Showing papers in "Journal of Animal Science in 1982"

Theory and Analysis of Threshold Characters

Abstract: Summary This paper deals with theory, methods and problems in the analysis of categorical data in animal breed/ng when a threshold model is postulated foi an underlying normal distribution of phenotypes Linear and nonlinear statistical models potentially useful for estimating parameters of the underlying and outward distributions are reviewed and extended Methods for evaluating the genetic value of candidates for selection from single or multiple populations are discussed comparatively

Utilization of the Intact Male for Red Meat Production: A Review

Abstract: Summary Castration has long been a traditional practice in the United States. Research studies indicate that intact males grow more rapidly, utilize feed more efficiently and produce a higher-yielding carcass with less fat and more edible product. The disadvantages of the intact male include aggressive behavior (bull and boar); undesirable odors and flavors (boar and ram); lower quality grade (bull); lower meat tenderness (bull and ram) and undesirable meat color (bull and ram). Research is needed to develop antemortem and(or) postmortem handling procedures that offset the disadvantages of the intact male so that the meat and livestock industry can take advantage of their rapid

Effects of Heat Stress during Pregnancy on Maternal Hormone Concentrations, Calf Birth Weight and Postpartum Milk Yield of Holstein Cows

Abstract: For an evaluation of the effects of heat stress during pregnancy on calf birth weight and postpartum maternal milk yield, 21 cows and 10 heifers were assigned to shade (S; n = 16) or no shade (NS; n = 15) treatments during the last trimester of pregnancy in June 1978. At parturition, all cows were removed from treatment and uniformly managed in the milking herd. At 4-d intervals from d 199 of pregnancy to parturition, respiration rates, rectal temperature, heart rate and Black Globe temperature were recorded and blood samples obtained via tail venipuncture between 1300 and 1600 h. Weekly prepartum body weights of dam, birth weight of calf and subsequent daily milk yield were recorded. Black Globe temperature, rectal temperature and respiration rates were higher in cows given NS. Calf birth weight was lower in the NS group. Milk yield was correlated in a linear manner with calf birth weight, and cows in group NS exhibited reduced lactation performance after calving. Plasma progestin concentrations were higher in heat-stressed cows (6.0 vs 5.1 ng/ml). Estrone-sulfate concentrations were reduced in plasma of NS cows (2,505 vs 4,433 pg/ml). Thus, hormone concentrations of maternal and fetal origin were altered by environment. Plasma thyroxine concentrations were lower in NS cows (51.2 vs 66.4 ng/ml), while plasma triiodothyronine concentrations were elevated (1.8 vs 1.5 ng/ml), indicating altered thyroid hormone metabolism in heat-stressed cows. Heat stress altered endocrine dynamics during pregnancy and reduced calf birth weight and may have indirectly altered subsequent milk yield.

Ovarian cysts in dairy cattle: a review

Abstract: Ovarian cysts in dairy cattle are generally defined as follicular structures of at least 2.5 cm in diameter that persist for at least 10 d in the absence of a corpus luteum. The incidence of ovarian cysts has been reported to be from 6 to 19% and, therefore, cystic ovarian disease is a serious cause of reproductive failure in dairy cattle. There have been several different hypotheses about the cause of ovarian cysts. After monitoring postpartum cows that spontaneously developed ovarian cysts and postpartum cows with or without ovarian cysts administered estradiol benzoate, the authors have suggested that postpartum ovarian cysts developed when the hypothalamus and pituitary appeared to be less responsive in releasing luteinizing hormone (LH) under the influence of estradiol. Spontaneous reestablishment of ovarian cycles occurred in about 60% of the cows that developed ovarian cysts before the first postpartum ovulation. In contrast, only about 20% of the cows that developed ovarian cysts after the first postpartum ovulation spontaneously reestablished ovarian cycles. The authors have also reported that even if ovarian cycles are not reestablished, ovarian cysts may regress, but only in the presence of follicular development, which subsequently develops into ovarian cysts. Investigators have shown that 40 to 80% of the cows with ovarian cysts reestablished ovarian cycles following treatment with products high in LH activity. Gonadotropin releasing hormone (GnRH), which stimulates reestablishment of ovarian cysts in about 80% of the cows treated, has more recently been recommended as a treatment for ovarian cysts. The GnRH-induced LH surge appears to stimulate luteinization of the ovarian cyst wall. Cows then exhibit estrus about 21 d following GnRH treatment. The conception rate at the first estrus after GnRH treatment has been reported to be 40 to 50%. The interval from GnRH treatment to estrus has been reduced by administering prostaglandin F2 alpha (PGF2 alpha) 9 d after GnRH. The PGF2 alpha appears to regress the luteinized ovarian cysts and cows exhibit estrus 2 to 3 d after PGF2 alpha treatment (11 to 12 d after GnRH). Gonadotropin releasing hormone has also been used to reduce the incidence of ovarian cysts in postpartum cows. To be effective in reducing the incidence of ovarian cysts, GnRH should be administered about 2 wk postpartum. However, cows may have a predisposition for cystic ovarian disease and treatments, therefore, are only temporary solutions. A better alternative would probably be to select against ovarian cysts.

Estimation of Stoichiometric Parameters for Rumen Fermentation of Roughage and Concentrate Diets

Abstract: A biochemical model coupled with an iterative nonlinear least-squares program was used to estimate stoichiometric parameters for fermentat ion of soluble carbohydrate, starch, hemicellulose, cellulose and protein in the rumen. Fermentat ion parameters were deduced for two sets of l i terature data, on (1) a roughage group of 60 diets fed to 137 animals and (2) a concentrate group of 48 diets fed to 374 animals. Soluble carbohydrate and starch fermentat ion parameters were much different for the roughage and concentrate groups. Differences were also noted in fermentat ion parameters for hemicellulose and cellulose. Model sensitivity to imposed changes of iteratively deduced parameters supported the conclusion that the estimated values are unique for all substrates except protein. In vitro estimates of isolated substrate fermentat ion from the literature agreed favorably with those indicated for hemicellulose. Cellulose fermentation was estimated to yield an acetate to propionate ratio of 7.8 to 13.1:1. This was higher than estimates in the li terature of 1.3 to 3.6:1. Predicted fermentat ion patterns were within the range of normal biological variation noted for actual patterns. Systematic error components were identified as lignin plus ash as a percentage of feed dry matter and percentage roughage in the diet for the roughage and concentrate groups, respectively. Significant bias remained only in the roughage group for acetate and butyrate. Predicted vs observed acetate, propionate and butyra te production, for diets where comparison data were available, had slopes (correlation coefficients) of .84

Effects of Postweaning Rate of Gain on Onset of Puberty and Productive Performance of Heifers of Different Breeds

Abstract: Angus, (n = 78), Hereford (93), Red Poll (61), Brown Swiss (47), Charolais (36) and Simmental (90) heifers were used in a study designed to evaluate the effects of breed and postweaning rate of gain (low, L = .4 kg/d; medium, M = .6 kg/d; high, Hi = .8 kg/d) on the onset of puberty and subsequent maternal performance. After a 184 d feeding period, one-half of the heifers in each group were moved to pasture and one-half were kept in the feedlot through breeding (70 d), then moved to pasture. Breeds differed (P less than .01) in weight, height and condition. Increased postweaning rates of gain resulted in increased heifer weight (P less than .01), height (P less than .10) and condition (P less than .01) before calving (198 to 635 d) but these differences were not observed after rebreeding (930 d). Quadratic regressions of percentage pubertal vs age were significantly influenced by the interaction between breed and postweaning rate of gain. Both mean age and weight at puberty were influenced by breed (P less than .01) and postweaning rate of gain (P less than .01). No interactions were observed (P greater than .10). Calf birth weight was influenced (P less than .01) only by breed. Milk production was influenced by breed (P less than .01) and postweaning rate of gain (P less than .10). Significant time after parturition and time X breed interaction effects on milk production were observed. Calf weight at 120 d and at weaning was influenced by breed (P less than .01), heifer postweaning rate of gain (P less than .05) and sex (P less than .05). These data suggest moderate underfeeding or overfeeding during the postweaning period may have a prolonged influence on the productive performance of heifers and demonstrate that breeds differ widely in age at puberty and later productivity under the type of management and environment of this study.

Association of an endophytic fungus with fescue toxicity in steers fed Kentucky 31 tall fescue seed or hay.

Abstract: Previous research has implicated an endophytic fungus as being associated with fescue toxicity (summer syndrome) in cattle grazing Kentucky 31 tall fescue (Festuca arundinacea Schreb.) pastures. Hay and seed were harvested from Kentucky 31 pastures known to be either fungus-free or heavily infested with an endophytic fungus identified as Acremonium coenophialum Morgan-Jones and Gams. Four diets containing either 60% fungus-free seed, 60% fungus-infested seed, 85% fungus-free hay or 85% fungus-infested hay were group-fed to three steers each (avg wt 239 kg) in a 53-d feeding trial. Presence of the fungus reduced (P less than .05) daily gains (kg/d) in steers fed either the seed diets (.96 vs .20) or the hay diets (.66 vs .28). Feed intake was depressed 36% for the seed diets and 8% for the hay diets when the fungus was present. Rectal temperatures were elevated .6 C (P less than .05) for both groups receiving diets containing the fungus, but respiration rate was elevated only in the fungus-infested seed group. In vitro dry matter disappearance was not decreased by presence of the fungus. Steers receiving fungus from either seed or hay were nervous and highly excitable, which resulted in large variations in plasma epinephrine and norepinephrine concentrations. The results of this experiment further implicate an endophytic fungus as being associated with fescue toxicity.

Induced corpora lutea in the postpartum beef cow. II. Effects of treatment with progestogen and gonadotropins.

Abstract: Seventy-three multiparous beef cows (21 to 35 d postpartum) were used in an experiment with a 2 X 4 factorial design to test the effects of pretreatment with norgestomet and preovulatory gonadotropic stimulation on the life span of corpora lutea induced by human chorionic gonadotropin (hCG) Cows were implanted subcutaneously for 9 d with norgestomet (3 mg; 35 cows) or sham-implanted (38 cows) HCG (1,000 IU) was administered in to all cows 36 h (time = 0) after implant removal Each cow received one of the following treatments: (1) pregnant mare's serum gonadotropin (PMSG; 750 IU) in a single subcutaneous injection 48 h prior to hCG (-48 h); (2) follicle stimulation hormone (FHS-P) in saline (10 mg) in a series of four subcutaneous injections (25 mg/injection) at -48, -36, -24 and -12 h; (3) FSH-P in 5% beeswax-sesame oil (10 mg) administered as in 2; or (4) saline, administered as in 2 Samples of serum taken at the time of implantation, at the time of implant removal and daily on d 5 to 20 after administration of hCG were assayed for progesterone Samples taken at 12-h intervals from -48 to +12 h were assayed for estradiol-17 beta Cows were observed for estrus at 6-h intervals from 24 to 60 h after implant removal and twice daily until d 22 Seventy-one percent of the cows (25/35) were in standing estrus from 29 to 60 h after removal of a norgestomet implant, compared to 16% of the sham-implanted cows (six of 38) As determined by progesterone in serum and by palpation of the ovaries, 88% of the cows (64/73) formed corpora lutea in response to hCG, with a tendency (P less than or equal to 10) for a positive effect of pretreatment with norgestomet (94 vs 82%) The life span of corpora lutea was longer (P less than or equal to 01) in cows treated with norgestomet (196 d) than in sham-implanted cows (134 d) Level of function of the induced corpora lutea as indicated by the pattern of daily concentrations of progesterone in serum was increased by pretreatment with either norgestomet (P less than 01) or gonadotropin (P less than 05), but there was no interaction of these treatments The mean level of estrogen before ovulation was increased (P less than 01) by pretreatment with norgestomet or any regimen of gonadotropin, and, again, there was no significant interaction Pretreatment with progestogen was associated with a higher pattern of concentration of estrogen over time (P less than 01)

Genetic, Environmental and Phenotypic Relationships among Gestation Length, Birth Weight, Growth Traits and Age at First Calving in Beef Cattle

Abstract: Data on the Red Angus, Angus and Hereford herds of Pioneer Hi-Bred International, Inc., Des Moines, Iowa, collected from 1968 to 1976, were analyzed for relationships among gestation length, birth weight, prenatal gain (birth weight adjusted for gestation length), growth traits and age at first calving. A total of 5,691 calf records, 1,783 listing gestation length, were included in the study. Paternal half-sib analyses and least-squares procedures were used to compute heritability estimates and genetic, environmental and phenotypic correlations among traits. Genetic correlations among growth traits, including prenatal gain, were high in all cases. Heritability estimates for gestation length and birth weight were .36 and .43, respectively, for bull calves and .37 and .35 for heifer calves. Genetic correlations between these traits were .25 and .22 for bull and heifer calves, respectively. Gestation length was negatively correlated (genetically) with all growth traits except birth weight. This result suggests that faster growing fetuses may trigger parturition earlier than average. Age at first calving was negatively correlated (genetically) with growth traits, indicating a favorable relationship between growth and early reproduction. Analysis of several selection indexes combining either birth weight and yearling weight or gestation length and yearling weight indicated that continued response to selection for growth without excessive increase in birth weight is feasible. Selection for growth and moderate birth weight would be more effective than selection for growth and shorter gestation, suggesting that the former method would both shorten gestation and alter the growth curve. Repeatability estimates for gestation length and birth weight were .20 and .22, respectively. Maternal effects accounted for approximately 10% of the variation in each trait.

Control of uterine and ovarian blood flow throughout the estrous cycle and pregnancy of ewes, sows and cows

Abstract: Current investigations strongly indicate a relationship between the function of adrenergic (vasoconstrictor) nerves innervating uterine and ovarian arteries and local concentrations of estrogen and progesterone. During the estrous cycle of ewes, cows and sows, the higher the estrogen:progesterone ratio in systemic blood, the greater is the quantity of blood flowing through the uterine vascular bed. When converted to a catechol form, estrogen may reduce uterine vasoconstriction by binding to and suppressing perivascular alpha-adrenergic receptor activity. Progesterone, in contrast to estrogen, augments the responsiveness of vascular smooth muscle to norepinephrine. Lymphatic vessels, which are in close linear apposition to the adventitia of the uterine vasculature may serve to transport steroids to the periarterial nerves. Vasodilation associated with steroid-induced changes in autonomic function appears to be modulated and amplified by estrogen-dependent changes in prostaglandin biosynthesis. During early pregnancy in ewes, cows and sows, vasodilation, mediated by the conceptus, occurs in the luteal and (or) uterine vascular beds on days critical for continuation of pregnancy in each species. In cows and sows, this vasodilatory effect of the conceptus is associated with increased concentrations of estrogens in the uterine lumen, as well as the lymph and blood draining the uterus. After the initial increase in blood flow to the uterus during early pregnancy, changes in the estrogen:progesterone ratio in fetal and maternal fluids appear to be unrelated to changes in uterine blood flow (UBF). This lack of association between the estrogen:progesterone ratio and UBF may result from a progressive reduction in number of adrenergic nerves observed in the uterus throughout pregnancy. If one accepts that the estrogen:progesterone ratio controls UBF through alterations in the function of periarterial adrenergic nerves, the impaired function of the nerves during mid and late gestation may preclude the effects of these steroids.

Influence of energy intake during lactation on the interval from weaning to first estrus in sows.

Abstract: A total of 191 crossbred sows were used to determine the effect of energy intake during one lactation on (1) sow and pig performance and (2) the percentage of sows in estrus by 7, 14, 21 and 70 d postweaning. Sows received 8 (Lo) or 16 (Hi) Mcal of metabolizable energy (ME)/d (Exp. 1 and 2) and 8 (Lo), 12 (Md) or 16 (Hi) Mcal of Me/d (Exp. 3) during a 28-d lactation period. All sows were fed an equal amount of crude protein, vitamins and minerals that met or exceeded the recommendations of the National Research Council. Each day after weaning, sows were fed 1.8 kg of a 14% crude protein diet and checked for estrus using boars. Serum samples were obtained weekly from sows not detected in estrus by 15 d postweaning for progesterone analysis. In Exp. 1 sows fed Lo lost more (P less than .01) weight and backfat, and weaned lighter weight (P less than .01) pigs than sows fed Hi. Fewer sows fed Lo exhibited estrus (P less than .01) by 7, 14, 12 and 70 d postweaning than sows fed Hi. In Exp. 2, sows fed Lo lost more (P less than .01) weight and backfat than sows fed Hi, but pig weaning weights did not differ. Fewer sows fed Lo expressed estrus by 7 d (P less than .01) postweaning than those fed Hi. In Exp. 3 sow weight and backfat loss decreased (P less than .01) linearly as energy intake increased. Pig weaning weights were not affected by energy intake. Fewer sows fed Lo expressed estrus (P less than or equal to .05) by 7, 14, 21 and 70 d postweaning than those fed Md and Hi. There was no difference in the percentage of sows fed Md or Hi that exhibited estrus by these time periods. Blood samples collected on d 110 of gestation and d 14 and 26 of lactation, indicated that energy intake did not influence hematocrit values, total serum protein or albumin concentrations. A significant energy intake by time interaction was observed for serum blood urea N. Three of the 25 sows bled for progesterone analysis had luteal tissue activity suggesting ovulation had occurred even in the absence of a detected behavioral estrus.

Effects of zearalenone (F2) on estrous activity and reproduction in gilts.

Abstract: The effects of zearalenone on swine reproduction were investigated in two trials involving a total of 82 gilts which were allotted into three groups at puberty, mated at second estrus and slaughtered 80 d postbreeding. A control diet without mycotoxin (group 1) or an experimental diet containing 3.61 ppm (first trial) or 4.33 ppm zearalenone (second trial) were fed at a mean daily level of 2 kg/animal. The experimental diet was fed from puberty to mating (group 2) or during pregnancy (group 3). No difference was observed between the two trials. When fed to nonpregnant gilts, zearalenone induced a pseudopregnancy state in 45% of the animals; no estrus was detected within 50 d following puberty and corpora lutea developed at puberty were maintained. The uterine horns were edematous. Reproductive performance measured at 80 d postmating (ovulation rate, weight of corpora lutea, number of normal and abnormal fetuses, embryonic mortality) were not affected by zearalenone intake. But when zearalenone was fed during pregnancy, weights of uterus, placental membranes and fetuses were significantly decreased in comparison with those of control gilts and heterogeneity of fetuses in the same litter was increased. Hematocrit and erythrocyte count were lower in fetuses from gilts ingesting zearalenone, but hematology of the dams remained unaffected. No mycotoxin residue could be detected in gilts or fetal tissues despite the great consequences observed on cyclicity of the females or on the development of embryos. This experiment showed evidence of the estrogenic properties of zearalenone in mature gilts.

The Effects of Bull Urine on Puberty and Calving Date in Crossbred Beef Heifers

Abstract: The effects of bull urine on the percentage of heifers reaching puberty and on subsequent calving dates were examined with 52 crossbred beef heifers. Heifers were palpated for ovarian condition and classified as prepubertal or pubertal before (Palpation I) and after (Palpation II) eight weekly oronasal treatments with bull urine or water. A larger percentage of urine-treated than water-treated heifers reached puberty during the experimental period (67 vs 32%; P less than .05), supporting the hypothesis that bull urine contains a priming pheromone. Body weight of urine-treated heifers that did not reach puberty by Palpation II was lower than that of water-treated heifers that did not reach puberty (P less than .05), indicating that an association exists between body weight and the response to pheromonal cues in bull urine. There were no treatment differences in pregnancy rate after a 90-d breeding period, and no differences in pregnancy rate between heifers that had reached puberty before the breeding season started and heifers that had not reached puberty. Urine-treated heifers reaching puberty during the experiment calved earlier (P less than .05) in the calving season than did water-treated heifers of the same category. The distribution of these calvings was also different (P less than .01), resulting in a shorter calving season for urine-treated heifers. More heifers that had reached puberty by Palpation II calved in the first 20 d of the calving season that did heifers that had not reached puberty by Palpation II, regardless of treatment group (P = .02). There was a tendency for urine-treated heifers to calve earlier than water-treated heifers, with the exception of urine-treated heifers that had not reached puberty by Palpation II. These data support the hypothesis that there is a priming pheromone in bull urine that can hasten the onset of puberty in beef heifers.

Puberty in beef bulls: acrosome morphology and semen quality in bulls of different breeds.

Abstract: Semen characteristics were evaluated every 2 wk from 7 through 13 mo of age in 31 beef bulls representing six breed groups (Hereford, Angus, Hereford x Angus crossbreeds, Angus x Hereford crossbreds, Red Poll and Brown Swiss). Breeds differed in age at puberty, defined as the age at which an ejaculate was first obtained that contained a minimum of 50 x 10(6) total spermatozoa with at least 10% progressive motility (Hereford, 326 +/- 9 d; Angus, 295 +/- 4 d; Hereford x Angus, 300 +/- 8 d; Angus x Hereford, 296 +/- 9 d; Red Poll, 283 +/- 9 d and Brown Swiss, 264 +/- 9 d). Significant breed differences also were observed in concentration of spermatozoa, progressive motility, seminal protein concentration, abnormal spermatozoa and acrosomal morphology. Considerable variation was observed for the majority of pubertal traits among the 31 bulls, indicating that differences in stage of pubertal development existed among and within breeds of beef bulls between 7 and 13 mo of age. However, adjustment of data to age at puberty negated breed differences (P greater than .10), indicating that the pubertal patterns of change occurring in each semen characteristic were similar for the breeds evaluated. Concentration of spermatozoa, progressive motility, seminal protein concentration, percentage spermatozoa with normal head and tail morphology and percentage spermatozoa with normal acrosomal morphology increased (P less than .01) from puberty through 16 wk after puberty in all bulls and all breds. During the first 6 wk after puberty, rapid increases (P less than .01) were observed in percentage spermatozoa exhibiting normal head morphology (excluding acrosomes) and progressive motility, and a rapid decrease (P less than .01) was observed in percentage spermatozoa with proximal cytoplasmic droplets, with values at +6 wk approaching those reported for mature bulls. Percentage spermatozoa with normal acrosomal morphology and concentration of spermatozoa improved more slowly and had not reached mature levels by 16 wk after puberty. Because age at puberty varied by 62 d among breeds and 88 d among bulls and important characteristics of semen quality improved slowly after puberty, careful evaluation of the stage of pubertal development in individual bulls is recommended before selecting young bulls for natural breeding or artificial insemination. Additional investigations are needed to define the patterns of pubertal development through sexual maturity in beef bulls and to establish relationships to fertility.

Effect of lasalocid, monensin or thiopeptin on lactic acidosis in cattle.

Abstract: Lasalocid, monensin or thiopeptin was administered intraruminally each at .33, .65 or 1.3 mg/kg body weight and evaluated for its effectiveness in preventing experimentally induced lactic acidosis in cattle. Four rumen-fistulated cattle were used for each dosage level and the design was a 4 x 4 Latin square with each animal receiving lasalocid, monensin, thiopeptin or no antibiotic. Acidosis was induced by intraruminal administration of glucose (12.5 g/kg body weight). Control cattle exhibited the typical drop in rumen pH and concurrent increases in L(+) and D(-) lactate concentrations commonly observed in cases of lactic acidosis. Alkali reserves were depleted in the control cattle as evidenced by a decrease in blood bicarbonate and a negative shift in base excess. In all three trials, cattle given lasalocid had higher rumen pH and lower lactate concentrations than did control cattle or cattle given monensin or thiopeptin. Cattle given monensin had a significantly higher rumen pH and a lower lactate concentration than the controls only at the .65 and 1.3 mg/kg body weight dosages, whereas thiopeptin was effective only at the 1.3-mg dosage. Concentrations of total VFA in rumen fluid decreased in the controls but remained unchanged in cattle given antibiotics. A significant reduction in the molar proportion of acetate and an increase in the molar proportion of propionate were observed in the rumen fluid of the cattle given antibiotics. Colony counts of Streptococcus bovis and Lactobacillus were significantly reduced in rumen fluid of cattle given 1.3 mg antibiotic/kg body weight. Counts of lactate-utilizing bacteria increased in both control cattle and cattle given antibiotics. Cattle given antibiotics showed no evidence of lacticacidemia, hemoconcentration or change in acid-base balance.

Prolactin and luteinizing hormone secretion after bromocryptine (CB-154) treatment in lactating sows and ovariectomized gilts.

Abstract: The effects of bromocryptine (CB-154) on prolactin (PRL) and luteinizing hormone (LH) secretion were studied in lactating sows and ovariectomized (OVX) gilts. In Exp]. 1, the litters of four sows were standardized to four pigs each at 20 to 30 d of lactation and a cannula was placed nonsurgically into the jugular vein of each sow. Twenty-four hours later (0800 h) blood samples were taken and two sows each were injected subcutaneously with 120 mg CB-154 or vehicle. Blood samples were then taken every 30 min for the next 23.5 h. An additional six sows whose litters were standardized to six pigs each at 28 to 30 d of lactation comprised EXp. 2. In Exp. 3, five puberal gilts were OVX. Forty-eight hours after OVX a cannula was placed into the jugular vein. The day after cannulation blood samples were drawn every 30 min from 0800 to 2400 h. Immediately after the sampling at 1200 h, two gilts were injected subcutaneously with 120 mg CB-154 and three were injected subcutaneously with vehicle. Exp. 4 was a repetition of Exp. 3 except that six gilts were OVX 10 d before the experiment and three each were treated with CB-154 of vehicle. Serum PRL concentrations were consistently depressed after CB-154 treatment in both the lactating sows (Exp. 1, from 35 to 5 ng/ml, and Exp. 2, from 45 to 7 ng/ml) and the OVX gilts (Exp. 3, from 20 to 13 ng/ml, and ?Exp. 4, from 9 to 2 ng/ml), but changes in serum LH concentrations after CB-154 treatment were not consistent among the four experimental groups. Therefore, we conclude that CB-154 depressed PRL secretion in the lactating sows and OVX gilts. In addition, CB-154 depressed LH secretion in the lactating sows, but the data are inconclusive as to whether or not BC-154 influenced LH secretion in the OVX gilts.

Nucleic acid, metabolic and histological changes in gilt mammary tissue during pregnancy and lactogenesis.

Abstract: Changes in mammary gland histology, dry weights, nucleic acids and in vitro rates of substrate oxidation in incorporation into lipid were measured in mammary biopsies of three gilts each on d 30, 45, 60, 75, 90, 105 and 112 of pregnancy, and d 1 and 4 of lactation. Histological changes noted were progressive duct growth early in pregnancy followed by rapid lobulo-alveolar development between d 75 and 90 to complete mammogenesis. Colostrum and lipid were evident by d 105 with marked distension of alveolar lumina on d 112. Complete differentiation of the secretory process was apparent on the day of parturition. Concentrtion of dry, fat-free tissue (DFFT) and DNA changed little before d 60 but increased fourfold between d 75 and 90. No further increases in DFFT or DNA were noted. RNA concentrations paralleled DNA through d 90, after which they steadily increased. Rates of acetate and glucose oxidation increased transiently during midpregnancy then declined and remained low until initiation of lactogenesis. Substrate incorporation into lipid increased slightly at midpregnancy and again at d 105, after which it increased markedly. Collectively, results indicate that mammogenesis is complete by d 90, after which lactogenesis is initiated in a two-stage process. Metabolic rates expressed on a DNA basis indicated considerable rates of oxidation, but not of lipogenesis by proliferating mammary tissue. Preferential metabolism of acetate vs glucose near parturition suggests coordination of metabolism between the mammary gland and other maternal tissues.

Milk production of quarter horse mares during 150 days of lactation.

Abstract: Milk production was measured in fourteen Quarter Horse mares at seven stages of a 150-d lactation period. Mares were divided into two groups of seven and fed diets containing either soybean meal or soybean meal and urea as nitrogen supplements. Rations were isocaloric, contained approximately 12.5% crude protein and were fortified with vitamins and minerals. Daily milk yield was estimated by the weigh-suckle-weigh method and milk composition was determined from samples taken by hand milking. Average daily milk yield ranged from 11.8 kg in early lactation to 9.8 kg in late lactation. Differences (P less than .01) in milk yield due to number of previous lactations were observed. Also, diet influenced (P less than .01) milk yield, with mares fed soybean meal producing an average of 1.2 kg more milk/d than mares fed urea as part of the N supplement. Further, stage (day) of lactation influenced (P less than .01) daily milk yield. The largest mean daily milk yield was measured at approximately 30 d postpartum, but the predicted lactation curve was linear (P less than .05) over the range of observations in this study. Average percentages of total solids, protein and fat over the 150-d lactation were 10.5, 2.1, and 1.3, respectively. All components decreased significantly with advancing lactation. There was a trend toward a positive association between milk yield and solids content of the milk, but it was not significant. Milk yield was not significantly related to fat content of the milk. However, milk yield and protein content were correlated (r = .23; p less than .05). As expected, solids content of the milk was positively associated with percentages of protein (r = .59; P less than .01) and fat (r = .44; P less than .01). Relationships among milk components were similar after adjustment for days in milk. However, yield of milk and composition were unassociated (P less than .05) when days in milk were held constant.

Effect of bovine growth hormone administered in various patterns on nitrogen metabolism in the Holstein steer.

Abstract: Understanding the relationship between the components of the growth hormone (GH) secretory pattern and metabolism may provide a basis for designing studies aimed at exploring how to manipulate GH secretion to stimulate protein gains. In a 4 X 4 Latin square design with one additional period to replicate the first treatment period, eight Holstein steers, 195 kg, were assigned to receive the following treatments: 1) 10-day iv infusion (1) of GH; 2) 10 d of six iv pulse injections (P) of GH daily; 3) 10-d combination of infusion and pulses (IP) and 4) controls (C) receiving no injections or infusions. The GH dose was 48 micrograms/kg-1.d-1. Daily feed, total urine and total fecal collections were made for nitrogen (N) determination. Individual samples for d 3 through 6 (collection A) and d 7 through 10 (collection B) were pooled for analysis. Concentrations of GH were determined in blood samples collected on d 10. In collection A, and N metabolism measures were similar among all treatment groups; however, in collection B, treatment of steers with exogenous GH increased the apparent digestion coefficients for dry matter (P less than .01) and dietary N (P less than .01) and also increased the percentage N retained (P less than .01) and the retention of metabolizable N (P less than .05). Metabolic responses were similar among the different patterns of administration. The positive effects on metabolism during collection B not found in collection A were due to length of treatment with GH, as indicated by the fact that none of the measures of metabolism were changed with time in the controls. Serum concentrations of GH were increased (P less than .001) in GH-treated steers compared with controls. These results support the hypotheses that treatment of normal, growing steers with exogenous GH stimulates nitrogen accretion and that pattern of administration does not significantly affect the N response.