Effect of timing of urea feeding on the yield and quality of embryos in lactating dairy cows

High protein diets, which lead to excess production of nonprotein nitrogen such as ammonia and urea, have been associated with reduced fertility in dairy cows. In this study we test the hypothesis that diets containing high levels of quickly degradable urea nitrogen (QDN) compromise embryo development. Lactating dairy cows were fed mixed silage and concentrates twice daily. At 60 days postpartum, a synchronized estrus was induced and the cows were subsequently superovulated and inseminated using a standard protocol. On Day 7 after insemination, the uteri were flushed and embryos retrieved. At the start of treatment, cows were randomly allocated into three nutritional groups: control (CONT, n = 8), long (L-) QDN (n = 8) and short (S-) QDN (n = 9). The L-QDN cows were fed a supplement of urea from 10 days before insemination, and the S-QDN cows were fed the supplement from insemination until embryo collection. Both L- and S-QDN diets produced significant increases in plasma ammonia and urea 3 h post-feeding. The S-QDN but not the L-QDN diet was associated with a significant reduction in embryo yield. Embryo quality was also significantly reduced in the S-QDN cows. This study indicates that there is no deleterious effect on the yield and quality of embryos recovered 7 days after breeding when QDN feeding is initiated during the previous midluteal phase. However, introduction of a similar diet 10 days later, at the time of insemination, was deleterious. We suggest that QDN is toxic to embryos but cows can adjust within 10 days.     

The effect of a diet containing excess quickly degradable nitrogen (QDN) on reproductive and metabolic hormonal profiles of lactating dairy cows

The objective of this experiment was to examine the effects of an excess intake of quickly degradable nitrogen (QDN) on metabolic and reproductive parameters in lactating dairy cows. Twenty-two lactating dairy cows were fed a total mixed ration once daily. The control diet was a typical ration for high producing cows in the UK (CP = 17.5%, ME = 11.8 MJ/kg DM). The cows were randomly divided into two groups, control diet (control; n = 12) and excess QDN diet (QDN; n = 10). The QDN group was fed an additional 250 g of urea per cow per day, from 10 days before insemination (day 0) until the end of the experiment, 17 days after the second insemination. Ten days before insemination, a synchronized oestrus was induced and the cows inseminated twice, 48 and 72 h after synchronization, with commercial frozen semen from a single sire. Ovaries were scanned using B-mode ultrasonography 10 days before insemination and then daily from 3 days before insemination. Eighteen of the cows (9 control and 9 QDN) were sampled more intensively to determine the pulsatile pattern of secretion of luteinizing hormone (LH) and growth hormone (GH). Cows were slaughtered 17 days after insemination, the reproductive tracts recovered and flushed to retrieve embryos. The excess QDN diet resulted in elevated (P < 0.05) plasma urea concentrations 3 days after starting urea feeding and these were maintained until the end of the experiment. However, the excess QDN diet did not significantly affect daily milk production or plasma concentrations of insulin and IGF-I. The QDN treatment did not significantly affect pulsatile patterns of secretion of LH and GH or the number of small (< 0.5 cm diameter) and medium to large follicles (> 0.5 cm diameter). Twenty cows ovulated following synchronization (control 11/12; QDN 9/10). There were no significant differences between the control and the QDN groups in the peak concentrations of oestradiol during the follicular phase or in the post-ovulatory pattern of plasma and milk progesterone secretion. Embryos and/or foetal membranes were recovered from 10 cows (5 control and 5 QDN). The results of the current study show that feeding excess QDN, as urea, for 27 days commencing 10 days before insemination had no effect on reproductive or metabolic hormonal parameters. Ovulation and the formation and function of the post-ovulatory corpus luteum were also unaffected by excess QDN. These data suggest that the harmful effects of excess intakes of QDN on fertility occur after 17 days following ovulation.     

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.     

Corpus luteum function and pregnancy rate in lactating dairy cows given human chorionic gonadotropin at middiestrus

The effect of human chorionic gonadotropin (HCG) on corpus luteum (CL) function in lactating dairy cows and its subsequent effect on pregnancy rates achieved with artificial insemination was studied in two parts. In Part 1, four IM injections at intervals of seven days or two IM injections at a 14 day interval of HCG (10,000 IU) were given to two groups of six cows each, groups A and B respectively, beginning on days 9, 10 or 11 of the estrous cycle. Ten control cows were given 10 ml of isotonic saline solution on days 9, 10 or 11. Interestrous intervals were prolonged by an average of 8.1 and 3.4 days for groups A and B respectively over controls. In Part 2, 200 lactating dairy cows on nine farms were assigned, on an alternate basis at insemination, to control or treatment groups to study the effect of CL prolongation via HCG on pregnancy rate. A single injection of HCG (10,000 IU) was given 10, 11 or 12 days after a first or second insemination. Pregnancy rates for control and treated cows were similar (64 101 = 63% and 58 99 = 59% respectively). Interestrous intervals of treated nonpregnant cows were prolonged by approximately five days. Providing additional time for developing embryos to become established in utero by delaying luteolysis did not improve pregnancy rates achieved with artificial insemination in lactating dairy cows.     

The effect of roughage to concentrate ratio in the diet on nitrogen and purine metabolism in dairy cows

Four lactating dairy cows were used in two experiments to study the effects of the roughage to concentrate ratio in the diet on nitrogen balance, plasma urea, urinary urea, milk urea and urinary purine derivatives. The use of the allantoin to creatinine ratio in spot samples of urine as an index of the urinary allantoin excretion was also evaluated. Four isoenergetic and isonitrogenous diets were formulated according to a 2 × 2 factorial arrangement. Factor I was concentrate content. The roughage to concentrate ratios were 65:35 and 35:65 for the high roughage and high concentrate diets, respectively. Factor II was fat content, which was 2.8% and 5.8% for the low and high fat diets, respectively. In Experiment 1 cows were fed diets with low fat content, and in Experiment 2 cows were fed diets with high fat content. In both experiments, diets were fed according to a change-over design. Nitrogen balance was not affected by the treatments. In cows fed high concentrate diets the amount and the proportion of nitrogen excreted in milk, as well as milk production was higher than in cows fed the high roughage diets. In both experiments, as an overall effect, the urea levels in plasma, urine and morning milk were higher, although the total urinary excretion of urea was lower, for the high concentrate diets. Urinary allantoin excretion was higher, although not significantly in Experiment 1, for the high concentrate diets. The allantoin to creatinine ratio in spot samples of urine showed the same pattern as the total allantoin excretion. Urinary creatinine excretion appeared to be affected by the diet.     

Preovulatory follicular status and diet affect the insulin and glucose content of follicles in high-yielding dairy cows

Insulin and glucose may be limiting factors for ovarian function in dairy cows genetically selected for high milk yield. The effects of nutrition on the intrafollicular content of insulin and glucose were investigated in Israeli Holstein dairy cattle fed a basic total mixed ration and producing 34-39kg of milk daily. In experiment 1, carried out in 11 oestrus-synchronised cows, little variation in insulin concentration was found in plasma sampled during the luteal phase, but high variation was found in plasma sampled during the follicular phase. Therefore, in order to prevent confounding the effects of diet and of phase in cycle in the following experiments, experimental diets were fed during the luteal phase of synchronised oestrus cycles. In experiment 2, designed as Latin-Square, six cows received sequentially diets containing 17.1 (control) or 19.7% of crude protein, using two sources of supplementary protein, i.e. soyabean meal (SBM) and corn gluten meal (CGM), differing in ruminal degradability and leucine content. When dry matter intake was used as covariant, plasma insulin on day 16 was 29.5 and 26.4% higher in cows fed diets containing SBM and CGM than in the control (P<0.05). In experiment 3, 17 cows were individually fed the basic diet and then switched to isoenergetic diets containing SBM (n=5), CGM (n=6) or corn grain (CG, n=6) given from day 10 to 16 of the synchronised oestrus cycle. On the eve of day 16, and in the morning of day 17, they were administered PGF(2alpha) and the content of 26 largest follicles was aspirated by using the transvaginal ovum pick-up technique. Follicles were sorted into two classes (preovulatory and subordinate) according to oestradiol concentration and the progesterone:oestradiol ratio in follicular fluid (FF). Higher concentrations of insulin (0.282 versus 0.127ng/ml, P<0.0001) and of glucose (0.614 versus 0.386g/l, P<0.002), were found in FF from preovulatory follicles. The insulin concentration in the FF of cows fed the CG diet was 26% higher than in their counterparts fed CGM (P<0.04), SBM being intermediate. Dietary effects did not reach significance in subordinate follicles.The finding that preovulatory follicular status is associated with increased intrafollicular insulin and glucose suggests that insulin is involved in follicular maturation. The nutritional effect on intrafollicular glucose and insulin may have practical implications to optimise feeding in dairy cows during phases of the oestrus cycle.     

Association between blood plasma urea nitrogen levels and reproductive fluid urea nitrogen and ammonia concentrations in early lactation dairy cows

Two experiments were conducted to study the relationship of blood plasma urea nitrogen (PUN) concentrations with NH3, urea nitrogen, K, Mg, P, Ca, and Na concentrations in fluid of preovulatory follicles (experiment 1) and the relationships of PUN concentration and stage of estrus cycle with ammonia and urea nitrogen concentrations in uterine fluids (experiment 2) in early lactation dairy cows. Mean PUN levels were used to distribute cows into two groups: cows with PUN>or=20 mg/dl (HPUN), and cows with PUN<20 mg/dl (LPUN). In experiment 1, blood and follicular fluids from preovulatory follicles of 38 early lactation dairy cows were collected on the day of estrus (day 0) 4h after feed was offered. Follicular fluid NH3 was higher (P<0.01) in HPUN cows (339.0 micromol/L+/-72.2) compared to LPUN cows (93.9 micromol/L+/-13.1). Follicular fluid urea N was higher (P<0.001) in HPUN cows (22.4 mg/dl+/-0.4) compared to LPUN cows (17.0 mg/dl+/-0.3). PUN and follicular fluid urea N were correlated (r2=0.86) within cows. In experiment 2, blood and uterine fluids were collected from 30 cows on day 0 and on day 7. Uterine fluid NH3 was higher (P=0.05) in HPUN cows (1562 micromol/L+/-202) than in LPUN cows (1082 micromol/L+/-202) on day 7, but not on day 0. Uterine fluid urea N was higher (P<0.001) in HPUN cows than in LPUN cows on day 0 (26.9 mg/dl+/-1.3 and 20.4 mg/dl+/-0.7) and day 7 (26.5 mg/dl+/-1.1 and 21.4 mg/dl+/-1.1). There was a correlation (r2=0.17) between PUN and uterine fluid urea N within cows. The results of this study indicate that high PUN concentrations were associated with elevated NH3 and urea N concentrations in the preovulatory follicular fluids on the day of estrus and in the uterine fluid during the luteal phase of the estrous cycle in early lactation dairy cows. Elevated NH3 or urea N concentrations in the reproductive fluids may contribute to reproductive inefficiency in dairy cows with elevated plasma urea nitrogen due to embryo toxicity.     

On the effects of the concentrate proportion of dairy cow rations in the presence and absence of a fusarium toxin-contaminated triticale on cow performance

The aim of the present study was to investigate the effects of a deoxynivalenol (DON) contaminated ration with a concentrate proportion of 50%, on the performance of dairy cows (Period 1), and to examine the effects when the concentrate proportion was elevated to 60% compared to a ration with 30% concentrates (Period 2). In Period 1, 13 lactating German Holstein cows (Myco group, on average 29 days in milk) were fed the experimental diet (on average 5.3 mg DON/kg DM) as total mixed ration over 11 weeks, while another 14 cows (on average 33 days in milk) received a control diet. Both rations contained 50% concentrates (on DM basis). In Period 2 (18 weeks), the same 27 cows plus five additional cows were divided into four groups: Control-30 (30% concentrates), Myco-30 (30% concentrates, 4.4 mg DON/kg DM), Control-60 (60% concentrates), Myco-60 (60% concentrates, 4.6 mg DON/kg DM). The overall performance level was characterised by a mean daily DM intake of 17.9 kg and a mean daily milk production of 26.7 kg fat corrected milk (FCM) in Period 1 and 17.3 kg DM intake and 24.5 kg FCM in Period 2, respectively. In both periods cows fed the Fusarium toxin-contaminated diets consumed more DM (in Period 2 only significant for group Myco-30) resulting from stimulating effects on the ingesta passage rate of the natural contaminated Fusarium-infected triticale. In Period 1, cows fed the Fusarium toxin-contaminated diet had a significantly higher milk yield, milk urea and somatic cell count, whereas milk fat and protein concentration and fat-to-protein-ratio (FPR) were significantly lower. In Period 2, on a low concentrate level, FCM was significantly higher in group Myco-30. On a high concentrate level, group Myco-60 produced significantly more milk, but milk fat and protein concentration, FPR and milk urea were significantly lower. A concentrate proportion of 60% had a depressing effect on milk fat concentration but was significantly more pronounced in the presence of Fusarium toxin-contaminated and Fusarium damaged-triticale.     

Differential abundance of IGF1, bile acids,and the genes involved in their signaling in the dominant follicle microenvironment of lactating cows and nulliparous heifers

It is well documented that incidence of fertility problems is high in lactating cows but not in heifers of the same genetic merit. Understanding the metabolic and molecular differences between fertile heifers and relatively infertile lactating cows will help us understand the pathogenesis of infertility in dairy cows. Follicular waves in lactating cows (30–50 days in milk; n = 12) and heifers (n = 10) were synchronized by ultrasound-guided follicle ablation. Follicular fluid and granulosa cells of the dominant follicle were collected by ultrasound-guided aspiration along with blood sampling on Day 6 after synchronization. Dominant and subordinate follicles were larger in lactating cows than in heifers. Metabolic stress in lactating cows was evidenced by lower glucose and higher ß-hydroxy butyric acid compared with heifers. Insulin-like growth factor 1 signaling was reduced in the dominant follicle in lactating cows through reduced insulin-like growth factor 1 concentrations in plasma and follicular fluid of the dominant follicle, and reduced expression of pregnancy-associated plasma protein A (PAPPA) in their granulosa cells. We also found increased levels of total bile acids in the follicular fluid of the dominant follicle of lactating cows compared with heifers. Granulosa cells of the dominant follicle had higher expression of SLC10A2 and GPBAR1 (bile acid transporter and receptor, respectively) in lactating cows. These novel data are indicative of increased bile acid signaling within the dominant follicles of lactating cows compared with heifers. Overall, we demonstrate in the present study the metabolic, endocrine, and molecular differences within the microenvironment of the dominant follicles in lactating cows and heifers. These differences in follicular microenvironment may contribute toward abnormal ovarian function in lactating dairy cows.     

The potential interaction between body condition score at calving and dietary starch content on productive and reproductive performance of early-lactating dairy cows

Improving reproductive performance is one of the most important factors affecting the profitability of dairy herds. This study investigated the effect of feeding a high starch (HS) diet and body condition score (BCS) at calving on blood metabolites, fertility and ovarian function and milk production in Holstein dairy cows. One hundred seventy-four multiparous cows were fed common close-up and early lactation diets during the first 15 days in milk (DIM). Cows were randomly assigned to 1 of 2 experimental diets from 16 until 50 DIM (n = 87 per group); normal starch (228 g/kg diet DM; NS) or HS (270 g/kg diet DM; HS) diets. Each treatment group was further subdivided based on BCS at calving as normal BCS (BCS ⩽ 3.5; normal BCS (NBCS); n = 45) or high BCS (HBCS) (BCS ⩾ 3.75; HBCS; n = 42). A significant difference was detected for increased milk production (47.24 v. 44.55 kg/day) and decreased milk fat (33.93 v. 36.33 g/kg) in cows fed HS or NS, respectively. Plasma glucose and insulin concentrations were significantly higher in cows fed the HS compared to the NS diet. Diets significantly affected DIM at first artificial insemination (AI, 79.51 ± 3.83 v. 90.40 ± 3.83 days for cows fed HS and NS diets, respectively). High BCS groups had greater milk fat content and elevated plasma nonesterified fatty acids (NEFA), β hydroxybutyrate (BHB) and bilirubin concentrations. In general, feeding higher starch diets to normal BCS cows during the first 50 DIM improved productive and reproductive performance of early-lactating dairy cows.     

Effect of a prolonged release formulation of recombinant bovine somatotropin on plasma concentrations of hormones and metabolites, and milk production in dairy cows.

The effect of a prolonged release formulation of recombinant DNA derived bovine somatotropin (rbST) on the plasma concentrations of growth hormone (GH), insulin-like growth factor-I (IGF-I), insulin, glucose, blood urea nitrogen (BUN) and nonesterified fatty acids (NEFA), and milk production in lactating dairy cows was studied. Eight cows were divided into two equal groups. One group was the noninjected control, and cows in the other group received a single subcutaneous injection of 640 mg rbST. Plasma GH levels in the rbST-treated cows were higher than in the control cows for 10 days after the injection. Plasma IGF-I concentrations were significantly higher in the rbST-treated cows than in the control for 14 days after the treatment. In the rbST-treated cows, the plasma concentrations of insulin and glucose tended to be higher than those in the control until 7 days after the injection. Also, plasma NEFA levels were higher in the rbST-treated cows for 10 days. In contrast, plasma BUN levels were significantly lower in the rbST-treated cows for 17 days after the treatment. For 28 days after the injection, the mean daily milk yield in rbST-treated cows was 4.5 kg (21.2%) more than that in the control cows. In the rbST-treated cows, a highly positive correlation was observed between the mean daily milk yield and the mean plasma concentration of IGF-I throughout the postinjection period.(ABSTRACT TRUNCATED AT 250 WORDS)     

Progesterone supplementation during the early fetal period reduces pregnancy loss in high-yielding dairy cattle

It was hypothesized that sub-optimal progesterone concentrations during the late embryo and early fetal period may act to compromise conceptus development in dairy cattle. The aim of the present study was to test this hypothesis by supplementing pregnant cows with exogenous progesterone following pregnancy diagnosis. The study population consisted of 1098 pregnant lactating cows. Pregnancy was diagnosed by transrectal ultrasonography between 36 and 42 days after insemination. Animals found to be pregnant were randomly assigned to the Control (untreated cows, n = 549) or Treatment (n = 549) groups. Cows in group Treatment were fitted at pregnancy diagnosis with a progesterone releasing intravaginal device (PRID) containing 1.55 g of progesterone, for 28 days. Cows were then subjected to a further diagnosis by palpation per rectum on Day 90 of gestation. Pregnancy loss was registered in 95 (8.7%) cows on Day 90 of pregnancy: 66 (12%) in group Control and 29 (5.3%) in group Treatment. Logistic regression analysis indicated that there were no significant effects of herd, bull, milk production, service number, days in milk at pregnancy and lactation number. Based on the odds ratio, treated cows were 2.4 (1/0.41) times less likely to miscarry, whereas the risk of pregnancy loss was 1.6 times higher in cows that became pregnant during the warm period in comparison to the cool period. These results support the hypothesis that sub-optimal progesterone concentrations in high producer dairy cows may compromise conceptus development. Under these conditions, intra-vaginal progesterone supplementation has the potential to reduce the incidence of pregnancy loss during the early fetal period.     

Nutritional management of the donor cow

Nutrition of the donor cow can influence oocyte and embryo quality, which can affect the success of embryo transfer. Severe undernutrition compromised ovarian follicular development, with implications for superovulatory response and embryo quality. In postpartum lactating cows, undernutrition or inability to consume sufficient nutrients delayed resumption of ovulation, reduced the number of follicles, and compromised oocyte quality. Moderate undernutrition of nonlactating cows was unlikely to affect embryo quality; conversely, nonlactating animals on maintenance diets usually had better superovulatory responses and improved oocyte competence and embryo quality. The negative effects of overfeeding are thought to be mediated by alterations in endocrine cues, such as hyperinsulinemia and increased glucose and IGF-I, which may interfere with glucose transport in the embryo and increase apoptosis. Manipulating energy sources such as carbohydrates and fatty acids (FA) may influence embryo viability, but the effects of FA were not consistent in vitro; increasing concentrations of unsaturated FA in follicular and embryonic cells usually improved embryo viability and resistance to cryopreservation. Excess protein intake and increased urea and ammonia in body fluids can be toxic to embryos, impairing their development; these effects seemed to be associated with alterations in uterine pH and granulosa cell function. Likewise, toxins in feeds (e.g. gossypol), reduced embryo development and increased pregnancy losses. Diet of donor cows should be formulated to optimize the supply of nutrients to meet needs; however, manipulating energy intake, source of FA and protein content of donor diets, particularly moderate underfeeding in nonlactating cows, may further optimize responses.     

Effects of lowering crude protein supply alone or in a combination with essential oils on productivity,rumen function and nutrient utilization in dairy cows

Lowering dietary protein concentration is known to decrease urinary nitrogen (N) losses and increase milk N efficiency in dairy cows, but it may negatively affect animal productivity. Plant-derived essential oils (EO) may alleviate these negative effects by improving the efficiency of rumen fermentation in cows fed reduced feed protein diets. The experiment was conducted to investigate the effects of lowering crude protein (CP) supply alone or in a combination with an EO product on feed intake, milk production and composition, rumen fermentation, total tract digestibility and N utilization in dairy cows. Twenty-one Holstein cows were used in a replicated 3 × 3 Latin square design experiment. Each period consisted of 14 days for adaptation and 14 days for data collection and sampling. Cows were randomly assigned to one of three experimental diets: a 165 g/kg CP diet (control), a 155 g/kg CP diet (LCP) and LCP supplemented with 35 g/day per cow EO (LCPEO). The dry matter (DM) intake was decreased by LCP and LCPEO compared with the control; there was no effect of EO on DM intake. Milk yield and composition and feed efficiency were similar among treatments. Ruminal pH, lactate, ammonia and volatile fatty acids concentrations were not affected by treatment, except increased valerate concentration by LCPEO compared with LCP. The supplementation of EO tended to decrease protozoal counts. The LCP and LCPEO increased total tract digestibility of DM and organic matter and decreased CP digestibility compared with the control. Supplementation with EO did not affect total tract digestibility of dietary nutrients compared with the control or LCP. The LCP and LCPEO decreased urinary and fecal N excretions and increased milk N efficiency; nitrogen losses were not affected by EO. In this study, lowering dietary CP by 10 g/kg decreased urinary and fecal N excretion without affecting productivity. The supplementation of EO to LCP had only minor effects on rumen fermentation and did not affect productivity, digestibility and N excretion in lactating dairy cows.     

Effect of human chorionic gonadotrophin on dominant follicles in cows: formation of accessory corpora lutea, progesterone production and pregnancy rates.

Thirty-four lactating Holstein cows were randomly assigned to four groups for treatment with human chorionic gonadotrophin (hCG, 1000 iu) at insemination day 0 (n = 8) or 7 (n = 9) or 14 days (n = 9) after insemination or with no hCG treatment (control, n = 8). Ultrasound imaging of the ovaries and plasma progesterone measurements were carried out to determine follicular dynamics and corpus luteum growth and function. Rates of formation of accessory corpora lutea were higher among cows treated on days 0 (three cows), 7 (seven cows) or 14 (four cows) than in the controls (one cow). Total corpus luteum diameter was greater (P less than 0.01) among hCG-treated cows than in controls 7-42 days after insemination. Concentrations of progesterone in plasma were significantly (P less than 0.05) higher in cows treated with hCG on days 7 or 14 than in those treated on day 0 or in controls, at days 18, 35 or 42 after insemination. Seven of the cows treated on day 7 became pregnant, whereas four, four and three cows treated on days 0 or 14 and control cows became pregnant, respectively. The results suggest that hCG treatment at 7 days after insemination could be used to produce accessory corpora lutea, raise plasma progesterone concentration and hence reduce the incidence of early embryonic mortality in cattle.     

Effects of feeding propylene glycol on dry matter intake, lactation performance, energy balance and blood metabolites in early lactation dairy cows

The objectives of this study were to evaluate effects of feeding propylene glycol (PG) on feed intake, milk yield and milk composition, blood metabolites and energy balance in Holstein dairy cows from 1 to 63 days in milk. Thirty-two multiparous cows, blocked by lactation number, previous 305-day milk production and expected calving date, were arranged into four groups in a randomized block design. Treatments were: control, low PG, medium PG and high PG with 0, 150, 300 and 450 ml PG per cow per day, respectively. The supplement of food grade PG (0.998 g/g PG) was hand-mixed into the top one-third of the daily ration. Cows were fed ad libitum a total mixed ration consisting of forage and concentrate (50 : 50, dry matter basis). Feed intake, milk yield and milk components were not affected (P > 0.05) by PG supplementation. Overall, body weight (BW) loss tended (P < 0.08) to be linearly reduced, and energy status was linearly improved with increasing PG supplementation. Concentrations of glucose in plasma were higher for cows fed PG relative to control (55.6 v. 58.9 mg/dl) and linearly increased (P < 0.01) with increasing PG supplementation. Plasma concentrations of non-esterified fatty acids and beta-hydroxybutyrate were linearly increased, but urine acetoacetate concentration was quadratically changed with the highest for control diet and the lowest for 450 ml/day of PG. These results indicated that supplementation of PG in the early lactating cow diets had minimal effects on feed intake and milk production, but may potentially reduce contents of milk fat and milk protein. Supplementation of early lactating dairy cow diets with PG is beneficial in terms of improving energy status and reducing BW loss.     

Effect of eCG on early resumption of ovarian activity in postpartum dairy cows

The purpose of the present study was to hasten the resumption of ovarian activity early postpartum in lactating dairy cows, using equine chorionic gonadotropin (eCG), to enhance follicular growth, followed by hCG, to induce ovulation. Primiparous Holstein dairy cows (n=21) were assigned equally into eCG, eCG-hCG and Control groups. Cows in the eCG and eCG-hCG groups received an i.m. injection of eCG (500 IU Folligon?) on Day 6 postpartum. Cows in the eCG-hCG group were also given an i.m. injection of hCG (500 IU Chorulon?), once dominant follicle reached the diameter of 13-16 mm following eCG injection. Cows in Control group did not receive any treatment. Daily blood sampling and ultrasound examination were conducted, starting at Day 6 postpartum until confirming the third ovulation. Follicles ≥10 mm in diameter were detected on Day 11.5±1.48, 10.1±0.52 and 11.1±1.36 after calving in Control, eCG and eCG-hCG groups, respectively (P>0.05). The first wave dominant follicle ovulated in 71.4% of cows treated with eCG and eCG-hCG. In contrast, none of the first wave dominant follicles ovulated in Control cows. By Day 20 postpartum, all cows in eCG group, 6/7 cows in eCG-hCG group and none of the cows in Control group ovulated (P<0.05). Short estrous cycles (≤16 days) were detected in 2/7, 1/7 and 6/7 cows in eCG, eCG-hCG and control groups, respectively (P<0.05). In conclusion, injection of eCG on Day 6 postpartum could assist the early resumption of ovarian activity by enhancing ovarian follicle growth and early ovulation in postpartum cows. In this context, subsequent hCG injection may not provide any more beneficial effect.     

Ovarian responses and embryo survival in recipient lactating Holstein cows treated with equine chorionic gonadotropin

The objectives of Experiment 1 were to determine a dose of eCG that would increase total luteal volume and plasma progesterone (P4) concentration on estrous cycle Day 7 in cows. The objectives of Experiment 2 were to determine the effects of treating embryo recipient lactating Holstein cows with eCG on pregnancy per embryo transfer (P/ET). In Experiment 1, lactating dairy cows at 63 ± 3 d postpartum (DIM) received no treatment (control, n = 10), or 600 (eCG6, n = 19), or 800 (eCG8, n = 19) IU of eCG 2 d after the start of the ovulation-synchronization protocol, Day -8 (Day -10 GnRH, Day -3 PGF_2α, Day 0 GnRH). Blood was sampled on Days -10, -8, -3, 0, 7, and 14 for P4 concentration. Ovaries were examined by ultrasound on Days -10, -3, 0, and 7. In Experiment 2, lactating dairy cows were paired according to parity and previous insemination (0 or > 1 insemination) and assigned to receive 800 IU of eCG (eCG8, n = 152) 2 d after the start of the ovulation-synchronization protocol (Day -10 GnRH, Day -3 PGF_2α, Day 0 GnRH) or to receive no treatment (control, n = 162). Blood was sampled on Days -10, -3, 0, 7, and 14 for determination of P4 concentration. Ovaries were examined by ultrasound on Days -10, -3, and 7, and cows with a CL > 20 mm in diameter on Day 7 received an embryo. In Experiment 1, P4 concentration on Day 7 was higher (P < 0.05) for eCG8 cows (2.3 ± 0.3 ng/mL) compared with control (1.2 ± 0.3 ng/mL) and eCG6 (1.1 ± 0.3 ng/mL) cows. In Experiment 2, eCG8 primiparous cows had more (P < 0.01) follicles > 10 mm on Day -3 compared with control primiparous cows (2.5 ± 0.9 vs 1.7 ± 0.5 mm), but multiparous control and eCG8 cows did not differ. A larger (P = 0.03) percentage of control cows received an embryo (87.5 vs 79.1%) compared with eCG8 cows. Among cows that received an embryo, total luteal volume on Day 7 was affected (P = 0.05) by treatment (eCG8 = 8.3 ± 0.4 cm³, control = 6.2 ± 0.4 cm³), but P4 concentration on Day 7 did not differ significantly between treatments. The percentage of cows pregnant 53 d after ET (overall, 24.2%) was not significantly different between control and eCG8 cows. In the current study, no differences in P/ET were observed between control and eCG8 cows and treatment with eCG increased the percentage of cows with asynchronous estrous cycle.     

Urea and short-chain fatty acids metabolism in Holstein cows fed a low-nitrogen grass-based diet

Three ruminally cannulated and multicatheterised lactating dairy cows were used to investigate the effect of different supplement strategies to fresh clover grass on urea and short-chain fatty acid (SCFA) metabolism in a zero-grazing experiment with 24-h blood and ruminal samplings. Fresh clover grass was cut every morning and offered from 0800 to 1500 h. Maize silage was fed at 1530 h. The three treatments, arranged in a Latin square, differed by timing of feeding rolled barley and soya-bean hulls relative to fresh clover grass. All diets had the same overall composition. Treatments were soya-bean hulls fed at 0700 h and barley fed at 1530 h (SAM), barley fed at 0700 h and soya-bean hulls fed at 1530 h (BAM), and both soya-bean hulls and barley fed at 1530 h (SBPM). The grass had an unexpectedly low content of crude protein (12.7%) and the cows were severely undersupplied with rumen degradable protein. The treatment effects were numerically small; greater arterial ammonia concentration, net portal flux of ammonia and net hepatic flux of urea during part of the day were observed when no supplementary carbohydrate was fed before grass feeding. A marked diurnal variation in ruminal fermentation was observed and grass feeding increased ruminal concentrations of propionate and butyrate. The net portal fluxes of propionate, butyrate, isovalerate and valerate as well as the net hepatic uptake of propionate, butyrate, valerate and caproate increased after feeding at 0700 h. The hepatic extraction of butyrate showed a relatively large depression with grass feeding with nadir at 1200 to 1330 h. The increased net portal absorption and the decreased hepatic extraction resulted in an approximately six-fold increase in the arterial blood concentration of butyrate. The gut entry rate of urea accounted for 70 ± 10% of the net hepatic production of urea. Saliva contributed to 14% of the total amount of urea recycled to the gut. Urea recycling to the gut was equivalent to 58% of the dietary nitrogen intake. Despite the severe undersupply of rumen degradable protein, the portal-drained viscera did not extract more than 4.3% of the urea supplied with arterial blood. This value is in line with the literature values for cows fed diets only moderately deficient in rumen degradable protein and indicates that cows maximise urea transfer across gut epithelia even when the diet is moderately deficient in rumen degradable protein.     

Dietary manipulations to improve embryonic survival in cattle

High-producing dairy cows are subfertile. Hormonal and metabolic responses associated with homeorrhetic and homeostatic regulatory responses to partition nutrients for lactation, coupled with management, contribute to the reduction in fertility. Systems of reproductive management partially restore herd reproductive performance and provide a basis to access the impact of targeted nutritional strategies to further improve postpartum health and reproduction. Increasing the number of days feeding prepartum diets with a negative dietary cation-anion difference (DCAD), combined with adequate energy, protein, amino acids, and trace/macrominerals, improves the subsequent pregnancy rate. Likewise, supplementation of organic Se in the transition period and lactation improves immune function, uterine health, and subsequent reproductive performance under conditions of Se insufficiency. A basic understanding of the regulatory processes between nutrient partitioning and reproduction has led to the development of dietary strategies that benefit both lactation and reproduction. Postpartum increases in dietary nonstructural carbohydrates (i.e., glucogenic diets) increases ovarian activity in either intensive or extensive systems. Furthermore, sequential feeding of glucogenic-lipogenic diets enhances the proportion of cows pregnant by 120 d of lactation. Fatty acids of the n-6 and n-3 families act as nutraceuticals, altering innate immune responses and subsequent gene expression within the uterus to complement the sequential processes of follicle and embryo development and survival of the embryo and fetus. Selective or sequential feeding of lipogenic diets can benefit reproductive and immunological responses of lactating dairy cows and extensively managed beef cows.