Conception rate and reproductive function of dairy cows fed different fat sources.

The objective of the experiment was to determine the effects of fat supplementation on cyclicity, progesterone concentration, follicular development, conception rate, embryo mortality, and plasma concentrations of prostalglandin F metabolite (PGFM) in cattle. The hypothesis of this experiment was that feeding flaxseed, which is a source rich in C18:3, would increase conception rate of dairy cows due to decreased plasma PGFM concentrations. A total of 138 lactating Holstein cows were allotted at calving to three groups of 46 cows, blocked for similar calving dates. Cows within each block were assigned to one of three isonitrogenous, isoenergetic, and isolipidic supplements based on either whole flaxseed (FLA), Megalac (MEG) or micronized soybeans (SOY). The diets were fed from calving to Day 50 of pregnancy for pregnant cows, or 120 day postpartum for those not diagnosed pregnant after AI. Detailed measurements of PGFM and follicle dynamics were only made on four cows for FLA and five cows for both MEG and SOY. The response in PGFM concentration following the oxytocin challenge administered around Week 11 of lactation was similar over time among treatments. Plasma progesterone concentrations from Days 17 to 21 of the estrous cycle starting around Week 9 of lactation and determined on a subsample of cows (n=for FLA and n=5 for both MEG and SOY) were higher for cows fed FLA than for those fed SOY (P=0.04) or MEG (P=0.06). Conception rates were similar among treatments. Total embryo mortality was lower (P=0.07) for cows fed FLA (0%) compared to those fed either MEG (15.4%) or SOY (8.0%). The mean size of the CL measured during a complete estrous cycle from Week 9 of lactation was smaller for cows fed SOY (16.3 mm) compared to those fed either FLA (19.1 mm) or MEG (18.3 mm). We inferred that pregnancy losses could be reduced by feeding whole flaxseed as a result of its effects on different factors such as modulation in concentration of progesterone and size of the CL.

Milk production and composition, ovarian function, and prostaglandin secretion of dairy cows fed omega-3 fats.

Four multiparous Holstein cows were used in a 4 x 4 Latin square experiment to study the effects of fat sources rich in omega-3 fatty acids on milk production and composition, follicular development, and prostaglandin secretion. All cows were fed a total mixed diet containing 60% grass silage and 40% concentrate. The four treatments were concentrates based either on Megalac, formaldehyde-treated whole linseed, a mixture (50:50, oil basis) of fish oil and formaldehyde-treated whole linseed, or no fat source in the concentrate but with 500 g per day of linseed oil being infused into the duodenum. Feed intakes and milk yield were similar among treatments. In general, the lowest digestibility was observed for the formaldehyde-treated whole linseed treatment. Feeding fish oil decreased milk fat and protein percentages. Alpha-linolenic acid increased from 1.0 to 13.9% of milk fatty acids with linseed oil infusion. This confirms the high potential to incorporate alpha-linolenic acid into milk, and suggests that the formaldehyde treatment had little effect to limit biohydrogenation in the rumen. Increasing the supply of alpha-linolenic acid to these cows did not result in an increase in the concentration of eicosapentaenoic acid in milk. Levels of 13,14-dihydro-15-keto-PGF2alpha in plasma were higher for cows receiving formaldehyde-treated linseed and fish oil. Increases in this metabolite in response to oxytocin challenge, tended to be lower for cows given linseed either as sole oil supplement in the diet or as a duodenal infusion of linseed oil. Follicle dynamics were similar among treatments. Larger corpora lutea (CL) were found with cows that received high levels of omega-3 fatty acids through the diet as formaldehyde-treated linseed or as a mixture of formaldehyde-treated linseed and fish oil, although CL were smaller when cows were infused with linseed oil into the duodenum. These results suggest that the improvement in gestation rate that was observed when feeding increased levels of alpha-linolenic acid in earlier work may partly result from lower levels of production of the dienoic prostaglandin PGF2alpha.

In vitro embryo production in the cow: an effective alternative to the conventional embryo production approach.

Development of new technology related to in vitro embryo production has allowed for the commercial use of this method of reproduction. In the present work, we evaluate the efficiency of this technology compared with conventional embryo production based on results obtained with a standard procedure, including the sexing of embryos. The donor animals were mature nonlactating dairy cows (n = 92) kept under a constant environment and feeding program in an ET center. Ultrasound guided transvaginal ovum pick-up following 48 h pre-treatment with FSH has been used for the IVF-IVC protocol. A total of 437 oocyte recovery sessions performed on 92 cows yielded 4145 oocytes, which were used in an IVF-IVC protocol. Using the conventional approach, 156 embryo collections on 49 cows yielded 1652 ova and embryos. All Quality 1 and 2 embryos were sexed by a PCR procedure, and embryos of the desired sex were transferred to synchronized recipients located at the center. The results obtained in the IVF protocol showed that 4 oocyte collections per cow performed within 60 d, yielded 38 oocytes, which resulted in 18.8 viable embryos, of which 7.05 were female. After transfer of the female embryos, an average of 3.8 recipients were pregnant at 60 d. One embryo collection under the conventional approach yielded an average of 1.2 female pregnancies, which was confirmed during the same 60-d time period. These results indicate that IVF procedures can effectively replace conventional embryo production methods when a predetermined number of pregnancies of known sex are needed within a short period of time.

Ovarian superstimulation after follicular wave synchronization with GnRH at two different stages of the estrous cycle in cattle.

The objective of this study was to evaluate superovulatory programs based on synchronization of follicular waves with GnRH at 2 different stages of the estrous cycle. Sixteen Holstein cows were randomly assigned to 1 of 3 groups and administered GnRH (Cystorelin, 4 ml i.m.) between Days 4 and 7 (Groups 1 and 3) or between Days 15 and 18 (Group 2) of the estrous cycle (estrus = Day 0). Four days after GnRH treatment, > or = 7-mm follicles were punctured in Groups 1 (n = 6) and 2 (n = 6) or were left intact in Group 3 (n = 4). All cows were superstimulated 2 d later (i.e., from Days 6 to 10 after GnRH treatment) with a total of 400 mg NIH-FSH (Folltropin-V) given twice daily in decreasing doses. The GnRH treatment caused a rapid disappearance of large follicles (P < 0.005), rapid decrease in estradiol concentrations (P < 0.003), and increase in the number of recruitable follicles (4 to 6 mm; P < 0.04), indicative of the emergence of a new follicular wave within 3 to 4 d of treatment. Between 4 and 6 d after GnRH treatment, the mean number of 4- to 6-mm follicles decreased (4.7 +/- 1.8 to 1.5 +/- 3.3) in the nonpunctured group but increased (3.9 +/- 1.0 to 7.3 +/- 1.9) in the punctured group of cows (P < 0.05). In response to FSH treatment, the increase in the number of > or = 7-mm follicles was delayed by approximately 2 d in the nonpunctured group (P < 0.006). Moreover, the mean number of > or = 7-mm follicles at estrus was higher (16.9 +/- 1.7 vs 11.5 +/- 3.0; P < 0.1) in the punctured than the nonpunctured group. The increase in progesterone concentration after estrus was delayed in the nonpunctured group (P < 0.1) compared with the punctured follicles. Mean numbers of CL as well as freezable (Grade 1 and 2) and transferable (Grade 1, 2 and 3) embryos were similar (P > 0.1) in punctured and nonpunctured groups. Spontaneous estrus did not occur prior to cloprostenol-induced luteolysis in any group, and stage of the estrous cycle during which GnRH was given did not affect (P > 0.1) hormonal and follicular responses in the punctured groups. In conclusion, GnRH given at different stages of the estrous cycle promotes the emergence of a follicular wave at a predictable time. Puncture of the newly formed dominant follicle increases the number of recruitable follicles (4 to 6 mm) 2 d later and, in response to superstimulation with FSH, causes a greater number and faster entry of recruitable follicles into larger classes (> or = 7 mm) and a faster postovulatory increase in progesterone concentrations.

Synchronization of ovarian follicular waves with a gonadotropin-releasing hormone agonist to increase the precision of estrus in cattle: a review.

Treatment with GnRH and PGF2 alpha is a practical method for controlling ovarian follicular and luteal functions and increasing the precision of estrus synchronization in cyclic and acyclic postpartum cows and heifers. This method reduces considerably the period of time needed for estrus detection; it synchronizes the estrous cycle of 70 to 80% of the cyclic cows to within a 4-d interval without any detrimental effect on the fertility rate (65 to 85%). Moreover, resumption of ovarian activity and normal fertility in acyclic cows in favored. Administration of GnRH eliminates the large follicles by ovulation or atresia and induces emergence of a new follicular wave within 3 to 4 d after treatment at any stage of the estrous cycle, but it limits further growth of these emerging follicles by increasing atresia. The precision of estrus and the unaltered fertility rate is due to the synchronized selection of a new larger growing follicle, which becomes the ovulatory follicle after PGF(2 alpha)-induced luteolysis 6 d after GnRH treatment. Also, fixed-time AI programs without the need for estrus detection may be possible using a second injection of GnRH in a GnRH-PGF(2 alpha)-GnRH protocol to ovulate the selected follicle at a precise time. We describe a physiological model to explain how the precision of estrus is improved following PGF(2 alpha)-induced luteolysis, via the effect of pretreatment with GnRH on follicular development and luteal functions in cattle. Application of this model to the development of reliable methods of fixed-time insemination is also explored.

Buserelin alters the development of the corpora lutea in cyclic and early postpartum cows.

Changes in proportions of luteal cells after buserelin treatment were studied in the corpus luteum (CL) that was present at the time of treatment (CLP) and in the buserelin-induced CL (CLI) of cyclic and acyclic postpartum cows. On d 0 of the experimental period, eight cyclic (Cyc-sal) cows were injected with saline, whereas eight cyclic (Cyc-bus) cows and eight acyclic (Acyc-bus) cows were treated i.m. with 8 micrograms of buserelin. On d 3 or 6, ovaries were collected and stained using histological techniques. As determined with the point-counting method, the number of nuclei in the CLP was similar on d 3 in Cyc-bus and Cyc-sal groups but was lower (treatment x day, P < .001) in the Cyc-bus group than in the Cyc-sal group on d 6. The volume of the CLP was similar on d 3 in the two groups but was greater (treatment x day, P < .04) in the Cyc-bus than in the Cyc-sal group on d 6. The number of nuclei in the CLI was greater (P < .001) in cyclic than in acyclic cows on d 3 and 6 after treatment. The volume of the CLI was lower (P < .001) in cyclic than in acyclic cows on d 3 and 6. Buserelin did not change the profile of progesterone in cyclic cows from d 0 to 6, but concentrations of progesterone increased (P < .01) in acyclic cows 3 to 6 d after buserelin treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of corpus luteum and induced ovulation on ovarian follicular dynamics in postpartum cyclic cows treated with buserelin and cloprostenol.

The influence of the corpus luteum (CL) at the time of buserelin treatment and of buserelin-induced ovulation on the dynamics of ovarian follicular development was determined in 18 postpartum cyclic beef cows injected i.m. with 8 micrograms of buserelin on d 0 (d of treatment) and with 500 micrograms of cloprostenol (PGF) 6 d later. From d 0 to onset of estrus, ovaries were examined ultrasonographically, and blood samples were collected daily. Number of medium (5 to 10 mm) follicles and diameters of the two largest (F1 and F2) follicles in each cow were recorded. Cows were grouped according to the presence (CL+) or absence (CL-) of an active CL before buserelin injection and the presence (OV+) or absence (OV-) of a buserelin-induced ovulation (OV). Three groups were formed: CL-OV+ (n = 8), CL+OV+ (n = 6), and CL+OV- (n = 4). Buserelin induced an ovulation in all CL- cows (progesterone [P4] < .3 ng/mL) and in CL+ cows that had P4 < 4 ng/mL but did not in CL+ cows that had P4 > 8 ng/mL. Within CL+ cows, buserelin-induced ovulation (OV+) was associated with a smaller (P < .0001) increase in F1 and F1-F2 diameters and a transient increase in the number of medium follicles that was greater (P < .03) and of a longer duration (P < .01) than in OV- cows. After PGF, the increase in F1 and F1-F2 diameters was still greater in OV+ than in OV- cows (day x OV; P < .05). In all cows, the selection of the preovulatory follicle occurred before PGF injection. Results indicate that a buserelin-induced ovulation was dependent on P4 concentrations at the time of treatment. Subsequently, ovarian follicular dynamics were altered by a GnRH-induced ovulation, but emergence and selection of a large growing follicle occurred in all cows within 6 d of treatment. This follicle became the preovulatory follicle following PGF-induced luteolysis.

Histological populations and atresia of ovarian follicles in postpartum cattle treated with an agonist of gonadotropin-releasing hormone.

Surface and histological changes of ovarian follicles and degree of atresia were characterized 3 and 6 d after a treatment with a GnRH agonist (buserelin) in postpartum beef cows. Sixteen cyclic cows on d 7 of their estrous cycle and eight acyclic cows were used. On d 0 of the experimental period, eight cyclic cows were injected with 2 mL of physiological saline and the remaining eight cyclic cows and the acyclic cows were injected i.m. with 8 micrograms of buserelin. Ovaries were collected 3 or 6 d later (n = 4 cows per group per day). All follicles (> 1.57 mm) were observed microscopically, measured using routine histological techniques, and classified as either nonatretic or atretic, with early or late atresia, and grouped into Class 1, 1.57 to 3.67 mm, Class 2, 3.68 to 8.56 mm, or Class 3, > 8.56 mm. Buserelin induced formation of new corpora lutea in all cows but one (acyclic cow). Class 1 follicles decreased on d 3 but increased on d 6 (day x treatment, P < .004), whereas those of Class 2 increased (P < .07) on both d 3 and 6 after buserelin treatment. However, within Class 2 follicles, we detected an increase on d 3 and 6 in the number (P < .01) and proportion (P < .07) of atretic follicles, an increase in the number of follicles in late atresia on d 6 (day x treatment, P < .03), and a decrease in the number (P < .06) and proportion (P < .03) of nonatretic follicles on d 6 (day x treatment).(ABSTRACT TRUNCATED AT 250 WORDS)

Synchronization of estrus and fertility in beef cattle with two injections of buserelin and prostaglandin.

Postpartum beef cows and heifers in Group 1 received 8 mug of buserelin on Day 0 (the beginning of the experiment) and 500 microg of cloprostenol (PGF) on Day 6 (GnRH I, n=54). In Group 2 (GnRH II, n=54), the females were injected with buserelin on Day 0 (8 microg) and Day 3 (4 microg), and PGF on Day 6 and Day 9 for females not detected in estrus previously. Animals were bred by AI 12 hours after the onset of estrus. Blood samples were collected on Day -11 and Day 0 to assess cyclicity and on Day 3 and Days 6 to 12 to examine luteal activity. Progesterone levels did not differ between the 2 groups between Days 0 to 9. In both groups, the proportion of spontaneous estruses from Days 0 to 6 was reduced. Precision of estrus was higher (P<0.005) in the GnRH II group than in the GnRH I group of cows that were detected in estrus between Days 6 and 9. The synchronization rate, interval to estrus, pregnancy and conception rates were similar in GnRH I and GnRH II groups. The conception rate and interval to estrus were similar in cyclic and acyclic cows. Increasing the number of buserelin injections enhanced the precision of estrus, but not the conception rate, without any detrimental effect on luteal activity and induced more estruses in postpartum acyclic beef cattle.

Influence of an agonist of gonadotropin-releasing hormone (buserelin) on estrus synchronization and fertility in beef cows.

The objective of this experiment was to determine the effect of sequential treatment with buserelin (a GnRH agonist) and cloprostenol (a prostaglandin F2 alpha analog) on estrous response and fertility in beef cattle with different ovarian conditions. On d 0 (1st d of treatment), the control group (n = 52, 10 heifers and 42 cows) and the GnRH group (n = 48, 10 heifers and 38 cows) received 2 mL of saline or 2 mL of Receptal (8 micrograms of buserelin), respectively. On d 6, all cows that had not exhibited spontaneous estrus were given i.m. 500 micrograms of cloprostenol (PGF). Ultrasonography on d 0 and assays of progesterone in blood on d -11, 0, and 6 were used to identify follicular and luteal status of animals. Cattle were observed for estrus from d 0 to 10. Cows showing estrus were bred artificially 12 h after onset of estrus. Over the 10-d period, the number of cows detected in estrus and pregnancy and conception rates were identical for the two groups. However, between d 0 and 6, the proportion of cows exhibiting estrus was lower (P less than .01) in the GnRH group than in the control group. Between d 6 and 10, the synchronization rate and precision of estrus were greater (P less than .01) in the buserelin-treated group than in the control group. Conception rate and interval from PGF injection to onset of estrus were not different between the two treatment groups. Presence of a large (greater than 10 mm) follicle on d 0 enhanced synchronization rate and precision of estrus.(ABSTRACT TRUNCATED AT 250 WORDS)