Insulin increases 17 beta-estradiol production by the dominant follicle of the first postpartum follicle wave in dairy cows

Prolonged anovulation following parturition has a negative impact on fertility in dairy cows. Insulin plays an important role in ovarian function in many species, and is profoundly depressed in dairy cows during early lactation. We hypothesized that hypoinsulinemia during early lactation represents a key indicator of nutritional status, resulting in delayed ovulation. Holstein cows (n = 10) were subjected to either a hyperinsulinemic-euglycemic clamp (INS) or saline infusion (CTL) for 96 h, beginning on day 10 after parturition during the first postpartum follicular wave. Insulin was infused continuously (0.3 microg/kg body weight per h) via a jugular catheter, and euglycemia was maintained by infusion of glucose. Circulating insulin concentrations were elevated 2.6-fold in INS cows compared with CTL cows (0.73 +/- 0.026 vs 0.28 +/- 0.026 ng/ml; P < 0.001). Insulin treatment did not affect (P > 0.05) luteinizing hormone (LH) pulse frequency, pulse amplitude or mean circulating LH. Circulating estradiol was elevated in INS cows (P < 0.01) and circulating testosterone also tended to be higher. The ratio of testosterone to estradiol was not different between treatments for the initial 30 h of infusion, but was significantly reduced thereafter in response to insulin (P < 0.01), suggesting that hyperinsulinemia increased follicular aromatase activity. Insulin treatment also resulted in reduced circulating nonesterified fatty acids, and increased circulating total and free insulin-like growth factor-I concentrations. Insulin infusion increased estradiol secretion by the dominant follicle of the first postpartum follicular wave in dairy cows, and this effect appears not to be mediated through changes in pulsatile LH release.     

Influence of uterine bacterial contamination after parturition on ovarian dominant follicle selection and follicle growth and function in cattle

First postpartum dominant follicles are preferentially selected in the ovary contralateral to the previously gravid uterine horn. The aim of the present study was to test the hypothesis that uterine bacterial contamination alters the location of ovarian follicle emergence and selection, and inhibits follicle growth and function. Swabs were collected from the uterine body lumen of cattle on days 7, 14, 21 and 28 after parturition. Bacteria were identified by aerobic and anaerobic culture; bacterial growth was scored semiquantitatively and animals were categorized into standard or high bacterial contamination categories on the basis of the number of colonies detected. Follicular growth and function were monitored by daily transrectal ultrasonography, and estimation of plasma FSH, oestradiol and progesterone concentrations. There was no effect of bacterial contamination on plasma FSH concentration profiles or emergence of the ovarian follicle wave. When uterine bacterial growth scores were high on day 7 or day 21 after parturition, fewer first (1/20 versus 15/50; P < 0.05) or second (1/11 versus 13/32; P < 0.05) dominant follicles were selected in the ipsilateral compared with the contralateral ovary, respectively. The diameter of the first dominant follicle was smaller in animals with a high day 7 bacterial score (P < 0.001), dominant follicle growth was slower (P < 0.05) and oestradiol secretion was decreased (P < 0.05). The present study provides evidence for an effect of the uterus on the ovary after parturition, whereby uterine bacteria have a contemporaneous localized effect on ovarian follicle selection and subsequent growth and function, but not on initial emergence.     

Relationship between metabolic hormones and ovulation of dominant follicle during the first follicular wave post-partum in high-producing dairy cows

Recent studies suggest that IGF-I is a crucial regulatory factor in follicular growth during early post-partum period. The aim of the present study was to determine in detail the changing profiles of metabolic and reproductive hormones in relation to ovulation of the dominant follicle (DF) of the first follicular wave post-partum in high-producing dairy cows. Plasma concentrations of related hormones in 22 multiparous Holstein cows were measured from 4 weeks pre-partum to 3 weeks post-partum, and the development of DF was observed with colour Doppler ultrasound. Thirteen cows showed ovulation by 15.2 days post-partum. Anovulatory cows showed higher GH and lower IGF-I levels than those in ovulatory cows during the peri-partum period. Each DF developed similarly, and a clear blood flow in the follicle wall was observed despite ovulation or anovulation. In addition, detailed endocrine profiles were analyzed in 9 out of the 22 cows. Five cows showed an increase in plasma oestradiol-17beta (E2) with follicular growth followed by E2 peak, LH surge and ovulation. In these cows, plasma IGF-I concentrations remained high until 10 days post-partum followed by a gradual decrease. Subsequently, the insulin level increased together with the E2 peak towards ovulation. These profiles were not observed in anovulatory cows. In conclusion, our data strongly support the concept that IGF-I and insulin represent 'metabolic signals' of the resumption of ovarian function post-partum in high-producing dairy cows. Moreover, we provide the first visual evidence that both ovulatory and anovulatory DFs of the first follicular wave post-partum are similarly supplied with active blood flow.     

An assessment of absorbable lysine requirements in lactating cows

Two experiments were conducted to ascertain lysine required for maintenance and milk production in lactating dairy cows. Multiparous Holstein cows fitted with abomasal cannulas were utilized in a replicated 3 x 3 extra-period Latin square design and infused with 0, 45, or 90 g of L-lysine-HCl daily (Experiment 1). In Experiment 2, 12 cows were utilized in a 5 x 5 Latin square design (with 2 replacement cows) and infused with 0, 22.5, 45, 90, and 180 g of L-lysine-HCl daily. Cows were housed in comfort stalls, milked at 0600 and 1700 h, exposed to a 16:8 h light:darkness cycle, and fed for ad libitum intake a 15.7% CP diet formulated to contain approximately 75% of dietary protein from corn-based feed ingredients. Milk yield was not affected in Experiment 1, but milk production increased linearly with lysine infusion level in Experiment 2. A linear response in daily yield of milk protein to lysine infusion was observed in both experiments. As lysine infusion increased, coccygeal plasma lysine concentrations tended to increase in Experiment 1, but in Experiment 2 free lysine increased linearly and quadratically in coccygeal plasma and increased linearly in plasma from the subcutaneous abdominal vein. The quadratic response in plasma free lysine (Experiment 2) suggested that lysine was the limiting AA for milk production from the composite protein flow to the small intestine. Using break-point analysis of plasma free lysine, it was estimated that the additional amount of abomasal lysine required to satisfy requirements was 64 g/d in cows producing about 30 kg of milk daily. Although additional lysine above microbial and undegraded intake protein lysine flow stimulated milk protein production, conversion efficiency to milk protein lysine was low.     

Preovulatory follicle characteristics and oocyte competence in repeat breeder dairy cows

The varied and elusive etiology of repeat breeding (RB) in dairy cows necessitates evaluation of oocytes and follicles, which have not previously been assessed together. Accordingly, we evaluated characteristics of preovulatory follicles and the competence of oocytes in control (CTL) and RB cows. The estrous cycles of 35 cows (18 CTL and 17 RB) were synchronized using PGF_2α and estrus detection. Cows with a corpus luteum were treated with PGF_2α and, 14 to 15 d after a visible behavioral estrus, they were administered a second PGF_2α, followed 48 h later by follicular fluid (FF) aspiration of the preovulatory follicles. Estradiol (E₂)-active preovulatory follicles did not differ in diameter between the 2 groups of cows. However, FF of RB cows had higher E₂ concentrations than that of CTL cows: 1,854.9 and 1,073.6 ng/mL, respectively, but similar androstenedione and progesterone concentrations. In the second part of the study, 14 consecutive ovum pick-ups (OPU) were performed in 5 CTL and 5 RB cows, at 3- to 4-d intervals. The RB and CTL cows did not differ in average numbers of follicles available per cow per session (7.1 and 7.3, respectively), oocyte recovery rates (42.2 and 44.1%, respectively), or cleavage rates (57.6 and 63.4%, respectively), but blastocyst production was markedly less in RB than in CTL cows (12.5 and 29.2%, respectively). We conclude that part of the RB cows' etiology occurs at an earlier phase of folliculogenesis, thereby impairing oocyte competence, and subsequently reducing the probability of normal fertilization, which diminish embryo vitality and development.     

Dietary unsaturated fatty acids influence preovulatory follicle characteristics in dairy cows

Dietary unsaturated fatty acids (UFAs) have been implicated in several reproductive processes in dairy cows through a variety of mechanisms. This study examined the effects of periparturient supplementation of rumen bypass fats low or high in proportion of UFAs (oleic and linoleic) on preovulatory follicle characteristics. Forty-two 256-day pregnant dairy cows were divided into three groups and were fed a control diet (n=14) or supplemented with fats either low (LUFA; n=14) or high (HUFA; n=14) in UFAs. At 14-15 days following behavior estrus, the cows received a prostaglandin F(2)(alpha) injection and 48 h later >7 mm follicles were aspirated. Progesterone (P(4)), androstenedione (A(4)), and estradiol (E(2)) were determined in the follicular fluid. Out of 75 follicles, 37 follicles that were aspirated between 55 and 70 days post partum were regarded as E(2)-active follicles (E(2)/P(4) ratio >1) and subjected for further analysis. The diameter of preovulatory follicles was greater in cows fed HUFA than in those fed control or LUFA. The concentrations and content of A(4) and E(2) in follicles and E(2)/P(4) ratio were higher in the HUFA group than in the other two groups. The P450 aromatase mRNA expression in granulosa cells that were collected from the aspirated preovulatory follicles was also higher in the HUFA cows than in the other groups. A significant correlation was observed between E(2) concentrations in preovulatory follicles and E(2) concentrations in plasma at aspiration. In conclusion, dietary UFA increased the size of and elevated steroid hormones in preovulatory follicles, which may be beneficial to consequent ovarian function.     

Vascular supply as a discriminating factor for pig preantral follicle selection

This research analyses how somatic and vascular compartments change during preantral follicle growth. To address this aim, theca-granulosa (somatic) proliferation indexes (PIs), proportion of proliferating endothelial cells (PE), vascular area (VA) and vascular endothelial growth factor A (VEGFA) expression were simultaneously recorded on single healthy preantral follicles, classified into six different stages on the basis of the diameter and the granulosa layers. An autonomous blood vessel network starts to appear only in class 3. Vascular remodelling requires VEGFA expression, and VEGFA mRNA and VA significantly increase between class 3 and classes 4 and 5 and, further, in class 6. In addition, a positive correlation exists between these parameters in classes 3-5. Despite variation in angiogenesis results from classes 3 to 5, the statistical analysis reveals that the vascular parameters are positively and strictly correlated with somatic PIs. Conversely, class 6, also characterized by higher values of somatic PIs, displays a stable proportion of PEs ( congruent with 40%) without showing any correlation among the different parameters analysed. To identify follicular subpopulations within different classes, a multivariate hierarchical cluster analysis was performed. This analysis reveals that the majority of classes 3 and 4 are quiescent follicles or structures that grow very slowly. Class 5 represents a transitory category, where half of the follicles maintain a low activity and the remaining express significantly higher levels of granulosa PI and VA. The follicles with this high activity are probably able to reach class 6 becoming dominant structures where somatic and vascular parameters are constantly on high levels and the VA remains the unique differentiating element.     

FGF10 inhibits dominant follicle growth and estradiol secretion in vivo in cattle

Fibroblast growth factors (FGFs) are involved in paracrine control of follicle development. It was previously demonstrated that FGF10 decreases estradiol (E(2)) secretion in granulosa cell culture and that theca cell FGF10 mRNA expression is decreased in healthy follicles from abattoir ovaries. The main objectives of this study were to evaluate FGF10 and FGFR2b mRNA expression during follicular development in vivo, to evaluate the effect of FGF10 on follicle growth using Bos taurus taurus cows as a model, and to gain more insight into the mechanisms through which FGF10 inhibits steroidogenesis. Messenger RNA encoding both FGF10 and FGFR2b (main FGF10 receptor) was significantly more expressed in subordinate follicles (SFs) than in dominant follicles (DFs). The intrafollicular injection of FGF10 into the largest growing follicle at 7-8?mm in diameter interrupted the DF growth in a dose-dependent manner (11±0.4, 8.3±1 and 5.9±0.3?mm for 0, 0.1, and 1?μg/ml FGF10, respectively, at 72?h after treatment; P<0.05). In a third experiment, follicles were obtained 24?h after FGF10 (1?μg/ml) or PBS treatment through ovariectomy. In theca cells, FGF10 treatment did not affect mRNA encoding steroidogenic enzymes, LHCGR and IGFBPs, but significantly upregulated FGF10 mRNA expression. The expression of CYP19A1 mRNA in granulosa cells was downregulated by FGF10 treatment, which was accompanied by a 50-fold decrease in E(2) production, and decreased cyclin D2 mRNA. These results have shown that FGF10 and its receptor FGFR2b are more expressed in SFs and provide solid in vivo evidence that FGF10 acts as an important regulator of follicular growth in cattle.     

Glucose requirements of an activated immune system in lactating Holstein cows

Accurately quantifying activated immune system energy requirements in vivo is difficult, but a better understanding may advance strategies to maximize animal productivity. Study objectives were to estimate whole-body glucose utilization following an i.v. endotoxin challenge. Lactating Holstein cows were jugular catheterized and assigned 1 of 3 bolus treatments: control (CON; 5 mL of saline; n = 6), lipopolysaccharide (LPS)-administered (LPS-C; 1.5 μg/kg of body weight; Escherichia coli 055:B5; n = 6), and LPS + euglycemic clamp (LPS-Eu; 1.5 μg/kg of body weight; 50% glucose solution infusion; n = 6). After LPS administration, blood glucose was determined every 10 min and glucose infusion rates were adjusted in LPS-Eu cows to maintain euglycemia for 720 min. Blood samples were obtained 180, 360, 540, and 720 min postbolus for further analysis. Cows were milked 360 and 720 min postbolus. Blood glucose was increased 84% in LPS-administered cows for up to 150 min postbolus; thereafter, circulating glucose was decreased 30% in LPS-C relative to LPS-Eu and CON cows. Mild hyperthermia (+0.5°C) occurred between 30 and 90 min postbolus in LPS-administered relative to CON cows; thereafter, rectal temperature did not differ between treatments. Milk yield and lactose percentage were decreased 80 and 11%, respectively, in LPS-administered relative to CON cows. Circulating insulin was increased 4 fold and nonesterified fatty acids, β-hydroxybutyrate, and ionized Ca were decreased ～50% in LPS-administered compared with CON cows. Plasma l-lactate, haptoglobin, and serum amyloid A increased ～160, 260, and 75%, respectively, in LPS-administered relative to CON cows. Overall, LPS-binding protein was increased 87% in LPS-administered relative to CON cows; however, at 720 min, it was decreased 25% in LPS-Eu compared with LPS-C cows. White blood cell count decreased ～90% in LPS-administered cows at 180 min and progressively increased to ～50% of CON values by 720 min. Total glucose deficit during the 720 min following LPS administration was calculated as the decrease in the amount of glucose required to synthesize milk (due to the decrease in milk yield relative to prebolus levels) plus the amount of glucose infused to maintain euglycemia (in LPS-Eu cows only) and was 461, 1,259, and 1,553 g for CON, LPS-C, and LPS-Eu cows, respectively. Our data indicate an acutely activated immune system uses >1 kg of glucose within 720 min and maintaining euglycemia did not rescue milk synthesis.     

Correlated selection responses for female fertility after selection for high protein yield or low mastitis frequency in Norwegian Red cows

Correlated selection responses in female fertility were estimated from a selection experiment with 2 groups of Norwegian Red cows selected for high protein yield (HPY) and low mastitis frequency (LCM), respectively. Genetic trends were calculated for nonreturn rate within 56 d after first insemination (NR56) for heifers, first-lactation cows, and second- and third-lactation cows, calving interval between first and second calving (CIN), and interval from calving to first insemination (CFI) for first-lactation cows and for second- and third-lactation cows. A total of 5,001 cows from the selection experiment had estimated breeding values for fertility, of which 2,806 were HPY and 2,195 were LCM cows. Permutation tests showed significant genetic differences between LCM and HPY for all fertility traits except CFI for second- and third-lactation cows. Observed differences between mean EBV in HPY and in LCM were, with few exceptions, far outside the range of the permutation test (i.e., significantly different from zero). LCM cows were, in general, genetically more fertile than HPY cows, with higher NR56 in heifers and cows, shorter CIN, and shorter CFI in first lactation. Genetic differences between HPY and LCM after 6 cow-generations were 2.5 percentage units NR56 in heifers, 2 percentage units NR56 in cows, and 4 d for CIN. No difference was found for CFI in second and third lactation. This is the first report of genetic change in female fertility as a correlated response after selection against mastitis.     

Selection responses for disease resistance in two selection experiments with Norwegian red cows

Genetic trends for clinical mastitis (CM), ketosis (KET), retained placenta (RP), and 305-d protein yield (PY305) were calculated for 2 Norwegian dairy cattle selection experiments. The first experiment, accomplished from 1978 to 1989, included groups selected for high (HMP) and low milk production (LMP). The second experiment started in 1989 and included selection for high protein yield (HPY) and low mastitis frequency (LCM). In both experiments proven sires from the active breeding program of Norwegian Red were used as sires. To take into account that selection of sires was external to the experiment, all available data from the Norwegian Red population, including disease records for 2.7 million first-lactation cows, were analyzed with a multivariate animal model. Estimated breeding values for cows in the experiments were extracted from this analysis to calculate genetic trends in the selection groups. Genetic trends for PY305 were, as expected, positive for the HMP and HPY groups, and negative for LMP and LCM. The HMP group showed increasing genetic trends for all 3 diseases, arguably a correlated response after selection for increased milk production, whereas the LCM group showed decreasing genetic trends for CM, KET, and RP. The genetic trends for KET and RP in the LCM group are most likely correlated responses after selection against CM. After 5 cow-generations the genetic difference between HPY and LCM was 10 percentage units CM, 1.5 percentage units KET, and 0.5 percentage units RP.     

Association between ovarian follicle development and pregnancy rates in dairy cows undergoing spontaneous oestrous cycles

Ovarian follicle development continues in a wave-like manner during the bovine oestrous cycle giving rise to variation in the duration of ovulatory follicle development. The objectives of the present study were to determine whether a relationship exists between the duration of ovulatory follicle development and pregnancy rates following artificial insemination (AI) in dairy cows undergoing spontaneous oestrous cycles, and to identify factors influencing follicle turnover and pregnancy rate and the relationship between these two variables. Follicle development was monitored by daily transrectal ultrasonography from 10 days after oestrus until the subsequent oestrus in 158 lactating dairy cows. The cows were artificially inseminated following the second observed oestrus and pregnancy was diagnosed 35 days later. The predominant pattern of follicle development was two follicle waves (74.7%) with three follicle waves in 22.1% of oestrous cycles and four or more follicle waves in 3.2% of oestrous cycles. The interval from ovulatory follicle emergence to oestrus (EOI) was 3 days longer (P < 0.0001) in cows with two follicle waves than in those with three waves. Ovulatory follicles from two-wave oestrous cycles grew more slowly but were approximately 2 mm larger (P < 0.0001) on the day of oestrus. Twin ovulations were observed in 14.2% of oestrous cycles and occurred more frequently (P < 0.001) in three-wave oestrous cycles; consequently EOI was shorter in cows with twin ovulations. Overall, 57.0% of the cows were diagnosed pregnant 35 days after AI. Linear logistic regression analysis revealed an inverse relationship between EOI and the proportion of cows diagnosed pregnant, among all cows (n = 158; P < 0.01) and amongst those with single ovulations (n = 145; P < 0.05). Mean EOI was approximately 1 day shorter (P < 0.01) in cows that became pregnant than in non-pregnant cows; however, pregnancy rates did not differ significantly among cows with different patterns of follicle development. These findings confirm and extend previous observations in pharmacologically manipulated cattle and show, for the first time, that in dairy cows undergoing spontaneous oestrous cycles, natural variation in the duration of post-emergence ovulatory follicle development has a significant effect on pregnancy rate, presumably reflecting variation in oocyte developmental competence.     

Short communication: genetic selection for milk production increases plasma ghrelin in dairy cows

Ghrelin is an endogenous ligand of the growth hormone secretagogue receptor and a potent orexigenic agent in human and rodent studies, but there is limited information about its effect in dairy cows. Twelve low genetic merit and 9 high genetic merit Holstein-Friesian dairy cows in peak lactation that were offered unrestricted access to fresh pasture were used to determine whether genetic selection for milk production resulted in an associated increase in plasma ghrelin concentration in grazing dairy cows. Blood samples were taken prior to the a.m. milking (i.e., baseline) and following 2 h of grazing after the a.m. milking on 2 consecutive wk during peak lactation. Milk production and dry matter intake were greater in high genetic merit cows compared with low genetic merit cows. Plasma ghrelin and growth hormone concentrations were elevated in high genetic merit cows pre- and postgrazing, and there was no significant interaction between genetic merit and time of sampling. Genetic merit did not affect the plasma nonesterified fatty acid or glucose concentration, but the plasma concentrations of metabolites and hormones measured were diminished 2 h after feeding. Data indicate an increase in plasma ghrelin associated with genetic selection for milk production, and an associated increase in dry matter intake.     

Local changes in blood flow within the preovulatory follicle wall and early corpus luteum in cows

Haemodynamic changes are involved in the cyclic remodelling of ovarian tissue that occurs during final follicular growth, ovulation and new corpus luteum development. The aim of this study was to characterize the real-time changes in the blood flow within the follicle wall associated with the LH surge, ovulation and corpus luteum development in cows. Normally cyclic cows with a spontaneous ovulation (n = 5) or a GnRH-induced ovulation (n = 5) were examined by transrectal colour and pulsed Doppler ultrasonography to determine the area and the time-averaged maximum velocity (TAMXV) of the blood flow within the preovulatory follicle wall and the early corpus luteum. Ultrasonographic examinations began 48 h after a luteolytic injection of PGF(2alpha) analogue was given at the mid-luteal phase of the oestrous cycle. Cows with spontaneous ovulation were scanned at 6 h intervals until ovulation occurred. Cows with GnRH-induced ovulation were scanned just before GnRH injection (0 h), thereafter at 0.5, 1, 2, 6, 12, 24 h and at 24 h intervals up to day 5. Blood samples were collected at the same time points for oestradiol, LH and progesterone determinations. Cows with both spontaneous and GnRH-induced ovulation showed a clear increase in the plasma concentration of LH (LH surge) followed by ovulation 26-34 h later. In the colour Doppler image of the preovulatory follicle, the blood flow before the LH surge was detectable only in a small area in the base of the follicle. An acute increase in the blood flow velocity (TAMXV) was detected at 0.5 h after GnRH injection, synchronously with the initiation of the LH surge. At 12 h after the LH surge, the plasma concentrations of oestradiol decreased to basal concentrations. The TAMXV remained unchanged after the initial increase until ovulation, but decreased on day 2 (12-24 h after ovulation). In the early corpus luteum, the blood flow (area and TAMXV) gradually increased in parallel with the increase in corpus luteum volume and plasma progesterone concentration from day 2 to day 5, indicating active angiogenesis and normal luteal development. Collectively, the complex structural, secretory and functional changes that take place in the ovary before ovulation are closely associated with a local increase in the blood flow within the preovulatory follicle wall. The result of the present study provides the first visual information on vascular and blood flow changes associated with ovulation and early corpus luteum development in cows. This information may be essential for future studies involving pharmacological control of blood flow and alteration of ovarian function.     

Optimizing ovulation to first GnRH improved outcomes to each hormonal injection of ovsynch in lactating dairy cows

Ovulatory response to the first GnRH of Ovsynch is the critical determinant for successful synchronization of ovulation in dairy cows. Our objective in this study was to develop a pre-Ovsynch treatment that increased the percentage of cows that ovulated in response to the first GnRH injection of Ovsynch. To accomplish our goal, we evaluated a hormonal strategy that consisted of PGF_2α and GnRH before the first GnRH of Ovsynch. Lactating dairy cows (n = 137) were assigned to receive either no treatment before Ovsynch (control) or 25 mg of PGF_2α (PreP) followed 2 d later by 100 μg of GnRH (PreG), administered 4 (G4G), 5 (G5G), or 6 (G6G) d before initiating the Ovsynch protocol. Transrectal ultrasonography was performed to assess follicular size and resulting ovulation, and blood samples were collected to measure circulating concentrations of progesterone and estradiol immediately before each hormonal injection. Cows were inseminated at a fixed time 16 h after final GnRH of Ovsynch. Pregnancy diagnosis was performed 35 d later by palpation per rectum of uterine contents. Proportion of cows that ovulated to first GnRH of Ovsynch was 56.0, 66.7, 84.6, and 53.8% for G4G, G5G, G6G, and controls, respectively, and was greater for G6G than for control cows. Luteolytic response to PGF_2α of Ovsynch was greater in all treated than control cows (92.0, 91.7, 96.2, and 69.2% for G4G, G5G, G6G, and control, respectively). Synchronization rate to Ovsynch was greater (92 vs. 69%, respectively) in G6G than in control cows. In addition, cows that ovulated in response to first GnRH of Ovsynch had greater response to PGF_2α of Ovsynch (92.7 vs. 77.1%, respectively) and greater synchronization rate to the overall protocol (87.9 vs. 62.9%, respectively) than those that did not ovulate. Concentrations of progesterone at PGF_2α of Ovsynch, and estradiol and follicle size at final GnRH of Ovsynch, were identified as significant predictors of probability of pregnancy 35 d after artificial insemination. In summary, a PGF_2α-and-GnRH based pre-Ovsynch strategy consisting of a 6-d interval between PreG and first GnRH of Ovsynch resulted in a greater ovulatory and luteolytic response to first GnRH and PGF_2α of Ovsynch, respectively, compared with control cows. This, in turn, optimized synchronization rate to Ovsynch.     

Two methods of inducing low plasma progesterone concentrations have different effects on dominant follicles in cows

The effects of two methods of inducing low progesterone concentrations on the shape of the plasma progesterone curve and on follicular characteristics in lactating cows were studied. A low ascending progesterone curve was elicited by three PGF2alpha injections on d 3 to 4 of the estrous cycle; a low constant curve by induction of corpus luteum regression on d 6 and insertion of two progesterone-containing intravaginal devices from d 6 to 15 of the cycle. Plasma progesterone concentration was highest in the untreated control group, intermediate in low ascending group, and lowest in the low constant group. On d 15, both control and low ascending groups had one large healthy and one large atretic follicle, suggesting a turnover of follicular waves; in the low constant group, the presence of only one very large healthy follicle indicated follicular persistence. Estradiol concentration in the follicular fluid and its production by granulosa cells were highest in the low constant, intermediate in the low ascending, and lowest in the control group. Androstenedione concentration in the follicular fluid and its production by theca cells were higher in the low constant than in the low ascending and control groups. The results indicate that the low ascending progesterone curve affected follicular development and steroidogenesis differently from the low constant curve. We suggest that the low ascending curve mimics the effects of naturally occurring low plasma progesterone concentrations better, and it might, therefore, be used as a model for studying the effects of low plasma progesterone on fertility.     

Energy balance, metabolic status, and the first postpartum ovarian follicle wave in cows administered propylene glycol

Mature Holstein cows were drenched daily with either 500 mL of water (control; n = 28) or propylene glycol (PPG; n = 28) from d 10 before parturition until d 25 postpartum. Follicular development was monitored thrice weekly by transrectal ultrasound. Blood samples were collected every 30 min from a subset of 10 cows per treatment on d −10, 2, and 25 to assess glucose and insulin response to treatments, and on d 10 postpartum, blood was collected every 10 min for 12 h to determine LH pulse profiles. Both insulin and glucose were elevated on d 2 and 25 following PPG administration, but only insulin was elevated on d −10. On d 10 postpartum, the number of LH pulses, mean LH, and pulse amplitude were not different between control and PPG cows. The proportion of first postpartum dominant follicles that became ovulatory, atretic, or cystic was not different between control and PPG cows. Despite evidence of improved metabolic status, PPG failed to increase LH pulse frequency, and failed to increase the proportion of first postpartum follicle waves resulting in ovulation. The dominant follicle of each cow was retrospectively categorized as being ovulatory (n = 17), nonovulatory high estradiol (n = 6), nonovulatory low estradiol (n = 24), or cystic (n = 8). Differences in dry matter intake and energy balance among cows in the different follicle categories were apparent as early as 3 wk before parturition. The nonovulatory low estradiol cows had lower pre- and postpartum dry matter intake and energy balance compared with ovulatory cows. The nonovulatory low estradiol cows also had postpartum metabolic hormone and metabolite profiles indicative of more severe negative energy balance.     

Commencement of luteal activity in three different selection lines for milk yield and fertility in Norwegian Red cows

Relationships among commencement of luteal activity (C-LA), milk yield, and energy balance (EB) were investigated in 3 selection lines of Norwegian Red cows at the Norwegian University of Life Sciences from 1994 through 2001. The cows were selected for low genetic merit for milk yield (LMP), high genetic merit for milk yield (HMP), and a combination of high indices for milk yield and fertility (HI). Breeding values for fertility were based on 56-d nonreturn rate. The material included 268 lactations from 147 cows. Milk samples for progesterone analysis were drawn 3 times weekly from 1994 through 1998, and 2 times weekly from 1999 to 2001. Commencement of luteal activity was defined as the first 2 consecutive measurements of progesterone concentration >3 ng/mL not earlier than 10 d after calving. Selection line was significantly related to C-LA, so that the least squares mean days from calving to C-LA were 22.5, 30.4, and 27.2 d for LMP, HMP, and HI cows, respectively. The HMP cows produced more milk than the LMP cows. The average milk yield in the sixth week of lactation was 24.0, 27.1, and 25.3 kg for LMP, HMP, and HI cows, respectively. The interval to C-LA decreased for the HMP and HI cows after phenotypic adjustment for EB in the model. Least squares means for the interval to C-LA were 23.2, 29.7, and 25.6 d for the LMP, HMP, and HI cows, respectively, in a model that included parity, selection lines, and EB as covariates. Cumulated EB during the first 4 wk of lactation, which itself differed between selection lines, did not fully account for differences in interval to C-LA between selection lines. Thus, the results of the present investigation indicate that selection for milk yield negatively affects C-LA over and above the effects caused by concurrent changes in EB. The increase in days to C-LA caused by selection for high yields can be reduced if selection for milk yield is combined with fertility in the breeding program.     

Derivation of the maintenance energy requirements and efficiency of metabolizable energy utilization for dry and lactating Jersey cows

Maintenance energy is the energy required to conserve the state of an animal when no work is completed. Dietary energy must be supplied to meet maintenance requirements before milk can be produced. The objectives of the current experiment were to quantify the maintenance energy requirement of Jersey cows when lactating or dry. Energetic measures were collected on 8 Jersey cows and evaluated across 3 physiological phases and nutritional planes: lactation, dry cows fed at maintenance, and fasted dry cows. Through total collection of feces and urine as well as using headbox-style indirect calorimeters, energy balance and heat production data were measured across all phases. Lactation data were collected across four 28-d periods. Data for cows fed at maintenance were collected after 14 d and fasting heat production was measured during the last 24 h of a 96-h fast. Net energy for maintenance (NE_M) requirements, and the efficiency of converting metabolizable energy (ME) into net energy were compared between lactating and dry (maintenance or fasting phase) cows. Heat production of dry cows fed at maintenance, which represents ME for maintenance, was 0.146 ± 0.0087 Mcal per unit of metabolic body weight (BW^0.75, MBW). Fasting heat production, which represents NE_M, was 0.102 ± 0.0071 Mcal/MBW. Energy balance was calculated as tissue energy plus milk energy. When estimated via regressing energy balance on ME intake, NE_M was not different between dry and lactating cows (0.120 ± 0.32 vs. 0.103 ± 0.0052 Mcal/MBW). However, the slope of the regression of energy balance on ME intake was greater for dry compared with lactating cows (0.714 ± 0.046 vs. 0.685 ± 0.010) when evaluated with a fixed intercept. This suggests that dry cows were more efficient at converting ME into net energy and that the efficiency of utilizing ME for maintenance may be greater than for lactation. Our measurements of NE_M and the slope of ME on energy balance were greater than the value used by the National Research Council (2001), which are 0.080 Mcal/MBW for NE_M and approximately 0.64 for the slope. Results of this study suggest that NE_M and the efficiency of converting ME into NE_M of modern lactating Jersey cows are similar to recent measurements on modern Holstein cows and greater than previous measurements.