J. Valencia

PREMATURE LUTEAL REGRESSION IN GOATS SUPEROVULATED WITH PMSG: EFFECT OF hCG OR GnRH ADMINISTRATION DURING THE EARLY LUTEAL PHASE

Twenty-two goats were superovulated with PMSG; 84 h after the onset of estrus the goats were treated with saline solution (control group n = 7), hCG (hCG group, n = 7), or GnRH (GnRH group, n = 8). The ovaries of all the goats were laparoscopically examined 3 and 6 d after the onset of estrus. In each case the CL were counted and classified according to their appearance as normal-looking or as regressing. Blood samples for progesterone determination were collected every 12 h from Day 1 to Day 6. Premature luteal regression was considered to have occurred if progesterone concentrations declined to less than 1 ng/mL by Day 6. According to progesterone concentrations, 57.5, 0 and 37.5% of the goats underwent premature luteal regression in the control, hCG and GnRH groups, respectively. Progesterone concentrations were higher in the hCG group than in the other groups on Days 5 and 6 post estrus (P < 0.05). The control group was the only one in which there was a significant (P < 0.05) increase in the number of regressing CL between Day 3 (1.6 +/- 1.4) and Day 6 (7.3 +/- 1.4). It was also the only group in which there was a significant decrease in the number of normal-looking CL between Day 3 (12.6 +/- 2.1) and Day 6 (2.6 +/- 2.1). On Day 6 the animals treated with hCG had significantly more normal-looking CL (12.0 +/- 2.3) than those in the control group (2.6 +/- 2.1). The number of large follicles present on the ovaries on Day 6 post estrus had negative correlations with progesterone concentrations (P = 0.05) and with the number of normal-looking CL (P < 0.05). It is concluded that the administration of hCG 84 h after the onset of estrus prevents premature luteal regression in goats superovulated with PMSG.

Reproductive performance of Alpine dairy goats in a semi-arid environment of Mexico under a continuous breeding system

Reproductive data from an Alpine dairy goat farm in a semi-arid area of Mexico were studied from 1987 to 1993. Goats were kept at night in confinement and pastured during the day with a male present all year. Yearly distributions of kidding (n = 589) were studied by months and seasonal period (Period 1, January–March; Period 2, April–June; Period 3, July–September; Period 4, October–December). Kidding was 75% from October to January. Seasonal kidding was 27% from January to March (n = 159), 11% from April to June (n = 65), 4% from July to September (n = 24), and 58% from October to December (n = 342). Average kidding interval (KI) was 345 (±70) days (n = 314), varying from 339(±72) days in yearlings to 346 (±70) days in adult goats. Seasonal KI was 324 (±68) days, 262 (+48) days, 481 (±50) days and 364 (±57) days for Period 1 (n = 82), Period 2 (n = 32), Period (n = 6) and Period 4 (n = 190), respectively, with a significant difference between periods (P < 0.05). Goats kidded for the first time at 14 months (±3), litter size of goats averaged 1.69 (±0.5) and seasonal distribution was 1.63 (±0.5), 1.50 (±0.5), 1.91 (±0.3) and 1.74 (±0.5), respectively. Kidding from July to September had a larger litter size. Although photoperiod is a factor governing the reproductive activity of these Alpine goats, other factors such as rain could influence the onset of the breeding season. It is concluded that with continuous male presence, seasonality in Alpine dairy goats under tropical conditions is not eliminated but some out-of-season breeding does occur. Overall, 85% of the breeding occurred between May and September. Therefore the continuous presence of a male increases the percentage of out-of-season kidding.

Estrus synchronization with melengestrol acetate in cyclic ewes. Insemination with fresh or frozen semen during the first or second estrus post treatment.

A total of 540 cyclic ewes were randomly allocated to 1 of 6 groups according to synchronization or not with melengestrol acetate (MGA), insemination with fresh or frozen semen, and insemination during the first or second estrus post treatment. The MGA was effective in synchronizing estrus, since the percentage of ewes showing estrus during the first 6 days after treatment was significantly higher (P<0.05) for treated (79.5%) than for nontreated ewes (33.5%); 74% of the treated ewes showed estrus during a 72-h period. Progesterone concentrations in plasma samples obtained at random from 34 treated ewes on Day 8 post estrus revealed that 94% of them ovulated and formed a functional CL. Synchronization was maintained during the second estrus post treatment, since 71.9% of the ewes showed the second estrus during a 72-h period. Treatment with 0.22 mg of MGA/head/d for 14 d had a detrimental effect on fertility when insemination was carried out during the first estrus post treatment. Delaying insemination until the second estrus post treatment caused a less marked reduction in conception rates. Thus, MGA can be a useful alternative for estrus synchronization of a large number of ewes. Artificial insemination can be delayed until the second estrus post treatment, improving fertility without loosing the advantages of estrus synchronization.

Effect of oxytocin infusion on luteal blood flow and progesterone secretion in dairy cattle

The objective of this study was to investigate the effects of oxytocin infusion on corpus luteum (CL) function during early to mid-diestrus by measuring luteal size (LS) and luteal blood flow (LBF) along with plasma levels of progesterone (P4) and prostaglandin metabolites (13,14-dihydro-15-keto-prostaglandin F2α, PGFM). On day (D) 7 of the estrus cycle (D1 = ovulation), seven cows received 100 IU of oxytocin (OXY) or placebo (PL) following a Latin square design. LS and LBF increased in both groups over time and no differences were observed between the groups. PGFM did not differ either within the groups over time or between the groups at any time point. P4 of the OXY group was higher compared to that of the the PL group 360 min after the infusion (p = 0.01) and tended to be higher at the time points 450 min, 48 h, and 72 h (all p = 0.08). Results from this study support the hypothesis that OXY is not directly involved in the mechanism(s) governing blood flow of the CL and has no remarkable effects either on luteal size or P4 and PGFM plasma levels. Further investigation is needed to elucidate the role of OXY in CL blood flow during early and late luteal phases.

Increased cleavage and blastocyst rate in ewes treated with bovine somatotropin 5 days before the end of progestin-based estrous synchronization.

Treatment with bovine somatotropin (bST) during estrous synchronization increased fertility and prolificacy in sheep. In the present study, a single dose of bST 5 days before the end of progestin treatment improved cleavage and embryo development. Stage of estrous cycle was synchronized in ewes (n=32) with progestin and superovulation was induced by use of FSH. Five days before the end of progestin treatment, ewes were randomly assigned to two groups: bST group (n=16) received a depot injection of 125 mg of bST sc (Lactotropina, Elanco, México) and the control group (n=16) received saline solution. Estrous was detected with rams fitted with an apron every 2 h and estrous sheep were mated every 8 h whilst in estrous. Embryos were recovered on Day 7 post mating, assessed microscopically and fixed in 4% paraformaldehyde. Cell number in blastocysts was counted after Hoechst 33342 staining. Plasma concentrations of IGF-I, insulin and progesterone were determined in eight sheep per group from the day of bST treatment to the day of embryo recovery. Cleavage rate, percentage of transferable embryos (transferable embryos/cleaved) and percentage of embryos reaching the blastocyst stage (blastocyst/cleaved) were compared between groups by logistic regression. IGF-I, insulin and progesterone plasma concentrations were analyzed by ANOVA for repeated measurements and cell number by ANOVA. Cleavage rate was greater (P<0.01) in bST treatment group (86%) than in the control group (62%). Similarly, the proportion of embryos reaching the blastocyst stage (bST=68.7 vs control=42.5) and the number of cells per blastocyst (bST group 91.8±5.5 compared to control group 75±6) were greater (P<0.01) in the bST-treated sheep. Plasma concentrations of IGF-I and insulin were greater (P<0.01) in the bST-treated group. No changes were observed in progesterone concentrations (P=0.5). It is concluded that bST injection 5 days before progestin removal increases cleavage rate and the proportion of embryos that reach the blastocyst stage. These effects are associated with an increase in IGF-I and insulin concentrations.

Lactational estrus induction in the Mexican hairless sow

The purpose of this study was to determine the effects on the reproductive performance of the Mexican hairless pig (MHP) while inducing fertile lactational estrus. Lactational estrus was induced on day 8, postpartum, in 20 primiparous sows during two consecutive reproductive cycles. Boar presence and temporary litter withdrawal were used as stimuli. Group I did not receive stimuli (control, C); group II had a 15 min boar stimulus (B); group III had litter withdrawal for 4 h (LW), and group IV received both stimuli (B + LW). Fertile estrus was detected by sow behavior, exfoliative vaginal cytology, and 17 beta-estradiol and progesterone samples. Individual stimuli did not induce fertile lactational estrus; nevertheless, when used together, both stimuli induced 100% of females into estrus, and 80% of them got pregnant while lactating. The partial withdrawal of the litter had a significant and positive effect on the number of live born piglets. Sows pregnant during lactation had shorter reproductive cycles, by not having non-productive days and litter size was greater. Pregnancy induction during lactation allowed the Mexican hairless sow to reduce the period between parturitions without diminishing the lactation length and litter performance.

Reproductive activity of Suffolk ewes in seasonal anestrus after being exposed to Saint Croix or Suffolk rams

The purpose of this study was to examine the hypothesis that rams of a tropical breed may be more effective than rams of temperate breed in inducing a reproductive response in ewes of temperate origin during the anoestrous period. Thirty Suffolk ewes in seasonal anestrus were assigned to one of three groups. In the control group (n=9), no males were present, while in the second group (Suffolk rams [SUF]; n=9) ewes were exposed to Suffolk males continuously for 13 days and twice per day from days 14-30, while in the third (Saint croix rams [SCR]; n=12), ewes were treated as in SUF, but rams were from the Saint Croix breed. Sexual receptivity was recorded daily for 30 days after introduction of the males and lambing data were recorded in the fall in SUF and SCR groups. In addition, serum progesterone (P4) concentration was used to monitor ovarian activity in all groups. No reproductive activity was observed in controls. In SUF, six ewes ovulated but did not show estrus, while in SCR all ewes showed estrus, ovulated and were mated. In addition, all but one of the ewes in SCR lambed. It was concluded the Saint Croix rams were more effective than Suffolk rams in inducing an estrous response, conception and pregnancy in anestrous Suffolk ewes.

Evaluation of the incorporation of GnRH into a superovulatory regimen for Zebu cattle

The objective of this study was to evaluate the utilization of gonadotropin releasing hormone (GnRH) as part of a superovulatory regimen for Zebu cattle. Forty Zebu cows were superovulated with 40 mg of follicle stimulating hormone-pituitary (FSH-P) divided in eight fractions of 5 mg injected at 12-h intervals. Luteolysis was induced with 15 mg of luprostiol injected at 48 h after the first injection of FSH-P. Half of the animals were injected with 200 ug of GnRH 3 h after the onset of standing estrus. The other 20 animals were not injected with GnRH. All the cows were inseminated three times at 12-h intervals, starting at the time of standing estrus. Embryos were recovered nonsurgically 7 d after the last insemination. Palpation per rectum performed immediately after collection of the embryos did not show differences in the number of corpora lutea between groups (P > 0.05). Likewise, there were no significant differences between treatments with respect to the total number of embryos plus ova, total number of embryos, or the number of transferable embryos recovered (P>0.05). The number of blastocysts, morulae, degenerated morulae and unfertilized ova was similar for the two groups. It is concluded that the incorporation of GnRH into a part of the superovulatory treatment for Zebu cattle does not improve the results of such treatment.

Effect of time and temperature of incubation of heparinized caprine blood on concentrations of progesterone detected in plasma

Blood samples from 12 pregnant does were collected in flasks containing heparin. Each sample was divided into 31 aliquots, the first of which was immediately centrifuged for plasma separation. Fifteen of the remaining aliquots from each goat were kept at 17 degrees C, while the remaining is were refrigerated at 4 degrees C. Centrifugation of these aliquots was carried out at half-hour intervals until completion of 6 h, and then at 8, 12 and 24 h post collection. The mean concentration of progesterone in the aliquots centrifuged initially was 4.0 +/- 0.3 ng/ml, and it was not significantly altered during incubation of the blood at 17 degrees C. In contrast, the concentrations of progesterone increased significantly to 5.0 +/- 0.3 (P < 0.05) during the first hour of incubation at 4 degrees C, remaining elevated most of the time. The stability of progesterone during incubation of heparinized caprine blood at 17 degrees C indicates that immediate centrifugation is not necessary. Refrigeration during the storage of blood samples is not recommended since progesterone levels are altered, probably due to separation of progesterone from the membranes of red blood cells during the hemolysis that is caused by incubation at low temperatures.

Exposure to the Male does not Exert a Luteolytic Effect in Cyclic Goats

Abstract Valencia, J., Arroyo, J., Trujillo, J., Magaña-Sevilla, H. and Zarco, L. 2010. Exposure to the male does not exert a luteolytic effect in cyclic goats. J. Appl. Anim. Res., 38: 181–184. To determine the influence of introduction of male to cyclic females on different days of estrous cycle twenty-four non lactating adult cross-bred cyclic dairy goats were divided in 4 equal groups. Does were completely isolated from males at least for 3 months before initiation of the experiment. Females in groups A, B and C were continuously exposed to the males from 15, 10 and 5 d post estrous until next estrus. Control group does remained completely isolated from males. Progesterone concentrations were determined in daily samples taken from, the day of the sponge removal until estrus. No difference (P>0.05) was found in the length of the luteal phase among does of all the groups. It is concluded that during the reproductive season, the introduction of the buck to a group of cyclic goats does not exert a luteolytic effect and consequently does not anticipate the next estrus.