Insulin and hydrocortisone, but not triiodothyronine, are required for the differentiation of pig preadipocytes in primary culture.

The objective of this study was to establish optimal conditions for the primary culture of pig preadipocytes. We cultured pig preadipocytes for 10 d and studied the effects of insulin, hydrocortisone, and triiodothyronine (T3) added to serum-free basal medium on differentiation and gene expression of lipoprotein lipase an early marker, and adipsin, a late marker of preadipocyte differentiation. Insulin alone and hydrocortisone alone stimulated a low level of cell differentiation, as indicated by an increase in glycerol-3-phosphate dehydrogenase activity. When added together, insulin and hydrocortisone had a synergistic effect on cell differentiation. When combined with insulin or hydrocortisone, T3 had no effect on cell differentiation, indicating that T3 is not required in porcine preadipocyte culture. Gene expression studies also showed that removal of insulin or hydrocortisone from complete serum-free medium reduced both early and late marker mRNA. As expected, removal of T3 had no effect on the gene expression of early and late marker mRNA. We conclude that insulin and hydrocortisone, but not T3, are required for the differentiation of pig preadipocytes in primary culture.

The effect of ewe body condition at lambing on colostral immunoglobulin G concentration and lamb performance.

Body condition was scored at lambing (BCSL) on 101 mature (4 to 7 yr old) Polypay ewes and related to colostral immunoglobulin G (IgG) concentration and lamb performance. Colostrum samples were collected from each ewe within 12 h of lambing and litters of more than two lambs were reduced to two within 2 h of lambing. Colostral IgG concentrations decreased rapidly with time (b = -3.28; R2 = .2132) and linear regression analysis projected that colostral IgG concentrations would diminish to zero milligrams/milliliter by 23 h postpartum. Body condition score at lambing varied from 2.5 to 3.5 and had no effect on colostral IgG concentration, which averaged 79 +/- 5.6 mg/mL, adjusted to the time of parturition. Total birth weights of lambs were higher for the oldest ewes (7 yr old), but this group had the lowest prolificacy. This age group weaned the lowest total lamb weight and number of lambs. Total weight of lambs born was not affected by BCSL. Lamb mortality from birth to weaning was 19.0% and was not affected by BCSL, sex, litter size, or breed of sire, but the older (7 yr old) ewes had greater lamb mortality. Total weight of lamb weaned was not affected by BCSL, although ewes with a BCSL of 3.0 tended ( P = .11) to wean more kilograms of lamb than ewes with a BCSL of 3.5. Ewes bred to Polypay rams weaned more total weight of lamb than those bred to Columbia rams, which was due to increased survival rate to weaning for the Polypay rams. We conclude that, within a range of 2.5 to 3.5, BCSL is not an important factor affecting the colostral IgG concentration, total weight of lamb born, lamb mortality, or total weight of lamb weaned.

Failure of gonadotropin-releasing hormone or human chorionic gonadotropin to enhance the fertility of repeat-breeder cows when administered at the time of insemination.

Repeat-breeder dairy cows failing to conceive to two previous inseminations were injected with saline (2 cc i.m.), gonadotropin-releasing hormone (GnRH, 2 cc i.m.) or human chorionic gonadotropin (hCG, 5000 IU i.v.) at the time of the third and succeeding inseminations. This field study involved 240 cows at three dairies. Mean conception rate was high (49.6%) for repeat-breeders, and did not differ among farms (P>0.10) or treatments (P>0.10), varying from 44.0 to 51.9% for farms and from 44.4 to 54.2% for treatments. The percentage of repeat-breeder cows bred during diestrus was very low on each of the three farms (mean = 7.9%). For this and other reasons discussed in the study, hormonal therapy was not successful in improving the conception rate of repeat-breeder cows under field conditions.

In vitro regulation of mammary glucose-6-phosphate dehydrogenase activity by palmitoyl coenzyme A, acetate, and polyamines.

An in vitro study was conducted to determine whether bovine mammary glucose-6-phosphate dehydrogenase (G6PD) activity was regulated by palmitoyl coenzyme A (CoA), acetate, spermidine, and putrescine and whether these effects were dependent upon stage of lactation. Early lactation explants incubated in media containing palmitoyl CoA or acetate had reduced (P less than 0.01) G6PD activity compared with incubated control explants. G6PD activity in early lactation explants was reduced (P less than 0.05) when incubated with 5 microM palmitoyl CoA or 1 mM acetate compared with 25 microM palmitoyl CoA or 10 mM acetate. Spermidine (0.4 mM) reversed (P less than 0.05) palmitoyl CoA-induced inhibition of early lactation G6PD activity at 5 microM, but not at 25 microM palmitoyl CoA. G6PD activity in early lactation explants was decreased (P less than 0.05) when treated with putrescine (0.4 mM) compared with explants treated with spermidine. Addition of acetate in combination with 5 microM palmitoyl CoA reversed G6PD inhibition (P less than 0.05 for 1 mM and P less than 0.01 for 10 mM) while addition of either level of acetate in combination with 25 microM palmitoyl CoA failed to reverse G6PD inhibition. G6PD activity was higher (P less than 0.01) in early lactation than mid-lactation explants. No statistical differences (P greater than 0.1) were found among any treatments in explants from mid-lactation cows. We conclude that palmitoyl CoA and acetate will inhibit G6PD activity in early lactation, but not mid-lactation explants; addition of spermidine will reverse this inhibition.

Response of the bovine corpus luteum to increased secretion of luteinizing hormone induced by exogenous gonadotropin releasing hormone.

Two experiments were conducted to investigate the response of the bovine corpus luteum to surges of luteinizing hormone (LH) induced by natural gonadotropin-releasing hormone (GnRH) administered twice during the same estrous cycle. In experiment 1, eight mature beef cows, each cow serving as her own control, were injected intravenously (iv) with saline on days 2 and 8 of the cycle (day of estrus = day 0 of the cycle), then with 100 micrograms GnRH on days 2 and 8 of the subsequent cycle. Jugular blood samples were taken immediately prior to an injection and at 15, 30, 45, 60, 120 and 240 min postinjection, to quantitate changes in serum luteinizing hormone. Blood was also collected on alternate days after an injection until day 16 of the cycle, to characterize changes in serum progesterone concentrations. Although exogenous GnRH caused release of LH on days 2 and 8 of the cycle, the quantity of LH released was greater on day 8 (P less than .025). Serum levels of progesterone after treatment with GnRH on day 8 of the cycle did not differ significantly from those observed during the control cycles of the heifers. Because exposure of the bovine corpus luteum to excess LH, induced by GnRH early during the estrous cycle, causes attenuated progesterone secretion during the same cycle, these data suggest that a second surge of endogenous LH may ameliorate the suppressive effect of the initial release of LH on luteal function. Duration of the estrous cycle was not altered by treatment (control, 20.4 +/- .5 vs. treated, 20.4 +/- .4 days).(ABSTRACT TRUNCATED AT 250 WORDS)

Interactions of nutrition and reproduction.

As dairy cattle achieve higher milk production, we are becoming aware of closer relationships between nutrition and fertility. An increasing body of evidence indicates that excessive protein intake in early lactation may be detrimental to postpartum fertility. In addition, protein solubility and degradability are important. Energy restriction in high producing cows may be detrimental to fertility through its effect on hypothalamic and ovarian function. Dairy producers are susceptible to advertisements advocating the addition of specific vitamins and minerals to the rations of high producing cows since inadequate or excessive quantities may be detrimental to fertility. This is particularly true for minerals. However, high producing cows do not usually receive grossly inadequate or excessive dietary sources of vitamins and minerals. Rather, they may be presented with a borderline intake of several vitamins and minerals, which together may be detrimental to fertility. Finally, new methods must be developed to provide a more sensitive indication of fertility. These are some of the research and educational needs of the dairy industry if it is to continue successfully increased milk production. Predictions of herd averages of 16,000 kg milk and individual records exceeding 30,000 kg have been made for the yr 2000.

Prostaglandin F2 alpha-induced release of oxytocin from bovine corpora lutea in vitro.

Two experiments were conducted to study the in vitro effects of prostaglandins F2 alpha (PGF2 alpha), E2 (PGE2), and luteinizing hormone (LH) on oxytocin (OT) release from bovine luteal tissue. Luteal concentration of OT at different stages of the estrous cycle was also determined. In Experiment 1, sixteen beef heifers were assigned randomly in equal numbers (N = 4) to be killed on Days 4, 8, 12, and 16 of the estrous cycle (Day 0 = day of estrus). Corpora lutea were collected, an aliquot of each was removed for determination of initial OT concentration, and the remainder was sliced and incubated with vehicle (control) or with PGF2 alpha (10 ng/ml), PGE2 (10 ng/ml), or LH (5 ng/ml). Luteal tissue from heifers on Day 4 was sufficient only for determination of initial OT levels. Luteal OT concentrations (ng/g) increased from 414 +/- 84 on Day 4 to 2019 +/- 330 on Day 8 and then declined to 589 +/- 101 on Day 12 and 81 +/- 5 on Day 16. Prostaglandin F2 alpha induced a significant in vitro release of luteal OT (ng.g-1.2h-1) on Day 8 (2257 +/- 167 vs. control 1702 +/- 126) but not on Days 12 or 16 of the cycle. Prostaglandin E2 and LH did not affect OT release at any stage of the cycle studied. In Experiment 2, six heifers were used to investigate the in vitro dose-response relationship of 10, 20, and 40 ng PGF2 alpha/ml of medium on OT release from Day 8 luteal tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Efficacy of morantel sustained release bolus against gastrointestinal nematodes in first season grazing Holstein calves.

The efficacy of the morantel sustained release bolus (MSRB) in reducing gastrointestinal parasitism in first season grazing calves was evaluated during the summer--autumn grazing seasons of 1982 and 1983 in western Oregon. Each of 38 calves (1982) and 40 calves (1983) were randomly assigned to either control or treatment groups which were given MSRB on the day of turnout onto pasture. Mean worm burdens from tracer calves grazed with treated animals in 1982 and 1983 showed overall reductions of 86.4% (P greater than 0.05) and 84.3% (P less than 0.01), respectively, compared to tracers grazed with controls. Ostertagia ostertagi, Cooperia oncophora and Nematodirus helvetianus were the primary nematodes collected at necropsy. Twelve full-season 1982 tracer animals (6 treated and 6 control) indicated an 88.1% (P less than 0.05) overall reduction in mean worm burdens. Mean fecal worm egg per gram (EPG) counts of treated animals reflected a reduction of 69% (P less than 0.05) in 1982 and 90% (P less than 0.05) in 1983. Autumn inhibition of O. ostertagi was observed. In the 1982 trial the control animals showed a slight mean weight gain advantage over the treated group from Day 84 until Day 160 (trial termination) when the mean difference was 7.9 kg. The final mean weight gain advantage of treated animals in 1983 was 13.5 kg (P less than 0.05). These trials demonstrated that the MSRB was an effective anthelmintic for reducing gastrointestinal parasitism in grazing calves and for decreasing pasture larval contamination.

Steroid hormone feedback on LH in prepubertal Holstein heifers.

A significant dose-response relationship between gonadotropin-releasing hormone (GnRH) and time to luteinizing hormone (LH) peak, peak serum LH and total serum LH was obtained in prepubertal Holstein heifers (28 weeks of age) (Experiment 1). For the second experiment, the effect of steroid feedback on the anterior pituitary was determined. A steady infusion of saline, estradiol-17 beta or progesterone was maintained for 24 h while GnRH, in various schemes, was administered 8 h after the beginning of steroid infusion. Estradiol-17 beta infusion (2.08 micrograms/h), although it did not affect peripheral concentrations of estrogen, caused an LH release 24 to 30 h later in 37.5% of the heifers. This amount of exogenous estrogen did not affect the LH response to a single GnRH (4 micrograms) challenge. When the same GnRH dosage (4 micrograms) was administered 6 times at hourly intervals, the heifers infused with estradiol had a lower response after the first 2 injections of GnRH and a greater response after the last 4 injections than heifers infused with saline. When GnRH was infused (4 micrograms/h) for 6 h, beginning 8 h after steroid infusion, estradiol infusion caused a significantly higher peak LH and total LH release than an infusion of either saline or progesterone (7.3 micrograms/h). The progesterone infusion had no effect on the GnRH-stimulated LH release. We conclude that prepubertal dairy heifers have an anterior pituitary capable of responding to the feedback effect of estrogen in a positive manner.

Effect of supplemental beta-carotene on incidence and responsiveness of ovarian cysts to hormone treatment.

Sixty-two multiparous and 35 primiparous Holstein cows were assigned randomly at 10 days postpartum to receive a ration with or without 300 mg beta-carotene/cow per day. Multiparous and primiparous cows were grouped separately and group-fed complete rations once daily. Incidence of ovarian cysts (26% by rectal palpation) was not affected by beta-carotene fed. Multiparous cows had greater incidence (39%) of ovarian cysts than primiparous cows (11%). Fifty-seven percent of cysts were classified follicular by rectal palpation. Progesterone concentration of milk also was used for diagnosis of type of cyst. Cows with ovarian cysts and with progesterone concentrations in milk less than 1 ng/ml were classified follicular, and those having concentration greater than 1 ng/ml were classified luteal. As determined by milk progesterone, rectal palpation was more accurate for diagnosis of luteal cysts than for diagnosis of follicular cysts. Progesterone concentrations of milk for animals with luteal and follicular cysts were 10.66 +/- 1.29 and .37 +/- .07 ng/ml. beta-Carotene did not affect response or days to respond to treatment with human chorionic gonadotropin or gonadotropin-releasing hormone. Supplemental beta-carotene was not beneficial for reducing incidence of ovarian cysts in cows receiving an adequate supply of beta-carotene in their diet.

Effect of photoperiod on milk production and prolactin of Holstein dairy cows.

Milk yield and composition were measured in 74 Holstein cows and first-calf heifers in two experiments comparing varying lengths of photoperiod. High pressure sodium vapor lamps provided light intensity at cow eye level of 254 +/- 26 lx during the day and 132 +/- 9 lx at night in a free stall barn open on two sides. The first experiment compared continuous light with 18 h light for 16 wk during the winter in animals previously exposed to continuous light. Photoperiod had no effect on milk yield or basal concentration of serum prolactin in either age group. Peak concentration of prolactin after injection of thyrotropin releasing hormone was not affected by photoperiod in heifers but was higher in cows exposed to 18 h light. The second experiment compared natural photoperiod (9 to 12 h light) with 18 h light for 9 wk during the winter in animals previously exposed to a natural photoperiod. Photoperiod had no effect on 4% fat-corrected milk in heifers whereas there was a significant interaction of photoperiod by week for 4% fat-corrected milk in cows. Basal concentration of serum prolactin was lower in cows than in heifers although there were no differences due to age or photoperiod after injection of thyrotropin releasing hormone. We conclude that multipara Holstein cows produce about 7% more 4% fat-corrected milk during winter months when exposed to 18 h light providing they were previously in a natural photoperiod environment. For reasons not understood, 18 h light failed to enhance milk yield of cows previously in a continuous light environment. Milk yield and composition in heifers were not affected by 18 h or continuous light.

Effect of artificial photoperiod on eating behavior and other behavioral observations of dairy cows.

Twenty-eight cows were assigned randomly to a daily photoperiod of 18 h light and 6 h darkness or to continuous light and were observed 1 day each month from December 1981 to February 1982. Lighting regimen did not affect eating behavior or milk production. Overall means of total eating time, number of eating bouts, and average time eating per bout on the 3 observation days were 270 to 280 min, 10 to 12 times, and 24 to 27 min. Eating behavior and milk production were not significantly correlated. Eating patterns were similar in both groups and across observation days. Peaks of eating activity occurred before sunset, bracketing the evening milking and after the offering of fresh feed in the morning. Approximately 80% of total eating activity occurred between 0900 and 2100 h in both groups. Cows had a clear preference for entry into the right or left side of the milking parlor, and entry order was repeatable. Milking order and milk production were not correlated. In one group, location of free stalls did not influence utilization; but in the other group, centrally located stalls were utilized more than stalls at either end of the alley. About 40% of cows had individual free stall preferences.

The effect of exogenous follicle stimulating hormone treatment on anterior pituitary and testicular function in the prepubertal bull.

The effect of exogenous follicle stimulating hormone (FSH) on testicular function was studied in twenty 4-month-old Holstein bulls during two seasons (ten in late winter and ten in summer). Five mg FSH or saline were given subcutaneously at 12-hour intervals (10 mg/day) for ten days, after which time the testes were removed, weighted, and incubated in vitro with 0, 15, or 150 ng luteinizing hormone (LH) for 3 hours. FSH treatment resulted in significantly heavier testes (38%) in the summer (39.3 +/- 1.6 vs. 28.5 +/- 1.5 g) but not in late winter. Epididymal weight was not affected. Across seasons, serum LH concentrations were higher (P = 0.06) in FSH-treated bulls (2.39 +/- 0.13 vs 1.80 +/- 0.13 ng/ml); the largest increase occurred in the summer. FSH treatment did not change serum testosterone levels in late winter, whereas in the summer serum testosterone concentrations were three-fold higher (0.90 +/- 0.06 vs 0.29 +/- 0.02 ng/ml; P less than 0.05) in the FSH-treated bulls. In addition, serum testosterone concentrations increased with time of FSH treatment. FSH treatment stimulated a 2.4-fold increase (P less than 0.05) in testosterone content of the testes across seasons and a three-fold increase (P less than 0.05) in testosterone synthesis in vitro in the summer. There was no dose effect of LH on vitro in the summer. There was no dose effect of LH on in vitro testosterone synthesis. We conclude that administration of exogenous FSH to intact prepubertal bulls is capable of altering testicular function, but that seasonal influences can modify this function.

Relationship of dietary crude protein to composition of uterine secretions and blood in high-producing postpartum dairy cows.

Effects of dietary crude proteins on constituents of plasma and uterine secretions were examined at various stages of the estrous cycle of high producing Holstein cows. Eighteen cows were assigned randomly to isocaloric diets (74% total digestible nutrients) containing either 12 or 23% crude protein (dry matter) on day 40 postpartum. Uterine secretion and coccygeal blood samples were collected at estrus, days 5 and 15 of the first estrous cycle after day 50 postpartum, and at the subsequent estrus. The 23% crude protein diet resulted in higher concentrations of ammonia in blood, urea in blood plasma and uterine secretion, and phosphorus and potassium in plasma. Zinc increased during the estrous cycle in plasma of cows fed 23% crude protein and decreased in cows fed 12% crude protein. Magnesium concentrations in uterine secretions were lower in cows on 23% crude protein. Potassium and phosphorus also were lower in uterine secretions of cows fed 23% crude protein but only during the luteal phase of the estrous cycle. Zinc concentrations in uterine secretions decreased faster during the estrous cycle in cows fed 12% crude protein than in cows fed 23% crude protein. Thus, the crude protein content of the diet altered concentrations in blood of ammonia and concentrations in plasma of urea, phosphorus, potassium, and zinc. Crude protein content of the diet altered concentrations in uterine secretion of urea, magnesium, potassium, phosphorus, and zinc.

Photoperiodic effects on serum glucocorticoids and fur growth in mink.

The relationship of glucocorticoid secretion to artificial light-induced, early winter priming of pelage in ranch mink was investigated. On December 13, 1977, 16 mature female mink were exposed to natural light. On June 26, 1978, the animals were assigned randomly to one of two groups. Animals in Group 1 were housed in a light-control facility and subjected to 6 hr of artificial light daily and ambient temperatures until November 27, 1978. Animals in Group 2 served as controls and were exposed to natural light. Samples of blood and measurements of the fur and vulva were taken biweekly throughout the year. Concentrations of total glucocorticoids in serum were determined by competitive protein-binding assay. The pelage of mink reared under reduced artificial light was fully prime by October 31, while that of control animals did not become prime until November 27 (time x light regimen interaction, P less than .05). A seasonal effect (P less than .01) on total glucocorticoid concentrations in serum of control mink was revealed by a pattern of three peaks over the 12-month period. The pattern of glucocorticoid secretion was not affected by exposure of mink to reduced artificial light. Maximum concentrations of total glucocorticoids in serum occurred on the same date (September 5) in both groups, although levels were significantly higher in the light-treated mink (44.5 +/- 10.4 ng/ml) than in the controls 26.9 +/- 5.7 ng/ml). Fur growth was positively correlated with total glucocorticoid concentrations in serum during the period from June to December (overall r = .14, P less than .05). Both length and width of the vulva increased (P less than .01) during February and March in animals reared under natural light. These data suggest that the increased secretion of glucocorticoids induced by exposure of mink to reduced artificial light may be involved in promoting early priming of the winter pelage of these animals.

Estrous behavior and ovarian activity in peripuberal heifers.

PIP: Estrous behavior and ovarian activity were investigated in peripuberal heifers. Reproductive tracts of 37 Holstein heifers were examined per rectum twice weekly beginning at least 30 days before the 1st ovulation and continuing until 10 days after the 7th ovulation. The signs of 1st estrus occurred at an average of 279 days of age and the 1st corpus luteum was not detected until 30 days later (p .01). The mean interestrual interval was 20 days for the 1st 7 cycles (p .05). The differences in interestrual intervals for cycles accompanied by silent, nonstanding, and standing estrous behavior, and by different ovarian conditions were not significant (p .05). Silent, nonstanding, and standing estrus occurred during 7, 25, and 68% of 245 estrous cycles, respectively. The occurrence of standing estrus increased from the 1st to 7th cycle (p .01). Normal corpora lutea occurred during 61% of 245 cycles, cystic corpora lutea during 14%, anovulaton during 14%, and cystic follicles during 11%. The occurrence of anovulation decreased from 1st to 7th estrus while the occurrence of corpora lutea increased during the same period (p .01).^ieng