Fed Melengestrol Acetate Research Articles

Managing Reproduction in Dairy Cattle. II. Response of Cows to Progestogen Treated Herdmates during the Postpartum Period

Sixty-eight lactating Holstein cows were handled as one unit but were either fed melengestrol acetate for 14 days or were contemporary controls. Cows that calved in a 21-day period were assigned to a treatment group. Those that calved during the subsequent 21 days served as controls and received no treatment. The alternating assignment was continued for 6 mo. Treated cows were between 14 to 35 days postpartum at the beginning of the feeding period. Data from all cows, combined, showed a decrease in days open (120 to 92) and services per conception (2.7 to 1.5) as compared with their previous year's record. The 34 control cows exhibited estrus over a period which coincided with that of 91% of the treated animals, with a slight delay in occurrence of first estrus. The observations suggest that control cows responded in some way to the treated cows in the early stages of the postpartum period.

Uterine Involution, Ovarian Activity, and Fertility after Melengestrol Acetate and Estradiol in Early Postpartum Cows

Twenty-seven Holstein cows were assigned to control, melengestrol acetate,22Melengestrol acetate was generously supplied by Dr. J. W. Lauderdale, The Upjohn Company, Kalamazoo, Michigan. or melengestrol acetate plus estradiol groups. Melengestrol acetate was fed 1 mg/cow per day for 14 days beginning 21 ±1 days after calving. Estradiol benzoate33Sigma Chemical Co. (500μg) was injected intramuscularly 48h after the last melengestrol acetate feeding. Cows were inseminated at first and any subsequent estrus after 50 days postpartum. Weekly palpation per rectum revealed diameter of the largest uterine horn decreased until 7 wk postpartum, but there was no significant difference among treatment groups. A temporary plateau in diameter of the largest uterine horn in cows treated with melengestrol acetate occurred the week after treatment. Cows receiving melengestrol acetate had more follicles>1.0cm diameter but only during treatment. There was no significant difference in interval to first ovulation or corpus luteum formation among the three groups. Control, melengestrol acetate, and melengestrol acetate plus estradiol group means for interval from calving to first estrus, days open for cows conceiving, and services per conception were 63±11, 37±9, and 41±7; 153±15, 83±6, and 101± 15; and 3.3±.8, 1.7±.3, and 2.1 ±.4. Values for the control group were higher than values for the other two groups. There was no difference in milk yield among the groups during the lactation in which melengestrol acetate was administered.

Chemical and physical characteristics of the macromolecular components of the cervical mucus from cows after synchronization of oestrus with melengestrol actate.

Summary. Samples of pooled cervical mucus from groups of animals fed melengestrol acetate (MGA) for 14 days were taken 3 and 4 days after cessation of treatment. The mucus samples were separated into protein and glycoprotein portions and the epithelial glycoprotein was isolated. The protein fraction was examined by disc electrophoresis and the epithelial glycoprotein was characterized by chemical analysis and determination of the molecular weight. The cervical mucus of one of the treated groups yielded a glycoprotein which had a reduced sulphate content when compared with that of the controls and did not show the lowered neuraminic acid content characteristic of the glycoprotein from untreated animals at oestrus. Two other groups of MGA-treated animals which received HCG 3 days after withdrawal of the progestagen did not show these anomalies. The protein in the MGA-treated samples of mucus contained considerably larger amounts of material migrating in the transferrin region of the electrophoretogram than did comparable controls.

Characteristics of Cervical Mucus from Progestagen-Treated Cattle

SUMMARY Five characteristics of cervical mucus were investigated to determine if abnormalities might be responsible for the lowered fertility observed in cattle following progestagen administration. Mucus from animals fed 1 mg of melengestrol acetate (MGA) daily for 3 and 14 days did not differ significantly from that of controls in quantity, crystallization patterns or alkaline phosphatase content. However, on the last day of MGA feeding (day 14) treated animals had thicker mucus (P Based on quantity, consistency and alkaline phosphatase content of mucus from treated animals on day 4 after MGA withdrawal and from control animals on the day of oestrus, there appears to be no reason to indict cervical mucus as the cause of lowered fertility in MGA-treated animals. However, the altered crystallization patterns and sperm migration might indicate changes of significance in relation to feritlity.

Feedlot Performance of Heifers Fed Melengestrol Acetate and Oxytetracycline Separately and in Combination

Twenty-eight crossbred yearling heifers were allotted at random to four groups to study the physiological effect of melengestrol acetate (MGA) and oxytetracycline (OTC), fed separately and in combination, on feedlot performance. All heifers were full-fed a ground snapped corn basal diet calculated to contain 11.6% crude protein, 10.3% crude fiber and 67.5% total digestible nutrients. Lot I served as a negative control; lot II received 75 mg OTC per head per day; lot III received 0.4 mg MGA per head per day; and lot IV received 75 mg OTC plus 0.4 mg MGA per head per day. Treatment did not significantly (P>.05) affect feedlot performance or carcass characteristics; however, the two groups of heifers fed MGA gained 6% faster and required about 9% less feed per unit of gain than non-MGA fed heifers. Estrus was suppressed in MGA treated heifers as reflected by visual observation during the feeding trial, absence of corpora lutea and the presence of greater amounts (P<.05) of follicular fluid. With the exception of a slight improvement in feed efficiency, a combination of OTC and MGA did not appear to be additive for any response criteria studied.

Synchronization of Estrus, Reproductive Performance, and Lactational Response of Holstein Heifers Treated with Melengestrol Acetate®,1

Effects of oral administration of melengestrol acetate on estrus synchronization and conception were investigated in 24 Holstein heifers. In addition, effects of feeding melengestrol acetate starting at 90 days postconception through 30 days postpartum on growth, gestation length, birth weight, and lactation were studied.Daily feeding of 1mg of melengestrol acetate to heifers for 14 consecutive days irrespective of stage of estrous cycle inhibited estrus during treatment and synchronized estrus following withdrawal. Treatment lowered (P<.05) conception at first post-treatment estrus. No difference in conception was observed between single and double inseminations. Services per conception for the treated animals were higher (P<.05) than controls (2.64 versus 1.54). Postconception feeding of melengestrol acetate resulted in no differences (P>.05) in weight gain, gestation length, or calf birth weight. There were no differences (P>.05) in lactation length, milk and fat production during post-treatment lactation.

Some carcass quality and endocrine criteria of Holstein heifers fed melengestrol acetate.

Body composition, tenderness, growth hormone levels, thyroid activity and adrenal cortical activity were measured after feeding melengestrol acetate (MGA) to Holstein heifers. MGA was administered at 0.45 mg per animal per day either from 2.5 months of age or from first estrus. The heifers were fed corn silage and hay ad libitum in addition to either 0.9 or 4.5 kg grain per head daily and killed at first estrus or at breeding size. MGA feeding increased growth rates by 9.95% (P<.05) in one analysis. Mean jugular growth hormone level was significantly lower in MGA treated animals, and was significantly and negatively related to growth rate. The results suggested that MGA may preferentially stimulate the growth of lean tissue. Adrenal weights were significantly reduced in animals receiving MGA in one analysis. Plasma cortisol, adrenal cortisol and adrenal corticosterone concentrations, and adrenal fasiculata layer widths were significant (P<.05) less in animals fed MGA than in comparable animals without MGA.

The effect of melengestrol acetate (MGA) on ovarian function and fertilization in beef heifers.

Heifers were given .5 or 1 mg/day of melengestrol acetate (MGA) for 14 days to investigate the effect of dose and time of initial treatment on the following parameters: 1) ovarian morphology 2) luteinizing hormone (LH) and progesterone levels in blood 3) cervical mucus index 4) estrus and 5) ovulation and fertilization following mating. Average time for estrus from last MGA feeding was 7.26 days in 1 mg MGA heifers (p less than .01) and 4.75 days in .5 mg MGA-synchronized heifers. 47% of the heifers given MGA on Day 15 failed to become synchronized whereas only 20% of those given MGA on Day 4 failed. Major physiologica l changes occurred in ovaries as a result of MGA treatment; there were f ewer mature follicles and more very large follicles compared with controls. Cervical mucus index coincided with estrus in only 1/3 of the MGA-treated heifers. Serum LH levels were higher (p less than .05) in those heifers first treated on Day 15 rather than on Day 4 and in animals receiving .5 mg MGA. MGA-treated heifers had more uncleaved ova indicating a higher rate of fertilization failure. It is concluded that fertility is reduced in matings at the first synchronized estrus following MGA treatment.

Effects of feeding melengestrol acetate (MGA) on occurrence of estrus, fertility and milk yield in dairy cows.

Effects of feeding melengestrol acetate (MGA) on occurrence of estrus, fertility and milk yield in dairy cows.

Control of ovulation in cattle with melengestrol acetate. IV. The effects of inducing ovulation with oestradiol cypionate on conception rate.

Summary. Sixty-three dairy and beef heifers were given single intravenous (i.v.) injections of 2, 5 or 10 mg of oestradiol cypionate (ECP®) during, on the last day, or on Day 1 or Day 2 after last feeding of melengestrol acetate (MGA®). Thirty-five heifers, which were used as controls, were fed MGA for intervals corresponding to those given ECP. The dairy heifers were checked for pregnancy by rectal palpation 35 to 45 days after service, but the beef heifers were slaughtered following breeding. Reproductive tracts were grossly examined for abnormalities and the oviducts were flushed for ova. Data were collected from both groups on the occurrence of oestrus, ovulation and on conception rate. ECP increased the overall incidence of oestrus. Ovulation, however, did not appear to be greatly affected by ECP, although there was a slight tendency for ovulation to occur sooner after oestrus in the heifers given ECP. ECP appeared to have a detrimental effect on the conception rate at the first controlled breeding, but the conception rate at subsequent breedings appeared normal. The reduced conception rate at first service following MGA plus ECP treatment appeared to be due to multiple causes: ovulation failure, ovum loss, fertilization failure and embryonic death. ECP would appear to have a favourable effect only when oestrus and/or ovulation failure was the primary cause of reduced conception rate.