R.J. Scaramuzzi

Heat stress and seasonal effects on reproduction in the dairy cow--a review.

In dairy cows inseminated during the hot months of the year, there is a decrease in fertility. Different factors contribute to this situation; the most important are a consequence of increased temperature and humidity that result in a decreased expression of overt estrus and a reduction in appetite and dry matter intake. Heat stress reduces the degree of dominance of the selected follicle and this can be seen as reduced steroidogenic capacity of its theca and granulosa cells and a fall in blood estradiol concentrations. Plasma progesterone levels can be increased or decreased depending on whether the heat stress is acute or chronic, and on the metabolic state of the animal. These endocrine changes reduce follicular activity and alter the ovulatory mechanism, leading to a decrease in oocyte and embryo quality. The uterine environment is also modified, reducing the likelihood of embryo implantation. Appetite and dry matter intake are both reduced by heat stress thus prolonging the postpartum period of negative energy balance and increasing the calving-conception interval, particularly in high producing dairy cows. The utilization of cooling systems may have a beneficial effect on fertility but dairy cows cooled in this way are still unable to match the fertility achieved in winter. Recent studies suggest that the use of gonadotropins to induce follicular development and ovulation can decrease the severity of seasonal postpartum infertility in dairy cows.

Fertility in postpartum dairy cows in winter or summer following estrus synchronization and fixed time AI after the induction of an LH surge with GnRH or hCG.

In this study, the fertility of postpartum dairy cows after a sequence of treatments with GnRH (Day 0), PGF2alpha (Day 7) and GnRH (Day 9) (GnRH group; n = 164) or hCG (Day 0), PGF2alpha (Day 7) and hCG (Day 9) (group hCG; n = 166) was investigated in summer and winter seasons. All cows were artificially inseminated without estrus detection, 16-18 h after the end of treatment. Control cows (CONT; n = 226) were not treated and were inseminated at natural estrus. The pregnancy rates at Day 90 (46% versus 33%; P < 0.05) and at Day 135 (76% versus 62%; P < 0.05) postpartum were significantly lower in CONT cows in summer compared to winter months but this effect was not observed in the two treated groups. The number of days from calving to conception was significantly lower in GnRH and hCG treatment groups compared to CONT cows in cold months (102 +/- 3.2, 106 +/- 4.2, 126 +/- 3.1, respectively; P < 0.001) and in hot months (112 +/- 3.2, 114 +/- 4.2, 139 +/- 3.1, respectively; P < 0.001). The concentration of insulin was significantly higher in winter (P < 0.001). There were no differences in average plasma concentration of glucose (P = 0.474), GH (P = 0.441) or IGF-I (P = 0.190). In conclusion, we have shown that veterinary supervision combined with a program of estrous synchronization and fixed time insemination can improve fertility of cows suffering heat stress.

The effects of exogenous growth hormone on follicular steroid secretion and ovulation rate in sheep

Growth hormone (GH) has diverse actions in many tissues, including the follicle. This paper summarizes three experiments that examined the effects of GH and insulin-like growth factor (IGF)-I on the ovary. Ewes given oGH and pregnant mane serum gonadotrophin were compared with control and pregnant mane serum gonadotrophin-treated ewes. Ewes, with synchronized cycles, were given varying doses of pregnant mane serum gonadotrophin and/or oGH to determine if oGH is able to augment ovulation rate (Experiment 1). Experiments 2 and 3 used the ovarian autotransplant model. Ewes were infused via the ovarian artery with oGH (Experiment 2) or insulin-like growth factor I (IGF-I) (Experiment 3). Both were administered for 12 hr on Day 10. In Experiment 2, ewes were given intravenous gonadotropin releasing hormone (150 ng i.v.) at -2.5 and 10.5 hr relative to infusion. Ovarian and jugular venous blood was collected every 15 min from -30 to 150 min relative to gonadotropin releasing hormone. In Experiment 3, luteolysis was induced at the end of infusion. Ovarian and jugular venous blood was collected every 3 hr from before and until 84 hr after the infusion. Estradiol and androstenedione were assayed in ovarian venous plasma and GH in jugular venous plasma. In Experiment 1, treatment with oGH increased the jugular venous concentration of GH. However, in Experiment 2 treatment with oGH via the ovarian artery did not increase jugular venous GH but did increase ovarian venous GH. Treatment with oGH had no effect on ovulation rate (Experiment 1) or the secretion of androstenedione and estradiol (Experiment 2). Infusion of IGF-I (Experiment 3) increased the secretion of estradiol during the follicular phase. These data show that short-term treatment of sheep with GH had no in vivo effects on the follicle and that IGF-I was a potent stimulator of follicular steroidogenesis in vivo.

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.

Glucose-stimulated insulin response in pregnant sheep following acute suppression of plasma non-esterified fatty acid concentrations

BackgroundElevated non-esterified fatty acids (NEFA) concentrations in non-pregnant animals have been reported to decrease pancreatic responsiveness. As ovine gestation advances, maternal insulin concentrations fall and NEFA concentrations increase. Experiments were designed to examine if the pregnancy-associated rise in NEFA concentration is associated with a reduced pancreatic sensitivity to glucose in vivo. We investigated the possible relationship of NEFA concentrations in regulating maternal insulin concentrations during ovine pregnancy at three physiological states, non-pregnant, non-lactating (NPNL), 105 and 135 days gestational age (dGA, term 147+/- 3 days).MethodsThe plasma concentrations of insulin, growth hormone (GH) and ovine placental lactogen (oPL) were determined by double antibody radioimmunoassay. Insulin responsiveness to glucose was measured using bolus injection and hyperglycaemic clamp techniques in 15 non-pregnant, non-lactating ewes and in nine pregnant ewes at 105 dGA and near term at 135 dGA. Plasma samples were also collected for hormone determination. In addition to bolus injection glucose and insulin Area Under Curve calculations, the Mean Plasma Glucose Increment, Glucose Infusion Rate and Mean Plasma Insulin Increment and Area Under Curve were determined for the hyperglycaemic clamp procedures. Statistical analysis of data was conducted with Students t-tests, repeated measures ANOVA and 2-way ANOVA.ResultsMaternal growth hormone, placental lactogen and NEFA concentrations increased, while basal glucose and insulin concentrations declined with advancing gestation. At 135 dGA following bolus glucose injections, peak insulin concentrations and insulin area under curve (AUC) profiles were significantly reduced in pregnant ewes compared with NPNL control ewes (p < 0.001 and P < 0.001, respectively). In hyperglycaemic clamp studies, while maintaining glucose levels not different from NPNL ewes, pregnant ewes displayed significantly reduced insulin responses and a maintained depressed insulin secretion. In NPNL ewes, 105 and 135 dGA ewes, the Glucose Infusion Rate (GIR) was constant at approximately 5.8 mg glucose/kg/min during the last 40 minutes of the hyperglycaemic clamp and the Mean Plasma Insulin Increment (MPII) was only significantly (p < 0.001) greater in NPNL ewes. Following the clamp, NEFA concentrations were reduced by approximately 60% of pre-clamp levels in all groups, though a blunted and suppressed insulin response was maintained in 105 and 135 dGA ewes.ConclusionsResults suggest that despite an acute suppression of circulating NEFA concentrations during pregnancy, the associated steroids and hormones of pregnancy and possibly NEFA metabolism, may act to maintain a reduced insulin output, thereby sparing glucose for non-insulin dependent placental uptake and ultimately, fetal requirements.

The Expression of Prostaglandin Endoperoxide Synthase 2 Messenger RNA and the Proportion of Smooth Muscle and Collagen in the Sheep Cervix During the Estrous Cycle

Abstract The use of transcervical artificial insemination in sheep is limited because of the anatomy of the cervix, which restricts the passage of an inseminating pipette into the uterine lumen. There is a degree of natural cervical relaxation at estrus that enables greater penetration with an inseminating pipette. We hypothesize that this relaxation may be regulated by cervical prostaglandin synthesis and remodeling of the cervical extracellular matrix. The present study investigated the changes in prostaglandin endoperoxide synthase 2 (PTGS2) mRNA expression and the proportion of smooth muscle and collagen in the sheep cervix during the estrous cycle. Sheep cervices were collected at four stages of the estrous cycle: prior to the LH surge, during the LH surge, after the LH surge, and during the luteal phase. The expression of cervical PTGS2 mRNA was determined by in situ hybridization, and the proportion of smooth muscle and collagen in the cervix was investigated by Masson trichrome staining. The expression of PTGS2 mRNA in the sheep cervix was greatest prior to the LH surge, when estradiol concentrations were also greatest. The increase in PTGS2 mRNA expression was associated with an increase in the proportion of collagen in the sheep cervix. We propose that prior to the LH surge, estradiol may stimulate PTGS2 mRNA expression and hence prostaglandin E2 synthesis in the sheep cervix to regulate cervical relaxation, most likely through the rearrangement of collagen bundles within the cervical extracellular matrix.

The mRNA expression of prostaglandin E receptors EP2 and EP4 and the changes in glycosaminoglycans in the sheep cervix during the estrous cycle

Transcervical artificial insemination in sheep is limited by the inability to completely penetrate the cervix with an inseminating pipette. Penetration is partially enhanced at estrus due to a degree of cervical relaxation, which is probably regulated by cervical prostaglandin synthesis and extracellular matrix remodeling. Prostaglandin E(2) acts via prostaglandin E receptors EP(1) to EP(4), and EP(2) and EP(4) stimulate smooth muscle relaxation and glycosaminoglycan synthesis. This study investigated the expression of EP(2) and EP(4) mRNA and glycosaminoglycans in the sheep cervix during the estrous cycle. Sheep cervices were collected prior to, during, and after the luteinizing hormone (LH) surge and during the luteal phase. The mRNA expression of EP(2) and EP(4) was determined by in situ hybridization, glycosaminoglycan composition was assessed by Alcian blue staining, and hyaluronan concentration was investigated by ELISA. The expression of EP(2) mRNA was greatest prior to the LH surge (P=0.02), although EP(2) and EP(4) were expressed throughout the estrous cycle. Hyaluronan was the predominant glycosaminoglycan, and hyaluronan content increased prior to the LH surge (P<0.05). Cervical EP(2) mRNA expression changed throughout the estrous cycle and was greatest prior to the LH surge. We propose that prostaglandin E(2) binds to EP(2) and EP(4) stimulating hyaluronan synthesis, which may cause remodeling of the cervical extracellular matrix, culminating in cervical relaxation.

The ovulation rate in anoestrous female goats managed under grazing conditions and exposed to the male effect is increased by nutritional supplementation

This experiment was conducted to determine if feed supplementation before exposure of anoestrous does to males increases ovulation rate. Does (n=50) grazing natural vegetation were divided into two groups (n=25). One group received no feed supplementation, while the other was supplemented daily, with a mixture of 950 g of alfalfa hay, 290 g of rolled corn and 140 g of soy bean per animal for 7 days before exposure to bucks. On April 7, all females were exposed to four adult sexually active bucks (two per group) for 15 days. The ovulation rate at the ovulation detected within 5 days of exposure to males, assessed by transrectal ultrasonography, was greater (P<0.05) in supplemented (1.6+/-0.2) than in non-supplemented females (1.0+/-0.2). In contrast, ovulation rate at the subsequent ovulation, detected between days 6 and 15 of contact with males, was not different (P>0.05) between supplemented (1.3+/-0.1) and non-supplemented females (1.3+/-0.2). Feed supplementation 7 days before exposure to sexually active bucks of females managed under grazing conditions increased their ovulation rate at the first male-induced ovulation but the stimulatory effect of supplementation did not persist and was not observed at the subsequent ovulation.

The expression of angiogenic growth factors and their receptors in ovarian follicles throughout the estrous cycle in the ewe

Healthy follicles are highly vascularized whereas those undergoing atresia have poor vascularity, suggesting a relationship between follicular vascularization and follicular function. Vascularization is regulated by angiogenic factors, and among them vascular endothelial growth factor (VEGF) and angiopoietin-Tie (Ang-Tie) systems are of central importance. The objectives of this study were to determine if VEGF, VEGF receptor-2 (VEGFR-2), and components of the Ang-Tie system are expressed in ovarian follicles at both the protein and mRNA levels and to explore if their expression is related to the stage of the estrous cycle in the ewe. Ovaries from cyclic ewes were collected during the luteal phase (n=5) or before (n=5), during (n=4), and after (n=4) the preovulatory luteinizing hormone (LH) surge. After fixation, ovaries were wax-embedded, serially sectioned, and analyzed for both protein and mRNA expression of VEGF, VEGFR-2, angiopoietin-1 (Ang-1), angiopoietin-2 (Ang-2), Tie-1 (mRNA only), and Tie-2. mRNA was studied by in situ hybridization using digoxigenin-11-UTP-labeled ovine riboprobes. A similar pattern of expression was observed for mRNA and protein for all of the factors. Both mRNA and protein expression of VEGF, VEGFR-2, Ang-1, Ang-2, Tie-1 (mRNA only), and Tie-2 in the granulosa and theca cells of follicles >or=2mm in diameter was significantly different among the stages of the estrous cycle, with the highest expression detected at the post-LH surge stage. Theca cells expressed significantly greater levels of the six angiogenic factors compared with granulosa cells at all stages of the estrous cycle. Expression levels in granulosa and theca cells were comparable between small (2.0 to 2.5mm) and medium (2.5 to 4.0mm) follicles, but large follicles (>4.0mm) expressed higher mRNA and protein levels (all P<0.05) for all factors at all stages of the estrous cycle. These data show (i) that VEGF, VEGFR-2, and the Ang-Tie system are present in both granulosa and theca cells of the ovarian follicle, (ii) that thecal cells consistently express greater levels of all of these factors compared with granulosa cells, and (iii) that their levels of expression are related to the stage of the estrous cycle and to follicle size.

Recent research on the effects of excess dietary nitrogen on the fertility of dairy cows

High concentrations of dietary nitrogen have been associated with reductions in the fertility of dairy cows, but the evidence is not conclusive and many studies have shown little or no effect. This paper reviews recent investigations of the effect of rapidly degradable sources of nitrogen on parameters of fertility, and concludes that high levels of dietary nitrogen do not routinely reduce fertility, even at intakes above those in normal dairy cow diets. It also concludes that cows may be able to adapt to high nitrogen diets so that diets that may reduce their fertility when introduced at critical periods, for example, when they are inseminated, do not reduce it when introduced at an earlier stage.