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Biomedical subjects

C J Wilcox

Publications and source records attributed to C J Wilcox.

At least 91 records · Page 5Linked to original sources
PubMed1985

Effects of climatic and management factors on conception rate of dairy cattle in subtropical environment.

Breeding records, representing 12,038 inseminations at Bassett's Dairy Farm (Monticello, FL), were analyzed to document effects of environmental and management factors on fertility of dairy cattle from January 1, 1975 to December 31, 1977. Conception rates of lactating cows decreased sharply when maximum air temperature on day after insemination exceeded 30 degrees C. In contrast, conception rates for heifers did not decline until 35 degrees C. Virgin heifers had higher conception rates for all services (50%) than lactating cows (34%) and suffered only slight depression of fertility during summer months. Heifers required 1.5 services per conception compared with 2.3 for lactating cows. Relationship between conception rate and rainfall on day after insemination was negative and curvilinear. Jerseys had higher conception rates (45%) than Holstein (39%) and Brown Swiss (41%). Services per conception were 1.7, 2.0, and 1.9. Substantial decreases of fertility were associated with advancing service number. Estrous status (standing; positive heat detection patch; mounting activity), inseminator, and year of service were related to variation of conception rate. Seasonal effects on fertility of lactating cows were marked. Thus, environmental management of the postpartum cow during hot summer months is warranted to maximize fertility.

Animal Husbandry↗
PubMed1985

Effects of relative humidity, maximum and minimum temperature, pregnancy, and stage of lactation on milk composition and yield.

Composite monthly single-day milk samples from the Florida Agricultural Experiment Station dairy herd 1959 to 1974 were analyzed for composition. Data were 22, 972 observations on five dairy breeds, but major statistical analyses were limited to Jerseys and Holsteins. Minimum relative humidity and maximum and minimum temperatures on day of evening sample were associated with 1.6 to 5.6% of variability within lactation (range for two breeds) of milk and milk constituent yields and 1.1 to 16.5% of constituent percentages. Yields of milk and constituents of the Holsteins seemed more sensitive to climatic variation than did Jersey, but Jersey constituent percentages were more sensitive. Yields were affected only slightly by increasing maximum daily temperatures from 8 to 29 degrees C but declined rapidly at greater than 29 degrees C; fat and protein percentages declined from 8 to 37 degrees C, whereas chloride content increased above 21 degrees C. Stage of lactation and pregnancy effects accounted for about 50% of the variability of yields and 3 to 23% of percentages. Effects were detected also for chloride and acidity percentages, specific gravity, and ratios solids-not-fat to fat and protein to fat.

Animals↗
PubMed1985

Production and physiological responses of dairy cows to varying dietary potassium during heat stress.

Objectives were to study influences of heat stress and dietary potassium content on production and physiological responses of 8 Jersey and 10 Holstein cows blocked by breed and assigned randomly to no shade or shade environments. Each cow received a different dietary potassium treatment (.66, 1.08, and 1.64% of dry matter) in each of three 30-day periods. Rates of potassium loss from skin were almost five times greater for no shade as for shade cows during the hottest part of the day (1300 to 1500 h). Overall, cows with no shade ate 56% less during the daytime (0800 to 1600 h), 19% more during nighttime (1600 to 0800 h), and 13% less total feed than cows with shade. Interactions of environment and breed with dietary potassium treatment suggest differences in feed intake and milk yield responses to increasing dietary potassium content. Total daily feed intake and milk yield of cows with no shade responded in curvilinear fashion to increasing dietary potassium, whereas responses in shade were small. Largest responses in no shade were as dietary potassium increased from .66 to 1.08%. Milk yield of Holsteins increased with increasing dietary potassium, but yield of Jerseys did not. Combined effects of elevated potassium loss from skin and reduced potassium and dry matter intake during heat stress suggested that lactating dairy cows may benefit from supplemental potassium.

Analysis of Variance↗
PubMed1985

Interrelationships of milk yield, body weight, and reproductive performance.

Records (2263) from a single north Florida herd for 3 yr were evaluated in a series of analyses. Environment was subtropical. Data set included only cows that had normal milk records and became pregnant. Holsteins and Jerseys averaged 6799 and 4504 kg milk, 587 and 418 kg postpartum body weight, 164 and 141 days open, and 2.3 and 2.1 services per subsequent pregnancy. Pooled within breed, repeatabilities and heritabilities of these performance measures were .37, .15; .53, .25; .20, .06; and .30, 0. Estimable genetic correlations were milk yield and body weight -.09, milk yield and services per conception .38, and services per conception and body weight .37; range of standard errors was .22 to .39. Substantial genetic antagonism may exist between milk yield and body weight, and efficient reproduction. If results of this research are verified elsewhere, breeders should be aware that selection for increased weight could lead to decreased reproductive efficiency.

Analysis of Variance↗
PubMed1984

Influence of dietary sodium and potassium bicarbonate and total potassium on heat-stressed lactating dairy cows.

Objectives were to study effects of heat stress, 0 or .85% sodium bicarbonate, 0 or 1.0% potassium bicarbonate, and 1.0 or 1.5% total dietary potassium on production and physiological responses of dairy cows. Eighteen lactating Holsteins were assigned to shade (control) or no shade (heat stress) lots continuously for three consecutive 35-day periods and to different dietary treatments each period. Basal diet was 25% cottonseed hulls and 75% concentrate. Daytime and nighttime feed intake and production were measured the last 2 wk of each period, and milk and blood were sampled the final day of each period. Black globe temperature, rectal temperature, respiration rate, and blood pH were higher in no shade. Daytime intake was 132% greater in shade, nighttime intake was not different between environments. Milk production was about 19% greater for evening and morning milkings in shade. Daytime intake, daytime and nighttime milk production were higher with sodium bicarbonate. Potassium bicarbonate reduced intake and production. Higher total dietary potassium increased total daily milk production. Lactating cows appear adept at withstanding environmental and dietary challenges to acid-base homeostasis. Supplementation of sodium bicarbonate and 1.5% dietary potassium, but not potassium bicarbonate, were beneficial to lactating dairy cows.

Animals↗
PubMed1983

Relationships between maternal hormones and weight of newborn sheep.

Intact and ovariectomized mixed-breed sheep were studied in chronic experiments during the last weeks of pregnancy. Measurements were made of the rate of uterine blood flow (ml/min and ml X min-1 X kg-1, combined weight of fetus, uterus, and placenta) and of arterial and uterine venous concentrations of progestagens, estrone, and estradiol. The birth weight of the lamb was directly related to mean maternal concentrations of estrone and estradiol and to the rate of progestagen release by the uterus and its contents (ng X ml-1 X kg-1), calculated by taking the product of the rate of blood flow and the arteriovenous progestagen difference. Ovariectomy altered the relationship between birth weight and progestagen release. Data suggest that rates of progestagen release both by the fetoplacental unit and by the ovary are proportional to the birth weight of the lamb.

Animals↗
PubMed1983

Climatological and genetic effects on milk composition and yield.

Results confirm most other research on milk composition and yield. All responses were affected by climate, some considerably more than others, if percent of error variance is the criterion. Jersey yields were less sensitive to climate than were Holstein, but Jersey milk composition appeared more sensitive. Somatic cell count (REF), a measure of mastitis, was affected by climate but less than all other variables except protein/fat and LM%. Needed are estimates of interactions between climatic effects and response surface models to quantify possible improvement in performance following environmental modification. Genetic correlations between milk yield and REF and chloride % suggest that single trait selection for milk yield might increase incidence of mastitis although phenotypic correlations indicate that high yields and absence of mastitis are correlated.

Animals↗
PubMed1983

Vital statistics and reasons for disposal of United States and Canadian artificial insemination dairy sires.

Vital statistics were evaluated for artificial insemination sires leaving service during 1939 through 1974. Data consisted of 11,704 sires of six breeds. The major cause for leaving service was reproductive failure at a frequency of 32.5%; next ranked was undesirable characteristics of offspring with a frequency of 20.7%. Overall culling rate for low yields of daughters was 14.8%, but after 1965 this cause accounted for about 30%. Mean life span was 3.4 yr with small differences among years. Breed differences were detected for service life and causes for leaving service. Modifications of classic life table techniques are needed to reflect entry of sires into service at various ages and evaluation of vital statistics subsequent to 1974.

Age Factors↗
PubMed1983

Comparison of teat dips with differing iodine concentrations in prevention of mastitis infection.

Six commercial dairy herds were used to test the relative efficacy of three concentrations of iodine as a teat dip over 12 mo. Concentrations were .1, .25, and 1% iodine with free iodine contents of 3.5, 4.0, and 1.0 ppm. Two concentrations were compared in each herd. The greatest number of new infections (71) occurred in approximately 120 cows whose teats were dipped with the 1% iodine dip, and the fewest (52) occurred in a similar number of cow quarters dipped in .1% iodine; however, differences were not significant. Clinical mastitis was highest in the 1% group. If all clinical mastitis were the result of infection, even if bacteria were not isolated from the pretreatment sample or from samples collected at the start of the study and those quarters were added to the totals, then reduction of new infection with the .1% product would be significant.

Administration, Topical↗
PubMed1982

Fetal death in utero: effect on estrone, estradiol-17 beta and progesterone levels in the ewe.

Polyvinyl catheters were placed in the maternal femoral artery (MA) and maternal uterine vein (UV) of 11 near-term ewes and in the umbilical vein of their fetuses. 1-5 days postoperatively 100 ml of air were injected into the umbilical vein of 7 fetuses. 4 fetuses served as controls. Samples of blood from MA were taken 15 min prior to air embolism and every 15 min for 3 h, then at +4, +5 and +6 h after air injection. Plasma levels of estrone (E1) estradiol (E2) and progesterone (P) were determined by radioimmunoassay. In MA and UV of treated ewes there was a significant decrease in P, but not in E1 or E2 after fetal death compared to control ewes. Control levels of P in MA were 9.6 ng/ml; values at 1, +2, +4 and +6 h were 8.8, 3.3, 2.3 and 1.2 ng/ml, respectively.

Animals↗
PubMed1982

Effects of heat stress during pregnancy on maternal hormone concentrations, calf birth weight and postpartum milk yield of Holstein cows.

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.

Animals↗
PubMed1982

Rumen and fecal tungstic acid precipitable nitrogen and total amino nitrogen in cows fed complete diets.

Tungstic acid precipitable N and nonprecipitable N were measured in feed, rumen and feces of cows fed complete diets, and changes in ratios of these components to chromic oxide were used to estimate net changes in true protein from feed to rumen to feces. Apparent digestible true protein leaving the rumen was assumed to be metabolizable protein. Rumen contents were hand mixed before sampling from rumen-fistulated cows so that samples would be as representative of total rumen contents as possible, and these samples were assumed to represent contents being passed to small intestine. Metabolizable protein percentages of three low protein basal diets containing 1.90, .95 and 0% urea and three similar diets with added soybean meal fit responses of milk yield obtained in a previous experiment much better than metabolizable protein estimated from literature values for various feedstuffs. Net true protein digestion estimates confirmed negative performance from 1.90% urea basal diets compared with performance from other basal diets. An experiment in which rumen samples were taken by stomach tube from intact cows showed rumen samples were not representative of total rumen contents, at least not for chromic oxide percentage, and, consequently, net true protein digestion could not be estimated a well as with fistulated cows.

Ammonia↗
PubMed1982

Induction of lactation: comparison of injections of estradiol-17 beta and progesterone for 7 or 21 days on prolactin response to thyrotropin releasing hormone and milk yield in dairy cattle.

Subcutaneous injections of estradiol-17 beta and progesterone (.10 and .25 mg/kg of body weight) for 7 (group I) or 21 (II) days were used. Dexamethasone (.028 mg/kg of body weight per day) or adrenocorticotropin (200 IU per day) was injected into cows in each group on days 18 to 20 (I) or 32 to 34 (II). Additionally, 100 mug of thyrotropin releasing hormone was injected intravenously on days 1, 7, 17 (I) or 1, 7, and 31 (II). Milking was initiated on days 21 (I) or 35 (II). Overall 13 of 14 cows had mean daily yields of milk greater than 5 kg; 12 had 305-day lactations. Yields of milk in cows injected for 21 days were greater on day 1 and increased more rapidly until peak was reached at 10 wk; daily mean production throughout lactation was greater (14.3 versus 10.1 kg) than for cows injected for 7 days. Lactation curves pooled within cow within treatment differed. Concentrations of estradiol, estrone and progesterone increased during steroid injections and were 2- to 3-fold higher on day 21 in II than on day 7 (I or II), but concentrations of prolactin and total glucocorticoids in plasma did not differ during this time. The quantity of prolactin released in response to injection of thyrotropin releasing hormone was greater 10 days after steroid injections than before or during steroid injections. Preinjection concentrations of prolactin were correlated with magnitude of postinjection response to thyrotropin releasing hormone, but response was not correlated with concentrations of steroids in plasma on day of injection.

Adrenocorticotropic Hormone↗
PubMed1982

Influences of environment and its modification on dairy animal health and production.

Physiological state of dairy animals is a predisposing factor in environmental influences on animal health. Critical phases of life cycle include neonatal period, postpubertal reproduction, and lactation. Primary effect of environment in neonatal period is increased disease incidence associated with reduced immunoglobulin content in plasma of calves. Cold stress has little effect on reproduction; in contrast, heat stress reduces libido, fertility, and embryonic survival in cattle. Heat stress in late gestation reduces fetal growth and alters endocrine status of the dam. Carryover effects of heat stress during late gestation on postpartum lactation and reproduction also are detectable. Heat stress of lactating cattle results in dramatic reductions in roughage intake and rumination. Decreases in roughage intake contribute to decreased volatile fatty acid production and may contribute to alteration in ratio of acetate/propionate. Rumen pH also declines during thermal stress. Electrolyte concentrations, in particular sodium and potassium, also are reduced in rumen fluid of heat stressed cattle. The decrease in sodium and potassium are related to increases in loss of urinary sodium and loss of skin potassium as well as decline in plasma aldosterone and increase in plasma prolactin. Reduction in thyroxine, growth hormone, and glucocorticoid concentrations in chronically heat stressed cattle appear to be related to decreases in basal metabolism.

Adaptation, Physiological↗
PubMed1981

Hormonal patterns during heat stress following PGF(2)alpha-tham salt induced luteal regression in heifers.

Ten, normally cycling, Holstein heifers were assigned to one of two environmental treatment groups (21.3 C, 59% RH or 32.0 C, 67% RH). PGF(2)alpha was used to induce luteal regression and synchronize estrus in order to evaluate temperature effects on various hormonal and physiological responses during the proestrous through metestrous periods. Environmental temperature (32.0 C) evoked a 1.4 C increase in rectal temperature and a 3.6 C increase in skin temperatures. Length of estrus was shorter (P<.10) for heifers at 32.0 C (16 vs 21 hr.). Average plasma progestin concentration between treatments was not different (P>.10). Mean estradiol concentrations were significantly (P<.10) lower in heifers at 32.0 C. No differences (P>.10) were detected in mean concentrations of LH between heifers at 21.3 C and 32.0 C. Preovulatory peak LH concentrations were 32.2 and 33.2 ng/ml plasma, respectively. All animals had a preovulatory surge of LH, suggesting that hyperthermia did not alter factors which regulate hypothalamic control of LH release. Mean basal concentrations of prolactin and corticoids were not different between temperature treatments (P>.10). However, mean corticoid response following ACTH was of lower magnitude, earlier to peak, and of shorter duration in heat stressed heifers. Heat stress did not appear to affect the hormonal milieu in peripheral plasma associated with corpus luteum regression (decrease in progestin) and ovulation (LH surge). However, duration of estrus, concentrations of estradiol at proestrus and corticoid response to injection of ACTH were reduced.

Journal Article↗
PubMed1981

Hormonal responses of lactating dairy cattle to TRH and ACTH in a shade management system within a subtropical environment.

Lactating cows (64) were balanced by breed (54 Holstein and 10 Jersey) and assigned randomly to shade (S) or no shade (NS) management treatments for a continuous 20 wk trial beginning 5-5-76. A sub-sample of Holstein cows, five S and five NS, were fitted with jugular catheters 84 days after initiation of experiment. Thyrotropin Releasing Hormone (TRH; 100 mug) was administered intravenously at 1200 h to evaluate prolactin responses. Two days later each cow received intravenously 200 IU of ACTH at 1100 h to compare acute corticoid responses to ACTH. Mean prolactin response to TRH was greater for NS cows (291 vs 169 ng/ml; P < .01) as was peak plasma concentrations at 20 min (467 vs 267 ng/ml; P < .01). Mean corticoid response to ACTH injection was less for NS cows (52 vs 70 ng/ml; P < .10). Corticoid concentrations of plasma in both treatments had declined 65% by 7 h postinjection. These endocrine differences may be associated with thermoregulation and/or metabolic adjustments of cows exposed to different environmental systems of management during a seasonal period of thermal stress.

Journal Article↗