.

Influence of dietary protein on reproductive performance of dairy cows

From 10 +/- 3.5 d after parturition to 149 +/- 3.5 d of lactation, 146 cows (109 Holstein and 37 Ayrshires) were fed either a 15 or 20% crude protein diet of 45% sorghum silage and 55% concentrate. Milk production was enhanced by the 20% protein diet, but percentage of milk fat and protein were unchanged. Average daily intake of DM was unaffected by diet. Actual decreases in body weight and condition were small, although cows on 15% protein lost more condition. Concentration of plasma urea nitrogen increased rapidly during the first 4 wk of the experiment with cows on the 20% protein diet maintaining a 10 mg/dl advantage after the 4th wk on experiment. Diet did not affect the postpartum interval to first normal corpus luteum and standing estrus. Cows were inseminated artificially between 55 and 145 d post-calving with one freeze batch of semen from one bull of each appropriate breed mainly by one inseminator. Overall, days open, services per conception, and percentage cows pregnant on experiment were 80, 1.40, and 85, respectively. Concentration of protein in the diet did not affect these reproductive traits. There was no conflict between the amount of dietary protein provided for lactation and reproduction in this experiment.

Effect of high crude protein on pituitary and ovarian function in Holstein cows

Intact and ovariectomized cows were used to determine the effect of high amounts of dietary crude protein on pituitary regulation of luteinizing hormone. Estrus was synchronized with prostaglandin F2 alpha in 10 intact dry cows fed 15 or 25% crude protein, and serum luteinizing hormone profiles were evaluated during both follicular and luteal phases of the estrous cycle. Serum progesterone, pituitary luteinizing hormone content, and luteinizing hormone-releasing hormone receptors were also measured. Basal concentrations of serum luteinizing hormone tended to be lower during the follicular phase and were significantly higher during the luteal phase in cows fed 25% crude protein. Serum progesterone was not affected by dietary treatment. In 10 ovariectomized cows fed 24% crude protein, amplitude of luteinizing hormone response to luteinizing hormone-releasing hormone challenge tended to be smaller than that of 8 cows fed 16% crude protein, although total luteinizing hormone released in response to luteinizing hormone releasing hormone challenge was not different between dietary treatments. In both intact and ovariectomized cows, pulsatile luteinizing hormone patterns, pituitary luteinizing hormone content, and luteinizing hormone-releasing hormone receptors were not influenced by treatment. High dietary crude protein did not have a primary effect on luteinizing hormone or progesterone in nonlactating cows.

Relationship of dietary crude protein to composition of uterine secretions and blood in high-producing postpartum dairy cows

Effects of dietary crude proteins on constituents of plasma and uterine secretions were examined at various stages of the estrous cycle of high producing Holstein cows. Eighteen cows were assigned randomly to isocaloric diets (74% total digestible nutrients) containing either 12 or 23% crude protein (dry matter) on day 40 postpartum. Uterine secretion and coccygeal blood samples were collected at estrus, days 5 and 15 of the first estrous cycle after day 50 postpartum, and at the subsequent estrus. The 23% crude protein diet resulted in higher concentrations of ammonia in blood, urea in blood plasma and uterine secretion, and phosphorus and potassium in plasma. Zinc increased during the estrous cycle in plasma of cows fed 23% crude protein and decreased in cows fed 12% crude protein. Magnesium concentrations in uterine secretions were lower in cows on 23% crude protein. Potassium and phosphorus also were lower in uterine secretions of cows fed 23% crude protein but only during the luteal phase of the estrous cycle. Zinc concentrations in uterine secretions decreased faster during the estrous cycle in cows fed 12% crude protein than in cows fed 23% crude protein. Thus, the crude protein content of the diet altered concentrations in blood of ammonia and concentrations in plasma of urea, phosphorus, potassium, and zinc. Crude protein content of the diet altered concentrations in uterine secretion of urea, magnesium, potassium, phosphorus, and zinc.

The effect of dietary and climatic factors on fertility, and on plasma progesterone and oestradiol-17 beta levels in dairy cows

The effects of high dietary protein concentrations, high ambient temperatures and low dietary beta-carotene levels on fertility and on plasma progesterone and oestradiol-17 beta levels in high-yielding dairy cows, are described. High-yielding dairy cows were fed diets containing 15 or 20% crude protein. Cows fed the higher level of protein were less fertile and had a lower plasma progesterone concentration during the oestrous cycle preceding the first insemination. This phenomenon was especially pronounced in cows fed a diet containing 85% concentrates and 15% hay, where plasma progesterone levels during days 9-17 of the oestrous cycle were 2.5-3.7 ng/ml in cows fed the high level of protein and 4.0-5.5 ng/ml in cows fed the low level of protein (P less than or equal to 0.05). In cows fed 50% more energy before parturition, plasma progesterone levels did not differ between animals fed the low and high protein diets. Heat stress, which caused a rise in body temperature, decreased fertility and plasma progesterone levels during the luteal phase of the oestrous cycle but increased plasma oestradiol-17 beta levels during the 36 h preceding the onset of oestrus from 5 to 7 pg/ml (P less than or equal to 0.005). The effect on fertility of supplementing the diet of dairy heifers and cows with beta-carotene is reviewed. In some of the experiments where the basal plasma beta-carotene levels were lower than 50 micrograms/100 ml, beta-carotene supplementation significantly increased fertility. However, in no case was fertility affected when plasma beta-carotene levels exceeded 150 micrograms/100 ml. The possible relationships among body weight changes, energy balance, plasma progesterone levels and fertility of dairy cows are discussed.